Fire - hydrogen

The incident occurred during the filling of six bundles of compressed hydrogen cylinders by means of a compressor. Each bundle consisted of 16 cylinders of 40-liter each. When approaching the final filling pressure, the bottom of one of the 40-liter containers was suddenly separated and ejected from the cylinder, with consequent high-pressure hydrogen release, explosion and fire.
The recoil reaction of the gas displaced the cylinder bundle causing an additional leak at filling manifold piping, so that the bundles were engulfed in flames on both side. The slate roof of the building was blown off by the shock wave caused by the cylinder rupture.

The post-incident investigation found that moisture had seeped in from the compressor and accumulated at the bottom of the container, causing corrosion pits, and that the cycling stress due to repeated filling had caused cracks to progress from the inside and reach a position 1 to 1.5 mm from the outer surface.

The INITIATING CAUSE was the sudden failure of the whole cylinder due to fatigue and corrosion.
The ROOT CAUSE was the incapacity to foresee and to detect a structural degradation of the high-pressure component progressing from inside (thus invisible to visual inspection). The corrosion and the consequent corrosion -assisted crack growth was caused by contaminants coming from the compressor. This reveal a lack of operative quality assessment and an overall risk assessment able to consider the whole connected system, and not just the risks related to each of the components individually.

cylinder

The workers had just carried out a leakage inspections of each cylinders at a pressure of 110 bar and found no abnormalities, after which they returned to the instrument room. The incident occurred at a pressure reached of 145 kg/cm2. The accident occurred when they were about to switch the valve to end filling.
The container in question had been in use for about 30 years, and the most recent re inspection had been carried out three years ago.

In this case, the operations had been performed according to the prescribed safe procedure. The cylinders had been regularly re-inspected and leak-checks performed during filling.
However, these preventive measures were not able to detect structural degradation of the high-pressure components progressing from inside (thus invisible to visual inspection).
The corrosion caused by water residues coming from the compressor could therefore proceed undetected, locally reducing the thickness of the cylinder wall and enabling the development of cracks which could grew due to the fatigue associated to the cycling stress from the filling. The inspection procedure was definitively not fit for the detection of this failure mode. The fact that this accidental scenario had not been taken into account has probably to do with the fact that the design of the cylinders and the related operative inspection procedures were designed individually, without considering external deterioration factors such contaminants not usually present in hydrogen gas, coming from the connection with other components (in this case, the compressor).