Mr. Thomas D. Petru
Assistant Director -LP-Gas Section
Railroad Commission of Texas
Gas Services Division
1701 North Congress Avenue
P.O Box 12967
Austin, TX 78711-2967

Dear Mr. Petru:

This responds to your letter requesting information about the use of acoustic emissions for retesting certain types of Compressed Natural Gas (CNG) containers installed on transit buses. Your letter was referred to us by the Federal Transit Administration. You stated that a study comparing acoustic emissions testing with hydrostatic testing would be beneficial. You asked for views concerning the possibility of the Texas Railroad Commission suspending the retesting of CNG containers that have expired until after such a study could be completed.

By way of background information, Congress has authorized NHTSA to issue Federal Motor Vehicle Safety Standards applicable to new motor vehicles and items of motor vehicle equipment. (49 U.S.C. 30101 et seq.) NHTSA, however, does not approve or endorse motor vehicles or motor vehicle equipment. Instead, the statute establishes a "self-certification" process under which each manufacturer is responsible for certifying that its products meet all applicable safety standards

NHTSA has no authority to require the retesting of motor vehicles or items of motor vehicle equipment after the vehicles or equipment are sold to consumers.

NHTSA has issued Federal Motor Vehicle Safety Standard No. 304, Compressed Natural Gas Fuel Container Integrity, (49 CFR 571.304), which specifies requirements for the integrity of new CNG containers used to fuel motor vehicles. The standard applies to all CNG containers manufactured on or after March 27, 1995 (the date the standard took effect), and requires that new CNG containers comply with a hydrostatic burst test. The manufacturers must certify that their containers meet the requirements at the point of sale. However, after the first consumer purchase of a motor vehicle or an item of motor vehicle equipment, NHTSA's authority is much more limited and does not extend to periodic retesting of motor vehicles or such equipment.

NHTSA has no position on the relative merits of acoustic emissions or hydrostatic testing. Nor is this agency planning to conduct a study to evaluate the relative merits of these two retesting methods.

The U.S. Department of Transportation=s Research and Special Programs Administration (RSPA) is authorized by Congress to issue standards for containers used to transport hazardous materials, including CNG containers. Such CNG containers may carry RSPA=s DOT specification or exemption markings, including retest markings. RSPA, however, does not have the statutory authority to regulate CNG containers that are used to fuel a motor vehicle. In other words, there are no Federal requirements applicable to the periodic retesting of CNG containers designed to fuel a motor vehicle.

I hope you find this information helpful. If you have any other questions, please contact Marvin Shaw at this address or by phone at (202) 366-2992.


Samuel J. Dubbin Chief Counsel

ref: 304 d:4/29/96