CNG Cylinder Inspection and Regulations 3 â Questions and Answers
Question 1: Beyond scheduled periodic inspections, what event triggers a mandatory out-of-schedule CNG cylinder inspection per NFPA 52?
- The vehicle odometer reaching 30,000 miles
- The cylinder being involved in any accident or fire event (Correct answer)
- The cylinder's exterior paint showing visible weathering or fading
- The vehicle changing ownership or operators
Correct answer: The cylinder being involved in any accident or fire event
NFPA 52 requires immediate cylinder inspection after any accident, fire, or event that may have damaged the fuel system, regardless of the scheduled inspection interval.
Question 2: Which NFPA standard specifically addresses compressed natural gas vehicular fuel systems?
- NFPA 30 (Flammable and Combustible Liquids Code)
- NFPA 54 (National Fuel Gas Code)
- NFPA 52 (Vehicular Natural Gas Fuel Systems Code) (Correct answer)
- NFPA 58 (LP-Gas Code)
Correct answer: NFPA 52 (Vehicular Natural Gas Fuel Systems Code)
NFPA 52 is the Vehicular Natural Gas Fuel Systems Code and is the primary standard governing CNG fuel systems installed on motor vehicles.
Question 3: As marked on a CNG cylinder, the term 'service pressure' refers to which of the following?
- The elevated pressure used during hydrostatic testing, above normal operation
- The pressure at which the thermally activated safety relief device opens
- The minimum pressure required for efficient engine combustion
- The maximum pressure the cylinder is designed for during normal fueling and operation (Correct answer)
Correct answer: The maximum pressure the cylinder is designed for during normal fueling and operation
Service pressure is the maximum operating pressure the cylinder is rated for during normal use, typically 3,000 or 3,600 psi for CNG vehicle cylinders.
Question 4: When a CNG cylinder reaches the manufacturer's specified service life limit, what is the only compliant action?
- Perform a hydrostatic test and recertify the cylinder for an additional 5 years
- Reduce the maximum fill pressure to 80% of the rated service pressure
- Permanently remove the cylinder from service and replace it with a new cylinder (Correct answer)
- Have a licensed engineer assess the cylinder and approve an extension in writing
Correct answer: Permanently remove the cylinder from service and replace it with a new cylinder
Once the service life limit is reached, the cylinder must be replacedâno hydrostatic test, engineering assessment, or pressure reduction can legally extend its service life.
Question 5: How must a condemned (rejected) CNG cylinder be rendered unusable before disposal?
- Attach a red warning tag and store in a locked hazardous materials facility
- Permanently disable it through methods such as drilling, crushing, or cutting the cylinder body (Correct answer)
- Return it to the manufacturer with full documentation of the rejection reason
- Sell it as scrap metal with a written disclaimer attached
Correct answer: Permanently disable it through methods such as drilling, crushing, or cutting the cylinder body
Condemned CNG cylinders must be permanently disabledâtypically by drilling or cuttingâto ensure they cannot be put back into pressurized service.
Question 6: Which record must be maintained for each CNG cylinder throughout its operational service life?
- A cylinder history record documenting all inspections, damage events, repairs, and service dates (Correct answer)
- Monthly pressure logs recorded at each refueling event
- Only the original purchase receipt and the initial installation certificate
- Engine and drivetrain maintenance records for the vehicle in which the cylinder is installed
Correct answer: A cylinder history record documenting all inspections, damage events, repairs, and service dates
NFPA 52 and industry standards require a complete cylinder history record to document inspection dates, damage events, and service life tracking.
Question 7: Which US federal agency administers FMVSS 304, the Federal Motor Vehicle Safety Standard for CNG fuel containers?
- EPA (Environmental Protection Agency)
- OSHA (Occupational Safety and Health Administration)
- NHTSA (National Highway Traffic Safety Administration) (Correct answer)
- CPSC (Consumer Product Safety Commission)
Correct answer: NHTSA (National Highway Traffic Safety Administration)
NHTSA (National Highway Traffic Safety Administration) administers FMVSS 304, which sets performance and labeling requirements for CNG fuel containers in motor vehicles.
CNG Cylinder Inspection and Regulations 3
Beyond scheduled periodic inspections, what event triggers a mandatory out-of-schedule CNG cylinder inspection per NFPA 52?