BY FRANK L. FIRE
A vesicant, or blister agent, as its name implies, causes painful burns and the formation of large blisters when it contacts the skin. These blisters are so painful that they cause the victim to become incapacitated. The effects of certain vesicants on the skin, such as mustard gas, might be delayed as long as 24 hours after exposure. If the exposure to the concentrated gas or vapor is long enough, the blisters will be so severe that they will take an extremely long time to heal and can cause the body to go into lethal shock. In addition to blistering and burning, blister agents (sometimes called mustard agents, urticants, or nettle agents) also cause severe tissue damage to the eyes, respiratory system, and internal organs.
The objectives of using blister agents are to produce injuries and to force enemy troops to wear cumbersome protective equipment that would lead them to fight less efficiently and be more easily defeated. Another reason for their use is to have enemy personnel withdraw from fighting to care for the victims of blister agents. Blister agents (with the exception of phosgene oxime) are persistent and will contaminate almost anything they touch for possibly days or weeks. Blister agents can penetrate cell membranes in most body tissues and many materials such as wood, rubber, and plants.
Blister agents, when pure, are colorless and nearly odorless. When an odor is present, the smell is similar to rotting onions or mustard. They, like other chemical weapons, can be thickened by adding a material such as a polymer. This thickening agent will cause the blister agent to adhere to almost any solid object it touches (including the victim) and, therefore, become more effective and persistent. At room temperature, blister agents are stable liquids with low volatility and thus will evaporate more slowly. In warmer climates, the mustards’ persistence is less, but higher concentrations of vapor will be generated. When mustards are dissolved in water, they hydrolyze at fast rates, yielding poly-alcohols and hydrochloric acid.
PHOSGENE OXIME
In the early 20th century, chemists were working on a particular class of chemicals called the “halogenated oximes.” They were first synthesized in the late 1920s, and phosgene oxime, the most irritating and toxic of the class, became recognized as a potential agent for chemical warfare because of the rapidity with which it adversely affected humans in several ways. It has a military designation of “CX” and is different from the pulmonary irritant (or choking agent) phosgene, which has a military designation of “CG.” Phosgene oxime has no industrial use, so any material that exists was made as a chemical warfare agent (CWA). Therefore, there is little chance of an accidental exposure, unless responders are involved in mitigating an incident at a terrorist’s clandestine phosgene oxime manufacturing operation or stored phosgene oxime is being transported and has been involved in an accident. Although the Germans, Russians, and Americans all studied it for its use as a CWA, there is no record of phosgene oxime’s ever being used in warfare. However, it was of some military interest because it rapidly rendered combatants helpless. It quickly penetrated uniforms, producing a rapid onset of severe and prolonged effects. It also had an immediate effect on the victims’ respiratory system, incapacitating them almost from the first breath.
Through chemical warfare testing, it has been discovered that phosgene oxime can be made more damaging by mixing it with other CWAs, such as nerve agents, and that the rapid skin damage it causes can make the victim even more vulnerable to the second agent that enters through the skin lesions. Although phosgene oxime is classified with blister agents, it does not cause true vesicles (small, fluid-filled blisters). It is actually an urticant or nettle agent that causes erythema (a redness of the skin as a result of a widening of the small blood vessels near its surface); raised reddened areas of the skin; itchy and pale or reddened irregular, elevated patches; and severe itching (hives). The reaction often occurs within 30 seconds, and victims have reported the pain as unbearable.
Phosgene oxime has also been called a corrosive agent, because of the extreme damage it can cause to tissue. It is categorized with vesicants because it produces eye, lung, and skin damage similar to (but more damaging than) the other blister agents that are true vesicants. It also causes damage much more rapidly than the normal blister agents. Where the formation of blisters may be delayed from a few hours to 24 hours, the rash, hives, and other raised patches of skin resulting from contact with phosgene oxime vapors (or other forms) will form almost immediately. It also has a corrosive action on metal.
TOXICITY
Phosgene oxime, when inhaled, will irritate the upper respiratory system and cause pulmonary edema at concentrations as low as 0.2 mg-min/m3. The vapors become unbearable at about 3.0 mg-min/m3. Phosgene oxime has an LCt50 of from approximately 1,500 to 3,200 mg-min/m3. The LCt50 is defined as the amount of gases, vapors, fumes, dusts, and other particulates in the air that will cause death to half the test animals exposed to the material within a specified time.
Any contact with phosgene oxime will cause immediate severe pain and tissue damage to the skin, eyes, and mucous membrane surfaces. Phosgene oxime is readily absorbed through the skin and can cause severe internal damage. The LD50 for skin exposure is estimated at 25 mg/kg. LD50 is defined as the weight of product, relative to body weight of the animal, that will produce lethality in 50 percent of the test animals within a specified exposure and post-exposure time. Any contact with vapor will cause severe eye damage (conjunctivitis and inflammation of the cornea); contact with the liquid may cause blindness or even death.
No record of human ingestion of phosgene oxime is available; but in the rare case where it might occur, it would be highly toxic to humans.
RANK AMONG OTHER BLISTER AGENTS
Phosgene oxime and lewisite are two blister agents that cause rapid reactions; other blister agents may have somewhat delayed reactions. The indications of phosgene oxime’s toxicity among all the blister agents may be somewhat irrelevant, since it acts on the human body so rapidly and there is no known antidote for it.
PERSISTENCY
Phosgene oxime is probably the least persistent of all the blister agents. It will last for up to two hours in soil; the vesicants may last from days to weeks, depending on soil and weather conditions. Adding thickening agents to phosgene oxime will increase the time it will remain in the environment but may not increase its persistency to that of other blister agents. Phosgene oxime hydrolyzes in water, and wet soil will cause it to break down more quickly than in dry or well-drained soil.
DESCRIPTION OF PHYSICAL AND CHEMICAL PROPERTIES
Phosgene oxime is a white crystalline corrosive deliquescent powder (when pure) with an unpleasant and irritating odor. It can be easily liquefied (the liquefied phosgene oxime is yellowish-brown). It is soluble in water and organic solvents but hydrolyzes (is broken down by water) fairly quickly, especially in the presence of an alkaline solution. It vaporizes at ambient temperatures because of its high vapor pressure. In low concentrations, it may have the odor of new-mown hay.
Phosgene oxime’s molecular formula is CCl2NOH (sometimes written CHCl2NO). Its boiling point is 128°C (262.4°F); its melting point is between 35°C and 40°C (95°F and 104°F). Its molecular weight is 113.93, which makes its vapor density 3.93 times greater than air. This, of course, means the vapors of phosgene oxime will flow downhill and tend to settle in low-lying areas. Its high vapor pressure means the solid will convert to a vapor at normal temperatures. It is corrosive to metals and will also decompose on contact with them.
Phosgene oxime has several synonyms, including dichloroformoxime, 1,2-dichloroformoxime, dichloroformaldoxime, dichloroximinomethane, dichlorformaldehyde-oxime, kohlensaure-dichlorid-oxime, dichlormethylen-hydroxylamine, and carbonyl chloride oxime. Its CAS Registry Number is 1794-86-1.
DELIVERY METHOD
On the battlefield, an explosive charge or mortar or artillery shell usually delivers blister agents to the target. Because of the blister agents’ high vapor density, they could also simply be released from their container and allowed to evaporate. In today’s world, terrorists will use any method necessary to deliver the phosgene oxime to the desired general area of release and then use one or more release methods. After converting the phosgene oxime to a liquid, the container may be left open to allow the liquid to evaporate and be spread if there is a breeze. The container will usually be glass or plastic, since phosgene oxime is corrosive to most metals. A metal container can be used if the phosgene oxime is poured into it quickly; the container will be left to corrode, and the contents will spill out and evaporate.
An explosive charge or some type of bomb can be used in a crowded marketplace, a building, or other venue where a crowd might congregate. The blast would kill and injure some people, creating havoc, while spreading the phosgene oxime over a wider area than if it were just allowed to evaporate. The reaction of the victims of the phosgene oxime vapor spread by the explosion would increase the panic and cause first responders to possibly waste valuable time by hunting for victims over a wide area.
A small hand-operated sprayer, like that used to spray a garden or lawn, can also be used to spread the liquid. Of course, anyone spraying phosgene oxime 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. Also, automatic equipment from the back of a pickup truck or a larger tank truck, such as that used by companies that treat homeowners’ lawns, could spray the phosgene oxime. A crop-dusting airplane might also be used to spread the blister agent over a larger area. The solid phosgene oxime could be left somewhere in an open container or just in a pile. It will vaporize over time, harming anyone coming in contact with the vapors.
DETECTION
The reactions of people exposed to phosgene oxime would be the first indication that it is present. Inhaled vapors would cause severe coughing, and vapors’ contacting the eyes would cause severe tearing and irritation, possibly even loss of sight. Contact with the skin, as noted above, would cause victims tremendous pain almost immediately. A severe rash would rapidly appear on the exposed victims’ skin. If you observe any of these reactions, suspect that phosgene oxime is present.
A variety of devices is available to detect blister agent vapors and liquids. The M256A1 detector kit is the most common and efficient way to detect the vapors. Simple liquid detectors such as the M8 and M9 papers may also be used, but they are effective on liquids only and may not work for phosgene oxime. Direct reading instruments available include specialized gas chromatographs (minicams) and ion mobility spectrometers such as the APD 2000. At least one reference lists the 18A2 kit as effective for CX. Since some of these detectors may not adequately detect phosgene oxime, you should be trained in the use and limitations of all the detection equipment available. The Department of Homeland Security (DHS) can provide the latest information concerning detection equipment and the proper techniques for their use.
PROTECTION
One of the reasons phosgene oxime was considered for use as a CWA is its ability to penetrate uniforms and rubber readily. This makes it difficult to suggest protective clothing. Some references recommend butyl toxicological agent protective gloves; chemical goggles and face shields; a complete set of protective clothing (undetermined composition); and M9, M40, or M17 masks. Other references call for masks and Level A protective clothing. Another reference calls for “special equipment,” including a respirator, military-grade NBC suit, gloves, and overboots. Since it penetrates rubber faster than the mustards, frequent changes of NBC gear are required.
First responders must be aware that phosgene oxime is very penetrating, and they must protect themselves against inhalation, ingestion, and eye and skin contact. Contact the DHS for the latest information concerning protective equipment and clothing.
DECONTAMINATION
Generally, for vesicants, flushing eyes with copious amounts of water is recommended. Wash the skin with large amounts of soap and water. Use the same methods for phosgene oxime decontamination, with the caveat that nothing to date has been found to be very effective for CX. Since phosgene oxime is subject to hydrolysis and the rate increases with the alkalinity of the solution, a water solution of sodium carbonate or a dilute solution of sodium hydroxide might be used. The sodium hydroxide solution must be diluted enough so that it does not damage the skin, since sodium hydroxide itself is a corrosive material.
SYMPTOMS
The number-one clue that phosgene oxime is present is the almost instantaneous and intense pain it causes, described as almost unbearable stinging and burning. This is evidenced by the rapid reddening of the skin where it was contacted by the vapor. The pain is so intense that first responders who have contacted phosgene oxime and should have known better have removed their protective gear in an attempt to alleviate the intense pain.
In the case where an aerosolized liquid or vapor attack has occurred, the eyes are the first organs to be affected. Immediate symptoms, in addition to pain, include chemical conjunctivitis with tearing, intense involuntary closing of the eyelids, inflammation of the eyelids, and inflammation of the cornea. Prolonged exposure can cause corneal damage and permanent blindness.
Phosgene oxime is such a powerful urticant that contact with just a drop of CX (which might be fatal) produces an immediate intense pain and itching. The skin will absorb it within a minute, and destruction of the skin begins, as evidenced by the skin’s turning white around the contact point, followed by the accumulation of fluid and the skin’s turning darkall occurring within 24 hours of contact. The affected skin dies and falls off the body; a discharge of pus follows. The entire area around the lesion is seriously inflamed. Severe skin exposures may also induce pulmonary edema and the formation of blood clots, usually several hours after exposure.
Inhalation of phosgene oxime will immediately irritate the respiratory tract and cause severe inflammation that will quickly lead to pulmonary edema. In addition, as the airways become inflamed, they will swell and fill with mucus, making breathing extremely difficult. Inhaling high concentrations of phosgene oxime can cause death.
ANTIDOTES
There is no known antidote for phosgene oxime. Treatment consists of decontamination as soon as possible by removing the phosgene oxime from the body and providing the proper medical care for the injuries in a hospital setting.
The use of pain relievers as determined by emergency room physicians is recommended to ease the pain caused by skin contact with CX. Contact the DHS for the latest in medical treatment for contact with phosgene oxime.
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., 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, 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.
