DOT Class / Label: 2.3 - 100%
Flammable Limits: 2.1 / Flammable
Molecular Weight: 26.04
Specific Gravity: 0.91 @ 70oF
Specific Volume: 14.5 ft3./lb @ 60oF
CGA Valve Outlet:       510
CAS Registry No.:  74-86-2
UN Number: 1001





Acetylene is simplest member of unsaturated hydrocarbons called alkynes or acetylenes. Most important of all starting materials for organic synthesis. Usefulness of acetylene is partly due to the variety of addition reactions which its triple bond undergoes and partly due to the fact that its weakly acidic hydrogen atoms are replaceable by reaction with strong bases to form acetylide salts.



Acetylene is a compressed gas that is used as a fuel and is stored in a liquid state. When the valve is opened and pressure is released a portion of the liquid turns to gas. This gas is then used by the device that the cylinder is connected to. Because acetylene is stored as a liquid, the cylinder will only work properly if the tank is used in the upright position. Using or storing the tank in any other position can be extremely dangerous. According to the U.S. Department of Labor General Industry Digest, 1994 (Revised):

“Acetylene cylinder shall be stored and used in a vertical, valve-end-up position only.”

The actual OSHA standard, 1,910.253(b)(3)(ii) says, Acetylene cylinders shall be stored valve end up.

Because acetylene is extremely sensitive to pressure, it should never be used at more than 15 p.s.i. Many workers have been injured or killed when using oxygen-acetylene welder and cutters because they allowed their rig to subject the acetylene fuel to pressures greater than 15 p.s.i. The actual OSHA standard, 1,910.253(a)(2) says maximum pressure, under no condition, shall acetylene be generated, piped (except in approved cylinder manifolds) or utilized at a pressure in excess of 15 psig (103 kPa gauge pressure) or 30 psia (206 kPa absolute). This requirement is not intended to apply to storage of acetylene dissolved in a suitable solvent in cylinders manufactured and maintained according to U.S. Department of Transportation requirements, or to acetylene for chemical use. The use of liquid acetylene shall be prohibited.



Pure acetylene is a colourless gas with a pleasant odour; as prepared from calcium carbide it usually contains traces of phosphine that cause an unpleasant garlic-like odour. Acetylene can be decomposed to its elements with the liberation of heat. The decomposition may or may not give rise to explosions, depending on conditions. Pure acetylene under pressure in excess of about 15 pounds per square inch or in liquid or solid form explodes with extreme violence.

Mixtures of air and acetylene are explosive over a wide range, from about 2.5% air in acetylene to about 12.5% acetylene in air. When burned with the correct amount of air, acetylene gives a pure, white light, and for this reason it was at one time used for illumination in locations where electric power was not available, e.g., buoys, miners’ lamps, and road signals.

The combustion of acetylene produces a large amount of heat, and, in a properly designed torch, the oxyacetylene flame attains the highest flame temperature (about 6,000°F, or 3,300°C) of any known mixture of combustible gases.

The hydrogen atoms in acetylene can be replaced by metallic elements to form acetylides–e.g., acetylides of silver, copper, or sodium. The acetylides of silver, copper, mercury, and gold are detonated by heat, friction, or shock. In addition to its reactive hydrogen atom, the carbon-carbon triple bond can readily add halogens, halogen acids, hydrogen cyanide, alcohols, amines, and amides. Acetylene can also add to itself or to aldehydes and ketones. Many of the reactions mentioned here are used for the commercial manufacture of various industrial and consumer products, such as acetaldehyde, the synthetic rubber neoprene, water-base paints, vinyl fabric and floor coverings, dry-cleaning solvents, and aerosol insecticide sprays. Acetylene is produced by any of three methods: by reaction of water with calcium carbide, by passage of a hydrocarbon through an electric arc, or by partial combustion of methane with air or oxygen.