CNG - Compressed Natural Gas Facility and Ventilation Requirements Questions and Answers

Question 1

A maintenance garage that services CNG vehicles is located in a cold climate. The manager needs to install a new heating system. According to NFPA 52, which of the following heating systems is prohibited from being installed directly within the service bay?

Accepted Answer

A direct-fired combustion air heater located below the ceiling.

Answer

NFPA 30A and NFPA 52 prohibit heating equipment that could present an ignition source in areas where flammable gases like CNG may be present. A direct-fired heater has an open flame and combustion process within the heated space, making it a significant and prohibited ignition source within the service bay.

Question 2

A facility is being upgraded to a major repair garage for CNG vehicles. Which statement correctly describes the requirements for the mechanical ventilation system's exhaust air intakes per NFPA 52?

Accepted Answer

They must be located at the highest practical point, within 12 inches of the ceiling.

Answer

Since CNG is lighter than air, it will rise and accumulate at the ceiling in the event of a leak. To effectively remove it, NFPA 52 requires that the exhaust (outlet) portion of the ventilation system be located at the highest point of the room to capture and expel the gas.

Question 3

A facility that performs minor maintenance on CNG vehicles, such as oil changes and tire rotations without opening the fuel system, is exempt from many requirements for major repair garages. This exemption is primarily because:

Accepted Answer

the maintenance performed does not involve the sealed fuel system.

Answer

NFPA 30A and NFPA 52 distinguish between major and minor repair garages. A key differentiator is whether the fuel system is opened or serviced. Facilities where fuel system integrity is not compromised are considered minor repair garages and have significantly less stringent requirements for ventilation, electrical classification, and heating systems.

Question 4

Which of the following is a key requirement for electrical equipment, such as lighting fixtures and junction boxes, located within 18 inches of the ceiling in a major CNG vehicle repair garage?

Accepted Answer

It must be rated for use in a Class I, Division 2 hazardous location.

Answer

According to NFPA 30A and NFPA 70 (National Electrical Code), the area within 18 inches of the ceiling in a major CNG repair garage is classified as a Class I, Division 2 hazardous location. This is due to the potential for lighter-than-air CNG to accumulate there. All electrical equipment in this zone must be specifically designed and rated (e.g., explosion-proof) to prevent it from becoming an ignition source.

Question 5

When a methane gas detection system is installed in a CNG maintenance facility, at what concentration must it activate an audible and visual alarm, according to NFPA 52?

Accepted Answer

At a concentration not exceeding 25% of the Lower Flammable Limit (LFL).

Answer

Gas detection systems are designed to provide an early warning well before a flammable atmosphere is created. NFPA 52 specifies that alarms must activate when the gas concentration reaches a level not exceeding 20-25% of the Lower Flammable Limit (LFL) to allow ample time for corrective action.

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG - Compressed Natural Gas Facility and Ventilation Requirements Questions and Answers