UN 1560 — Arsenic trichloride

Arsenic trichloride, also known as arsenous trichloride or arsenous chloride, is a chemical compound with the CAS number 7784-34-1. It is classified as a DOT class 6 substance, which means it is toxic and/or corrosive. Arsenic trichloride is widely used in the production of semiconductors, pesticides, and pharmaceuticals. As a result, firefighters may encounter arsenic trichloride during industrial fires or spills. The scale of production and transport of arsenic trichloride is significant, with thousands of tons being manufactured and shipped every year. Arsenic trichloride is a colorless to pale yellow oily liquid with a pungent, acrid odor. It is highly reactive with water, producing toxic and corrosive hydrogen chloride gas and arsenic acid.

Hazard overview: Arsenic trichloride is a highly toxic and corrosive substance that can cause severe injury through inhalation, ingestion, or skin contact. The LC50 value for arsenic trichloride is 10-50 mg/m3, and the IDLH value is 10 ppm. Arsenic trichloride can also react violently with water, producing toxic and corrosive gases, including hydrogen chloride and arsenic acid. The vapor density of arsenic trichloride is 7.0, which is much heavier than air, making it a significant hazard in enclosed spaces. In the worst-case scenario, arsenic trichloride can cause severe burns, respiratory problems, and even death. Firefighters should be aware of the potential for arsenic trichloride to produce white clouds of hydrochloric acid and arsenic trioxide in moist air.

Response guidance: In the event of an arsenic trichloride spill, the isolation area should be at least 25-50m in all directions, according to ERG 157. For large spills, the isolation area should be 100m, and evacuation should be considered up to 300m downwind. If a tank or rail car is involved in a fire, the isolation area should be 800m in all directions. Firefighters should use dry chemical, CO2, or dry sand to suppress the fire, but should not use water or foam due to the violent reaction with arsenic trichloride. Decontamination procedures should include washing the affected area with soap and water, and CHEMTREC should be contacted immediately. Evacuation zones should be established, and firefighters should stay upwind, uphill, and/or upstream of the spill.

Firefighter training notes: Firefighters responding to an arsenic trichloride spill should be trained in the hazards of toxic and corrosive substances, including the risks of skin absorption and inhalation. A common tactical error when responding to an arsenic trichloride spill is not wearing the correct PPE, which can result in severe injury or death. Firefighters should also be aware of the potential for arsenic trichloride to react violently with water, and should be trained in the use of dry chemical and other suppression agents. The ICS position of the firefighter should be aware of the potential for arsenic trichloride to spread and contaminate other areas, and should establish a plan for containment and decontamination.

Regulatory context: Arsenic trichloride is classified as a DOT class 6 substance, which means it is toxic and/or corrosive. The OSHA PEL for arsenic trichloride is 0.01 mg/m3, and the TLV is 0.01 mg/m3. Arsenic trichloride is also listed on the CERCLA list, which means it is a hazardous substance that requires special handling and disposal procedures.

Storage & handling: Arsenic trichloride should be stored in a cool, dry place, away from incompatible materials such as strong oxidizers and acids. The temperature limit for arsenic trichloride storage is 30C (86F), and the ventilation standard should be designed to prevent the accumulation of arsenic trichloride vapors. The container type for arsenic trichloride storage should be made of a material that is resistant to arsenic trichloride, such as stainless steel or glass.