	Introduction

Experts believe that terrorist use of chemical agents is an event with low probability, but potentially high consequences. While terrorist groups may or may not have an increased interest in chemical agent acquisition and use, the domestic vulnerability of the United States to chemical attack remains an issue. The possibility that terrorist groups might obtain insecure chemical weapons led to increased scrutiny of declared Libyan chemical weapon stockpiles following the fall of the Qadhafi regime. Experts have expressed similar concerns regarding the security of Syrian chemical weapons, reportedly including stocks of nerve (sarin, VX) and blister (mustard gas) agents, and their potential use. For analysis of chemical weapons possession and use in Syria, see CRS Report R42848, Syria's Chemical Weapons: Issues for Congress , coordinated by [author name scrubbed]. Additionally, military and civilian chemical agent detection has developed with little coordination, so that civilian toxic industrial chemical kits and military chemical weapons detectors have varying sensitivities and detection capabilities. Treatments for chemical exposure vary on a chemical by chemical basis. This report describes the different types of chemical weapons and toxic industrial chemicals, their availability, treatment, and detection. Different chemical weapons cause different symptoms in and injuries to their victims. Military planners generally categorize chemical agents into at least four classes: nerve, blister, choking, and blood agents. This method organizes chemical agents by their biological effects. Nerve agents interfere with the nervous system, causing overstimulation of muscles. The combination of these two chemicals removes cyanide, the active compound in blood agents, from the body. Decontamination is especially important in those cases where victims have encountered liquid chemical agents, and may have significant amounts of chemical agent trapped in their garments. Detection of Chemical Agents

Chemical weapons detection has been predominantly an area of concern for military planners, although the manufacture of some of these agents for commercial use requires detection capabilities at manufacturing plants and by first responders trained to handle hazardous materials. Another is to identify the chemical agent used in an attack. Handheld detectors, such as the Chemical Agent Monitor (CAM), are able to detect some chemical agents, namely mustard agents and nerve agents. On the other hand, chemical agents might be effectively used as weapons of terror in situations where limited or enclosed space might decrease the required amounts of chemical. As a weapon of mass destruction used against civilians, the comparatively low lethality of choking agents complicates their use as a weapon of mass destruction, since very large volumes would be needed. The quick dispersal of blood agents, combined with the large amounts necessary to cause mass casualties, make such agents difficult to use on a mass scale.
The potential for terrorist use of chemical agents is a noted concern highlighted by the Tokyo sarin gas attacks of 1995. The events of September 11, 2001, increased congressional attention towards reducing the vulnerability of the United States to such unconventional attacks. The possibility that terrorist groups might obtain insecure chemical weapons led to increased scrutiny of declared Libyan chemical weapon stockpiles following the fall of the Qadhafi regime. Experts have expressed similar concerns regarding the security and use of Syrian chemical weapons, reportedly including stocks of nerve (sarin, VX) and blister (mustard gas) agents. For analysis of chemical weapons in Syria, see CRS Report R42848, Syria's Chemical Weapons: Issues for Congress, coordinated by [author name scrubbed].
Military planners generally organize chemical agents, such as chemical weapons and toxic industrial chemicals, into four groups: nerve agents (such as sarin and VX), blister agents (such as mustard gas), choking agents (such as chlorine and phosgene), and blood agents (such as hydrogen cyanide). While the relative military threat posed by the various chemical types has varied over time, terrorist use of these chemicals against civilian targets is viewed as a low probability, high consequence event.
Chemical weapons and toxic industrial chemicals cause a variety of symptoms in their victims. These symptoms depend on the chemical agent used, and a victim of chemical exposure may exhibit a combination of symptoms. Some chemical agents cause death by interfering with the nervous system. Some chemical agents inhibit breathing and lead to asphyxiation. Other chemical agents have caustic effects on contact. As a result, effective chemical attack treatment depends on identifying at least the type of chemical agent used. Additionally, chemical agents trapped on the body or clothes of victims may place first responders and medical professionals at risk.
Civilian protection from and detection of chemical agents is an area of federal concern. Whether terrorist groups are capable of using chemical agents as weapons of mass destruction is unclear. Some experts have asserted that the volumes of chemicals required to cause mass casualties makes that scenario unlikely. They claim that chemical terrorism is more likely to be small in scale. Other experts have suggested that there has been an increase in terrorist interest regarding chemical agents, and that this interest could lead to their use in terrorist attacks. Some experts assert that insecure stockpiles of military-grade chemical agents would lower the barrier to terrorist acquisition of chemical agents and thus increase the possibility that terrorists might use them. The change of regimes in Libya and Egypt and recent events in Syria have increased concern that such military-grade chemical agents might transition into terrorist hands and then be used to attack U.S. sites either domestically or abroad.