An alarm sounded at a recently inaugurated hydrogen fueling station in a major metropolitan area. One out of a total of 120 high-pressure hydrogen cylinders, located on the roof of the fueling station, failed in service. Gaseous hydrogen was leaking from a screw fitting of the cylinder, but the hydrogen was not ignited. Three hydrogen gas sensors detected the leakage and triggered an alarm that resulted in an immediate emergency shutdown, isolating the leaking high-pressure cylinder bank from the other three banks and notifying the local fire department. No personnel were allowed to enter the roof area, approximately 7-9 meters above ground level.

The police isolated the area around the fueling station within a radius of 200 meters. The maximum content of the leaking cylinder bank was determined to be ~ 70 kg of hydrogen at 800 bar. The leak rate at the high-pressure storage bank was ~5 kg/hr.

After 2.5 hours, the hydrogen supplier's technician manually opened a bypass line to let the hydrogen escape through a vent line. This action was taken from the ground-floor control room well outside an area that might have exposed personnel to additional hazards.

About four hours later, the leaking high-pressure bank was essentially empty, with a pressure of around 1 bar. The cylinder with the failed teflon-sealed screw fitting was sealed with a plug with the intention of never using it again. There was no threat to employees or the public from this incident.