Plaster dust was released into the area surrounding a plaster manufacturing plant following a malfunction on a stack’s electrostatic precipitator. The operator received a call from the town hall at around 4 p.m. informing it of complaints received from residents. The facilities are shut down. An intervention was performed on a probe measuring the dust concentration of the gaseous effluents, and on a component used in their recycling. A product overloading problem was also corrected on the electrostatic precipitator.

Causes of the accident

The technicians in the control room had been observing the instantaneous value indicated by the electrostatic precipitator probe at time t. They had therefore not been paying attention to the value over time and were thus unable to quickly detect anomalies unless the alarm had been triggered.

In addition, when the electrostatic precipitator is too loaded with dust, a recycling system should typically return it to the circuit. The device had not been functioning correctly on the day of the incident.

No cleaning schedule for the probe had been established.

Measures taken

The operator plans to install a second control probe. A procedure was also drafted outlining the actions to be undertaken in case of a malfunction. The value of the dust emissions will be checked twice a day with measurements recorded in a logbook.

Given the risk of dust accumulation on the probe, the supplier recommends that it be cleaned every 6 months. Preventive maintenance will thus be carried out quarterly.