At around 4:30 p.m., strong-smelling and unusual fumes were detected in a company specialising the cleaning of heat exchanger bundles for refining and petrochemical companies. An exchanger, which had been recovered and transported to the site by truck, was in the process of being high-pressure cleaned. The employees, inconvenienced by the smell, had suspended their operations. Measurements performed by a 4-gas detector indicated an abnormally high presence of VOCs. The component was ventilated with outside air and then returned to its original site.

At the same time, firefighters were called to the neighbouring site, a transport company, located downwind, which had reported a strong smell. Four people in this company had been affected by the odour.

Measurements taken by the fire brigade indicated the presence of benzene and toluene in the vicinity of the equipment at the cleaning company’s site, but no or almost no levels outside despite a noticeable odour. Medical tests were performed on all the exposed employees.

It would appear that the smell had been noticed as soon as the part had arrived on site, but it was amplified by the cleaning operation. DMDS (dimethyl disulphide) on the outside of a heat exchanger bundle may have spread into the air during the high-pressure cleaning operation. The cleaning company processes only decontaminated parts, but the decontamination reports do not include measurements of DMDS, which is toxic if inhaled and possesses a very low olfactive threshold.

The inspection authorities for classified facilities noted that the operator had not taken the necessary steps in the cleaning area to limit the spread of odours outside the site.

The Inspection requested that the operator implement the following measures:

• improve its heat exchanger acceptance procedure. The pollution control report, the safety sheet and waste slip are made available at receiving operation. The inspections to be conducted before washing operations are specified;
• indication of the measures taken to process the 4 similar exchangers on standby at the original site.