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

0.1%

Answer

5.3%

Answer

15%

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

Rise and dissipate at the top of the tank

Answer

Mix evenly throughout the tank atmosphere

Answer

React preferentially with nitrogen in the atmosphere

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

The mixture becomes most easily ignited

Answer

The mixture is too lean in fuel to ignite

Answer

Ignition produces the most intense explosion

Question 4

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

Accepted Answer

4% and 75%

Answer

1.4% and 7.6%

Answer

4% and 44%

Answer

2.5% and 80%

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

The tank atmosphere is safe for hot work

Answer

The sensor requires recalibration before use

Answer

No flammable vapors remain in the tank

Question 6

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

Accepted Answer

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

Answer

The liquid begins to boil and generate large quantities of vapor

Answer

The liquid ignites spontaneously without an external ignition source

Answer

The vapor concentration reaches the UEL

Question 7

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

Accepted Answer

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

Answer

The tank poses an immediate explosion hazard from any spark

Answer

The atmosphere can be ignited directly without any heating

Answer

The vapor concentration is between the LEL and UEL