An oven for drying the outer sides of glass bulbs containing purified water for injectable solutions was cited as the source of an explosion that took place inside a pharmaceutical plant’s washing room. Fire-fighters very quickly intervened to secure the zone. The plant’s internal emergency plan was activated. A process of sterilisation by spraying fine droplets of hydrogen peroxide and ethylene oxide, which was ongoing in a nearby workshop at the time of the explosion, could apparently be excluded as a potential accident cause. The lack of fire outbreak in the vicinity of the oven served to reject the hypothesis of electrical malfunction. 42,180 of the 53,580 2-ml bulbs filled with this purified water shattered due to heat and pressure: the large quantity of water released (84 litres) vaporized (transition from liquid to vapour phase) and gave rise to an explosion. Two observations lend support to this hypothesis: 2 technicians noticed a white ball just before the explosion (water vapour?), and both the floor and rock wool in the workshop did not get wet from the free water. Neither the temperature reached nor the heating period was known with accuracy, as no recording device had been placed on the oven.

Malfunction of the oven’s temperature regulator led to a substantial temperature rise; for a rated threshold of 80°C, the temperature inside the oven had actually risen to between 134° and 147°C. This regulator malfunction was due to its obsolescence. Moreover, a slowing of air flow inside the oven due to a large load of glass bulbs, along with shutdown of the general ventilation circuit extractor, contributed to this accident. A study of the burst temperature of these 3-ml bulbs dried in a non-ventilated enclosure was conducted. According to its conclusion, the burst temperature threshold was situated at around 190°C, while the threshold temperature to avoid bursting was approx. 180°C.

The operator modified the facility’s drying process by using an autoclave at 80°C. A safety valve was introduced to protect the enclosure by limiting pressure in the event of a temperature regulation malfunction.