5Selecting Hazard

Evaluation Techniques

The ability to ensure process safety at a facility is influenced by many things: forexample, employing appropriate technology in design and construction, anticipatingthe effects of external circumstances, understanding and dealing with humanbehavior, and having effective management systems. One of the cornerstones of aneffective process safety management system is a successful hazard evaluation (HE)program.

A successful HE program requires tangible management support; sufficient,technically competent people (some of whom must be trained to use HE techniques);an adequate, up-to-date information database; and the right tools to perform HEstudies. Fortunately, a variety of flexible HE techniques exist. Each techniquepresented in these Guidelines has been applied in the chemical process industry andis appropriate for use in a wide variety of situations.

In an effective HE program, excellent performance is based on successfullyexecuting individual HE studies. A successful HE study can be defined as one inwhich (1) the need for risk information has been met, (2) the results are of highquality and are easy for decision makers to use, and (3) the study has been performedwith the minimum resources needed to get the job done. Obviously, the techniqueselected has a great bearing on each HE study's success.

Many factors can affect which HE technique is chosen. Before dealing with thetechnical aspects of this decision, it is worthwhile to address an often overlookedquestion that can also significantly influence the success of an HE study: who shoulddecide which HE technique is used? It is appropriate and necessary thatmanagement define the basic charter for an HE study: the main objective of thestudy, the type of decision making information (results) needed, and the initialresources and deadlines for performing the work. But the technical project managerand/or HE team leader should select the most appropriate HE method to fulfill thestudy's charter.

Many organizations have developed policies that specify that analysts usecertain types of HE techniques.1"4 Usually, providing this guidance does not presenta problem as long as the hazard analyst can use an alternate HE method if it canbetter satisfy the study's charter. For example, suppose a corporate safety group hasdecided that facilities under their jurisdiction must use the HAZOP Analysistechnique to perform the majority of HE studies. The HE team leader for a majorprocess modification project is requested to perform an analysis of the distributedcontrol system (DCS) that is being installed in conjunction with the project. In thiscase the team leader believes, based on his experience, that the HAZOP Analysis

approach is not the most efficient method to investigate the ways that the DCS cancause hazardous situations. Instead, the leader wants to use the FMEA technique,which, for this type of analysis problem, he has seen work more efficiently thanHAZOP Analysis. Management listens to the leader's recommendation and allowshim to use the FMEA technique.

Hazard evaluation specialists should be allowed some freedom to select a propermethod for the job. Selecting the most appropriate HE method is a critical step inensuring the success of an HE study.

Since selecting an appropriate HE technique is more an art than a science,there may be no "best" method for a particular application. And it may turn outthat a plant's need for better risk information cannot be met by HE techniques alone(see Section 1.2). Nonetheless, assuming that it is appropriate to use hazardevaluation techniques, this chapter discusses a strategy for selecting a method thatis likely to contribute to the success of a study.

5.1 Factors Influencing the Selection of Hazard Evaluation Techniques

Each HE technique has its unique strengths and weaknesses. Chapter 4describes many of the attributes of the 12 HE techniques covered in these Guidelines.Understanding these attributes is prerequisite to selecting an appropriate HEtechnique. The process of selecting an appropriate HE technique may be a difficultone for the inexperienced practitioner because the "best" technique may not beapparent. As hazard analysts gain experience with the various HE methods, the taskof choosing an appropriate technique becomes easier and somewhat instinctive.

The thought process behind selecting HE techniques is complex, and a varietyof factors can influence the decision-making process,5"* ТШе 5 Л lists six categoriesof factors that analysts should consider when selecting an HE technique for a specificapplication. The importance that each of these categories has on the selectionprocess may vary from facility to facility, company to company, and industry toindustry. However, the following general observations about the relative significanceof these factors should be true for nearly every situation.

1. The motivation for the study and type cf results needed should be the mostimportant factors that analysts consider. The selected technique should bethe most effective way to provide the information required to satisfy thereasons for the study. Other factors should not overshadow theseconcerns; otherwise, the product of the study may not meet anorganization's risk management needs. The motivation for the study andthe need for particular results usually determine how important otherselection factors are.

2. The type of information available, characteristics of the analysis problem, andperceived risk associated with the process or activity are factors dealing withthe inherent boundary conditions of the subject analysis; these factorsrepresent conditions over which the analyst typically has no control. Ifthese factors dominate the analyst's choice, he or she may not be able tochoose any techniques except those allowed by these factors.

Tkble 5.1 Categories of lectors That Could Influence the Selectionof HE Tbchnkjues

Motivation for the studyType of results neededType of information available to perform the studyCharacteristics of the analysis problemPerceived risk associated with the subject process or activityResource availability and analyst/management preference

For example, if all other factors lead an analyst to believe that the FaultTtee Analysis technique should be used for a particular situation, but thereare no detailed process drawings available from which to define the systemand its failure characteristics, then the analyst must either correct theinformation deficiency (i.e., get detailed drawings) or choose anothertechnique. If the drawings are not available because they have not beenupdated, then it may be possible (although time-consuming and expensive)to develop updated drawings. On the other hand, if the subject process isin the conceptual design phase, then it will be impossible to obtain detaileddrawings. Another technique should be selected unless the HE teamleader believes that the Fault Нее Analysis technique can be applied in aless detailed fashion and still satisfy the objectives of the HE study.

3. The last category involves resource availability and analyst/managementpreference. Although important considerations, they should not dominatethe selection of HE techniques. Tbo often, though, these factors are themain ones the analyst considers. Choosing an HE technique based solelyon its low cost or because the particular technique is frequently used canlead to inefficient, low-quality, or unsuitable results.

The following sections discuss each category and provide examples of factorsthat analysts should consider when selecting an appropriate HE technique.

Motivation for Ae HE Study

This category of factors should be the most important to eveiy hazard analyst.Performing an HE study without understanding its motivation and without havinga well-defined purpose is likely to waste safety improvement resources. A numberof issues can shape the purpose of a given study. For example, what is the impetusfor doing the study in the first place? Is the study being chartered as part of a policyfor performing HE studies of new processes? Are insights needed to make riskmanagement decisions concerning the improvement of a mature, existing process?Or is the study being done to satisfy a regulatory or legal requirement?

Hazard analysts responsible for selecting the most appropriate technique andassembling the necessary human, technical, and physical resources must be provideda well-defined, written purpose so that they can efficiently execute the study's charter.

Type of Results Needed

Depending on the motivation for an HE study, a variety of results could beneeded to satisfy the study's charter. Defining the specific type of informationneeded to satisfy the objective of the HE study is an important part of selecting themost appropriate HE technique. The following are five categories of informationthat can be produced from HE studies:

9 List of hazards• List of potential accident situations• List of alternatives for reducing risk or areas needing further study• Prioritization of results• Input for a quantitative risk analysis

As described in Chapter 3, some HE techniques can be used solely to identifythe hazards associated with a process or activity. If that is the only purpose of thestudy, then a technique can be selected that will provide a list or a "screening" ofareas of the process or operation that possess a particular hazardous characteristic.

Nearly all HE techniques can provide lists of potential accident situations andpossible risk reduction alternatives (i.e., action items); a few of the HE techniquescan also be used to prioritize the action items based on the team's perception of thelevel of risk associated with the situation that the action item addresses. Chapter 7discusses the use of HE techniques for prioritizing the results of an HE study. If anorganization can anticipate that their need for risk management information is notlikely to be satisfied by a qualitative analysis, then a hazard analyst may elect to usean HE technique that provides more definitive input as a basis for performing aQRA, in the event that such an analysis is needed.

Type of Information Available to Perform the Study

There are two conditions that define what information is available to the HEteam: (1) the stage of life the process or activity is in when the study needs to beperformed and (2) the quality and currentness of the available documentation. Thefirst condition is fixed for any HE study, and the analyst cannot do anything tochange it. ТШе 5.2 shows what information becomes available through the plant'sevolution.

The process's stage of life establishes the practical limit of detailed informationavailable to the HE team. For example, if an HE study is to be performed on theconceptual design of a process, it is highly unlikely that an organization will havealready produced a P&ID for the proposed process. Thus, if the analyst must choosebetween HAZOP Analysis and What-If Analysis, then this Mphase-of-life" factorwould dictate that the What-If Analysis method should be used, since there is notenough information to perform an adequate HAZOP Analysis. Figure 5.1 illustrateswhich techniques are commonly used for HE studies at various phases of a process'slifetime.

An analyst cannot accelerate the development of a process just so he or she canuse a certain HE technique. However, analysts may use a detailed technique in a lessdetailed way. Ultimate^ if the analysts believe that, because of the lack cf information,the objectives of the study amnot be met using an appropri^

Tkble5.2 Typical Information Available to Hazard Analysts

Type of InformationIncreasing

Level of Detail

Time When InformationBecomes Available from

Project Inception

Specific operating experienceOperating proceduresExisting equipmentP&IDsPFDsExperience with similarprocessesMaterial inventoriesBasic process chemistryMaterial, physical, andchemical data

R&D

Conceptual Design

Pilot Plant Operation

Detailed Engineering

Construction/Start-Up

Routine Operation

Expansion or Modification

Incident Investigation

Decommissioning

Rarely used orinappropriate

Commonlyused

Figure 5.1 Typical uses for HE techniques.

recommend to management that their objectives be reexamined or the study be delayeduntil sufficient information becomes available.

The second condition deals with the quality and currentness of thedocumentation that does exist. For an HE study of an existing process, hazardanalysts may find that the P&IDs are not up-to-date or do not exist in a suitableform. Using any HE technique on out-of-date process information is not only futile,it is a waste of time and resources. Thus, if all other factors point to using atechnique (e.g., the HAZOP Analysis technique) for the proposed HE study thatrequires such information, then the analysts should ask management to have thenecessary, up-to-date process drawings created. As discussed in Chapter 2, animportant part of an overall HE program is establishing a foundation to support HEstudies. Good planning in the creation of this information can help avoid delays in theperformance of HE studies.

Characteristics of tine Analysis Problem

Tb choose an HE technique, an analyst should look at certain characteristicsof the plant or process being studied. These characteristics can be divided into fiveareas: (1) the complexity and size of the problem, (2) the type of process, (3) thetype of operation(s) included in the process, (4) the nature of the inherent hazards,and (5) the accident events or situations of concern.

The complexity and size of the problem are important because some HEtechniques can get bogged down when used to analyze extremely complicatedproblems. The complexity and size of a problem are functions of the number ofprocesses or systems being analyzed, the number of pieces of equipment in eachprocess or system, the number of operating steps, and the number and types ofhazards and effects being analyzed (e.g., toxic, fire, explosion, economic, orenvironmental).

It is particularly important that hazard analysts select a level of resolution thatis compatible with the purpose of the study. For example, if a large facility is to beanalyzed, a prudent HE team leader should divide the facility into as many smallerpieces as necessary for analysis. Different techniques may be used to analyze eachpan of the process, depending on the characteristics of each analysis problem.However, if the purpose of the HE study is primarily to screen hazards (e.g., developemergency response plans), analysts should choose a level of resolution that looksat systems rather than individual components. For emergency planning purposes, ananalyst might use a What-If Analysis to identify general types of accident sequencesthat can have an impact on the plant population.

For many HE techniques, considering a larger number of equipment items oroperating steps will increase the time and effort needed to perform a study. Forexample, using the FMEA technique will generally take 5 times more effort for aprocess containing 100 equipment items than for a process containing 20 items. TheHAZOP meeting time for analyzing a batch reactor system consisting of SO operatingsteps will take about twice as long as for a batch process with 25 steps. Thus, thetypes and number of hazards and effects being evaluated is proportional to the effortrequired to perform an HE study, although in some cases it may not be a linearrelationship.

Analysts should carefully consider the extra time and effort it will take toanalyze a variety of hazards in a complex system. For example, analyzing all types

of hazards in a complex process at the same time may make it difficult for theanalysts to focus consistently on the significance of accident situations involving oneclass of the analyzed hazards. On the other hand, complex systems that have manysimilar or redundant pieces of equipment or features may not take as long to analyze.

The type of process (Tkble 5.3) also affects the selection of an HE technique.Individual processes can be composed of one or more of these process types. Mostof the HE techniques covered in these Guidelines can be used for almost any type orcombination of process types. However, certain HE techniques are better suited forparticular processes than others. For example, the FMEA approach has a well-deserved reputation for efficiently analyzing the hazards associated with electronicand computer systems, whereas the HAZOP Analysis approach may not work as wellfor these types of systems.

The type of operations included in the subject process also influences theselection of HE techniques. Whether an operation is (1) a fixed facility or atransportation system; (2) permanent or transient; and (3) continuous, semi-batch,or batch can affect the selection of techniques. All of the techniques in theseGuidelines can be used for analyzing fixed facilities or for transportation operations.Because potential accidents involving transportation systems typically involve single,discrete events (e.g., vehicle failures due to impact), single-failure analysis methodssuch as FMEA, What-If Analysis, or What-If/Checklist Analysis are used more oftenthan FTA. However, sometimes ETA is used to consider the combination ofcircumstances surrounding a spill from a transport vehicle.

The permanency of the process can affect the selection decision in the followingway: if all other factors are equal, analysts may use a more detailed, exhaustiveapproach if they know that the subject process will operate continuously over a longperiod of time. The more detailed, and perhaps better documented, analysis of thepermanent operation could be used to support many PSM activities. For example,a HAZOP table listing the detailed evaluation of types of upsets, causes,consequences, safeguards, etc., could be used in an operator training program.

Tkble5.3 Types of Processes

Process Type

Chemical

Physical

Mechanical

Biological

Electrical

Electronic

Computer

Human

Example

Catalytic reaction in a chemical reactor vessel

Separation of a chemical mixture in a distillation column

Dry material handling in a screw conveyor

Fermentation in an incubation chamber

480V ac power supply system

Integrated circuits in a PLC

Microprocessor-based digital control system

Manual mixing of two chemicals in an open vat

On the other hand, analysts may choose a less extensive technique if the subjectactivity is a "one-time" operation. An analyst may be better served using the SafetyReview method to evaluate a one-time maintenance activity. However, analysts arecautioned to recognize that a temporary operation can present significant hazardsand could justify the use of a more detailed HE technique, such as Fault IteeAnalysis.

Finally, some methods such as What-If Analysis, What-If/Checklist Analysis,HAZOP Analysis, ETA, and HRA are better able to analyze batch processes thanothers (e.g., FTA, FMEA, CCA) because the latter methods cannot easily deal withthe need to evaluate the time-dependent nature of batch operations.

The nature of the hazards associated with the process has a minor influence onthe selection of an HE technique. Tbxicity, fire, explosion, and reactivity hazards canall be analyzed with any of the HE techniques covered in these Guidelines, althoughsome of the published Relative Ranking indexes will cover only certain hazards (e.g.,the Dow F&EI only covers fire and explosion hazards).

The charter of an HE study may address a variety of types of failures, events, orsituations of concern. Whether a study focuses on (1) single failures versus multiplefailures; (2) simple loss of containment events; (3) loss of function events; (4) processupsets; or (5) hardware, procedure, software, or human failures can affect thetechnique selection decision. The biggest influence in this category of factors iswhether the analysis is directed at evaluating complex, multiple failure situations.Fault Ttee Analysis, Event TVee Analysis, Cause-Consequence Analysis, and HumanReliability Analysis techniques are primarily used for these situations. Single-failure-oriented methods such as HAZOP Analysis and FMEA are not normally used forthis purpose, although they can be extended to evaluate a few simple accidentsituations involving more than one event. The remaining factors in this categoryhave a relatively minor impact on the selection process.

Perceived Risk of the Subject Process or Activity

If all HE studies were perfect, then it would not matter which HE techniqueis used or who performs the analysis. But, unfortunately, neither the techniques,analysts, nor studies can ever be perfect. An important contributor to thisimperfection is one of the important limitations of HE techniques and studiesdiscussed in Chapter 1 — the issue of completeness. Neither an HE technique noran analyst can guarantee that all possible accident situations involving a process havebeen identified.

Organizations deal with the limitation of completeness in two main ways. First,they use interdisciplinary teams to perform the analysis, capitalizing on the teammembers' combined experience. This "many heads are better than one" strategy isthe key to performing high-quality HE studies when using certain techniques (e.g.,HAZOP Analysis, What-If/Checklist Analysis). Second, organizations tend to usemore systematic techniques for those processes that they believe pose higher risk (or,at least, for situations in which accidents are expected to have severe consequences).Thus, the greater the perceived risk of the process, the more important it is to useHE techniques that minimize the chance of missing an important accident situation.

Recall from Chapter 1 that an organization has several types of information atits disposal to help the analysts understand the inherent risk of a process or activity:

• The amount of experience with the process• The nature of the experience with the process• The continued relevance of process experience

The most important experience factor is the length of time over which theexperience is gained. Has the process been operating for over 30 years, and are theremany such processes operating within the organization and the industry? Or is theprocess relatively new? For a new process involving first-of-its-kind technology thatis still in the design phase, an organization may have absolutely no experience withthe subject process. Sometimes, there may be some similar company or industryexperience that members of an organization can draw upon to derive theirunderstanding of risk.

The next experience factor deals with the actual operating record of the process.Have there been frequent, high-consequence accidents? Or have there only been afew minor incidents and near misses? Sometimes a process will have operated formany years and never have experienced a major accident, even though the potentialhas always existed. The most immediate "experience11 that has the greatest impacton an organization's risk perception is a recent accident that motivates managers toperform an HE study as a part of the follow-up investigation.

The last experience factor deals with the current relevance of the experiencebase to the subject process. There may have been many changes to the process thatinvalidated the operating experience as a current indicator of process risk. Or theremay have been only a few minor changes over the years that have been adequatelydealt with by the organization's management of change policy. In the latter case theorganization may justifiably have confidence that the existing experience base maybe a good predictor of the subject process's future safety performance.

All of these factors contribute to the level of confidence or concern that anorganization has about process risk. Typically, when (1) the subject process hasoperated relatively free of accidents over a long time and the potential for a high-consequence accident is perceived to be low, and (2) there have been few changes tothe process that would invalidate this experience base, then organizations will tendto select less exhaustive, less systematic, more experience-based HE techniques, suchas Safety Review and Checklist Analysis. When the opposite is perceived, morerigorous, predictive techniques are generally preferred, such as HAZOP Analysis,What-If/Checklist Analysis, Fault Ttee Analysis, and so forth.

Resource Availability and Preference

A variety of other factors can influence the selection of hazard evaluationtechniques. Some factors that customarily affect technique selection are:(1) availability of skilled and knowledgeable personnel, (2) target dates by which toperform the study, (3) financial resources, (4) preference of the hazard analysts, and(5) preference of the manager(s) that charters the HE study.

Generally, two types of personnel must be available for the HE study: skilledleaders and practitioners of the particular HE technique chosen and peopleknowledgeable in the process or activity being analyzed. Chapter 2 describes thetypes of technical knowledge that may be needed for an HE study. If the necessarydesign engineers, operators, maintenance personnel, etc., are not available, then the

quality of the HE study is in jeopardy. People skilled in the use of particular HEtechniques are also important for the effective performance of HE studies. Sometechniques, because of their inherent systematic nature, may require less practicedleaders than would other techniques. However, experience has shown that having anHE team leader who is a veteran of many such studies increases the chance of havinga successful study.

Many hazard evaluation techniques require the creative interaction ofparticipants on a team. Tbam meetings can typically last for days, weeks, or months,depending upon the complexity of the subject process. Other techniques (e.g., FaultTtee Analysis) may be performed primarily by individuals working alone. However,these detailed, single-analyst approaches require a "gestation period" to enable theanalyst to create realistic models of the causes of potential accidents. Ibamsituations may not be as helpful when using these techniques; however, these modelsmay be constructed based on information derived from a team meeting or mayefficiently be reviewed in a team meeting environment. Altogether, scheduleconstraints should take a back seat to other technical concerns. However, if thedecision concerning selection of a technique comes down to two otherwise equalapproaches, then the hazard analyst should select the one that will produce thedesired results using the fewest resources in the least time.

Realistic estimates for funding HE studies are necessary for an organization toadequately plan for the performance of all process safety management activities.Ikble 5.4 summarizes the technical effort estimates presented in Chapter 4 forperforming HE studies of simple/small systems and complex/large processes. Theseestimates are provided only to give analysts a rough idea of the relative scale of effortthey should plan for in performing an HE study. In addition, because there are somany other factors that influence time and effort, analysts should use these estimateswith great caution. The actual time required for a study may be much longer (orsomewhat shorter) than these estimates indicate. As analysts and organizations gainexperience with each HE technique, they should become better equipped toaccurately estimate the size of HE studies for their facilities and become moreefficient in performing HE studies.

Hazard evaluation studies done on a shoestring budget, marginally staffed, andunder tight schedule constraints are usually not destined for success. The quality ofthe results from an HE study are inevitably a strong/unction of the quality of the team'seffort. If adequate in-house personnel are unavailable to lead HE studies, then anorganization should acquire training for its prospective hazard analysts. Undertighter schedule constraints, outside consultants can be used to lead and documentHE studies. In the end, organizations should try to do as many of these studies aspossible using in-house personnel to better capitalize on the overall learningexperience.

Ideally, HE studies should be performed using techniques that are most familiarto the HE team leader and other study participants. In addition, management maysometimes have a preference for one technique over another. However, managementpreference should not overshadow other technical reasons for selecting a particularmethod. Tb avoid unproductive disputes concerning selection of HE techniques,hazard analysts should help educate management with tangible examples of thebenefits, strengths, limitations, and relative costs of each technique (see Chapter 4).

Tkble5.4 Summary of Typical Staff Effort Estimates for HE Techniques

PtaeeofHEStudy

|JQ(^inifflt^tftnHEvaluationMaddingTt« ичи • тЛтптшжтсрвпюооlechnique

Simptc/Smafl ComptayLargc

System Process

Complex/Large

Process

Simple/Small

System

Compka/Large

Pi'occat»SrnipkVS™11

System

Compftei/Large

Process

Shnpte/Smiill

System

4 to 8h 3 to 6d

4 to 8h 2 to 4d

4 to 8h 3 to 5d

1 to 2d 4 to 7d

1 to 2d 1 to 3w

4 to 8h 1 to 3w

2 to 6d 2 to 6w

1 to 3d 2 to 4w

3 to 5d 3 to 5w

3 to 5d 3 to 5w

3 to 5d 3 to 5w

3 to 5d 1 to 3w

3to5d

3to5d

3to5d

4to7d

3to5d

4to7d

1 to3w

1 to3w

1 to4w

1 to2w

1 to2w

1 to2w

4 to8h

4to8h

4to8h

1 to2d

4to8h

6 to 12h

1 to 3d

1 to 3d

2to4d

1 to2d

1 to 3d

1 to2d

na

na

na

na

na

na

na

na

2to3w

1 to2w

1 to2w

1 to2w

na

na

na

na

na

na

na

na

3to6d

1 to 3d

1 to 3d

Ito3d

Ito3d

1 to 3d

1 to 3d

1 to 3d

1 to 3d

1 to 3d

2to4d

1 to 3d

4to6d

4to6d

4to6d

1 to 3d

2 to 4h°

2to4h

2to4h

4 to8h

4 to8h

6 to 12h

8 to 12h

2to6h

Ito3d

1 to2d

1 to2d

4to8h

Safety Review

Checklist Analysis

Relative Ranking

PHA

What-If Analysis

What-ШChecklist Analysis

HAZOP Analysis

FMEA

Fault Tree Analysis

Event Tree Analysis

Cause-ConsequenceAnalysis

Human ReliabilityAnalysis

0 h=hours, d=days, w=weeks, m=months, and na=not applicable.

5.2 Decision-Making Process for Selecting Hazard Evaluation Techniques

Each HE technique has unique strengths and weaknesses. Moreover, eachindustry, organization, facility, and process/activity will have unique objectives andneeds when it comes to performing HE studies. The six categories of factorsdiscussed in Section S.I may have varying degrees of importance, depending upon thecircumstances for each particular application of HE techniques. Thus, it is difficultto construct a universal decision-making flowchart that would be correct for everyorganization and facility. However, it is possible to suggest a logical order forconsidering the factors discussed in Section 5.1.

Figure 5.2 illustrates a general order for considering the various factors thatcould influence which HE technique is used for a given study. Certainly, the factorsinvolving motivation and type of results should be most important to everyorganization; these factors provide the basic definition for satisfying the need forgreater risk understanding, which likely precipitated the charter for an HE study.The information available, characteristics of the problem, and perceived risk mayhave varying degrees of importance placed upon them, depending upon the cultureof the sponsoring organization and facility. The amount of resources needed tosupport an HE team should be the last factor considered in technique selection,although it should be wisely used to select between otherwise equal analysistechnique alternatives.

53 Example Using the Proposed Selection Criteria

Even though it is difficult to develop a universally applicable decision logic fororganizations to use in selecting HE techniques, it is appropriate to illustrate theprocess one would use to develop such a framework. Figure 5.3 is a detailedflowchart that organizations may use (1) to directly select HE techniques or (2) tohelp develop their own internal guidelines and philosophies regarding the use of HEtechniques. The following abbreviations for the HE techniques (in parentheses) areused in the flowchart.

• Safety Review (SR)

• Checklist Analysis (CL)

• Relative Ranking (RR)

• Preliminary Hazard Analysis(PHA)

• What-If Analysis (WI)

• What-If/Checklist Analysis(WI/CL)

• Hazard and Operability Analysis(HAZOP)

• Failure Modes and Effects Analysis(FMEA)

• Event Ttee Analysis (ET)

• Fault Ttee Analysis (FT)

• Cause-Consequence Analysis (CCA)

• Human Reliability Analysis (HRA)

DEFINE MOTIVATIONNew reviewRecurrent reviewSpecial requirement

DETERMINE TYPE OF RESULTS NEEDED

List of hazardsHazard screening

List of problems/accidents

Action itemsPrioritization of results

Input for QRA

IDENTIFY PROCESS INFORMATION

Materials

ChemistryInventories

Similar experience

РГОP&JD

Existing process

ProceduresOperating history

EXAMINE CHARACTERISTICS OF THE PROBLEM

Complexity/size

simple/smallcomplex/large

Type of process

chemicalphysicalmechanical

biological

electricalelectroniccomputer

human

Type of operation Nature of hazard

fixed facilitypermanent

continuous С

transportation

temporary

semi-batch batch

toxicityflammability

explosivity

reactivityradioactivity

other

Situation/accident/event of concern

single failure

multiple failure

simple loss ofcontainment event

loss of function event

process upset

hardware

procedure

software

human

CONSIDER PERCEIVED RISK AND EXPERIENCELength of experience Accident experience Relevance of experience Perceived risk

longshortnoneonly with similarprocess

current

manyfewnone

no changes

few changesmany changes

high

mediumlow

CONSIDER RESOURCES AND PREFERENCES

Availability of skilled personnelTime requirements

Funding necessaryAnalyst/management preference

SELECT THE TECHNIQUE

Figure 5.2 Criteria for selecting HE techniques.

Start

Define input infor-mation for selec-

tion process

Use Figure 5.2 tocollect information

Is HE studyfor regulatory

purposes?

Is specificHE methodrequired?

Yes

No

Yes

No

Use required HEtechnique

Is this arecurrentreview?

No

Consider using and revalidating previous HE study

Revalidation Requirements

1. Is adequatedocumenta-tion avail-able frompreviousstudy?

2. Has it notbeen toolong sincethelaststudy?

3. Have there beenno major processor knowledgechanges sincethe last study?

4. Is the hazardassociatedwith the pro-cess not toohigh?

5. Has recent oper-ating experiencebeen devoid ofsignificant inci-dents?

IfallareYes If any are NoConsider this to be

a new/first-timeHE study

Consider revali-dating the previous

HE study

What typeof results are

needed?Follow one path Follow one path

Primarily, roughscreening or general

hazards list

Primarily, a list ofsafety improvement

alternatives

List of specific acci-dent situations plussafety improvement

alternatives

Figure 5.3 Example flowchart for selecting an HE technique.

Primarily, roughscreening or general

hazards list

Consider using SR,CL, RR, PHA, WI, or

WI/CL

Is ranking ofhazardous areas

or processesdesired?

Consider usingPHAorRR

Yes

No

Consider using SR,CL,WI, or WI/CL

Is a significantexperience baseassociated with

the process?

No

Yes

Consider usingSRorCL

Is a checklistavailable or can one

be developed?Consider using CL

Yes

No

Consider using SR

Figure S3 (continued)

Consider usingWI or WI/CL

Use additional factorsfrom Fig. 5.2 to select a

particular technique

Use additional factorsfrom Fig. 5.2 to select a

particular technique

Primarily, a list ofsafety improvement

alternatives

Consider usingSR, CL, PHA, WI,

or WI/CL

Is a significantexperience baseassociated with

the process?

Consider usingSRorCL

Is the processalready inoperation?

Consider using SR

Figure 53 (continued)

Yes NO

No Can a relevantchecklist beobtained?

YesConsider using CL

Use additional factorsfrom Fig. 5.2 to select a^ particulartechnique ,

Consider using WI,PHA, or WI/CL

No

Yes

List of specific acci-dent situations plussafety improvement

alternatives

Will these resultsbe used as input to

a QRA study?

No Consider using WI,PHA, WI/CL,

HAZOP, FMEA, FT,. ET,CCA,orHRA^

Yes

Consider usingHAZOP, FMEA, FT,

ET,orHRA

Is the processoperating? Are

proceduresavailable?

Yes

No

Does theprocess include4

human actions? Arehuman errorsthe greatestconcern?

Consider using HRAYes

No

Consider usingHAZOP, FMEA,

FT, or ET

YesIs detaileddesign information

available?

No

STOPObtain adequate

informationbefore performing

an HE study

Figure 5 J (continued)

Consider using WI,PHA,WI/CL,

HAZOP,FMEA,ET,CCA,HRA

Is theprocess operating?

Are proceduresavailable?

YesDoes the

process include"1 ,human actions? Are

human errorsthe greatestconcern?

YesConsider using HRA

No

Is detaileddesign information

available?

Yes

No

^Consider using WI/4

PHA,WI/CL,HAZOP,FMEA,FT,ET,orCCA

No

YesIs basic processinformationavailable?

No

STOP

Obtain adequateinformation before

performing anHE study

Figure 53 (continued)

Consider usingWI,PHA,or

WI/CL

rlJse additional factors ^[from Fig. 5.2 to select a

particular technique

Consider usingWI,PHA,W1/CL,FMEA, HAZOP,FT, ET, or CCA

r Are the" accidents likely to4

be single or multiple,failure events^

Single failure events Multiple failure events

'"Consider using"*WI,PHA,WI/cL,FMEA,orHAZOP

Consider usingHAZOP, FMEA,FT, ET, or CCA

Is theperceived risk

high?

No Consider usingWIorPHA

YesConsider usingWI/CL, FMEA,

or HAZOP

Use additional factorsfrom Fig. 5.2 to select a

particular technique

Is the processa mechanical orelectrical sytem?

Yes Consider usingFMEA

Ts an exhaus-"1

tive list of fail-ure modes re-

quired?

No Consider usingHAZOP or

^ FMEA .

Yes

Consider usingFTorET

Use additional factorsfrom Fig. 5.2 to select aj

particular technique

No

Consider usingWI/CL or HAZOP

Use additional factorsLfrom Fig. 5.2 to select a]

particular technique

Use additional factorsfrom Fig. 5.2 to select a

particular technique '

Figure 53 (continued)

Is processsimple/small?

Consider usingCCA

ЬConsider usingIAZOP, FMEA,

FT, or ET

References

1. J. Stephenson, System Safety 2000 —A Practical Guide for Planning, Managing,and Conducting System Safety Programs, (ISBN 0-0442-23840-1), Van NostrandReinhold, New York, 1991.

2. Risk Analysis in the Process Industries, European Federation of ChemicalEngineering Publication No. 45, Institution of Chemical Engineers, Rugby,England, 1985.

3. Process Safety Management, Chemical Manufacturers Association, Washington,DC, 1985.

4. E P. Lees, Loss Prevention in the Process Industries, Vols. 1 and 2,Butterworth's, London, 1980.

5. D. E Montague, "Process Risk Evaluation — What Method to Use?,* ReliabilityEngineering and System Safety, Vol. 29, Elsevier Science Publishers Ltd.,England, 1990.

6. S. L. Nicolosi and E L. Leverenz, "Selection of Hazard Evaluation Methods,"AIChE Summer National Meeting, Denver, August 1988.

7. P. E McGrath, "Using Qualitative Methods to Manage Risk," ReliabilityEngineering and System Safety, Vol. 29, 1990.

8. M. G. Gressel and J. H. Gideon, "An Overview of Process Hazard EvaluationTechniques," American Industrial Hygiene Association Journal, Vol. 52, No. 4,

A _ •« 4ГХ^Ч4

Figure 53 (continued)

Consider usingHAZOP

,No

Is the process amechanical or elec-

trical sytem?

YesConsider using

FMEA

Use additional factorsfrom Fig. 5.2 to selecta particular technique

]Consider using

FMEA or HAZOPConsider using

FT or ET

Single failure events Multiple failure events

Are the accidentslikely to be single or

multiple failureevents?

Consider usingHAZOP, FMEA,

FT, or ET