Introduction13otherinternational standardorganisationshaveissuedstandardsforriskassessmentorriskbaseddesign.OGP(formerlyE&PForum)has,however,issuedguidelinesonHESmanagement(OGP,1994).OtherISO standards thatare essential:Safety aspects-Guidelines for their inclusion in standards,ISO/IEC Guide51:1999 (ISO, 1999a)Risk management vocabulary, guidelines for use in standards, ISO/IECGuide73:2002(ISO,2002)ISOWGRiskmanagement (underpreparation)Theterminology used in this book is accordancewiththeterminology of ISO/IECGuide73:2002.Thedefinitionsgiven at theback, see Page 549,areextracted fromthis standard,whererelevant.There are several national guidelines or standards for HES management, butthesearenotcoveredhere.TheonlynationalstandardforriskassessmentistheNorwegianoffshorestandardisationorganisation(NORSOK)document:GuidelinesforRiskandEmergencyPreparednessAnalysis,Z-013(NOR-SOK,2001)Thepresentation inthisbookisbasedontheNORSOKstandard,for instanceinrelation to terminology.Thereis some distinctions between thedefinitions adoptedintheNORSOK standard and the currentNorwegian legislation,howevertheNORSOKversionshavebeenchosen.1.8LimitationsThis book is focused on offshore risk assessment i.e.,the analysis of offshore risksand thepresentation and evaluation of results.The emphasis is firstof all onrisk topersonnel, secondly on risk to the environment and risk to assets is the leastemphasised subject.As a consequence of thesepriorities, there are some areas that are notfocusedonormaybenotconsideredatall.Thissectionsummarisessomeofthesesubiects1.8.1RiskManagementRisk management is discussed in depth in a parallel book Risk Management, withApplicationsfromtheOffshorePetroleumIndustry(Aven andVinnem,2007).Thissubject is thereforenotaddressed inthepresentbook.1.8.2SubseaProductionDeep waterproduction implies subsea production systems tied into floating pro-ductionfacilitiesorpipelinesdirectlytoonshorefacilities.Thisbookcoversexten-sively the floating production facilities and theassociated hazards
Introduction 13 other international standard organisations have issued standards for risk assessment or risk based design. OGP (formerly E&P Forum) has, however, issued guidelines on HES management (OGP, 1994). Other ISO standards that are essential: x Safety aspects – Guidelines for their inclusion in standards, ISO/IEC Guide 51:1999 (ISO, 1999a) x Risk management vocabulary, guidelines for use in standards, ISO/IEC Guide 73:2002 (ISO, 2002) x ISOWG Risk management (under preparation) The terminology used in this book is accordance with the terminology of ISO/IEC Guide 73:2002. The definitions given at the back, see Page 549, are extracted from this standard, where relevant. There are several national guidelines or standards for HES management, but these are not covered here. The only national standard for risk assessment is the Norwegian offshore standardisation organisation (NORSOK) document: x Guidelines for Risk and Emergency Preparedness Analysis, Z–013 (NORSOK, 2001) The presentation in this book is based on the NORSOK standard, for instance in relation to terminology. There is some distinctions between the definitions adopted in the NORSOK standard and the current Norwegian legislation, however the NORSOK versions have been chosen. 1.8 Limitations This book is focused on offshore risk assessment i.e., the analysis of offshore risks, and the presentation and evaluation of results. The emphasis is first of all on risk to personnel, secondly on risk to the environment and risk to assets is the least emphasised subject. As a consequence of these priorities, there are some areas that are not focused on or may be not considered at all. This section summarises some of these subjects. 1.8.1 Risk Management Risk management is discussed in depth in a parallel book Risk Management, with Applications from the Offshore Petroleum Industry (Aven and Vinnem, 2007). This subject is therefore not addressed in the present book. 1.8.2 Subsea Production Deep water production implies subsea production systems tied into floating production facilities or pipelines directly to onshore facilities. This book covers extensively the floating production facilities and the associated hazards
14OffshoreRiskAssessmentThe subsea production systems are usually at a significant distancefrom thesurfacefacilities, in which case anyfailure of the subseafacilities is nota sourceofrisk for the personnel on the surface installations. Such failures may cause hydro-carbon leaks,whichmay cause spill and subsequent oil pollution.This last aspectis within the scope of this book.One crucial aspect associated with such leaks isthe detection of leaks, whichmaynot beeasy ifnot extensive.The main challenge with subsea production facilities is the reliability of theproduction function, due to the extensive costs and sometime delays involved inmaintaining subsea production facilities. This aspect is not considered at all in thisbook.1.8.3ProductionRegularityA subject which is closely associated with risk analysis is regularity analysis, eitheras production and/or transport regularity.This aspect is coupled withrisk to assets,and has littledirectconnectiontoriskto personnel andrisktotheenvironmentSome of the hazardous events that may lead to fatalities or spills may also causeproduction disruption, and thus have an impact on the regularity. Traditionally,however, production regularity studies disregard such rare events in any caseProduction regularity is outsidethe scopeof thisbookMoreover,thetermRAMS'(Reliability,Availability,Maintainability,Safety)is not covered in full, in accordance with what is discussed above
14 Offshore Risk Assessment The subsea production systems are usually at a significant distance from the surface facilities, in which case any failure of the subsea facilities is not a source of risk for the personnel on the surface installations. Such failures may cause hydrocarbon leaks, which may cause spill and subsequent oil pollution. This last aspect is within the scope of this book. One crucial aspect associated with such leaks is the detection of leaks, which may not be easy if not extensive. The main challenge with subsea production facilities is the reliability of the production function, due to the extensive costs and sometime delays involved in maintaining subsea production facilities. This aspect is not considered at all in this book. 1.8.3 Production Regularity A subject which is closely associated with risk analysis is regularity analysis, either as production and/or transport regularity. This aspect is coupled with risk to assets, and has little direct connection to risk to personnel and risk to the environment. Some of the hazardous events that may lead to fatalities or spills may also cause production disruption, and thus have an impact on the regularity. Traditionally, however, production regularity studies disregard such rare events in any case. Production regularity is outside the scope of this book. Moreover, the term ‘RAMS’ (Reliability, Availability, Maintainability, Safety) is not covered in full, in accordance with what is discussed above
2RiskPicture-DefinitionsandCharacteristicsThis chapter defines risk quantitatively and presents the dimensions and elementsofrisk.The chapter further gives an extensive illustration of howrisk is expressedFurtherdiscussion about interpretationof risk maybefound in Aven and Vinnem(2007)andAven(2003)2.1Definition of Risk2.1.1 Basic Expressions of RiskThe term ‘riskis according to international standards (such as ISO 2002)‘combination of theprobability oran eventand its consequence.Other standards,likeISO13702(ISO1999b),havea similardefinition:Atermwhichcombinesthe chance that a specified hazardous event will occur and the severity of theconsequences ofthe event.Risk may be expressed in several ways, by distributions, expected values,singleprobabilitiesofspecificconsequences,etc.Mostcommonlyused isprobablythe expected valueAn operational expression for practical calculation of risk is the following,which underlines how risk is calculated, by multiplying probability and numericalvalue of the consequence for each accident sequence i, and summed over all (1)potential accident sequences:?(2.1)where:p=probability of accidentsC=consequence ofaccidents
2 Risk Picture – Definitions and Characteristics This chapter defines risk quantitatively and presents the dimensions and elements of risk. The chapter further gives an extensive illustration of how risk is expressed. Further discussion about interpretation of risk may be found in Aven and Vinnem (2007) and Aven (2003). 2.1 Definition of Risk 2.1.1 Basic Expressions of Risk The term ‘risk’ is according to international standards (such as ISO 2002) ‘combination of the probability or an event and its consequence’. Other standards, like ISO 13702 (ISO 1999b), have a similar definition: ‘A term which combines the chance that a specified hazardous event will occur and the severity of the consequences of the event.’ Risk may be expressed in several ways, by distributions, expected values, single probabilities of specific consequences, etc. Most commonly used is probably the expected value. An operational expression for practical calculation of risk is the following, which underlines how risk is calculated, by multiplying probability and numerical value of the consequence for each accident sequence i, and summed over all (I) potential accident sequences: ¦ i i Ci R ( p ) ( 2.1) where: p = probability of accidents C = consequence of accidents
16Offshore Risk AssessmentThis formulaexpresses risk as an expected consequence.Theexpression mayalsobereplacedbyanintegral,iftheconsequencescanbeexpressedbymeansofacontinuousvariable.It should be noted that the expression of risk as expected consequence is astatistical expression, which often implies that the value in practice may never beobserved.When dealing with rare accidents, an averagevalue will have to beestablishedoveralongperiod,withlowannualvalues.Ifduring40yearswehavefivemajoraccidents withatotaloftenfatalities,thiscorrespondstoanannual average of 0.25fatalitiesperyear,whichobviously can never be observed.Thedefinition inEquation2.1is sometimes calledstatistical riskortechno-logical risk.Someauthorshavereferredtothisexpressionas‘real riskorobjec-tiverisk'.Thesetwolasttermsgivemisleading impressionofinterpretationofrisk.‘Risk'is alwaysreflecting interpretations andsimplificationsmadeby,for instancetheanalyst,and as suchto some extent subjective.It is therefore misleading to givethe impression that some expressions aremore objectivethan others.'Risk aversion' is sometimes included in the calculation of risk, see for instanceEquation 2.9.Risk will bea combination of theprobabilityof an accidenttheseverity of the consequence,and the aversion associated withthe consequenceThis is not supported by the author. It is acknowledged that risk aversion is animportantaspectassociated withtheassessmentofrisk,inparticularrelatingtotheevaluation of risk results.However,risk aversion should not be mixed withtechnological risk analysis.Risk aversion isa complexphenomenon.It is misleadingtogivethe impressionthatthiscomplexprocessmaybeadequatelycaptured byasingle parameter, risk aversion, a.Furtherdetailsaboutriskdefinitions,riskaversionandethicaladjustmentoftherisk assessments are presented in Aven and Vinnem (2007).2.1.2DimensionsofRiskWhenaccident consequences are considered,thesemayberelated topersonnel,tothe environment, and to assets and production capacity.These are sometimescalleddimensions of risk',which arethose shown inthe listbelow.Some sub-categories are also presented in thefollowing:Personnelriskfatalityrisk (see Section2.1.3fordefinition)oimpairmentrisk (seeSection2.1.4fordefinition)OEnvironmental risk(seeSection2.1.5fordefinition)Assetrisk (seeSection2.1.6fordefinitions)materialdamageriskOproduction delay risk.oIt mightbe considered that fatality risk is a subset of injury risk, and that the latteristhegeneral category.Fatalityriskand injuryriskarenevertheless quantified insodifferentwaysthatitmayseemcounterproductivetoconsiderthesetwoaspectsas onecategory
16 Offshore Risk Assessment This formula expresses risk as an expected consequence. The expression may also be replaced by an integral, if the consequences can be expressed by means of a continuous variable. It should be noted that the expression of risk as expected consequence is a statistical expression, which often implies that the value in practice may never be observed. When dealing with rare accidents, an average value will have to be established over a long period, with low annual values. If during 40 years we have five major accidents with a total of ten fatalities, this corresponds to an annual average of 0.25 fatalities per year, which obviously can never be observed. The definition in Equation 2.1 is sometimes called ‘statistical risk’ or technological risk. Some authors have referred to this expression as ‘real risk’ or ‘objective risk’. These two last terms give misleading impression of interpretation of risk. ‘Risk’ is always reflecting interpretations and simplifications made by, for instance the analyst, and as such to some extent subjective. It is therefore misleading to give the impression that some expressions are more objective than others. ‘Risk aversion’ is sometimes included in the calculation of risk, see for instance Equation 2.9. Risk will be a combination of the probability of an accident, the severity of the consequence, and the aversion associated with the consequence. This is not supported by the author. It is acknowledged that risk aversion is an important aspect associated with the assessment of risk, in particular relating to the evaluation of risk results. However, risk aversion should not be mixed with technological risk analysis. Risk aversion is a complex phenomenon. It is misleading to give the impression that this complex process may be adequately captured by a single parameter, risk aversion, a. Further details about risk definitions, risk aversion and ethical adjustment of the risk assessments are presented in Aven and Vinnem (2007). 2.1.2 Dimensions of Risk When accident consequences are considered, these may be related to personnel, to the environment, and to assets and production capacity. These are sometimes called ‘dimensions of risk’, which are those shown in the list below. Some subcategories are also presented in the following: & Personnel risk o fatality risk (see Section 2.1.3 for definition) o impairment risk (see Section 2.1.4 for definition) & Environmental risk (see Section 2.1.5 for definition) & Asset risk (see Section 2.1.6 for definitions) o material damage risk o production delay risk. It might be considered that fatality risk is a subset of injury risk, and that the latter is the general category. Fatality risk and injury risk are nevertheless quantified in so different ways that it may seem counterproductive to consider these two aspects as one category
17RiskPicture-DefinitionsandCharacteristicsItshouldbenotedthatrisktopersonnel ismainlyfocusedonfatalityrisk,oraspectsthatarevital forminimisationoffatalityrisk.This reflectsthefocus of theQRAonmajor accidents,as opposedtooccupational accidentsas noted intheintroduction.This focus may,on the other hand, underscore the fact that occupa-tional accidents are a major contribution to fatality risk.In Norwegian operationsforinstanceallfatalitiesoninstallationsduringthelast20yearshavebeenduetooccupationalaccidentsThere is no universal definition of the termmajor accident'.One often usedinterpretation is that ‘major accidents'are accidentswhich havethe potential tocause five fatalities or more.Somebodymayreacttotheclassificationofimpairmentrisk'asa sub-categoryof'personnel risk'.Impairment risk is discussed in greater depth in Section2.1.4.At this point it is sufficient to notethat although the impairment mechanisms arerelated physical arrangements (such as escape ways),it is indirectly an expressionof risk to personnel.2.1.3FatalityRiskFatalityriskassessmentusesa numberof expressions, such as,platformfatalityrisk, individual risk, group risk and f-N curve. It should be noted that some ofthese expressions are calculated in a particular way in the case of offshoreinstallations.The offshore way of expressing risk is the main option chosen, butdifferences are indicated.2.1.3.1Platform Fatality RiskThe calculation of fatalityrisk starts with calculating the Potential Loss of Life,PLL.Sometimes, this is also called Fatalities Per PlatformYear,FPPY.PLL orFPPYmaybeconsidered asthefatalityriskfortheentire installation,if itiscalcu-latedfortheentire installation.TherearetwowaystoexpressPLL:Accident statistics,PLL =No offatalities experience in a period (usuallyper year).Fatalityrisk assessment (throughQRA),wherebyPLL iscalculatedaccordingtoEquation2.2below.From the PLL,either Individual Risk (IR) or Group Risk (GR) may be computed.ThePLLvaluecan,basedona QRA,beexpressedasfollows:PLL-Z(uCm)(2.2)nwhere:fu=annualfrequency ofaccident scenario (eventtreeterminal event)n withpersonnel consequencejexpected number of fatalities for accident scenario (event tree terminalCnj=event)nwithpersonnelconsequencej
Risk Picture – Definitions and Characteristics 17 It should be noted that risk to personnel is mainly focused on fatality risk, or aspects that are vital for minimisation of fatality risk. This reflects the focus of the QRA on major accidents, as opposed to occupational accidents as noted in the introduction. This focus may, on the other hand, underscore the fact that occupational accidents are a major contribution to fatality risk. In Norwegian operations for instance, all fatalities on installations during the last 20 years have been due to occupational accidents. There is no universal definition of the term ‘major accident’. One often used interpretation is that ‘major accidents’ are accidents which have the potential to cause five fatalities or more. Somebody may react to the classification of ‘impairment risk’ as a sub-category of ‘personnel risk’. Impairment risk is discussed in greater depth in Section 2.1.4. At this point it is sufficient to note that although the impairment mechanisms are related physical arrangements (such as escape ways), it is indirectly an expression of risk to personnel. 2.1.3 Fatality Risk Fatality risk assessment uses a number of expressions, such as; platform fatality risk, individual risk, group risk and f–N curve. It should be noted that some of these expressions are calculated in a particular way in the case of offshore installations. The offshore way of expressing risk is the main option chosen, but differences are indicated. 2.1.3.1 Platform Fatality Risk The calculation of fatality risk starts with calculating the Potential Loss of Life, PLL. Sometimes, this is also called Fatalities Per Platform Year, FPPY. PLL or FPPY may be considered as the fatality risk for the entire installation, if it is calculated for the entire installation. There are two ways to express PLL: & Accident statistics, PLL = No of fatalities experience in a period (usually per year). & Fatality risk assessment (through QRA), whereby PLL is calculated according to Equation 2.2 below. From the PLL, either Individual Risk (IR) or Group Risk (GR) may be computed. The PLL value can, based on a QRA, be expressed as follows: ¦ ¦ j nj nj n PLL ( f c ) ( 2.2) where: fnj = annual frequency of accident scenario (event tree terminal event) n with personnel consequence j cnj = expected number of fatalities for accident scenario (event tree terminal event) n with personnel consequence j