Explosion of hydrogen compressors due to the an earthquake

The incident occurred on a compression unit installed on the roof of a four-story building.
The Great East Japan Earthquake caused the rupture of the flexible piping and the outlet piping of the two compressors making up the unit. The leaked hydrogen ignited and exploded. The fire went out naturally without any firefighting efforts being made. There were no injuries.
The compressor was connected to a hydrogen storage system, but the quantity of hydrogen was limited because the earthquake activated also the seismic sensor of the system, which interrupted the hydrogen supply from the buffer tank.

The INITIAL CAUSE was the external environmental condition induced by the earthquake.
The ROOT CAUSE was the fact that the design of the facility did not take into account the possibility of an earthquake of this dimension, so that safety preventive measure did not work as planned. However, one seism-related measure did work, the isolation of the storage from the compression stage, and thanks to this automatic measure probably further escalation was avoided.

Detailed causes of the accident
(i) The two compressor units were installed on the rooftop due to limited installation space.
(ii) Considering their weight, the vibrations transmitted to the floors below and the distance from the equipment to the rooftop, a compact air-cooled oil-free compressor was selected, which can be vibration-proofed.
(iii) Due to the constraints of the rooftop's load-bearing capacity, a frame was constructed about 2.5 m above the rooftop, and the compressor units were placed in a soundproof case and installed on the frame.
(iv) A major earthquake was not anticipated, and the strength of the bolts fixing the soundproof case were designed only to prevent the case from shifting.
(v) After the earthquake, the air springs of the compressor units were damaged by vibrations, causing the compressor units to move. Furthermore, the fixing bolts of the suction snubber tank were also damaged, and the flexible piping and compressor outlet pipes were damaged, causing hydrogen to leak.
(vi) Due to a power outage from caused by the earthquake, the ventilation fans inside the soundproof cases were not working, so the leaked hydrogen could cumulate inside the sealed soundproof cases. Both compressors ignited and exploded due to some kind of ignition source (static electricity, frictional heat, impact sparks, etc., difficult to identify).
(vii) The area around this building is a plateau, with the bedrock of the foundation about 30m to 40m deep, so the earthquake caused great damage to the buildings and equipment in the surrounding area.

flexible hose, outlet piping,
compressor

The incident occurred during the earthquake of 2011

No injury

(1) When designing high-pressure gas equipment, in the accidental scenarios related to leakage, fire and explosion also the effect of earthquake should be considered. In particularly when installing equipment on the roof of buildings, preventing measures are necessary, which take into account the resistance to and the insolation from to vibrations.
(2) In this accident, the ventilation fans inside the soundproof case of the compressor unit did not work due to the power outage after the earthquake. In order to avoid an explosion in the event of a gas leakage, it is necessary to consider an optimal exhaust system, possibly based on natural ventilation, with redundancy and able to work under the condition expected by an earthquake.
(3) Immediately after the earthquake, the emergency generators at the plant did not work, causing a total blackout. In order to avoid a blackout during an earthquake, it is necessary to design the backup generators to function reliably under all possible conditions.

(1) The compressor was changed to a water-cooled type and installed at ground level.
(2) In the event of a shutdown or malfunction, the hydrogen in the compressor will be vented to the outside via a pressure relief valve.
(3) The compressor room was equipped with natural ventilation to prevent formation of hydrogen-air flammable mixture in the case of a leak.