Odorless, although garlic-like or ''gassy" odor often detectable because of trace impurities

Extremely flammable gas; simple asphyxiant.

Acetylene is relatively nontoxic and has been used as an anesthetic. Inhalation of acetylene can be hazardous because of its action as a simple asphyxiant. Concentrations of about 10% in air cause slight intoxication, and levels of 20% in air may produce headaches and labored breathing. At higher concentrations (33% and above), acetylene acts as a narcotic, causing unconsciousness in 7 min or less, with rapid and full recovery normally seen on removal from exposure of less than several hours. Concentrations of acetylene above 50% in air can cause death by asphyxiation within 5 min. Commercially available acetylene may contain highly toxic impurities, including phosphine, arsine, and hydrogen sulfide; the presence of these impurities must be considered in setting acceptable exposure levels to acetylene. For example, the concentration of acetylene containing 95 ppm of phosphine impurity (which has a TLV of 0.3 ppm) should not exceed 3160 ppm to stay within the TLV for phosphine.

There is no evidence that acetylene is a human carcinogen or reproductive toxin.

Acetylene is a highly flammable gas and forms explosive mixtures with air over an unusually wide range of concentrations (2 to 80%). Acetylene can polymerize exothermically, leading to deflagration. With a very high positive free energy of formation, acetylene