In a chemical plant, a release of acid vapour occurred at 9:40 p.m. when a 33-litre drum of triflic anhydride (TAA) was opened. The internal emergency plan was activated. A white cloud had formed when the TAA reacted with the air. The operator in charge of the unloading operation, having been sprayed on his PPE, rinsed himself off under a safety shower while his colleague sounded the alarm. The in-house first responders were mobilised but did not have to intervene. The cloud in the premises then dissipated within ten minutes. The internal emergency plan was lifted at 10 p.m. An estimated 10 litres of TAA and less than 500 g of SO2 was lost.

The production line involved in the accident processes both triflic acid (TA) and triflic anhydride (TAA). At the beginning of the TAA production series, residues from previously produced TA had remained in the processing line and were drawn into the first barrel of the newly produced TAA series. This drum was set aside as it did not meet the quality standards. This drum was then stored for more than a year, during which time the two incompatible products slowly reacted to produce SO2. Moreover, it had been left for two days in the sun before being opened, which catalysed the reaction between these two products. The pressure in the drum’s vapour space thus gradually increased and released the TAA and SO2 when it was opened for recycling.

The operator is modifying the processing line into two separate lines, each dedicated to a specific product. The monitoring of non-compliant drums intended for recycling has been reinforced and their storage time reduced. A study is currently underway to determine the feasibility of recycling during manufacturing operations. A procedure for reprocessing non-compliant drums of TAA has been set up.