The kinds of chemical agents that might be useful to terrorists are blood agents, such as hydrogen cyanide or cyanogen chloride, which block the blood's oxygen-carrying capacity; choking agents, such as chlorine, phosgene, and chloropicrin, which cause plasma to enter the lungs from the bloodstream; and blistering agents, such as sulfur mustard and nitrogen mustard gases, which can linger for weeks and induce nausea and vomiting. Reasons why terrorists might use such devastating weapons are ease of implementation coupled with dramatic effects, the need to introduce new and dramatic elements of fear into terrorist tactics, and the availability of such weapons from states that support terrorism. Terrorists might acquire chemical agents for weapons from industrial sites, from World War II munitions, and from patron states. The most effective deterrent to the threat of chemoterrorism is to deny terrorists access to these weapons and the chemicals needed for their production. 18 notes