The accident occurred while residues were being cleared from a nitrotoluene distillation still. A fireball shot out of the still and badly damaged two nearby office buildings, causing the deaths of five employees and seriously injuring two more (ENDS Report 212, pp 10-11 ).
After an investigation, the Health and Safety Executive (HSE) brought a prosecution under section 2(1) of the Health and Safety at Work Act 1974. The company pleaded guilty to the charge of failing to ensure the safety of its workers when the case was heard at Leeds Crown Court on 30 July.
The court heard how Hickson's management decided to clear out the still without full regard for the possible consequences. The operation was unusual and had never been carried out in the 30-year life of the still.
The company decided to soften the residues by heating them with steam, even though they contained nitrotoluenes and were thermally unstable. Although staff were told not to let the temperature of the mixture exceed 90° C, they had no adequate means of measuring the temperature.
The thermometer inside the vessel was above the level of the residues and did not accurately measure their temperature. The mixture eventually exploded in a massive fireball which shot out of the open hatch of the still and devastated a control room building and a nearby office block.
The prosecution told the court that a multiplicity of possible charges could have been brought against the company, but the HSE had decided to combine these into a single charge. Apart from the decision to clean out the still, other major breaches included the faulty construction of the control room building and inadequacies in smoke protection in the office block.
Four of the five fatalities occurred in the control room building, which was built of wood and had doors opening inwards. Following the 1974 Flixborough disaster in which 28 people were killed after a caprolactam plant exploded, industry guidelines have specified that such buildings should be built to withstand explosive impacts.
The fifth person died of smoke inhalation in the office block after the smoke protection systems were breached. The HSE's investigation found that services installed above a suspended ceiling had breached the building's smoke barriers.
The defence acknowledged that the accident happened because Hickson & Welch had no means of ensuring that its operations benefitted from new technical knowledge. The company has since created a method-study committee and established more stringent design criteria for control rooms.
In summing up, Mr Justice Holland said that the tragedy was "not just a casual breach of an employer's duty" but a "plain gap in an employer's management that should never have occurred". Hickson & Welch was fined o250,000 and ordered to pay costs of o150,000.
The fine is one of the largest ever imposed under the 1974 Act. British Rail was fined the same amount after the Clapham rail disaster in December 1990 when an electrical signalling fault resulted in the deaths of 35 people.
Nobels Explosives, a subsidiary of ICI, was also fined o250,000 after a delivery van exploded in Peterborough in March 1989. The blast killed a fireman and injured 100 others. Tate and Lyle was fined o250,000 in April 1990 after an employee was suffocated at its Greenock sugar refinery. However, the fine was reduced to o100,000 on appeal.
Recent major fines under the 1974 Act have included o100,000 each for Allied Colloids and Shell. The former related to the incorrect storage of chemicals which caused a major blaze last year at the company's Bradford site (ENDS Report 217, p 42 ). And Shell was fined last January for maintenance failures which almost caused a catastrophic explosion at its Stanlow refinery.
Meanwhile, hardly had the case in Leeds been concluded when a blast rocked Hickson International's Pharmachem plant at Ringaskiddy, near Cork, Eire. Two employees were taken to hospital suffering from shock and minor injuries. The explosion destroyed one of the plant's two production lines.