Which gas vented in an enclosed environment poses an explosion risk?

• A. Hydrogen
• B. Oxygen
• C. Nitrogen
• D. Argon

Answer: (A)

Gas vented into an enclosed space poses an explosion risk when the gas is flammable and can form an explosive mixture with air. Hydrogen fits this description best. It is extremely flammable and has a wide flammability range in air—roughly 4% to 75% by volume—so even small leaks can become explosive if an ignition source is present. It also has a very low ignition energy, meaning a tiny spark can ignite a hydrogen–air mixture. In an enclosed environment, leaked hydrogen can spread and accumulate, creating a dangerous situation quickly.

Oxygen, while it supports combustion, is not a fuel and won’t explode by itself without a fuel present. Nitrogen and argon are inert and do not burn or form explosive mixtures with air, so they don’t pose the same explosion risk in this context.