An explosion occurred in a drying drum at a livestock feed production facility at 7:15 a.m. The drying line was in the process of being started.

A pocket of dust inside the drum is likely to have been the cause of the accident. This dust pocket may have been generated by the re-granulation of the wood over the previous 2 weeks on a system parallel to the drying line. The feed belt is used to supply either the drying drum or the grinding-granulation system. Ultra-fine dust, stirred up by the drum’s natural draught, would appear to have passed through the auger and then collected in the drum over the 2-week period.

The furnace is switched on and allowed to warm up for an hour during the sawdust drying drum’s start-up phase. During this warm-up period, the hatch between the furnace and the drum remains closed. The drum is started once the furnace is hot. This operation probably placed the ambient dust in suspension. When the trap door was opened and the main fan started, the sharp rise in temperature and sparks entered an environment conducive to an explosion.

Property damage was extensive. The inside of the drum was damaged, the cyclone was out of service and the roof was blown off. The installation had to be shut down for several months for repair. The water used to clean the site was confined before treatment, and the sawdust was directed to other facilities until the plant could be restarted.

The IIC (“Inspection des Installations Classées”, Classified Installations Inspectorate) urged the operator to remove asbestos from its site as the explosion had ripped away several asbestos sheets from the roof. The IIC also requested that a cold ventilation phase of about ten minutes be included in the dryer furnace’s start-up procedure and that a cleanliness inspection be conducted on the dryer entrance during the weekly check of the plant’s installations.

The very next day, a memo about the accident was sent to all the group’s sites. This memo was issued at the request of the IIC and stipulated that a mandatory ventilation phase was to be implemented in the drying lines before the furnace was lit. This instruction was incorporated into the plant start-up procedures. The verification of the dryer inlet’s cleanliness was also required.

As the cause of the accident was linked in part to a lack of sealing between the pelleting/grinding system and the drying drum, the IIC requested that the operator reinforce the seal between the two systems. Furthermore, since the wood drying activity was added to the forage dehydration activity, this activity is not regulated. The IIC has proposed a prefectoral order imposing emergency measures requiring that the resumption of the dust granulation activity be conditional upon an updated hazard study on the process part of the installation. It also proposed a formal notice requiring the operator to submit, within   months, a file outlining the modification of the plant’s operating conditions related to the wood drying activity.