CHEMICAL DATA NOTEBOOK SERIES #103: ARSINE

CHEMICAL DATA NOTEBOOK SERIES #103: ARSINE

BY FRANK L. FIRE

Arsine is an extremely toxic, flammable, colorless gas with a mild, garlic-like odor. It is used as a doping agent for solid-state electronic parts, as a military poison, and as an intermediate chemical to synthesize several organic chemicals. Arsine is shipped as a liquefied compressed gas in steel cylinders under its own vapor pressure of 219.7 psia (pounds per square inch absolute). It usually is sold in ultra-high purity grades (99.9995+ percent) primarily for use in the electronic industry. A blood and nerve poison, it is fatal if inhaled in sufficient quantity.

PROPERTIES

Arsine is not only extremely toxic but also flammable. Since it is a gas, it has no flash point. There is no listed ignition temperature, but it decomposes into arsenic and hydrogen at 446°F. It has an extremely wide explosive (flammable) range in air of from 4.5 to 64.0 percent, probably due to the hydrogen in the molecule. The specific gravity of the liquefied arsine is 2.7, it has a molecular weight of 78, and the gas has a vapor density of 2.69. It boils at -80.5°F, freezes at -178.4°F, and is slightly soluble in water. Its molecular formula is AsH3.

The molecular structure of arsine is similar to that of ammonia. This is so because both nitrogen and arsenic appear on the Periodic Table of Elements in Group V (or Group VA in some Tables). The Periodic Table lists all the known elements in order of increasing atomic number (the number of protons in the nucleus of each atom of that element). The Table is further arranged according to groups or families of elements, all having the same number of electrons in the outer orbital (or ring) of their atomic structures. Since the elements nitrogen and arsenic both have five electrons in their last orbital ring, they will react in similar fashion and thus form similar compounds. (For an explanation of the above-mentioned atomic structure, see the first chapter of The Common Sense Approach to Hazardous Materials, published by Fire Engineering Books.) Phosphine, as will be seen in a future article, also has a structure identical to ammonia and arsine, with a phosphorus atom surrounded by three hydrogen atoms. This is because phosphorus is the other nonmetallic element of Group V.

HAZARDS

Arsine`s major hazard is that it is a Class A poison gas. It is such an extremely toxic gas that it attacks the nervous and circulatory systems simultaneously and can be fatal if inhaled in sufficient quantity. A powerful destructor of red blood cells, its victims may have symptoms delayed for up to 24 hours. Both chronic and acute exposures to arsine are very dangerous. Symptoms of a single (acute) inhalation exposure can include abdominal pain, severe anemia, darkening of the urine, diarrhea, dizziness, headache, nausea, rapid intravascular hemolysis, pallor, palpitation, renal failure, respiratory tract irritation, tiredness, vomit, and collapse. Exposures to concentrations of 500 ppm (parts per million of air) for just a few minutes can be lethal, while at least one reference claims the lethal concentration of arsine in air is 10 ppm.

Pulmonary edema may occur following acute overexposure. This filling of the lungs with fluid may occur after a delay of several hours (before any warning signs or symptoms). Gastric disturbances and intense coloration of the skin may also result.

Effects of chronic (repeated) overexposure may result in damage to the nervous system, hyperpigmentation, keratosis, cardiovascular disease, and progressive anemia. Other effects of overexposure include pulmonary edema, jaundice, and severe hem-olytic anemia. Severe kidney, liver, and cardiac damage may occur as well.

Arsine`s TLV-TWA (threshold limit value-time weighted average) is 0.05 ppm. This is higher than the OSHA (Occupational Safety and Health Administration) PEL (permissible exposure limit).

There is evidence (from reports of the National Toxicology Program and the International Agency for Research on Cancer) that inorganic arsenic compounds are skin and lung carcinogens in humans. Arsine is covalently bonded but still may fall into the carcinogenic category because of the reactions that occur when it converts to arsenic and/or inorganic arsenic compounds.

Arsenic also is considered a flammable gas. This may be a misnomer for the following reason: Arsine decomposes into its elemental components (arsenic and hydrogen) at temperatures near 446°F (well within reach of all common ignition sources). It is probably the hydrogen generated from the breakdown of arsine, rather than the arsine itself, that ignites and explodes. Hydrogen, of course, is an extremely flammable gas with an explosive (flammable) range of from four to 75 percent and an ignition temperature of 1,060°F. It burns very hot and liberates almost all of its energy as heat–which explains why a hydrogen explosion is much more dangerous than that of a simple flammable gas.

In any event, arsine is a gas, so treat it as flammable.

Arsenic, the other constituent of arsine, will be liberated as the element but may burn when the released hydrogen burns or may burn in the ensuing fire caused by the ignition of arsine (or hydrogen). This will lead to the formation of another extremely hazardous material–arsenic trioxide. Arsenic trioxide, which is extremely toxic, is also a carcinogen. Continued oxidation (burning) of arsenic trioxide will yield arsenic pentoxide, another deadly poison.

Ironically, the release of arsine gas from its own container is not responsible for most arsine poisonings. The generation of arsine in the cleanup of tank cars and containers used to transport other materials (through the action of acids or oxidizing agents) usually causes these accidents. These “other” materials include, but are not limited to, arsenic compounds (such as arsenic trioxide) and the ores of metals that contain arsenic (copper ferrite, copper sulfide, other copper ores, lead carbonate, lead sulfate, lead sulfite, and other lead ores). Arsenic compounds usually are found interspersed with these ores in nature and will be present until the ore is smelted and the pure metal is extracted. Arsenic compounds will be the by-products of the smelting process. However, accidents can occur where pure arsine is being produced, transported, stored, or used, and they will be much more dangerous because of the quantity of the gas involved.

Arsine is considered a stable compound. It is slightly soluble in both water and organic solvents. It reacts readily with oxidizing agents such as the halogens (bromine, chlorine, fluorine, and iodine), nitric acid, nitrogen trichloride, potassium permanganate, and sodium hypochlorite to form arsenic compounds. Although arsine is stable at room temperature, it begins to decompose into its constituent elements at around 446°F to 464°F (230°C to 240°C).

Arsine`s vapor density of 2.69 is another hazard of the gas. As it is released from its container or origin as a liquid or a gas, it will flow along low spots in the terrain and accumulate in low areas or confined spaces. Anyone entering such an accumulation without the proper respiratory protection probably will be fatally poisoned in a relatively short period of time. Because of its wide explosive range (4.5 to 64 percent), it is almost impossible to find a concentration too rich to ignite; and, therefore, any ignition source can cause an explosion of the vapors.

NONFIRE RELEASE

The release of arsine from a transportation container, a storage container, or a vessel in a manufacturing or processing operation is a very serious concern for anyone exposed and should activate the community`s emergency response plan. This plan should require the presence of not only hazardous-materials response team members but also firefighting personnel, police, environmental authorities, and all personnel who can offer aid and protection for exposed people potentially affected by the exposure to arsenic or other highly toxic materials produced when arsine burns.

Whenever an incident causes the presence of arsine in open air, evacuate all nonemergency personnel from the danger area immediately. Self-contained breathing apparatus and full-coverage Class A protective clothing are absolutely required for any emergency personnel who must enter the area of the leak. The proper procedure in such a release of poison gas would be to initiate corrective actions to stop the leak. However, since the gas is also flammable, the presence of any ignition source will cause an explosion of the accumulated gas. This will necessitate the use of sparkproof tools in all operations involving arsine.

In the event of a leaking container, ventilate the area surrounding the leak and move the leaking container to a well-ventilated area far enough away to avoid exposure to personnel or the local population. Always be mindful of the flammability of the gas and the explosion that can occur on ignition. Only trained, professional salvage personnel should take this action–while emergency personnel provide ventilation. Using a high-pressure water spray or fog (knowing that the water used will be contained to prevent contamination of the soil or waterways) can protect against accumulation of vapors.

Deliberate ignition of a flammable, highly toxic gas is always a viable mitigation technique. However, do not undertake this measure if the ignition will cause an explosion dangerous to the human population or produce an even more dangerous situation than the existing one. The incident commander should use deliberate ignition only after careful consultation with all available resources has led him to believe that it will save lives and prevent damage to the environment and property.

If the liquefied gas is released, employ all procedures normally used for flammable liquids and all personnel protection against a Class A poison.

Professionals should carry out cleanup and salvage procedures. All stressed containers will be extremely dangerous and capable of failure at any time.

FIRE RELEASE

All fires involving toxic materials are infinitely more dangerous than materials that are simply flammable or combustible. When those toxic materials are compressed or liquefied gases, the danger is even greater. Arsine presents a still greater danger, since its combustion products are also highly toxic and one of them is a carcinogen. Extreme care must be exercised anytime emergency responders intervene in an incident of this type.

Follow all standard operating procedures for potential explosions and releases of toxic chemicals, flammable gases, and flammable and combustible liquids meticulously and according to your training.

In a release fire, keep all containers involving arsine cool with water delivered from unmanned appliances to prevent rupturing. Firefighters never should get between an approaching fire and containers of materials capable of exploding.

Since all containers holding Class A poison gas have no safety relief valve, they have no way to relieve internal pressure that has been increased by heat energy from the fire. Catastrophic failure resembling a BLEVE (boiling-liquid, expanding-vapor explosion) is virtually certain if the containers cannot be cooled. No emergency responders should be close enough to exploding containers to be harmed by the explosion, the resulting fire, or the toxic effects of the arsine or its combustion products.

Fight fires with carbon dioxide, dry chemicals, foam, or water. Contain all water and water products, since the water will be con-taminated with arsenic trioxide and possibly arsenic pentoxide. The environmental authorities will determine how much soil has to be removed. Dispose of all materials in accordance with federal, state, and local regulations.

Never handle gas containers (or, for that matter, those containing liquids) that have been involved in or exposed to a fire. The stress inflicted by the fire on these containers may be so great that any fire involvement could cause them to fail, releasing the materials within them. Any Class A poison container that has not failed during the fire will be full of the product and, therefore, extremely dangerous.

PROTECTIVE CLOTHING AND EQUIPMENT

Provide protection against exposure to skin contact and inhalation of arsine vapors. This means total face, hand, foot, and body protection. Consult manufacturers of total-encapsulating suits for their recommendations.

Whenever working in an atmosphere with arsine, it is always safest to use positive-pressure self-contained breathing apparatus with full face piece.

FIRST AID

If a victim has inhaled or is suspected of having inhaled arsine, rescuers (after donning proper protective clothing and equipment) should move him to fresh air immediately. Keep him calm and warm. If the victim`s breathing has stopped or become labored, administer artificial respiration, being aware that such action might expose the first-aid giver to the material in the victim`s lungs and/or vomit. Do not induce vomiting. Seek immediate medical attention.

Arsine is known to be absorbed through the skin. All cases of exposure require immediate treatment by a physician who is knowledgeable of this gas and its toxic properties, even if no symptoms are present.

For eye contact with the liquefied gas, flush the eyes immediately for at least 15 minutes, lifting the eyelids occasionally. Immediate medical attention is required.

For skin contact with the liquefied gas, gently apply tepid (not hot) water to the affected areas of the body. Remove clothing carefully so as not to aggravate damage to frostbitten skin.

In the highly unlikely event that a liquefied gas is ingested, severe frostbite damage will occur to the mouth and esophagus. Seek medical attention. n

SYNONYMS

arsenic hydride

arsenic trihydride

arseniuretted hydrogen

arsenious hydride

hydrogen arsenide

IDENTIFICATION NUMBERS AND RATING

CAS

(Chemical Abstract Services)

7784-42-1

STCC

(Standard Transportation Commodity Code)

4920135

RTECS

(Registry of Toxic Effects of Chemical Substances)

CG3850000

UN/NA

(United Nations/North America)

2188

DOT

(U.S. Department of Transportation)

poison gas, 2.3

IMO

(International Maritime Organization)

2.3, poison gas

FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He is an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of The Common Sense Approach to Hazardous Materials and an accompanying study guide, Combustibility of Plastics, and Chemical Data Notebook: A User`s Manual, published by Fire Engineering Books. He is an editorial advisory board member of fire Engineering.

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