Three Hazop Questions:
"What could go wrong?"
"How would we know it?"
"What could we do about it?"
Process Safety Management, within which the Hazard and Operability (HAZOP) discipline is a key component, has been unquestionably successful in reducing the incidence and mitigating the consequences of major accidents in all industries dealing with toxic, reactive, flammable and explosive substances. There has not been quite another Flixborough much less a Bhopal type incident since the widespread advent of these procedures. This means protecting the communities adjacent to such facilities as well as the workers within them.
For the current practitioner, there is an emphasis on this site to the founding purposes and the excellence observed in the initial work. This seems significant now when there have been fewer catastrophes on the front pages of the newspapers. And especially now with a new generation seeking to ensure safe operations of what are by their component nature, although providing essential goods to the societies we live in, potentially dangerous facilities.
"At about 16:53 hours on Saturday 1 June 1974 the Nypro (UK) site at Flixborough was severely damaged by a large explosion. Twenty-eight workers were killed and a further 36 suffered injuries. It is recognized that the number of casualties would have been more if the incident had occurred on a weekday, as the main office block was not occupied. Offsite consequences resulted in fifty-three reported injuries. Property in the surrounding area was damaged to a varying degree.
"Prior to the explosion, on 27 March 1974, it was discovered that a vertical crack in reactor No.5 was leaking cyclohexane. The plant was subsequently shutdown for an investigation. The investigation that followed identified a serious problem with the reactor and the decision was taken to remove it and install a bypass assembly to connect reactors No.4 and No.6 so that the plant could continue production.
"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. This resulted in the escape of a large quantity of cyclohexane. The cyclohexane formed a flammable mixture and subsequently found a source of ignition. At about 16:53 hours there was a massive vapour cloud explosion which caused extensive damage and started numerous fires on the site.
"Eighteen fatalities occurred in the control room as a result of the windows shattering and the collapse of the roof. No one escaped from the control room. The fires burned for several days and after ten days those that still raged were hampering the rescue work."
Citation from the HSE: {3}"Its shock waves echoed all around Britain as neighbours of similar or older plants deluged politicians with fears about nearby installations. Within days, the government decided that a Public Inquiry was necessary to allay public concern." Citation from The Chemical Engineer (April 2005): {4}
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Personal recollections from some of those impacted by the Flixborough accident are collected here. "No claim is made for the veracity of these notes. They represent half-remembered, apocryphal experiences... because the sadness and the shock, if nothing else, were real and true." |
"Great Britain has a tradition of health and safety regulation going back over 150 years. The recent system came into being in 1974 when the HSW Act set up new institutions and provided for the progressive revision and replacement of all health and safety law then existing." {5}
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"A body of up to ten people... One of the present members.. represent(s) the public interest. HSC's primary function is... the health safety and welfare of people at work, and the public... including proposing new laws and standards, conducting research, providing information and advice, and controlling... dangerous substances." {5} |
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"Three people appointed by the Commission (and local government)... The executive's staff, approximately 4000, include inspectors, policy advisors, technologists and scientific and medical experts - collectively known as HSE." {5} |
"The Health and Safety Commission met for the first time on October 1, 1974. HSC's annual report for 1977/78 states: 'Our overriding concern is... to stimulate awareness of the risks and encourage the joint participation of workers and management to eliminate them.' The new Act, which largely reflected recommendations of the 1972 Robens Report, introduced a broad goal-setting, non-prescriptive model, based on the view that 'those who create risk are best placed to manage it.'" {6}
As a result of the Europen Union's "Seveso" Directive of 1982 (more on that, below) the HSC implemented the Control of Industrial Major Accident Hazards (CIMAH) legislation for the UK in 1984. And again, in 1999, the HSC made the regulation even more robust with Control of Major Accident Hazards (COMAH).
Comments on the facts of this case.
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First of all- cyclohexane {9}. While at Flixborough this molecule was one of the feed components for the production of nylon, the reader may more easily relate as it is also a component in gasoline - molecules selected because they ignite with air easily to produce lots of energy. With six carbon atoms, a boiling point of 178F, a low flash (-4F) and a wide flammable/explosive range (1.3% - 8.4%); it is smack in the middle of the 500 molecules we typically find in gasoline (Carbons: 3-12; Boiling Points: 86F - 428F) {10}. Potentially dangerous stuff! |
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Second of all - the quantities of it. Only 6% was converted with each pass - Trevor Kletz has likened this to a flight from London to New York where only 6% of the passengers disembark at each leg. That meant that 40 tonnes (88,000 pounds) was available to feed the fires... anecdotal evidence from some insurance sites suggests that 10,000 pounds of highly reactive/ flammable/ toxic material is generally found in incidents with a major impact on the community. |
So...regardless of whether the initiating event was the rupture of the 20" line, built on staging without any engineering - a highly unusual, third-party-responsible, unlikely to be replicated event, or whether it was simply a loose flange on an 8" line, likely to occur anywhere... it was inherently unsafe to have so much of such highly flammable material without substantially more stringent safeguards in design, operation, maintenance, change control, start-up, human factors and overall management oversight.
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Created on ... July 21, 2006