CTR 156CT Propane Practice Test

Why is propane heavier than air a safety concern?

It evaporates quickly and leaves no hazard It can accumulate in low spots and create a flammable vapor pocket It attracts moisture It reduces the risk of fire

Correct Answer:

It can accumulate in low spots and create a flammable vapor pocket

Explanation:

Propane’s density relative to air means leaks don’t rise but instead settle in low spots, such as basements, crawl spaces, or any low-lying area. When propane escapes, it forms a heavier-than-air vapor that can accumulate near the floor and create a flammable pocket. If this vapor reaches the right concentration in air and encounters an ignition source, it can ignite or explode. That’s why it’s a safety concern: a leak can quietly build up in places people don’t expect, turning a potential ignition into a dangerous fire or blast. The other ideas don’t describe the hazard correctly—propane isn’t inherently moisture-attracting, it doesn’t magically disappear or reduce fire risk, and the danger comes from the accumulating vapor, not from evaporation alone.

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