Industrial Chemicals as Weapons: Chlorine
Certain recent events in Iraq have elevated long-standing fears that terrorist groups may use poisonous chemicals, especially elemental chlorine, as toxic weapons against vulnerable populations. These concerns rest on a solid factual basis: many chemicals produced for industrial purposes are inherently dangerous due to their possession of one or more of the following properties: reactivity, flammability, explosiveness, toxicity, or carcinogenicity. In particular, the toxic industrial gases anhydrous ammonia, hydrogen fluoride, and elemental chlorine (often referred to as toxic inhalation hazards, or TIH) are of utmost concern from both safety and security standpoints. Any of these chemicals when released in the course of an accident or a deliberate attack can form a toxic gaseous plume that when carried by wind is capable of inflicting potentially catastrophic loss of life on the population in its path. The worst industrial accident in history is illustrative: 40 metric tons of methyl isocyanate was released from a Union Carbide pesticide plant in Bhopal, India, on December 3, 1984. The resulting plume killed at least 3,000 people downwind and injured more than 100,000. A sufficiently large release of elemental chlorine may be capable of exacting a comparable toll, particularly if it were to be discharged in a highly populated civilian area.
This issue brief describes the properties, hazards, and the legitimate applications of chlorine, as well as its use for weapons purposes during World War I and currently in Iraq. The vulnerability of America's chemical infrastructure to deliberate attack (including the facilities that produce, consume, and transport chlorine), as well as efforts currently underway to achieve infrastructure security, are also examined. The brief concludes with an evaluation of alternative approaches to mitigating the potential threat posed by a deliberate chlorine release.
Properties of Chlorine
Chlorine (Cl) is a highly reactive, pale green gas produced industrially by the electrolysis of readily available aqueous sodium chloride (table salt). Worldwide, the annual production of chlorine totals approximately 55 million metric tons. In 2006, the American chemical industry produced 12.2 million metric tons of chlorine, making it one of the ten most produced chemicals in the United States by weight. Chlorine and its derivative chemicals serve myriad functions in modern society. The most important use of chlorine itself is as a disinfectant; for example, chlorine is employed worldwide in drinking water treatment facilities. In addition, chlorine derivatives (materials containing chlorine atoms chemically bound to other elements) are used as bleaching agents, construction materials (especially polyvinyl chloride, or PVC), high purity silicon precursors (e.g. trichlorosilane) for use in computer chip manufacture, pharmaceutical compounds (including "blockbuster" drugs such as Singulair, Plavix, and Norvasc), and many other functional materials.
The high toxicity of chlorine gas tempers the many beneficial uses of the chemical. Chlorine gas is heavier than air, and therefore will disperse slowly into the atmosphere after release. Because chlorine is water soluble, exposure to the gas irritates the mucous membranes and eyes at concentrations (in air) of under 3 parts per million (ppm)., Moderate irritation of the upper respiratory tract occurs at 5-15 ppm, followed by chest pain, vomiting, and dyspnea at 30 ppm. Above 50 ppm, lung inflammation and pulmonary edema occurs. Chlorine is deadly at concentrations of several hundred ppm or higher. According to the National Institute for Occupational Safety and Health, a chlorine concentration of 10 ppm is considered to be immediately dangerous to life or health.
Military and Terrorist Use of Chlorine
In what many consider to be the dawn of modern chemical warfare, chlorine was first employed as a "choking agent" in the early days of World War I. On April 22, 1915, during the second battle of Ypres, the German military released approximately 168 metric tons of chlorine from 5,730 buried gas cylinders. The heavy green plume was carried by prevailing winds to the Allied lines, where French and French Algerian soldiers, not suspecting a chemical attack, were taken by surprise and quickly overwhelmed by the chlorine. The attack claimed the lives of at least 800 soldiers, and injured thousands more. While this incident underscores the potential lethality of chlorine, both sides soon realized that chlorine is not a militarily effective chemical weapon against a prepared adversary. In particular, chlorine possesses both a visible color and a strong odor, which alerts people of its presence and enables avoidance. Moreover, the effects of chlorine exposure may be completely or somewhat mitigated using simple countermeasures, such as wearing a gas mask or even covering the nasal passages with a wet cloth. Therefore, chlorine was quickly abandoned in favor of more fearsome chemical agents (e.g. phosgene and mustard gas). Despite its nefarious usage, its widespread manufacture and distribution for industrial and sanitary purposes has continued.
In Iraq, militias or terrorists have detonated bombs rigged to cylinders containing chlorine that originally were intended for water treatment and other industrial uses, with the intention of dispersing the gas over their targets (primarily Iraqi police and civilians). The US military believes that terrorist groups affiliated with Al Qaeda are primarily responsible for these types of attacks. According to the United Nations Monitoring, Inspection, and Verification Commission (UNMOVIC), at least 10 attacks involving chlorine have occurred in Iraq up to June 1, 2007, resulting in dozens of civilian deaths and an unknown number of injuries. An attack on June 3, 2007 targeted a United States military forward operating base and resulted in making 65 US service members ill from chlorine exposure. The perpetrators have used relatively small, easily transportable quantities of chlorine in the attacks, no more than several tons. Deaths have been attributed primarily to the effects of the explosives themselves, not the chlorine. It is reasonable to assume that the efficacy of these attacks will increase as terrorists modify their methods of chlorine dispersion based on past experience.
The attacks in Iraq utilizing chlorine have re-raised simmering questions in the United States: Is the country's chemical infrastructure, especially the sub-sector that makes and stores elemental chlorine, vulnerable to attacks by terrorist elements that would result in the large-scale release of TIH chemicals over population centers? Would facilities where chlorine is stored be attractive to those who seek to harm civilians?
Chlorine presents both disadvantages and some advantages to domestic terrorists. On the one hand, chlorine is not nearly as potent a toxin as other chemical weapons used in terrorist attacks, such as the fluoroorganophosphate nerve agent sarin released on the Tokyo subway on March 20, 1995 by the religious cult Aum Shinrikyo, killing 12. However, nerve agents require substantial finances, advanced equipment, appropriate chemical precursors, and personnel with specialized training in synthetic organic chemistry to prepare. Even then, nerve agent synthesis and dispersion is non-trivial. For example, Aum Shinrikyo used impure sarin coupled with a crude and relatively ineffective delivery system for the subway attack, despite mustering all the resources mentioned above. On the other hand, chlorine does not need to be chemically synthesized (given its abundance), and as a gas does not require active aerosolization for efficient dispersal. Most importantly, a large release of chlorine may inflict mass casualties on unprepared civilians. According to a 2004 report by the Homeland Security Council, a deliberate release of 60,000 gallons of liquefied chlorine from an industrial facility in a highly populated area may result in 17,500 civilian deaths, while the Department of Homeland Security (DHS) estimates that a "worst-case" chemical release would result in fewer than 10,000 deaths.
Chemical Facility Security
According to the Environmental Protection Agency (EPA), in the United States there are approximately 15,000 facilities, including about 2,000 water systems, which store more than the threshold quantities of hazardous chemicals necessary to trigger EPA regulation. A "worst-case" chemical release from any one of 123 such facilities could expose more than 1,000,000 people to toxic gases. In the aftermath of September 11th, the chemical industry has recognized its potential vulnerability and moved rapidly to enhance facility security. In 2002, the American Chemistry Council (ACC), a chemical industry association whose members control approximately 2,000 facilities, established the Responsible Care[®] Security Code, a mandatory private security initiative. The Security Code requires member facilities to complete vulnerability assessments, perform physical security enhancements, invite an independent, third party audit of these enhancements, conduct employee training and drills, and perform periodic security self-audits. These requirements apply to members of the Chlorine Institute, a trade association and Responsible Care[®] partner whose membership includes 98% of chlorine producers and 100% of chlorine packagers in the United States. According to the ACC, its companies have invested about $3 billion in security improvements since September 11th, and all member facilities have completed security upgrades and subsequent independent audits.
Although private security initiatives have garnered justifiable praise, they are also widely viewed as inadequate. Investigative journalists have easily penetrated dozens of chemical facilities nationwide, including many housing chlorine, over the past several years. For example, in 2003, a reporter was able to approach storage tanks holding approximately 1,000 tons of chlorine gas at the Sony Technology Center in Westmoreland County, Pennsylvania. In 2005, reporters from the New York Times were able to approach and loiter near chlorine storage tanks on an industrial site in densely populated Northern New Jersey, only miles from New York City. In addition to the gaps in physical security, facility employees and emergency response personnel are often inadequately prepared to handle a deliberate chemical release. Clearly, comprehensive chemical security requires, in addition to private initiatives, the participation of the public sector in order to safeguard the public most effectively.
At the federal level of government, DHS is responsible for chemical sector security. Until very recently, however, DHS had not received a Congressional mandate to implement and enforce industry-wide security measures. The situation changed in October 2006, when President Bush signed the Homeland Security Appropriations Act, H.R. 5441, which gave DHS interim (3 year) authority to regulate security at chemical facilities. On April 2, 2007, DHS issued the interim final rule regulating chemical facility security, known as the Chemical Facility Anti-Terrorism Standards. The rule requires facilities possessing a threshold quantity of one or more of 342 chemicals of interest, including chlorine, to file a report known as a "top screen" with DHS. For chlorine, this threshold level currently is 1,875 lbs or more. Using this data, DHS will perform a risk assessment and categorize "at risk" facilities according to a tiered system, with Tier 1 facilities considered the highest risk and Tier 4 facilities the lowest. A number of factors are considered in the assessment, including the type and amount of chemical(s) stored as well as the layout and location of the facility. DHS currently estimates that 5,000-8,000 facilities will be assigned a ranking in the tier system, with fewer than 1,000 assigned to Tiers 1 & 2. The facilities assigned to a risk tier will be required to submit vulnerability assessments and site security plans, subject to DHS verification, with failure to comply resulting in daily fines and/or shutdown of the facility in violation. Chemical manufacturers have embraced the new rule's risk-based approach, although others, including environmental groups, have highlighted several apparent weaknesses., For example, the rule contains no timetable for compliance, no whistleblower protections, and may preempt more stringent state and local regulations. Furthermore, the rule is not applicable to water and waste treatment facilities that utilize chlorine for disinfection, and does not require these or other chemical facilities to consider replacing chlorine with safer alternatives (see below). Recent thefts of chlorine cylinders from a California water treatment facility have served to underscore the final point.
Security of Chlorine Rail Shipments
Industrial chemicals, like all commodities, must be transported from production facilities to various consumers. For TIH chemicals such as chlorine, freight railroad offers the most viable transportation option for large-scale shipment. Of the approximately 12 million tons of chlorine produced annually in the United States, almost 3 million tons are shipped by rail, usually in 90 ton pressurized tank cars.6 Rail shipment of hazardous materials (hazmat) is very reliable; 99.997% of the ca. 1.8 million annual hazmat shipments in the United States arrive without incident. Although rail accidents involving chlorine are exceedingly rare, when chlorine tank cars are breached, the consequences often are fatal. On June 28, 2004, near San Antonio, Texas, a head-on collision of two trains resulted in a chlorine tank car breach. Two people died of chlorine inhalation, and 50 more were hospitalized for exposure. On January 6, 2005, in Graniteville, South Carolina, another head-on collision resulted in the derailment of three cars containing chlorine. The resultant chlorine plume killed 8 people, injured 240 more, and led to the evacuation of 5400 people from the spill area.
The railroad infrastructure (including trains, tracks, stations, etc.) is vast and relatively accessible, a necessity for rapid and inexpensive exchange of people and goods. The US rail system is comprised of approximately 171,000 miles of track and covers an area of 3,200 square miles. The open nature of rail systems renders them particularly prone to attacks by terrorists and other groups, as no feasible security plan can possibly protect the entire infrastructure simultaneously and at all times. The RAND Corporation estimates that 181 terrorist attacks against railroads worldwide occurred in the period between 1998 and 2003. Most attacks were directed against transit systems, as exemplified by the more recent bombings of the Madrid, London, and Mumbai commuter rail systems. The US freight rail system is as vulnerable as the European rail systems, and many lines pass through densely populated, high threat urban areas (HTUA's), most notably in the Northeastern corridor. Given the large quantities of chlorine shipped by rail, as well as the potentially catastrophic consequences of a large chlorine release, chlorine-containing tanker cars may represent an attractive target for terrorists.
Freight rail security, especially hazmat and TIH chemical transport, has attracted concern since September 11th and, even more so, after the Graniteville, S.C. chlorine accident in 2005. The freight rail industry, through programs initiated by the Association of American Railroads (AAR), has taken a more proactive stance on security issues since September 11th. The Terrorism Risk Analysis and Security Management Plan designed by AAR forms the basis for post-9/11 freight rail security. The plan includes over 50 security enhancements, addressing a number of general issues such as physical security, risk assessment, communications, and enhanced employee security training. The railroads also, through the Transportation Community Awareness and Emergency Response Program (TRANSCAER) and the ACC's Chemical Transportation Emergency Center (Chemtrec), train and inform emergency responders to help them deal with hazmat emergencies. With respect to chlorine and other TIH chemicals, the Union Pacific railroad recently signed a memorandum of understanding with Dow Chemical to upgrade the TIH railcar fleet and procedures for TIH transport. The memorandum calls for the installation of global positioning satellite units on all TIH tank cars, the design of a new, more robust tank car for TIH chemicals, as well as a reduction in the time that TIH tank cars lay idle in urban areas.
There has existed considerable variation in the approaches of local and federal governments to the threat of chlorine rail shipments. Many local governments, particularly HTUA's, are examining the possibility of banning chlorine rail shipments in proximity to highly populated areas. Citing the threat of chlorine, the Washington, D.C. city council voted on February 1, 2005 to ban all hazmat shipments within 2.2 miles of the Capitol, thus forcing rail companies to reroute shipments of chlorine around the city center. CSX Transportation challenged the law in court and received an injunction, which remains in effect as of this writing. The railroad industry argues that: (1) rerouting increases the risk of accidental of deliberate hazmat exposure, due to increased mileage, (2) rerouting simply shifts exposure risk to other populations, and (3) regulatory variations at each locality would impose significant cost and time burdens on the industry. The federal government, represented by the Department of Justice, supported the railroad industry position in this case, arguing that the regulation of interstate commerce is its Constitutional responsibility. The federal agency responsible for freight rail security, the Transportation Security Administration (TSA), has not yet sought to force railroads to reroute chlorine and other TIH chemicals around HTUA's, as it currently is not currently required to do so by law. Rather, TSA and the Department of Transportation (DOT) have issued voluntary security action items to guide private railroad efforts to secure chlorine and other TIH railcars. TSA is also engaged in formulating rules and pilot programs in cooperation with the railroad industry, aimed at reducing the potential for attack on chlorine tankers. In conjunction with other federal, state, and local government agencies, TSA is currently conducting comprehensive reviews of rail corridor security, with a focus on HTUA rail corridors. However, many have perceived federal funding for surface transportation security, including rail security, to be inadequate. The American Public Transportation Association noted in early 2007 that the federal government has allocated $549 million for rail transit security (including both passenger and freight rail security) since September 11, 2001, in contrast to over $24 billion for aviation security.
Although prior security efforts have no doubt made a positive impact on rail security, freight railroads, and the chlorine transported on them, remain poorly protected. Publicly disclosed reports and media investigations over the past five years have identified gaping vulnerabilities in freight rail security. For example, a 2006 report published by the Citizens for Rail Safety (a public interest group) concluded that rail facilities are not sufficiently secure: cars containing hazmat, including TIH such as chlorine, often sit idle and unprotected, rail workers are poorly trained with respect to security, and emergency responders and citizens are ill-prepared for a hazmat emergency. In early 2007, a reporter from the Pittsburgh Tribune-Review published an article describing how he gained access to a number of hazmat-containing (including chlorine) railcars throughout the country. The reporter was not stopped by employees or rail police, and found hazmat-containing railcars unprotected on rails controlled by 12 railroads. These reports followed the publication in 2005 of two Teamsters Rail Conference surveys of rail workers, which reported significant physical security lapses and a notable lack of security training for workers.,
Partially in response to the problems cited above, the US Congress passed new homeland security legislation (H.R. 1: Improving America's Security Act of 2007) on July 27, 2007. President Bush has indicated that he will sign the bill into law in August 2007. The legislation will provide significant enhancements in TIH rail transportation security. Provisions in the legislation call for significantly enhanced funding for freight rail safety and security, including hazmat transportation security, infrastructure improvement, and research and development aimed at secure rail car technologies. Specifically, language in the bill encourages the adoption of wireless communications to track the positions of TIH railcars and monitor their status in real-time. Furthermore, DHS and the DOT must require rail carriers shipping TIH chemicals to develop and submit risk mitigation plans to be enacted when the Homeland Security Advisory System threat levels are high or severe. These plans are to include rerouting of TIH chemical shipments away from high consequence targets, including densely populated areas, landmarks, and other important national resources, as designated by DHS. The legislation also calls for the establishment of a "rail worker security training program" and introduces federal whistleblower protections to protect rail employees who report rail security lapses and violations. This legislation promises to mitigate some of the problems currently facing rail security, but the ongoing evolution of public and private measures must continue.
Inherently Safer Technologies
An alternate approach to mitigating the risk posed by chlorine may be to reduce levels of chlorine consumption by replacing chlorine with inherently safer technologies (ISTs). As noted in a 2006 study by the National Academy of Sciences, "The most desirable solution to preventing chemical releases is to reduce or eliminate the hazard where possible, not to control it." The adoption of ISTs to replace TIH chemicals is strongly supported by a number of interested parties, including environmental groups and the railroad industry. Depending on the industrial application, chlorine may in fact be readily replaced with cost-effective alternatives. According to a 2006 study by the Center for American Progress, 207 waste treatment plants and drinking water facilities have replaced chlorine gas with safer disinfectants such as sodium hypochlorite (chlorine bleach) and ultraviolet light since 1999. Adoption of ISTs not only eliminates the TIH risk of chlorine at the chemical facility, but also reduces the risk of chlorine release in transit. For example, since 1999, 25 water facilities in the United States that previously received chlorine shipments by freight rail have switched to ISTs, and six others plan to do so. Despite this progress, over 2,000 water treatment facilities continue to use chlorine gas, with 37 continuing to receive freight rail shipments. These facilities should be encouraged to adopt ISTs, especially in light of the current situation in Iraq and the thefts of chlorine in California in 2007 (see above).
However, chlorine cannot be easily replaced with IST in totality due to its chemical versatility. Notably, water treatment accounts for only about 5% of chlorine consumption. Chlorine remains a central ingredient in the manufacture of other chemicals and materials, most notably plastics, and a cost-effective replacement may not be apparent in many cases. In addition, a main byproduct of chlorine manufacture, sodium hydroxide (caustic soda), is itself an important industrial chemical (the chlorine production process is known as the Chlor-Alkali process for this reason). Eight million metric tons of sodium hydroxide was produced in the United States in 2006. Thus, an analysis of chlorine replacement by IST must explore the economic impact of lowered chlorine and sodium hydroxide production. The replacement of chlorine by IST is a worthy pursuit, but it will be a long-term endeavor.
It is indisputable that should a large chlorine release such as the Graniteville accident take place in the future, it would pose a substantial danger to the public. Moreover, recent studies demonstrate convincingly that chlorine-containing facilities, whether they are chemical plants or railroad infrastructure, may be infiltrated with ease and regularity by trespassers. It may be argued that there exist more readily accessible targets for terrorist attack, including even smaller quantities of chlorine transported by truck. However, given the toll that a large-scale chlorine release could inflict on a population, facilities and railcars containing multi-ton quantities of chlorine warrant increased attention. The DHS and TSA have both worked well with industry to create voluntary chemical security guidelines, yet to date neither agency has imposed stringent regulations governing chlorine security. The establishment of a coherent national policy (which adequately addresses the concerns of individual localities) regarding the issue of TIH railcar rerouting around HTUA's is particularly vital. The recently approved federal legislation addresses rerouting of TIH shipments in times of elevated threat, but a permanent, satisfactory solution for a non-threat environment will also be required. Further, the new Chemical Facility Anti-Terrorism Standards issued by DHS do not require the chemical industry to examine adopting ISTs to replace chlorine and other TIH chemicals. While chlorine replacement with an IST should not necessarily be mandatory, incentives should be considered to persuade the chemical industry to adopt safer practices. The federal government should also consider an increase in funding for research aimed at the development of ISTs. If a viable, cost effective IST exists for a given chemical process, it is in the best interest of the chemical industry to adopt it of their own accord in order to safeguard employees, facilities, and the surrounding communities. Increased funding for fundamental research and development of ISTs will hasten this progression. Finally, perhaps the best countermeasure against a large attack using chlorine or other TIH chemicals is public awareness and education. Militarily, it has been known for 80 years that the deleterious effects of chlorine may be attenuated using simple methods. Both private industry and governments at all levels, especially those with chlorine facilities in their jurisdictions, should enhance education and outreach efforts to the public regarding appropriate courses of action (e.g. shelter in place protocols) in the case of a chlorine release incident.
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 It is important to note that while elemental chlorine is toxic, it does not necessarily follow that chlorine derivatives pose health hazards.
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This material is produced independently for NTI by the James Martin 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, or agents.
Benjamin Brodsky analyzes the potential impact of terrorist groups using poisonous chemicals, especially elemental chlorine, as toxic weapons against vulnerable populations.