CMC Flammable and Combustible Materials 2

Question 1

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

Accepted Answer

1.4%

Answer

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

Question 2

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

Accepted Answer

Sink and accumulate in low-lying areas and bilges

Answer

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.

Question 3

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

Accepted Answer

The mixture is too rich in fuel to ignite

Answer

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.

Question 4

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

Accepted Answer

4% and 75%

Answer

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.

Question 5

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

Accepted Answer

The concentration may exceed the UEL, rendering the sensor ineffective

Answer

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.

(CMC) Certified Marine Chemist Practice Test

(CMC) Certified Marine Chemist Practice Test

CMC Flammable and Combustible Materials 2