UN 1001 — Acetylene, dissolved

Acetylene, dissolved, is a highly flammable and explosive gas, classified as a DOT Class 2 substance. It is widely used in industrial processes, such as welding and cutting, and is also used as a fuel. First responders may encounter acetylene in various settings, including industrial facilities, transportation accidents, and storage facilities. The scale of production and transport of acetylene is significant, with millions of tons being produced and transported each year. Acetylene is also known by its synonyms, including Ethyne, Narcylen, and Vinylene. The chemical identity of acetylene is characterized by its CAS number, 74-86-2.

Hazard overview: Acetylene is extremely flammable and will form explosive mixtures with air. It will be easily ignited by heat, sparks, or flames, and may react explosively even in the absence of air. The vapor density of acetylene is 0.9, which is lighter than air, and it has a faint ethereal odor when pure, and a garlic-like odor when impure. The LC50 of acetylene is not well-established, but it is known to be highly toxic and may cause severe injury or death if inhaled or absorbed through the skin. In a worst-case scenario, acetylene may ignite spontaneously and cause a large-scale explosion, resulting in significant damage and loss of life.

Response guidance: In the event of an acetylene spill or leak, first responders should isolate the area to a distance of 800m in all directions, and evacuate the area to a distance of 1600m downwind if a tank or rail car is involved in a fire. The correct suppression agent for acetylene is CO2, dry chemical, or water spray for cooling cylinders, and no foam is needed for gas. Decontamination procedures should be followed, and CHEMTREC should be contacted for assistance. It is also important to note that acetylene may react explosively with other substances, such as disilane and silane, and may ignite spontaneously in air.

Firefighter training notes: First responders should be trained to recognize the hazards of acetylene, including its extreme flammability and explosive potential. They should also be trained to use the correct PPE and suppression agents, and to follow decontamination procedures. A common tactical error when responding to an acetylene incident is to underestimate the potential for explosion, and to fail to isolate the area sufficiently. ICS position needs and mutual aid criteria should also be considered when responding to an acetylene incident.

Regulatory context: Acetylene is classified as a DOT Class 2 substance, and is subject to the regulations of the Department of Transportation. The OSHA PEL for acetylene is not well-established, but it is known to be highly toxic and may cause severe injury or death if inhaled or absorbed through the skin. Acetylene is also listed on the CERCLA list, which requires special handling and reporting procedures.

Storage & handling: Acetylene should be stored in a well-ventilated area, away from heat sources and ignition sources. The temperature limit for acetylene storage is not well-established, but it should be kept away from incompatible materials, such as disilane and silane. The container type for acetylene storage is typically a cylinder, and it should be handled with caution to prevent accidents and injuries.