Pollution
Humain
Environnement
Economique

In a plant manufacturing glues and polymers, an explosion occurred in a feed hopper of a mixer followed by a fire at about 8 p.m. A technician was loading an organic resin in granulate form into the mixer’s feed hopper and then started the extractor hood which sends the dust to an anti-static filter outside the workshop before release into the atmosphere. The explosion occurred at this filter, creating a fireball of 2.5 to 3 m in diameter, and combustion of the filter. The plant’s staff was able to extinguish the fire with fire extinguishers, and the firefighters noted that the situation was under control. The affected production line was shut down, and the Classified Facilities Inspection authorities came to the site the following day.

No one was injured in the explosion, but the technicians were shocked. The filter and the installation were damaged and out of service; the roof, just under the hopper, was partially deformed and the raw materials in the hopper were burned (1 m³).

A specialised company was called in to conduct an expert assessment of the accident. The ignition source was of electrostatic origin. It was either a spark from a 1-m section, isolated from the ground, or a slippery surface discharge due to the inner surface of the pipe covered with insulating paint.

The accident sequence was as follows: electrostatic discharge causing ignition of a powder storage area, intake of incandescent dust by the dust collector into the filter, ignition of the filter and shutdown of the dust collector at the same time, declogging initiated 180 s after the dust collector had stopped, ignition of the dust in the air leading to the explosion and, finally, propagation of the explosion to the installation.

A new dust collection system had to be installed. The sleeves of the anti-static filter must comply with specifications, the pipes must not have internal linings, and the suction system was to be redesigned. The facility operator planned to modify the organisation to include regular monitoring of equipotential connections and the presence of dust in the pipes. The dust collector is to be equipped with a flame arrester and an explosion hatch. Finally, the entire procedure is to be reviewed. The Classified Facilities Inspection authorities proposed that the Prefect issue an emergency order to supervise the restart of the unit.