Alfalfa pellets caught fire in a 12,000 t flat-bottom silo at Sunday. A pungent smell of smoke could be detected in the neighbouring town. The combustion zone was located 4–5 m in the middle of the pile of pellets. The temperature of the hot spot was between 400 and 500 °C. The operator removed 500 t of pellets that day and 750 t the following day. The unburnt alfalfa pellets were analysed and then transferred to another site in the group. Their temperature was checked on arrival. Firefighters, alerted about the fire, helped to define the procedure for emptying the remaining pellets. Two days later, emptying resumed after an overnight break and the frequency of the trucks arriving to take the pellets away round the clock was ramped up. The firefighters began spraying the burning pile sparingly to lower its temperature and knock down dust. After 850 t had been taken away, the removal operations were suspended once hot pellets were reached. The firefighters then changed procedure and started dumping the hot pellets at an unloading area created on the site. They doused the burning pellets. The firewater was collected in a pond created on the site. The fire was extinguished four days later.

The hypothesis of a water leak in the silo’s roof or water intrusion via its slab was ruled out because the hot spot was located 4 m in the middle of the pile. Intrusion would have created a rat-hole-type hot spot (from the top of the pile to its bottom). Likewise, a process problem appeared unlikely as the pellets in the silo were from the first alfalfa cut of April 2017. Before being placed in the silo, the pellets had been stored in another silo for three months and monitored. They had also been sifted several times to remove dust. The possibility of incoming load that had been wetted by rain or a storm because a carrier failed to adequately cover was also ruled out because no rain had fallen during the period that the silo was being filled. However, in its post-accident analysis, the operator wondered about a truck delivery of a formulation consisting of a mixture from three storage bins. However, it admitted that this possibility seemed unlikely given the small amount delivered, the non-excessive temperature detected, the absence of customer complaints about this formulation, and the lack of other convincing evidence from the delivery silo.

Before repairing the silo, the operator revised the procedures for managing shipments and deliveries and for working at the silo. Temperature monitoring in the silo was changed and enhanced and the silo was overhauled.