What was the Flixborough disaster?

On 1 June 1974 the Nypro UK site at Flixborough, which produced nylon, was severely damaged by a large explosion.

Such was the force of the blast pressure wave that 1,800 homes were damaged within a mile radius of the site. 28 workers were killed with 35+ more suffering injuries.

Had the accident taken place during a weekday then it’s likely that there would have been further casualties - the flame jet hit the office block which would have had more than 50 people at work and 200 people at the factory.

What caused the Flixborough explosion?

The cause of ignition is unknown, however prior to the accident it was discovered that reactor #5 was leaking - as a precaution the plant was shut down.

A bypass to reactors #4 and #6 was installed which failed - this caused a fire and ruptured some other process pipes, allowing product to escape and form a large flammable cloud. At around 5pm the cloud found its way to an ignition source, causing the explosion. 

The explosion caused extensive damage and the fire burned for 10 days.

What can the industry learn from the Flixborough disaster?

It transpired that a plant modification occurred without a full assessment of the potential consequences - only limited calculations were undertaken to assess the integrity of the bypass line.

Study of the remaining vessels and items on-site suggest the kind of overpressures experienced during the blast. Calculation for the vapour cloud and its air fuel mass also helped predict the size equivalent to an explosive measure in this case.

Various reports conclude that the net crushing pressure on the skirts of these vessels must have been in excess of 760 kPa (7.6 bar) and that the explosion itself is as much as 15 bar.