CNG - Compressed Natural Gas CNG Properties and Safety Questions and Answers

Question 1

In the event of a leak, how will compressed natural gas (CNG) behave in an open environment?

Accepted Answer

It will dissipate rapidly upwards into the atmosphere.

Answer

It will pool on the ground, creating a concentrated hazard.

Answer

It will remain close to the leak source, forming a visible cloud.

Answer

It will react with moisture in the air and become inert.

Question 2

A technician is inspecting a CNG vehicle involved in a minor collision. The technician notices a slight hissing sound and detects a gas leak near a cylinder valve. What should be the technician's IMMEDIATE action?

Accepted Answer

Close the manual shut-off valve for that specific cylinder, if accessible.

Answer

Attempt to tighten the valve fitting to stop the leak.

Answer

Drive the vehicle to a designated outdoor repair area.

Answer

Use a portable fan to disperse the leaking gas.

Question 3

Which of the following represents the correct flammability range for CNG in air?

Accepted Answer

5% to 15%

Answer

1% to 5%

Answer

15% to 25%

Answer

20% to 30%

Question 4

What is the primary function of a Pressure Relief Device (PRD) on a CNG cylinder?

Accepted Answer

To safely vent the gas in the event of high temperature or pressure.

Answer

To regulate the flow of gas to the engine.

Answer

To indicate the current pressure level inside the cylinder.

Answer

To prevent overfilling during the refueling process.

Question 5

Compared to gasoline, the auto-ignition temperature of CNG is significantly:

Accepted Answer

Higher, making it less likely to ignite from contact with hot surfaces.

Answer

Lower, making it easier to ignite.

Answer

Approximately the same.

Answer

Variable and dependent on atmospheric pressure.

Question 6

According to Federal Motor Vehicle Safety Standards (FMVSS) and industry best practices, how often must a detailed visual inspection of CNG cylinders be performed?

Accepted Answer

Every 36 months or 36,000 miles, whichever comes first.

Answer

Every 12 months or 12,000 miles.

Answer

Only after a vehicle fire or collision.

Answer

At every scheduled oil change.