Hydrogen Fuel Tank Release Causes Fire at AC Transit Fuel Station
A hydrogen fuel tank release caused a fire at an AC Transit fuel station, prompting authorities to, as a precaution, evacuate several businesses and a high school and to close a number of intersections.The failure of a pressure relief valve triggered the immediate release of approximately 30 kg of hydrogen in the first minute. This rapid release of hydrogen mixed with air in the vent tube and subsequently ignited producing the loud boom reported by eye and ear witnesses. After the pre-mixed gases were consumed the venting hydrogen produced a jet flame emanating from the outlet of the vent system.The flames from this vent scorched the top of the canopy of the manual dispenser causing combustion of the paint and dust and superficial damage to the canopy.
Event Date
May 4, 2012
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
A pressure valve in a hydrogen storage tank malfunctioned, causing it to leak.The root cause of the incident was the use of materials in the failed valve that are incompatible with hydrogen services the (440C steel is embrittled by hydrogen service).A factor contributing to the escalation of the event has been the lack of timely information regarding the status of the system.Another contributing factor has been the design (interaction of canopy and venting system.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
The incident occurred at a fueling station; pressure relief valve located on the high-pressure storage tubes
Storage/Process Medium
Location Type
Location description
Inhabited Area
Operational Condition
Pre-event Summary
The hydrogen fueling station at the Emeryville AC Transit facility comprises a number of components including a low-pressure liquid hydrogen storage tank, an electrolyzer, high pressure storage tubes and dispensers for both heavy-duty vehicles (buses) and light-duty vehicles (cars). The station is capable of fueling 12 buses in a 24-hours period using hydrogen made on site with an electrolyzer (65 kg/day) and liquid hydrogen vaporized into a gas for fueling. The liquid hydrogen supply is replenished via truck delivery, typically every five or ten days. On average, the station contains 1800 to 1900 kg of hydrogen.The station has 18 high-pressure storage tanks, which are protected by pressure relief valves designed to open well before pressures are high enough to rupture the storage tank itself. On May 4, 2012, at approximately 7.45am, one of these valves failed even though the pressure was far below the design opening value. The valve failure caused the release of approximately 300kg of hydrogen gas. The gas ignited at the exit of the vent pipe and burnt for 2-1/2 hours until technicians were allowed by the Emeryville Fire Department (EFD) to enter the station and stop the flow of the gas.The root cause of the incident was the use of materials in the valve that are incompatible with hydrogen service. Apart from the failed valve, the hydrogen system functioned as designed, venting the hydrogen gas at a safe distance above surrounding structures and keeping the subsequent fire away from personnel and equipment. Post incident analysis was performed and a number of recommended actions have been identified in order to reduce the risk at AC Transit District.
Consequences
Number of Injured Persons
50
Number of Fatalities
2
Currency
Lessons Learned
Lessons Learned
1)Replace pressure relief valves with devices specifically designed for hydrogen service. This requires an analysis of the materials used in components throughout the system (440c stainless steel should not be used for valves. Type 316 austenitic stainless steel is an example of suitable material and is used extensively in gaseous hydrogen systems). 2)Update communications plan relative to all responsible parties. In particular establish process responsibility or ownership to better centralize the flow of information. 3)Update training documentation based on timeline analysis.4)Perform refresher training and table-top drills with key personnel. Incorporate continuous improvement principles. 5)Modify the vent systems to ensure relief vent outlets are sufficiently above and oriented away from vulnerable equipment.6)Improve process system considering isolation of sub-sets of the storage system. 7)Modify the fire detection systems to identify hydrogen flames on the system.8)Improve sub-contractor and sub-supplier qualification process for those companies who provide safety critical equipment
Event Nature
Emergency Action
Immediately after the valve failed emergency services were contacted by phone and fire alarm pull stations. Meanwhile, consistent with written procedures, an AC Transit employee activated an emergency stop for the hydrogen station, isolating the incident to the high-pressure storage tubes.At 8:17 am AC Transit District employees evacuated the facilities, with the exception of one senior supervisor who remained on duty in the Operations Control Centre (OCC).When the Emeryville Fire Department (EFD) arrived they were advised to let the Hydrogen flame burn itself out.At 9:47 am EFD ordered the evacuation of a one-block radius surrounding the station. This area included Pixar Animation Studios, Emeryville High School and surrounding businesses.At 10:00 am the Incident Commander permitted technicians to enter the station compound, where they manually closed a control valve to stop the flow of the hydrogen gas, extinguishing the flame at approximately 10:12 am.EFD rescinded the evacuation and street closure orders.
Emergency Evaluation
Written safety procedures were followed immediately after the valve failure.Communications were hampered by wireless communication that did not function properly, traffic delays as key personnel were on route to the site, and traffic controls that prevented technicians from approaching the site
Release Type
Release Substance
Release Duration (s)
9000
Release Rate (kg/s)
0.03
Release Amount (kg)
300.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
A. P. Harris and C. W. San Marchi
Investigation of the Hydrogen Release Incident at the AC Transit Emeryville Facility(Revised), SANDIA REPORT SAND2012-8642, October 2012
Available at https://prod-ng.sandia.gov/techlib-noauth/access-control.cgi/2012/12864…