Biological Agents

A release of a biological agent will have strong similarities to the outbreak of a naturally occurring disease and may take days to first become apparent and weeks to evolve. For this reason, biological attacks can be hard to detect and/or identify.

Examples of biological agents include:

bacteria, such as anthrax and plague

viruses, such as smallpox and viral haemorrhagic fevers e.g. Ebola

fungi, such as that causing Valley Fever and histoplasmosis

biological toxins, such as ricin and botulinum

Radiation

The harmful effects of radiological and nuclear agents (i.e. radionuclides) results from the radiation they emit. This gives rise to two types of radiological hazard: from external exposure through absorption of radioactive material into the body.

There are three main types of radiation: alpha or beta particles and gamma rays, which have differing abilities to penetrate matter both between a person and the source and within the body.

Alpha particles (2 protons + 2 neutrons ≈ He core) can scarcely penetrate the dead, outer layer of human skin and are, therefore, not hazardous unless they are taken into the body through breathing or eating or through a skin wound.

Beta particles (negative electrons or also positrons) are much more penetrating than alpha particles and can penetrate the outer layers of skin and may penetrate a centimetre or so of tissue, depending on their energy. Beta particles are therefore hazardous to superficial tissues of the body but not to internal organs unless they are taken into the body (e.g. through inhalation or ingestion).

Gamma rays (electromagnetic rays) can pass through the body, so radionuclides that emit them may be hazardous whether on the outside or inside of the body. Gamma rays can penetrate most materials, requiring a substantial thickness of earth, lead, concrete or water to provide an effective barrier.

Radionuclides

Radionuclides can be grouped into three categories, according to their half-lives.

The categories are:

Very short-lived radionuclides with half-lives of less than a day (e.g. Technetium-99m and iodine-120). Even if a very large quantity were released, it would decay away within days.

Short-lived radionuclides with half-lives of up to 3 weeks (e.g. phosphorus-32, molybdenum-99, iodine-131). Even a substantial amount of radioactivity of this kind would decay away within months.

Radionuclides with half-lives longer than 3 weeks. These will take at least years to decay away. Radionuclides in this category may be grouped according to whether their hazard is predominantly gamma, beta or alpha emissions:

Gamma emitters (such as caesium-137 and iridium-192);

Beta emitters

Betaemitters (e.g. strontium-89 and strontium-90);;

Alpha emitters

Alpha emitters (such as plutonium-238 and curium-242).

Although NBC agents differ substantially, in broad terms they present four main types of hazard:

Contact

Inhalation

Injection

Ingestion

Radiological agents present a significant additional hazard resulting from the radiation they emit.

Chemical, Biological and Radiological Hazards

Contact:

Chemical and biological hazards are created by agents in solid, liquid or vapour form that can be absorbed into the skin or through the eyes. Radiation can be absorbed through the skin or when in contact with the skin.

Inhalation:

Chemical and biological hazards are created by vapours, aerosols or contaminated dust inhaled into the lungs. Radiation particles are inhaled into the lungs providing a direct dose of radiation which can also form concentrations in the bones and thyroid.

Injection:

Chemical and biological hazards are created by direct injection into a vein or artery, or an agent moving into the blood stream from an injected area. Radiation can be injected through open wounds or on contaminated foreign bodies such as shrapnel.

Injestion:

Chemical agents typically present inhalation, ingestion and contact hazards. Some can be delivered as vapour or aerosols and cause poisoning by inhalation.

There are two broad categories of chemical agents:

toxic industrial chemicals, including commercially produced chemicals, such as:

chlorine

ammonia

hydrogen cyanide

phosgene

chemical warfare agents, which include:

nerve gases, such as sarin, soman, tabun, GF and VX

blister agents, such as mustard gas and Lewisite

riot control agents such as CS and tear gas