It was found that multiple flammable hazardous chemicals with high risks of explosion and fire were used in the washing process room of Building 56 at the Hanwha Aerospace Daejeon business site, where seven people were killed or injured.
According to the Hanwha Aerospace workplace environment measurement report released on the 4th by the office of Rep. Cho Ji-yeon of the People Power Party on the Climate, Energy, Environment and Labor Committee, which received it from the Korea Occupational Safety and Health Agency, the process room where the accident occurred handled large quantities of chemicals, including 8,240 kg of cleaning agents per month, 36,000 kg of propellant, and 730 liters of by-product fuel oil.
The components of the cleaning agents and propellant include 1,2-dichloroethylene, aluminum (metal dust), toluene, and magnesium oxide. 1,2-dichloroethylene is used as an industrial degreaser and precision cleaning agent, and is used for degreasing metal product surfaces, removing grease, and cleaning precision electronic parts.
In particular, as a highly volatile organic compound, inhalation in an enclosed space can cause central nervous system depression, and because it is highly flammable, strict ventilation facilities are required when handling it in industrial settings.
Metal dust is also known to pose a very high risk of explosion when it meets an ignition source. Toluene is also used as a main ingredient in explosives, and because it has a very low flash point, it can explode or burn rapidly even from static electricity.
Despite the union's consistent demands to improve ventilation equipment, the introduction of large-scale ventilation facilities reportedly stalled. The company also explained in the early stages of the accident that because both chemicals and water were used in the washing process, the risk of fire or explosion was low. In response, criticism is emerging that while handling highly hazardous substances, complacency about safety may have worsened the human toll.
The fact that propellant residue was stored inside the process room in nonconductive wooden boxes is also being cited as a cause of the disaster.
However, Hanwha Aerospace explained that it did not use propellant in the process room and that even the waste propellant generated during cleaning was less than 3,600 kg. It also said that 1,2-dichloroethylene and aluminum powder are designated as "non-hazardous materials" by the Korea Fire Institute (KFI).
Police and labor authorities on the day conducted search and seizure at the Daejeon business site, Hanwha headquarters, and the Hanwha R&D Campus, and are determining responsibility for the accident. Hanwha Aerospace decided to suspend operation of the production line entirely on Apr. 4–5 except for some essential processes, and to conduct special safety inspections and safety training.