Flixborough: a bypass pipe on a chemical plant exploded — 28 dead and a new safety law

On 1 June 1974, the Nypro chemical plant at Flixborough, England, was destroyed by a massive explosion of cyclohexane. The disaster was caused by a hastily installed temporary bypass pipe connecting two reactors after one was removed for repairs. The pipe was designed by chemical engineers — no mechanical engineer was on site, as the post of Works Engineer had been vacant since January 1974. No calculations were performed for the pipe stresses, no drawing was made, and the assembly was not pressure tested to the required British Standard.

The bypass pipe, measuring 20 inches in diameter, ruptured under pressure, releasing tonnes of hot cyclohexane. The vapour cloud ignited almost immediately, causing a fuel-air explosion that demolished the entire site. 28 people were killed — 18 in the control room alone. 36 others were seriously injured. Approximately 2,000 buildings within a mile radius were damaged.

The Court of Inquiry found that the disaster was caused by 'a number of unlikely errors in the design and installation of a modification.' The Flixborough disaster led directly to the UK's Control of Major Accident Hazards Regulations and contributed to the European Seveso Directive, which established the modern framework for regulating major industrial hazards across Europe.