At around 3.20 p.m., at a plant performing custom manufacturing and packaging of petroleum and petrochemical products, a fire broke out on an electric boiler located in the boiler room of a 2,000m² building. The temperature controller was heating oil to 120°C to supply a small circuit. It was equipped with a safety device for a maximum temperature of 300°C. The team of second responders used two 50kg powder extinguishers. The operator triggered the internal emergency plan and confined the site. The fire fighters used the firm’s private network to extinguish the fire at around 4 p.m. Less than 10m³ of water was used. The emergency responders then cooled the area for 15 minutes and performed monitoring patrols with a thermal imaging camera. After the fire fighters had left, the operator maintained patrols every hour to take further temperature readings.

Hydrocarbon combustion fumes (50 litres of oil) were visible from outside for half an hour.

After searching for the causes of the incident, the operator expressed the possible explanation of excessively sudden heating of the boiler during restarting after a 15-day stoppage. The set-point value was 200°C on a cold system. Since cold fluid is thicker, the circulation pump did not offset the pressure drop and the oil remained blocked in the combustion chamber. The fluid overheated due to the power of the electric immersion heaters (60kW). The temperature and pressure therefore increased in the expansion tank until its safety plug broke. The oil then spilled outside the boiler and ignited.

The operator took the following measures:

• installation of the replacement boiler in a plant room separate from the workshop, with a 2-hour fire resistance;
• drafting of a heating procedure to require a gradual temperature rise for restarting after a prolonged stoppage;
• installation of a fire protection unit opposite the workshops to supplement the extinguishers.