CHEMICAL DATA NOTEBOOK SERIES #43 PHOSGENE
HAZARDOUS MATERIALS
PHOSGENE IS AN extremely toxic, water-reactive, corrosive, irritating, colorless-to-light-yellow gas with an odor that ranges front newly mowed grass at low concentrations to very pungent at high concentrations. It is usually shipped and stored as a liquefied gas. Phosgene is used in the manufacture of dyes, herbicides, insecticides, pharmaceuticals, some plastics, and many other chemicals. It is useful in metallurgy and was previously used as a poison gas in wartime. Its chemical formula is COCl2
PROPERTIES
Phosgene is nonflammable, has a vapor density of 3.41, and has a specificgravity of 1.392 in the liquid state. It has a molecular weight of 98.9, boils at 45.7°F, freezes at – 194.8°F, and is very slightly soluble in water, with which it reacts slowly.
HAZARDS
Phosgene is considered a deadly poisonous gas. It can be detected by odor at levels ranging from 0.125 ppm (parts per million of air) to 1.0 ppm. This upper level of odor detection is 10 times higher than the TLV-TWA of 0.1 ppm. Levels as low as 50 ppm can be fatal in 30 minutes or less, and 25 ppm is dangerous for periods of exposure longer than 30 minutes. At 12.5 ppm, death can occur from exposure ranging from 30 minutes to one hour. Even short exposures of a minute or less can cause severe lung damage at a level of 20 ppm. The reason for the overlap in exposure levels at odor detection level is partly because people have different responses.
Phosgene’s high order of toxicity combined with its very high vapor density made it an almost perfect poison gas in World War I. It could be released from high ground and it would flow downhill to lower areas, collecting in trenches occupied by enemy troops. Since all gases are fluids (that is, they will flow), phosgene would even move along the trench, pulled by the air currents caused by the action of men running from it, or it would simply flowalong the trench, pushed by additional phosgene flowing down from above.
The action caused by phosgene’s high vapor density poses exactly the same danger for firefighters and emergency responders in an incident involving phosgene. Although the first smell of phosgene may be very strong, the damage caused to the olfactory nerve maybe such that the sense of smell is destroyed, and the exposed person will not notice the next few inhalations of the gas. Death can follow rapidly. Therefore, exposed persons must wear positive-pressure, self-contained breathing apparatus at all times wherever phosgene may be present. The emergency responder must be particularly wary of low spots in the terrain or confined spaces, where the gas tends to collect. With a vapor density of 3-41 (phosgene is 3.41 times as heavy as air), it will “hang together” as it flows for some time and for some distance if strong breezes are not present.
Phosgene reacts slowly when in contact with water. This reaction produces carbon dioxide (C02and hydrogen chloride (HC1). The hydrogen chloride immediately dissolves in the moisture, to form hydrochloric acid. Hydrogen chloride is an irritant gas and is much less dangerous than phosgene, although hydrogen chloride is a hazardous chemical (see Fire Engineering, “Chemical Data Notebook Series #21,” February 1988).
Because of this slow reaction with water, phosgene, if inhaled in less than immediately fatal quantities, can produce a delayed reaction that might be fatal 24 to 36 hours later. For this reason, any exposure to phosgene without respiratory protection must be considered life-threatening, even if no immediate discomfort or other symptoms are present. Symptoms of exposure to phosgene (when they can be felt) include dryness or a burning sensation in the throat, numbness, tightness and pain in the chest, bronchitis, shortness of breath, coughing, choking, headache, nausea, dizziness, chills, pulmonary edema, pneumonia, and finally death.
Contact by liquid phosgene with the eyes causes severe damage and/or blindness. High concentrations of the gas cause corneal damage. Contact by the liquid w ith the skin causes severe irritation and/or burns. Anhydrous phosgene is not corrosive, but any contact with water begins its slow decomposition into carbon dioxide and hydrogen chloride, then hydrochloric acid. Hydrochloric acid can attack both human tissue and metals and can destroy tissue if in a high enough concentration. When metals are corroded by hydrochloric acid, flammable hydrogen gas may be liberated.
Phosgene, like other commercially valuable gases, is liquefied for economy in shipping and storage. Gases may be liquefied by applying pressure, by cooling the gas below its boiling point, or by a combination of cooling and pressurization. Phosgene’s boiling point is so high that a simple cooling below 45.7°F will liquefy it, and confinement in a container will keep it liquefied.
Phosgene is considered a stable chemical but it reacts violently with such common chemicals as alcohols (particularly isopropyl alcohol), amines, iron salts, lithium, potassium, sodium, and powdered aluminum. IFj also reacts with complex chemicals’ such as amino lithium; hexafluoroiso-propylidene; sodium azide; tertiary butyl azidoformate; and 2,4-hexadiyn-l ,6-diol. Liquid phosgene may also attack different types of rubber and plastic. ⅛
NONFIRE SCENARIO
Phosgene is a gas but is almost always found in the liquefied state since more; of any material can be stored in a container in liquid form than in gasi form. Any opening in the container releases either gas under pressure or liquid. Escaping liquid is also discharged by the gas pressure within the container, and it is propelled in a stream traveling some distance rather thanflowing down the side of the container.
SYNONYMS
carbonic acid dichloride
carbonic dichloride
carbon oxychloride
carbonyl chloride
CG
chloroformyl chloride
NCI-c60219
diphosgene
At the first instance of a leak or other accidental release of phosgene, consider evacuation of all persons downwind of the incident scene immediately. A phosgene release is an example of a “worst case” scenario (there are other hazardous materials that fit into this category, including other Poison A materials, explosives, and radioactive materials), and the immediate threat to human life must be the first consideration of firefighters and other emergency responders. Notify the proper environmental authorities as soon as possible, but the immediate threat to human life is much greater than the threat to the environment. In such an incident, the Local Emergency Planning Committees, as mandated by SARA Title III, must implement and coordinate rescue and evacuation activities.
If the phosgene in any form is escaping its container, emergency responders should not attempt to stop the leak unless they are fully protected from the chemical. If the source of the leak is a small hole in the container, emergency plugs driven into the hole may stop the flow of gas. (Liquid may be more difficult to stop because of the spraying and resultant loss of visibility.) Since phosgene is nonflammable, there are no restrictions on the plug’s material, but corrosion is possible, given phosgene’s water-reactivity and subsequent production of hydrogen chloride and hydrochloric acid. Water spray or fog may be effective in dispersing phosgene gas, but the runoff water must be contained.
If the leak is a stream of liquid phosgene, the liquid begins to boil as it heats up to its boiling point of 45.7°F, assuming the ambient temperature is at that level or higher. Once the liquid is no longer under the pressure of confinement, conversion of the material from liquid to gas occurs at any ambient temperature, with the fastest rate of evaporation occurring at its boiling point. Boiling begins as the liquid contacts objects warmer than 45.7°F. Any water used to disperse the gas accelerates gas formation if it is allowed to contact the liquid stream.
Small amounts of liquid phosgene may be flushed with large amounts of water if there is little or no exposure of humans to the gas formed. If large amounts of liquid phosgene are released, the spill should be contained as quickly as possible to prevent its spread. If possible, a containment pond should be created by building dikes of earth, sand, clay, or other materials around the spill. A containment pit is a better mitigation technique if one can be dug fast enough, using trenches to lead the liquid to the pit from the spill. A pit is better because the surface area of the liquid exposed to the atmosphere is less in a pit than a containment pond, and evaporation of a liquid occurs more rapidly when a larger surface area of the liquid is exposed. Also, it is easier to cover a pit with a sheet of some impervious material.
Consult foam manufacturers to determine what type foam might be effective in covering phosgene to slow the evolution of gas. One reference cites the technique of applying a layer of water over the liquid phosgene. Since the phosgene has a specific gravity higher than water, it will remain below the water. However, the reference says this technique may not have been perfected yet. Consult manufacturers of phosgene to determine if this technique is safe.
Phosgene percolates into the soil regardless of whether it is contained by a pond or pit. The environmental authorities will have to direct the removal of the contaminated soil, which must be disposed of in accordance with federal, state, and local regulations. To remove the liquid remaining in the pit, vacuum or pump it into secure containers with compatible equipment. Then absorb any remaining liquid with soil, sand, clay, or other sorbent material. Any contaminated soil or sorbents must be handled in the same way as the hazardous material itself, since phosgene gas continues to be generated by any remaining material. Only professionals who are properly educated, trained, equipped, and supervised should conduct salvage and cleanup.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
75-44-5
STCC
(Standard Transportation Commodity Code)
4920540
RTECS
(Registry of Toxic Effects of Chemical Substances)
SY5600000
RCRA
(Resource Conservation and Recovery Act)
P095
UN/NA
(United Nations/North America)
1076
CHRIS
(Chemical Hazard Response Information System)
PHG
DOT
(U.S. Department of Transportation)
Poison A
IMO
(International Maritime Organization)
2.3, poison gas
Block entrances to sewers and waterways to prevent the liquid from entering. Any phosgene entering sewers will pose a problem throughout the system. Hie sewers may fill up with gas as the liquid evaporates (the gas itself can also flow into the sewer opening), forcing gas out of the sewers and into the streets or the basements (and bathrooms) of homes and threatening human life. Notify the sewage treatment plant immediately that phosgene gas and possibly hydrochloric acid are flowing toward the facility.
If the liquid enters a waterway, the phosgene will sink to the bottom and flow downstream underwater. All downstream users of the water must be notified immediately. The phosgene and the water slowly begin to react, any hydrogen chloride formed dissolves in the water, and the resulting acid is diluted by the rest of the water.
In slow-moving streams, liquid phosgene will collect underwater in lowspots and may be pumped into secure containers. Small dams placed below the surface of the water will facilitate collection and then the product can be pumped out. If these techniques are not feasible, diverting the stream into a lowlying area may make salvage possible. This can contaminate the collection area, however.
FIRE SITUATIONS
If the container of phosgene is not leaking, radiant heat from the fire will be absorbed by the container, thus warming the liquefied gas, causing it to evolve gas more rapidly. If the container is leaking, the escaping product will be ejected faster due to increased pressure. It is very important to note that containers holding Poison A materials do not have any pressure relief devices. The rationale here is that there is more danger to human life caused by venting poison gas or vapor than if the container were to catastrophically fail and release all its contents. Reduction of internal pressure through a spring-loaded valve would unnecessarily release deadly gas, and container failure may be prevented by cooling the container with unmanned monitors from as far away as possible. Firefighters should never allow themselves to be caught between the fire and exposed containers of any sort.
Since phosgene is nonflammable, there is no possibility of the classic BLEVE occuring—the classic BLEVE occurs with an easily liquefiable gas (which phosgene is ) that is flammable (which phosgene isn’t). When the design strength of the container is surpassed by rapidly rising internal pressure, the container comes apart in a pressure-relief explosion accompanied “by flying shrapnel and the spewing of the contents. One school of thought describes just this action as the BLEVE, and it certainly fits the description of The acronym: boiling-liquid, expandingvapor explosion. However, another school of thought says the explosion part of the acronym arises from the ignition of expanding flammable vapors released from the container when it explodes from overpressurization. The classic BLEVE, then, is really in two parts: The first is the pressure-relief explosion of the container itself, and the second is the explosive ignition of flammable gas resulting in a tremendous fireball.
GLOSSARY
Anhydrous—a chemical term meaning “no water present.”
Boiling point—the minimum temperature at which the vapor pressure of a liquid just equals atmospheric pressure.
BLEVE—acronym for boiling-liquid, expanding-vapor explosion.
Evaporation—the process by which a liquid changes to a vapor; it is always accompanied by an increase in energy of the molecules evaporating.
Metallurgy—the science of extracting metals from their ores or of purifying metals.
Poison A—A gas or liquid so toxic that an extremely small amount of the gas or vapor from the liquid is dangerous to life.
Safety relief device—any device that relieves internal pressure before the design strength of the container is reached.
Spring-loaded valve—a valve held in place by a spring with a built-in design strength, probably one-fourth that of the tank. When internal pressure surpasses the strength of the spring, the valve opens and relieves the pressure, at which point the valve reseats itself and the container is resealed.
Water-reactive—a material that reacts with water in a violent or dangerous manner, including the evolution of hazardous products, heat, or violent spattering.
Phosgene, like any liquefied gas or liquid, produces its maximum amount of vapors at its boiling point. The act of evaporation is one that requires energy input, and therefore evaporation of any liquid has a cooling effect on anything that it contacts. Thus under normal circumstances a pool of liquid phosgene would be evaporating at ambient temperature, and the act of evaporation would cool the remaining liquid, thus slowing the evaporation slightly. However, if the pool of liquid is exposed to a fire’s radiated heat, the cooling effect of evaporation would be negligible, and the continued evaporation would be at its maximum rate. Therefore, it might be recommended that water spray or fog be used to cool the pool of liquid while dispersing the evaporated gas that is evolving.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment that prevents contact of the liquefied or gaseous phosgene with the eyes, skin, or respiratory system. Select splash-proof chemical goggles and face shields for eye protection and use positive-pressure, self-contained breathing apparatus for all levels of phosgene concentration. Rubber boots, gloves, and aprons offer some protection, but wear total encapsulating suits if contact with phosgene is possible. Since phosgene may attack some types of rubber and plastic, consult manufacturers of such suits as to which materials offer protection.
FIRST AID
For inhalation of phosgene, remove the victim to fresh air and keep warm and quiet. If the victim’s breathing becomes difficult or stops, provide artificial respiration, being careful not to come in contact with the product in the victim’s lungs or vomit. Maintain an open airway with the victim’s body reclined and feet elevated. Seek medical attention immediately. For eye contact immediate medical attention is mandatory. Until it is provided, flush the eyes with water for at least 15 minutes, lifting the lids periodically.
For skin contact with the material, remove all contaminated clothing and wash all contacted areas with large amounts of water. Immediate medical attention is necessary.
For ingestion, do not induce vomiting. Call for immediate medical attention while making sure the victim is warm and comfortable.
