Future — NBC Incidents

Current Threats
Terrorist Attacks
A Big Event
Immediate Effects
Delayed Effects
Radioactive Contamination
Effects on the Atmosphere and Climate
Physics of Nuclear Weapon Effects
Fireball Physics
Ionising Radiation Physics
Air & Surface Bursts
Air Bursts
Surface Bursts
Sub-surface Bursts
Electromagnetic Effects
Damage and Injury
Thermal Damage and Incendiary Effects
Blast Damage and Injury
Radiation Injury
Method of Dispersal
Types of Biological Agent
Logistics of Chemical Warfare
Time to Take Effect
Chemical Warfare Protection
Method of Dispersal
Types of Chemical Agent
Blister Gas
Blood Gas
Choking Gas
Nerve Gas
Tear Gas
Vomiting Gas
Incapacitating Agent


Current Threats

There are no great threats to the UK of a WW3 nuclear holocaust since the break up of the USSR but that does not rule out the possibility of a full-scale nuclear war elsewhere in the world.

India-Pakistan relations' pose a threat; the attack on the Indian parliament on December 2001 was even more destabilizing — resulting as it did in new calls for military action against Pakistan, and subsequent mobilization on both sides.  The chance of war between these two nuclear-armed states is higher than at any point since 1971.  If India were to conduct large-scale offensive operations into Pakistani Kashmir, Pakistan might retaliate with strikes of its own in the belief that its nuclear deterrent would limit the scope of an Indian counter attack. Both India and Pakistan are publicly downplaying the risks of nuclear conflict in the current crisis. It is possible, however, that a conventional war — once begun — could escalate into a nuclear confrontation.

Whilst the WW3 nuclear threat has diminished since the break-up of the USSR, the threat of an adversary using biological or chemical weapons against the UK has increased. At present no ‘rouge state' has the ability to strike the UK using ICBM but the bio/chemical threat, if it materialises, is likely to be performed on the UK mainland by hostile intelligence agencies or other insurgents.

Terrorist Attacks

Fortunately there have only been a few instances of terrorists using NBC weapons:

  • In 1995, citizens of Tokyo had no warning when members of the cult Aum Shinri Kyo released Sarin into Tokyo's subways. The result of this terrorist attack was 12 casualties and 5000 injuries.
  • There have been at least seven chemical and biological attacks in the US since 1984.
  • 1984 contamination of salad bars in The Dalles, Oregon, by a religious cult involved a common salmonella strain.
  • In 1998 attacks at US abortion clinics have shown how easy the use of a simple chemical, butyric acid is.
  • In 2002 anthrax attacks in the US killed five people, infected scores, placed 13,000 people on antibiotics and paralysed the Washington DC mail system.

Some of the global terrorist networks are actively seeking to develop and use NBC weapons. Al-Qa'ida have publicly pronounced that they considers it their religious duty to obtain them (NBC weapons). And the Japanese "Aum" cult, which several years ago used self-made chemical weapons in the Tokyo subway, reportedly possessed enough nerve gas to kill four million people — that cult apparently also spent millions of dollars to purchase a nuclear device.

Terrorist groups worldwide have ready access to information on chemical, biological, and even nuclear weapons via the Internet, and al-Qa'ida is working to acquire some of the most dangerous chemical agents and toxins. Documents recovered from al-Qa'ida facilities in Afghanistan show that they were pursuing a sophisticated biological weapons research program and was seeking to acquire or develop a nuclear device. Al-Qa'ida may be pursuing a radioactive dispersal device — what some call a "dirty bomb".

The use of chemical weapons would be devastating but does have limits. The effects of a chemical agent are immediate, but it is possible to turn victims into patients by rapidly administering antidotes. The use of radiological or nuclear weapons by terrorists is less likely. The process of research, development and deployment of these weapons by non-state actors is extremely complex. The infrastructure required is difficult to hide or move — particularly for a non-state actor — and there are numerous ways to detect their development using existing methods and technologies. The danger here is that terrorists could either be given materials or weapons by a sympathetic state, could steal them from a poorly guarded facility, or could even buy them from a disgruntled or poorly paid guard or scientist.

Chemical agents exist as solids, liquids or gases. Dusts, liquids, gases, vapours, mists and aerosols are all relatively easy to deliver, and the agent's persistence will depend on its volatility and the prevailing weather conditions. The effects of a chemical agent may be immediate or apparent within a few hours. Some chemicals that may be used as weapons have characteristic odours, for example, garlicky, fishy fruity, mothballs or peppery; but others may be odourless and tasteless.

Biological weapons give greatest cause for concern. There is a significant difference between biological and other threats because with a biological attack it may not be possible to work out when, where, or how it was launched for some time after the event. The added complexity of the biological threat lies in the highly infectious nature of many of its agents — such as diseases like smallpox or the plague — which multiplies the initial effect exponentially if allowed to spread through a population. These "silent killers" cannot be seen, do not announce themselves until symptoms arise, and the onset of those symptoms is often delayed until long after the initial exposure. This uncertainty, in contrast to the visible, finite explosion of a bomb, can cause considerable panic and paranoia, in addition to fatalities.

Radiological materials may be in solid or liquid forms, the most probable form of delivery being by dispersal using fire or explosives. The radiation emitted by such materials is odourless and invisible. Low radiation doses that one might expect from a letter or small package will have no immediate ill effects, and people would not necessarily be aware that they had been exposed. The primary health effect at low levels is a long-term increase in the risk of developing cancer.

Fortunately, the terrorist is more likely to use a radiological device rather than a full-blown nuclear weapon. And, if nuclear weapons are used, they are likely to be small (in the kilotons) rather than large (megatons) military devices.

The main chemical threats we face are water contamination, an attack on an important building, a shopping mall or on public transport (a main station or the underground). A serious strike may lead to civil unrest.

Nuclear Blasts

Picture of a Big Event

The ground for several miles vaporizes. The atmosphere is ripped through by the massive shock wave. Aircraft will be thrown from the sky by the shock wave. For hundreds of miles in all directions the shock wave will radiate outward destroying everything in its path. Buildings, trains, airplanes, people, animals are pummeled to death by the overpressure of the explosion. Almost all man-made structures will be destroyed for miles in all directions.

Seconds after impact/detonation this shockwave will push a large quantity of the atmosphere upward and away from the planet. Vast amounts of the atmosphere will be shoved violently into space, forever lost to the planet. Huge, billowing clouds will form near, above and in all directions around the impact site. Life within many miles will cease to exist in less than ten seconds. Massive lightning storms will develop around the explosion within a few minutes.

Anyone caught above ground in this shockwave will be killed by the shock wave, by the ensuing heat wave that follows it, or by flying debris if they are some distance behind it. None will be alive to see the lightning storms. Within a few seconds of impact/detonation, the secondary shock wave on the ground and within the planet will be radiating outward. This will level homes and buildings.

The combination of the two shock waves, then the heat wave and finally the earthquakes will kill any creatures in one or the other of the effects. The sunlight is block out by debris and smoke thrown into the atmosphere. For the next day (and for the next months) no bright sunshine will be seen for a long time to come. Day and night are difficult to distinguish around the globe. The northern and southern latitudes are spared some of the effects of the smoke and dirt in the air, but everything is hazy and dim for months to come.

A few animals had avoided the initial destruction, and at first they seemed to manage surprisingly well. Most of the plant eaters could still find food, although the settling dust added a gritty texture to it all. Some of the carnivores were accustomed to hunting in the dark, although they had never experienced blackness such as this. But the ultimate source all food, the sun, had been effectively blocked out. Without sunlight, there was no photosynthesis, no creation of sugar and starch from carbon dioxide and water.

Unseen by the animals, the plants were turning from green to yellow and then to brown.

Without sunlight, the temperature of much of the Earth began to drop. On much of the land the temperature soon fell below freezing. Warm-blooded creatures had an advantage in their ability to endure the cold, but they also required more food. The coastal regions had temperatures moderated by the oceans. Tremendous storms were generated by the great temperature differences between the oceans and the landmasses.

The storms rained the nitrous and sulphuric acids onto land and sea. The tiny particles of dust high in the atmosphere began to stick to each other, agglomerating into larger particles, which fell to Earth more quickly. All over the dust settled to form a layer about a half-inch thick.

Famine, thirst, starvation and death are everywhere.

Overview of Immediate Effects

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

The three categories of immediate effects are: blast, thermal radiation (heat), and prompt ionising or nuclear radiation. Their relative importance varies with the yield of the bomb. At low yields, all three can be significant sources of injury. With an explosive yield of about 2.5 kt, the three effects are roughly equal. All are capable of inflicting fatal injuries at a range of 1 km.

The equations below provide approximate scaling laws for relating the destructive radius of each effect with yield:

r_thermal = Y0.41 * constant_th
r_blast = Y0.33 * constant_bl
r_radiation = Y0.19 * constant_rad

If Y is in multiples (or fractions) of 2.5 kt, then the result is in km (and all the constants equal one). This is based on thermal radiation just sufficient to cause 3rd degree burns (8 calories/cm2); a 4.6-psi blast overpressure (and optimum burst height); and a 500-rem radiation dose.

The underlying principles behind these scaling laws are easy to explain. The fraction of a bomb's yield emitted as thermal radiation, blast, and ionising radiation are essentially constant for all yields, but the way the different forms of energy interact with air and targets vary dramatically.

Air is essentially transparent to thermal radiation. The thermal radiation affects exposed surfaces, producing damage by rapid heating. A bomb that is 100 times larger can produce equal thermal radiation intensities over areas 100 times larger. The area of an (imaginary) sphere centred on the explosion increases with the square of the radius. Thus the destructive radius increases with the square root of the yield (this is the familiar inverse square law of electromagnetic radiation). Actually the rate of increase is somewhat less, partly due to the fact that larger bombs emit heat more slowly which reduces the damage produced by each calorie of heat. It is important to note that the area subjected to damage by thermal radiation increases almost linearly with yield.

Blast effect is a volume effect. The blast wave deposits energy in the material it passes through, including air. When the blast wave passes through solid material, the energy left behind causes damage. When it passes through air it simply grows weaker. The more matter the energy travels through, the smaller the effect. The amount of matter increases with the volume of the imaginary sphere centred on the explosion. Blast effects thus scale with the inverse cube law, which relates radius to volume.

The intensity of nuclear radiation decreases with the inverse square law like thermal radiation. However nuclear radiation is also strongly absorbed by the air it travels through, which causes the intensity to drop off much more rapidly. These scaling laws show that the effects of thermal radiation grow rapidly with yield (relative to blast), while those of radiation rapidly decline.

In the Hiroshima attack (bomb yield approx. 15 kt) casualties (including fatalities) were seen from all three causes. Burns (including those caused by the ensuing fire storm) were the most prevalent serious injury (two thirds of those who died the first day were burned), and occurred at the greatest range. Blast and burn injuries were both found in 60-70% of all survivors. People close enough to suffer significant radiation illness were well inside the lethal effects radius for blast and flash burns, as a result only 30% of injured survivors showed radiation illness. Many of these people were sheltered from burns and blast and thus escaped their main effects. Even so, most victims with radiation illness also had blast injuries or burns as well.

With yields in the range of hundreds of kilotons or greater (typical for strategic warheads) immediate radiation injury becomes insignificant. Dangerous radiation levels only exist so close to the explosion that surviving the blast is impossible. On the other hand, fatal burns can be inflicted well beyond the range of substantial blast damage. A 20-megaton bomb can cause potentially fatal third degree burns at a range of 40 km, where the blast can do little more than break windows and cause superficial cuts.

It should be noted that the atomic bombings of Hiroshima and Nagasaki caused fatality rates were ONE TO TWO ORDERS OF MAGNITUDE higher than the rates in conventional fire raids on other Japanese cities. Eventually on the order of 200,000 fatalities, which is about one-quarter of all Japanese bombing deaths, occurred in these two cities with a combined population of less than 500,000. This is due to the fact that the bombs inflicted damage on people and buildings virtually instantaneously and without warning, and did so with the combined effects of flash, blast, and radiation. Widespread fatal injuries were thus inflicted instantly, and the many more people were incapacitated and thus unable to escape the rapidly developing fires in the suddenly ruined cities. Fire raids in comparison, inflicted few immediate or direct casualties; and a couple of hours elapsed from the raid's beginning to the time when conflagrations became general, during which time the population could flee.

A convenient rule of thumb for estimating the short-term fatalities from all causes due to a nuclear attack is to count everyone inside the 5-psi blast overpressure contour around the hypocenter as a fatality. In reality, substantial numbers of people inside the contour will survive and substantial numbers outside the contour will die, but the assumption is that these two groups will be roughly equal in size and balance out. This completely ignores any possible fallout effects.

Damage Type 10 KT Airburst 1,980' 1 MT Airburst 8,000' 20 MT Airburst 17,500'
Vaporization Point — Everything is vaporized by the atomic blast. 98% fatalities. Overpressure = 25 psi. Wind velocity = 320 mph. ½ 2 ½ 8 ¾
Total Destruction — All structures above ground are destroyed. 90% fatalities. Overpressure = 17 psi. Wind velocity = 290 mph. 1 3 ¾ 14
Severe Blast Damage — Factories and other large-scale building collapse. Severe damage to highway bridges. Rivers sometimes flow counter current. 65% fatalities, 30% injured. Overpressure = 9 psi. Wind velocity = 260 mph. 1 ¾ 6 ½ 27
Severe Heat Damage — Everything flammable burns. People in the area suffocate due to the fact that the fires consume most available oxygen. 50% fatalities, 45% injured. Overpressure = 6 psi. Wind velocity = 140 mph. 2 ½ 7 ¾ 31
Severe Fire & Wind Damage — Residency structures are severely damaged. People are blown around. 2nd and 3rd-degree burns suffered by most survivors. 15% dead. 50% injured. Overpressure = 3 psi. Wind velocity = 98 mph. 3 10 35

A detonation in or over water will produce a tsunami.

Overview of Delayed Effects

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

Radioactive Contamination

The chief delayed effect is the creation of huge amounts of radioactive material with long lifetimes (half-lives ranging from days to millennia). The primary source of these products is the debris left from fission reactions. A potentially significant secondary source is neutron capture by non-radioactive isotopes both within the bomb and in the outside environment.

When atoms fission they can split in some 40 different ways, producing a mix of about 80 different isotopes. These isotopes vary widely in stability, some our completely stable while others undergo radioactive decay with half-lives of fractions of a second. The decaying isotopes may themselves form stable or unstable daughter isotopes. The mixture thus quickly becomes even more complex; some 300 different isotopes of 36 elements have been identified in fission products.

Short-lived isotopes release their decay energy rapidly, creating intense radiation fields that also decline quickly. Long-lived isotopes release energy over long periods of time, creating radiation that is much less intense but more persistent. Fission products thus initially have a very high level of radiation that declines quickly, but as the intensity of radiation drops, so does the rate of decline.

A useful rule-of-thumb is the "rule of sevens". This rule states that for every seven-fold increase in time following a fission detonation (starting at or after 1 hour), the radiation intensity decreases by a factor of 10. Thus after 7 hours, the residual fission radioactivity declines 90%, to one-tenth its level of 1 hour. After 7x7 hours (49 hours, approx. 2 days), the level drops again by 90%. After 7x2 days (2 weeks) it drops a further 90%; and so on for 14 weeks. The rule is accurate to 25% for the first two weeks, and is accurate to a factor of two for the first six months. After 6 months, the rate of decline becomes much more rapid. The rule of sevens corresponds to an approximate t-1.2 scaling relationship.

These radioactive products are most hazardous when they settle to the ground as "fallout". The rate at which fallout settles depends very strongly on the altitude at which the explosion occurs, and to a lesser extent on the size of the explosion.

If the explosion is a true air burst (the fireball does not touch the ground), when the vaporized radioactive products cool enough to condense and solidify, they will do so to form microscopic particles. These particles are mostly lifted high into the atmosphere by the rising fireball, although significant amounts are deposited in the lower atmosphere by mixing that occurs due to convective circulation within the fireball. The larger the explosion, the higher and faster the fallout is lofted, and the smaller the proportion that is deposited in the lower atmosphere. For explosions with yields of 100 kt or less, the fireball does not rise above the troposphere where precipitation occurs. All of this fallout will thus be brought to the ground by weather processes within months at most (usually much faster). In the megaton range, the fireball rises so high that it enters the stratosphere. The stratosphere is dry, and no weather processes exist there to bring fallout down quickly. Small fallout particles will descend over a period of months or years. Such long-delayed fallout has lost most of its hazard by the time it comes down, and will be distributed on a global scale. As yields increase above 100 kt, progressively more and more of the total fallout is injected into the stratosphere.

An explosion closer to the ground (close enough for the fireball to touch) sucks large amounts of dirt into the fireball. The dirt usually does not vaporize, and if it does, there is so much of it that it forms large particles. The radioactive isotopes are deposited on soil particles, which can fall quickly to earth. Fallout is deposited over a time span of minutes to days, creating downwind contamination both nearby and thousands of kilometres away. The most intense radiation is created by nearby fallout, because it is more densely deposited, and because short-lived isotopes haven't decayed yet. Weather conditions can affect this considerably of course. In particular, rainfall can "rain out" fallout to create very intense localized concentrations. Both external exposure to penetrating radiation, and internal exposure (ingestion of radioactive material) pose serious health risks.

Explosions close to the ground that do not touch it can still generate substantial hazards immediately below the burst point by neutron-activation. Neutrons absorbed by the soil can generate considerable radiation for several hours.

The megaton class weapons that were developed in the US and Russia during the fifties and sixties have been largely retired, being replaced with much smaller yield warheads. The yield of a modern strategic warhead is, with few exceptions, now typically in the range of 200-750 kt. Recent work with sophisticated climate models has shown that this reduction in yield results in a much larger proportion of the fallout being deposited in the lower atmosphere, and a much faster and more intense deposition of fallout than had been assumed in studies made during the sixties and seventies. The reduction in aggregate strategic arsenal yield that occurred when high yield weapons were retired in favour of more numerous lower yield weapons has actually increased the fallout risk.
Effects on the Atmosphere and Climate

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

Although not as directly deadly as fallout, other environmental effects can be quite harmful.

Stress Intensity & Extent Process of effects Eco system effects
Local, global radioactive fallout from nuclear detonation and nuclear facilities >= 100 rem avg. background; >= 200 rem over large area in N.H. Direct health effects; immune system depression; differential radio-sensitivities of species; genetic effects Alteration in trophic structures; pest outbreaks; replacement by opportunistic species; genetic and ontogenetic anomalies
Enhanced UV-B 4-fold increase over N.H. Suppression of photo-synthesis; direct health effects; differential sensitivities of species; damage to vision systems; immune system depression Reduction in primary productivity; alterations in marine trophic structures; blindness in terrestrial animals; behavioural effects of insects including essential pollinators
Fire Secondary fires widespread over N.H.; >= 5% of terrestrial ecosystems affected Direct loss of plants; damage to seed stores; changes in albedo; habitat destruction Deforestation and desertification
which continues via positive feedback; local climatic changes; large-scale erosion and siltation; species extinction; nutrient dumping
Chemical pollution of surface waters Pyrotoxins; release from chemical storage areas Direct health effects; differential sensitivities among species; bio concentration Loss of organisms; continued contamination of surface and groundwater systems; loss of water for human consumption
Chemical pollution of atmosphere Major releases of NOx, O3, and pyrogenic pollutants from detonations; major releases of toxic organics from secondary fires in urban areas, chemical storage facilities Direct health effects; differential sensitivities among species; acid precipitation Widespread smog; freshwater acidification; nutrient dumping
Harm to the Ozone Layer

The high temperatures of the nuclear fireball followed by rapid expansion and cooling, cause large amounts of nitrogen oxides to form from the oxygen and nitrogen in the atmosphere (very similar to what happens in combustion engines). Each megaton of yield will produce some 5000 tons of nitrogen oxides. The rising fireball of a high kiloton or megaton range warhead will carry these nitric oxides well up into the stratosphere, where they can reach the ozone layer. A series of large atmospheric explosions could significantly deplete the ozone layer. The high yield tests in the fifties and sixties probably did cause significant depletion, but the ozone measurements made at the time were too limited to pick up the expected changes out of natural variations.

Nuclear winter

It is believed that the amount of energy needed to create a nuclear winter on the Earth as a result of nuclear war is about 8,000 megatons, or a NEO strike of a 450-metre object, or a similar force of an erupting volcano. Any of these catastrophic events could cause a nuclear winter.

This effect is caused by the absorption of sunlight when large amounts of soot are injected into the atmosphere by the widespread burning of cities and petroleum stocks destroyed in a nuclear attack. Similar events have been observed naturally when large volcanic eruptions have injected large amounts of dust into the atmosphere. The Tambora eruption of 1815 (the largest volcanic eruption in recent history) was followed by "the year without summer" in 1816, the coldest year in the last few centuries.

The famous TTAPS (Turco, Toon, Ackerman, Pollack, and Sagan) proposal regarding a potential nuclear winter following a large scale nuclear war was met with significant skepticism and criticism, later and more sophisticated work by researchers around the world have confirmed it in all essential details. These studies predict that the amount of soot that would be produced by burning most of the major cities in the US and Russia would severely disrupt climate on a worldwide basis. The major effect would be a rapid and drastic reduction in global temperature, especially over land. All recent studies indicate that if large-scale nuclear attacks occur against urban or petrochemical targets, average temperature reductions of at least 10°C would occur lasting many months. This level of cooling far exceeds any that has been observed in recorded history, and is comparable to that of a full scale ice age. In areas downwind from attack sites, the cooling can reach 35°C. It is probable that no large-scale temperature excursion of this size has occurred in 65 million years.

Smaller attacks would create reduced effects of course. But it has been pointed out that most of the world's food crops are subtropical plants that would have dramatic drops in productivity if an average temperature drop of even one degree were to occur for even a short time during the growing season. Since the world maintains a stored food supply equal to only a few months of consumption, a war during the Northern Hemisphere spring or summer could still cause deadly starvation around the globe from this effect alone even if it only produced a mild "nuclear autumn".

Within a day the amount of sunlight will be reduced to about 1% of normal. After a week the average mid-continent temperatures will drop to around -20°C to -30°C and it will take over 100 days for the skies to clear (for an average nuclear exchange).

The main effect of a nuclear winter will be famine, with an expected 9 Billion (109 or 1,000,000,000 or a Thousand Million) dying from starvation worldwide. Survivors will need to be well sheltered, well clothed and able to use a lot of energy keeping warm.

Reduced light

Ash and earth from the impact/blast will be ejected into the atmosphere, spreading all over the world. Additional ash and smoke, mainly from urban fires but also from rural grassland or forest fires, will compound the situation.

Forest plants generally have the greatest ability to withstand darkness. But with a 99% loss of light, most plants will be prevented from growing — they will use up their reserves of nutrients and eventually die. This will effectively kill off the base of the terrestrial food chain and produce resulting starvation for all species. Similarly in the oceans, low light is likely to kill off phytoplankton that forms the basis of the food chain for many species.

Reduced light will have other impacts on the survivors who have to face a harsh world in the dark.

Reduced temperatures

In addition to the loss of the vast majority of sunlight, the eco system faces freezing temperatures. Nearly all plants inland will be killed or severely damaged by the cold if the nuclear winter occurs in the spring or summer due to the tremendous temperature drop and the loss of sunlight will make matters worse. If the nuclear winter happens late in the season (autumn or winter) then some plants may have already prepared themselves for cold and be less shocked by the freezing.

All terrestrial food production will be brought to a halt for the first year. Only after they have been re-sown or re-sprouted will plants have a chance to grow again but this cannot happen in freezing conditions and low light.

Many animals die at temperatures higher than freezing, so at the low temperatures expected few will survive. Some invertebrate animals will survive freezing but vertebrates will either not survive or they will at least die later of the consequences of the dire conditions. Cattle, sheep and goat breeds can survive low temperatures but poultry and swine breeds cannot. All surviving animals would face competition for limited forage.

Surface water and lake water will freeze, greatly reducing the drinking water of all species. Most pooled water will freeze to about a metre depth. The freezing depth of surface water can be calculated by the following equation:

I = a (FDD) ½

I = the ice thickness in centimetres
a = a constant (3.41 in ideal conditions but varying between 1.7 and 3.07 in practice)
FDD = cumulative freezing degree-days

Because the freezing will not affect deep water, marine life will fare better, but the low light will affect everything. It is expected that the lack of sunlight will kill off phytoplankton that form the basis of the food chain for many species.

Weather conditions

Due to the cold, less precipitation is expected and what comes will fall as ice or snow. Rainwater run off will fall by a half, or more, of usual levels and within a month rivers will be reduced by ¾ of their normal volume as a result.

Coasts will be warmer than inland areas as the sea is able to contain its stored heat better than land. The temperature differences on the coasts will produce particularly violent weather conditions. This will prevent fishing for food and make coastal regions hazardous.

Lack of food and water

Studies have shown that, in general, urban dwellers keep only 2 to 7 days supply of food – choosing to visit the supermarkets or local shops regularly. Within a week urban survivors will be without adequate food. Rural survivors may fare better and are less likely to be as disrupted as town dwellers; as a result they will be better prepared and organised to withstand the competition for resources that people moving out of the cities will produce. The country folk will also be protecting their homes and on known territory and within the people they know whilst the town people will be on unfamiliar territory and possible disorganised and split up from family and friends.

Under normal circumstances the UK produces 60% of its food needs – these will not be normal circumstances. Fruit and vegetables that are primarily imported won't arrive. All food production and imports will effectively stop.

Food storage will primarily be in rural districts where farms store food for livestock and grain for sowing or have grain after harvesting. However, those in most need of food will be in urban areas and there will be no transport systems or social organisation to distribute it. Grain storage may help feed the population and sustain adequate calories and proteins but people will become malnourished in vitamins B 12, C, A, riboflavin, calcium and iron (and vitamin D because of the lack of sunshine).

Water will be short due to the freezing temperatures and low rainfall. All shallow surface water will be frozen and deep water will freeze to about a metre.

If the nuclear winter was caused by a nuclear exchange then both food and water may be contaminated. Although this is not likely to prevent its use in the short term, long-term affects are likely to be dire.

Agriculture will be practically impossible for the first year. On average 600kg of goods and supplies must be delivered from factory to farm for each hectare that is cultivated. Even if the supplies were there the structure to transport the goods or organise a labour force will not be present.

Social structure

After a nuclear blast (or a meteor strike) studies suggest that 40% of survivors may sustain multiple injuries (burns, physical traumas, shock etc); a greater proportion will have flash blindness. Flash blindness, received at the speed of light from the intense brightness of the strike, prevents many people avoiding dangers from the blast that they may otherwise have avoided. It should be noted that flash blindness could affect you even if you do not look directly at the blast; studies, during nuclear testing, have proven that even reflected light (off of a light wall for instance) from a nuclear explosion is sufficiently strong to inflict blindness.

There will be an overwhelming desire to flee the area of destruction hindered by blindness. This immediate exodus of people fleeing the target area will reverse within a day to a tremendous influx of people in search of relatives and friends.

Social order will not be maintained with intense competition, almost immediately, for basic requirements (shelter, clothing, food and water). Survivability, in the early days, will rest on four subjects:

  • Adequate shelter;
  • Safe food and water;
  • Medical care for serious injuries;
  • Self-protection from blast, fire and human threats.

It is estimated that 50% of survivors of the strike area will suffer from severe mental and behavioural disturbances.

The low light levels and freezing temperatures will limit travel, communications, interaction and organisation.

People will group, initially into family units but later to form extended family units so that they have companionship, safety and assistance.

As time passes there will be increasing competition for scarce resources. Malnutrition of survivors will lead to chronic illnesses from protein and vitamin deficiencies. Inadequate diet and cold temperatures will lover people's natural resistance to communicable diseases such as measles and diphtheria and respiratory diseases such as streptococcal and pneumococcal infections and tuberculosis. Inadequate sanitation will lead to enteric diseases – hepatitis, cholera, dysentery and typhoid.

Uncontrolled insect growth will add to the problem and help spread tetanus, rabies and plague.


A summary of effects over time is given in the following tables:

Time after nuclear war
First few months
End of first year
Next decade
I. Natural Ecosystems: Terrestrial
Extreme cold, independent of season and widespread over Earth would severely damage plants, particularly in mid-latitudes in the Northern Hemisphere and in the tropics. Particulates obscuring sunlight would severely curtail photosynthesis, essentially eliminating plant productivity. Extreme cold, unavailability of fresh water, and near darkness would severely stress most animals, with widespread mortality. Storm events of unprecedented intensity would devastate ecosystems, especially at margins of continents. Many hardy perennial plants and most seeds of temperate plants would survive, but plant productivity would continue to be depressed significantly. As the atmosphere clears, increased UV-B would damage plants and impair vision systems of many animal species. Limited primary productivity would cause intense competition for resources among animals. Many tropical species would continue to suffer fatalities or reduced productivity from temperature stress. Widespread extinction of vertebrates. The basic potential for primary and secondary productivity would gradually recover; however, extensive irreversible damage to ecosystems would have occurred. Ecosystems structure and processes would continue to respond unstably to perturbations, and long period of time might follow before functional redundancies would re-establish ecosystem homeostasis. Massive loss of species, especially in tropical areas, would lead to reduced genetic and species diversity.
I. Natural Ecosystems: Aquatic
Temperature extremes would result in widespread ice formation on most fresh- water bodies throughout the Earth, particularly in the Northern Hemisphere and in mid-latitude continental areas. Marine ecosystems would be largely buffered from extreme temperatures, with effects limited to coastal and shallow tropical areas. Light reductions would essentially terminate phytoplankton productivity, eliminating the support base for many marine and freshwater animal species. Storms at continental margins would stress shallow­-water ecosystems and add to sediment loadings. Potential food sources would not be accessible to humans or would be contaminated by radionuclides and toxic substances. Early loss of phytoplankton would continue to be felt in population collapses in many herbivore and carnivore species in marine ecosystems; benthic communities would not be as disrupted. Freshwater ecosystems would begin to thaw, but many species would have been lost. Organisms in temperate marine and freshwater systems adapted to seasonal temperature fluctuations­ would recover more quickly and extensively than in tropical regions. Recovery would proceed more rapidly than for terrestrial ecosystems. Species extinctions would be more likely in tropical areas. Coastal marine ecosystems would begin to contain harvestable food sources, although contamination could continue.
II. Agroecosystems
Extreme temperatures and low light levels would preclude virtually any net productivity in crops anywhere on Earth. Supplies of food in targeted areas would be destroyed, contaminated, remote, or quickly depleted. Non-targeted importing countries would lose subsidies from N. America and other food exporters. Potential crop productivity would remain low because of continued though much less extreme temperature depressions. Sunlight would not be limiting but would be enriched with UV-B. Reduced precipitation and loss of soil from storm events would reduce potential productivity. It is unlikely that organized agriculture would occur, and modern subsidies of energy, fertilizers, pesticides, etc., would not be available. Stored food would be essentially depleted, and potential draught animals would have suffered extensive fatalities and consumption by humans.
The biotic potential for crop production would gradually be restored. Limiting factors for return of agriculture would relate to human support for water, energy, pest and disease protection, etc.
II Human Societal Systems
Survivors of immediate effects (from blast, fire, and initial ionising radiation) would include perhaps 50—75% of Earth's population. Extreme temperatures, near darkness, violent storms, loss of shelter and fuel supplies would result in widespread fatalities from exposure, lack of drinking water, and multitudes of synergisms with other impacts, such as radiation exposure, malnutrition, lack of medical systems, psychological stress, etc. Societal support systems for food, energy, transportation, medical care, communications, etc., would cease to function. Climatic impacts would be considerably reduced, but exposure would remain a stress on humans. Loss of agricultural support would dominate adverse human health impacts. Societal systems could not be expected to be functioning and supporting humans. With the return of sunlight and UV-B, widespread eye damage could occur. Psychological stresses, radiation exposures, and many synergistic stresses would continue to impact humans adversely. Epidemics and pandemics would be likely. Climatic stresses would not be the primary limiting factors for human recovery. Rates of return of societal order and human support systems would limit rates of human population growth. Human carrying capacities could remain severely depressed from pre-war conditions for a very long period of time, at best.


As the air clears, too much UV-B (many times the normal amount) could cause blindness and melanomas. Many other species may die from UV radiation. Greenhouse gasses in the atmosphere may lead to a big swing of temperatures from well below freezing to above the norm. Such temperature swings of 50°C or more over a few days may kill off some of the surviving species.

Following a nuclear winter, crop production might be at best 1-10% of normal. If a hectare of land is cultivated by hand then it will take 1,200 hours of labour (as apposed to 40 hours in a mechanical farm). Social structures will be disorganised or non-existent and restarting the farming and associated food industries may be very difficult.

Those that survive will be in a poor state. It is likely that everyone will be malnourished and many will be ill. Many areas of disease will exist. Unrestricted insect and rodent growth will lead to epidemics such as plague. People will continue to die from starvation.

Nuclear War Effect Timescales (large)

If the nuclear winter affected the entire globe, which is likely, then recovery will be a very long process stretching into years. If some of the southern hemisphere countries were unaffected then they could assist the troubled countries to recover. Those areas that required a large proportion of food imports before the nuclear winter, such as hot desert regions, will continue to experience dire starvation long after more fertile countries have begun to recover.

Physics of Nuclear Weapon Effects

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

Thermal radiation and blast are inevitable consequences of the near instantaneous release of an immense amount of energy in a very small volume, and are thus characteristic to all nuclear weapons regardless of type or design details. The release of ionising radiation, both at the instant of explosion and delayed radiation from fallout, is governed by the physics of the nuclear reactions involved and how the weapon is constructed, and is thus very dependent on both weapon type and design.

Fireball Physics

The fireball is the hot ball of gas created when a nuclear explosion heats the bomb itself, and the immediate surrounding environment, to very high temperatures. As this incandescent ball of hot gas expands, it radiates part of its energy away as thermal radiation (including visible and ultraviolet light); part of its energy also goes into creating a shock wave or blast wave in the surrounding environment. The generation of these two destructive effects are thus closely linked by the physics of the fireball. In the discussion below I assume the fireball is forming in open air, unless stated otherwise.

The Early Fireball

Immediately after the energy-producing nuclear reactions in the weapon are completed, the energy is concentrated in the nuclear fuels themselves. The energy is stored as (in order of importance): thermal radiation or photons; as kinetic energy of the ionised atoms and the electrons (mostly as electron kinetic energy since free electrons outnumber the atoms); and as excited atoms, which are partially or completely stripped of electrons (partially for heavy elements, completely for light ones). All matter emits Thermal (blackbody) radiation. The intensity and most prevalent wavelength is a function of the temperature, both increasing as temperature increases. The intensity of thermal radiation increases very rapidly — as the fourth power of the temperature. Thus at the 60-100 million degrees C of a nuclear explosion, which is some 10,000 times hotter than the surface of the sun, the brightness (per unit area) is some 10 quadrillion (1016) times greater! Consequently about 80% of the energy in a nuclear explosion exists as photons. At these temperatures the photons are soft x-rays with energies in the range of 10-200 KeV.

The first energy to escape from the bomb is the gamma rays produced by the nuclear reactions. They have energies in the MeV range, and a significant number of them penetrate through the tampers and bomb casing and escape into the outside world at the speed of light. The gamma rays strike and ionise the surrounding air molecules, causing chemical reactions that form a dense layer of "smog" tens of meters deep around the bomb. This smog is composed primarily of ozone, and nitric and nitrous oxides. X-rays, particularly the ones at the upper end of the energy range, have substantial penetrating power and can travel significant distances through matter at the speed of light before being absorbed. Atoms become excited when they absorb x-rays, and after a time they re-emit part of the energy as a new lower energy x-ray. By a chain of emissions and absorptions, the x-rays carry energy out of the hot centre of the bomb, a process called radiative transport. Since each absorption/re-emission event takes a certain amount of time, and the direction of re-emission is random (as likely back toward the centre of the bomb as away from it), the net rate of radiative transport is considerably slower than the speed of light. It is however initially much faster than the expansion of the plasma (ionised gas) making up the fireball or the velocity of the neutrons.

An expanding bubble of very high temperatures is thus formed called the "iso-thermal sphere". It is a sphere where x-rays have heated everything to a nearly uniform temperature, initially in the tens of millions of degrees. As soon as the sphere expands beyond the bomb casing it begins radiating light away through the air (unless the bomb is buried or underwater). Due to the still enormous temperatures, it is incredibly brilliant (surface brightness trillions of times more intense than the sun). Most of the energy being radiated is in the x-ray and far ultraviolet range to which air is not transparent. Even at the wavelengths of the near ultraviolet and visible light, the "smog" layer absorbs much of the energy. Then too, at this stage the fireball is only a few meters across. Thus the apparent surface brightness at a distance, and the output power (total brightness) is not nearly as intense as the fourth-power law would indicate.

Blast Wave Development and Thermal Radiation Emission

As the fireball expands, it cools and the wavelength of the photons transporting energy drops. Longer wavelength photons do not penetrate as far before being absorbed, so the speed of energy transport also drops. When the isothermal sphere cools to about 300,000°C (and the surface brightness has dropped to being a mere 10 million times brighter than the sun), the rate of radioactive growth is about equal to the speed of sound in the fireball plasma. At this point a shock wave forms at the surface of the fireball as the kinetic energy of the fast moving ions starts transferring energy to the surrounding air. This phenomenon, known as "hydrodynamic separation", occurs for a 20 kt explosion about 100 microseconds after the explosion, when the fireball is some 13 meters across. A shock wave internal to the fireball caused by the rapidly expanding bomb debris may overtake and reinforce the fireball surface shock wave a few hundred microseconds later.

The shock wave initially moves at some 30 km/sec, a hundred times the speed of sound in normal air. This compresses and heats the air enormously, up to 30,000°C (some five times the sun's surface temperature). At this temperature the air becomes ionised and incandescent. Ionised gas is opaque to visible radiation, so the glowing shell created by the shock front hides the much hotter isothermal sphere inside. The shock front is many times brighter than the sun, but since it is much dimmer than the isothermal sphere it acts as an optical shutter, causing the fireball's thermal power to drop rapidly.

The fireball is at its most brilliant just as hydrodynamic separation occurs, the great intensity compensating for the small size of the fireball. The rapid drop in temperature causes the thermal power to drop ten-fold, reaching a minimum in about 10 milliseconds for a 20 kt bomb (100 milliseconds for 1 Mt bomb). This "first pulse" contains only about 1 percent of the bomb's total emitted thermal radiation. At this minimum, the fireball of a 20 kt bomb is 180 meters across.

As the shock wave expands and cools to around 3000°C , it stops glowing and gradually also becomes transparent. This is called "breakaway" and occurs at about 15 milliseconds for a 20 kt bomb, when the shock front has expanded to 220 meters and is traveling at 4 km/second. The isothermal sphere, at a still very luminous 8000 degrees, now becomes visible and both the apparent surface temperature and brightness of the fireball climb to form the "second pulse". The isothermal sphere has grown considerably in size and now consists almost entirely of light at wavelengths to which air is transparent, so it regains much of the total luminosity of the first peak despite its lower temperature. This second peak occurs at 150 milliseconds for a 20 kt bomb, at 900 milliseconds for a 1 Mt bomb. After breakaway, the shock (blast) wave and the fireball do not interact further.

A firm cut-off for this second pulse is impossible to provide because the emission rate gradually declines over an extended period. Some rough guidelines are that by 300 milliseconds for a 20 kt bomb (1.8 seconds for a 1 Mt) 50% of the total thermal radiation has been emitted, and the rate has dropped to 40% of the second peak. These figures become 75% total emitted and 10% peak rate by 750 milliseconds (20 kt) and 4.5 second (1 Mt). The emission time scales roughly as the 0.45 power of yield (Y0.45).

Although this pulse never gets as bright as the first, it emits about 99% of the thermal radiation because it is so much longer.

Ionising Radiation Physics

There are four types of ionising radiation produced by nuclear explosions that can cause significant injury: neutrons, gamma rays, beta particles, and alpha particles. Gamma rays are energetic (short wavelength) photons (as are X-rays), beta particles are energetic (fast moving) electrons, and alpha particles are energetic helium nuclei. Neutrons are damaging whether they are energetic or not, although the faster they are, the worse their effects.

They all share the same basic mechanism for causing injury though: the creation of chemically reactive compounds called "free radicals" that disrupt the normal chemistry of living cells. These radicals are produced when the energetic radiation strikes a molecule in the living issue, and break it into ionised (electrically charged) fragments. Fast neutrons can do this also, but all neutrons can also transmute ordinary atoms into radioactive isotopes, creating even more ionising radiation in the body.

The different types of radiation present different risks however. Neutrons and gamma rays are very penetrating types of radiation. They are the hardest to stop with shielding. They can travel through hundreds of meters of air and the walls of ordinary houses. They can thus deliver deadly radiation doses even if an organism is not in immediate contact with the source. Beta particles are less penetrating, they can travel through several meters of air, but not walls, and can cause serious injury to organisms that are near to the source. Alpha particles have a range of only a few centimetres in air, and cannot even penetrate skin. Alphas can only cause injury if the emitting isotope is ingested.

The shielding effect of various materials to radiation is usually expressed in half-value thickness, or tenth-value thickness: in other words, the thickness of material required to reduce the intensity of radiation by one-half or one-tenth. Successive layers of shielding each reduce the intensity by the same proportion; so three tenth-value thicknesses reduce the intensity to one-thousandth (a tenth-value thickness is about 3.3 half-value thicknesses). Some example tenth-value thickness for gamma rays are: steel 8.4-11 cm, concrete 28-41 cm, earth 41-61 cm, water 61-100 cm, and wood 100-160 cm. The thickness ranges indicate the varying shielding effect for different gamma ray energies.

Even light clothing provides substantial shielding to beta rays.

Sources of Radiation

Prompt Radiation

Radiation is produced directly by the nuclear reactions that generate the explosion, and by the decay of radioactive products left over (either fission debris, or induced radioactivity from captured neutrons).

The explosion itself emits a very brief burst (about 100 nanoseconds) of gamma rays and neutrons, before the bomb has blown itself apart. The intensity of these emissions depends very heavily on the type of weapon and the specific design. In most designs the initial gamma ray burst is almost entirely absorbed by the bomb (tamper, casing, explosives, etc.) so it contributes little to the radiation hazard. The neutrons, being more penetrating, may escape. Both fission and fusion reactions produce neutrons. Fusion produces many more of them per kiloton of yield, and they are generally more energetic than fission neutrons. Some weapons (neutron bombs) are designed specifically to emit as much energy in the form as neutrons as possible. In heavily tamped fission bombs few if any neutrons escape. It is estimated that no significant neutron exposure occurred from Fat Man, and only 2% of the total radiation dose from Little Boy was due to neutrons.

The neutron burst (itself) can be a significant source of radiation, depending on weapon design. As the neutrons travel through the air they are slowed by collisions with air atoms, and are eventually captured. Even this process of neutron attenuation generates hazardous radiation. Part of the kinetic energy lost by fast neutrons as they slow is converted into gamma rays, some with very high energies (for the 14.1 MeV fusion neutrons). The duration of production for these neutron scattering gammas is about 10 microseconds. The capture of neutrons by nitrogen-14 also produces gammas, a process completed by 100 milliseconds.

Immediately after the explosion, there are substantial amounts of fission products with very short half-lives (milliseconds to minutes). The decay of these isotopes generates correspondingly intense gamma radiation that is emitted directly from the fireball. This process is essentially complete within 10 seconds.

The relative importance of these gamma ray sources depends on the size of the explosion. Small explosions (20 kt, say) can generate up to 25% of the gamma dose from the direct gammas and neutron reactions. For large explosions (1 Mt) this contribution is essentially zero. In all cases, the bulk of the gammas are produced by the rapid decay of radioactive debris.

Delayed Radiation

Radioactive decay is the sole source of beta and alpha particles. They are also emitted during the immediate decay mentioned above of course, but their range is too short to make any prompt radiation contribution. Betas and alphas become important when fallout begins settling out. Gammas remain very important at this stage as well.

Fallout is a complex mixture of different radioactive isotopes, the composition of which continually changes as each isotope decays into other isotopes. Many isotopes make significant contributions to the overall radiation level. Radiation from short-lived isotopes dominates initially, and the general trend is for the intensity to continually decline as they disappear. Over time the longer-lived isotopes become increasingly important, and a small number of isotopes emerge as particular long-term hazards.

Radioactive isotopes are usually measured in terms of curies. A curie is the quantity of radioactive material that undergoes 3.7x1010 decays/sec (equal to 1 g of radium-226). More recently the SI unit bequerel has become common in scientific literature, one bequerel is 1 decay/sec. The fission of 57 grams of material produces 3x1023 atoms of fission products (two for each atom of fissionable material). One minute after the explosion, this mass is undergoing decays at a rate of 1021 disintegrations/sec (3x1010 curies). It is estimated that if these products were spread over 1 km2, then at a height of 1 m above the ground one hour after the explosion the radiation intensity would be 7500 rads/hr.

Isotopes of special importance include iodine-131, strontium-90 and 89, and cesium-137. This is due to both their relative abundance in fallout, and to their special biological affinity. Isotopes that are readily absorbed by the body, and concentrated and stored in particular tissues can cause harm out of proportion to their abundance.

Iodine-131 is a beta and gamma emitter with a half-life of 8.07 days (specific activity 124,000 curies/g) its decay energy is 970 KeV; usually divided between 606 KeV beta, 364 KeV gamma. Due to its short half-life it is most dangerous in the weeks immediately after the explosion, but hazardous amounts can persist for a few months. It constitutes some 2% of fission-produced isotopes — 1.6x105 curies/kt. Iodine is readily absorbed by the body and concentrated in one small gland, the thyroid.

Strontium-90 is a beta emitter (546 KeV, no gammas) with a half-life of 28.1 years (specific activity 141 curies/g); Sr-89 is a beta emitter (1.463 MeV, gammas very rarely) with a half-life of 52 days (specific activity 28,200 Ci/g). Each of these isotopes constitutes about 3% of total fission isotopes: 190 curies of Sr-90 and 3.8x104 curies of Sr-89 per kiloton. Due to their chemical resemblance to calcium these isotopes are absorbed fairly well, and stored in bones. Sr-89 is an important hazard for a year or two after an explosion, but Sr-90 remains a hazard for centuries. Actually most of the injury from Sr-90 is due to its daughter isotope yttrium-90. Y-90 has a half-life of only 64.2 hours, so it decays as fast as it is formed, and emits 2.27 MeV beta particles.

Cesium-137 is a beta and gamma emitter with a half-life of 30.0 years (specific activity 87 Ci/g). Its decay energy is 1.176 MeV; usually divided by 514 KeV beta, 662 KeV gamma. It comprises some 3-3.5% of total fission products — 200 curies/kt. It is the primary long-term gamma emitter hazard from fallout, and remains a hazard for centuries.

Although not important for acute radiation effects, the isotopes carbon-14 and tritium are also of interest because of possible genetic injury. These are not direct fission products. They are produced by the interaction of fission and fusion neutrons with the atmosphere and, in the case of tritium, as a direct product of fusion reactions. Most of the tritium generated by fusion is consumed in the explosion but significant amounts survive. Tritium is also formed by the capture of fast neutrons by nitrogen atoms in the air: N-14 + n - > T + C-12. Carbon-14 in also formed by neutron-nitrogen reactions: N-14 + n - > C-14 + p. Tritium is a very weak beta emitter (18.6 KeV, no gamma) with a half-life of 12.3 years (9700 Ci/g).

Carbon-14 is also a weak beta emitter (156 KeV, no gamma), with a half-life of 5730 years (4.46 Ci/g). Atmospheric testing during the fifties and early sixties produced about 3.4 g of C-14 per kiloton (15.2 curies) for a total release of 1.75 tonnes (7.75x106 curies). For comparison, only about 1.2 tonnes of C-14 naturally exists, divided between the atmosphere (1 tonne) and living matter (0.2 tonne). Another 50-80 tonnes is dissolved in the oceans. Due to carbon exchange between the atmosphere and oceans, the half-life of C-14 residing in the atmosphere is only about 6 years. By now the atmospheric concentration has returned to within 1% or so of normal. High levels of C-14 remain in organic material formed during the sixties (in wood, say, or DNA).

Air Bursts and Surface Bursts

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

It might seem logical that the most destructive way of using a nuclear weapon would be to explode it right in the middle of its target — i.e. ground level. But for most uses this is not true. Generally nuclear weapons are designed to explode above the ground — as air bursts (the point directly below the burst point is called the hypocenter). Surface (and sub-surface) bursts can be used for special purposes.

Air Bursts

When an explosion occurs it sends out a shock wave like an expanding soap bubble. If the explosion occurs above the ground the bubble expands and when it reaches the ground it is reflected — i.e. the shock front bounces off the ground to form a second shock wave traveling behind the first. This second shock wave travels faster than the first, or direct, shock wave since it is traveling through air already moving at high speed due to the passage of the direct wave. The reflected shock wave tends to overtake the direct shock wave and when it does they combine to form a single reinforced wave.

This is called the Mach Effect, and produces a skirt around the base of the shock wave bubble where the two shock waves have combined. This skirt sweeps outward as an expanding circle along the ground with an amplified effect compared to the single shock wave produced by a ground burst.

The higher the burst altitude, the weaker the shock wave is when it first reaches the ground. On the other hand, the shock wave will also affect a larger area. Air bursts therefore reduce the peak intensity of the shock wave, but increase the area over which the blast is felt. For a given explosion yield, and a given blast pressure, there is a unique burst altitude at which the area subjected to that pressure is maximized. This is called the optimum burst-height for that yield and pressure.

All targets have some level of vulnerability to blast effects. When some threshold of blast pressure is reached the target is completely destroyed. Subjecting the target to pressures higher than that accomplishes nothing. By selecting an appropriate burst height, an airburst can destroy a much larger area for most targets than can surface bursts.

The Mach Effect enhances shock waves with pressures below 50-psi. At or above this pressure the effect provides very little enhancement, so air bursts have little advantage if very high blast pressures are desired.

An additional effect of air bursts is that thermal radiation is also distributed in a more damaging fashion. Since the fireball is formed above the earth, the radiation arrives at a steeper angle and is less likely to be blocked by intervening obstacles and low altitude haze.

Surface Bursts

Surface bursts are useful if local fallout is desired, or if the blast is intended to destroy a buried or very hard structure like a missile silo or a dam. Shock waves are transmitted through the soil more effectively if the bomb is exploded in immediate contact with it, so ground bursts would be used for destroying buried command centres and the like. Some targets, like earth-fill dams, require actual cratering to be destroyed and would be ground burst targets.

Sub-Surface Bursts
Exploding a bomb below ground level can be even more effective for producing craters and destroying buried structures. It can also eliminate thermal radiation and reduce the range of blast effects substantially. The problem, of course is getting the bomb underground. Earth-penetrating bombs have been developed that can punch over one hundred feet into the earth.

Electromagnetic Effects

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

The high temperatures and energetic radiation produced by nuclear explosions also produce large amounts of ionised (electrically charged) matter that is present immediately after the explosion. Under the right conditions, intense currents and electromagnetic fields can be produced, generically called EMP (Electromagnetic Pulse), that are felt at long distances. Living organisms are impervious to these effects, but they can temporarily or permanently disable electrical and electronic equipment. Ionised gases can also block short wavelength radio and radar signals (fireball blackout) for extended periods.

The occurrence of EMP is strongly dependent on the altitude of burst. It can be significant for surface or low altitude bursts (below 4,000 m); it is very significant for high altitude bursts (above 30,000 m); but it is not significant for altitudes between these extremes. This is because EMP is generated by the asymmetric absorption of instantaneous gamma rays produced by the explosion. At intermediate altitudes the air absorbs these rays fairly uniformly and does not generate long-range electromagnetic disturbances.

The formation EMP begins with the very intense, but very short burst of gamma rays caused by the nuclear reactions in the bomb. About 0.3% of the bomb's energy is in this pulse, but it lasts for only 10 nanoseconds or so. These gamma rays collide with electrons in air molecules, and eject the electrons at high energies through a process called Compton scattering. These energetic electrons in turn knock other electrons loose, and create a cascade effect that produces some 30,000 electrons for every original gamma ray.

In low altitude explosions the electrons, being very light, move much more quickly than the ionised atoms they are removed from and diffuse away from the region where they are formed. This creates a very strong electric field that peaks in intensity at 10 nanoseconds. The gamma rays emitted downward however are absorbed by the ground, which prevents charge separation from occurring. This creates a very strong vertical electric current that generates intense electromagnetic emissions over a wide frequency range (up to 100 MHZ) that emanate mostly horizontally. At the same time, the earth acts as a conductor allowing the electrons to flow back toward the burst point where the positive ions are concentrated. This produces a strong magnetic field along the ground. Although only about 3x10-10 of the total explosion energy is radiated as EMP in a ground burst (106 joules for 1 Mt bomb), it is concentrated in a very short pulse. The charge separation persists for only a few tens of microseconds, making the emission power some 100 gigawatts. The field strengths for ground bursts are high only in the immediate vicinity of the explosion. For smaller bombs they aren't very important because they are strong only where the destruction is intense anyway. With increasing yields, they reach farther from the zone of intense destruction. With a 1 Mt bomb, they remain significant out to the 2-psi overpressure zone (5 miles).

High altitude explosions produce EMPs that are dramatically more destructive. About 3x10-5 of the bomb's total energy goes into EMP in this case, 1011 joules for a 1 Mt bomb. EMP is formed in high altitude explosions when the downwardly directed gamma rays encounter denser layers of air below. A pancake shaped ionisation region is formed below the bomb. The zone can extend all the way to the horizon, to 2500 km for an explosion at an altitude of 500 km. The ionisation zone is up to 80 km thick at the centre. The Earth's magnetic field causes the electrons in this layer to spiral as they travel, creating a powerful downward directed electromagnetic pulse lasting a few microseconds. A strong vertical electrical field (20-50 KV/m) is also generated between the Earth's surface and the ionised layer, this field lasts for several minutes until the air recaptures the electrons. Although the peak EMP field strengths from high altitude bursts are only 1-10% as intense as the peak ground burst fields, they are nearly constant over the entire Earth's surface under the ionised region.

The effects of these field on electronics is difficult to predict, but can be profound. Enormous induced electric currents are generated in wires, antennas, and metal objects (like missiles, airplanes, and building frames). Commercial electrical grids are immense EMP antennas and would be subjected to voltage surges far exceeding those created by lightning, and over vastly greater areas. Modern VLSI chips are extremely sensitive to voltage surges, and would be burned out by even small leakage currents. Military equipment is generally designed to be resistant to EMP, but realistic tests are very difficult to perform and EMP protection rests on attention to detail. Minor changes in design, incorrect maintenance procedures, poorly fitting parts, loose debris, moisture, and ordinary dirt can all cause elaborate EMP protections to be totally circumvented. It can be expected that a single high yield, high altitude explosion over an industrialized area would cause massive disruption for an indeterminable period, and would cause huge economic damages (all those damaged chips add up).

A separate effect is the ability of the ionised fireball to block radio and radar signals. Like EMP, this effect becomes important with high altitude bursts. Fireball blackout can cause radar to be blocked for tens of seconds to minutes over an area tens of kilometres across. High frequency radio can be disrupted over hundreds to thousands of kilometres for minutes to hours depending on exact conditions.

Mechanisms of Damage and Injury

Credit: Nuclear, Biological and Chemical Warfare by K. Bhushan, G. Katyal

The different mechanisms are discussed individually, but it should be no surprise that in combination they often accentuate the harm caused by each other. I will discuss such combined effects wherever appropriate.

Thermal Damage and Incendiary Effects

Thermal damage from nuclear explosions arises from the intense thermal (heat) radiation produced by the fireball. The thermal radiation (visible and infrared light) falls on exposed surfaces and is wholly or partly absorbed. The radiation lasts from about a tenth of a second to several seconds depending on bomb yield (it is longer for larger bombs). During that time its intensity can exceed 1000 watts/cm2 (the maximum intensity of direct sunlight is 0.14 watts/cm2). For a rough comparison, the effect produced is similar to direct exposure to the flame of an acetylene torch.

The opaque surface layer of the material on which it falls absorbs the heat, which is usually a fraction of a millimetre thick. Naturally dark materials absorb more heat than light coloured or reflective ones. The heat is absorbed much faster than it can be carried down into the material through conduction, or removed by re-radiation or convection, so very high temperatures are produced in this layer almost instantly. Surface temperatures can exceed 1000 degrees C close to the fireball. Such temperatures can cause dramatic changes to the material affected, but they do not penetrate in very far.

More total energy is required to inflict a given level of damage for a larger bomb than a smaller one since the heat is emitted over a longer period of time, but this is more than compensated for by the increased thermal output. The thermal damage for a larger bomb also penetrates further due to the longer exposure.

Thermal radiation damage depends very strongly on weather conditions. Cloud cover, smoke, or other obscuring material in the air can considerably reduce effective damage ranges over clear air conditions.

For all practical purposes, the emission of thermal radiation by a bomb is complete by the time the shock wave arrives. Regardless of yield, this generalization is only violated in the area of total destruction around a nuclear explosion where 100% mortality would result from any one of the three damage effects.

Incendiary effects refer to anything that contributes to the occurrence of fires after the explosion, which is a combination of the effects of thermal radiation and blast.

Thermal Injury

The result of very intense heating of skin is to cause burn injuries. The burns caused by the sudden intense thermal radiation from the fireball are called "flash burns". The more thermal radiation absorbed, the more serious the burn. The table below indicates the amount of thermal radiation required to cause different levels of injury, and the maximum ranges at which they occur, for different yields of bombs. The unit of heat used are gram calories, equal to 4.2 joules (4.2 watts for 1 sec). Skin colour significantly affects susceptibility, light skin being less prone to burns. The table assumes medium skin colour.

Severity 20 KT 1 MT 20 MT
1st Degree 2.5 cal / cm2 (4.3 km) 3.2 cal / cm2 (18 km) 5 cal / cm2 (52 km)
2nd Degree 5 cal / cm2 (3.2 km 6 cal / cm2 (14.4 km) 8.5 cal / cm2 (45 km)
3rd Degree 8 cal / cm2 (2.7 km) 10 cal / cm2 (12 km) 12 cal / cm2 (39 km)

Convenient scaling laws to allow calculation of burn effects for any yield are:

r_thermal_1st = Y0.38 * 1.20
r_thermal_2nd = Y0.40 * 0.87
r_thermal_3rd = Y0.41 * 0.67

Range is in km, yield is in kt; the equations are accurate to within 10% or so from 1 kt to 20 Mt.

First-degree flash burns are not serious, no tissue destruction occurs. They are characterized by immediate pain, followed by reddening of the skin. Pain and sensitivity continues for some minutes or hours, after which the affected skin returns to normal without further incident.

Second degree burns cause damage to the underlying dermal tissue, killing some portion of it. Pain and redness is followed by blistering within a few hours as fluids collect between the epidermis and damaged tissue. Sufficient tissue remains intact however to regenerate and heal the burned area quickly, usually without scarring. Broken blisters provide possible infection sites prior to healing.

Third degree burns cause tissue death all the way through the skin, including the stem cells required fir regenerating skin tissue. The only way a 3rd degree burn can heal is by skin re-growth from the edges, a slow process that usually results in scarring, unless skin grafts are used. Before healing 3rd degree burns present serious risk of infection, and can cause serious fluid loss. A 3rd degree burn over 25% of the body (or more) will typically precipitate shock in minutes, which itself requires prompt medical attention.

Even more serious burns are possible, which have been classified as fourth (even fifth) degree burns. These burns destroy tissue below the skin: muscle, connective tissue etc. They can be caused by thermal radiation exposures substantially in excess of those in the table for 3rd degree burns. Many people close to the hypocenter of the Hiroshima bomb suffered these types of burns. In the immediate vicinity of ground zero the thermal radiation exposure was 100 c/cm2, some fifteen times the exposure required for 3rd degree burns, most of it within the first 0.3 seconds (which was the arrival time of the blast wave). This is sufficient to cause exposed flesh to flash into steam, flaying exposed body areas to the bone.

At the limit of the range for 3rd degree burns, the time lapse between suffering burns and being hit by the blast wave varies from a few seconds for low kiloton explosions to a minute of so for high megaton yields.

Incendiary Effects

Despite the extreme intensity of thermal radiation, and the extraordinary surface temperatures that occur, it has less incendiary effect than might be supposed. This is mostly due to its short duration, and the shallow penetration of heat into affected materials. The extreme heating can cause pyrolysis (the charring of organic material, with the release of combustible gases), and momentary ignition, but it is rarely sufficient to cause self-sustained combustion. This occurs only with tinder-like, or dark, easily flammable materials: dry leaves, grass, old newspaper, thin dark flammable fabrics, tar paper, etc. The incendiary effect of the thermal pulse is also substantially affected by the later arrival of the blast wave, which usually blows out any flames that have already been kindled. Smoldering material can cause re-ignition later however.

The major incendiary effect of nuclear explosions is caused by the blast wave. Collapsed structures are much more vulnerable to fire than intact ones. The blast reduces many structures to piles of kindling, the many gaps opened in roofs and walls act as chimneys, gas lines are broken open, storage tanks for flammable materials are ruptured. The primary ignition sources appear to be flames and pilot lights in heating appliances (furnaces, water heaters, stoves, ovens, etc.). Smoldering material from the thermal pulse can be very effective at igniting leaking gas.

Although the ignition sources are probably widely scattered a number of factors promote their spread into mass fires. The complete suppression of fire fighting efforts is extremely important. Another is that the blast scatters combustible material across firebreaks that normally exist (streets, yards, fire lanes, etc.).

The effectiveness of building collapse, accompanied by the disruption of fire fighting, in creating mass fires can be seen in the San Francisco earthquake (1906), the Tokyo-Yokahama earthquake (1923), and the recent Kobe earthquake (1995). In these disasters there was no thermal radiation to ignite fires, and the scattering of combustible materials did not occur, but huge fires still resulted. In San Francisco and Tokyo-Yokohama these fires were responsible for most of the destruction that occurred.

In Hiroshima the fires developed into a true firestorm. This is an extremely intense fire that produces a rapidly rising column of hot air over the fire area, in turn powerful winds are generated which blow in to the fire area, fanning and feeding the flames. The fires continue until all combustible material is exhausted. Firestorms develop from multiple ignition sources spread over a wide area that create fires that coalesce into one large fire. Temperatures in firestorm areas can reach many hundreds of degrees, carbon monoxide reaches lethal levels, and few people who see the interior of a firestorm live to tell about it. Firestorms can melt roads, cars, and glass. They can boil water in lakes and rivers, and cook people to death in buried bomb shelters. The in-blowing winds can reach gale force, but they also prevent the spread of the fires outside of the area in which the firestorm initially develops. The firestorm in Hiroshima began only about 20 minutes after the bombing.

Nagasaki did not have a firestorm; instead it had a type of mass fire called a conflagration. This is a less intense type of fire; it develops and burns more slowly. A conflagration can begin in multiple locations, or only one. Conflagrations can spread considerable distances from their origins. The fires at Nagasaki took about 2 hours to become well established, and lasted 4-5 hours.

Eye Injury

The brightness and thermal output of a nuclear explosion presents an obvious source of injury to the eye. Injury to the cornea through surface heating, and injury to the retina are both possible risks. Surprisingly, very few cases of injury were noted in Japan. A number of factors acted to reduce the risk. First, eye injury occurs when vision is directed towards the fireball. People spend relatively little time looking up at the sky so only a very small portion of the population would have their eyes directed at the fireball at the time of burst. Second, since the bomb exploded in bright daylight the eye pupil would be expected to be small.

About 4% of the population within the 3rd degree burn zone at Hiroshima reported keratitis, pain and inflammation of the cornea, which lasted several hours to several days. No other corneal damage was noted.

The most common eye injury was flash blindness, a temporary condition in which the visual pigment of retina is bleached out by the intense light. Vision is completely recovered as the pigment is regenerated, a process that takes several seconds to several minutes. This can cause serious problems though in carrying out emergency actions, like taking cover from the oncoming blast wave.

Retinal injury is the most far-reaching injury effect of nuclear explosions, but it is relatively rare since the eye must be looking directly at the detonation. Retinal injury results from burns in the area of the retina where the fireball image is focused. The brightness per unit area of a fireball does not diminish with distance (except for the effects of haze); the apparent fireball size simply gets smaller. Retinal injury can thus occur at any distance at which the fireball is visible, though the affected area of the retina gets smaller as range increases. The risk of injury is greater at night since the pupil is dilated and admits extra light. For explosions in the atmosphere of 100 kt and up, the blink reflex protects the retina from much of the light.

Blast Damage and Injury

Blast damage is caused by the arrival of the shock wave created by the nuclear explosion. Shock waves travel faster than sound, and cause a virtually instantaneous jump in pressure at the shock front. The air immediately behind the shock front is accelerated to high velocities and creates a powerful wind. The wind in turn, creates dynamic pressure against the side of objects facing the blast. The combination of the pressure jump (called the overpressure) and the dynamic pressure causes blast damage.

Both the overpressure and dynamic pressure jump immediately to their peak values when the shock wave arrives. They then decay over a period ranging from a few tenths of a second to several seconds, depending on the strength of the blast and the yield. Following this there is a longer period of weaker negative pressure before the atmospheric conditions return to normal. The negative pressure has little significance as far as causing damage or injury is concerned. A given pressure is more destructive from a larger bomb, due its longer duration.

There is a definite relationship between the overpressure and the dynamic pressure. The overpressure and dynamic pressure are equal at 70 psi, and the wind speed is 1.5 times the speed of sound. Below an overpressure of 70 psi, the dynamic pressure is less than the overpressure; above 70 psi it exceeds the overpressure. Since the relationship is fixed it is convenient to use the overpressure alone as a yardstick for measuring blast effects. At 20 psi overpressure the wind speed is still 500 mph, higher than any tornado wind.

As a general guide, city areas are completely destroyed (with massive loss of life) by over pressures of 5 psi, with heavy damage extending out at least to the 3-psi contour. The dynamic pressure is much less than the overpressure at blast intensities relevant for urban damage, although at 5 psi the wind speed is still 162 mph — close to the peak wind speeds of the most intense hurricanes.

Humans are actually quite resistant to the direct effect of overpressure. Pressures of over 40 psi are required before lethal effects are noted. This pressure resistance makes it possible for unprotected submarine crews to escape from emergency escape locks at depths as great as one hundred feet (the record for successful escape is actually an astonishing 600 feet, representing a pressure of 300 psi). Loss of eardrums can occur, but this is not a life threatening injury.

The danger from overpressure comes from the collapse of buildings that are generally not as resistant. The violent implosion of windows and walls creates a hail of deadly missiles, and the collapse of the structure above can crush or suffocate those caught inside.

The dynamic pressure causes can cause injury by hurling large numbers of objects at high speed. Urban areas contain many objects that can become airborne, and the destruction of buildings generates many more. Serious injury or death can also occur from impact after being thrown through the air.

Blast effects are most dangerous in built-up areas due to the large amounts of projectiles created, and the presence of obstacles to be hurled against.

The blast also magnifies thermal radiation burn injuries by tearing away severely burned skin. This creates raw open wounds that readily become infected.

These many different effects make it difficult to provide a simple rule of thumb for assessing the magnitude of harm produced by different blast intensities. A general guide is given below:

PSI Effects on Buildings Effects on People
1 psi Window glass shatters Light injuries from fragments occur
3 psi Residential structures collapse Serious injuries are common, fatalities may occur
5 psi Most buildings collapse Injuries are universal, fatalities are widespread
10 psi Reinforced concrete buildings are severely damaged or demolished Most people are killed.
20 psi Heavily built concrete buildings are severely damaged or demolished. Fatalities approach 100%.

Suitable scaling constants for the equation r_blast = Y0.33 * constant_bl are:

constant_bl_1_psi = 2.2
constant_bl_3_psi = 1.0
constant_bl_5_psi = 0.71
constant_bl_10_psi = 0.45
constant_bl_20_psi = 0.28

where Y is in kilotons and range is in km.

Radiation Injury

Ionising radiation produces injury primarily through damage to the chromosomes. Since genetic material makes up a very small portion of the mass of a cell, the damage rarely occurs from the direct impact of ionising radiation on a genetic molecule. Instead the damage is caused by the radiation breaking up other molecules and forming chemically reactive free radicals or unstable compounds. These reactive chemical species then damage DNA and disrupt cellular chemistry in other ways — producing immediate effects on active metabolic and replication processes, and long-term effects by latent damage to the genetic structure.

Cells are capable of repairing a great deal of genetic damage, but the repairs take time and the repair machinery can be overwhelmed by rapid repeated injuries. If a cell attempts to divide before sufficient repair has occurred, the cell division will fail and both cells will die. As a consequence, the tissues that are most sensitive to radiation injury are ones that are undergoing rapid division. Another result is that the effects of radiation injury depend partly on the rate of exposure. Repair mechanisms can largely offset radiation exposures that occur over a period of time. Rapid exposure to a sufficiently large radiation dose can thus cause acute radiation sickness, while a longer exposure to the same dose might cause none.

By far the most sensitive is bone marrow and lymphatic tissues — the blood and immune system forming organs of the body. Red blood cells, which provide oxygen to the body, and white blood cells, which provide immunity to infection, only last a few weeks or months in the body and so must be continually replaced. The gastrointestinal system is also sensitive, since the lining of the digestive tract undergoes constant replacement. Although they are not critical for health, hair follicles also undergo continual cell division resulting in radiation sickness' most famous symptom — hair loss. The tissues least sensitive to radiation are those that never undergo cell division (i.e. the nervous system).

This also means that children and infants are more sensitive to injury than adults, and foetuses are most sensitive of all.

If the individual survives, most chromosome damage is eventually repaired and the symptoms of radiation illness disappear. The repair is not perfect however. Latent defects can show up years or decades later in their effects on reproductive cells, and in the form of cancer. These latent injuries are a very serious concern and can shorten life by many years. They are the sole form of harm from low-level radiation exposure.

Units of Measurement for Radiation Exposure

Three units of measurement have been commonly used for expressing radiation exposure: roentgens (R), rads and rems — the "three r's" of radiation measurement. In the scientific literature these are dropping out of use in favour of the SI (System Internationale) units grays (Gy) and sieverts (Sv). Each of the "three r's" measures something different. A rad is a measure of the amount of ionising. A roentgen measures the amount of ionising energy, in the form of energetic photons (gamma rays and x-rays) energy to which an organism is exposed. This unit is the oldest of the three and is defined more the convenience of radiation measurement, than for interpreting the effects of radiation on living organisms. Of more interest is the rad, since it includes all forms of ionising radiation, and in addition measures the dose that is *actually absorbed* by the organism. A rad is defined as the absorption of 100 ergs per gram of tissue (or 0.01 J/kg). The gray measures absorbed doses as well; one gray equals 100 rads. The rem is also concerned with all absorbed ionising radiations, and also takes into account the *relative effect* that different types of radiation produce. The measure of effect for a given radiation is its Radiation Biological Effect (RBE). A rem dose is calculated by multiplying the dose in rads for each type of radiation by the appropriate RBE, then adding them all up. The sievert is similar to the rem, but is derived from the gray instead of the rad. Sieverts use a somewhat simplified system of measuring biological potency — the quality factor (Q). One sievert is roughly equal to 100 rems. The rem and the sievert are the most meaningful unit for measuring and discussing the effects of radiation injury.

Type Of Radiation RBE Q
Gamma rays/X-rays 1 1
Beta Particles 1 1
Alpha Particles 10-20 20 (ingested emitter)
Neutrons (fast) 10 Overall effects
    1 Immediate Effect
    4-6 Delayed cataract formation
    10 Cancer Effect
    20 Leukaemia Effect
Types of Radiation Exposure

An important concept to understand is the distinction between _whole body doses_ and radiation exposures concentrated in particular organs. The radiation dose units described above are defined per unit weight of tissue. An exposure of 1000 rems can thus refer to an exposure of this intensity for the whole body, or for only a small part of it. The total absorbed radiation energy will be much less if only a small part of the body is affected, and the overall injury will be reduced.

Not all tissues are exposed equally even in whole body exposures. The body provides significant shielding to internal organs, so tissues located in the centre of the body may receive doses that are only 30-50% of the nominal total body dose rate. For example there is a 50% chance of permanent female sterility if ovaries are exposed to 200 rems, but this internal exposure is only encountered with whole body doses of 400-600 rems.

Radiation exposures from nuclear weapons occur on three time scales:

  • The shortest is exposure from the prompt radiation emitted by the fireball that lasts about one minute. This can cause very intense exposures for individuals close to the burst point. Neutron bombs rely on prompt radiation as the primary damage mechanism, in this case the prompt radiation arrives in a fraction of a second.
  • The second scale is due to early (tropospheric) fallout from ground bursts. Fallout particles begin settling to the ground within an hour to a few hours after an explosion, most of the fallout descend within a day or two. At any particular site, the fallout deposition will last no more than several hours. Radiation exposure is accumulated as long as an individual remains within the fallout deposit zone, but due to the rapid initial decay most of the radiation exposure is incurred within the first few days. Exposures can be very large during the first few days.
  • The third scale is long-term exposure to low levels of radiation, lasting months or years. This may be due to any of several causes:
    • Prolonged residence in areas contaminated by early fallout;
    • Exposure to delayed (stratospheric) fallout;
    • Exposure to radioisotopes absorbed by the body.
  • Long-term exposures are not intense, but large total doses can accumulate over long periods of time.

The effects of radiation exposure of usually divided into acute and latent effects. Acute effects typically result from rapid exposures; the effects show up within hours to weeks after a sufficient dose is absorbed. Latent effects take years to appear, even after exposure is complete.

Since the latent effects of radiation exposure are cumulative, and there does not appear to be any threshold exposure below which no risk is incurred, radiation safety standards have been set to minimize radiation exposure over time. Current standards are:

Occupational Exposure  
0.3 rem/wk (whole body exposure)
1.5 rem/yr (whole body exposure for pregnant women)
5.0 rem/yr (whole body exposure)
15 rem/yr (eye tissue exposure)
50 rem/yr (limit for any tissue)
200 rem lifetime limit (whole body exposure)  
Public Exposure  
0.5 rem/yr (whole body exposure)
5.0 rem/yr (limit for any tissue)

The occupational exposure limits are likely to be reduced soon (if they have not been already).

The normal human annual radiation exposure varies considerably with location (elevation and surface mineral composition), and medical treatment. Typical values are 0.1 rems from natural radiation and 0.08 rems from medical x-rays, for a total of 0.18 rem/yr. In the US, Colorado has one of the highest natural backgrounds (0.25 rem) since high altitudes cause greater cosmic ray exposures, and granite rock formations contain uranium series radioisotopes. If natural radioisotopes are unusually concentrated, levels as high as 0.5-12 rems/yr have been recorded (some areas of Sri Lanka, Karalla India, and Brazil). This does not count indoor radon exposure that depends heavily on building design, but can easily exceed all other exposure sources combined in regions with high soil radon levels. This source has been known to cause lung exposures in the home of 100 rem/yr (a risk factor comparable to heavy smoking)!

Prompt Radiation Emission From Nuclear Explosions

Although the subject is complex, a simplified guide to estimating the prompt radiation exposure from nuclear explosions is given here. The following scaling law can be used to determine the lethal radius with yield:

r_radiation = Y0.19 * constant_rad
If Y is in kilotons, range is in meters, and the dose standard is 1000 rads then: constant_rad_1000 = 700 m  

This can then be scaled for distance by adjusting for attenuation with range using the table below. The table lists tenth-ranges, the distance over which the dose decreases (for greater distance) or increases (for shorter distance) by a factor of 10.

1 kt 330 m
10 kt 440 m
100 kt 490 m
1 Mt 560 m
10 Mt 670 m
20 Mt 700 m

So, for example to calculate the radiation dose for a 10 Mt bomb at 5000 m, we calculate:
dose = (1000 rads) / 10[(5000- [100000.19] *700)/670] = 35 rads

This guide assumes 100% fission yield for bombs <100 kt, and 50/50 fission/fusion for higher yields. Due to the enhanced radiation output of low-yield neutron bombs different factors need to be used:

constant_rad_1000 = 620 m
tenth-range 385 m

Acute Radiation Sickness

This results from exposure to a large radiation dose to the whole body within a short period of time (no more than a few weeks). There is no sharp cut-off to distinguish acute exposures from chronic (extended) ones. In general, higher total doses are required to produce a given level of acute sickness for longer exposure times. Exposures received over a few days do not differ substantially from instantaneous ones, except that the onset of symptoms is correspondingly delayed or stretched out. Nuclear weapons can cause acute radiation sickness either from prompt exposure at the time of detonation, or from the intense radiation emitted by early fallout in the first few days afterward.

The effects of increasing exposures are described below. A notable characteristic of increasing doses is the non-linear nature of the effects. That is to say, a threshold exists below which observable effects are slight and reversible (about 300 rems), but as exposures rise above this level the possibility of mortality (death) begins and increases rapidly with dose. This is believed to be due in part to the saturation of cellular repair mechanisms.

The total energy absorbed by a 75 kg individual with a whole body exposure of 600 rads (fatal in most cases) is 450 joules. It is interesting to compare this to the kinetic energy of a .45 caliber bullet, which is about 900 joules.

A power law for scaling radiation effects for longer term exposures has been proposed in which the dose required for a given effect increases by t0.26, where time is in weeks. For exposures of one week or less the effect of rem of radiation is assumed to be constant. Thus an exposure capable of causing 50% mortality is 450 rems if absorbed in a week or less, but is 1260 rems if it occurs over a year.

Acute Whole Body Exposure Effects

Below 100 REMS

In this dose range no obvious sickness occurs. Detectable changes in blood cells begin to occur at 25 rems, but occur consistently only above 50 rems. These changes involve fluctuations in the overall white blood cell count (with drops in lymphocytes), drops in platelet counts, and less severe drops in red blood cell counts. These changes set in over a period of days and may require months to disappear. They are detectable only by lab tests. At 50 rems atrophy of lymph glands becomes noticeable. Impairment to the immune system could increase the susceptibility to disease. Depression of sperm production becomes noticeable at 20 rems; an exposure of 80 rems has a 50% chance of causing temporary sterility in males.

100-200 REMS

Mild acute symptoms occur in this range. Tissues primarily affected are the haematopoietic (blood forming) tissues; sperm forming tissues are also vulnerable. Symptoms begin to appear at 100 rems, and become common at 200 rems. Typical effects are mild to moderate nausea (50% probability at 200 rems), with occasional vomiting, setting in within 3-6 hours after exposure, and lasting several hours to a day. This is followed by a latent period during which symptoms disappear. Blood changes set in and increase steadily during the latency period as blood cells die naturally and are not replaced. Mild clinical symptoms return in 10-14 days. These symptoms include loss of appetite (50% probability at 150 rems), malaise, and fatigue (50% probability at 200 rems), and last up to 4 weeks. Recovery from other injuries is impaired and there is enhanced risk of infection. Temporary male sterility is universal. The higher the dosage in this range, the more likely the effects, the faster symptoms appear, the shorter the latency period, and the longer the duration of illness.

200-400 REMS

Illness becomes increasingly severe, and significant mortality sets in. Haematopoietic tissues are still the major affected organ system. Nausea becomes universal (100% at 300 rems); the incidence of vomiting reaches 50% at 280 rems. The onset of initial symptoms occurs within 1-6 hours, and last 1-2 days. After this a 7-14 day latency period sets in. When symptoms recur, the may include epilating (hair loss, 50% probability at 300 rems), malaise, fatigue, diarrhoea (50% prob. at 350 rems), and haemorrhage (uncontrolled bleeding) of the mouth, subcutaneous tissue and kidney (50% prob. at 400 rems). Suppression of white blood cells is severe; susceptibility to infection becomes serious. At 300 rems the mortality rate without medical treatment becomes substantial (about 10%). The possibility of permanent sterility in females begins to appear. Recovery takes 1 to several months.

400-600 REMS

Mortality rises steeply in this dose range, from around 50% at 450 rems to 90% at 600 (unless heroic medical intervention takes place). Haematopoietic tissues remain the major affected organ system. Initial symptoms appear in 0.5-2 hours, and last up to 2 days. The latency period remains 7-14 days. The symptoms listed for 200-400 rems increase in prevalence and severity, reaching 100% occurrence at 600 rems. When death occurs, it is usually 2-12 weeks after exposure and results from infection and haemorrhage. Recovery takes several months to a year; blood cell counts may take even longer to return to normal. Female sterility becomes probable.

600-1000 REMS

Survival depends on stringent medical intervention. Bone marrow is nearly or completely destroyed, requiring marrow transfusions. Gastrointestinal tissues are increasingly affected. Onset of initial symptoms is 15-30 minutes, last a day or two, and are followed by a latency period of 5-10 days. The final phase lasts 1 to 4 weeks, ending in death from infection and internal bleeding. Recovery, if it occurs, takes years and may never be complete.

Above 1000 REMS

Very high exposures can sufficient metabolic disruption to cause immediate symptoms. Above 1000 rems rapid cell death in the gastrointestinal system causes severe diarrhoea, intestinal bleeding, and loss of fluids, and disturbance of electrolyte balance. These effects can cause death within hours of onset from circulatory collapse. Immediate nausea occurs due to direct activation of the chemoreceptive nausea centre in the brain.

In the range 1000-5000 rems the onset time drops from 30 minutes to 5 minutes. Following an initial bout of severe nausea and weakness, a period of apparent well being lasting a few hours to a few days may follow (called the "walking ghost" phase). This is followed by the terminal phase that lasts 2-10 days. In rapid succession prostration, diarrhoea, anorexia, and fever follow. Death is certain, often preceded by delirium and coma. Therapy is only to relieve suffering.

Above 5000 rems metabolic disruption is severe enough to interfere with the nervous system. Immediate disorientation and coma will result; onset is within seconds to minutes. Convulsions occur which may be controlled with sedation. Victim may linger for up to 48 hours before dying.

The U.S. military assumes that 8000 rads of fast neutron radiation (from a neutron bomb) will immediately and permanently incapacitate a soldier.

It should be noted that people exposed to radiation doses in the 400-1000 rem range following the Chernobyl disaster had much higher rates of survival than indicated above. This was made possible by advances in bone marrow transfusions and intensive medical care, provided in part by Dr. Robert Gale. However two caveats apply:

Such care is only available if the number of cases is relatively small, and the infrastructure for providing it is not disrupted. In the case of even a limited nuclear attack it would be impossible to provide more than basic first aid to most people and the fatality rates might actually be higher than given here.

Many of the highly exposed Chernobyl survivors have since died from latent radiation effects.

Acute Localized Tissue Exposure

Localized acute exposure is important for two organs: the skin, and the thyroid gland.

Beta Burns

Beta particles have a limited range in tissue. Depending on their energy, betas are completely absorbed by 1 mm to 1 cm of tissue. External exposures to beta particles from fallout thus primarily affect the skin, causing "beta burns". Due to the poor penetrating power of betas, these injuries only occur if there is direct skin exposure to fallout particles, or if an individual remains outdoors in a strong radiation field. Remaining indoors, wearing substantial clothing, and decontamination by washing can prevent this type of exposure. Beta burns were encountered in Marshall Islanders, and the crew of a Japanese fishing vessel, following the Castle Bravo test that unexpectedly dumped high fallout levels over a large area.

The initial symptom for beta burns are an itching or burning sensation during the first 24-48 hours. These symptoms are marked only if the exposure is intense, and do not occur reliably. Within 1-2 days all symptoms disappear, but after 2-3 weeks the burn symptoms appear. The first evidence is increased pigmentation, or possibly erythema (reddening). Epilating and skin lesions follow.

In mild to moderate cases damage is largely confined to the epidermis (outer skin layers). After forming a dry scab, the superficial lesions heal rapidly leaving a central de-pigmented area, surrounded by an irregular zone of increased pigmentation. Normal pigmentation returns over a few weeks.

In more serious cases deeper ulcerated lesions form. These lesions ooze before becoming covered with a hard dry scab. Healing occurs with routine first aid care. Normal pigmentation may take months to return.

Hair re-growth begins 9 weeks after exposure and is complete in 6 months.

Thyroid Exposure

The short-lived radioisotope iodine-131 (half-life 8 days) presents a special risk due to the tendency for ingested iodine to be concentrated in the thyroid gland. This risk is mitigated by the facts that direct ingestion of fallout is rare, and easily avoided. Iodine-131 typically enters the body through the consumption of contaminated milk, which in turn results from milk cows consuming contaminated fodder.

The short half-life means that the initial radiation intensity of I-131 is high, but it disappears quickly. If uncontaminated fodder can be provided for a month or two, or if dry or canned milk can be consumed for the same period, there is little risk of exposure.

If I-131 contaminated food is consumed, about one-third of the ingested iodine is deposited in the thyroid gland, which weighs some 20g in adults, and 2g in infants. This can result in very high dose rates to the gland, with negligible exposures to the rest of the body. Due to the smaller glands of infants and children, and their high dairy consumption, they are particularly vulnerable to thyroid injury. Some Marshallese children received thyroid doses as high as 1150 rems. Most of the children receiving doses over 500 rems developed thyroid abnormalities within 10 years, including hypothyroidism and malignancies.

I-131 exposure can be prevented by prompt consumption of potassium iodide supplements. Large doses of potassium iodide saturate the body with iodine and prevent any subsequent retention of radioiodine that is consumed.

Foetal Injury

Acute radiation exposure during pregnancy can cause significant harm to the foetus. At Hiroshima and Nagasaki adverse effects were seen when pregnant women who were exposed to 200 rems of radiation or more. When exposure occurred during the first trimester a significant increase in mentally impaired children were noted. When exposure occurred during the last trimester, there was a marked increase in stillbirths and in elevated infant mortality during the first year of life.

Chronic Radiation Exposure

Long-term radiation exposure results from residing in fallout contaminated area for an extended period (external exposure), consuming food produced in a contaminated area (internal exposure), or both. If the exposure rate is low enough, no symptoms of radiation sickness will appear even though a very large total radiation dose may be absorbed over time. Latent radiation effects (i.e. cancer, genetic damage) depend on total dosage, not dose rate, so serious effects can result. An exposure of 0.25 rem/day over 5 years would accumulate 450 rems with little chance of overt sickness, but it would have a high mortality rate if the exposure were acute.

The exposure time scaling law given above also indicates that a slow onset of symptoms characteristic of acute radiation sickness can occur. As an example, the most heavily contaminated location of the Rongelap atoll (160 km downwind of the March 1, 1954 15 Mt Castle Bravo test), received a total accumulated exposure of 3300 rads. Of this, 1100 rads was accumulated during the interval from 1 month to 1 year following the test. If the site had been occupied during this period, the effective exposure for radiation sickness effects would be 1100/(48 weeks)0.26 = 403 rads.

External Exposure

When an area is contaminated by gamma emitting isotopes, a radiation field is created that exposes all organisms that are not shielded from it. Only gamma rays have the necessary range and penetration to create a significant hazard. The principal source of long-term external exposure is cesium-137 (30 year half-life, 0.6 MeV gamma energy).

A megaton of fission yield produces enough Cs-137 to contaminate 100 km2 with a radiation field of 200 rad/year. A megaton-range ground burst can contaminate an area of thousands of square kilometres with concentrations that would exceed occupational safety guidelines. 3,000 megatons of fission yield, if distributed globally by stratospheric fallout, would double the world's background radiation level from external exposure to this isotope alone.

It is possible to substantially reduce external exposure in contaminated areas by remaining indoors as much as possible. Exposure can be reduced by a factor of 2-3 for a frame house, or 10-100 for a multi-story building, and adding additional shielding to areas where much time is spent (like the bedroom) can increase these factors substantially. Since the half-life of Cs-137 is long, these would be permanent lifestyle adjustments. Such measures have been necessary (especially for children) in areas of Belarus that were heavily contaminated by Chernobyl.

Internal Exposure

Internal exposure to radiation is the most serious chronic risk from fallout if food grown in contaminated areas is consumed. Widespread contamination from a nuclear war, or a major radiation accident (like the Kyshtym and Chernobyl disasters), may leave no other practical choice. Alternatively, people residing in contaminated areas may come to disregard safety instructions about locally produced food (as has happened in the Marshall Islands and Ukraine).

Radioisotopes may be taken up into plants through the root system, or they may be contaminated by fallout descending on the leaves. Gross contamination of food plants or fodder from the fallout plume of a ground burst is an obvious hazard, but the gradual descent of worldwide fallout is also a problem.

The primary risks for internal exposure are cesium-137 and strontium-90. Strontium-89, transuranics alpha emitters, and carbon-14 are also significant sources of concern.

Only a few curies of radioisotopes per km2 are sufficient to render land unsuitable for cultivation under current radiation safety standards. A megaton of fission yield can thus make some 200,000 km2 useless for food production for decades. Depression of leukocyte levels have been observed in people in Belarus living in areas that were contaminated with only 0.2 curies/km2.


This alkali metal has chemistry resembling that of potassium. As a result, it is readily absorbed by food plants, and by animal tissues. Once consumed caesium distributes itself fairly evenly through the body, which means that Cs-137 absorption causes whole body exposure (a fact further aided by the penetrating nature of its gamma emissions). Caesium has a moderate residence time in the body, the residence half-life ranging from 50-100 days, so that the body will be cleared of the isotope once consumption of contaminated material ceases in a matter of several months, to a few years.

Strontium 90 and 89

Strontium is chemically similar to calcium, and is deposited in bone along with calcium. Most of the strontium ingested does not end up in bone; it has a biological half-life only 40 days. Somewhat less than 10% of the Sr is retained in the bone, but it has a biological half-life of 50 years. Since the bone marrow is among the most sensitive tissue in the body to radiation, this creates a very serious hazard.

Sr-90 (28.1 yr half-life) thus can cause long-term damage, while Sr-89 (52 days) can cause significant short-term injury. Safety exposure standards impose an Sr-90 body burden limit of 2 micro curies (14 nanograms) for occupational exposure, 0.2 micro curies for individual members of the general population, and 0.067 microCi averaged over the whole population. It is estimated that 10 microCi per person would cause a substantial rise in the incidence of bone cancer. The explosion of several thousands of fission megatons in the atmosphere could raise the average body burden of the entire human race to above the occupational exposure limit for Sr-90 for a couple of generations. Contamination of 2 curies of Sr-90 per km2 is the U.S. limit for food cultivation.

Alpha emitting heavy elements can be serious health risks also. The isotopes of primary concern here are those present in substantial quantities in nuclear weapons: short lived uranium isotopes (U-232 and U-233) and transuranic elements (primarily Pu-239, Pu-240, and Americium-241). These elements are hazardous if ingested due to radio toxicity from the highly damaging alpha particles. The quantities of these isotopes present after a nuclear explosion are negligible compared to the amount of fission product radioisotopes. They represent a hazard when nuclear weapons are involved in "broken arrow" incidents, that is, accidents where the fissile isotopes inside are released. The exposure areas are of course small, compared to the areas threatened by fallout from a nuclear detonation. A typical nuclear weapon will contain some 300-600 curies of alpha emitter (assuming 5 kg plutonium). The isotope breakdown is approximately: 300 curies Pu-239, 60 curies Pu-240, and up to 250 curies of Am-241.

If small particles of alpha emitters are inhaled, they can take up permanent residence in the lung and form a serious source of radiation exposure to the lung tissue. A micro curie of alpha emitter deposited in the lungs produce an exposure of 3700 rems/yr to lung tissue, an extremely serious cancer risk.

Uranium and the transuranic elements are all bone-seekers (with the exception of neptunium). If absorbed, they are deposited in the bone and present a serious exposure risk to bone tissue and marrow. Plutonium has a biological half-life of 80-100 years when deposited in bone, it is also concentrated in the liver with a biological half-life of 40 years. The maximum permissible occupational body burden for plutonium-239 is 0.6 micrograms (.0375 micro curies) and 0.26 micrograms for lung burden (0.016 microCi).

Carbon-14 is a weak beta particle emitter, with a low level of activity due to its long half-life. It presents a unique hazard however since, unlike other isotopes, it is incorporated directly into genetic material as a permanent part throughout the body. This means that it presents a hazard out of proportion to the received radiation dose as normally calculated.


The most serious long term consequence of radiation exposure is the elevation of cancer risk. Estimates of the carcinogenicity of radiation, especially of low exposures, have tended to increase over the years as epidemiological data has accumulated.

The current state-of-the-art in low-level risk estimation is the 1990 report issued by the National Academy of Sciences Committee on Biological Effects of Ionising Radiation (BEIR) entitled _Health Effects of Exposure to Low Levels of Ionising Radiation_, also known as BEIR V.

As a general rule of thumb, it appears that cancer risk is more or less proportional to total radiation exposure, regardless of the quantity, rate or duration. 500 rems received over a decade is thus as serious a risk as 500 rems received all at once, and 50 rems is one-tenth as bad as 500. There is no evidence of a threshold effect or "safe dose". Safety standards are established primarily to keep the increased incidence of cancer below detectable levels.

Significant deviations from the above rule of proportionality for total exposure do occur. In particular, low doses (for which the risk is small anyway) received over an extended period of time are significantly less carcinogenic (by about a factor of 2) than the same dose received all at once.

Cancer risk to radiation exposure can be expressed as the increase in the lifetime probability of contracting fatal cancer per unit of radiation. The current estimate of overall risk is about a 0.8% chance of cancer per 10 rems for both men and women, averaged over the age distribution of the U.S. population. Thus a 1000 rem lifetime whole body radiation exposure would bring about an 80% chance of contracting fatal cancer, in addition to the normal incidence of cancer (about 20%). The risk for children appears to be about twice as great (due at least partly to the fact that they will live longer after exposure, and thus have greater opportunity to contract cancer).

There are also risk coefficients for specific tissue exposures. These are (approximately):

Female Breast 1.0%/100 rems
Bone Marrow 0.2%/100 rems (0.4% for children)
Bone Tissue 0.05%/100 rems
Lung 0.2%/100 rems  

Genetic Effects

Radiation damage to the germ cells of the reproductive organs can cause mutations that are passed on to subsequent generations. Although this is very important, it can nonetheless be overplayed. It may seem surprising, but no elevated mutation rate from radiation has ever been detected in the human population, not even in the substantial population of atomic bomb survivors and descendants. One reason for this is that humans are wild animals, that is, they have not been subjected to controlled breeding and thus have a high incidence of natural genetic variability and disorders, compared to laboratory and domestic animals. About 10% of the human population has detectable genetic disorders (most are not serious). This makes it difficult to detect additional mutations unless the rate is also high.

Two factors act to limit the effective radiation exposure for genetic effects, one for acute exposures, and the other for chronic exposures. High acute exposures to the reproductive organs can cause permanent sterility, which prevents transmission of genetic effects. The cumulative effect of chronic exposure is limited by the fact that only exposures prior to reproduction count. Since most reproduction occurs before the age of 30, exposures after that age have little effect on the population.

It is estimated that the dose to reproductive tissue required to double the natural incidence of genetic disorders is 100-200 rems. The initial rate of observable disorders (the first generation) is only about 1/3 of the eventual rate once genetic equilibrium is established. Of course increases in the rate of genetic disorders (especially in a large population) is a _permanent_ alteration of the human species.


Eye tissue exposed to radiation shows an increased incidence of cataracts at dose levels below which most tissues show increased cancer rates. This makes cataract risk the most important tissue dose criterion for establishing safety standards.

Indicators of a Possible Radiological Incident

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Unusual numbers, of sick or dying people or animals As a first responder, strong consideration should be given to calling local hospitals to see if additional casualties with similar symptoms have been observed. Casualties may occur hours to days or weeks after an incident has occurred. The time required before symptoms are observed is dependent on the radioactive material used and the dose received. Additional symptoms include skin reddening and, in severe cases, vomiting.
Unusual metal debris Unexplained bomb/munitions-like material.
Radiation Symbols Containers may display a radiation symbol.
Heat Emitting Material Material that seems to emit heat without any sign of an external heating source.
Glowing material/particles If the material is strongly radioactive, then it may emit a radio luminescence.

Biological Agents

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A biological agent is a living microorganism or a toxin. Many pathogenic (disease producing) microorganisms are bacteria or viruses, but rickettsia and fungal organisms are also potential agents. Toxins, although not living, are produced by certain species of microorganisms, plants or animals. Many biological agents are easily manufactured; a single 100-litre fermenter can be used to produce ten thousand million infectious doses of anthrax spores within a week.

A biological weapon is simply the agent combined with a means of dispersing it. Delivery systems range from cluster bombs and missile warheads to a variety of simple spray devices that may be mounted in aircraft, Unmanned Aerial Vehicles, land vehicles and ships. Portable devices may also be employed and placed in clandestine ways. All of these can spread the agents in aerosol form. Dispersal in food or water is also possible. Biological agents are extremely potent. Although meteorological conditions will influence the effectiveness of an attack, even low technology dissemination systems could spread a harmful dose of material over wide areas.

When living biological agents enter the body they infect the individual, multiply and then cause the symptoms of their characteristic disease. The incubation period will depend on the agent and the dosage; it may be two days for plague, but several weeks for some others. Toxins are different. Their natural origin is biological; but, because they are chemicals rather than living agents, they do not require an incubation period before they produce their effect. A few will produce symptoms of poisoning in a matter of minutes; a short delay of a few hours is more typical.

Biological agents are normally in solid or liquid form and may be delivered as dust or powder, liquid or aerosol. Powders will usually be white to brown in colour. Liquids will usually be brownish in colour. Smells may vary but will probably be meaty/rotten. The effects of most biological agents do not usually become apparent for several days, because of the incubation period. The toxic route for biological agents is frequently by inhalation, although food and water are potential targets. When symptoms are observed at an early stage, the effects of some of them may be treatable.

Unusual numbers, of sick or dying people or animals Any number of symptoms may occur. As a first responder, strong consideration should be given to calling local hospitals to see if additional causalities with similar symptoms have been observed. Casualties may occur hours to days to weeks after an incident has occurred. The time required before symptoms are observed is dependent on the agent used and the dose received. Additional symptoms likely to occur include unexplained gastrointestinal illnesses and upper respiratory problems similar to flu/colds.
Unscheduled and unusual spray being disseminated Especially if outdoors during periods of darkness.
Abandoned spray devices Devices will have no distinct odours.

Biological weapons consist of pathogenic microbes such as bacteria, viruses, rickettsia, and others that are poisonous to people, animals, plants, and food supplies. Insects, ticks, rodents, agricultural pests, and other biological agents can also carry these poisonous microbes. The difference between the chemical weapons and the biological weapons is that the chemical agents cause direct injury; the biological weapons cause disease, which results in injury.

Spread of viruses

Using tracer viruses, researchers found that contamination of just a single doorknob or table top results in the spread of viruses throughout office buildings, hotels, and health care facilities. Within 2 to 4 hours, the virus could be detected on 40 to 60 percent of workers and visitors in the facilities and commonly touched objects, according to research presented at the 54th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), an infectious disease meeting of the American Society for Microbiology held in Sep 2014.

There is a simple solution, though, says Charles Gerba of the University of Arizona, Tucson, who presented the study. "Using disinfecting wipes containing quaternary ammonium compounds (QUATS) registered by EPA as effective against viruses like norovirus and flu, along with hand hygiene, reduced virus spread by 80 to 99 percent," he says.


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The time that the biological agent is active and dangerous varies greatly. The persistence varies from several weeks, if carried by mosquitoes, fleas, flies, and lice, to several years if carried by mites. Mites are the extreme because they are capable of bearing offspring with the disease, rather than dying from the disease themselves. Rodents, such as rats and mice, can carry fleas that spread the disease faster and farther, although these rodents die from the disease just as humans do. In post-war periods, insecticides can be used to control or eradicate the majority of insects that may be carrying the disease. Insects can also contaminate food, just as fallout does. The food that comes into contact with insects, insecticides, and fallout must be washed thoroughly. All dead bodies, whether animal or human, should be buried.


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Pathogen Ave Incubation Time Days
Infect ious
Observation Period (Days)
Quarantine Period and Condition
Bubonic Plague 1-3 Very 8 6 days
Anthrax 1-3 Not very 8 8 days infection by inhalation
Rabbit Fever 3-6 Not 6 NA
Meliodosis 2-3 Yes 14 14 days infection by contact
Malleomyces 2-3 Yes 14 14 days infection by contact
Cholera 1-3 Very 6 days
Botulism Toxin 1-2 Not 2 NA
Q Fever 10-20 Not 26 NA
Rocky Mountain Spotted Fever 3-10 Not 14 NA
Smallpox 13-14 Very 17 days
Equine Encephalomyelitis 2-10 Not 21 NA
Yellow Fever 3-6 Yes 12 12 days
Psittacosis 8-15 Yes 15 5 days infection by contact
Coccidioi-domycosis 10-14 Not 15 NA
Category Disease Effect
Bacteria Anthrax Incubation period of 1-6 days after which respiratory distress normally develops rapidly. Shock and death usually follow within 24-36 hours.
Bacteria Plague Following 2-3 days of incubation, fever, coma and respiratory failure occur, leading to death in 48 hours.
Viruses Venezuelan Equine Encephalitis (VEE) After an incubation of 1-5 days a sudden fever, headache and extreme sensitivity to light are typical, lasting for 24-72 hours. Lethargy may follow with full health regained after 1-2 weeks. But it can be fatal.
Rickettsia Q-fever Incubation period of 10-20 days after which a fever, with associated cough and chest pain, may last 2 days to 2 weeks. Can be fatal.
Toxins Botulism Toxins Onset of symptoms may be very rapid. Death can result within hours from progressive paralysis and respiratory failure. Symptoms include dry mouth, visual difficulty, difficulty in speech and swallowing, nausea, vomiting, dizziness.


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The method of dispersing biological warfare agents is similar to the chemical warfare agents, except that drinking water supplies can be contaminated locally by introducing contaminants applied by a person at the site.

Types of Biological Agent

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The "bacteria caused" diseases produced by biological weapons that can be expected during wartime are bubonic plague, malignant anthrax, meliodosis, brucellosis, tularemia, and cholera. Bacteria can be killed and controlled by disinfectants, boiling, and destroyed by sunlight. Some forms however, such as anthrax and tetanus, are transformed into spores that have a great resistance to disinfectants, boiling, and sunlight. Low temperatures and freezing do not affect bacteria. Bacteria are visible only under a microscope, since their size ranges from .5 to 5.0 microns. Under ideal conditions, they can multiply by simple division every 20 to 30 minutes.


The viruses that may be dispersed during wartime as a result of biological weapons are: smallpox, equine, encephalomyelitis, denque fever, yellow fever, and psittacosis. These microbes are the smallest organisms. Their size is approximately a hundred thousand times smaller than bacteria and they cannot be seen using an ordinary microscope. Unlike bacteria, viruses require living tissue to multiply. Viruses are also resistant to drying and freezing.


The diseases caused by rickettsia that may be dispersed during wartime as a result of biological weapons are: Typhus, Q fever, Rocky Mountain Spotted Fever, and Tsutsugamushi disease. These microbes are approximately the same size as bacteria, but require infected tissue to survive and reproduce.


The fungi that cause diseases and may be dispersed during wartime as a result of biological weapons are: coccidial mycosis, nocardiosis, and blastomycosis. Fungi are like bacteria but are resistant to sunlight and more resistant to disinfectants.


The toxins that cause disease that may be dispersed during wartime as a result of biological weapons are: botulism, tetanus, and diphtheria. Some microbes themselves are not poisonous but produce toxins that are. Microbes that produce toxins that are poisonous are listed above. Although there are over l000 toxins that are able to produce damage to people, animals, and plants, only a few can be delivered as biological weapons.

The diseases that may be dispersed during wartime as a result of biological weapons used against animals are: hoof-and mouth disease, large horn cattle plague, pig plague, African swine plague, malignant anthrax, glanders and brucellosis.

The diseases that may be dispersed during wartime as a result of biological weapons used against agricultural products are: wheat rust, pyriculariosis, and potato phytophthora. The choice of biological weapons depends on a number of factors such as: the immunity of the population to resist infection, the level of sanitary conditions, the state of preventative medical treatment and anti-epidemic decontamination facilities, the living conditions of the people at the target site, and the season of the year.

With biological contamination, the sickness does not develop immediately. There is an incubation period in which the disease takes time to develop before disabling the person. The incubation period depends on the biological agent and the general physical condition of the person. Of particular importance are the diseases that can be transmitted from an infected person to a healthy person such as bubonic plague, cholera, and smallpox. This transmission must be considered before taking any people into the shelter that were not part of the original group.

Chemical Agents

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A chemical agent is a compound which, when suitably disseminated, produces incapacitating, damaging, or lethal effects on people, animals, plants, or materials. People are vulnerable through inhalation, ingestion, or absorption through the skin. Most chemical agents are liquid, not gas. They tend to be fast acting, taking from a minute to a few hours. They can be made and dispersed easily, but relatively large quantities are required if they are to be used to cover wide areas. For an effective military capability, approximately one tonne of chemical agent per square mile is required. Although chemical agents can be dispersed in most meteorological conditions, principally the weather conditions and the terrain features in the area of the target will determine the effectiveness.

As with a biological weapon, a chemical weapon is the agent combined with the means of dispersing it. This may be a shell or a mine, or an aircraft delivering missiles, bombs, or spray; or even a ballistic missile. Any of these conventional weapons, suitably modified, can be filled with chemical agents. Volatile agents vaporise on dissemination and are carried on the wind. There are also agents with low volatility, often referred to as persistent agents. These remain in the liquid state and can contaminate areas for long periods.

Dead animals, birds or fish Not just an occasional road kill, but also numerous animals (wild and domestic, small and large), birds and fish in the same area.
Lack of insect life If normal insect activity (ground, air, and/or water) is missing, then check the ground/water surface/shore line for dead insects. If near water, check for dead fish/aquatic birds.
Physical Symptoms Numerous individuals experiencing unexplained water-like blisters, wheals (like bee stings), pinpointed pupils, choking, respiratory ailments and/or rashes.
Mass casualties Numerous individuals exhibiting unexplained serious health problems ranging from nausea to disorientation to difficulty in breathing to convulsions to death.
Definite pattern of casualties Casualties distributed in a pattern that may be associated with possible agent dissemination methods.
Illness associated with confined geographic area Lower attack rates for people working indoors versus outdoors, or outdoors versus indoors.
Unusual liquid droplets Numerous surfaces exhibit oily droplets/film; numerous water surfaces have an oily film. (No recent rain.)
Areas that look different in appearance Not just a patch of dead weeds, but trees, shrubs, bushes, food crops, and/or lawns that are dead, discoloured, or withered. (No current drought.)
Unexplained odours Smells may range from fruity to flowery to sharp/pungent to garlic/horseradish-like to bitter almonds/peach kernels to new mown hay. It is important to note that the particular odour is completely out of character with its surroundings.
Low-lying clouds Low-lying cloud/fog-like condition that is not explained by its surroundings.
Unusual metal debris Unexplained bomb/munitions-like material, especially if it contains a liquid. (No recent rain.)

A chemical weapon is composed of chemical compounds. It is distinguished from other toxic agents based on its much greater damaging characteristics. Chemical agents can penetrate by air moving through buildings that are not airtight. The most important characteristic of a chemical agent, which is designed and used as a chemical weapon, is its ability to enter through buildings or vehicles. Even in minute doses, chemical agents can render animals and humans helpless or dead in seconds or minutes. As opposed to radioactive fallout, which cannot make another material or substance radioactive, the chemical weapon has the opposite characteristic. Chemical agents can be transferred, at full, from person to person by physical contact with contaminated clothing or water.


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Persistence is the length of time the chemical agents remain potent. Chemical agents are classified as persistent or non-persistent. Non-persistent agents would persist for a few minutes to a few hours. One non-persistent agent, which is lethal for only a few minutes, is used in United States chambers. Another non-persistent agent is Sarin, which is one of the original developed in Germany in 1938. Sarin would persist on a battlefield for one to ten hours. Non-persistent agents would be used against targets that are to be taken over and controlled very quickly.

Persistent agents would remain on the battlefield for up to a week. These agents would be used against targets not in the direct line of attack. Defence against this type of agent requires shielding for extended periods of time. Sulphur-mustard agents produced more casualties in World War I than any other single agent. It is not as toxic as nerve gas but presents a great danger on the battlefield because there is no antidote to counter the effects.

The factors affecting their length of persistence vary according to a number of factors. Wind causes the chemical agents to dissipate in the atmosphere if they are in gas or vapour form. Sunlight reduces the coverage of by as much as 60 percent because it causes chemical decomposition. This is why most chemical agents are dispersed at night. When the weather is cold, the chemical agents ability to spread out is greatly reduced. This, in turn, causes higher concentration in smaller areas. When the weather is warm, the chemical agents sink more to the ground, which makes inhalation less likely. Mustard gas will last up to 8 weeks in the winter and only approximately 7 days in the summer. Soldiers will also be wearing heavy clothing during winter, making skin agents the least effective. Moisture tends to wash the chemical agents away and this, in turn, can contaminate drinking water supplies. This condition of contaminated water only exists until the concentrations are diluted to non-toxic levels. When chemical agents come in contact with porous soil, the chemical agents are retained for a longer period of time. Nonporous soil cannot absorb as much of the chemical agents, and any moisture or rain tends to wash the chemical agents away. Chemical agents in gaseous form tend to follow the contour of the land and settle in the valleys. For this reason, a chemical agent may be released on a mountain above the enemy and allowed to flow down and settle towards the enemy in the valley or low area.


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Some of the reasons for using one chemical agent over another are based on the purpose and problems associated with the use of the weapon. It would seem that it would be easiest just to use nerve gas, since it is so potent and acts so quickly, but the problem is that this gas creates decontamination problems. Even if a person or vehicle leaves the contaminated area, the vehicle is contaminated and requires hundreds of gallons of water to decontaminate. Decontaminating a chemical agent is far more complicated than decontaminating radioactive fallout, which simply has to be brushed away or washed off. Special agents are used in the water to decontaminate a vehicle or person exposed to chemical agents.

The harassment weapons can be used more freely without endangering one's own troops. This is especially true when the persistence time is very short. Harassment chemicals are very often fired on troops about to be attacked in order to weaken their defence. This action can be taken over a period of hours or days. Depending on the persistence time, the chemical agents form excellent barriers against enemy movements. It should also be noted that harassment chemicals are not used to be humane, but are used to discourage the soldier from fighting by two methods.

First, the effects of chemical agents require a soldier to wear cumbersome protective gear, which reduces voice communication and vision by 25 to 50 percent. Also, if the weather is warm, the soldiers can wear the protective gear for only a few hours a day without suffering from heat prostration. It is also very difficult to eat, sleep, drink, or urinate in heavy protective clothing.

Secondly, soldiers become demoralised after talking to other soldiers who have been exposed to chemical weapons. Such contact makes even the best soldiers lack the initiative to fight. Bad news travels quickly, and a soldier who lives to tell many other soldiers about his experience with chemical weapons has more of a damaging effect, militarily, than one soldier's death.


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Different agents require different time periods to take effect. Nerve gas is the fastest of the inhaled gases, followed by blood gases. Mustard and blister gases attack the eyes first. This contact is made from hand to face. Whatever concentration is required to affect the eyes, it will take 10 times this amount to blister the skin and 50 times this amount to inflict fatal injuries. Knowing this concentration may allow a person to determine what concentrations were used in the field and approximately how long to stay clear of the area.


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There are basically three methods of protecting against chemical air agents:

  • Gas Masks — During the Gulf War many people learned through experience that a gas mask could only be worn for a few hours. Common problems experienced by both military and civilian personnel were severe headaches due to the face pressure of the mask, overheating, and exhaustion due to the amount of work necessary for a person to draw air through the carbon filter in a gas mask. Compounding these problems was the inability to eat or drink while wearing a gas mask. Gas masks only protect against agents that are inhaled and will do nothing to protect against skin blistering agents like the Mustard Gas used during World War I. Gas masks are extremely limiting and very difficult for children to use. During the Gulf War, some parents were not aware that many gas masks are shipped with a plastic cover over the carbon in the gas mask filter that must be removed to breath in fresh air. Consequently some children suffocated when they were forced to keep them on for fear of SCUD missiles carrying chemical agents. Another interesting phenomena during the Gulf War was when tens of thousands of gas masks were purchased by civilians but virtually none thought to purchase a chemical warfare detection kit to determine when to put the gas mask on!
  • Internal Room Filter — A battery powered internal room filter can be used to bring fresh filter air into a room in a house and pressurize the room. This method allows normal living and functioning. The only company manufacturing a commercial unit suitable for an NBC environment Radius Engineering Inc. Radius manufactures a product called the NBC Lifecell which is a coffee table size self contained battery powered unit designed to provide life support in nuclear-biological and chemical warfare environments where no electricity is available. It will deliver high-pressure filtered air, removing all NBC agents, into a room placing the room in positive pressure. Thus, gas masks are not needed. The room that is usually used to create an isolated clean environment is the bathroom or bedroom. Depending on the geographic location, it may be critical that the amount of heat generated by sunlight entering through the room window be restricted. This can be accomplished by simply taping white paper to the inside of the window to control the temperature of the room. It is psychologically important to be able to look out the window so some "peek hole" that is 3 inches in diameter for viewing is a good idea. The most common problem in small environments is overheating. The bathroom is advantageous because it is usually small and contains a toilet and bathtub for water storage. The entire house should be caulked to stop all filtration leaks. This does not require any procedure unique to NBC environments, just common sense to keep outside air from being blown into the house through cracks around doors and windows. Of particular importance is where the house walls and floor meet the top of the basement wall. Leaks must be sealed along the top of this basement wall. Once the house is sealed, the NBC Lifecell is placed inside the room and the door of the room is simply closed. A portable chemical toilet should be used. If electricity is available, the bathtub can be filled with water for drinking if a disaster water tank was included in disaster preparation plans. A plastic shower curtain should be placed on the water surface to prevent evaporation and reduce the amount of moisture in the bathroom. When weapon agents are reported on the radio, television or detected by an optional military chemical warfare detection kit, the NBC Lifecell is turned on.
  • Underground Shelters — The third and best method is an underground NBC shelter, which have nuclear, biological and chemical filters allowing normal living for extended periods of time.


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Missiles, artillery, mortar shells, bombs, aircraft spray, land mines, mail, UPS, cars, and backpacks can deliver chemical warfare agents. Both FROG (free rockets over ground) and SCUD (surface to air missiles) can deliver chemical warfare agents to airfields, supply depots, harbours and military command stations up to 250 miles away. Many countries are able to deliver chemical agents by intercontinental ballistic missiles. The most common method of dispersal is by aircraft spraying. This is the method that will most likely be used during the opening stages of a war since it is the most effective. During the later stages, when tanks and artillery are shipped and dropped into theatre, rocket launchers such as the BM-21 will be used. This particular rocket launcher can deliver large quantities of an agent with no warning.


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Chemical agents, used as chemical weapons, derive their name usually based on what they do to the human body. Below, the chemical agents are listed with the two-digit United States Army code name listed in parenthesis.

Blister Gas
Blister gas can be either an inhaled agent or a contact agent. It cannot be smelled easily and is used to harass rather than kill. The time it takes to affect an individual depends on many factors, but it causes severe skin blisters, completely destroys the skin tissue, and has a persistence time of 1 to 54 days. This form of injury is particularly ugly. Blister gas is a Soviet development, based on improvements in Mustard gas used extensively during World War I. Mustard gas was one type of blister gas used extensively in World War I and many veterans have proof by long-lasting scars. Vesicants or skin-blistering agents (e.g. mustards, Lewisite). Mustards do not immediately cause pain or irritation or warn of their presence, they are detected by their garlic odour and by automatic electronic detectors. Mustards readily penetrate ordinary clothing, leather and skin. After a latent period of several hours the effects become apparent on the skin, eyes, respiratory and gastrointestinal tracts. Eye inflammation may develop in one hour and skin blisters form about 12 hours after exposure. All lesions are susceptible to infection and damaged tissues are slow to heal (risk of permanent eye damage, bronchopneumonia, chronic bronchitis). Systemic effects on bone marrow and lymphatic system resemble the effects of ionising radiation. There is no specific therapy. Treatment is only symptomatic and supportive. Skin decontamination should be carried out immediately with copious amounts of soap and water, and the eyes should be thoroughly irrigated with water. Mustards have been shown to be mutagenic, carcinogenic and teratogenic. Lewisite is a vesicant liquid with similar affects to the mustards but has a more immediate action as it rapidly penetrates rubber, plastic and skin, causing immediate and severe pain with rapid incapacitation, and deeper necrosis. It hydrolyses rapidly and is thus less persistent in moist climates. Decontamination should be carried out immediately. Symptomatic and supportive treatment is required. The specific therapy for Lewisite include: DMSA, DMPS, DMPA and dimercaprol (British Anti-Lewisite, BAL).

Agent Type Blister Agent
Chemical Agent Distilled Mustard
Formula (CLCH2CH22S)
Symbol HD
Molecular Weight 159.08
State at 20°C Colourless to pale yellow liquid
Vapour Density (air=1) 5.4
Liquid Density (g/cc) 1,268 @ 25°C
Freezing Point °C 14.45
Boiling Point °C 217
Vapour Pressure (mg/m2) 0.072 @ 20°C
Volatility (mg/m3) 610 @ 20°C
Flash Point 105°C; ignited by large explosive charges
Decomposition Temp. (°C) 149-177
Heat Of Vaporization (°C) 94
Odour Garlic
Median Lethal Dosage (mg/min./m2) 1,500 by inhalation; 10,000 by skin exposure
Median Incapacitating Dosage (mg/min./m2) 200 by eye effect; 2000 by skin effect
Rate Of Detoxification Very low, cumulative
Eye and Skin Toxicity Eyes very susceptible, skin less so
Rate of Action Delayed hours to days
Physiological Action Blisters; destroys tissues, injures blood vessels
Protection Required Protective mask and clothing
Stability Stable in steel
Decontamination Bleach, fire, DS2, M258 kit
Means of Detection in Field M256A and M18A2 kits
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Nitrogen Mustard
Formula (CLCH2CH2)2NC2H5
Symbol HN-1
Molecular Weight 170.08
State at 20°C Dark liquid
Vapour Density (air=1) 5.9
Liquid Density (g/cc) 1.09 @ 25°C
Freezing Point °C -34
Boiling Point °C 194
Vapour Pressure (mg/m2) 0.24 @ 25°C
Volatility (mg/m3) 1,520 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Decomposes before boiling point is reached
Heat Of Vaporization (°C) 77
Odour Fishy or musty
Median Lethal Dosage (mg/min./m2) 1,500 by inhalation; 20,000 by exposure
Median Incapacitating Dosage (mg/min./m2) 200 by eye effect; 9,000 by skin effect
Rate Of Detoxification Not detoxified, cumulative
Eye and Skin Toxicity Eyes susceptible to low concentration; less toxic to skin
Rate of Action Delayed action, 12 hours or longer
Physiological Action Blisters; affect respiratory tract; destroys tissues, injures blood vessels
Protection Required Protective mask and clothing
Stability Adequate
Decontamination Bleach, fire, DS2, M258 kit
Means of Detection in Field M256A and M18A2
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Nitrogen Mustard
Formula (CLCH2CH2)2NCH3
Symbol HN-2
Molecular Weight 156.07
State at 20°C Dark Liquid
Vapour Density (air=1) 5.4
Liquid Density (g/cc) 1.15 @ 20°C
Freezing Point °C -60 to -65
Boiling Point °C 75 @ 15mm Hg
Vapour Pressure (mg/m2) 0.29 @ 20°C
Volatility (mg/m3) 3,580 @ 25°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Below boiling point; polymerises with heat generation
Heat Of Vaporization (°C) 78.8
Odour Soapy in low concentrations; fruity in high concentrations
Median Lethal Dosage (mg/min./m2) 3,000 by inhalation
Median Incapacitating Dosage (mg/min./m2) Less than HN-1; more than HN-3; 100 for eye effect
Rate Of Detoxification Not detoxified-cumulative
Eye and Skin Toxicity Toxic to eyes; blister skin
Rate of Action Skin Effect delayed 12 hours or longer
Physiological Action Similar to Distilled Mustard, Bronchopneumonia may occur after 24 hours
Protection Required Protective mask and clothing
Stability Unstable
Decontamination Bleach, fire, DS2, M258 kit
Means of Detection in Field M256A and M18A2 kits
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Nitrogen Mustard
Formula N(CH2CH2)3
Symbol HN-3
Molecular Weight 204.54
State at 20°C Dark Liquid
Vapour Density (air=1) 7.1
Liquid Density (g/cc) 1.24 @ 25°C
Freezing Point °C -3.7
Boiling Point °C 256
Vapour Pressure (mg/m2) 0.0109 @ 25°C
Volatility (mg/m3) 121 @ 25°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Below boiling point
Heat Of Vaporization (°C) 74
Odour None if pure
Median Lethal Dosage (mg/min./m2) 1,500 by inhalation; 10,000 by skin exposure (est.)
Median Incapacitating Dosage (mg/min./m2) 200 by eye effect; 2500 by skin effect
Rate Of Detoxification Not detoxified-cumulative
Eye and Skin Toxicity Eyes very susceptible, skin less so
Rate of Action Serious effects same as for HD; minor effect sooner
Physiological Action Similar to HN-2
Protection Required Protective mask and clothing
Stability Stable
Decontamination Bleach, fire, DS2, M258 kit
Means of Detection in Field M256A and M18A2 kits
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Phosgene oxime dichloroforoxime
Formula CCL2NOH
Symbol CX
Molecular Weight 113.94
State at 20°C Colourless solid or liquid
Vapour Density (air=1)
Liquid Density (g/cc)
Freezing Point °C 39 to 40
Boiling Point °C 53 to 54 at 28 mm Hg
Vapour Pressure (mg/m2) High
Volatility (mg/m3)
Flash Point
Decomposition Temp. (°C) Decomposes slowly at normal temp.
Heat Of Vaporization (°C)
Odour Sharp, penetrating
Median Lethal Dosage (mg/min./m2)
Median Incapacitating Dosage (mg/min./m2)
Rate Of Detoxification
Eye and Skin Toxicity Powerful irritant to eyes and nose
Rate of Action Immediate effects on contact
Physiological Action Violently irritates mucus membrane of eyes and nose
Protection Required Protective mask and clothing
Stability Decomposes slowly
Decontamination None is entirely effective; wash
Means of Detection in Field M256A, M151A2N, M18A2
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Lewisite
Formula (CLCH1CH)2A3CL
Symbol L
Molecular Weight 207.35
State at 20°C Dark oily liquid
Vapour Density (air=1) 7.1
Liquid Density (g/cc) 1.89 @ 20°C
Freezing Point °C -18
Boiling Point °C 190
Vapour Pressure (mg/m2) 0.394 @ 20°C
Volatility (mg/m3) 4,480 @ 20°C
Flash Point None
Decomposition Temp. (°C) Above 100
Heat Of Vaporization (°C) 58 (from 190 to 0°C)
Odour Variable may resemble geraniums
Median Lethal Dosage (mg/min./m2) 1,200 to 1,500 by inhalation; 100,000 by skin exposure
Median Incapacitating Dosage (mg/min./m2) Below 300 by eye effect; over 1,500 by skin effect
Rate Of Detoxification Not detoxified
Eye and Skin Toxicity 1,500 mg/min/m2 exposure severely damages cornea; skin less susceptible
Rate of Action Rapid
Physiological Action Similar to HD plus may cause systemic poisoning
Protection Required Protective mask and clothing
Stability Stable in steel and glass
Decontamination Bleach, fire, DS2, caustic soda M258 kit
Means of Detection in Field M18A2 kit
Typical Use Moderately delayed casualty agent
Agent Type Blister Agent
Chemical Agent Mustard Lewisite
Formula Mustard/Lewisite mixture
Symbol HL
Molecular Weight 186.4
State at 20°C Dark oily liquid
Vapour Density (air=1) 6.5
Liquid Density (g/cc) 1.66 @ 20°C
Freezing Point °C 25.4
Boiling Point °C Below 19
Vapour Pressure (mg/m2) 0.248 @ 20°C
Volatility (mg/m3) 2,730 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Above 100
Heat Of Vaporization (°C) 58 (from 190 to 0°C)
Indeterminate value Odour Garlic like
Median Lethal Dosage (mg/min./m2) 1,500 by inhalation; 10,000+ by skin exposure
Median Incapacitating Dosage (mg/min./m2) 200 by eye effect; 1,500 to 2000 by skin
Rate Of Detoxification Not detoxified
Eye and Skin Toxicity Very high
Rate of Action Prompt stinging; delayed (approx 13 hr) for blistering
Physiological Action Similar to HD but may cause systemic poisoning
Protection Required Protective mask and clothing
Stability Stable in lacquered steel
Decontamination Bleach, fire, DS2, caustic soda, M258 kit
Means of Detection in Field M18A2
Typical Use Delayed-action casualty agent
Agent Type Blister Agent
Chemical Agent Phenyldichloroarsine
Formula C6H5AsCL2
Symbol PD
Molecular Weight 222.91
State at 20°C Colorless liquid
Vapour Density (air=1) 7.7
Liquid Density (g/cc) 1.65 @ 20°C
Freezing Point °C -20
Boiling Point °C 252 to 255
Vapour Pressure (mg/m2) 0.033 @ 25°C
Volatility (mg/m3) 39 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) 69
Odour None
Median Lethal Dosage (mg/min./m2) 2,600 by inhalation
Median Incapacitating Dosage (mg/min./m2) 16 as vomiting agent; 1,800 as blistering agent
Rate Of Detoxification Probably rapid
Eye and Skin Toxicity 633 mg-min./3 produces eye casualty; less toxic to skin
Rate of Action Immediate eye effect; skin effects 1/2 to 1 hour
Physiological Action Irritates, causes nausea and vomiting, blistering
Protection Required Protective mask and clothing
Stability Stable
Decontamination Bleach, DS2, caustic soda; M258 kit
Means of Detection in Field M18A2 kit
Typical Use Delayed casualty agent
Agent Type Blister Agent
Chemical Agent Ethyldichloroarsine
Formula C2H5ASCL2
Symbol ED
Molecular Weight 174.88
State at 20°C Colourless liquid
Vapour Density (air=1) 6.0
Liquid Density (g/cc) 1.66 @ 20°C
Freezing Point °C -65
Boiling Point °C 156
Vapour Pressure (mg/m2) 2.09 @ 20°C
Volatility (mg/m3) 20,000 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) 52.5
Odour Fruity but biting; irritating
Median Lethal Dosage (mg/min./m2) 3,000 to 5,000 by inhalation;100,000 by skin effect
Median Incapacitating Dosage (mg/min./m2) 5 to 10 by inhalation
Rate Of Detoxification Rapid
Eye and Skin Toxicity Vapour Harmful only on long exposure; liquid blisters less than L
Rate of Action Immediate irritation; delayed blistering
Physiological Action Damages respiratory tract, affects eyes, blisters can cause death
Protection Required Protective mask and clothing
Stability Stable in steel
Decontamination None needed in field; bleach caustic soda, or DS2 in closed spaces, M258 kit
Means of Detection in Field M18A2 kit
Typical Use Delayed action casualty agent
Agent Type Blister Agent
Chemical Agent Methyldichloroarsine
Formula CH3ASCL2
Symbol MD
Molecular Weight 160.86
State at 20°C Colourless liquid
Vapour Density (air=1) 5.5
Liquid Density (g/cc) 1.83 @ 20°C
Freezing Point °C -55
Boiling Point °C 133
Vapour Pressure (mg/m2) 7.76 @ 20°C
Volatility (mg/m3) 74,900 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) 49
Odour None
Median Lethal Dosage (mg/min./m2) 3,000 to 5,000 (estimated)
Median Incapacitating Dosage (mg/min./m2) 25 by inhalation
Rate Of Detoxification Rapid
Eye and Skin Toxicity Cornea damage possible; blisters less than HD
Rate of Action Rapid
Physiological Action Irritates respiratory tract, injures lungs and eyes, causes systemic poisoning
Protection Required Protective mask and clothing
Stability Stable in steel
Decontamination Bleach, caustic soda, DS2; M258 kit
Means of Detection in Field M18A2 kit
Typical Use Delayed action casualty agent
Blood Gas
Blood gas is an inhaled agent that can be smelled; however, it takes effect in humans in less than 6 minutes and causes convulsions and suffocation, as all blood gases do because they interfere with the absorption of oxygen by the blood in the lungs. Blood gas is used to kill, not to harass, and it has a persistence time of approximately 8 minutes. This gas is valued for the ability to act quickly for tactical situations requiring surprise. Systemic agents or blood gases (e.g. hydrogen cyanide) — hydrogen cyanide is a volatile liquid (boiling point at 26°C) that produces a gas that is lighter than air and disperses very rapidly. It acts extremely fast, and it is difficult to protect against because it can be absorbed by inhalation and ingestion (and through the skin in case of liquid hydrogen cyanide). However, it is difficult to maintain effective concentrations and so is unlikely to be useful for large civilian attacks. Once the cloud has dissipated, people who are still alive will most probably recover. Later sequelae are rare. Cyanogen halides cause lacrimation and possibly eye injury, and irritation of respiratory tract similar to lung damaging agents. Rapid and effective life support care is vital: assisted ventilation, cardiovascular resuscitation and correction of metabolic acidosis. Several antidotes are available: dicobalt edetate, amylnitrite, sodium nitrate and sodium thiosulfate in combination, hydroxocobalamin and also oxygen.

Agent Type Blood Agent
Chemical Agent Hydrogen Cyanide
Formula HCN
Symbol AC
Molecular Weight 27.02
State at 20°C Colourless gas or liquid
Vapour Density (air=1) 0.93
Liquid Density (g/cc) 0.687 @ 10°C
Freezing Point °C -13
Boiling Point °C 25.7
Vapour Pressure (mg/m2) 742 @ 25°C
Volatility (mg/m3) 1,080,000 @ 25°C
Flash Point 0°C, ignited 50% of time when disseminated from artillery shell.
Decomposition Temp. (°C) 65.5+
Heat Of Vaporization (°C) 233
Odour Bitter almonds
Median Lethal Dosage (mg/min./m2) Varies widely with concentrations
Median Incapacitating Dosage (mg/min./m2) Varies widely with concentrations
Rate Of Detoxification Rapid 0.017 mg/kg/min.
Eye and Skin Toxicity Moderate
Rate of Action Very rapid
Physiological Action Interferes with use of oxygen by body tissues; accelerated rate of breathing
Protection Required Protective mask and clothing
Stability Stable if pure, can inflame on shell explosion
Decontamination None needed in field
Means of Detection in Field M18A2 kit
Typical Use Quick acting casualty agent
Agent Type Blood Agent
Chemical Agent Cyanogen chloride
Formula CNCI
Symbol CK
Molecular Weight 61.48
State at 20°C Colourless gas
Vapour Density (air=1) 2.1
Liquid Density (g/cc) 1.18 @ 10°C
Freezing Point °C -6.9
Boiling Point °C 12.8
Vapour Pressure (mg/m2) 1000 @ 25°C
Volatility (mg/m3) 2,600,000 @ 12.8°C
Flash Point None
Decomposition Temp. (°C) 100+
Heat Of Vaporization (°C) 103
Odour Bitter Almonds
Median Lethal Dosage (mg/min./m2) 11,000
Median Incapacitating Dosage (mg/min./m2) 7500
Rate Of Detoxification Rapid 0.02 to 0.01 mg/kg/min.
Eye and Skin Toxicity Low, lachrymatory and irritating
Rate of Action
Physiological Action Chokes, irritates, causes slow breathing rate
Protection Required Protective mask
Stability Tends to polymerise; may explode
Decontamination None needed in field
Means of Detection in Field M18A2 and M256A
Typical Use Quick acting casualty agent
Agent Type Blood Agent
Chemical Agent Arsine
Formula AsH3
Symbol SA
Molecular Weight 77.93
State at 20°C Colorless gas
Vapour Density (air=1) 2.69
Liquid Density (g/cc) 1.34 @ 20°C
Freezing Point °C -16
Boiling Point °C -62.5
Vapour Pressure (mg/m2) 11,100 @ 20°C
Volatility (mg/m3) 30,900,000 @ 0°C
Flash Point Below shell detonation temp; mixtures with air may explode spontaneously
Decomposition Temp. (°C) 280+
Heat Of Vaporization (°C) 53.7
Odour Mild garlic
Median Lethal Dosage (mg/min./m2) 5,000
Median Incapacitating Dosage (mg/min./m2) 2500
Rate Of Detoxification Low
Eye and Skin Toxicity None
Rate of Action Delayed action to 2 hours to as much as 11 days
Physiological Action Damages blood, liver, and kidneys
Protection Required Protective mask
Stability Not stable in uncoated metal containers
Decontamination None needed
Means of Detection in Field None
Typical Use Delayed action casualty agent
Choking Gas
Choking gas can be smelled in the battlefield and takes approximately 10 hours to take effect. This gas is used to kill and causes coughing and suffocation. The persistence time is approximately 6 minutes. This was known as one of the first modern warfare chemical agents and was responsible for almost 80 percent of the fatalities in World War I where the gas was used. Chemical research is producing more efficient substitutes for this chemical. Lung gases, choking or asphyxiants (e.g. phosgene, chlorine) – Phosgene is the most irritant: severe pulmonary oedema occurs after a latent period of up to 48 hours. Painful coughing, bronchial hypersecretion, vomiting, dyspnoea occurs. Patients suffer distress and fear. They die from cardiac failure or asphyxia 24 to 28 hours after exposure, or later, from secondary infection. If the eyes are contaminated, intense irritation and severe pain and corneal lesions may lead to permanent blindness. No antidote exists and treatment is essentially symptomatic and supportive, using mechanical ventilation and steroids. There is no specific therapy. Skin and eye decontamination should be carried out immediately.

Agent Type Choking Agent
Chemical Agent Phosgene
Formula COCL2
Symbol CG
Molecular Weight 98.92
State at 20°C Colourless Gas
Vapour Density (air=1) 3.4
Liquid Density (g/cc) 1.37 @ 20°C
Freezing Point °C -128
Boiling Point °C 7.6
Vapour Pressure (mg/m2) 1.173 @ 20°C
Volatility (mg/m3) 4,300,000 @ 7.6°C
Flash Point None
Decomposition Temp. (°C) 800
Heat Of Vaporization (°C) 59
Odour New mown hay, green corn
Median Lethal Dosage (mg/min./m2) 3,200
Median Incapacitating Dosage (mg/min./m2) 1,600
Rate Of Detoxification Not detoxified-cumulative
Eye and Skin Toxicity None
Rate of Action Immediate to 3 hours
Physiological Action Damages and floods lungs
Protection Required Protective mask
Stability Stable in steel if dry
Decontamination None needed in field, aeration in closed spaces
Means of Detection in Field M18A2 Kit, odour
Typical Use Delayed or immediate action, casualty agent
Agent Type Choking Agent
Chemical Agent Diphosgene
Symbol DP
Molecular Weight 197.85
State at 20°C Colourless Liquid
Vapour Density (air=1) 6.8
Liquid Density (g/cc) 1.65 @ 20°C
Freezing Point °C -57
Boiling Point °C 127 to 128
Vapour Pressure (mg/m2) 4.2 @ 20°C
Volatility (mg/m3) 45,000 @ 20°C
Flash Point None
Decomposition Temp. (°C) 300-350
Heat Of Vaporization (°C) None
Odour New mown hay, green corn
Median Lethal Dosage (mg/min./m2) 3,200
Median Incapacitating Dosage (mg/min./m2) 1,600
Rate Of Detoxification Not detoxified, cumulative
Eye and Skin Toxicity Slightly lachrymatory
Rate of Action Immediate to 3 hours depending on concentration
Physiological Action Damages and floods lungs
Protection Required Protective mask
Stability Unstable, tends to convert to CG
Decontamination None needed in field, aeration in closed spaces
Means of Detection in Field Odour
Typical Use Delayed or immediate action casualty agent
Nerve Gas
Nerve gas is also known as Tabun GA, Sarin GB, Soman GD, CMPF, GP, VR-55, and VX. Nerve gas interferes with the transmission of messages in the nervous system of the body. This is the most widely used and stockpiled agent by both the United States and what use to be the Soviet Union. It cannot be smelled easily and is very lethal, although it can be used in harassing concentrations. It takes approximately 6 to 8 minutes to take effect and causes death by convulsions and suffocation. It can be designed to have a persistence time from 10 minutes to 112 days. Nerve agents (e.g. Sarin, VX) — highly toxic chemicals, originally used as pesticides effective at very low concentrations and virtually odourless. Produces salivation, myosis, bronchoconstriction, and paralysis (most importantly, of the respiratory muscles). In liquid or vapour state, organophosphate nerve agents rapidly penetrate all normal clothing and mucous surfaces including the cornea, and the vapour is quickly absorbed by upper and lower respiratory tracts. Exposure to high concentrations causes irregular shallow breathing, bradycardia, convulsions and death within a few minutes. Smaller doses cause nausea and vomiting, constriction of the pupils, tightness of the chest and a runny nose. Effective life support is vital. Antidotes are available. Three main groups of drugs can be used: atropine, oximes and diazepam. Pre-treatment with pyridostigmine may be beneficial. Toxicological analysis can most readily be performed by an indirect method, measuring the level of red cell cholinesterase activity.

Agent Type Nerve Agent
Chemical Agent Tabun
Formula (CH3)2 NP(O)(C2H5O)(CN)
Symbol GA
Molecular Weight 162.3
State at 20°C Colourless to brown liquid
Vapour Density (air=1) 5.63
Liquid Density (g/cc) 1.073 @ 25°C
Freezing Point °C -50
Boiling Point °C 240
Vapour Pressure (mg/m2) 0.07 @ 25°C
Volatility (mg/m3) 610 @ 25°C
Flash Point 78°C
Decomposition Temp. (°C) 150
Heat Of Vaporization (°C) 79.56
Odour Faintly fruity, none when pure
Median Lethal Dosage (mg/min./m2) 400 for resting men
Median Incapacitating Dosage (mg/min./m2) 300 for resting men
Rate Of Detoxification Slight but definite
Eye and Skin Toxicity Very high
Rate of Action Very rapid
Physiological Action Cessation of breath, death may follow
Protection Required Protective mask and clothing
Stability Stable in steel at ordinary temp.
Decontamination Bleach slurry; dilute alkali, or DS2, steam and ammonia in confined area, M258 kit.
Means of Detection in Field M256A and M18A2 kits
Typical Use Quick action casualty agent
Agent Type Nerve Agent
Chemical Agent Sarin
Formula (CH3)2CHO (CH3)FPO
Symbol GB
Molecular Weight 140.10
State at 20°C Colourless liquid
Vapour Density (air=1) 4.86
Liquid Density (g/cc) 1.0887 @ 25°C
Freezing Point °C -56
Boiling Point °C 158
Vapour Pressure (mg/m2) 2.9 @ 25°C
Volatility (mg/m3) 22,000 @ 25°C
Flash Point Non-flammable
Decomposition Temp. (°C) 150
Heat Of Vaporization (°C) 80
Odour Almost none when pure
Median Lethal Dosage (mg/min./m2) 100 for resting men
Median Incapacitating Dosage (mg/min./m2) 75 for resting men
Rate Of Detoxification Cumulative
Eye and Skin Toxicity Very High
Rate of Action Very Rapid
Physiological Action Cessation of breath and death may follow
Protection Required Protective mask and clothing
Stability Stable when pure
Decontamination In confined area steam and ammonia; hot soapy water
Means of Detection in Field M256A and M18A2 kits
Typical Use Quick action casualty agent
Agent Type Nerve Agent
Chemical Agent Soman
Formula (CH3)3CCH(CH3)OPF(O)CH3
Symbol GD
Molecular Weight 182.178
State at 20°C Colourless liquid
Vapour Density (air=1) 6.33
Liquid Density (g/cc) 1.0222 @ 22°C
Freezing Point °C -42
Boiling Point °C 198
Vapour Pressure (mg/m2) 0.4 @ 25°C
Volatility (mg/m3) 3,900 @ 25°C
Flash Point High enough not to interfere with military use.
Decomposition Temp. (°C) 130
Heat Of Vaporization (°C) 72.4
Odour Fruity, camphor odour when pure
Median Lethal Dosage (mg/min./m2) 100-400 for resting men
Median Incapacitating Dosage (mg/min./m2) 75-300 for resting men
Rate Of Detoxification Low essentially cumulative
Eye and Skin Toxicity Very High
Rate of Action Very Rapid
Physiological Action Cessation of breath and death may follow
Protection Required Protective mask and clothing
Stability Stable when pure
Decontamination Bleach slurry, dilute alkali, hot soapy water, M258 kit
Means of Detection in Field M256A and M18A2 kits
Typical Use Quick action casualty agents
Agent Type Nerve Agent
Chemical Agent VX
Symbol VX
Molecular Weight 267.38
State at 20°C Colourless liquid
Vapour Density (air=1) 9.2
Liquid Density (g/cc) 1.0083 @ 20°C
Freezing Point °C Below -51
Boiling Point °C 298
Vapour Pressure (mg/m2) .0007 @ 25°C
Volatility (mg/m3) 10.5 @ 25°C
Flash Point 159°C
Decomposition Temp. (°C) Half life of 36 hours @ 150°C
Heat Of Vaporization (°C) 78.2 @ 25°C
Odour Odourless
Median Lethal Dosage (mg/min./m2) 100
Median Incapacitating Dosage (mg/min./m2) 50
Rate Of Detoxification Low; essentially cumulative
Eye and Skin Toxicity Very High
Rate of Action Rapid
Physiological Action Produces casualties when inhaled or absorbed
Protection Required Protective mask and clothing
Stability Relatively stable at room temperature
Decontamination STB slurry or DS2 solution; hot soapy water, M258 kit
Means of Detection in Field M256A and M18A2 kits
Typical Use Quick acting causality agent
Tear Gas
Tear gas is an inhaled agent. It can be smelled and takes approximately 1 minute to take effect. It is non-lethal and depending on the variant, can cause severe coughs, involuntary defecation, and vomiting. Although this agent is non-lethal, it is able to render soldiers totally helpless and is used very often on the battlefield as a harassing agent. It has a persistence time of 30 minutes. Sensory irritants (riot agents) (e.g. CS, CN, CR) act very rapidly as lacrimators (some may be vomiting or sternutator agents, e.g. DM, adamsite). Exposure to CS gas causes eye irritation and severe pain, blepharospasm, intense lacrimation and photophobia; skin blistering, burning sensation in the mouth, salivation and vomiting, nose discomfort, cough, sneezing and tightness in the chest. Only massive, prolonged exposure may pose a vital risk. Decontamination and symptomatic treatment is needed. There are no antidotes. No biological or environmental toxicological analyses are recommended.

Agent Type Tear Agent
Chemical Agent Chloroacetophenone
Formula C6H5COCH2CL
Symbol CN
Molecular Weight 154.59
State at 20°C Solid
Vapour Density (air=1) 5.3
Liquid Density (g/cc) 1.318 @ 20°C (solid)
Freezing Point °C 54
Boiling Point °C 248
Vapour Pressure (mg/m2) 0.0041 @ 20°C
Volatility (mg/m3) 343 @ 20°C
Flash Point High enough not to interfere with military use
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) 98
Odour Apple blossoms
Median Lethal Dosage (mg/min./m2) 14,000
Median Incapacitating Dosage (mg/min./m2) 80
Rate Of Detoxification Rapid
Eye and Skin Toxicity Temporary severe eye irritation; mild skin irritation
Rate of Action Instantaneous
Physiological Action Lachrymatory; irritates respiratory tract
Protection Required Protective mask
Stability Stable
Decontamination Aeration in open; soda ash solution or alcoholic caustic soda in closed spaces
Means of Detection in Field M-nitrobenzene and alkali in white-band tube or detector kit
Typical Use Training and riot control agent
Agent Type Tear Agent
Chemical Agent Chloroacetophenone in chloroform
Symbol CNC
Molecular Weight 128.17 on basis of components
State at 20°C Liquid
Vapour Density (air=1) 4.4
Liquid Density (g/cc) 1.40 @ 20°C
Freezing Point °C 0.23
Boiling Point °C Variable 60 to 247
Vapour Pressure (mg/m2) 127 @ 20°C
Volatility (mg/m3) Indeterminate
Flash Point None
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) Not applicable
Odour Chloroform
Median Lethal Dosage (mg/min./m2) 11,000 (estimated)
Median Incapacitating Dosage (mg/min./m2) 80
Rate Of Detoxification Rapid
Eye and Skin Toxicity Temporary severe eye irritation; mild skin irritation
Rate of Action Instantaneous
Physiological Action Lachrymatory, irritates respiratory tract
Protection Required Protective mask
Stability Adequate
Decontamination Aeration in open; soda ash solution or alcoholic caustic soda in closed spaces
Means of Detection in Field M-nitrobenzene and alkali in white-band tube or detector kit
Typical Use Training and riot control agent
Agent Type Tear Agent
Chemical Agent Chloroacetophenone and chloroform
Symbol CNS
Molecular Weight 141.78 on basis of components
State at 20°C Liquid
Vapour Density (air=1) Approximately 5
Liquid Density (g/cc) 1.47@ 20°C
Freezing Point °C 2
Boiling Point °C Variable 60 to 247
Vapour Pressure (mg/m2) 78 @ 20°C
Volatility (mg/m3) 610,000 @ 20°C (includes solvent)
Flash Point None
Decomposition Temp. (°C) Stable to boiling point
Heat Of Vaporization (°C) Not applicable
Odour Flypaper
Median Lethal Dosage (mg/min./m2) 11,400
Median Incapacitating Dosage (mg/min./m2) 60
Rate Of Detoxification Slow because of effect of PS
Eye and Skin Toxicity Irritating; not toxic
Rate of Action Instantaneous
Physiological Action Acts as vomiting and choking agent as well as tear agent
Protection Required Protective mask
Stability Adequate
Decontamination None needed in field; hot solution of soda ash and sodium sulfite in closed spaces
Means of Detection in Field CN test, as alkaline sulfite in blue-band tube of detector kits
Typical Use Former training and riot control agent
Agent Type Tear Agent
Chemical Agent Chloracetophenone in benzene and carbon tetrachloride
Symbol CNB
Molecular Weight 119.7 on basis of components
State at 20°C Liquid
Vapour Density (air=1) Approximately 4
Liquid Density (g/cc) 1.14 @ 20°C
Freezing Point °C -7 to -30
Boiling Point °C Variable 75 to 247
Vapour Pressure (mg/m2) Variable mostly solvent vapour
Volatility (mg/m3) Indeterminate
Flash Point Below 4.44
Decomposition Temp. (°C) Above 247
Heat Of Vaporization (°C) Not applicable
Odour Benzene
Median Lethal Dosage (mg/min./m2) 11,000 (estimated)
Median Incapacitating Dosage (mg/min./m2) 80
Rate Of Detoxification Rapid unless large amounts of solvent is inhaled
Eye and Skin Toxicity Temporary severe eye irritation; mild skin irritation
Rate of Action Instantaneous
Physiological Action Powerfully lachrymatory
Protection Required Protection mask
Stability Adequate
Decontamination Aeration in open; soda ash solution or alcoholic caustic soda in closed spaces
Means of Detection in Field M-nitrobenzene and alkali in white-band tube of detector kit
Typical Use Former training and riot control agent
Agent Type Tear Agent
Chemical Agent Bromobenzylcyanide
Formula BrC6H4CH2CN
Symbol CA
Molecular Weight 196
State at 20°C Liquid
Vapour Density (air=1) 6.7
Liquid Density (g/cc) 1.47 @ 25°C
Freezing Point °C 25.5
Boiling Point °C Decomposes at 242
Vapour Pressure (mg/m2) 0.011 @ 20°C
Volatility (mg/m3) 115 @ 20°C
Flash Point None
Decomposition Temp. (°C) 60 to 242
Heat Of Vaporization (°C) 55.7
Odour Soured fruit
Median Lethal Dosage (mg/min./m2) 8,000 to 11,000 (estimated)
Median Incapacitating Dosage (mg/min./m2) 30
Rate Of Detoxification Rapid in low dosage
Eye and Skin Toxicity, Irritating; not toxic
Rate of Action Instantaneous
Physiological Action Irritates eye and respiratory passages
Protection Required Protective mask
Stability Fairly stable in glass, lead, or enamel
Decontamination 20% alcoholic caustic
Means of Detection in Field M-nitrobenzene and alkali in white-band tube of detector kit
Typical Use Former training and riot control agent
Agent Type Tear Agent
Chemical Agent O-chlorobenzylmalononitrile
Formula CLC6H4CHC(CN)2
Symbol CS
Molecular Weight 188.5
State at 20°C Colourless solid
Vapour Density (air=1)
Liquid Density (g/cc) 1.04 @ 20°C (solid)
Freezing Point °C 93 to 95
Boiling Point °C 310 to 315(w/decomposition)
Vapour Pressure (mg/m2)
Volatility (mg/m3) 0.71 @ 25°C
Flash Point 197°C
Decomposition Temp. (°C)
Heat Of Vaporization (°C) 53.6
Odour Pepper
Median Lethal Dosage (mg/min./m2) 61,000
Median Incapacitating Dosage (mg/min./m2) 10 to 20
Rate Of Detoxification Rapid; sub lethal in 5 to 10 minutes
Eye and Skin Toxicity Highly irritating; not toxic
Rate of Action Instantaneous
Physiological Action Highly irritating; but not toxic
Protection Required Protective mask and clothing
Stability Stable
Decontamination Water, 5% sodium bisulphide, and water rinse
Means of Detection in Field None
Typical Use Training and riot control agent
Vomiting Gas
Vomiting gas (DM) is an inhaled agent. It cannot be smelled easily and takes approximately l minute to take effect. It is non-lethal and causes headaches, coughing, and nausea. It has a persistence time of approximately 30 minutes. This gas is basically a very strong tear gas. It is a favourite chemical weapon and is used for clearing out enemy troops in congested or very built-up areas.

Agent Type Vomiting Agent
Chemical Agent Diphenylchloroarsine
Formula (C6H5)2ASCL
Symbol DA
Molecular Weight 264.5
State at 20°C White to brown solid
Vapour Density (air=1) Forms little vapour
Liquid Density (g/cc) 1.387 @ 50°C
Freezing Point °C 41 to 44.5
Boiling Point °C 333
Vapour Pressure (mg/m2) 0.0036 @ 45°C
Volatility (mg/m3) 48 @ 45°C
Flash Point 350°C
Decomposition Temp. (°C) 300
Heat Of Vaporization (°C) 56.6
Odour None
Median Lethal Dosage (mg/min./m2) 15,000 estimated
Median Incapacitating Dosage (mg/min./m2) 12 over 10 minute periods
Rate Of Detoxification Rapid
Eye and Skin Toxicity Irritating; not toxic
Rate of Action Very rapid
Physiological Action Like cold symptoms plus headache, vomiting, nausea
Protection Required Protective mask
Stability Stable if pure
Decontamination None needed in field, caustic soda or chlorine in closed spaces
Means of Detection in Field None
Typical Use Former training and riot control agent
Agent Type Vomiting Agent
Chemical Agent Adamsite
Formula C6H4(ASCL)(NH)C6H4
Symbol DM
Molecular Weight 277.57
State at 20°C Yellow to green solid
Vapour Density (air=1) Forms little vapour
Liquid Density (g/cc) 1.65 (solid) @ 20°C
Freezing Point °C 195
Boiling Point °C 410
Vapour Pressure (mg/m2) Negligible
Volatility (mg/m3) Negligible
Flash Point None
Decomposition Temp. (°C) Above boiling point
Heat Of Vaporization (°C) 80
Odour None
Median Lethal Dosage (mg/min./m2) 15,000
Median Incapacitating Dosage (mg/min./m2) 22 for 1 minute exposure; 8 for 60 min.exposure
Rate Of Detoxification Rapid in small amounts
Eye and Skin Toxicity Irritating; relatively non-toxic
Rate of Action Very rapid
Physiological Action Like cold symptoms plus headache, vomiting, nausea
Protection Required Protective mask
Stability Stable in glass or steel
Decontamination None needed in field; bleach or DS2 in confined spaces
Means of Detection in Field None
Typical Use Former training and riot control agent
Agent Type Vomiting Agent
Chemical Agent Diphenylcyanoarsine
Formula (C6H5)2ASCN
Symbol DC
Molecular Weight 255.0
State at 20°C White to pink solid
Vapour Density (air=1) Forms little vapour
Liquid Density (g/cc) 1.3338 @ 35°C
Freezing Point °C 31.5 to 35
Boiling Point °C 350
Vapour Pressure (mg/m2) 0.0002 @ 20°C
Volatility (mg/m3) 2.8 @ 20°C
Flash Point Low
Decomposition Temp. (°C) 300 (25% decomposed)
Heat Of Vaporization (°C) 71.1
Odour Bitter almond garlic mixture
Median Lethal Dosage (mg/min./m2) 10,000 (estimated)
Median Incapacitating Dosage (mg/min./m2) 30 for 30second exposure; 20 for 5 min. exposure
Rate Of Detoxification Rapid
Eye and Skin Toxicity Irritating; not toxic
Rate of Action More rapid than DM or DA
Physiological Action Like cold symptoms plus headache, vomiting, nausea
Protection Required Protective Mask
Stability Stable
Decontamination None needed in field, alkali solution or DS2 in closed spaces
Means of Detection in Field None
Typical Use Former training and riot control agent
Incapacitating Agent
An incapacitating agent renders its victims physically dysfunctional and is considered a separate category by itself. Not as much is known about this type of agent and a great deal of research is still required. Psychotropic agents (e.g. BZ) are incapacitating agents, capable of temporarily preventing personnel from performing their duties (without permanent injury). For a variety of reasons, they have not generally been used in overt warfare. Anticholinergics (e.g. BZ or 3-Quinuclidinyl benzilate) produce delirium following an absorbed dose of less than 1 mg. This lasts for 2 to 3 days. Reversal of the effects of BZ by physostigmine and other anticholinesterase agents has been clearly demonstrated to be both effective and safe when properly used in otherwise healthy individuals. Incapacitation produced by less likely candidates such as LSD and other indole derivatives, psychedelic phenethylamines, and potent opioids is theoretically possible, but it is unlikely that any of these compounds would be employed in the warfare context. Treatment is always symptomatic.

Agent Type Incapacitating Agent
Chemical Agent BZ
Symbol BZ
Molecular Weight 337.4
State at 20°C
Vapour Density (air=1) 11.6
Liquid Density (g/cc) Bulk 0.51 solid
Freezing Point °C 167.5
Boiling Point °C 412
Vapour Pressure (mg/m2) 0.03 @ 70°C
Volatility (mg/m3) 0.5 @ 70°C
Flash Point 246°C
Decomposition Temp. (°C) Begins at 170°C
Heat Of Vaporization (°C) 62.9
Median Lethal Dosage (mg/min./m2)
Median Incapacitating Dosage (mg/min./m2)
Rate Of Detoxification
Eye and Skin Toxicity
Rate of Action Delayed action 1 to 4 hours
Physiological Action Fast heartbeat; dizziness, vomiting, dry mouth, blurred vision, stupor, increase-random activity
Protection Required Protective mask
Stability Adequate
Decontamination Wash with soap and water; shake or brush; hypochlorite or caustic alcoholic solutions; detergent vetting solutions
Means of Detection in Field None
Typical Use Former delayed action temporarily incapacitating agent