CNG - Compressed Natural Gas Cylinder Inspection and Regulations Questions and Answers 1 — Questions and Answers
Question 1: According to U.S. DOT regulations (FMVSS 304), what is the mandatory detailed visual inspection interval for CNG cylinders on a vehicle with a Gross Vehicle Weight Rating (GVWR) of 8,500 pounds?
- Every 12 months.
- Every 24 months or 24,000 miles, whichever comes first.
- Every 36 months or 36,000 miles, whichever comes first. (Correct answer)
- Only after a collision or fire.
Correct answer: Every 36 months or 36,000 miles, whichever comes first.
U.S. Department of Transportation's Federal Motor Vehicle Safety Standard (FMVSS) No. 304 specifies that for vehicles with a GVWR of less than 10,000 pounds, CNG cylinders must undergo a detailed visual inspection at least every 3 years (36 months) or 36,000 miles, whichever occurs first.
Question 2: A technician is performing a detailed visual inspection on a Type 4 CNG cylinder. Which of the following findings would be the LEAST critical in determining whether the cylinder should be condemned?
- A deep gouge in the composite wrap with loose fibers.
- Discoloration and blistering on the cylinder surface near the exhaust pipe.
- Minor surface scratches on the protective gel coat that do not penetrate to the fiber wrap. (Correct answer)
- A dent with a sharp crease on the dome of the cylinder.
Correct answer: Minor surface scratches on the protective gel coat that do not penetrate to the fiber wrap.
Minor surface scratches on the protective gel coat of a Type 4 cylinder that do not expose or damage the underlying composite fiber wrap are generally considered acceptable. However, deep gouges with loose fibers, signs of heat damage (discoloration/blistering), and dents with sharp creases are all serious conditions that compromise the structural integrity and would likely require the cylinder to be removed from service.
Question 3: A fleet manager discovers that a CNG vehicle's cylinder has passed its manufacturer-specified expiration date, which is clearly marked on the label. What is the correct course of action?
- Send the cylinder for hydrostatic re-testing to extend its service life.
- Continue using the cylinder until the next scheduled vehicle maintenance.
- Have a qualified technician defuel, decommission, and destroy the cylinder. (Correct answer)
- Perform a detailed visual inspection; if it passes, it can remain in service for one more year.
Correct answer: Have a qualified technician defuel, decommission, and destroy the cylinder.
CNG cylinders have a finite, manufacturer-determined service life and cannot be requalified or have their life extended once they reach the expiration date. The only safe and compliant action is to have the cylinder properly and safely removed from service, which includes defueling, decommissioning, and rendering it unusable (destroying it) to prevent accidental reuse.
Question 4: Which of the following standards is the most comprehensive for the design, manufacture, and testing of CNG vehicle fuel containers in North America?
- ISO 19078
- FMVSS 304
- NFPA 52
- CSA/ANSI NGV 2 (Correct answer)
Correct answer: CSA/ANSI NGV 2
While FMVSS 304 sets the minimum legal requirements in the U.S. and NFPA 52 covers fuel system installation, the CSA/ANSI NGV 2 standard is widely recognized as the most comprehensive standard for the material, design, manufacturing, and testing of the CNG cylinders themselves.
Question 5: During a routine pre-trip inspection, a driver notices that the protective shield covering a CNG cylinder is dented and pushed inward after hitting road debris. What is the appropriate immediate action?
- Note the damage in the logbook and have it checked at the next scheduled service.
- Remove the vehicle from service immediately until a detailed visual inspection can be performed by a qualified inspector. (Correct answer)
- Attempt to pull the dent out of the shield and continue with the route.
- Continue driving but avoid refueling the vehicle until the shield is repaired.
Correct answer: Remove the vehicle from service immediately until a detailed visual inspection can be performed by a qualified inspector.
Any damage to a cylinder's protective shield, especially a dent, indicates a potential impact to the cylinder itself. Standard safety procedure requires the vehicle to be taken out of service immediately for a detailed visual inspection by a qualified CNG fuel system inspector to assess for any underlying cylinder damage.
Question 6: A CNG-powered commercial bus with a GVWR of 33,000 pounds is involved in a minor collision with no visible damage to the fuel system. According to regulations, what inspection is required?
- A cursury visual inspection by the driver is sufficient.
- No inspection is needed if there is no audible leak.
- A detailed visual inspection of the cylinder and fuel system by a qualified inspector. (Correct answer)
- The cylinders must be hydrostatically tested before the vehicle returns to service.
Correct answer: A detailed visual inspection of the cylinder and fuel system by a qualified inspector.
Federal regulations (FMVSS 304) and industry best practices mandate that a detailed visual inspection of the CNG cylinders must be performed by a qualified inspector after any motor vehicle accident or fire, regardless of the vehicle's GVWR or the apparent severity of the incident.
CNG - Compressed Natural Gas Cylinder Inspection and Regulations Questions and Answers 1
According to U.S.
DOT regulations (FMVSS 304), what is the mandatory detailed visual inspection interval for CNG cylinders on a vehicle with a Gross Vehicle Weight Rating (GVWR) of 8,500 pounds?