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CVEF Issues Technical Bulletin on Temperature Compensation

The Clean Vehicle Education Foundation (CVEF) has issued Reliable Temperature Compensation Is Critical to CNG Vehicle Safety, a technical bulletin that addresses the potential hazards created by the failure of CNG dispensers to accurately compensate for temperature. Proper temperature compensation is essential to safely fuel CNG vehicles, regardless of station type, as serious incidents have resulted from the overfilling of CNG containers at both fast-fill and time-fill facilities.

The bulletin makes three recommendations:

1. Station operators should contact their fast- and time-fill dispenser suppliers to make sure they have—and are using—the latest set of written instructions and maintenance schedules as required in NFPA 52-2013.
2. Station operators should schedule annual temperature and pressure calibrations and function checks in early fall to allow time for any needed corrective action before winter temperatures.
3. Station operators should also ask their dispenser suppliers whether existing dispensers comply with the requirements of NFPA 52-2013.

The bulletin explains that limiting the maximum pressure in the cylinder is not as simple as limiting the pressure dispensed to the vehicle. The temperature of the gas in a CNG container may increase after fueling if the temperature of the environment increases before the fuel is used. This may occur with warming outdoor temperatures or when parking indoors. In these situations, there is the possibility of the pressure actuated PRD used on some vehicles to rupture and vent down the cylinder if the temperature was not properly compensated for during fueling. This issue is especially important to address prior to the cold temperatures many parts of the country experience during winter months. CVEF and NGVAmerica are coordinating efforts to disseminate the bulletin to inform station owners, operators and other parties of this issue.

The bulletin is available on both the CVEF and NGVAmerica websites and can be viewed here.