MCC-NH Gas Fitters Practice Exam

Which of the following is NOT an approved test medium gas?

1. Carbon Dioxide

2. Nitrogen

3. Oxygen

4. Argon

The correct answer is: Oxygen

The use of approved test media for gas systems is crucial for ensuring safety during pressure testing. In this context, the primary purpose of a test medium is to verify that a gas system is leak-free and can safely hold pressure without introducing any materials that could be hazardous or reactive. Oxygen, while commonly used in various industrial applications such as welding and to support combustion, is not typically used as a test medium for gas systems. This stems from its highly reactive nature, especially when combined with flammable materials or in high concentrations, where it can pose significant risks of combustion or explosion. Therefore, using oxygen as a testing medium could lead to dangerous situations if leaks are present. In contrast, carbon dioxide, nitrogen, and argon are considered inert or non-reactive in most scenarios, making them safer and more suitable options for pressure testing gas systems. They do not react with the materials commonly found in gas installations, therefore minimizing the risk during the testing process. This characteristic is what makes nitrogen a prevalent choice for pressure testing, as it is readily available and helps ensure a safe environment during the testing phase.