You can fit compression fittings onto copper pipes or PVC of various sizes for some gas applications. Gas can be flammable or nonflammable. Flammable gas such as LPG (liquefied petroleum gas) or LNG (liquefied natural gas) runs through pipes as a liquid and then changes into gas when released into a burner. OSHA regulates the use of pipes and fittings for flammable liquids and gases.
PVC for Gas
Low-pressure, nonflammable gas such as oxygen and nitrogen can travel through PVC and use compression fittings. Hospitals use PVC tubing on oxygen lines to assist patients in breathing. Telecommunications sites use PCV tubing to fill cables from transmitters to antennas with nitrogen or dry air to prevent moisture build-up. Fit compression fittings on flexible PVC tubing where you will need to move things around. Fit compression fittings on rigid PVC pipes for stationary applications. Never try to use a compression fitting made for copper on PVC pipe or tubing.
Copper for Gas
Although compression fittings for copper usually are used for water, there is no reason why you can’t use them for low-pressure, nonflammable gas. The fittings have soft brass ferrules that compress against the copper pipe and the inside walls of the fitting as you tighten the nut onto the fitting body. Because these fittings can’t withstand stress or motion, don’t fit them onto implements you need to move around. Never try to use a brass compression fitting on PVC pipe or tubing.
In section 1910.110(b)(8)(iv) of “Storage and Handling of Liquefied Petroleum Gases,” OSHA requires that “pipe joints may be screwed, flanged, welded, soldered, or brazed with a material having a melting point exceeding 1,000 deg. F. Joints on seamless copper, brass, steel, or aluminium alloy gas tubing shall be made by means of approved gas tubing fittings, or soldered or brazed with a material having a melting point exceeding 1,000 deg. F.” Since OSHA only includes “screwed” and “flanged” and not compression fittings in this requirement, you cannot use them with copper tubing or with PVC for LP gas