The potential harm to public health and the environment from a large release of hazardous chemicals has long concerned the U.S. Congress. The sudden, accidental release in December 1984 of methyl isocyanate in an industrial incident at the Union Carbide plant in Bhopal, India, and the attendant loss of thousands of lives and widespread injuries spurred legislative proposals to reduce the risk of chemical accidents in the United States. For example, federal environmental laws were enacted in 1986 and 1990 to mitigate and reduce the risk of accidental releases of hazardous chemicals from manufacturing facilities, processing plants, and storage tanks. (These laws are discussed below.) The Hazardous Materials Transportation Act of 1975 was passed to protect the public and environment in the event of an accident during transportation of chemicals. Other federal laws coordinate preparedness planning and response to significant chemical spills (e.g., the Comprehensive Environmental Response, Compensation, and Liability Act). The threat of terrorism manifested on September 11, 2001, prompted renewed congressional attention to the potential risks to public health and the environment posed by facilities handling large quantities of hazardous chemicals. Congress addressed chemical facility security when it enacted legislation establishing the Department of Homeland Security (DHS; P.L. 107-296 ). The law requires analysis of vulnerabilities and suggestions for security enhancements for "critical infrastructure." The Public Health Security and Bioterrorism Preparedness and Response Act of 2002 ( P.L. 107-188 ) and the Maritime Transportation Security Act (MTSA, P.L. 107-295 ) require vulnerability assessments, security plans, and incident response plans for some chemical facilities which supply drinking water or are located in ports. Many other chemical facilities remain unregulated with respect to terrorism. Thus, the 109 th Congress continued to discuss the risks and consequences of potential terrorist attacks on chemical facilities and possible actions the federal government might take to prevent or reduce them. This report provides background information and summarizes issues relevant to existing and proposed requirements aimed at reducing risks to the general public of exposure to hazardous chemicals as a result of terrorist acts at U.S. facilities where chemicals are produced, processed, stored, or used. It considers the likelihood and severity of harm that might result from terrorist attacks on chemical facilities, as well as from illicit use of such facilities to gain access to hazardous chemicals (or to precursor chemicals that can be used to produce hazardous chemicals). Federal requirements for contingency planning and responding to chemical emergencies after they occur are not the focus of this report. In addition, it does not consider hazardous materials transport (or storage incidental to transport). The report first describes the range of terrorist acts that might threaten chemical facilities and summarizes publicly available information relevant to risks: recent trends in terrorist activity, including chemical use by terrorists; expert estimates of the harm that might be inflicted through chemical terrorism; and assessments of the vulnerability of chemical facilities. The next section of the report discusses existing federal mandates and incentives for reducing risks of accidental releases from chemical facilities. The remainder of the report summarizes recent Administration and private sector initiatives to improve chemical site security; analyzes policy options and key issues; and describes legislation in the 109 th Congress. Potential terrorist acts against chemical facilities might be classified roughly into two categories: direct attacks on facilities or chemicals on site, or efforts to use business contacts, facilities, and materials (e.g., letterhead, telephones, computers, etc.) to gain access to potentially harmful materials. In either case, terrorists may be employees (saboteurs) or outsiders, acting alone or in collaboration with others. In the case of a direct attack, traditional or nontraditional weapons may be employed, including explosives, incendiary devices, firearms, airplanes, or computer programs. In obtaining chemicals, a terrorist's intent may be to use them as weapons or to make weapons, including explosives, incendiaries, poisons, and caustics. Access to chemicals might be gained by physically entering a facility and stealing supplies, or by using legitimate or fraudulent credentials (e.g., company stationary, order forms, computers, telephones or other resources) to order, receive, or distribute chemicals. According to February 2003 testimony by the Director of the Federal Bureau of Investigation (FBI) to the U.S. Senate, there were 353 known or suspected acts of terrorism (including terrorist acts by Americans) perpetrated within the United States between 1980 and 2001. Only a few incidents involved chemical facilities. Attacks during the 1990s claimed 182 lives and injured over 1,932 individuals. In comparison, during the 1980s, although there were many more terrorist or suspected terrorist incidents, only 23 people were killed and 105 were injured. Thus, although the total number of terrorist acts in the United States declined toward the end of the 20 th century, the casualties due to terrorism increased. The same trends have been evident internationally, although there is considerable variation from year to year. The year 2003 had 208 international terrorist attacks on noncombatants, a few more than 2002, but 42% fewer than in 2001. There were 725 persons killed in 2002 and 625 persons (35 U.S. citizens) in 2003. In terms of U.S. casualties due to international terrorism, 2001 is the most costly year on record, with 2,689 people killed. As noted by the FBI Executive Assistant Director for Counterterrorism and Counterintelligence, the attack of September 11, 2001, "marked a dramatic escalation in a trend toward more destructive terrorist attacks which began in the 1980s." The September 11 attack also reflected a trend toward more indiscriminate targeting among international terrorists. The vast majority of the ... victims of the attack were civilians. In addition, the attack represented the first known case of suicide attacks carried out by international terrorists in the United States. The September 11 attack also marked the first successful act of international terrorism in the United States since the vehicle bombing of the World Trade Center in February 1993. Other potentially important trends identified by intelligence agencies include: an increase in activity by loosely affiliated extremists, both domestically and internationally; and the propensity of such groups to focus on producing mass casualties. With respect to chemical and biological terrorism, hoaxes and unsuccessful attempts by terrorists to use chemicals increased throughout the 1990s. Loosely affiliated terrorist groups, in particular, have demonstrated a growing interest in chemical weapons and other weapons of mass destruction, but explosives are still the most frequently employed weapons. During the 1990s, both international and domestic terrorists attempted to use explosives to release chemicals from manufacturing and storage facilities. Most of these attempts were abroad in war zones such as Croatia, including attacks on a plant producing fertilizer, carbon black, and light fraction petroleum products; other plants producing pesticides; and a pharmaceutical factory using ammonia, chlorine, and other hazardous chemicals. All of these facilities were close to population centers. In the United States, there were at least two instances during the late 1990s when criminals attempted to cause releases of chemicals from facilities. One involved a large propane storage facility, and the other a gas refinery. Evidence that U.S. chemical facilities may be used by terrorists to gain access to chemicals also exists. For example, one of the 1993 World Trade Center bombers, Nidal Ayyad, became a naturalized U.S. citizen, graduated from Rutgers University, and worked as a chemical engineer at Allied Signal, from which he used company stationery to order chemical ingredients to make the bomb. According to a U.S. Prosecutor in the case against the bombers, though "some suppliers balked when the order came from outside official channels, when the delivery address was a storage park, or when [a co-conspirator] tried to pay for the chemicals in cash," others did not. Moreover, testimony at the trial of the bombers indicated that they had successfully stolen cyanide from a chemical facility and were training to introduce it into the ventilation systems of office buildings. More recently, chemical trade publications reportedly were found in al Qaeda hideaways. The validity of any risk assessment depends on how much is known about the hazard, risks (probabilities), adverse effects, events and conditions that lead to or modify adverse effects or risks, and populations or environments that influence or experience adverse effects. The most accurate, and therefore the most useful, risk assessments generally are for familiar, frequently occurring hazards and events with impacts that are experienced with some regularity, such as severe storms or floods. In contrast, the risk of terrorist activity is unfamiliar (at least in the United States), rarely experienced, and likely to vary significantly over time, depending on rather unpredictable social and political phenomena. The risk of terrorism targeting chemical facilities is particularly difficult to assess for at least three reasons: There are few prior examples of terrorists targeting chemical facilities; Numerous factors theoretically may increase or decrease risks; and Interactions among factors influencing risks are dynamic and changing. In part, these difficulties stem from the nature of terrorism and the terrorists' deliberate efforts to do what is least expectedâthat is, to defy prediction. For these reasons, most experts have not tried to quantify risks; existing analyses of chemical terrorism risks in the open literature are speculative and qualitative. Until the mid to late 1990s, reports focused on the acquisition and use of chemical weapons, such as sarin or mustard gas. One of the most comprehensive of these reports was a 1995 review of the open literature on terrorism that was prepared for the Canadian Security Intelligence Service. According to this review of the literature, "[t]hose authors who have speculated about the future terrorist use of chemical agents in particular have generally rated its likelihood as quite high." According to some, the risk also appears to be increasing. Many experts today believe that factors that might have inhibited proliferation and use of chemicals as weapons in the past are eroding. For example, some experts hypothesized several years ago that the combination of chemical and strategic skills necessary to create and deploy chemical weapons would prevent the lone terrorist from using them.