In a chemical plant manufacturing polyamide fibres, a temperature drop alarm on the heating fluid occurred at 5:40 a.m. in the control room. The roundsman sent to verify the problem discovered, around 6 a.m., thermal fluid leaking from a flange on a heat exchanger while a pressurised nitrogen test was being carried out in the polymerization building.
Degenerating leak of heat transfer fluid
The 600 litres of fluid, at 280 °C and at 3 bar, contained in the secondary loop of the exchanger, spread by gravity to the lower three floors through the non-hermetic flooring. The gradual shutdown was initiated when a fire broke out on the exchanger at around 6:40 a.m. (hot spots present while the product was above its flash point). The emergency services were alerted at 6:45 a.m. because the site’s internal fire brigade had difficulty fighting a very smoke-filled fire in a confined space. The internal contingency plan was initiated at 7:00 a.m. The 40 employees present at that time were evacuated. The utilities were shut down, and the thermal fluid system was quickly drained.
The fire spread through the ducts and roof
The fire had spread to the entire floor of the building by around 8:15 a.m. At about 9:50 a.m., the flames from falling siding enabled the fire to spread to the roof of the control room, which then filled with smoke and had to be evacuated. The response was hampered by the risks associated with the presence of radioactive sources in the sensors and by the compressed air system that was fanning the flames. The fire spread via the cable trays, containing oligomer dust deposits, to the asphalt roof of the neighbouring drawing building. Fighting the fire was complicated owing to the significant release of black smoke from the burning roofs. The roof fire was contained around 2:30 p.m. and the fire brigade left the site at 5 p.m.
Fifty-two of the 130 employees were technically unemployed for 3 months. Direct damages were estimated at €2 million: the 1,000 m² polymerisation building was destroyed, as well as the roof of the drawing building and the control room. The 60 m³ of extinguishing water mixed with the fluid was stored on site and then sent to be incinerated. The 40 m³ of textile-plastic covering and 50 m³ of titanium oxide suspension (raw or intermediate materials), plus solidified polymers, were sent to be incinerated. The mayors of the neighbouring communities visited the site with journalists, and the operator issued a press release.
An investigation was conducted to determine the origin of the leak. The following assumptions were made:
- flange seal assembly problem
- flange tightening problem
- poorly-controlled stop/start procedure
- design problem.
