CNG Facility and Ventilation Requirements 3 — Questions and Answers
Question 1: What minimum separation distance is typically required between a CNG dispensing unit and the nearest building opening such as a window or door?
- 5 feet
- 10 feet (Correct answer)
- 15 feet
- 20 feet
Correct answer: 10 feet
NFPA 52 requires CNG dispensers to be located at least 10 feet from building openings to prevent gas from entering the structure.
Question 2: In a CNG facility, what must automatically activate when a gas detector reaches 25% of the lower explosive limit (LEL)?
- Automatic suppression system
- An audible and visual alarm (Correct answer)
- Emergency gas supply shutoff
- Emergency lighting system
Correct answer: An audible and visual alarm
At 25% LEL, gas detection systems must trigger audible and visual alarms to alert personnel before concentrations reach dangerous levels.
Question 3: Which of the following facility configurations requires the highest level of ventilation per NFPA 52?
- Open-sided canopy CNG dispenser island
- Partially enclosed CNG fueling area with two open walls
- Fully enclosed CNG vehicle storage and maintenance building (Correct answer)
- Outdoor CNG compressor pad with no roof
Correct answer: Fully enclosed CNG vehicle storage and maintenance building
Fully enclosed buildings trap gas most readily and therefore require the most stringent mechanical ventilation to maintain safe atmospheric conditions.
Question 4: What action must occur automatically when a gas detector in a CNG facility reaches 50% of the lower explosive limit?
- Only an alarm sounds; no automatic shutoff is required
- The compressor slows to 50% capacity
- Emergency shutoff of gas supply to the facility (Correct answer)
- Sprinkler system activates
Correct answer: Emergency shutoff of gas supply to the facility
At 50% LEL, NFPA 52 requires automatic emergency shutoff of the gas supply to prevent further accumulation and potential ignition.
Question 5: CNG storage cylinders located inside a building must be stored in an area that meets which ventilation requirement?
- No special ventilation required if cylinders are within date
- Ventilated to the outside at both high and low points (Correct answer)
- Only low-point ventilation is required since gas is heavy
- A positive-pressure clean room environment
Correct answer: Ventilated to the outside at both high and low points
Storage areas for CNG cylinders must be ventilated at both high and low points to address any leakage regardless of whether the gas rises or condenses with heavier air components.
Question 6: What is the purpose of classifying areas around CNG dispensers as hazardous locations?
- To restrict public access to the fueling area
- To mandate special electrical equipment that won't ignite released gas (Correct answer)
- To increase insurance premiums for the facility operator
- To limit the quantity of fuel that can be stored on site
Correct answer: To mandate special electrical equipment that won't ignite released gas
Hazardous location classification ensures all electrical devices in the area are rated to prevent sparks that could ignite any CNG release.
Question 7: How far must the exhaust ventilation outlet of a CNG compressor enclosure be located from any ignition source?
- 3 feet
- 5 feet
- 10 feet (Correct answer)
- 15 feet
Correct answer: 10 feet
Ventilation exhaust outlets must discharge at least 10 feet from any ignition source to prevent expelled gas from igniting near the building.
CNG Facility and Ventilation Requirements 3
What minimum separation distance is typically required between a CNG dispensing unit and the nearest building opening such as a window or door?