This accident occurred on a boiler near a 70 m³ propane tank in an agricultural seed production facility. The propane is heated by the boiler connected to a heat exchanger. At around 8 p.m., the boiler was rocked by 3 explosions. The personnel gathered at the rally point, the emergency services were alerted and the installations were secured. The unit’s electrical power supply was disconnected, and the tank valves were closed. The firefighters noted that a flare had formed, with flames shooting upward to heights of 3 m, on the automatic purgers and the hot water network valve feeding the exchanger. They set up a safety perimeter of 140 m and sprayed the tank down with a fire hose.

The boiler room was destroyed: doors were blown off, chimneys blown out, and safety devices destroyed. The amount of propane released was estimated at 900 kg.

The Classified Facilities Inspection Authorities went to the site and noted several discrepancies with the site’s operating permit: incorrect boiler locations, absence of gas and control detectors, inadequate inspections. Following the inspection, a Prefectural Order was issued regarding the emergency measures to be taken to guarantee the propane tank’s safety.

The analysis conducted by the site’s operator and the tank’s owner revealed a crack in one of the heat exchanger’s propane vaporisation tubes. Owing to the pressure difference, the propane was released into the hot water piping. For an undetermined reason, the hot water system’s isolation equipment did not fulfil its job. The propane was able to enter the entire network: boiler, safety valve and purge elements. According to the operator, the first explosion occurred when the propane gas, released by the valve, came into contact with the boiler’s flame.

The expert assessment attributed the cracking in the tube to the freezing temperatures the installation had experienced. The operator did not have an appropriate operating procedure to deal with this phenomenon. To prevent the water in the heat exchanger tubes from freezing when the propane expands (notably during boiler shutdowns), the heat exchanger manufacturer recommends that glycol be added to the water. The operator added water without adding glycol and did not monitor its concentration.

The operator decided to replace the hot water vaporiser coupled to a boiler with an electric vaporiser.