The alkylation unit was going into shut down. Two contractors were fixing a copper tube to a T-piece of a drain. During the work they turned the T-piece over 90°. Due to this fact a valve on the T-piece was opened and an amount of HF was released. One of the contractors was very seriously wounded, while the other person was only lightly wounded. On-site the victim was given an antidotum (calciumgluconate) and an ambulance brought both victims to a hospital specialised in treating burn injuries.

One of the contractors was very seriously injured. His eyes, nose and mouth were burned and he inhalated HF fumes, which caused internal injuries. The second person only had small injuries around his mouth.

Because the alkylation unit was shut down, the biggest equipment was already emptied and the installation was cleaned with nitrogen. Then it was decided to drain the unit to remove all fluids left. The drain consisted of two valves and a blind flange. The blind flange was removed and replaced by a T-piece consisting of a manometer and a small valve. The T-piece was mounted in a horizontal way. A permit was written for two contractors to add a copper tube to the small valve on the T-piece. Because it was not easy to work with the T-piece mounted horizontally they decided to rotate the T-piece. While rotating the piece, the handle of the small valve touched a pipeline and the valve opened and 360ml HF was released. This amount of HF was situated between the two large valves and the small valve on the T-piece.

The T-piece on the drain was a temporary piece only installed for the shutdown. There was no standard in the company to which temporary pieces had to comply. The T-piece used screw thread which made it possible to turn the T-piece. The accident showed that a standard for temporary pieces must be drawn up. In the company it was seen as normal that the manual valves in the line on which the T-piece was fitted had a small internal leak. So in the work permit protective clothing should have been specified for working on this line since they should have anticipated that HF would build up between the fixed (leaking) valves and the quarter turn valve on the temporary T-piece. A Quarter turn valve is easily manipulated accidently, certainly while doing mechanical work in the immediate vicinity.