At around 1:40 a.m., a fire broke out on a dust filter at the asphalt plant of an asphalt products company while 15 t of asphalt was being produced. The fire broke out in a confined environment. A technician activated the emergency stop. The plant’s power supplies were shut off. Firefighters used 3 m³ of water to contain the fire. Production was shut down until the filter could be repaired. The plant was scheduled to resume operations three weeks later. The filter was completely replaced during the following scheduled shutdown. The accident produced 5 t of waste.

Causes of the accident

Following a lack of sand supply to the rotary dryer, the filter temperature rose very quickly to 220 °C and ignited the bag filters. Furthermore, the accident was compounded by multiple technical and human failures:

• Failure of the alarm systems:

Failure of the switch, which is supposed to use a warning light to alert the loader driver and the technician that the feed system is one-third full and needs to be reloaded.

Failure of the flow switch, which slows down the production line when the feed system is empty and sends an alert signal to the technician’s control screen. An analysis revealed that the switch was not correctly configured in the PLC.

• No shutdown of the gas burner by the safety sensors.

Measures taken

The following actions were taken:

• the various sensors/switches were checked and (where necessary) repaired and the frequency of the checks was changed;
• the setpoint entered in the PLC and used to shut off the burner was adjusted and is now regularly checked;
• the temperature threshold of one of the sensors was lowered;
• access to security data is now protected by a password.