Release of hydrogen from LH2 storage tank

A leak occurred at a of a liquid withdrawal valve of a liquid hydrogen storage tank. The hydrogen escaped at the flange between the valve body and the upper part of the valve (flange with tongue and groove). 40 kg of hydrogen were lost.
The accidental release was due to the use of bolts different from those prescribed. By using the wrong ones (old bolts), the bolt material was able to flow at the specified tightening torque. This meant that there was insufficient tightening torque, which led to a leak.

The INITIATING CAUSE was the lack of tightness of a flange, due to the erroneous use of bolts on a flange.

The ROOT CAUSE is related to a human error, to lack of knowledge and to the absence of clear procedures.

flange, bolts

The source does not mention when the wrong installation of the old bolts occurred and how much time passed between that moment and the start of the release.

40 kg of hydrogen were released.

Closure of the adjacent street
Closure of airspace

Although the source does not provide details regarding the moment when the wrong bolts were installed, it is plausible to conclude from the available evidence that this happed during a repair or replacement phase. If correct, the event is a typical example of "things gone wrong during maintenance". The human error is only a component of the root cause, the other being a shortcoming of measures able to prevent the human error.

1. Replace bolts, nuts and spring washers according to manufacturer's instructions.
2. Check the bolts after 12 hours and re-tighten if necessary.
3. Weekly check of the tightening torques for 4 weeks, then every six months.
4. If bolts need to be tightened during the above checks, replacement of the seal should be planned.
5. Plant-specific training for staff. The number must be determined so that trained people are continuously available.
6. Setting up a camera system that provides insight into the areas of the valves and the filter skid.
7. Renewed “awareness” training for the local fire department.
8. Minimizing the time by which a competent person from a specialist company is on site.
9. Creation of work instructions for the fitters, which stipulate that when using refurbishment kits, the kit is checked and only the new components are used.