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The Flixborough Explosion



On the afternoon of Saturday 1st July 1974 a major explosion destroyed part of the Nypro chemical plant at Flixborough, near Scunthorpe, North lincolnshire. The blast was the equivalent of 15 tonnes of TNT. A total of 28 people lost their lives on-site, a further 36 were seriously injured and there were 53 off-site injuries.
The BBC made a documentary programme analysing the events on that day, which is available as a safety training DVD called "Flixborough Disaster".



Nypro (UK), owner of the Flixborough plant, was set up as a joint venture between the British National Coal Board (NCB) and the Dutch state mines (De Nederlandse Staatmijnen or DSM). The Flixborough plant been built to supply caprolactam, used in the production of nylon. Production began in 1967.

The chemical process to produce caprolactam involves the oxidation of cyclohexane. Cyclohexane is highly combustible, and it was a vapour cloud of this chemical that destroyed the plant in an explosion.


Background to the Explosion

On 27th March 1974 it was noticed that cyclohexane was leaking from Reactor Number 5, and the plant was shut down for safety reasons. Investigations revealed a vertical crack in Reactor Number 5 was allowing cyclohexane to escape.
In order to continue production it was decided to isolate temporarily the damaged reactor by linking Reactors 4 and 6 using a 20-inch diameter pipe. The modification was quickly completed and production was resumed.
Unfortunately, the modification was made following only rudimentary calculations being made, and no allowance at all was made for the fact that the pipe had to be kinked. Furthermore the pipe was not tested under pressure before being put into service. A few months later these factors had fatal consequences.


The Explosion

In the late afternoon on 1st July 1974 the temporary bypass pipe carrying cyclohexane under pressure at 150 degrees Centigrade ruptured. About 40 tons escaped and formed a vapour cloud hundreds of feet in diameter. The vapour cloud came into contact with a source of ignition and exploded, destroying the plant.

There were no survivors in the Control Centre, where eighteen people were killed by flying glass from the shattered windows and by the collapsing of the roof.



A Public Inquiry

A public inquiry was held following the disaster. This criticized the inadequacy of the change control arrangements and the incorrect use, under high pressure, of a pipe which could flex, on supports which could flex and linked by bellows which could deform.



Safety Training Material

The BBC's "Flixborough Disaster" DVD is about the explosion at Flixborough. Details can be found here.


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