A new piping system may NOT be tested with which gas?

Testing a new piping system with oxygen is not permitted, primarily due to safety concerns. Oxygen is a highly reactive gas that can significantly increase the risk of combustion if it comes into contact with hydrocarbons or other materials that may be present or introduced into the piping system. In high concentrations, oxygen can turn a normal environment into one that is hazardous, leading to potential explosions or fires.

In contrast, nitrogen is commonly used for pressure testing because it is inert and does not react with most materials, making it a safe choice. Hydrogen, while also flammable, can be utilized in controlled environments, and propane, being the gas intended for use in the piping system, is often tested in instances where it’s contained or where safety measures are in place to manage its characteristics. However, using oxygen poses unique risks that make it unsuitable for testing new piping systems, hence it's not allowed.