Tata Steel UK failed repeatedly to act on the recommendations of a process hazard review (PHR), which identified the loss of cooling water to the plant's benzole separation process as an "intolerable risk".
On 17 June 2011, a large quantity of benzole vapour -- a known carcinogen and highly flammable -- was released through an open sight glass (inspection porthole). The vapour cloud, a mixture of benzene and toluene, spread across the site leaving two workers with breathing difficulties and risking the death of five if the cloud had ignited.
The 2007 PHR by engineering contractor ABB recommended that Tata Steel UK replace missing glass on portholes on two benzole plants. It also advised installing a trip system to isolate the steam supply and fitting a pressure alarm. None of the suggestions were acted on in 2007, nor in 2008 or 2009 after ABB carried out follow-up reviews.
Hull Crown Court was told on 11 August that the open portholes were unofficially used for venting pressure in the plants, which produce benzole as a by-product of the site's coke ovens.
Alarms on one of the plant's cooling water pumps -- which failed, allowing the pressure to build -- were not working. Separate temperature alarms were incorrectly set.
On the day of the incident, five repair and maintenance contractors were called to mend a major steam leak on No 2 plant, which involved replacing a seal on the top of a vessel. Operations on No 1 plant continued while the repairs were made.
When the cooling water pump failed -- stopping the supply to No 1 plant -- the plant pressure built up and the porthole half way up this plant started "gushing brown liquid".
Two of the exposed workers experienced breathing difficulties when they were enveloped by the white vapour cloud, which the liquid gave off and had spread across the plant. Both were sent to hospital but were discharged the next day.
Sentencing, Judge Jeremy Richardson said Tata Steel UK's worst failing was its disregard of the warnings in ABB's PHR reports which flagged the potential for a release at Scunthorpe, classified as a top-tier facility under the Control of Major Accidents Hazards Regulations.
He said: "The fact that it took several years for the eventual near catastrophe to occur is scant mitigation when the system is seriously flawed -¦ For a company the size of the defendant to adopt such a slap-dash attitude was, and remains, frankly, deplorable".
Judge Richardson told the court that he had asked for an estimate of what it would have cost Tata Steel UK to undertake the work to remedy the PHR hazards identified in 2007, 2008 and 2009.
"Precise figures are not available, but having liaised with the current owners of the plant, the cost was estimated to be in the region of £25,000," he said. "That was not a high sum of money for very estimable gains in terms of health and safety in a company of the size and importance of the defendant."
The judge decided that Tata Steel UK's level of culpability was high under the sentencing guidelines and the seriousness of harm was level A, with a medium likelihood of harm. This produced a final harm category of 2, which the judge adjusted upward to 1 before setting the fine, to reflect Indian-owned Tata Steel Europe's turnover of more than £2.18bn.
The starting point for the penalty was £2.4m and the judge applied discounts for the fact that Tata Steel UK is loss-making and "faces an uncertain future in an unpromising world for steel and by-products" and for its guilty plea at the earliest opportunity. As well as the £930,000 fine, Tata Steel UK must pay costs of £70,000.
In 2016 Tata Steel UK sold the Scunthorpe works for £1 to British Steel, a company formed the same year to make long-steel products.
Health and Safety Executive inspector Steve Hargreaves told IOSH Magazine: "Although there weren't major consequences that came from this incident, there was a very large potential and the company knew that there was before it happened. It was completely foreseeable that this could occur.
"Had [the vapour] ignited on the day-¦ we could have been talking multiple fatalities."
