CNG Emergency Procedures and Response 3 — Questions and Answers
Question 1: What is the function of a pressure relief device (PRD) on a CNG cylinder?
- Maintain consistent fuel pressure during normal operation
- Vent gas to prevent cylinder rupture from excessive heat or pressure (Correct answer)
- Alert the driver when the fuel level is low
- Prevent overfilling during the fueling process
Correct answer: Vent gas to prevent cylinder rupture from excessive heat or pressure
PRDs are thermally and/or pressure-activated safety devices that release gas to prevent catastrophic cylinder failure under abnormal conditions.
Question 2: In the context of CNG emergencies, BLEVE stands for:
- Basic Level Emergency Vehicle Evacuation
- Boiling Liquid Expanding Vapor Explosion (Correct answer)
- Below Lower Explosive Vapor Emission
- Bulk Liquid Emergency Venting Escape
Correct answer: Boiling Liquid Expanding Vapor Explosion
A BLEVE occurs when a pressurized container fails catastrophically, releasing a rapidly expanding vapor cloud that can ignite explosively.
Question 3: What is the recommended minimum safe distance for first responders from a CNG vehicle fully engulfed in fire?
- 25 feet
- 50 feet
- 100 feet
- 300 feet (Correct answer)
Correct answer: 300 feet
A 300-foot safety perimeter is recommended for CNG vehicle fires due to the risk of PRD venting, cylinder rupture, and projectile hazards.
Question 4: Why should water be continuously applied to CNG cylinders during a vehicle fire?
- To extinguish the CNG flame directly
- To cool cylinders and delay or prevent PRD activation or structural failure (Correct answer)
- To neutralize the natural gas odorant
- To prevent toxic fume release
Correct answer: To cool cylinders and delay or prevent PRD activation or structural failure
Cooling cylinders with water reduces heat buildup that would otherwise trigger PRD venting or compromise cylinder structural integrity.
Question 5: After a CNG vehicle is involved in a collision, the driver should immediately:
- Leave the engine running to maintain emergency communications
- Shut off the fuel system and exit the vehicle (Correct answer)
- Drive to a safe location before stopping
- Open the hood to inspect the CNG cylinder
Correct answer: Shut off the fuel system and exit the vehicle
Shutting off the CNG fuel system after a collision eliminates the gas supply and significantly reduces fire and explosion risk.
Question 6: Which condition requires a CNG cylinder to be immediately removed from service?
- Cylinder pressure reading 100 psi below rated maximum
- Minor surface scratches on the outer protective jacket
- Visible bulging, deep denting, or evidence of fire/heat damage (Correct answer)
- Cylinder age exceeding five years from manufacture
Correct answer: Visible bulging, deep denting, or evidence of fire/heat damage
Physical deformation, deep denting, bulging, or thermal damage compromises the structural integrity of a CNG cylinder, making it unsafe to use.
Question 7: When first responders arrive at a CNG vehicle accident, their FIRST priority should be:
- Determining the cause of the accident
- Interviewing witnesses for their reports
- Securing the scene and identifying CNG system components (Correct answer)
- Contacting the vehicle manufacturer
Correct answer: Securing the scene and identifying CNG system components
Scene security and identification of CNG system components allow responders to assess fire and explosion risks before taking further action.
CNG Emergency Procedures and Response 3
What is the function of a pressure relief device (PRD) on a CNG cylinder?