At 11.30 am, about 750,000 m3 of gas were released from a section of pipework of a blast furnace. The gas was both flammable and toxic, containing 21% carbon monoxide and 5% hydrogen. The on-site emergency plan was not formally initiated but the workers sheltered in toxic gas refuges and the fire service attended as a precaution.

The blast furnace was shutdown, with all the gas being discharged through the flarestack. Since the flarestack was out of order (the flare had been in alarm for at least 10days) because the pilot flame was not alight, the gas was released unburnt.

Fortunately, the gas did not ignite (thanks to the heavy rain and wind ?). A concentration of 400 ppm carbon monoxide was measured 200 metres away, but no off-site effects were reported.

A ruptured seal on a valve in the blast furnace gas pipework caused the initial release. This rupture is due to the conjunction of technical and organisational failures. The Competent Authority investigation revealed that in total 130 tonnes of gas was lost from the ruptured valve together with 77 tonnes from the flarestack.

The iron and steel works was a newly classified top tier SEVESO establishment because of the inventory of toxic and flammable gas in the blast furnaces and in storage. Little previous work has been done to evaluate the management system in place to prevent and mitigate potential major accidents. The Competent Authority required the company to modify operating and work control procedures. The blast furnace remained shut down for over 1 week at a cost of over £1 million.