fire on a flexible hose during transfer

A hydrogen fire occurred at a hydrogen refuelling station (HRS). The HRS hydrogen storage consisted of two trailers at 200 bar, both connected via flexible hoses to the station delivery system using a compressor.
The incident happened when switching empty trailer(s) with new full one(s). The hydrogen release occurred at the connection between a flexibles hose and the the trailer outlet. A nut part of this connection was damaged and failed when the high-pressure valve of the trailer was opened. The hose was diconnected and sparked the leaked hydrogen, resulting in a fire and injuries to the trailer driver and a HRS operator.

Post incident investigation found out that the nut which failed was different, with a thinner neck than the others used for hose connections. The nut failed at the neck under the pressure of the trailer hydrogen, probably due to additional stress caused by a too high tightening force.

The INITIATING CAUSE was the failure of the connection between the flexible hose and the trailer outlet, due to a nut not meeting specification.

According to the authors of the article, the ROOT CAUSE was a combination of the following factors:
(i) the quality management of the nut quality was along the supply chain, from nut manufacturer to hose producer up to the HRS operator was insufficient.
(ii) There was a lack of validated procedures for the fastening of high-pressure hoses.
(iii) The consequence of the connection failure was made worse by the lack of an emergency shut-off valve on the hydrogen tube trailer, because it was impossible to stop the supply of hydrogen to the leak.

nut, threaded connection, flexible hose

The leak occurred when switching the HRS hydrogen storage from an empty trailer to a full one.

Two workers were injured in the fire: the charging station driver and the trailer driver suffered face and leg burns, respectively.

According to the authors of the article, the incidents is a combination events and causes, with the following as main root causes:
(1) The nuts used to connect the high-pressure hose to the tube trailer is not legally standardised.
(2) The quality management system of the precision machine company which delivered the nut There was an insufficient.
(3) Similarly, the quality management system of the piping construction company was insufficient.
(4) Standards or procedures for fastening high-pressure hoses are missing.
(5) Personnel were insufficiently trained on hydrogen safety and safety work.
(6) The installation of an emergency shut-off valves on hydrogen tube trailer is not legally prescribed.
As general recommendation it could be concluded that a lack of general standards and technical regulations related to standardisation of component and legally prescribed safety measures contributed to create the condition for the incident.