Hydrogen fire at a gas production facility

A leak occurred while loading a trailer carrying hydrogen gas cylinders. The trailer was loaded with 4 bundles of 60 cylinders at 200 bar which were beeing refilled.
The leak was heard, and an employee closed the supply valve but the leak ignited and reached the trailer's tires. The vehicle caught fire, causing a plume of black smoke visible from a distance. The plant operator evacuated the personnel and activated the emergency response plan. The water sprayers in the filling station and the site was shut down. The firemen and the operator prevented the spread of the fire beyond the 3 other trailers parked at the loading station. After approximately 2 hours, the firemen brought the fire under control.
Early in the morning of the day after approximately 10 hours since the extinction of the fire, the fire broke out again on the tires of a semi-trailer. The firefighters used twice the firefighting flow of the first phase. After 5 hours , the firefighters finished extinguishing the semi-trailer. They checked that there were no hot spots using a thermal camera. The operator called off the emergency plan.
There were no injuries but the material consequences of the fire were severe: 11 cylinders within one bundle bursted and two adjacent hydrogen trailers partially burnt.
The plant operator activated a post-accident crisis unit to study how to empty the trailers from the remaining hydrogen and to purge them.
(ARIA database)

INITIATING CAUSE: several potential sources of hydrogen leakage were identified at the level of the trailer: either on a connection loop between a cylinder and a manifold, or on the manifold, or on a cylinder. Most probably, a small leak on fitting caused a rupture of a pigtail which induced a hydrogen jet fire, igniting the tyres and causing the cylinders to burst.

ROOT CAUSE:
(i) shortcoming in procedures for maintenance and inspection of the trailer/bundles design.
(ii) lack of effective prevention and mitigation measures during filling, probably related to shortcoming of the risk assessment

semi-trailer, hydrogen cylinders

Three semi-trailers showed significant destruction, resulting in an economic loss of 488 k€. The hydrogen conditioning installations required a repair estimated at 50 k€.
The site was shut down and production was relocated.

The study of the smoke plume concluded that there was no toxic effect in the vicinity of the site. The analysis of the extinguishing water shows a quality allowing its discharge into the natural environment.

Pending the outcome of the investigation, the plant operator has removed from the company's fleet a batch of semi-trailers of the same model as the one involved.