A heat exchanger used for an alkaline spray degreasing bath (6.8 m³) on a surface treatment line for paint occurred at a plant that was closed for an extended holiday weekend. The plant manufactures chimney flues. The heat exchanger’s gas burner operated beyond the setpoint temperature (84°C for a maximum of 54°C). The firefighters were alerted at 7:40 a.m. by the evaporation-vapour detector but the plant managers could not be reached. The firefighters and the production manager finally arrived on the scene at around 10:00 a.m. The burner’s gas supply and the treatment line’s electrical supply were cut off. The water level in the degreasing tank was topped up to completely cover the heat exchanger once again. No environmental impacts were reported.
The fire had two causes. First, the burner failed to automatically cut out when the setpoint temperature of the bath was reached and second, the line controller turned on the bath heater although it was a public holiday and the time program should have been changed beforehand. In addition, the operator usually shuts down the treatment line at the end of each week. However, it did not do so on the evening before the public holiday. The operator fitted several safety devices and malfunction detection systems:
- manual emergency cut-out switch for the burner’s electrical supply.
- fail-safe thermostat to turn off the burner if it overheats; manual restart required. If this temperature-monitoring system fails, the system shuts off except for the ventilation.
- fail-safe low-level sensor for the treatment bath that automatically shuts off the system except for the ventilation.