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Flixborough England Disaster 1974

 

The Flextorog disaster was an explosion at
a chemical plant near the village of Flextoro in North Lincolnshire, England,
on Saturday, 1 June 1974. Twenty-eight people were killed and 36 seriously
injured at the site at the time. . The
casualties could have been much higher, if the explosion occurred on a weekday,
when the head office was occupied. “Shock
waves shook the confidence of all chemical engineers in the country,”
wrote a contemporary operational safety activist
The disaster
is involved and may be the result of a hasty change. There
was no large on-site manager with experience in mechanical engineering (almost
all of the plant management had chemical engineering qualifications); managers
who agreed to mechanical engineering problems had been neglected with the
modification, and the seriousness of the possible consequences of their failure
was not appreciated

Flixborough has caused a public outcry over
the safety of the processing plants. In
parallel with the adoption of the Occupational Health and Safety Act in the
same year, a more systematic approach to process safety in the UK’s process
industries was introduced (and often cited), and – in in
conjunction with the Seveso disaster and therefore the EU Seveso Directives –
to clarify the UK Government’s regulation of plant treatment or storage of
large stocks of hazardous materials, currently (2014) under the Hazardous
Materials Regulations Major
Accident Report of 1999 (COMAH).

In
the DSM process, cyclohexane was heated to about 155 ° C before moving into a
series of six reactors. The
reactors were constructed of mild steel with a stainless steel liner; in
operation, they contained a total of about 145 tons of flammable liquid at an
operating pressure of 8.6 bar pressure 125 psi. In
each of the reactors, compressed air was passed through the cyclohexane,
causing oxidation of a small percentage of cyclohexane and production of
cyclohexanone, with some cyclohexanol also being produced. Each
reactor was slightly less than 14 inches lower than the previous one, so that
the reaction mixture flowed from one to the other by gravity through truncated
tubes with a nominal diameter of 28 inches DN 700 mm with bellows recessed. The
inlet of each reactor was deflected so that the liquid enters the reactors at a
low level; the
outflow flowed down a spillway with a ridge slightly above the top of the
outlet pipe. The
mixture leaving the reactor 6 was treated to remove the reaction products, and
the unreacted cyclohexane only about 6% reacted at each pass and then returned
to the beginning of the reactor loop.
Although
the operating pressure was maintained by an automatically controlled purge
valve once the installation was stabilized, the valve could not be used at
startup, in the absence of air supply, the installation being pressurized with nitrogen. During
startup, the purge valve was normally insulated and there was no way to escape
excessive pressure; the
pressure was kept within acceptable limits (slightly wider than those obtained
under automatic control) by the intervention of the operator (manual operation
of the vent valves A pressure relief valve with a pressure of 11 kg / cm 2 (156
psi) was installed.
At
approximately 16:53 on Saturday, 1 June 1974, there was a massive release of
hot cyclohexane in the lost reactor area 5 shortly after the resulting
flammable vapor cloud ignited and a huge explosion at the plant. Demolition of the site. The
incident occurred on the weekend, relatively few people were on site:
immediately, 28 people were killed and 36 injured. The fires continued on site
for more than ten days. Abroad,
deaths have not occurred, but 50 cases have been reported and about 2,000
properties have been damaged.
The
occupants of the factory laboratory saw the removal and evacuated the building
before it was released. Most survived. None
of the 18 occupants of the plant control room survived, more than the plant
surveys. The
explosion appeared to have occurred in the general area of ??the reactors, and
after the incident two sites were identified

 

 

the report concluded that the 20-inch
hypothesis involving ‘a single low-probability event’ was overall more credible
than the 8-inch hypothesis according to ‘a succession of events, most of which
are improbable
The
survey report identified “lessons learned” that he presented under
different headings; “General
comment (on the cultural problems underlying the disaster),” specific
lessons
directly
relevant to the disaster, but of general applicability are reported below; there
were also “general lessons” and “various lessons” of lesser
importance for the disaster. The
report also commented on the issues to be addressed by the Major Hazards
Advisory Committee.
No
one in the design or construction of the plant has considered the possibility
of a major disaster occurring instantly. It
was now obvious that such a possibility exists when large quantities of
potentially explosive materials are processed or stored. It
was of utmost importance that plants presenting an instantaneous disaster risk
as opposed to a growing disaster be identified. Once
identified, steps should be taken both to prevent such a disaster to the
greatest extent possible and to minimize its consequences, despite all the
necessary precautions. There
should be coordination between the planning authorities and the health and
safety committee so that planning authorities can be advised on safety issues
before granting planning permission; Similarly,
emergency services should have information to develop an emergency plan.
The
investigation summarized its findings as follows:
We
believe, however, that if the measures we recommend are implemented, the
similar risk of disaster, already low, will be reduced. We
use the term “already far” wisely because we want to make it clear
that we did not find anything that suggests that the facility, as originally
designed and built, created an unacceptable risk. The
disaster was caused entirely by the coincidence of a number of improbable
errors in the design and installation of a modification. Such
a combination of errors is very unlikely to be repeated. Our
recommendations should ensure that no similar combination occurs again and that
even if this happens, errors will be detected before serious consequences occur.

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