Pollution
Humain
Environnement
Economique

In a plant manufacturing dyes and miscellaneous additives, a hydrogen and butyl acetate release caught fire on the vent of a hydrogenation reactor. The accident occurred when a safety valve opened; the roof vent was equipped with a flame arrestor. The increase in pressure inside the reactor was due to excess hydrogen resulting from a faulty pressure measurement which was brought on by a clogged pressure tapping on the reactor itself. The rector’s hydrogen supply and the injection of nitrogen in the installation were stopped. During a post-accident inspection, the Classified Installations Inspectorate reported that the operator had not defined an explosive zone in the area around the vent despite the presence of electrical equipment in the immediate vicinity (lighting, ventilation, air conditioners). Some of this equipment was explosion-proof, although it could not be established with certainty whether or not the class of gasses, for which this equipment was designed, includes hydrogen. The Classified Installations Inspectorate also noted that the opening of the valve and the release of gases and flammable vapours were detected belatedly. The operator was required to implement a safety improvement program: technical and organisational measures to prevent such an event from happening in the future, designation of explosive zones (under the terms of the ministerial order of March 31, 1980) around all vents in the building likely to release flammable gases or vapours into the atmosphere and to search for such zones in the site’s other installations, and verification of the compatibility of the explosion-proof equipment near the vent involved with the hydrogen. Several technical provisions were undertaken before the workshop was restarted: doubling up of safety devices to disconnect the supply of hydrogen in the event of overpressure, improvement of the pressure tapping and implementation of preventive maintenance for this device.