Uranium-bearing products were dispersed in a temporary drum storage area at a plant that produces products such as uranium hexafluoride. The unburned uranium tetrafluoride fluoridation residues are packed in metal drums which, pending neutralisation and recycling, are stored in a building outside the production unit. A rise in ambient temperature due to a heat wave caused the pressure in one of the drums to rise and the rupture of its seal provided by the lid. The associated degassing of hydrofluoric acid was detected by the activation of the automatic detection system. A few hundred grammes of powder were scattered around the room and the mass of HF is not thought to have exceeded 500 g. The drum was cooled immediately, the atmosphere in the room was purified and the area surrounding the drum was decontaminated. Temporary measures were adopted to improve the temperature control in the room. Samples were taken from the environment. According to the operator, staff safety was not affected. This incident followed a similar type of event that occurred on 30 May last year. Since that incident, a sprinkler system had been installed in the building’s roof to limit the effects of solar radiation during the summer. This system, reactivated in the summer, proved to be incapable of preventing a recurrence of this event.