At about 09.20 a.m., there were 2 explosions, followed by flames, in a washer in the liquid smoke production workshop at a specialised beech wood smoke production plant. The workshop was located in a 1,400m² building. The 3 employees on site raised the alarm and left the building. Staff assembled at the site entrance. Police shut off access to the road. The site’s utilities were shut off. Firefighters sprayed the flames for 20 minutes and prevented spreading to other buildings. The building was ventilated to extract the large amount of smoke generated.

Firefighting water was contained via absorption with beech wood sawdust. The machine that caused the incident was damaged, and 3 employees were laid off. Production was shut down for several days.

It would appear that a pressure increase due to the gas build-up caused the washer to explode and catch fire. This phenomenon was due to progressive clogging of the condensation column, which then reduced smoke condensation and increased gas flow into the washer. This higher gas input accelerated clogging of both the filter and burner. The pressure drop between the condensation column and the burner caused overpressure in the washer until it exploded. The fire was then triggered by the presence of gas, oxygen, and energy from the explosion.

The preventive measures in place, i.e., daily cleaning of the condensation column and presence of a pressure sensor shutting down the system in case of excess pressure, proved insufficient. Historic records showed that overpressure was detected at the time of the explosion. This means the sensor was poorly positioned to prevent the explosion.

To prevent a similar accident from happening again, the operator installed:

• a pressure sensor between the gas washer and the burner, with running of the facility linked to this sensor;
• a valve to extract gas in case of overpressure.