CNG Emergency Procedures and Response 2 — Questions and Answers
Question 1: What is the flammability range of natural gas in air?
- 1–4% by volume
- 5–15% by volume (Correct answer)
- 20–30% by volume
- 35–50% by volume
Correct answer: 5–15% by volume
Natural gas is flammable only when its concentration in air falls between approximately 5% and 15% by volume.
Question 2: When a CNG leak is detected inside a vehicle, what is the FIRST action the driver should take?
- Call 911 immediately from inside the vehicle
- Shut off the engine and exit the vehicle (Correct answer)
- Open all windows to ventilate the cabin
- Drive to the nearest service station
Correct answer: Shut off the engine and exit the vehicle
Shutting off the engine eliminates a major ignition source, and immediately exiting removes personnel from the hazard zone.
Question 3: In an enclosed building, released CNG will tend to accumulate:
- Near floor level
- At mid-height
- Near the ceiling (Correct answer)
- Uniformly throughout the space
Correct answer: Near the ceiling
Natural gas (methane) is lighter than air, causing it to rise and collect at ceiling level in enclosed spaces.
Question 4: The odorant added to natural gas to assist in leak detection smells like:
- Ammonia
- Rotten eggs or sulfur (Correct answer)
- Bleach
- Gasoline
Correct answer: Rotten eggs or sulfur
Mercaptan (ethyl mercaptan) is added to odorless natural gas and produces a distinctive rotten egg or sulfur odor.
Question 5: Compared to a gasoline spill, an outdoor CNG release is generally safer because:
- CNG burns at a lower temperature
- CNG is non-toxic at all concentrations
- CNG disperses upward rather than pooling on the ground (Correct answer)
- CNG requires a higher ignition energy
Correct answer: CNG disperses upward rather than pooling on the ground
Being lighter than air, CNG rises and dilutes in the atmosphere instead of forming a ground-level liquid pool that can spread fire.
Question 6: Which fire extinguisher class is appropriate for a natural gas (CNG) fire?
- Class A
- Class B (Correct answer)
- Class C
- Class K
Correct answer: Class B
CNG fires are classified as Class B (flammable gas) fires, which are addressed with CO2, dry chemical, or similar agents.
Question 7: Upon detecting a natural gas odor inside a building, you should:
- Turn on ventilation fans to disperse the gas
- Flip a light switch to illuminate the area
- Evacuate immediately without operating any electrical switches (Correct answer)
- Check the gas meter reading before leaving
Correct answer: Evacuate immediately without operating any electrical switches
Electrical switches can generate sparks that may ignite accumulated gas; immediate evacuation without activating any device is essential.
CNG Emergency Procedures and Response 2
What is the flammability range of natural gas in air?