On March 20, 1995, terrorism changed. For the first time, terrorists used a chemical agent against a civilian population. The nerve agent sarin (GB) was released in the Tokyo subway system by the Aum Shinrikyo cult causing over 5,500 people to seek medical attention. Whether or not one believes that this cult will strike again, the point has been made: Chemical agents are now terrorist weapons.

Most chemical warfare agents are liquids. However, chemical agents in liquid form must be dispersed in order to be maximally effective. This can be done in three general ways:

• Aerosolizing it with an aerial sprayer (such as done
  with pesticides)
• Aerosolizing it in an explosion
• Allowing it to evaporate and dispersing the vapor

When used outside, a vapor will not remain in place because even a light wind will dilute and carry it away. However, when dispersed inside a structure where no wind is present, the vapor will remain and the concentration will build, at least until the ventilation system removes it—or possibly disperses it even further.

There are five principal classes of chemical agents:

• Nerve agents
• Vesicants (blistering agents)
• Cyanide
• Pulmonary agents
• Riot control agents

Responding to a Chemical Attack

When responding to a chemical accident, one of the first things responders should do is establish a clean treatment area at least 300 yards upwind of the contaminated area. The clean treatment area is referred to as the “cold zone,” while the contaminated area is called the “hot zone.”

Separating the hot and cold zones is the “warm zone” where decontamination occurs. The warm zone should be several hundred yards upwind from the contamination, and at least 50 yards from the cold zone. All responders must leave the hot zone via specially designated pathways into the warm zone where they will be decontaminated. (See Chapter 6, Decontamination)

If there are multiple casualties who have severe, lifethreatening
injuries, two medical care responders should work in the contaminated area, one to triage and one to administer emergency care, including the possible intramuscular administration of nerve agent antidotes, such as atropine. These responders must be in full protective equipment, including mask, gloves, suit, etc.