CIMAH Continued

7/26/2019 CIMAH Continued

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MAJOR HAZARDS AND

CIMAH


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FLIXBOROUGH ACCIDENT,

ENGLAND

Accident occurred on a Saturday in June 1974.

It had a major impact on chemical engineering in the UK.As a result, safety achieved a much higher priority in thecountry.

The plant was designed to produce 70,000 tons per yearof caprolactam, a basic raw material for the production ofnylon.

The process uses cyclohexane which has propertiessimilar to gasoline.

Under the process conditions in use at Flixborough(155oC and 7.9 atm), the cyclohexane volatizesimmediately when depressurized to atmosphericconditions.


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Several months before accident, reactor 5 in the serieswas found to be leaking. Inspection showed a vertical

crack in its stainless steel structure. Disaster due to bypass pipe section ruptureddue to

inadequate support and overflexing of the pipe sectionas a result of internal reactor pressures.

Upon ruptured, an estimated 30 tons of cyclohexanevolatized and formed a large vapor cloud. The cloud wasignited by an unknown source 45 seconds after therelease.

The resulting explosion leveled the entire plant facility,

including the administrative offices. A total of 28 peopledied and 36 others were injured. 18 of these fatalitiesoccurred in the control room when the ceiling collapsed.


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Some Lessons From Flixborough

Siting of major hazard installations

Licensing of storage of hazardous materials

Regulations for pressure vessels and systems; The structure, thepeople, the systems and procedures, and the safety office

Relative priority of safety and production

Use of standards and codes of practice Engineering of plants for high reliability

Design and location of control rooms and other buildings

Planning for emergencies

Unconfined VCE

Control of plant and process modifications Restart of plant after discovery of a defect

Decision-making under operational stress.


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Industrial Activities Covered by

CIMAH

(i) Process operationsinvolve a

dangerous substance which is either

toxic, explosive or flammable.

(ii) Isolated storage covers sites such as

separate tank farms, warehouses and

fuel storage and must involve a

dangerous substance.


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(a) On-Site Emergency Plans

Regulation requires manufacturers to prepare anon-site emergency plan, and provides forconsultation with appropriate bodies.

(b) Off-Site Emergency Plans

Manufacturers are not responsible for thepreparation of the off-site emergency plan. Thisis a duty placed on local authorities. However,manufacturers are required to provideinformation to local authorities adequate to

enable them to draw up off-site plans. Thisinformation will cover major accident hazards,possible consequences and any specialemergency measures.


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(c) Informing Members of the Public

- Regulation requires that persons outside the site whoare likely to be affected by a major accident at an

industrial activity should be informed about the activityand associated hazards so that they have advancewarning of the likely effects of such an accident and ofthe precautionary action they should take.

- The responsibility for providing this information is

placed on the manufacturer, who has to try to reach anagreement with the local authority for the local authorityto pass on the information to the public, else themanufacturer must himself disseminate the informationto the public.

- It is for HSE to identify the public information zonewhere people may be at risk and in which informationshould be provided.


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Information on Potential Major Accidents andTheir Prevention and Mitigation

Regulation requires a detailed consideration ofthe dangerous substances, their properties andthe conditions under which they are processedor stored.

The potential source of a major accident hazard-normally involves a failure of the containmentsystem (bulk vessels, pipework, pumps, processupsets via relief system etc), leading to a releaseof the dangerous substance.

Quantification of the consequences of suchhazards and preventative measures taken.


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An estimate of the number of people onsite who may be exposed to the hazardsconsidered in the report.

Information about the emergencyprocedures laid down for dealing with a

major accident occurring at the site. A diagram of any plant in which the

industrial activity is carried on, sufficient toshow the features which are significant asregards the potential for a major accidentor its prevention or control.


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Information Relating to Every DangerousSubstance Involved in the Activity

The name of the dangerous substance andchemical formula;

A general description of the analytical methodsavailable to the manufacturer for determining thepresence of the dangerous substance, or

references to such methods in the scientificliterature;

A brief description of the hazards which may becreated by the dangerous substance;

The degree of purity of the dangerous substance,and the names of the main impurities and theirpercentages.


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Information Relating to the Installation

A map of the site and its surrounding area to a scale

large enough to show any features that may besignificant in the assessment of the hazard or riskassociated with the site;

A scale plan of the site showing the locations andquantities of all significant inventories of the dangerous

substance; A description of the processes or storage involving the

dangerous substance and an indication of the conditionsunder which it is normally held; and

Information about the nature of the land use and the sizeand distribution of the population in the vicinity of theindustrial activity to which the report relates.


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Site Main Controller

- He will be primarily concerned withcoordinating the required actions acrossthe site, advising the Emergency Servicesabout the way the incident islikely to

develop and arranging backup support forthe Incident Controller.

- More information are required about thecurrent situation, likely weather changes,

resource availability, etc. Personnel in Emergency Team


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(2) Setting Out the Plan Arrangements

Plan initiation

Raising the alarm

Emergency control centre or centres must be

off-site

Safeguarding people on-site, for instance,upgrading the evacuation procedures and safe

locations

Action by the emergency teamthis is to protect

those in danger and arrangements for caring for

those affected by an accident.


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- During an emergency, it is important to provide sufficientand adequate information. Hence, there must be goodcommunication between the control room and othersources of data.

- All sorts of information related to the current situation areneeded by the controller. This will make task easier todirect the emergency services and emergency team.

- Information also needs to be provided for the publicthrough media.

- The level of response depends on the level of theincident. Initially, small fires or releases should bebrought under control and low priority alarms raised. If

the situation escalates and VCE or BLEVEs lookimminent, all personnel should be evacuated.


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Off-Site Plan

Based on the events identified which would affect peopleand the environmental off-site. Any relevant informationon the nature, extent and likely effects of the incidentsare required.

Need to cater in detail all identified events as being mostlikely.

Should be flexible enough to permit the remedialmeasures to be extended and increased to deal withextremely adverse combinations of circumstances andconsequences.

Information provided must be detailed, unambiguous andcomprehensive for the dangers to be understood, so thatthe necessary protective measures can be provided.


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Several different responses may be necessary at asingle site, depending on the size and characteristics ofthe incidents.

The plan must ensure coordination of existing servicesand their readiness for the specific hazards andproblems which may appear in an incident.

Identification of key personnel, their duties and proper

training achieved. Set out a command structure and identify the respective

roles and responsibilities of the senior personnelinvolved.

Set out the immediate action to protect those in danger.

Set out arrangements for caring people and environmentaffected by an incident.


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- In case of accident, off-site population is

subjected either to blast, missiles impact, flash

fire or exposure to thermal radiation.- In the event of a major release of LPG, all roads

in the vicinity should be sealed off to avoid

ignition sources entering the gas cloud and

emergency services to get through.

- Thus, every effort should be made to stop traffic

by appropriate police action. All trains should be

informed to stop since the railway is on the limitof lethality for a flash fire when the flow of LPG is

perpendicular to the track.


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- People should go or stay indoors and shut allwindows and doors and turn off fans or air

conditioning.- As there may be some overpressure affects fromexplosions, it would be best for the people tostay in a room preferably facing away from thescene of the incident and to listen to local radio

for further information or action.- People may also suffer more harm from a short

exposure during an evacuation then they wouldexperience while sheltering.

- Sheltering gives the best protection in mostcases involving the release of flammables(LPG).

Documents

CIMAH Continued