Practice Test Geeks(CMC) Certified Marine Chemist Practice Test
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Flammable and Combustible Materials Flashcards

7 cards from real CMC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the approximate lower explosive limit (LEL) of gasoline vapor in air?

    Answer: 1.4%

    Gasoline vapor has an LEL of approximately 1.4% and a UEL of about 7.6% by volume in air.

  2. A flammable vapor with a density greater than air (vapor density >1) will tend to:

    Answer: Sink and accumulate in low-lying areas and bilges

    Vapors heavier than air (density >1) sink and pool in low areas such as bilges, pump rooms, and tank bottoms where they can form explosive concentrations.

  3. The upper explosive limit (UEL) represents the vapor concentration above which:

    Answer: The mixture is too rich in fuel to ignite

    Above the UEL the fuel-to-air ratio is too high (too rich) for combustion to be sustained; there is insufficient oxygen to support ignition.

  4. Hydrogen gas has an exceptionally wide flammable range. Its approximate LEL and UEL are:

    Answer: 4% and 75%

    Hydrogen has a LEL of 4% and a UEL of 75% by volume in air, making it one of the most easily ignitable and widely flammable gases encountered in marine environments.

  5. On a catalytic combustion CGI, a reading of 0% LEL in a tank recently discharged of petroleum cargo most likely indicates:

    Answer: The concentration may exceed the UEL, rendering the sensor ineffective

    Catalytic bead sensors can be poisoned or saturated above the UEL and may read zero in an over-rich atmosphere that is actually above the flammable range — a potentially fatal misreading.

  6. The flash point of a liquid is the minimum temperature at which:

    Answer: The liquid produces sufficient vapor to form an ignitable mixture near its surface

    Flash point is the lowest temperature at which a liquid generates enough vapor to flash momentarily when an ignition source is applied near the surface, as determined by standardized test methods.

  7. If a tank atmosphere registers 50% LEL on a combustible gas indicator, which statement is TRUE?

    Answer: The vapor concentration is at half the value of the lower explosive limit

    A 50% LEL reading means the actual vapor concentration is half of the LEL value — still below the LEL and therefore below the explosive range, though continued rise would be hazardous.