In a chemical adhesives plant, liquid methylene chloride (CH2Cl2, irritant, toxic by inhalation, and highly odorous), being used as a solvent, was being reheated when a product spill was discovered at about 7 a.m. on the ground floor of the solvent-based adhesive manufacturing unit. Two technicians climbed to the floor where the heater was located and discovered a 20-litre methylene chloride vapour leak on the steam condenser safety valve associated with the mixer receiving the heated product. As the atmosphere became unbreathable, the technicians were able to manually open the smoke extraction hatches before one of them collapsed. The other technician, feeling ill, called for help. They were evacuated from the workshop by co-workers, and then received care from the emergency response services who had been alerted by the guard station. After receiving oxygen, they returned to their post around 11:30 a.m. The mixer was stopped and cooled down while the building was ventilated.

The investigation conducted by the operator shows that the heater set point temperature had been programmed at 42 °C (the set point temperature of flammable adhesives) although the boiling temperature of the solvent is 40 °C. Overheating caused the solvent in the mixer to boil, liquid methylene chloride vapours to be transferred to the condenser, and the safety valve to open. The recent installation of a nitrogen injection system in the mixer, designed to inert the mixer’s vapour space (which is a risk with flammable glues), accentuated the accidental spill. There was no emergency procedure in place to manage an eventual release of methylene chloride vapours.

The operator modified the manufacturing procedures for methylene chloride adhesives and the temperature set points. In addition, the nitrogen inerting process was stopped during the manufacture of non-flammable adhesives. Staff were reminded that there is a device to automatically open the smoke extraction hatches from the ground floor level.