CARAT An Oprational Approach to Risk Assssmnt Dfinitions, Procsss, and Studis K.G. Phillips <phillig@novachm.com> NOVA Chmicals Corporation, PO Box 5006, Rd Dr, Albrta, T4N 6A1. Introduction Risk Assssmnt mans diffrnt things to diffrnt popl. In many cass a givn risk assssmnt trm can hav a varity of manings dpnding on th background, ducation, and xprinc of th individual using th trm. This ambiguity maks it difficult to communicat concpts and procsss for conducting risk assssmnts and can rsult in confusion among stakholdrs. For xampl, th trm 'Risk Assssmnt' could man a dtaild Quantitativ Risk Assssmnt to on prson, but anothr may simply intrprt th trm as a dtaild hazard rviw. Th potntial for confusion incrass as th usag crosss national boundaris and trms ar translatd into diffrnt languags. Th Chmical Accidnt Risk Assssmnt Thsaurus (CARAT) is a databas of ntris that rprsnt laws, rgulations, guidanc documnts and dfinitions of trms rlatd to th risk assssmnt of accidntal rlass of chmicals from fixd installations. Th databas also contains ntris on th application of risk assssmnt using spcific xampls of potntial chmical rlass. Ths ntris do not simply rproduc th original documnts but convrt th documnts into oprational languag, thrby rducing or liminating confusion that oftn ariss with th intrprtation of spcific wording or translation from on languag to anothr. Th data is basd on a common st of oprational trms that hav bn slctd as appropriat translations of th intndd maning drivd from th sourc documnt. Th CARAT contains information ntrd by various intrnational and national agncis, chmical companis, and individuals rgarding risk assssmnt procsss rlatd to chmical rlass. Th ntir systm is accssibl via th Intrnt at http://www1.ocd.org/hs/carat/v3.0/htm/dfault.htm Th CARAT is a usful rsourc for dvloping rquirmnts for risk assssmnt of chmical accidnts and comparing rsults to xisting guidanc. For xampl, th rports gnratd by th sarchs ar abl to clarly show how risk assssmnts should b conductd undr law, fr of th complxitis of how rgulations ar draftd in a jurisdiction. In th cas of spcific risk assssmnt ntris, th basic procsss and assumptions can b dtrmind basd on a consistnt hirarchy. Dfinitions of trms ar rprsntd in oprational languag in a standard format indpndnt of th languag or styl of th sourc. Background As a rsult of a workshop on Risk Assssmnt hld in Paris in July, 1995, th Working Group on Chmical Accidnts of Organization for Economic Coopration and Dvlopmnt (OECD) rcognizd th potntial for problms associatd with misintrprtation of trms, which, in turn, crats uncrtainty of th significanc of th rsults obtaind. Thy urgd th dvlopmnt of a Thsaurus to improv communication daling with risk assssmnt of hazardous installations. A task tam was stablishd to addrss this concrn and was givn th mandat to stablish a tool that would rduc and possibly liminat th potntial for such confusion. Th rsult of this work is th Chmical Accidnt Risk Assssmnt Thsaurus (CARAT). Th difficulty of communication is basd in larg part on th fact that crtain "trms of art" hav diffrnt manings in diffrnt countris and culturs, or that diffrnt trms of art ar usd to addrss th sam concpt. Th CARAT is dsignd to circumvnt ths difficultis, and is spcially usful as a tool to analyz th dfinitions of trms rlatd to risk assssmnt. Hnc, th dvlopmnt of th Chmical Accidnt Risk Assssmnt Thsaurus was initiatd: To mak mor transparnt th various approachs to risk assssmnt of th accidntal rlas of chmicals from fixd installations usd in diffrnt countris; To promot undrstanding of, and communication about, chmical accidnt risk assssmnt procsss including th commonaltis and diffrncs among th various approachs; and To facilitat communication concrning chmical accidnt risk assssmnt btwn, and within, countris, hlping to ovrcom th problms introducd bcaus of diffrnt culturs and languag.
Th CARAT dos not attmpt to harmoniz or stablish standard trminology or to mak judgmnt on th valu of various risk assssmnt mthodologis. Instad, th CARAT capturs only what risk assssmnt profssionals undrstand to b th stat of undrstanding of particular laws, rgulations, or procdurs currntly in ffct or in us. It can b viwd as a "translation ngin" which capturs th intndd maning of a risk assssmnt itm and "translats" it into objctiv or oprational languag. This is th subjct mattr of th databas. Th Systm has volvd ovr svral dvlopmnt cycls, and was prviously known as th OECD Computr Dictionary/Thsaurus of Risk Assssmnt Procsss, or simply th OECD Dictionary/Thsaurus. Structur and Hirarchy of th Entris Thr ar four classs of information that can b ntrd into th Systm: 1. Dfinitions of words and phrass associatd with risk assssmnt; 2. Laws and rgulations concrning risk assssmnt of hazardous facilitis; 3. Guidlins, policis or cods rlatd to risk assssmnt; and 4. Spcific risk assssmnt studis that hav bn conductd on particular cass. Prsons making an ntry into th databas intrprt th maning thy attach to thir ntry by rsponding to a sris of qustions that lad th prson through th Systm hirarchy and, at ach lvl, probs succssivly dpr using mor spcific xprssions to convy th maning. Thr ar fiv lvls in th hirarchy: 1. Gnric lmnts, a st of rlatd, oprationally dfind procss stps; 2. Sub-lmnts, on of th oprationally dfind procss stps containd in a Gnric Elmnt; 3. Trms, th concpt which is th subjct of th procss dfind in th Sub-lmnt; 4. Catgoris, a st of xampls usd to giv spcific oprational maning to a Trm; and 5. Dscriptors, singl xampls illustrativ of spcific oprational situations in th Catgory. At its highst lvl, th CARAT hirarchy consists of four broad gnric lmnts rprsnting th commonly accptd stags in th procss of assssing th risks associatd with hazardous installations. Thy can b loosly dscribd as hazard idntification; hazard rlas and xposur scnarios; sourc and subjct intraction; and xprssion of th risk. In addition, thr ar two othr lmnts that may b utilizd to captur aspcts that ar gnrally considrd outsid th risk assssmnt procss, pr s. A Pr-assssmnt lmnt capturs faturs that ar judgd to prcd risk assssmnt procsss, such as a statmnt of th scop of th ntry; and a Postassssmnt lmnt that dscribs faturs that gnrally follow th risk assssmnt procss itslf, such as, risk managmnt or risk communication. Th Pr- and Post-assssmnt lmnts ar fr-form txt facilitis, lacking th hirarchical structur of th four gnric lmnts. Th four Gnric Elmnts ar prsntd in Figur 1. Bcaus th risk assssmnt procss is prsntd in oprational languag, i.., uss no trms of art, th languag of th Gnric Elmnts tnds to b wordy, and uss words that lack immdiat connction to any spcific risk assssmnt.
Figur 1- Th Four Gnric Elmnts of CARAT Gnric Elmnt I: Idntification of sourcs with th potntial to caus undsird outcoms to subjcts of concrn that is th focus of th stimation of liklihood. Gnric Elmnt II: Idntification of possibl squncs of vnts lading to loss of containmnt of th potntial to caus undsird outcoms to a subjct of concrn rsulting in its ntry into a domain of th cosystm. Estimation of possibl distributions of both th rlasd potntial and th subjcts of concrn ovr tim priods within compartmnts dlimitd by spcifid boundaris or nd-points. Gnric Elmnt III: Idntification and dscription of how th spcifid undsird outcom is rlatd to th intnsity, tim, and mod of contact of a spcifid potntial to caus th undsird outcom to th subjct(s) of concrn. Gnric Elmnt IV: Consists of two parts: Part A: Idntification of th mthods for stimating and xprssing th liklihood of a spcifid ffct and dscribing th quality of such stimats. Part B: Idntification of th basis for comparing drivd stimats of liklihood to spcifid guidlins and dscribing th dpndnc of ths stimats on xplicitly spcifid altrnativ assumptions. Gnric lmnts hav varying numbrs of sub-lmnts. Sub-lmnts ar procdural in natur and rprsnt oprations, mthodologis, actions, or procss stps that ncompass a phas of th gnric lmnt in th risk assssmnt procss. Each sub-lmnt has an associatd trm that is th subjct of th action dfind by th sub-lmnt. In grammatical trminology, trms ar noun phrass, lacking any notion of action, and sub-lmnts ar vrb phrass, containing th notion of action on a subjct. Figur 2 illustrats sub-lmnts and trms for Gnric Elmnt I. Figur 2. - Sub-lmnts and Trms Corrsponding to Elmnt I Elmnt I Sub-lmnt I i: Idntification of sourcs with th potntial to caus undsird outcoms to subjcts of concrn Trm I i: Sourcs with th potntial to caus undsird outcoms Sub-lmnt I ii: Idntification subjcts of concrn Trm I ii: Subjcts of concrn Sub-lmnt I iii: Idntification undsird outcoms to subjcts of concrn Trm I iii: Undsird outcoms to subjcts of concrn Each trm is dividd into catgoris of spcific sts of dscriptor xampls that ar th oprational rprsntation of th intndd maning. Dscriptors allow th prson ntring an itm to dscrib th risk assssmnt opration with ultimat spcificity. Figur 3 shows th Catgoris associatd with Sub-lmnt I, Trm 2.
Figur 3 - Catgoris Corrsponding to Elmnt I, Sub-lmnt I, Trm 2: Subjcts of concrn Catgoris: Popl Ecosystms/nvironmnt Cultural assts Proprty and physical systms Facilitis Othr subjcts of concrn In Figur 4, on can trac a spcific path through th hirarchical structur. Elmnt I dals with th opration of idntifying sourcs of th potntial to caus undsird outcoms to subjcts of concrn. This is dcomposd into thr Sub-lmnts (oprations), on of which is Idntification of subjcts of concrn. Th Trm for this Sub-lmnt is Subjcts of concrn. Associatd with this Trm ar Catgoris of dscriptors such as popl, proprty, cosystms tc. Each catgory contains spcific Dscriptors. For xampl, th Catgory popl contains Dscriptors such as rsidnts, workrs, prgnant womn, tc. Th systm also contains provisions for ntring additional dscriptors in a Catgory, or indd nw Catgoris if th suggstd ons do not dirctly captur th intndd maning in a givn situation. Elmnt I Figur 4 Partial Hirarchical Path for Subjcts of Concrn Sub-lmnt I ii: Idntification subjcts of concrn Trm I 2: Subjcts of concrn Catgoris: Popl Dscriptors: Rsidnts Snsitiv rsidnt populations Prgnant rsidnts Transint popl Workrs at facilitis containing a sourc with potntial to caus undsird outcoms Trans-boundary populations Undfind popl Othr In summary, Tabl I shows th amount of dtail into which a risk assssmnt procss can b dcomposd.
Tabl I - Hirarchy of th OECD CARAT Hirarchical Fatur Numbr of Componnts Elmnts 4 Sub-lmnts 19 Trms 19 Catgoris 70 Dscriptors 368 Spcific aspcts of th Entry Procss Th data ntry procss provids th opportunity to add lvls of dtail or to provid gnral dscriptions of th spcific rfrnc bing ntrd. Ths itms includ th following: th nam of th ntry for sarch purposs, th idntify of th country to which th ntry applis, and th nam of th organization that is making th ntry. full rfrnc information that will allow clints to rqust th sourc matrial from public sourcs. th URL of an Intrnt wb sit whr th rfrnc might b viwd or downloadd if th documnt is availabl on th wb. th ability to skip an lmnt or sub-lmnt if thy ar not addrssd in th itm bing ntrd th ability to add nw dscriptors to th systm to captur nw usag and approachs. th clint may slct undfind as th dscriptor if th catgory is not spcific in rgard to charactrizing th catgory. th clint nds to dcid whthr th ntry addrsss th itm xplicitly or implicitly. th clint can indicat that thr ar ithr critria and/or tools associatd with th slction and ntr th dtails of ths itms. th clint can giv rfrnc dtails that will allow for library rtrival of th rfrnc matrial rlatd to th particular itm. a fr-txt commnt fild is availabl that allows th clint to laborat on th rasons for, or xplanation of, th particular slction. th clint is prmittd to add othr dscriptors. Th clint may typ in wording that bttr dscribs th maning undr that catgory. Th systm adds th nw itm to th xisting list. As many additional dscriptors as ar rquird for th ntry may b ntrd. All ntris ar placd into th working spac in th systm. Whn th data ntry procss is compltd and th clint is satisfid with th ntry s accuracy and compltnss, th clint informs th CARAT Application Managr lctronically that th ntry is complt. Th Application Mangr will thn xamin th ntry for typographical rrors, obvious inconsistncis, conformanc to crtain standards of ntry, and omissions of crtain rquird data filds. Aftr rviw, th ntry is transfrrd to th public spac in th CARAT whr it is availabl for accss by th gnral public along with all othr finalizd ntris. Qury Capability Th gratst valu to th usr is probably th public accss to th information containd in th CARAT by mans of th qury modul. Th qury modul can sarch th CARAT for its ntris and prsnt th rsults on-scrn for immdiat xamination or snd th rsults of th sarch to a local printr. A Comparison facility allows th usr to mak a sid-by-sid comparison of th CARAT ntris of laws, rgulations, Spcific Risk Assssmnts, Risk Assssmnt Guidanc, or dfinitions, in any combination. Th comparison can b mad at th lmnt, trm, catgory, or dscriptor lvls. Th final qury can prform sarchs by idntifying ntris that contain ithr crtain combinations of hirarchical dtails (Hirarchy sarchs), or crtain combinations of dscriptor dtails (Dscriptor sarchs). Both typs can b conductd in Boolan and/or mod, and th Dscriptor sarchs can spcify itms that ar to b xcludd from th sarch.
Exampl 1 Comparison of Two Risk Assssmnts of Chlorin Storag Editorial Not: In this rport, th chck marks indicat that th hirarchical itm is addrssd in th ntry. Th boldd txt is th spcific slction by th data ntry prson of th appropriat dscriptor, indicating furthr whthr th ntry addrsss th itm xplicitly () or implicitly (i). Cas 1 Chlorin Truck Storag QRA Cas 2 Continuous Chlorin Rlas from On Tonn Containr 1 2 Addrssd: xplicitly i implicitly i Elmnt I Idntification of sourcs with th potntial to caus undsird outcoms to subjcts of concrn that is th focus of th stimation of liklihood Idntification of sourcs with th potntial to caus undsird outcoms to subjcts of concrn Substancs Enrgy Toxic to humans Prssur Physical situations Systms containing rgulatd chmicals Lgally spcifid sourcs Listd substancs Idntification of subjcts of concrn Popl Rsidnts Snsitiv rsidnt populations Transint popl Workrs at facilitis containing a sourc with potntial to caus undsird outcoms Idntification of undsird outcoms to subjcts of concrn undsird outcoms for popl Dath Immdiatly dangrous to lif or halth Elmnt II Idntification of squnc of vnts that can lad to loss of containmnt of th potntial to caus undsird outcoms and its ntry into a domain dfind by spcifid boundaris. Idntification of th basis for stimating th distribution of both th rlasd potntial and th subjcts of concrn within this domain Idntification of th basis for gnrating squncs of vnts lading to a loss of containmnt rsulting in th ntry of th potntial to caus undsird outcoms into a domain that may b occupid by a subjct of concrn
i i Squnc of vnts basd on past vnts or xprinc Insuranc or industry rcords Profssional judgmnt Squnc of vnts basd on tchnical analysis Fault-tr analysis for squnc of vnts Evnt-tr analysis for squnc of vnts HazOp What If Idntification of th basis for stimating distributions of th rlasd potntial within domains of intrst Distributions basd on tchnical analysis Evnt-tr analysis for distribution of th rlas SAFETI modl WHAZAN Computr modling Idntification of th basis for stimating distributions of subjcts of concrn within domains of intrst Historical data Cnsus data Local Survys Survy of plant and nighbor work locations Idntification of th basis for stablishing boundaris that dlimit stimats of th distribution of th rlasd potntial Boundaris or nd-points basd on tchnical analysis Chlorin inhalation dos-rspons rlationship Immdiatly Dangrous to Lif or Halth Elmnt III Idntification and dscription of how th spcifid undsird outcom is rlatd to th intnsity, tim and mod of contact of a spcifid potntial to caus th undsird outcom to th subjcts of concrn Idntification of th way th spcifid potntial to caus th undsird outcom maks contact with to th subjct of concrn to caus th spcifid undsird outcom Mod of contact btwn th potntial to caus undsird outcoms and popl Inhalation Idntification of th basis of th rlationship usd to prdict how th undsird outcom is rlatd to contact with th potntial to caus th undsird outcom Rlationship to popl Human pidmiological data Dscription of th dimnsions/masurmnt units of th potntial to caus th undsird outcoms that ar usd to prdict th undsird outcom Concntration of th substanc with th potntial to caus th spcifid undsird outcom that intracts with th subjct ovr a spcifid tim priod
i i Actual dos rspons rlationship for inhalation of chlorin ppm ovr an unspcifid priod of tim Dscription of th dimnsions/masurmnt units usd to xprss th undsird outcom rspons Numbr of th undsird outcom vnts xprincd by th spcifid population of subjcts Numbr of daths Frquncy of th undsird outcom vnts xprincd by th spcifid population of subjcts Frquncy of daths Elmnt IV Consists of two parts: Part A: Idntification of th mthods for stimating and xprssing th liklihood of a spcifid ffct and dscribing th quality of such stimats. Part B: Idntification of th basis for comparing drivd stimats of liklihood to spcifid guidlins and dscribing th dpndnc of ths stimats on xplicitly spcifid assumptions Idntification of th basis of stimating th liklihood that spcifid undsird ffcts will occur, that is, that a spcifid undsird outcom of a spcifid magnitud for a spcifid subjct of concrn will occur Quantitativ mthods of stimating liklihood Quantitativ vnt-tr analysis for stimating liklihood Quantitativ fault-tr analysis for stimating liklihood SAFETI modl Smi-quantitativ mthods of stimating liklihood Spcific smi-quantitativ mthod of stimating liklihood Mthods of stimating liklihood basd on historical data Mthod of stimating liklihood basd on xtrapolation of historical data Idntification of th mthod of xprssing th liklihood that spcifid undsird ffcts will occur, that is, that a spcifid undsird outcom of a spcifid magnitud for a spcifid subjct of concrn will occur Quantitativ xprssions Frquncy Probability of a spcifid squnc of vnts rsulting in a spcifid undsird ffct in a spcifid tim priod Probability of a spcifid undsird ffct if a spcifid squnc of vnts occurs Probability of a spcifid undsird ffct in a spcifid tim priod Idntification of th undsird outcom of a spcifid magnitud for a spcifid subjct of concrn for which th liklihood is bing stimatd Spcifid mmbr of th population of concrn that xprincs a spcifid undsird outcom Avrag mmbr of th population of concrn Avrag mmbr of a spcifid cohort of th population of concrn Mmbr closst to th rlas of th potntial Mmbr at a spcifid location
Spcification of a group of N or mor subjcts of th population of concrn that xprincs a spcifid undsird outcom simultanously N or mor spcifid mmbrs of th population of concrn Spcification of th undsird outcom rsulting from th prsnc at spcifid location(s) of th spcifid potntial at concntrations/intnsitis ovr tim that would b sufficint to caus th undsird outcom for spcifid subjcts of concrn Dath to rsidnts Idntification of dscription of th quality/uncrtainty of stimats of liklihood Charactrization of stimat Bst stimat Idntification of th approach usd to compar th stimats of liklihood with rlvant standards and guidlins Typ of standard or guidlin Businss Idntification of th mtrics or othr information ndd for comparisons of stimatd liklihood against standards or guidlins Comparison mtrics Th liklihood of a spcifid undsird outcom for any mmbr in a population of th subjcts of concrn rsulting from a spcifid sris of vnts Th liklihood of a spcifid undsird outcom for any mmbr in a population of th subjcts of concrn rsulting from a spcifid sris of vnts if th facility mployd all practicabl masurs to rduc th liklihood and magnitud (ALARP) Plots of th frquncy pr yar of squncs of vnts (accidnts) rsulting in N or mor fatalitis to popl as a function of th numbr of fatalitis An stimat of th avrag numbr of fatalitis pr unit tim in a population of subjcts of concrn Contours of aras within which th liklihood of a subjct xprincing a spcifid undsird outcom is gratr than an stimatd lvl An assssmnt of th adquacy of masurs for prvnting or containing rlass using mthodology and spcifications for adquacy, using masurs of prvntion and containmnt dfind in th law, guidlin, or standard that is th basis of th comparison Comparison of nw to xisting facility Idntification of spcifid altrnativ assumptions on th stimats of liklihood Altrnativ assumptions Considration of shltring in plac Application of th CARAT Systm Most comparisons using CARAT will focus on comparing various laws and rgulations, dfinitions or spcific risk assssmnts. But th systm is much mor powrful, spcially to corporat usrs. Companis can put spcific standards, guidlins, risk assssmnts, or othr risk-rlatd applications into th systm and us th comparison fatur to dtrmin whr th spcific input may b at varianc with th lgal systm in th country. For a company lik NOVA with facilitis in svral countris, a comparison of th risk assssmnt standard to th laws and rgulations in th various countris can vrify that th standard
mts th rquirmnts of all or som of th countris. This typ of comparison provids guidanc rgarding aras whr changs should b mt to assur complianc. Th systm sourc cod can also b obtaind from th OECD and installd on a company s local srvr. Using this facility th company can ntr spcific standards and cods of practic and compar work from th various sits to assur that th rquirmnts hav bn mt. Th systm could also b usd as rpository for spcific risk assssmnts. Ths could b accssd by mploys within th company and usd as guidanc for othr risk assssmnts. It would also provid an archiv facility for thos wishing to updat risk assssmnts on a rgular basis. Usrs of th databas can compar ntris to dtrmin aras of conformity and aras of diffrnc. This is spcially important whn xisting programs or procsss ar b usd to mt lgal rquirmnts in diffrnt countris or jurisdictions. Th systm can also b usd to assur that spcific risk assssmnts mt th rquirmnts outlind in spcific lgislation or guidanc. Although th xprinc in using CARAT in th arlir dvlopmntal stags indicatd that th data ntry procss rquird an intnsiv ffort, participants notd a numbr of bnfits that xtndd byond th mr ntry of risk assssmnt approachs into a computr systm. Rmarkably, participants notd a dpning undrstanding of thir own country s or agncy s laws and rgulations, and thy gaind insight into aras of waknss or ambiguity. Through th clarity of oprational languag, th CARAT is a convnint sourc of guidanc on th risk assssmnt procsss rquird at individual facilitis, and assists, in gnral, in dsigning and managing risk assssmnt programs. Acknowldgmnt Th Chmical Emrgncy and Prpardnss Offic of US Environmntal Protction Agncy sponsord this rsarch work undr Cooprativ Agrmnt 826583 at th bhst of th OECD Working Group on Chmical Accidnts. Additional support was providd by th Nthrlands Ministry of Housing, Spatial Planning and Environmnt.