At around 2:20 p.m., work was underway in an ammonium nitrate-based fertiliser plant to cut empty heat exchanger piping containing nitric acid (HNO3) when a fire broke out. An oxycutter was being used for the cutting operation in the plant’s scrap facility. White steam fumes were emitted. The internal emergency plan was initiated, and first responders wearing self-contained breathing apparatus sprayed the exchanger with water to cool it down. Racks near the scrap facility, containing oxygen and acetylene cylinders, were evacuated. Firefighters using three fire hoses were able to put out the fire at around 4 p.m. Toxicity measurements were unable to detect NOx in the fumes released. Meanwhile, site employees armed with fire hoses continued the cooling operations. The fire extinguishing water was stored on site. Production operations were not affected, and only the unloading operations were disrupted for 2 hours. The operator informed the neighbouring factories and the local authorities of the accident.
The cutting operations were carried out by an external company, and a prevention plan was established. Part of the piping was made of titanium and it was this titanium piping that triggered the fire by heat transfer (spontaneous combustion) although it was not directly in contact with the oxycutter that was cutting the shell. The fire stopped spontaneously when the tube bundle was consumed.
Following a series of tests, the operator modified the technique for cutting exchangers consisting of titanium tubes and a steel shell: the shell is cut by oxyacetylene cutting techniques, and then the tubes are cut using a hydraulic shear. Oxyacetylene cutting must not be used when titanium is present since the hotspot cannot be sufficiently controlled to prevent a transfer of heat which could lead to the spontaneous combustion of this metal. The operator is also studying how to improve its coordination with the emergency services during an intervention, following problems encountered during the 1st intervention by the external firefighters.
