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

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?

Accepted Answer

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

Answer

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?

Accepted Answer

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

Answer

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?

Accepted Answer

CSA/ANSI NGV 2

Answer

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?

Accepted Answer

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

Answer

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.

(CNG) Compressed Natural Gas Practice Test

(CNG) Compressed Natural Gas Practice Test

CNG - Compressed Natural Gas Cylinder Inspection and Regulations Questions and Answers