Which statement best describes the hazard of hydrogen gas in these scenarios?

• A. Hydrogen gas is not flammable.
• B. Hydrogen gas can form explosive mixtures with air.
• C. Hydrogen gas is heavier than air and pools in low areas.
• D. Hydrogen gas cannot be ignited.

Answer: (B)

The main hazard with hydrogen gas is its ability to form explosive mixtures with air. Hydrogen is highly flammable and can ignite from a small ignition source—like a spark or heat—so leaks can become dangerous very quickly. It has a wide flammability range in air, meaning many concentrations of hydrogen mixed with air can ignite, and the resulting combustion can be rapid or even detonate in confined spaces, causing significant blast and fire hazards. Because hydrogen is much lighter than air, leaks tend to rise and accumulate near ceilings, not pool in low areas, which affects how and where it can ignite and how it should be vented and detected. The statements claiming hydrogen isn’t flammable or can’t be ignited are incorrect, and the idea that it’s heavier than air and pools in low areas is also false.