Government scientists have secretly reopened the investigation into the cause of the blast, which killed 28 and injured 53. The explosion in June 1974 at the plant, which was sited on the banks of the River Trent in Lincolnshire and produced the raw materials for nylon, caused devastation over a huge area. Blast waves were felt four miles away in Scunthorpe.
The BBC2 regional programme Close up North tonight reveals that tests being conducted by the Health and Safety Executive centre on the theory that water may have leaked into a tank of cyclohexane, a chemical used in the manufacture of nylon, causing a steep rise in pressure that blew piping apart.
The results of a public inquiry in 1974 suggested plant operators may have been negligent in letting the pressure rise. The water leak theory was suggested at the time of the inquiry by Ralph King, an engineer who was advising the plant operators. He claims his evidence was suppressed by lawyers.
Relatives of the dead workers have not been told of the new tests, which are understood to have been ordered by the Environment minister Michael Meacher.
Professor Jim Venart, an expert on industrial accidents, says: "The operators ... were innocent. Their families should have no shame." Experts have misinterpreted the size of the blast, he says. The report concluded up to 60 tonnes of cyclohexane were ignited. He believes only 10 tonnes were involved. That means safety measures introduced because of the blast may be inadequate.
"It's a probability that plants have been built too close to residential areas because this event has been fundamentally misunderstood," he says.
n Close Up North, BBC2, 7.30pm, Yorkshire and Lincolnshire regions.Reuse content