Science Fair Project Encyclopedia
The chemical plant, owned by Nypro (UK) and in operation since 1967, produced caprolactam, a precursor chemical used in manufacture of nylon. The process involved oxidation of cyclohexane with air in a number of reactors to produce a mixture of cyclohexanol and cyclohexanone. Two months prior to the explosion, a leak discovered in one of the reactors caused a plant shut down. While the reactor was repaired, a temporary 50 cm (20 inch) diameter bypass pipe was installed to enable continued operation of the plant.
Just before 17:00 on 1 June, there was a rupture in the bypass pipe containing cyclohexane at 150 °C and 1 MPa pressure. Within a minute, about 40 tonnes of the plant's 400 tonne store of cyclohexane leaked from the pipe and formed a vapour cloud of 100–200 m diameter. The cloud, on finding an ignition source (probably a furnace at a nearby hydrogen production plant) exploded, completely destroying the plant. Around 1800 buildings within a mile radius of the site were damaged.
The fuel-air explosion was estimated to be equivalent to 15 tonnes of TNT (60 gigajoules) and it killed all employees in the nearby control room. It happened late on a Saturday afternoon, and observers have said that had it occurred on a weekday, more than 500 plant employees would likely have been killed. Resulting fires raged in the area for over 10 days.
The official inquiry into the accident determined that the bypass pipe had failed due to unforeseen lateral stresses in the pipe during a pressure surge. The bypass had been designed by engineers who were not experienced in high-pressure pipework, was inadequately tested, and was mounted on temporary scaffolding poles that allowed the pipe to twist under pressure.
The disaster led to a widespread public outcry over industrial plant safety, and significant tightening of the UK government's regulations covering hazardous industrial processes.
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