CNG Fueling Station Operations 3 — Questions and Answers
Question 1: If a CNG fire ignites at a fueling station, what is the FIRST recommended action?
- Attempt to extinguish the flame with a dry chemical extinguisher
- Activate the emergency fuel shutoff and evacuate the area (Correct answer)
- Spray water on surrounding equipment to cool it
- Cover the flame source with a fire blanket
Correct answer: Activate the emergency fuel shutoff and evacuate the area
The first priority in a CNG fire is activating the emergency shutoff to cut fuel supply, followed by immediate evacuation and calling 911 — extinguishing a gas fire without stopping flow creates an explosive cloud.
Question 2: What is the lower explosive limit (LEL) of natural gas (methane) in air?
- 1%
- 3%
- 5% (Correct answer)
- 10%
Correct answer: 5%
Methane's LEL is approximately 5% by volume in air; below this concentration, the mixture is too lean to ignite.
Question 3: Which NFPA code is the primary national standard for CNG vehicular fueling system safety?
- NFPA 30
- NFPA 30A
- NFPA 52 (Correct answer)
- NFPA 58
Correct answer: NFPA 52
NFPA 52, Vehicular Natural Gas Fuel Systems Code, is the primary standard covering CNG fueling station design, installation, and operational safety.
Question 4: At what percentage of the LEL should a fixed combustible gas detector alarm at a CNG station?
- 5% LEL
- 10% LEL
- 20% LEL (Correct answer)
- 50% LEL
Correct answer: 20% LEL
Industry practice sets alarm thresholds at 20% LEL to provide early warning well before gas concentrations reach an ignitable range.
Question 5: What type of portable fire extinguisher is most appropriate for use at a CNG fueling station?
- Water-type extinguisher
- CO2 extinguisher
- Dry chemical ABC-rated extinguisher (Correct answer)
- Foam extinguisher
Correct answer: Dry chemical ABC-rated extinguisher
ABC dry chemical extinguishers are appropriate at CNG stations because they handle ordinary combustibles, flammable gases/liquids, and energized electrical equipment.
Question 6: What is the correct action if a CNG dispenser hose coupling begins leaking during an active fueling operation?
- Continue fueling at a reduced flow rate
- Stop fueling immediately and depressurize the hose before inspecting (Correct answer)
- Tighten the connection while gas is still flowing
- Complete the fill and replace the hose afterward
Correct answer: Stop fueling immediately and depressurize the hose before inspecting
A leaking coupling requires an immediate fueling stop and full hose depressurization before any inspection or repair is attempted.
Question 7: Under NFPA 52, what is the minimum required distance between a CNG dispenser and a building opening (door, window, or air intake)?
- 5 feet
- 10 feet (Correct answer)
- 20 feet
- 50 feet
Correct answer: 10 feet
NFPA 52 requires CNG dispensers to be located at least 10 feet from building openings to prevent gas accumulation inside structures.
CNG Fueling Station Operations 3
If a CNG fire ignites at a fueling station, what is the FIRST recommended action?