On the morning of Sunday 27 June 1982 two explosions occurred at the premises of Staveley Chemicals Limited. The source of the explosions was a pit containing drums of sulphur trioxide and of oleum. The drums of sulphur trioxide had been returned from customers more than 10 years previously and had then been stored in the open. Over the following years minor leaks developed through corrosion, and sulphur trioxide vapour began to escape as a visible fume. In November 1981 the company decided to overcome the problem by surrounding the drums with an absorbent solid. A pit was dug out on some open land within the works site, the drums placed within the pit, then covered over with a proprietary absorbent material and topped with crushed blast furnace slag. No special provision was made for drainage of the pit, nor to prevent ingress of ground water or rain. Drums of oleum were included together with the drums of sulphur trioxide in the pit.

The first explosion occurred at 10:45 hours on June 27th. Two drums were blown out of the site, over a public highway, to fall into open ground outside the works boundary and about 300 metres from the containment pit. Fortunately no injury to persons or damage to property was caused by these events. Further, but less intense explosions continued until the following day. A cloud of white acid mist billowed up from the site.

The Fire Brigade could not use water hoses because of the possibility of causing a violent reaction with any escaping oleum or liquid sulphur trioxide within the containment pit. It was decided that the best immediate course of action would be to put anhydrous sodium sulphate powder into the open pit in order to absorb liquid and suppress fuming. Several bags of this powder were thrown in and by 12:00 hours the mist emission was lessening. However, a second explosion occurred at 12:30 hours with a large release of acid mist but without ejecting any drums. There was a third explosion at about 14.30 hours. Tarpaulins were put over the pit to prevent the ingress of rain. The last explosion was at about 03:00 hours, the following morning. This explosion was minor compared with those on the previous day.

On Monday 28 June, a heavy steel grid was placed over the pit to reduce the risk of further drums being ejected. Temperature measurements were made in the pit, and found to be as high as 90°C in places. Subsequently the drums were all taken out of the pit and put on to open ground nearby. There were 32 sound drums remaining, and 25 corroded and empty or nearly empty.

KEY ISSUES:
• DRUM / CYLINDER HANDLING

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