CNG - Compressed Natural Gas Cylinder Inspection and Regulations 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?

Accepted Answer

Every 36 months or 36,000 miles, whichever comes first.

Answer

Every 12 months.

Answer

Every 24 months or 24,000 miles, whichever comes first.

Answer

Only after a collision or fire.

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?

Accepted Answer

Minor surface scratches on the protective gel coat that do not penetrate to the fiber wrap.

Answer

A deep gouge in the composite wrap with loose fibers.

Answer

Discoloration and blistering on the cylinder surface near the exhaust pipe.

Answer

A dent with a sharp crease on the dome of the cylinder.

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?

Accepted Answer

Have a qualified technician defuel, decommission, and destroy the cylinder.

Answer

Send the cylinder for hydrostatic re-testing to extend its service life.

Answer

Continue using the cylinder until the next scheduled vehicle maintenance.

Answer

Perform a detailed visual inspection; if it passes, it can remain in service for one more year.

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?

Accepted Answer

CSA/ANSI NGV 2

Answer

ISO 19078

Answer

FMVSS 304

Answer

NFPA 52

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?

Accepted Answer

Remove the vehicle from service immediately until a detailed visual inspection can be performed by a qualified inspector.

Answer

Note the damage in the logbook and have it checked at the next scheduled service.

Answer

Attempt to pull the dent out of the shield and continue with the route.

Answer

Continue driving but avoid refueling the vehicle until the shield is repaired.

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?

Accepted Answer

A detailed visual inspection of the cylinder and fuel system by a qualified inspector.

Answer

A cursury visual inspection by the driver is sufficient.

Answer

No inspection is needed if there is no audible leak.

Answer

The cylinders must be hydrostatically tested before the vehicle returns to service.