In a plastics factory, an explosion occurred around 1:30 am near one of the two 1cu.m intermediate bulk containers (IBC) containing bleach (NaOCl), adjacent to the facility’s cooling tower. Internal fire-fighters were deployed and the internal emergency plan activated. The IBC explosion generated projectiles over a 10-m radius, with the plug being found on the other side of the cooling tower. The second IBC was toppled yet without any loss of confinement. A bleach and/or chlorine smell was perceptible within a 100-m radius, while the blast could be heard 1 to 2 km away. The Classified Facilities Inspectorate conducted an investigation after an analysis performed by the site operator. An (annual) inspection of the bleach supplier’s transfer-storage zone indicated that the bleach had been stored in a 30cu.m polyethylene, UV-protected tank featuring a vent and cladding on all sides. This facility was extracting NaOCl at the base of its storage zone to fill the reusable IBCs, which were not dedicated to storing NaOCl and therefore did not contain either any UV protection or a vent. Moreover, these containers were installed on wooden pallets. The suspect IBCs had remained exposed to air without any protection from the heat or sun for a full day at the supplier’s premises, then on 6th October until the explosion adjacent to the cooling tower at the operator’s site. The hypothesis forwarded by the operator related to the season’s high temperature, coupled with the amount of time these IBCs spent in storage, a time that was capable of decomposing the NaOCl along with generating chlorine and causing pressure to rise. As a matter of fact, the half-life of NaOCl drops from 100 days at 20°C to 5 days at 40°C. Also, the analysis of IBC remnants (darkened only at the base) suggested a gland leak on the valve at the base of the IBC, thus triggering an exothermic oxidation reaction of NaOCl on the wooden pallet and accelerating the decomposition phenomenon, which would explain why just one of the two IBCs was involved. A series of immediate measures were adopted, namely a supplier change, prohibition of partitioning IBCs, and storage in a room protected from both light and heat.