OOSC, Part II, Item 7. Fuel Systems b, Gaseous Fuels - Flammable Gas Detection Meters

Current North American Standard Out-of-Service Criteria (OOSC) for CNG, LNG, and LPG vehicles indicate 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. Given that inspectors would be much more likely to use a flammable gas detector than a bubble test to verify leaks of CNG/LNG vehicles, 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.

With an increasing number of CNG and LNG commercial vehicles on the nation's roads it is important to provide commercial vehicle inspectors with the tools necessary to ensure that these vehicles are operated safely, including a practical method to declare CNG and LNG vehicles out of service for verified fuel leaks.

CVSA should develop a threshold definition for the concentration reading (parts per million) on a flammable gas detector that would constitute verification of a leak in a CNG, LNG, or LPG fuel system on a commercial vehicle. Such definition should be low enough to identify vehicles with an imminent hazard so that they can be removed from service, but high enough to guard against false positive leak indications, due to the presence of other flammable gases in ambient air at roadside, so as not to put vehicles out of service unnecessarily. I would recommend 5,000 ppm as the leak definition. This is based on the principle that any concentration above 25% of the lower flammable limit of a gas in air presents a significant hazard. A leak should be considered verified if there is a reading of 5,000 ppm or greater within any enclosed compartment on the vehicle, or at at specific potential leak location within the vehicle fuel system.