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Chemical, Biological, Radiological, Nuclear (explosive) event

Hazard Knowledge

CBRN(e) terrorism entails the assumption or knowledge, based on intelligence or actual evidence, of actual or threatened dispersal of chemical, biological, radiological or nuclear material (either on their own or with explosives), with deliberate, criminal, malicious or murderous intent, targeted at a given population or economic or symbolic points. The CBRN material may initially be expelled in all directions and spread over a wide area from the point of release. The fallout of the explosion may also contain undetonated explosive material.

A CBRN(e) event has many elements. The impact and response will vary depending on the nature of the material and event, for example:

  • A chemical attack may produce rapid onset of severe symptoms. Many chemical agents can be readily detected and potentially identified with specialist equipment
  • A biological release may not be identified for some time and may only be recognised through health monitoring. The scene of any release may be unidentified
  • A radiological release may be accompanied by explosives (a dirty bomb), or the dispersal of radioactive particulates into the air with no obvious sudden onset of symptoms
  • A nuclear attack is likely to be readily identified and result in immediate, with catastrophic consequences and a long-lasting radiation hazard
  • Explosives may be used as a means of dissemination for the above materials or as an additional method of attack. In the context of this document the lower case (e) is used to differentiate the use of explosives only as a means of dissemination

Whilst any such incident is ongoing there will be a continued threat to life. Uncertainty about release locations, spread of contamination and the intent and capability of the terrorists means that the management of life-saving interventions may be much more difficult than for other major incidents.

The hazard area of a CBRN(e) event will vary in size depending on the following factors:

  • The type and concentration of CBRN material; this can be affected by water and temperature
  • The form of the material (gas, vapour, liquid, solid)
  • Method of distribution
  • The movement of contaminated people, vehicles and objects
  • Weather and topography

A CBRN(e) event, over and above a hazardous materials event, may have the potential for:

  • Multiple events caused by secondary devices
  • More than one area of release
  • Material being intentionally spread or channelled
  • Perpetrators to use virulent agents that may be both persistent and difficult to identify
  • Perpetrators or terrorists present
  • Safety signage or information to be changed, removed or concealed
  • Locations to be selected that exploit the characteristics of the attack
  • Increased public and emergency responder exposure

CBRN(e) may be difficult to recognise, resulting in initial responders being deployed to the scene. Initial responders could inadvertently drive into or through a contaminated area en route to the incident. Airborne contamination is not easily identifiable although some visual indicators may be present.

Casualties of a CBRN(e) attack may be traumatised by witnessing the incident and the effect it is having on others, or because of being contaminated themselves. Casualties may act unexpectedly; for example, they may be unresponsive to commands or unaware of the potential danger they are in.

CBRN materials


Chemical agents used as weapons can cause temporary incapacity, permanent harm or death. There may be a rapid onset of medical symptoms, such as nausea, vomiting, burns or skin rashes. There may be visual indicators such as a coloured residue, dead foliage, pungent odour or dead animals.

Chemical agents can be classified as:

  • Nerve agents such as sarin, VX or VR – these usually gain access to the body through the skin or lungs
  • Respiratory agents such as chlorine or phosgene – these are inhaled and either cause damage to the lungs, or are transmitted to the body via the lungs
  • Blister agents such as mustard gas or nerve agents – these are absorbed through the skin, either damaging it, or are transmitted to the body via the skin, or both

A further classification is based on the duration of the hazard. Persistent agents such as mustard gas may remain in the affected area for several weeks. They:

  • Are usually substances of low volatility
  • Contaminate surfaces
  • Have the potential to damage the skin on contact and may release vapours which are inhaled
  • May be used to create obstacles, contaminate strategic places or equipment, thereby making access difficult

Non-persistent agents, such as hydrogen cyanide or phosgene, evaporate or disperse quickly. They:

  • Are usually volatile substances
  • May be used to incapacitate people in an area that the perpetrator is trying to gain access after the release
  • Do not usually contaminate surfaces
  • Cause harm through inhalation and may damage the skin

Chemical agents used as weapons are effective because of their toxicity, that is, their chemical action can cause death, permanent harm or temporary incapacity.

Chemical incidents are characterised by the rapid (minutes to hours) onset of medical symptoms, e.g. nausea, vomiting, burns/rash, etc. and readily observed signatures (coloured residue, dead foliage, pungent odour, and dead insect and animal life).


The deliberate release of biological agent is intended to infect people with pathogenic microorganisms such as viruses. Biological agents can multiply in a host over time. In the case of a biological incident, the onset of symptoms requires days to weeks and there may be no immediate symptoms. Because of the delayed onset of symptoms in a biological incident, the area affected may be much greater due to the movement of infected people.

Biological agents used as weapons are those that achieve their intended effects by infecting people with pathogenic microorganisms and other replicative entities, including viruses, infectious nucleic acids and prions. The chief characteristic of biological agents is their ability to multiply in a host over time. The disease they may cause is the result of the interaction between the biological agent, the host (including the host’s genetic constitution, nutritional status and the immunological status of the host’s population) and the environment (e.g. sanitation, temperature, water quality, population density).

Because the onset of symptoms at a biological incident can sometimes be delayed, the area affected may be much greater due to the migration of infected individuals. This may need to be considered when determining cordon sizes.

Biological agents are commonly classified according to their taxonomy (e.g. fungi, bacteria, viruses). This classification is important because of its implications for detection, identification, prophylaxis and treatment.


Radiological materials are not recognisable by the senses, as they are colourless and odourless. Specialised equipment is required to determine the size of the affected hazard area and if the level of radioactivity presents an immediate or long-term health hazard. The onset of symptoms often requires days to weeks. Because of the delayed onset of symptoms in a radiological incident, the affected area may be much greater due to the movement of contaminated people.

Radiological dispersal devices (RDD) are designed to disperse radioactive material to cause destruction, contamination, and injury from the radiation produced by the material. An RDD can be almost any size, defined only by the amount of radioactive material and explosives.

  • A passive RDD is a system in which unshielded radioactive material is dispersed or placed manually at the target
  • An explosive RDD, often called a dirty bomb, is any system that uses the explosive force of detonation to disperse radioactive material
  • An atmospheric RDD is any system in which radioactive material is converted into a form that is easily transported by air currents

Use of an RDD could result in health, environmental, and economic effects as well as political and social effects. It will cause fear, injury, and possibly lead to levels of contamination requiring costly and time-consuming clean-up efforts.


An improvised nuclear device (IND) is intended to cause a yield-producing nuclear explosion. An IND could consist of diverted nuclear weapon components, a modified nuclear weapon, or indigenous-designed device. Unlike RDDs, that can be made with almost any radioactive material, INDs require fissile material (such as highly-enriched uranium or plutonium) to produce nuclear yield.