During the vacuum transfer of liquid waste into steel tanks at a dangerous waste treatment centre, hydrogen sulphide (H2S) was released from the vent of a receiving tank. As they could not be treated on site, these wastes (received in drums and mixed in the tank) had to be transported to another site. The body of a forklift truck operator was found nearby, and 5 people intoxicated by H2S were hospitalised. Upon their arrival, the firemen did not detect a high concentration of H2S and left the scene. The police requested that the suction pipe be emptied into the tank. The vacuum pump was restarted and a second release of H2S caused the truck driver to pass out. The police ordered that operations be stopped and the fire department and an emergency physician were called to the scene. In all, the accident resulted in: 1 death and 6 intoxications with hospitalisation (2 employees, 2 members of the rescue team and 2 agents from another company). The release of H2S resulted from a chemical reaction between 2 liquid wastes, an organosulphur compound and an organic acid.

This accident demonstrates a faulty organisational structure: inappropriate identification, evaluation and documentation regarding the handling of dangerous products, procedures for vacuum pumping of waste from drums to the tank without a clear indication of the order to be followed, secondary chemical reactions… No safety system was foreseen in the event of a gaseous release from the tank vent. A judicial inquiry was conducted.

The mixing of dangerous wastes in the vacuum tanks was stopped and the drums were treated at another site. The administration proposed a series of preventive measures: identification of dangerous wastes alone or in a mixture, safety criteria regarding their treatment (pH…), procedures relative to the storage of products not in compliance with criteria and for mixing with an indication of the order in which they are to be added according to the characteristics of the dangerous materials, connection of the vent to a gas treatment system, and restricted access to the vacuum pumping zone.

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