An excerpt from my training notes from many years ago:
Acetylene forms explosive compounds with copper, brass, copper salts, mercury/mercury salts, silver/silver salts and nitric acid. Under no circumstances should acetylene gas come in contact with unalloyed copper, except in a torch. Any contact of acetylene with high-alloyed copper piping will generate copper acetylide, which is extremely reactive and invariably results in a violent explosion. An explosion hazard will also occur if the gas comes into contact with silver bearing materials such as those used in silver-brazed pipeline joints
Acetylene is a highly reactive and inherently unstable, and is very sensitive to pressure and temperature and is extremely easy to ignite, the energy capable of igniting acetylene is lower than for any other fuel gas except hydrogen, hence the strict regulations governing the supply and storage of Acetylene gas bottles.