The medical effects of a CBRN agent depend on a number of characteristics that affect not only the medical presentation of casualties but also the delivery method, type of response, physical protection and additional resources required such as decontamination or isolation. Important characteristics include agent class, physical properties and onset of effects (latency):
Chemical agents: The main classes of chemical agents are:
- Nerve agents (organophosphorus compounds).</li>
- Blistering agents (vesicants) agents.
- Cyanides (also known as blood agents).
- Pulmonary agents (choking or lung damaging agents).
- Incapacitants (mental and physical).
- Toxic industrial chemicals (TICs). While this class of agent is used, there is significant overlap with other classes of chemical agents especially cyanides and pulmonary agents.
- Riot-controlled agents (RCAs). These agents used by law enforcement agencies are not prohibited by international conventions but may still have harmful effects.
- This class includes illicit and commercial drugs usually at supra-therapeutic or toxic doses.
Biological agents: The two classes of biological agent are:
- Live agents such as bacteria including rickettsia and chlamydia, viruses and fungi
- Toxins – chemical agents that are of biological origin and include those derived from bacteria, fungi, plants and animals (venom)
Radiological material: This hazard can be classed by the type of ionising radiation present:
- Alpha – a relatively large subatomic particle (similar to a helium nucleus) with limited range in air (millimetres) but significant damaging effects
- Beta – a small subatomic particle similar to an electron with a range in air of centimetres
- Gamma/X-ray – high-energy photons with no mass but highly penetrating
- Neutrons – normally associated with nuclear material and the fission (nuclear) process which are highly penetrating and variable damaging effects
The term nuclear material is generally used to describe material involved in the nuclear power or weapon industry, or as having fissile properties, i.e. the potential for the nucleus to be split and therefore generate energy, fission products and further neutron emissions.
The physical properties of an agent may vary across a class of agent (e.g. nerve agents). These properties determine the optimal delivery system, route of exposure and continuing presence in the environment (persistency). The physical properties of an agent determine whether the agent is a:
- Gas: A substance that exists in the air at ambient (room) temperature (non-persistent hazard).
- Vapour: A substance that diffuses into the air (evaporates) but is normally a liquid at ambient (room) temperature (non-persistent hazard, but may condense into clothing and wound dressings).
- Liquid: Persistent hazard although the degree of persistency is dependent on volatility of the substance with water often considered a reference point (i.e. petrol < water while water < VX).
- Aerosols: Some solids and liquids can be aerosolised and therefore present a dropletor airborne hazard requiring respiratory protection. (These may remain a persistent hazard as particles settle on to surfaces with a risk of re-aerosolisation or evaporation if liquid.)
- Ionising radiation: Radioactive material may be in any of the physical forms just described, but irradiation itself does not present a contamination hazard.