Mechanical Code…
Means and includes a material composed pre-dominantly of any of the following hydrocarbons or mixtures of them: propane, propylene, butane’s (normal butane or isobutane), and butylenes. When reference is made to liquefied petroleum gas in this code, it shall refer to liquefied petroleum gases in either the liquid or gaseous state.
(Uniform Mechanical Code® 214.0)