By Frank L. Fire
Chlorine is classified as a choking agent (or pulmonary agent). This class of chemical warfare agents (CWAs) incapacitates enemy combatants by attacking the respiratory system, causing the victims to cough violently, choke, and therefore become incapacitated. The nasal passages, bronchi, mucous membrane surfaces, and the lungs are all primary targets. Pulmonary agents in high concentrations or long exposures will cause pulmonary edema, suffocation, and eventually death. For soldiers, wearing gas masks to protect themselves from chlorine (or any other gaseous warfare agent) would be so confining that they would add to the soldiers’ discomfort and limit their efficiency on the battleground. In addition, chlorine’s corrosiveness will adversely affect skin that comes in contact with it.
Choking agents were the first CWAs used successfully in combat. Even before the science of chemistry evolved, armies used fire on the battlefields whenever wind conditions were right so that the smoke would blind the adversaries and cause them to choke and become disoriented. Unbeknown to the attackers, this tactic made use of acrolein, a compound found in the combustion products of wood and wood materials, which to this day causes choking and coughing and sometimes incapacitates firefighters not donning respiratory protection or campers sitting around a campfire when there is a shift in the wind.
Choking agents were also the first CWAs used successfully in modern warfare. In 1915, during World War I, the Germans took advantage of chlorine’s relatively high vapor density and emptied containers of it from high ground, allowing the gas to flow downhill and into trenches. Anyone without proper respiratory protection was afflicted with violent coughing, restriction of the airways, and even death. The British retaliated, and chemical warfare was born.
Today, with few exceptions, CWAs are not used on the battlefield. Instead, terrorists use them to spread chaos, confusion, and death among their enemies. To date, the weapons of choice have been bombs, ranging from artillery shells and mortar shells to improvised explosive devices (IEDs) and suicide bombs. These last two types of bombs are set up to explode on roads or places crowded with people or are strapped to the chests of zealots who try to place themselves where their self-inflicted deaths by explosion will do the most harm, cause the most disruption, and kill the most people. The terrorists have finally begun to put together their explosives and CWAs by using car bombs to explode canisters of choking agents, mainly chlorine.
MOLECULAR STRUCTURE OF CHLORINE
Chlorine was first discovered when it was isolated as a gas in 1774, but it was not until 1810 that it was determined to be an element. The chemical symbol for chlorine is Cl; the molecular formula is Cl2. The difference is that the element chlorine, represented by the symbol Cl (which stands for one atom of chlorine), is too active chemically to exist in nature as free atoms and must combine with other atoms to form compounds. Sodium chloride (common table salt) is one of the most familiar compounds containing chlorine. Chlorine in its gaseous form is really Cl2, the compound in its molecular form.
As an element, chlorine is a member of the family of elements known as the halogens and can be found on the Periodic Table of the Elements as Group VIIA. This is the second-from-the-right long vertical column headed by the element fluorine (chemical symbol F) and above bromine (Br), iodine (I), and astatine (At).
Chlorine is plentiful in seawater, where it exists in compounds such as sodium chloride, potassium chloride, magnesium chloride, and the chlorides of other metals. It is produced by the electrolysis of concentrated solutions of sodium chloride in water or the electrolysis of molten sodium chloride. Electrolysis is defined as the breakdown of a chemical compound by passing electricity through it.
As a compound (the state in which chlorine exists as a gas, Cl2), it is a yellowish-greenish gas with a distinctive, sharp, pungent odor and an acrid taste. It is a powerful oxidizing agent (it will support combustion very efficiently); a reactive toxic; and a corrosive, irritating, noncombustible, dense gas.
It ranks annually in or near the 10 highest volume chemicals produced in the United States. It is used primarily in the manufacture of bleaches and oxidizing agents, paper, and cloth; for water purification; in food processing; and in the manufacture or synthesis of organic chlorides, acids, refrigerants, insecticides, herbicides, and fungicides. Another major use is in the manufacture of polyvinyl chloride (PVC) and other plastics, which are made from the polymerization of monomers that contain chlorine. This means that chlorine is available almost everywhere in the United Statesin the chemical industry, metals industry, pulp and paper industry, electronics industry, and the environmental protection industry.
Chlorine may be shipped as a gas under pressure or as a liquefied gas. It is available in 100- and 150-pound cylinders, one-ton (2,000-pound) containers, 15- to 20-ton tank trucks, and 90-ton rail tank cars.
PHYSICAL AND CHEMICAL PROPERTIES
Molecular chlorine (chlorine gas) is a toxic, corrosive, oxidizing, noncombustible, greenish yellow gas (many times shipped as a liquid) with a pungent, suffocating odor. It has a specific gravity of 1.47 (liquid), a molecular weight of 70.9, and a vapor density of 2.44. It boils at −29.3°F, freezes at −149.8°F, and is soluble in water.
As noted, its molecular formula is Cl2, and its Chemical Abstract Service (CAS) registry number is 7782-50-5. Its United Nations/North American (UN/NA) designation is 1017; its Standard Transportation Commodity Code (STCC) number is 4904120; its National Fire Protection Association 704 hazard rating is 3-0-0-OXY; its Chemical Hazard Response Information System (CHRIS) designation is CLX; its U.S. Department of Transportation (DOT) classification is nonflammable gas, poison gas 2.3, corrosive; and its International Maritime Organization (IMO) classification is Poison Gas, 2.3. Its Registry of Toxic Effects of Chemical Substances (RTECS) designation is FO2100000. It may also be called molecular chlorine, bertholite, or dichlorine. It is a recognized CWA with the military designation of CL.
Chlorine vapors are 2.44 times heavier than airotherwise known as its vapor density. The vapor density of any gas or vapor can be calculated by dividing the molecular weight of the gas, or vapor, by 29, which is the average vapor density of air. Chlorine is a diatomic molecule, and its molecular weight is 70.9, which, when divided by 29, yields 2.44.
Chlorine is a toxic material that is useful as a pulmonary agent because of its effects on unprotected victims. Terrorists use it to spread panic in addition to killing as many people as possible. In certain nonlethal concentrations, chlorine will totally disable its victims, causing violent coughing and choking spasms and probable damage to the respiratory system.
HOW IT IS DELIVERED
Historically, chlorine was delivered on the battlefield simply by securing the high ground above the enemy and releasing the gas from its container, allowing it to flow downhill to the enemy personnel positions, where it was expected to settle around the troops. In some cases, liquefied chlorine could be sprayed in a straight stream downward toward the enemy. The success of this tactic, of course, depends on the wind (or rather the absence of it), the topography of the battlefield, and the placement of the enemy troops. The users of the chlorine also had to be protected, in case of a surprise breeze that blew the gas back on them as it was released or after it had begun its downward movement toward the enemy.
All of these variables made the use of a highly toxic warfare agent such as chlorine very unpredictable in its effectiveness and in the potential danger for the aggressors themselves. This reason and the ease with which the enemy could retaliate with attacks of chlorine convinced the combatants in World War I that it was too much trouble to use chlorine as a weapon.
Today, terrorists have readopted chlorine as a warfare agent. The nature of chlorine hasn’t changed. It is still a highly dangerous pulmonary agent, toxic, and highly effective under the proper circumstances. What has changed is that it is no longer necessary to protect the attackers against the toxic effects of the gas. The delivery method has changed. Now, the terrorist drives a vehicle into a crowded marketplace, military encampment, police barracks, or some other target area. The vehicle is loaded with a bomb that is surrounded by containers of chlorine. The bomb is detonated, killing military personnel or civilians with its concussive effect or shrapnel and shattering the chlorine containers. The chlorine then expands outward, perhaps injuring or killing people who survived the bomb’s blast. This, of course, can be done remotely.
The suicide bombing scenario aside, chlorine can still be released using the conventional method in a crowded venue selected for any of a number of strategic reasons. The attack doesn’t necessarily have to kill large numbers of people or do tremendous damage. It can be symbolic, showing authorities that we are vulnerable to their terrorist strategies. In the meantime, if large numbers of people are killed or injured, if great damage is inflicted, or if lasting panic is generated, it is just so much more icing on the terrorist’s cake.
This system of delivery may not be as dangerous as simply releasing the gas from its container in crowds. Since chlorine is a powerful oxidizing agent, during its release from containers in an explosion (and its subsequent high temperature because of the explosion), it may be consumed to some degree by working with the oxygen in the air to speed the reaction of the explosion and help support the fires following that explosion. This would intensify the fires and increase the consumption of chlorine by raising the surrounding temperatures. This could be a self-accelerating depletion of chlorine that would cause more damage by fire.
The force of the explosion may also help to disperse the chlorine to levels below the toxic concentration. This could still cause choking and incapacitation to some degree, but probably less than in a simple release. The explosion will kill some people and injure others, but it also would cause exposed people to flee to safety, thus getting out of the chlorine-contaminated atmosphere.
Liquefied chlorine can also be spread by a small hand-operated sprayer like one a homeowner might use to spray a garden or lawn. Of course, any person seeking to protect himself while spraying liquid chlorine would have to be totally covered with an impervious material and wear SCBA. This would make a terrorist quite conspicuous or cleverly disguised as a municipal employee spraying for mosquitoes. However, a terrorist is not necessarily interested in self-protection and might just be a little careful to spray downwind as long as he could do it before becoming affected by the gas.
It could also be sprayed by automatic equipment from the back of a pickup truck or a larger tank truck like that used by lawn service companies. A crop-dusting airplane could be used to spread a larger amount of the liquid chlorine over a larger area, but this might be impractical. The liquid chlorine could also be left somewhere in an open container to boil away. It will vaporize over time, causing severe harm to anyone who comes in contact with the gas. There are many ways people willing to sacrifice their lives can steal chlorine from many sources and use dispersal methods that appear “normal” to Americans in their everyday lives.
The fact that chlorine may be the most widely used chemical among terrorists makes it likely it will be used against us in this country. With more than 50,000 tank cars of chlorine shipped each year, plus countless other containers filled with chlorine, this material can be found almost anywhere.
TOXICITY
Chlorine is naturally corrosive; water exacerbates this corrosivity and, therefore, the toxicity. When chlorine dissolves in water, hypochlorous acid (HClO) and hydrochloric acid (HCl) form. The hypochlorous acid is unstable and breaks down, releasing oxygen free radicals. Therefore, when a person is exposed to chlorine, the chlorine dissolves in the eyes, damp skin, and upper respiratory tract, which contain moist tissues, and is corrosive to those organs.
Low concentrations of chlorine gas can irritate the nasal passages and constrict the chest; larger amounts can cause death by asphyxiation. Exposures of 15 ppm for short periods of time will irritate the throat, exposures up to 50 ppm will cause serious damage, and a few breaths at 1,000 ppm can be fatal. An LC50 of 430 ppm for 30 minutes has been reported. LC50 is the concentration in air that will kill half the exposed animals in the specified time, and an LD50 of 19,000 mg·min/m3 has been reported. LD50 is the dose fed to animals that will kill half of them.
PERSISTENCY
Being a gas, chlorine exhibits no persistency in the environment. Even if released as a liquid, chlorine will quickly vaporize to its natural state. Any movement of the wind will cause chlorine to disperse, even though it may travel along low spots in the terrain. In moist conditions, chlorine will react with water to form acidic solutions, which will react vigorously with metals, but any free chlorine will dissipate in a relatively short time, unless confined.
SYMPTOMS
After exposure to chlorine, coughing and choking, watering and burning of the eyes, blurred vision, tightness in the chest, and burning feelings in the throat and nose will occur. With high concentrations, the victim will have difficulty breathing, followed by pulmonary edema and eventually death if he is not removed to fresh air. Even if first aid is applied quickly and the victim recovers, he may later develop pneumonia and chronic bronchitis.
DETECTION
The human nose can detect chlorine at concentrations ranging from 0.3 to 3.0 ppm. It has a penetrating, irritating odor, reminiscent of bleach. Therefore, it is not necessary to use devices or materials to detect the presence of chlorine. In high concentrations, you may see the greenish-yellow color of chlorine.
PROTECTION
You can protect against chlorine by wearing goggles, full face shields, chemical suits impervious to chlorine, rubber gloves, rubber shoes, and the proper National Institute for Occupational Safety and Health-approved respirator. Self-contained breathing equipment must also be available for repeated entry into an area where there is a dangerous chlorine concentration.
Chlorine producers in the United States and Canada have joined to form the Chlorine Institute, an organization dedicated to the safe use of chlorine, and have developed a mutual-assistance program to assist in chlorine emergencies. Certainly this program, known as CHLOREP (for Chlorine Emergency Plan), could be helpful in a terrorist attack involving chlorine. Assistance in emergencies can be obtained from CHEMTREC (1-800-424-9300), with whom the Institute is now affiliated.
DECONTAMINATION
Remove the victim to fresh air, usually in an outdoor environment higher than where the exposure took place. Quickly remove the victim’s clothing; seal it in a plastic bag and place it in another sealed plastic bag. Eventually, inform the proper authorities where the contaminated clothing is and what was done to it.
Wash the victim’s body as quickly as possible with copious amounts of soap and water. Rinse the victim’s eyes with water for 15 minutes if he complains of burning sensations. Administer proper medical attention as soon as possible.
ANTIDOTE
There are no specific known antidotes for chlorine exposure. The only effective relief of symptoms occurs with proper medical treatment. With effective medical management, the victim usually completely recovers.
For exposure to chlorine gas, treatment for inhalation must precede treatment for other forms of exposure. For inhalation of chlorine, immediately remove the victim to fresh air. Trained personnel should administer oxygen; if breathing stops, administer artificial respiration.
For eye contact, flush the affected eye with water for at least 15 minutes while forcibly holding the eyelid open. Then, turn the victim over to a physician.
In case of skin contact, remove the clothing immediately and flush the affected area with water. A physician must approve any other first-aid treatment of affected skin. Ingestion of chlorine is not likely.
FRANK L. FIRE has worked for 40 years in the plastics industry and retired as executive vice president of sales, marketing, and international from Americhem, Inc., in Cuyahoga Falls, Ohio, a provider of raw materials to thermoplastics processors. He has taught “Chemistry of Hazardous Materials” to firefighters and other emergency responders for 32 years in the Fire Protection Technology program at the University of Akron (OH) Stark State College; the National Fire Academy in Emmitsburg, Maryland; and, most recently, to civil support teams of the National Guard in Missouri and Minnesota. He has a B.S. degree in chemistry and an M.B.A. degree from the University of Akron. He is the author of The Common Sense Approach to Hazardous Materials; The Common Sense Dictionary for Emergency Responders; A Study Guide to the Common Sense Approach to Hazardous Materials; Combustibility of Plastics;and Chemical Data Notebook: A User’s Manual and a co-author of SARA, Title III: Intent and Implementation of Hazardous Materials Regulations. He has written more than 120 articles on individual hazardous materials for Fire Engineering.
