While transferring concentrated liquid waste inside a chemical plant, a tanker lorry driver died. He arrived at 9:30 am at the reception area and was joined in the transfer zone by the plant’s safety engineer. The transfer from tank to 2 of the cistern’s 4 compartments (20 m³) then began. At the end of the transfer operation, the driver shut off the end-of-filling alarm horn and closed the bottom valves in order to isolate the tanker compartments. He moved to the other side of the lorry (the left side) to isolate the vacuum pump and returned to the right side to proceed with the operation but collapsed near the lorry cab. The engineer came to the rescue but felt bad when approaching the fallen driver; he turned away then attempted another rescue while holding his breath. He asked an employee to call the rescue team, prohibited access to all staff and put on a self-breathing apparatus to turn off the lorry engine. Given the engineer’s condition, fire-fighters called a 2nd ambulance; the driver, evacuated in the 1st ambulance, died shortly thereafter.

The autopsy revealed that death was due to an inhalation of H2S. The safety engineer did not sustain any long-term impairment. Analyses showed that both the cistern and tank contained an H2S-saturated solution. Hydrogen sulphide (H2S) is released when manufacturing an active ingredient included in pharmaceutical products (12% by weight compared to the synthesised substance). H2S must be neutralised according to a strict and exacting procedure: introducing soda and hydrogen peroxide, then adding bleach until all sulphide ions have disappeared. The hydrogen peroxide initially planned was in fact replaced by bleach. Given the absence of an H2S measurement device, the reaction could only be controlled through the technician’s sense of smell; treatment was carried out by successive additions without any oversight of the reaction sequence and without following instructions. The effluent generated, which was uncontrolled and still contained non-neutralised H2S, was sent to tank. During transfer into the lorry tanker, the vacuum pumping of effluent loaded with dissolved and partially-neutralised H2S allowed extracting the H2S discharged via the pump exhaust.

Subsequent to this accident, the operator adopted a set of strict guidelines, written procedures and highly-detailed instructions, in addition to submitting several documents to the Classified Facilities Inspectorate, namely the revised and corrected operating protocol relative to the H2S-producing reaction, the protocol regarding sulphide destruction and storage, the procedure for transferring concentrated effluent, the prevention plan signed with the firm contracted to collect plant waste, all internal memoranda on implemented measures, the causal trees and action plans examined with a consultant, the procedure for transferring concentrated effluent from workshops to holding tanks, and the consultant’s report on validating the action plan by the operator.

Download the detailed report in .pdf format (85 Kb)