Which gas is explicitly stated as usable as an alternative fuel for OFC?

• A. Propane
• B. Acetylene
• C. Natural gas
• D. Helium

Answer: (C)

The question tests knowing which gas the standards explicitly allow as an alternative fuel for oxy-fuel cutting (OFC). Natural gas is the gas that is explicitly stated as usable as an alternative fuel for OFC, which is why it’s the best choice here. Helium isn’t a fuel at all—it's inert and used for shielding or purge, not combustion. Propane and acetylene are common fuels, but the prompt points to the gas specifically named as an alternative in the OFC guidelines, and natural gas fits that criterion.