Flixborough Cyclohexane Explosion


A Nypro factory was located at Flixborough where large quantities of cyclohexane were used to produce nylon. Oxidisation of the cyclohexane produced a mixture of cyclohexanone and cyclohexanol The oxidisation took place in a series of six reactors, the reactors being joined by short 28 inch pipes with bellows. Each pass through the convertors only converts about 6% of the cyclohexane, and a large amount of recovery and recycling takes place.

When reactor five developed a crack, a temporary 20 inch bypass pipe was used to connect reactors four and six and remove reactor five from the chain to allow repairs to take place.

A work engineer was yet to be replaced at the time that the modification was performed, even though the designers of the piping had considerable experience. The design of the piping was done in chalk on the workshop floor by personnel unaware of the implications of the requirements on the piping to withstand 150C and 10 bar. The plant was online again in a few days.

The bypass pipe was fixed at either end to the bellows, but the scaffolding was used to support the bypass pipe proved to be inadequate, and the pipe was free to squirm when the pressure increased.

On June 1st, 1974 the pipe ruptured and allowed 40 tons of cyclohexane to be released in approximately one minute. With cyclohexane having properties somewhat similar to petrol, explosions occurred and an inferno took hold for 24 hours.

Had the explosion occurred on a weekday, more people may have been killed, including many of the 550 who worked there.

29 people died and over 100 were injured. The plant was destroyed, and 100 nearby homes were destroyed or badly damaged.

Although most resources relating to this incident blame the modification, some evidence to the contrary is raised in "Great Disasters" edited by John Canning.

Fix?

The inventory of 400 tons of cyclohexane may have made matters worse than if a more efficient process was used. The application of intensification, a form of inherent safety, may have been a good idea.

Fix?

Better safety requirements, expertise and configuration change control may have produced a bypass pipe that was suitable.

Similar?

The use of unsuitable piping also resulted in the Westralia fire.

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Flixborough 20 years after by Kletz looks at the (lack of) long term change as a result of the incident.