Pollution
Humain
Environnement
Economique

A wheat spill occurred around 3:00 p.m. after the metal wall of a storage bin inside a 13,790 m3 square silo failed during a turning operation (movement of grain from one storage bin to another). A total of 200 tonnes of wheat spilled out between the silo and the fence surrounding the site until 4:00 p.m. Most the wheat was recovered, but 20 tonnes had to be composted. The silo, which was built in 1976, consists of 24 vertical open-top storage bins having a nominal capacity of 420 tonnes and measuring 22 m in height. An investigation conducted on 25 January by the inspection authorities for classified facilities found that the outer walls of the three other storage bins had been either repaired or reinforced following similar accidents. The investigation revealed that the accident and other events had not been reported, the separation distances relative to the administration buildings were insufficient, the gallery over the storage bins was coated with a thick layer of dust, the silo’s structure had not been periodically inspected and the conveyor belt on the gallery over the storage bins was not fitted with a drift detection device. Formal notification to bring the facilities into compliance was issued. An order for emergency measures was issued and recommended putting up a safety cordon to prohibit access to engulfment hazard areas, prohibiting further turning operations until the facilities were brought up to safety standards and having the stability of the silo’s structure inspected by an appropriate body. Following the accident, the silo operator planned to implement a system for monitoring ageing of the silo structures on all its sites.

An analysis of the storage capacities, conducted by an inspection body, revealed design and manufacture defects. For example, the storage-bin angle piles made of vertical welded flat bars are not fitted with inner stiffeners or diaphragms to prevent diamonding deformation of the cross-section. Also, the welded flat-bar assembly is not fitted with any reinforcing cover strips and the quality of the welds is insufficient (non-penetration welds). The deformation phenomenon was intensified by the dissymmetric loading of the storage bins (side-by-side full and empty capacities), an unavoidable part of silo operation. The inspectors suggested reworking the poorly executed or cracked welds, fitting stiffeners for the outer storage bins and filling the piles of the central storage bins with concrete.

The assessment report of a silo, built the same year as this one and using the same methods, was submitted in November 2014. It revealed that the angle piles of storage bins are subject to diamonding when the storage bins are dissymmetrically loaded. It appears that these piles are not fitted with inner stiffeners. Deformation increases the fatigue of the inner welds. It also appears that these welds are of poor quality. The report suggested strengthening the piles by reworking the inner welds along the entire height and filling with concrete.