What gas should never be used to test gas lines?

Oxygen should never be used to test gas lines due to its highly reactive nature, especially in the presence of flammable gases. When testing gas lines, the primary goal is to ensure that there are no leaks which could lead to dangerous situations. Oxygen can significantly increase the risk of fire or explosion if it comes into contact with any flammable gas that may be present in the system.

Additionally, using oxygen can lead to false readings in the pressure tests, making it challenging to accurately assess the integrity of the gas lines. In areas where a gas mixture is involved, introducing pure oxygen could alter the properties of the gas, potentially leading to unexpected reactions.

On the other hand, nitrogen and helium are safely used in testing because they are inert gases that do not react with the materials in the gas lines or with other substances present. Carbon dioxide, while also not typically recommended, poses significantly less risk than oxygen in terms of fire hazards.

Therefore, using oxygen presents not only safety challenges but also compromises the reliability of the integrity testing of gas lines.