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SYMPOSIUM SERIES NO. 156 Hazards XXII # 2011 IChemEMany Power Stations have been assessed using PHR in the last few years and the paper describes

typical process safety issues that have been identified. It is typical for a relatively large number of

recommendations to be raised. The paper will describe a methodology developed to help develop

recommendations into clear actions, using a risk based approach and simple cost-benefit analysis.

KEYWORDS: Process Hazard Review, Process Safety, Risk Assessment, Power Sector

INTRODUCTIONThe accident at BPs Texas City refinery has createdincreased awareness of the potential for major accidentson high hazard facilities. Many companies manage safetyperformance by focussing on injury rates without realisingthat control measures for process safety may have becomeseriously impaired.

The causes of these accidents are dreadfully familiar,nearly always involving multiple failures in the layers ofprotection. The Baker report [Ref 1] on the BP Texas Cityaccident states that The passing of time without a processaccident is not necessarily an indication that all is welland may contribute to a dangerous and growing sense ofcomplacency.

Improving process safety performance requires anunderstanding that a different approach is needed. Asshown in Figure 1, process safety relates to low frequencyand high consequence events that are outside the experienceof most facilities. By comparison, personal safety relates toslips, trips and falls type injuries that occur on a fairlyregular basis. Process safety requires a risk managementapproach with the following essential elements:

. Credible hazardous events identified

. Severity estimated in terms of harm tenvironment

. Key risk control systems to reduce risk tolevel identified

. Testing and inspection arrangements in plthe reliability of safety critical equipment

. Weaknesses in risk control systems idimprovement plan developed

INCREASED RISKS ON AGEING ASSETMany power stations are being operated beyoinal design life increasing the risk of a procesdent due to the following factors.

. No hazard analysis during the design phanot available to the operating team.

. Process safety information incomplete, mof-date. For example; process P&IDs, hadrawings, relief system design calculationsfor safety instrumented systems, emergenc

. Lack of information on major accident hazaof safety adopted at the design stage.

. Organisational changes resulting in poor uof the key risk control systems.REDUCING THE POTENTIAL FOR MAJOR AGENERATION SECTOR BY UTILISING OPER

Graeme R Ellis, ABB Engineering Services, Warrington, Chesh

Accidents at Texas City and Buncefield in 20

similar accidents in the UK Power Generation

recognised, and the need to focus on the p

release of flammable substances or release of e

electrical systems.

Many companies have been implementing Pr

the risks from their existing operations and impro

been a challenge due to the wide range of techn

fossil fuels to renewable sources, plus many age

This paper will describe how a hazard iden

within the chemical sector has been applied to

Review (PHR) technique was originally deve

safety concerns on operational plants following

older plants.

A team of knowledgeable operations and tec

sider each process system and use guidewords

of the event is assessed, and the reliability and r

against site experience and relevant good pract

staff to identify gaps or weaknesses in the risk420TIONAL EXPERIENCE

UK

have increased awareness of the potential for

tor. The importance of process safety has been

tial for major accidents associated with the

gy from high speed machinery or high voltage

ss Safety Management (PSM) systems to assess

the performance of risk control systems. This has

gy within the sector, with energy sources from

assets within the UK fleet of power stations.

ation and assessment methodology developed

erational Power Stations. The Process Hazard

ed in the 1990s by ICI to identify process

veral serious accidents within the company on

cal staff led by a process safety specialist con-

dentify credible hazardous events. The severity

stness of existing risk control measures judged

The overall aim is to utilise the knowledge of

ntrol measures, including procedural controls,

SYMPOSIUM SERIES NO. 156 Hazards XXII # 2011 IChemE. Changes to the process and operating procedures notproperly assessed for process safety.

. Poor identification of process safety incidents and lackof investigation to identify the root causes.

If no action is taken to tackle these issues it is possiblethat a serious process safety accident may occur, as shown inFigure 2. An intervention is required on a periodic basis,typically every 5 years, to identify the main process safetyrelated concerns and implement targeted changes to hard-ware and procedures to achieve continuous improvement.

PROCESS SAFETY IN THE UK POWER SECTORSafety in the Power Generation sector was traditionallycontrolled by the Central Electricity Generating Board(CEGB). Fragmentation of the industry has occurred sinceprivatisation, with existing power stations split betweencompanies including; EON, RWE npower, Scottish Power,Scottish & Southern Energy and EDF Energy. Each ofthese companies own stations using a range of powersources such as; natural gas, coal, fuel oil, nuclear, windand water.

Traditionally, the sector has focussed safety improve-ment efforts on personal safety performance. This is evidentwhen visiting power stations, with example such as signs atEON site entrances stating We do not hurt people, boards

Figure 2. The need for periodic process safety reviews

Figure 1. Comparison between different types of safety421with safety statistics, and clearly marked walkways on-site.The accident at the BP Texas City refinery and the sub-sequent investigation of management failings chaired byJames Baker, has greatly increased awareness of the needfor the Power Generation sector to focus equally onprocess safety.

There have been several process safety type acci-dents in the UK Power Generation sector, mostly involvingthe sudden rupture of high pressure steam pipework due tovarious deterioration mechanisms. This has highlightedissues with ageing plant that is being addressed by a crossindustry working group, Coal Safety and Generators Pro-gramme (GENSIP). More dramatic accidents have occurredoutside of the UK, including an explosion at a hydro-electricplant in Russia in 2009 that killed nearly 70 people, and anexplosion at a gas fired power station in the US in 2010during commissioning, that killed nearly 20 people.

Typical process safety hazards on power stations withthe potential for multiple fatalities include the following:

. Releases of fuel (e.g. gas, oil or coal) with fire andexplosion hazard

. Sudden rupture of high pressure steam systems

. Catastrophic failure of high speed machinery (e.g. tur-bines, compressors) with missile hazard

. Electrical explosions on HV equipment (e.g. Transfor-mers, HV switchgear)

. Chemical reaction hazards with water treatment systems(e.g. strong acids and alkalis)

. Blade failures on wind turbines with missile hazard

. Release of anhydrous ammonia with toxic hazard(ammonia is now being used for emissions control oncoal fired power stations)

Most companies in the Power Generation sectorhave active programmes for Process Safety Management(PSM) to increase awareness of process safety andimprove the management systems needed to control thistype of hazard. A key element of an effective PSM systemis Process Hazard Analysis (PHA), requiring identificationof potential process safety hazards, assessment of potentialconsequences, and analysis of the risk controls measuresrequired to reduce risks to as low as reasonably prac-ticable. This knowledge is essential in order to shape therest of the PSM system to maintain these risks at an accep-table level.

Several companies have looked outside of the sectorto find well established and effective PHA techniques. TheProcess Hazard Review (PHR) methodology described inthis paper was developed by the multi-national chemicalcompany ICI in the early 1990s following several seriousaccidents on ageing chemical plants within the UK. A keydevelopment for the Power Generation sector was toextend the focus from loss of containment incidents invol-ving dangerous substances, to include release of energyincidents. The latter provides a focus on the potential forserious accidents with high pressure steam, high speedmachinery and HV electrical equipment.

SYMPOSIUM SERIES NO. 156 Hazards XXII # 2011 IChemEPROCESS HAZARD REVIEW METHODOLOGYMany companies carry out retrospective HAZOP studieson existing facilities. These are difficult due to the lack ofaccurate design data and can take excessive time due tothe detailed nature of the study. They often result in anexcessive number of actions focussed towards hardwarechanges to improve operability rather than more effectiveactions aimed at reducing risk.

The Process Hazard Review (PHR) methodology[Ref 2] was developed by ICI for the petrochemical industryduring the early 1990s and has since been used widely inmany sectors including Oil & Gas and Power Generation.Unlike HAZOP studies, PHR reviews each process systemon a plant in sequence, such as a fuel storage system, andidentifies credible hazardous events. PHR is thereforemuch quicker than HAZOP whilst being better at findingdetailed concerns relating to process safety.

The essential requirement for an effective PHR isa team of knowledgeable operations and technical stafffrom the site led by an independent and experienced pro-cess safety specialist. The process drawings are reviewed,ideally P&IDs if available but otherwise Process FlowDiagrams. For each system the team use the guidewordsin Figure 3 to identify credible loss of containmentor release of energy events, utilising direct experiencefrom the site under review.

The PHR team assess the immediate and ultimateconsequences in terms of harm to people or environment,using modelling data if available. It is important at thisstage to ignore any safeguards such as trip systems, inorder to identify what might happen when all the layers ofprotection have failed.

For major accident hazards events the team identifythe current measures for prevention, control and mitigation,including passive, active and procedural safeguards. Theexperience of the team is used to identify weaknesses onthe plant, for example a level sensor on a safety criticaltrip system that is known to regularly fail. The essentialelements of procedural controls are tested with the PHRteam, and further checks carried out on site to confirmthat the procedures are being applied.

Recommendations for improvements are raisedfocussed towards major accident hazards and known

Internal Explosion Reaction

Extreme Pressure Extreme Temperature

Puncture Excess Loading

Long term weakening Overfill

Opening Leak

Figure 3. PHR guidewords422problem areas. These fall into the following genericcategories, with a bias towards making procedural controlsmore robust rather than costly hardware changes.

. Simple risk reduction measures, for example fittingblank flanges to drain valves on hazardous lines.

. Improvements to operating or maintenance proceduresto ensure that key elements are being followed andthat best practices are followed

. Improved inspection and testing of safety critical equip-ment, for example vent lines on storage tanks liable toblockage

. New layers of protection for high risk events to meetcurrent company or international standards

. Research into poorly understood hazards such as staticcontrol measures or consequence modelling to deter-mine the extent and severity of fires, explosions ortoxic releases.

Plant tours are regularly made by the team leaderaccompanied by an experienced operator. This providesan opportunity to check the condition of safety criticalequipment in the field and confirm procedural controls dis-cussed at the team meetings. For example, the road tankeroffloading valves at and acid/alkali bulk storage systemswere specified to be fitted with a padlock to prevent offload-ing to the wrong tank in error. It was found during the planttour that the padlock was missing from the valve as shownin Figure 4, increasing the risk of an error resulting in areaction hazard within the tank.

Most companies have a process safety risk matrixsimilar to the example in Figure 5. All the identifiedevents are placed on the matrix by estimating the eventseverity and likelihood using suitable word models andthe judgement of the PHR team. The completed matrixshowing the risk level for each hazardous event is a power-ful tool to indicate the areas of concern and allow for prior-itisation of the recommendations.

Figure 4. Missing lock on road tanker offloading valve

all the operating facilities on the site, involving a team of were identified.sist-ny.venthe

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SYMPOSIUM SERIES NO. 156 Hazards XXII # 2011 IChemEexperienced operating and technical staff.The events identified during the PHR were positioned

on the company standard risk matrix, as shown in Figure 5.This helped to prioritise the recommendations raised bythe team. The results were 1 scenario rated very highrisk, 61 high risk, 214 medium risk, and 81 lowrisk. High risk issues were raised on the followingsystems reflecting the high hazard potential.

. Gas supply and pressure reducing station

. Heavy fuel oil receipt from jetty and circulation

. Fuel gas supply to gas turbines

. Hydraulic and lube oil systems

. Steam raising systems and steam turbines

. Fuel gas and oil burner systems

. Hydrogen system

. Water treatment chemicals

. Site transformers and LV/HV switch rooms

The company is working through a prioritised actionplan for the site that will provide an assurance that processsafety risks are under suitable control. The key benefits fromthe PHR were considered to be:

. Rapid identification of process safety hazards across theentire power station.

. Agreed review methodology that can be applied conently across all power stations owned by the compa

. Use of the structured PHR technique that is well prothroughout the process industries and valued byregulatory authorities.

IMPLEMENTING IMPROVEMENTSCompleting a PHR is the first stage of the improvemprocess and it is essential that the recommendations raare then addressed promptly. From experience a numof challenges exist for companies trying to resolve recmendations:

. Continuity, does the person responsible for acunderstand what is required?

. Workload, are suitable resources available, canrecommendations be prioritised?

. Execution, can the recommendation be resolvednecessary action taken in a timely manner and howthe work to be paid for?

Simple low cost improvements should be immented at the earliest opportunity to reduce risksshow a commitment to the improvement process. Technassessments are then required to identify practical improment options and carry out some form of cost-benCASE STUDY: POWER STATION PHRA PHR was carried out on a large gas and oil fired powerstation to address company concerns about the time likelyto be required using conventional PHA techniques such asHAZOP studies. The PHR took four weeks and covered

Figure 5. Risk matrix showin423. Assessment of current safeguards and development of alist of prioritised recommendations for reducing risks toas low as reasonably practicable.

. Efficient use of busy operations staff whose detailedknowledge was essential in ensuring that concerns

ll hazardous events identified

CONCLUSIONSReading investigation reports on accidents such asthe explosion at Texas City, it is easy for site managersto think that such accidents could never happen on theirfacilities. To be confident that process safety risks arein control, it is important to have identified potentialmajor accident hazards, assessed the status of the safetycritical risk reduction measures based on operationalexperience, and monitored the status of planned improve-ments.

In this paper a methodology has been outlined to effi-ciently carry out reviews using knowledgeable operationsstaff to identify concerns. This is followed by targetedchanges and monitoring of the effectiveness of the keyrisk control systems, including key elements of proceduralcontrols. Such reviews can be carried out on a regularbasis, typically every five years, to revalidate the assessmentbased on new experience.

The approach can provide senior management of highhazard facilities, such as Power Stations, with the opportu-

SYMPOSIUM SERIES NO. 156 Hazards XXII # 2011 IChemEanalysis. This is required to convert the recommendationsinto a series of specific actions with owners and completiondates.

The cost of making changes to an operational site ishigher than those made during the initial design stage. Acommon problem is making decisions on expenditurewhere the benefits are limited to reducing risks. Eventsjudged to be at high risk require urgent attention andchanges to reduce risk regardless of cost.

A simple cost-benefit tool such as that shown inFigure 6 can be used to determine the priority of eventsat medium or low risk, where risk is judged tolerable ifrelevant good practice is being followed. The approach ishelpful for screening with the option for a quantified cost-benefit analysis for high cost improvements.

Figure 6. Risk based cost-benefit analysis tool424nity to demonstrate continuous improvement in processsafety performance. It can also increase confidence that allreasonable steps are being taken to control the risk of aserious process safety accident.

REFERENCES1. Baker J.A., The report of the BP U.S. Refineries Indepen-

dent Safety Review Panel, Jan 2007.

2. Ellis G.R., Action against accident hazards, Graeme Ellis,

ABB Engineering Services UK, evaluates the Process

Hazard Review (PHR) methodology, March 2005, Hydro-

carbon Engineering.

3. API 754, Recommended Practice, Process Safety

Performance Indicators for the Refining and Petrochemical

Industries, draft 14 Sep 2009, American Petroleum

Institute.

IntroductionIncreased Risks on Ageing AssetsProcess Safety in the UK Power SectorProcess Hazard Review MethodologyCase Study: Power Station PHRImplementing ImprovementsConclusionsReferencesFigure 1Figure 2Figure 3Figure 4Figure 5Figure 6

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