Emergency services' response to bomb attack
As a terror attack is being simulated in London to test the responses of the emergency services, BBC News Online looks at what might happen in the immediate aftermath of a chemical biological or radiological attack.
An incident occurs and police attempt to establish if it is a CBRN (chemical, biological, radiological or nuclear). Once it is clear what has happened, they isolate an area around the explosion while checking for possible further devices. Anyone injured is taken to hospital.
The fire brigade and police define three clear zones at the scene: hot, warm and cold. The hot zone - managed by the fire brigade - is the most contaminated, while mass decontamination of the public takes place in the warm zone. The cold zone is used for investigation, command and control vehicles, and loading ambulances. An inner cordon separates the warm and cold zones, while the entire area is sealed off by an outer cordon.
People within the hot zone are kept there until they are decontaminated. The fire and ambulance services set up decontamination shower units in the warm zone. Members of the public are taken through and their clothing and personal effects removed, tagged and kept as evidence.
While this is happening, the fire brigade's hazardous material team, liaising with the Environment Agency, takes samples and readings from the scene. The size of the zones are varied depending on the information gleaned from these investigations. Wind direction is also taken into account.
Once members of the public have been decontaminated, they are taken to local hospitals by ambulance. The relevant NHS trust is notified by the emergency services so decontamination units can be set up at the receiving hospitals for further treatment.
The police consider evacuation procedures for people living and working in the vicinity. Initially, people are likely to be advised to stay indoors with windows and doors closed.
Sources: International Emergency Technical Rescue Institute (iETRI) and Home Office guidelines.