CNG - Compressed Natural Gas Emergency Procedures and Response Questions and Answers 1 — Questions and Answers
Question 1: A CNG vehicle is involved in a fire, and flames are impinging on the fuel cylinders. According to standard emergency response guidelines, what is the correct action to take regarding the application of water?
- Apply a fog stream to the top of the cylinders to keep the PRDs cool.
- Direct a straight stream of water at the base of the fire to suppress it.
- Do not apply water to the CNG cylinders, as it can prevent the PRDs from activating. (Correct answer)
- Apply water to the vehicle body to cool it and prevent fire spread to the cylinders.
Correct answer: Do not apply water to the CNG cylinders, as it can prevent the PRDs from activating.
Applying water to CNG cylinders exposed to fire is extremely dangerous because it can cool the cylinder and the thermally-activated Pressure Relief Devices (PRDs). This cooling effect can prevent the PRDs from reaching their activation temperature (typically 212°F - 220°F), which would otherwise allow them to safely vent the gas. If the PRD fails to activate, the pressure inside the cylinder can build to a catastrophic level, leading to a rupture or explosion. The standard procedure is to let the fire burn and protect exposures.
Question 2: A technician needs to perform maintenance that requires depressurizing the low-pressure side of a CNG fuel system. After closing the manual cylinder valves, what is the next critical step in the procedure?
- Immediately open the bleed valve at the regulator.
- Disconnect the fuel line at the engine.
- Start and run the engine until it stalls from lack of fuel. (Correct answer)
- Use a sniffer to check for leaks around the cylinder valves.
Correct answer: Start and run the engine until it stalls from lack of fuel.
After isolating the high-pressure cylinders by closing their manual valves, the correct procedure to depressurize the lines leading to the engine is to run the engine until it consumes the remaining fuel in the lines and stalls. This safely purges the low-pressure side of the system. Only after the engine has stalled and the ignition is secured should a technician proceed to bleed any minimal remaining pressure.
Question 3: A driver reports a strong 'rotten egg' smell inside the cab of a CNG vehicle while it is parked indoors. Which of the following actions should be taken IMMEDIATELY?
- Start the engine to burn off any excess gas.
- Turn on the ventilation fans to clear the air.
- Ventilate the area, eliminate ignition sources, and move the vehicle outdoors if safe to do so. (Correct answer)
- Use a spray bottle with soapy water to find the source of the leak.
Correct answer: Ventilate the area, eliminate ignition sources, and move the vehicle outdoors if safe to do so.
The 'rotten egg' smell is from the mercaptan odorant added to natural gas for leak detection. In an enclosed space, the primary concern is the accumulation of gas to a flammable concentration. The immediate priorities are to ventilate the area by opening doors and windows, eliminate all potential ignition sources (including electrical switches and fans), and then, if it can be done safely, move the vehicle to an open area. Starting the engine or turning on electrical fans would introduce a potential ignition source, which is extremely dangerous.
Question 4: During a post-accident inspection, a technician finds that a thermally-activated PRD has vented, which is evident by a missing fusible plug and soot around the vent line. What is the correct service procedure?
- Clean the valve and reinstall a new fusible plug.
- Replace the entire PRD assembly with a new, approved unit. (Correct answer)
- Test the PRD valve for leaks and reuse it if it seals properly.
- Cap the vent line and repressurize the system to check for other leaks.
Correct answer: Replace the entire PRD assembly with a new, approved unit.
Pressure Relief Devices (PRDs) are single-use safety devices. If a PRD activates due to temperature or pressure, it is not serviceable and must be completely replaced with a new unit approved by the cylinder manufacturer. Attempting to repair, clean, or reuse an activated PRD is a serious safety violation that compromises the integrity of the fuel system.
Question 5: A CNG vehicle has been partially submerged in flood water, with the water level reaching the bottom of the fuel cylinders. After retrieving the vehicle, which of the following is a mandatory first step before attempting to start or service the fuel system?
- Start the engine briefly to see if it runs.
- Pressurize the system at the fueling station to check for water intrusion.
- Disconnect the battery and perform a detailed inspection of the entire fuel system. (Correct answer)
- Drain the engine oil and check for water contamination.
Correct answer: Disconnect the battery and perform a detailed inspection of the entire fuel system.
After a vehicle has been submerged, especially in water that could contain contaminants, the first and most critical step is to ensure the vehicle is safe. This involves disconnecting the battery to prevent any electrical shorts or sparks. A thorough inspection of all fuel system components, including cylinders, valves, regulators, and electrical connections, must be performed by a qualified technician before any attempt is made to start the vehicle or pressurize the system. Water and debris can cause corrosion or damage that may not be immediately apparent.
Question 6: When responding to a CNG leak in an open-air environment like a parking lot, which factor is most critical for establishing a safe perimeter?
- The current pressure reading on the fuel gauge.
- The direction of the wind. (Correct answer)
- The type of CNG cylinder (Type 1-4).
- The time of day.
Correct answer: The direction of the wind.
Natural gas is lighter than air and will rise and dissipate. In an open-air environment, the wind will carry the dispersing gas cloud. Therefore, the most critical factor for establishing a safe perimeter is the wind direction. Emergency responders and technicians should position themselves and any necessary equipment upwind from the leak to avoid being in the path of the flammable gas mixture. Safe perimeters are typically established at a minimum of 100 feet.
CNG - Compressed Natural Gas Emergency Procedures and Response Questions and Answers 1
A CNG vehicle is involved in a fire, and flames are impinging on the fuel cylinders.
According to standard emergency response guidelines, what is the correct action to take regarding the application of water?