Acetylene (C2H2) is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities.
Acetylene is a flammable gas which easily creates an explosive mixture. Its explosive concentration in the air is 2-81% in volume. In addition to the low pressure of the regulator, the increase in gas acetylene pressure should not be allowed above 1.5 atmospheres. Do not use acetylene connections made of clean copper. Do not use silver fighting for repair. Contact between mercury and zinc and acetylene should be avoided. Acetylene cylinders must be stored upright, with the valve facing up. Do not transfer acetylene from one roll to another and should not be mixed with any other gas. Slowly remove the acetylene gas from the cylinder. In the case of overheating of an acetylene cylinder, it must be cooled in a stream of water, in abundance. When a flame breaks out in the cylinder's pressure regulator, immediately close the cylinder valve (if possible). At the end of the work, it is necessary to leave in the acetylene cylinder, pressure of 1/2 atmosphere in the winter and 1 atmosphere in the summer. It is recommended to use dedicated flame absorbers for this gas.
At atmospheric pressure, acetylene cannot exist as a liquid and does not have a melting point.
The triple point on the phase diagram corresponds to the melting point (−80.8 °C) at the minimal pressure at which liquid acetylene can exist (1.27 atm).
At temperatures below the triple point, solid acetylene can change directly to the vapour (gas) by sublimation.
The sublimation point at atmospheric pressure is −84.0 °C.