At 6 a.m., an employee at a waste treatment centre discovered a fire on a swath of shredded plants in the process of being composted. He alerted the fire brigade and a site manager. It took firefighters two hours to put out the flames using tanker trucks. They then returned to the site on 28/09 to put out another fire, despite the regular monitoring of the temperature of the swaths since the first incident. Over the course of the following days, the homogenate was spread out using a large-volume shovel to allow it to cool down. Most of the extinguishing water was absorbed by the vegetal homogenate, while the remainder flowed into the centre’s lagoon. Samples and analyses of the lagoon water were foreseen to confirm that no environmental impact had occurred.

The accident was caused by runaway temperatures in the composting process. In the days leading up to the accident, precipitation had penetrated deeply into the swaths of homogenate, bringing with it dissolved oxygen and accelerating the fermentation. Furthermore, additional homogenate had been recently added on top of the existing swaths, forming a second “layer”. The hot spots generated by over-fermentation at the bottom of the swath then ignited the homogenate that had been recently placed on top of it.

Following the accident, the operator decided to prohibit the layering of additional homogenate on top of a swath that was already being composted to avoid this “layering” effect. Also, during the accident, the operator increased the frequency of the temperature measurements on the waste being composted at its other composting centres located nearby, which were likely to be in the same configuration (also having received recent heavy rainfall) as that of the centre involved.