The pressure inside a 100 °C vacuum distillation assembly (10 l glass column) used at the laboratory of a Seveso-classified essential oils plant rose at around 12:15 p.m. The pressure blew the reboiler and column apart, spraying three technicians with a hot intermediate used to manufacture a fragrance. They were taken to hospital, where they were treated for slight burns and discharged in the late afternoon.

The lab’s electrical power supply was cut off and access to the laboratory was blocked off. The fire-fighters and gendarmerie arrived on the scene.

The rise in pressure was caused by the decomposition of either the product or a by-product during the reaction, which had been carried out at the lab since 1995. The thermal runaway was due to a combination of factors: inadequate cooling (change in the scale of the batch following an increase in demand), excessive temperature or insufficient vacuum, variable quality of the product, etc.

The operator analysed the incident and introduced the following measures to ensure safe distillation:

•  Continuous distillation supplemented, on a case-by-case basis and after analysis of the risk, with a batch step.
•  Additional analytical tests (differential scanning calorimetry, peroxide value, acid value) before each step in the process that requires heating.
•  Obligation to set up the assembly for this product under a fume hood (the operation had not been performed under one because (i) it was not practicable, (ii) there was a limited amount of equipment and (iii) the choice was left up to each technician).
•  Long-sleeved latex gloves must be used when working under the fume hood. The PPE (Personal Protection Equipment) that used to be worn (goggles, smock and gloves) left certain parts of the body exposed.
•  Written procedure of what to do in case of emergency with this product (alert and response). The reason why there were three people was because two had come to help the technician bring the process back under control.

The operator also re-evaluated the chemical hazards for all the reactions carried out at the laboratory and ranked the most hazardous ones, for which additional measures will be introduced. It will also provide PPE that offers better protection of the wrists and forearms.