comes from oil or natural gas which is refined and 'cracked' by
heating ethane, propane or butane or naptha from oil. For example
the cracking process for methane may be represented as follows:
C2H2 + 3H2
by-products of these processes including hydrogen can be burned
to provide energy on site and propylene is reclaimed as is valuable.
These by-products are flammable but are not toxic nor cancer forming.