Flixborough disaster

Mechanical engineering issues with the modification were overlooked by the managers who approved it, and the severity of potential consequences due to its failure were not taken into account.The chemical works, owned by Nypro UK (a joint venture between Dutch State Mines (DSM) and the British National Coal Board (NCB)) had originally produced fertiliser from by-products of the coke ovens of a nearby steelworks.This was originally produced by hydrogenation of phenol, but in 1972 additional capacity was added, built to a DSM design in which hot liquid cyclohexane was partially oxidised by compressed air.The foundations of properties severely damaged by the blast and subsequently demolished can be found on land between the estate and the village, on the route known as Stather Road.Each reactor was slightly (approximately 14 inches, 350 mm) lower than the previous one, so that the reaction mixture flowed from one to the next by gravity through nominal 28-inch bore (700mm DN) stub pipes with inset bellows.It was decided to install a temporary pipe to bypass the leaking reactor to allow continued operation of the plant while repairs were made.[e] Immediately after the accident, New Scientist commented presciently on the normal official response to such events, but hoped that the opportunity would be taken to introduce effective government regulation of hazardous process plants.With the passage of time these sentiments are diluted into bland reports about human error and everything being well under control – as happened with the Summerland fire.Nypro had recognised this to be a weakness and identified a senior mechanical engineer in an NCB subsidiary as available to provide advice and support if requested.At a working level the offset was accommodated by a dog-leg in the bypass assembly; a section sloping downwards inserted between (and joined with by mitre welds) two horizontal lengths of 20-inch pipe abutting the existing 28-inch stubs.Nor did anyone appreciate that the hydraulic thrust on the bellows (some 38 tonnes at working pressure) would tend to make the pipe buckle at the mitre joints.[i]The Inquiry noted further that "there was no overall control or planning of the design, construction, testing or fitting of the assembly nor was any check made that the operations had been properly carried out".[j] The claim argued by experts retained by Nypro and their insurers[3] was that the disaster's cause was that the 20-inch bypass was not what would have been produced or accepted by a more considered process.The metal of the pipe would have experienced hard-to-detect deformation, microscopic cracks, and structural weakness as a result, increasing the likelihood of failure.We use the phrase "already remote" advisedly for we wish to make it plain that we found nothing to suggest that the plant as originally designed and constructed created any unacceptable risk.[q] Of one proponent the report noted gratuitously that his examination by the court 'was directed to ensuring that we had correctly appreciated the main steps in the hypothesis some of which appeared to us in conflict with facts which were beyond dispute'.[6]The HSE website as of 2014 said that "During the late afternoon on 1 June 1974 a 20 inch bypass system ruptured, which may have been caused by a fire on a nearby 8-inch pipe".[t] This hypothesis has however been revived, with the tears being caused by fatigue failure at the top of the reactor 4 outlet bellows because of flow-induced vibration of the unsupported bypass line.It was postulated that there had been bulk water in reactor 4 and a disruptive boiling event had occurred when the interface between it and the reaction mixture reached operating temperature.Historically good process safety performance at Wilton had been marred in the late 1960s by a spate of fatal fires caused by faulty isolations/handovers for maintenance work.[22] The more onerous requirements were justified as follows: Why do we need the [ICI Heavy Organic Chemicals Division][O] rules on the isolation and identification of equipment for maintenance?The terms of reference of the Court of Inquiry did not include any requirement to comment on the regulatory regime under which the plant had been built and operated, but it was clear that it was not satisfactory.Construction of the plant had required planning permission approval by the local council; while "an interdepartmental procedure enabled planning authorities to call upon the advice of Her Majesty's Factory Inspectorate when considering applications for new developments which might involve a major hazard"[27] (there was no requirement for them to do so), since the council had not recognised the hazardous nature of the plant[3] they had not called for advice.As the New Scientist commented within a week of the disaster: There are now probably more than a dozen British petrochemical plants with a similar devastation-potential to the Nypro works at Flixborough.The company would have to show that "it possesses the appropriate management system, safety philosophy, and competent people, that it has effective methods of identifying and evaluating hazards, that it has designed and operates the installation in accordance with appropriate regulations, standards and codes of practice, that it has adequate procedures for dealing with emergencies, and that it makes use of independent checks where appropriate" For most 'notifiable installations' no further explicit controls should be needed; HSE could advise and if need be enforce improvements under the general powers given it by the 1974 Health and Safety at Work Act (HASAWA), but for a very few sites explicit licensing by HSE might be appropriate;[y] responsibility for safety of the installation remaining however always and totally with the licensee.ACMH felt that for major hazard installations[z] the plan should be formal and include Safety documents were needed both for design and operation.We believe that to this end considerable formality is essential in relation to such matters as permits to work and clearance certificates to enter vessels or plant areas.[aa]The ACMH's second report (1979) rejected criticisms that since accidents causing multiple fatalities were associated with extensive and expensive plant damage the operators of major hazard sites had every incentive to avoid such accidents and so it was excessive to require major hazard sites to demonstrate their safety to a government body in such detail: We would not contest that the best run companies achieve high standards of safety, but we believe this is because they have .... achieved what is perhaps best described as technical discipline in all that they do.