An exercise was conducted at an industrial adhesives plant as part of its internal emergency plan. The firefighters and subprefect were in attendance. The scenario was an exothermic reaction resulting in smoke, with one victim in a production room. The exercise sequences included the use of smoke generators to trip the fire alarm, closing of the main door, manual activation of the CO2 injection system to inert the room (automatic trip controlled by the temperature detectors), ventilation of the facility, positioning of the pretend victim and evacuation of the victim by two people wearing SCBAs and waiting behind the main door. The circuits supplying the extinguishing systems in the other rooms were disconnected. As a cost-cutting measure, the 76 kg cylinders connected to these circuits (and which were soon to be retested) were used. That morning, a maintenance technician connected them to the circuit of the room that was to be used for the exercise.

The smoke generators were turned on at 9:25 a.m. and the employees working in the room were evacuated. However, the maintenance technician took longer than planned to connect the cylinders. A 9:53 a.m., the exercise supervisor, who was standing near the emergency exit, manually activated the CO2 injection system while the pretend victim and three other employees were present. Due to the delay, the situation became somewhat confusing. It was the pretend victim who actually was supposed to turn on the CO2 injection system. Without waiting for the room to be ventilated, the pretend victim (an experienced security officer) went inside while CO2 was still being injected. He quickly lost consciousness (hypercapnia) and fell. Holding his breath, the exercise supervisor ran to the unconscious man and began pulling him backwards towards the exit. However, as he did so, he fell into the pit of an aerial work platform. The force of the impact caused him to inhale and lose consciousness in turn. Both unconscious men, lying near the emergency exit, were pulled out of the room by the three employees who were waiting outside. One of them went to seek medical assistance, but at first was not taken seriously because the exercise was still under way. The three employees were slightly affected. The two employees who were wearing SCBAs and waiting in front of the door to evacuate the pretend victim did not react due to the poor visibility and lack of radio instructions from the exercise supervisor. A leak on the CO2 line supplying the room where the exercise was being held occurred at the same time, resulting in the entire building being evacuated. After several confusing minutes, the exercise was halted and the firefighters were called in to revive the two unconscious men and ventilate the room. The two men were then taken to hospital by helicopter and placed in a hyperbaric chamber. The three affected employees were kept in hospital for a few hours. The supervisor and the security officer were discharged that evening. The inspection authorities for classified facilities were informed. The security officer could not say why he went into the room without waiting for it to be ventilated.

An inspection of the inerting system found a defective valve. Although this was unrelated to the accident, it caused the CO2 backup injection line to be accidentally activated and 13 cylinders to be struck instead of the nine that were initially planned.