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Process safety

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Katie Henson

on 13 January 2016

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Transcript of Process safety

Process safety management
Case studies
Flixborough 1974
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On the 1st July 1974 the temporary bypass pipe carrying cyclohexane under pressure at 150 degrees Centigrade ruptured. About 40 tonnes escaped and formed a vapour cloud hundreds of feet in diameter. The vapour cloud came into contact with a source of ignition and exploded, destroying the plant. 28 people were killed and 36 injured.
This incident led to the CIMAH and COMAH to form.
Process safety management is an analytical tool focused on preventing releases of any substance defined as a "highly hazardous chemicals" by the EPA or OSHA.Process Safety Management (PSM) refers to a set of inter-related approaches to manage hazards associated with the process industries and is intended to reduce the frequency and severity of incidents resulting from releases of chemicals and other energy sources.
Seveso 1976
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At approximately 12:37 on Saturday 10th July 1976 a bursting disc on a chemical reactor ruptured. Maintenance staff heard a whistling sound and a cloud of vapour was seen to issue from a vent on the roof. A dense white cloud, of considerable altitude drifted offsite.

Among the substances in the white cloud was a small deposit of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (‘TCDD’ or ‘dioxin’), a highly toxic material.

The release lasted for some twenty minutes. Over the next few days following the release there was much confusion due to the lack of communication between the company and the authorities in dealing with this type of situation.

The nearby town of Seveso, located 15 miles from Milan, had some 17,000 inhabitants. No human deaths were attributed to TCDD but many individuals fell ill. 26 pregnant women who had been exposed to the release had abortions. Thousands of animals in the contaminated area died and many thousands more were slaughtered to prevent TCDD entering the food chain.
Process Vs Personal Safety
Personal safety incidents (slips,trips and falls) are high frequency with a low consequence incident.
Process safety incidents can be seen as low frequency with a high consequence incident.
Process safety is a blend of engineering and management skills focused on preventing catastrophic accidents and near misses, particularly structural collapse, explosions, fires and toxic releases associated with loss of containment of energy or dangerous substances such as chemicals and petroleum products. These engineering and management skills exceed those required for managing workplace safety
(Adapted from Center for Chemical Process Safety of the American Institute of Chemical Engineers)
Piper Alpha 1988
Flixborough 1974
Seveso 1976
Mexico city 1984
Pipa Alpha 1988
Texas city 2005

Process safety
Bhopal 1984
In November 1984, most of the safety systems were not functioning and many valves and lines were in poor condition. In addition, several vent gas scrubbers had been out of service as well as the steam boiler, intended to clean the pipes. Another issue was that Tank 610 contained 42 tons of MIC, more than safety rules allowed for. During the night of 2–3 December 1984, water entered a side pipe that was missing its slip-blind plate and entered Tank E610, which contained 42 tons of MIC. A runaway reaction started, which was accelerated by contaminants, high temperatures and other factors. The reaction was sped up by the presence of iron from corroding non-stainless steel pipelines. The resulting exothermic reaction increased the temperature inside the tank to over 200 °C and raised the pressure. This forced the emergency venting of pressure from the MIC holding tank, releasing a large volume of toxic gases. About 30 tonnes of MIC escaped from the tank into the atmosphere in 45 to 60 minutes. As a result thousands of people were killed.
Mexico city 1984
A petroleum gas pipe line between storage spheres failed, leading to LPG release which caught fire. The flames caused a boiling liquid expanding vapour explosion. This triggered a domino effect as one sphere after another exploded. Due to this incident 550 people were killed.
The installation of a more effective gas detection and emergency isolation system could have averted the incident. The plant had no gas detection system and therefore when the emergency isolation was initiated it was probably too late.
The accident was primarily caused by maintenance work simultaneously carried out on one of the high-pressure condensate pumps and a safety valve, which led to a leak in condensates.
After the removal of one of the gas condensate pump's pressure safety valve for maintenance, the condensate pipe remained temporarily sealed with a blind flange as the work was not completed during the day shift. Not aware of the maintenance being carried out on one of the pumps, a night crew turned on the alternate pump. Following this, the blind flange including firewalls failed to handle the pressure, leading to several explosions.
The fire at the platform intensified due to the failure in closing the flow of gas from the Tartan Platform. The automatic firefighting system had remained deactivated since divers worked underwater before the incident. Helicopter operations were hampered due to the amount of heat and smoke. Due to this incident 169 people were killed.
Following the tragedy, an inquiry into the accident commenced in November 1988 headed by Lord Cullen, which was published in November 1990. The inquiry was conducted in two parts. The first part studied the causes of the tragedy and the second part presented recommendations to avert future occurrence. It presented 106 recommendations for changes to North Sea safety procedures.

The inquiry brought about great changes in the offshore industry with regard to safety management, regulation and training. A major impact was responsibility for North Sea safety shifting from the Department of Energy to the Health and Safety Executive. Also, automatic shut-down valves were made mandatory on rigs, to starve a fire of fuel.
Texas city 2005
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