Explosion at a water treatment facility

This incident occurred when subcontractor two workers were widening air vents on the roof of a building hosting a tank containing hydrogen chloride solution. This intervention was necessary to to improve hydrogen venting from the tank storage area. The hydrogen gas was a by-product of the chlorine-making process.
The two workers were operating an angle grinder, producing sparks which ignited the flammable atmosphere which evidently containing hydrogen. An explosion followed, with one casualty and one injured worker.
The HSE, in charge of the investigation, concluded: "The company failed to take adequate steps to prevent the risk of an explosion occurring during the construction work that was taking place at the plant near to a source of hydrogen gas."

The incident inquiry by the Health and Safety Executive found that the water service company was to blame for management shortcoming in risk assessment, safety measures implementation, operative procedures, and management of external workers. The workers were unaware of the existence of hydrogen gas or the hazards involved, and that they did not see any health and safety or danger signs on the building.

vent, tank

The involved tanks were originally installed as an open-air facility, which was self-venting. However, the company decided to create a building around it, to avoid exposure to the elements.

These were the findings of the forensic investigation:
(1) The explosion occurred because of a build-up of hydrogen in the ducting beneath the roof, likely ignited by the grinder.
(2) The plant should have been shut down.
(3) No permit had been given for the work being carried out.
(4) A specific risk assessment should have been carried out, but had not been done.
(5) The area should have been verified safe, for example by means of gas detectors.
(6) Safety and hazard warning signs would have helped, but none were present on the roof of the building, and that there were very poor communication channels.
(7) That tanks involved should not have been enclosed (they were originally installed as an open-air facility, which was self-venting. However, the company had decided to create a building around it. to avoid exposure to the elements).
(8) Gas detectors should have been provided.
(9) The workers should have been supervised by the plant operator.