Which type of gas used in plumbing is lighter than air?

• A. Propane
• B. Butane
• C. Natural Gas
• D. Methane

Answer: (C)

Gas buoyancy is key here: a gas that is lighter than air will rise and disperse if it leaks, while a heavier gas will tend to collect in low areas. Natural gas is used in plumbing as a fuel and is mainly methane, which has a density lower than air. Because methane is lighter than air, natural gas leaks tend to rise and dissipate instead of pooling at floor level. Propane and butane, on the other hand, are heavier than air and would collect in lower spaces if leaked. Methane itself is lighter than air, and natural gas shares that buoyant property, making natural gas the gas lighter than air.