In a textile fibre production plant, the excessive concentration of 4,4′-methylene diphenyl diisocyanate (MDI) caused a runaway reaction and formation of a polymer inside a reactor beginning at 7 am; 3 tonnes of MDI were injected instead of 1 tonne. Reactor supply was shut off, the temperature of the medium rose from 120° to 160°C. In order to limit medium expansion inside the reactor and rack the polymer on the lower part, nitrogen was injected into the upper part, yet the medium mass could not be extracted. In order to lower temperature and release an expansion volume, the operator decided at 1:30 pm to open the manhole on the upper part of the reactor. A small-scale explosion occurred, causing one employee to fall to the ground and another to be burned by chemicals on the arm. Emergency services transported both injured employees to the hospital, in addition to setting up a 50-m safety perimeter and suspending local traffic. A 3rd employee suffered from a malaise.

The bursting disc on the vent broke, thus indicating a pressure topping 4 bar. The roof of the reactor exhibited a few traces of solvent liquid stemming from condensation of the vapours released and were dripping into the room. As a precautionary measure, the external stormwater network was confined. The reactor temperature dropped around 6 pm, though the polymer level was actually rising, reaching 15 cm from the manhole. The reactor supply lines were drained. At 6:50 pm, with the temperature still decreasing, the polymer overflowed by 20 cm above the manhole. Fire-fighters kept the area under surveillance.