hemical warfare (CW) agents are poisonous, man-made chemicals that may take the form of gases, liquids, or powders. When absorbed through the lungs or the skin, these substances have incapacitating or lethal effects on humans or animals. Although many CW agents are liquids, the explosion of a bomb or the use of a sprayer system can transform a liquid agent into an aerosol, or superfine mist of microscopic droplets,that can be inhaled into the lungs.

CW agents vary greatly in their persistence and volatility, or tendency to evaporate:

• Nonpersistent agents pose mainly a threat to the lungs and tend to dissipate (fall below a lethal concentration when inhaled) within a few hours.
• Persistent agents pose mainly a skin contamination threat and may remain hazardous for as long as a month when deposited on soil, vegetation, or objects.

Most CW agents fall into four categories: blister, choking, blood, and nerve.

Burns caused by exposure
to mustard agent.

• Blister agents, such as sulfur  mustard and lewisite, are oily liquids that cause severe chemical burns of the skin, resulting in large, fluid-filled blisters, temporary or permanent blindness, and severe damage to lung tissue. These symptoms develop after a "latent period" lasting one to eight hours, during which time a person exposed to the agent would not experience any effects. Mustard can be absorbed by direct contact with the skin or eyes, or by inhalation of aerosol or vapor. Historical evidence from World War I and the Iran-Iraq War (1980-88) suggests that mustard can inflict large numbers of casualties, of which less than five percent are fatal. No antidotes (drugs that counteract the effects of poisons) or effective treatments are available.
• Choking agents, such as chlorine and phosgene, were used on a large scale during World War I. They cause severe damage to the bronchial tubes of the lungs, causing them to fill with fluid so that victims "drown" in their own secretions. Most choking agents dissipate rapidly in the open air. They could potentially cause mass casualties, however, if released by terrorists in an enclosed space such as a subway station or a sports arena. Some choking agents are commonly used industrial chemicals, requiring little investment in specialized weapons laboratories. Because of resistance from the U.S. chemical industry, the Department of Homeland Security has been reluctant to impose stringent regulations on the use and transport of these chemicals and the physical security of chemical plant sites.
• Blood agents, such as hydrogen cyanide and cyanogen chloride, interfere with cellular respiration and cause rapid death. Lighter than air, these gases are extremely volatile and dissipate rapidly, but they could have deadly effects in an enclosed space. Manuals detailing the manufacture of weapons designed to release hydrogen cyanide gas have been developed by both Al-Qa'ida and Jemaah Islamiah, the terrorist group responsible for the Bali nightclub bombings..
• Nerve agents, such as sarin and VX, are the most lethal chemical poisons known: they disrupt the functioning of the nervous system and kill within minutes. Sarin, the most volatile of the nerve agents, evaporates at about the same rate as water. In an enclosed space with poor ventilation, the evaporation of a few liters of sarin can produce a lethal concentration in the air. Outdoors, much larger quantities are required to compensate for the effects of wind and atmospheric turbulence. VX is a dense, oily liquid that acts mainly by penetrating the skin and can persist in the environment for several days or weeks depending on temperature. The lethal dose of VX for a grown man is about 10 milligrams, equivalent to a single drop.

Detailed information on these  chemical agents  can be found in the multimedia section.

For a chemical attack, terrorists would probably not use mustard gas, which causes symptoms after a delay of several hours and is usually not fatal. Because terrorists would seek to create the maximum possible impact in the shortest possible time, they would be more likely to acquire chemical nerve agents such as sarin, whose lethal effects occur more rapidly.

This material is produced independently for NTI by the Center for Nonproliferation Studies at the Monterey Institute of International Studies and does not necessarily reflect the opinions of and has not been independently verified by NTI or its directors, officers, employees, agents.
Copyright © 2004 by MIIS.