1. Detection

Fast detection is crucial as some nerve agents can kill within minutes, while the effects of mustard gas can remain unnoticed - and so unprotected against - for hours after exposure.

"In vapour you can wave it until you're blue in the face and it won't turn colour" Biochemical weapons specialist Dave Butler of Bruhn Newtech

British troops usually carry two types of chemical detector paper. Both work only with liquid chemicals and respond in less than a minute.

One-colour paper changes colour in contact with any harmful chemical.

Three-colour detector paper turns either red, yellow or green to indicate two types of nerve agent and one blister agent.

Agents in vapour form can be detected using a more complicated "residual vapour detector" which sucks air over paper or through tubes containing indicator chemicals.

Other devices are available which analyse particles to determine the presence and concentration of chemical agents, or the presence and type of biological agents.

One of these, the Chemical Agent Monitor (CAM), is widely used but is reported to have given some false readings when exposed to other substances such as engine exhausts.

A vehicles is sprayed to decontaminate it

2. Decontamination

The British military uses a clay-based substance known as "Fuller's Earth" for decontamination of chemical agents.

Supplied in a puffer bottles and on pads in sachets, it traps particles of the agent, stopping it from vaporising or permeating the skin.

It is applied to any areas exposed to the agent and then brushed off, although this must be done with care as the substance can irritate the eyes and, if inhaled, the lungs.

"Fuller's Earth has proved to be quite effective, but it hasn't been used in anger for some time" Biochemical weapons specialist Dave Butler of Bruhn Newtech

Eyes and wounds are flushed out with water and the area around them decontaminated.

Soap and water can also be used to remove many chemical agents, while solutions of sodium hypochloride – household bleach - can be used to decontaminate people and equipment from most biological agents.

3. Antidote

Soldiers carry antidote injection kits which can save their lives if they are exposed to a nerve agent.

"Combopens" contain the antidote atropine and two other drugs which counter symptoms such as sweating and sickness.

"If in doubt give the injection" Biochemical weapons specialist Dave Butler of Bruhn Newtech

An initial dose is administered as soon as a casualty shows signs of exposure such as a running nose, salivation, difficulty breathing and pupils shrinking to pin-points.

Two more doses may follow at 15 minute intervals, but atropine itself is poisonous and any more than three injections can risk killing the patient.