Fire from a hydrogen pipeline under maintenance

This event regards the accidental release and ignition of hydrogen from a pipe under maintenance.
Two workers had a work permit to remove filters from a hydrogen line. An operator visited the scene and answered the mechanics’ question as to whether the line should be de-pressurised and that it indeed should be so. The workers replaced the low-pressure side (4 bar) suction strainer at which point they noticed that there was pressure inside the pipe. They released gas inside the pipe into a piping leading to the flare. In the afternoon, they carried out a similar filter replacement on the high-pressure side (34 bar).

The standard procedure is to remove a flanged pipe section of 50 cm from the piping, after which the suction strainer is pulled out and cleaned. The flange is opened by first removing every second bolt. After that, the remaining bolts are undone. When starting to loosen the remaining bolts, the mechanics noticed that there was pressure inside the pipe. A flow of gas from the opened flange started immediately. When one of the mechanics went to check the pipe pressure from the gauge, the hydrogen was ignited, apparently due to an electrostatic charge.

INITIATING cause: a hydrogen pressurised pipe being opened without check to verify that the line had been depressurized.
ROOT CAUSE: lack of operational procedure and communication. It was just assumed that someone had taken care of it. Also lack of proper training.

pipeline

The hydrogen release occurred during maintenance

On of the two mechanic workers was caught in the flames, and the lower part of his overalls caught fire. He was taken to an occupational health clinic to receive first aid, after which he was taken to a hospital by an ambulance. The burns sustained by the mechanic were of classes I and II, covering about 30–35% of his skin. The other worker was not involved only because we went to check a manometer when hydrogen took fire.