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.
- Hydrogen Storage Equipment
- Gas cylinder
The hydrogen supplier installed a fire-resistant material board adjacent to the high-pressure hydrogen storage banks to prevent any potential jet flames from affecting adjacent high-pressure cylinders for several minutes. The 0.25 mm sandwich board of fiberglass-reinforced, lightweight concrete is easy to maintain and does not rot under outside conditions. This safety measure was implemented just three days after the incident occurred, although it had been planned for a long time.
The hydrogen supplier installed a semi-automated sprinkler system to cool the high-pressure hydrogen storage banks to prevent any potential escaping hydrogen gas that might ignite in jet flames from affecting other hydrogen cylinders. In addition, the dry piping system above the high-pressure hydrogen storage banks can be flooded with water by the fire department in case of fire or leakages in the high-pressure banks.
The alarm system was refined to send automated messages to relevant personnel informing them of gas/fire alarms.
The remote control room where service personnel are monitoring the fueling station is now equipped with an additional audio system to draw faster attention to alarms.
All plans and emergency procedures have been reviewed, adjusted and edited to document changes and fully capture the lessons learned.
Other learnings: Training for worst-case scenarios is recommended in order to be prepared for those siutations.