OOSC, Parte II, Artículo 7. Sistemas de combustible b, Combustibles gaseosos - Medidores de detección de gases inflamables

This issue had been discussed in the spring meeting and it was regarding the current North American Standard Out-of-Service Criteria (OOSC) for CNG, LNG, and LPG vehicles indicating that a vehicle should be put out of service for any fuel system leak "detected by smell", "detected audibly" or "detected visibly" and "verified by either a bubble test...or flammable gas detection meter". Industry standards provide clear direction as to what result indicates a leak when conducting a soap bubble test - the presence of "persistent bubbling" indicates a leak. However, there is no clear industry standard as to what reading on a flammable gas detector would indicate a "leak", particularly in the context of a roadside inspection, where ambient air may contain some concentration of flammable gases from other sources. It was discussed that inspectors would be much more likely use a bubble test to verify leaks of CNG/LNG vehicles than detection meters at this point, it was not critical that the change be made but it was agreed that in the interest of fairness, the OOSC should reflect a standard that is imminent hazard in cases where the meters are used. CVSA should provide clear direction as to how inspectors should interpret flammable gas detector readings at roadside when making out of service decisions for CNG/LNG leaks. During discussion, it was determined that it was a good idea to put a standard in the OOSC because we could potentially be putting vehicles OOS that shouldn’t be. It was requested not to remove the bubble test. This would force agencies to buy meters. It was clarified that the meter test does not remove other viable tests. Keeping in mind that “any leak with a detection meter” is already in the OOSC. This is not suggesting that inspectors must obtain meters, but rather what reading is imminent hazard if a meter is used.

There is currently nothing stopping people/inspectors from buying meters and using them and if they do, they will put trucks OOS for 1 PPM based on the current criteria. The training provided by FMCSA indicates that “any leak” is not an imminent hazard when under the 25% of flammability limit. It was indicated that during the training, there are leaks that can be detected by a meter that you cannot get to in order to conduct a bubble test, because the leak is in an enclosed space that only the meter would be able to get at. It was also pointed out that there is no bubble test in OOSC for LNG, this should be looked at to determine if there should be one. Attendees in the spring meeting were asked to obtain further information from contacts to determine if 5000 PPMs was the right amount before amending the OOSC.

Consultation with experts in the field indicated that the typical value used to indicate danger was 50% of the lower explosive limit (LEL). The LEL for natural gas and propane are different, but to keep this section simple, it made sense to use a single value. The recommended level is 5000 parts per million (ppm).

It was further discussed that the entire section could be cleaned up by consolidating the OOSC for CNG and LPG into sub paragraph (a) and remove sub paragraphs (b) and (c) as well as adding more than 5,000 ppm measured with a detection meter for CNG, LPG, and LNG. The motion also added the bubble test as an acceptable LNG test. The committee unanimously voted to the revisions as outlined below:

7. FUEL SYSTEMS . . .

b. Gaseous Fuels . . .

(1) CNG or LPG

(a) Any fuel leakage from the CNG or LPG system detected visibly, audibly or by smell and verified by either a bubble test using non-ammonia, non-corrosive soap solution or a reading of more than 5000 PPM on a flammable gas detection meter. (396.3(a)(1))

NOTE: Verification is needed to ensure that the sound is not either internal to the fuel system (such as gas flowing in a pressure regulator, or pressure equalizing between manifolded tanks) or a leak in the air brake system.

NOTE: Some brief fuel leakage or decompression may occur during refueling, causing temporary frosting of CNG or LPG fuel system parts. If the vehicle has been refueled shortly before inspection, care must be taken to distinguish these temporary frosting occurrences from actual leaks.

(2) LNG

OCCUPATIONAL SAFETY NOTE: LNG is a cryogenic material and presents a potential safety hazard due both to the extremely cold temperature of its liquid and the flammability of its vapor. Personnel inspecting such systems should exercise utmost caution including the wearing of proper eye protection, gloves and clothing.

NOTE: LNG liquid and vaporized gas is odorless and undetectable by the human sense of smell. Frost buildup is not necessarily evidence of leakage. Many components of LNG fuel systems are extremely cold and will exhibit an even coat of frost produced by moisture in the surrounding air condensing and freezing on them.

(a) A cloud of water vapor coming from any component of the fuel system. (396.3(a)(1))

NOTE: It is normal, particularly in humid conditions, for water vapor to collect around many portions of a LNG fuel system.

(b) Any fuel leakage from the LNG system detected visibly or audibly and verified by either a bubble test using non-ammonia, non-corrosive soap solution or a reading of more than 5000 PPM on a flammable gas detection meter. (396.3(a)(1))

(c) Dripping liquid that boils or vaporizes in the air. (396.3(a)(1))

NOTE: The motion was passed by Executive Committee.