References - ftp.feq.ufu.brftp.feq.ufu.br/Luis_Claudio/Books/E-Books/Safety/GUIDELINES_Hazar… · the HE team leader assembles a qualified team, determines the physical and analytical

References

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

2. H. R. Greenberg and J. J. Cramer, eds., Risk Assessment and Risk Managementfor the Chemical Process Industry, (ISBN 0-442-23438-4), Van NostrandReinhold, New York, 1991.

3. Chemical Process Hazard Review, ACS Symposium Series 274, AmericanChemical Society, Washington, DC, 1985.

6.6 What-IiTCbccklist Analysis

Technical Approach

The What-ItfChecklist Analysis technique is acombination of two previously discussed HE methods:What-If Analysis (Section 6.5) and Checklist Analysis(Section 6.2). The method is usually performed by ateam of personnel experienced with the subjectprocess. The team uses the What-If Analysistechnique to brainstorm the various types of accidentsthat can occur within the process. Then the teamuses one or more checklists to help fill in any gapsthey may have missed. The checklists used in thisportion of the analysis differ somewhat fromtraditional checklists of desired design, procedural, and operating attributes (seeSection 6.2). Rather than focusing on a specific list of design or operating features,checklists used in a What-H7Checklist Analysis are more general and focus on sourcesof hazards and accidents. These checklists are intended to inspire creative thoughtabout the types and sources of hazards associated with the process.

The combined use of these two methods emphasizes their main positivefeatures (i.e., the creativity of What-If Analysis and the experience-basedthoroughness of a checklist) while at the same time compensating for theirshortcomings when used separately. For example, a traditional checklist of a subjectprocess, by definition, is based on the relevant project experience the author is ableto accumulate from various sources. Sometimes, particularly if there is little relevantindustry or company experience available on the subject process, the checklist islikely to provide incomplete insights into the design, procedural, and operatingfeatures necessary for a safe process, and a more general checklist is required. TheWhat-If part of the analysis uses a team's creativity and experience to brainstormpotential accident situations. Since the What-If Analysis method is usually not asdetailed, systematic, or thorough as some of the more regimented approaches (e.g.,HAZOP Analysis, FMEA), use of a checklist permits the HE team to fill in any gapsin their thought process.

The What-WChecklist Analysis technique can be used for any type of processor activity at virtually any stage in the life of the process. Normally, the method isused to examine the potential effects and significance of accident situations at a more

Previous Page

general level than some of the more detailed approaches. For example, a What-ItyChecklist Analysis might consider the issue "What happens if the reactor feedstream is contaminated?" Ultimately, the level of resolution of a What-WChecklistAnalysis can be as detailed as the HE team chooses.

Analysis Procedure

A What-IiyChecklist Analysis consists of the following steps: (1) preparing forthe review, (2) developing a list of What-If questions and issues, (3) using a checklistto cover any gaps, (4) evaluating each of the questions and issues, and (5)documenting the results.1"4 A variation of this procedure is for the team to reversethe order of steps 2 and 3 or to develop What-If questions concurrently as theyprogress through a detailed checklist.

Preparing for the Review. Chapter 2 of these Guidelines provides generalguidance for preparing for team-based HE studies. For a What-ItfChecklist Analysis,the HE team leader assembles a qualified team, determines the physical andanalytical scope for the proposed study, and, if the process/activity is rather large,divides it into functions, physical areas, or tasks to provide some order to the reviewof the process. (Section 6.5 discusses the important aspects of preparing for a What-If Analysis; these will not be repeated here.) For the checklist portion of thisanalysis, the HE team leader should obtain or develop an appropriate checklist forthe team to use in conjunction with the What-If Analysis. The checklist should focuson general hazardous characteristics of the process or operation. Appendix Вcontains an example of a detailed checklist that an HE team leader could use as thebasis for constructing checklists appropriate for almost any analysis.

Developing a List of What-If Questions and Issues. Section 6.5 describes theapproach an HE team uses when meeting to develop questions and issues involvingpotential accident situations.

Using a checklist to cover any gaps. Once the team has identified all of thequestions and issues it can in a particular area or step of the process or activity, theHE team leader will use the checklist he or she previously obtained (or prepared).The team considers each checklist item to see whether any other potential accidentsituations or concerns arise. If so, these are evaluated in the same way as theoriginal What-If questions (the checklist is reviewed for each area or step in theprocess or activity). In some cases it may be more desirable to have the HE teambrainstorm the hazards and potential accident situations of a process before using thechecklist.1 In other situations, effective results can be obtained by beginning with achecklist and using items in it to create What-If questions and issues that might nototherwise have been considered, However, if the checklist is used first, leadersshould take precautions to avoid letting the checklist restrict the creativity andimagination of the team.

Evaluating Each of the Questions and Issues. After developing questions andissues involving potential accident situations, the team considers each accidentsituation or safety concern; qualitatively determines the potential effects of theaccident implied by the situation or concern; and lists existing safeguards to prevent,

mitigate, or contain the effects of the potential accident. The team then evaluatesthe significance of each situation and determines whether a particular safetyimprovement option should be recommended. This process is repeated for each areaor step of the process or activity. Sometimes this evaluation is performed by specificteam members outside the team meeting and is subsequently reviewed by the team.

Documenting the Results. The results of a What-If/Checklist Analysis aredocumented in the same way as the results for a What-If Analysis (see Section 6.5).Usually the scribe will use a marking board, chart pad, or word processor linked toan overhead projector to record questions, issues, effects, safeguards, action items,etc., during the meeting. Following the meeting the HE team leader and scribeusually summarize these results in a tabular form similar to that shown in ТШе 6.7.For a What-If/Checklist Analysis, the HE team may also document the completionof the checklist to help illustrate the completeness of the study.

Anticipated Work Product

A typical report contains a listing of potential accident situations, effects,safeguards, and action items generated in the meetings — often in tabular form.However, some analysts document the results in a narrative text format. Sometimesthe HE team will provide management with more detailed explanations of theanalysis recommendations. Chapter 7 provides additional information concerninganalysis follow-up considerations.

Computer Software Aids

SAFEPLAN (DuPont, Westlake Village, California) is the only softwareprogram specifically designed to perform What-If/Checklist Analysis that was foundto be commercially available. Hazard analysts should also be able to use the softwarelisted in the What-If Analysis, Checklist Analysis, and HAZOP Analysis sections.In addition, standard word processing and spreadsheet programs can help analystsdocument the results of What-If/Checklist Analysis studies.

Example

Tb increase production, the K. R. Mody Chemical Company has installed a newtransfer line between its existing 90-ton chlorine storage tank and its reactor feedtank. Before each batch, the operator must transfer one ton of chlorine into the feedtank; the new line will allow this to be done in about one hour (with the old line ittook about three hours). Nitrogen pressure will be used to force the liquid chlorinethrough the mile-long, uninsulated, welded pipeline in the elevated rack between thebarge terminal and the process unit. Both the storage tank and the reactor feed tankoperate at ambient temperature. Figure 6.2 is a schematic of the new feed lineconfiguration.

Tb transfer chlorine, the operator sets PCV-1 to the desired pressure, opensHCV-1, and verifies that the level in the feed tank is rising. When the high level

Figure 6.2 Schematic for the chlorine feed line example.

alarm in the feed tank signals that one ton of chlorine has been transferred, theoperator closes HCV-1 and PCV-1. HCV-2 is normally left open between batchesso liquid chlorine will not be trapped in the long pipeline.

An HE team is chartered to perform a What-WChecklist Analysis of thisprocess modification and meets to consider potential accidents of concern andwhether there is adequate protection against them. The What-If portion of themeeting generates the issues listed in Tkble 6.10. Subsequently, the team uses thetwo checklists shown in Figure 6.3 and Tkble 6.11 to supplement their What-Ifquestions.1 ТШе 6.12 lists the additional safety concerns the team identifies usingthe checklists; these concerns may have gone unnoticed had only the What-IfAnalysis method been used.

References

1. A E Burk, "What-If/Checklist — A Powerful Process Hazards ReviewTechnique," presented at the AIChE 1991 Summer National Meeting,Pittsburgh, August, 1991.


3. Chemical Process Hazard Review, ACS Symposium Series 274, AmericanChemical Society, Washington, DC, 1985.

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

TOSCRUBBER

250psig PRESSURE

,CONTROL VALVE

1 MILE

TOSCRUBBER

N2 (200 psig)

CL2

STORAGETANK

(90 TONS)

(LEVEL CHECKED MONTHLY)

N2PURGE

(50 psig)

TOSCRUBBER

250psig

FEEDTANK

(1 TON)

TOREACTOR

Tkblc 6.10 What-If Questions for the Chlorine Feed Line Example

• What if there is moisture left in the line?• What if the operator transferred a double batch of chlorine?• What if HCV-1 is left closed?• Will the pipeline overpressure and rupture if left full of liquid chlorine

during the summer?• Is the piping material rated for temperatures below -20 degrees F?• What if there is reverse flow from the feed tank to the storage tank?• Can chlorine leak into and contaminate the nitrogen system?• What can be done to isolate the header if there is a major rupture such as

that caused by vehicle impact?• What is the design basis of the scrubber? Can it handle all of the chlorine

if the pipeline needed to be depressured quickly in an emergency?• What if HCV-2 is inadvertently closed?• What if the level indicator/alarm fails in the feed tank?• What if air enters the system? Can it cause an accident in the reactor?

Figure 6.3 Example of a simplified checklist for hazards analysis. (Source: Adapted fromA. F. Burk, " What-I#Checklist— A Powerful Process Hazards Review Tech-nique," presented at the AIChE Summer National Meeting, Pittsburgh, PA,August 1991.)

STORAGE OF RAW MATERIALS, PRODUCTS, AND INTERMEDIATES

Storage Tknks

Dikes

Emergency Valves

Inspections

Procedures

Specifications

Limitations

MATERIALS HANDLING

Pumps

Ducts

Conveyors, Mills

Procedures

Piping

Design, Separation, Inerting, Materials ofConstruction

Capacity, Drainage

Remote Control-Hazardous Materials

Flash Arresters, Relief Devices

Contamination Prevention, Analysis

Chemical, Physical, Quality, Stability

Temperature, Time, Quantity

Relief, Reverse Rotation, Identification,Materials of Construction

Explosion Relief, Fire Protection, Support

Stop Devices, Coasting, Guards

Spills, Leaks, Decontamination

Ratings, Codes, Cross-Connections, Materialsof Construction

Figure 63 (cont'd)

PROCESS EQUIPMENT; FACILITIES, AND PROCEDURESProcedures

Conformance

Loss of Utilities

Vessels

Identification

Relief Devices

Review of Incidents

Inspections, Tfests

Hazards

Electrical

Process

Operating Ranges

Ignition Sources

Compatibility

Safety Margins

PERSONAL PROTECTION

Protection

Ventilation

Exposures

Utilities

Hazards Manual

Environment

Start-Up, Normal, Shutdown, Emergency

Job Audits, Shortcuts, Suggestions

Electrical, Heating, Coolant, Air, Inerts,Agitation

Design, Materials, Codes, Access, Materials ofConstruction

Vessels. Piping. Switches. Valves

Reactors, Exchangers, Glassware

Plant, Company, Industry

Vessels, Relief Devices, Corrosion

Runaways, Releases, Explosions

Area Classification, Conformance, Purging

Description, Tfest Authorizations

Temperature, Pressure, Flows, Ratios,Concentrations, Densities, Levels, Time,Sequence

Peroxides, Acetylides, Friction, Fouling,Compressors, Static Electricity, \fclves,Heaters

Heating Media, Lubricants, Flushes, Packing

Cooling, Contamination

Barricades, Personal, Shower, Escape Aids

General, Local, Air Intakes, Rate

Other Processes, Public, Environment

Isolation: Air, >Шег, Inerts, Steam

Tbxicity, Flammability, Reactivity, Corrosion,Symptoms, First Aid

Sampling, Vapors, Dusts, Noise, Radiation

Figure 63 (ooot'd)

SAMPLING FACILITIES

Sampling Points

Procedures

Samples

Analysis

MAINTENANCE

Decontamination

Vessel Openings

Procedures

FIRE PROTECTION

Fixed Protection

Extinguishers

Fire Walls

Drainage

Emergency Response

Accessibility, Ventilation, living

Pluggage, Purging

Containers, Storage, Disposal

Procedures, Records, Feedback

Solutions, Equipment, Procedures

Size, Obstructions, Access

Vessel Entry, Welding, Lockout

Fire Areas, Water Demands, DistributionSystem, Sprinklers, Deluge, Monitors,Inspection, Testing, Procedures, Adequacy

Type, Location, Training

Adequacy, Condition, Doors, Ducts

Slope. Drain Rate

Fire Brigades, Staffing, Training, Equipment

CONTROLS AND EMERGENCY DEVICES

Controls

Calibration, Inspection

Alarms

Interlocks

Relief Devices

Emergencies

Process Isolation

Instruments

WASTE DISPOSAL

Ditches

Vents

Characteristics

Ranges, Redundancy, F&il-Safe

Frequency, Adequacy

Adequacy, Limits, Fire, Fume

Tests, Bypass Procedures

Adequacy, Vent Size, Discharge, Drain,Support

Dump, Drown, Inhibit, Dilute

Block \folves, Fire-Safe Valves, Purging

Air Quality, Time Lag, Reset Windup,Materials of Construction

Flame Traps, Reactions, Exposures, Solids

Discharge, Dispersion, Mists

Sludges. Residues. Fouling Materials

Ikblc6.ll Example of a Hazard Checklist

Acceleration (uncontrolled — too much, too little)• Inadvertent motion• Sloshing of liquids• Translation of loose objects

Deceleration (uncontrolled — too much, too little)• Impacts (sudden stops)• Failures of brakes, wheels, tires, etc.• Falling objects• Fragments or missiles

Chemical Reaction (nonfire, can be subtle over time)• Disassociation, product reverts to separate components• Combination, new product formed from mixture• Corrosion, rust, etc.

Electrical• Shock• Burns• Overheating• Ignition of combustibles• Inadvertent activation• Explosion, electrical

Explosions• Commercial explosive present• Explosive gas• Explosive liquid• Explosive dust

FlammabUity and Fires• Presence of fuel — solid, liquid, gas• Presence of strong oxidizer — oxygen, peroxide, etc.• Presence of strong ignition force — welding torch, heaters

Heat and Temperature• Source of heat, nonelectrical• Hot surface burns• Very cold surface burns• Increased gas pressure caused by heat• Increased flammability caused by heat• Increased volatility caused by heat• Increased activity caused by heat

MechanicalSharp edges or pointsRotating equipmentReciprocating equipmentPinch pointsWeights to be liftedStability/toppling tendencyEjected parts or fragments

Tkblc6.ll (cont'd)

PressureCompressed gasCompressed air toolPressure system exhaustAccidental releaseObjects propelled by pressureWater hammerFlex hose whipping

Static• Container rupture• Overpressurization• Negative pressure effects

Leak of Material• Rammable

Tbxic• Corrosive• Slippery

Radiation• Ionizing radiation• Ultraviolet light• High intensity visible light• Infrared radiation• Electromagnetic radiation• Laser radiation

Tcodcity• Gas or liquid

— Asphyxiant— Irritant— Systemic poison— Carcinogen— Mutagen

• Combination product• Combustion product

Vibration• Vibrating tools• High noise source level• Mental fatigue• Flow or jet vibration• Supersonics

Miscellaneous• Contamination• Lubricity

Tkble 6.12 Additional Safety Issues Generated by Using Hazard Checklists in theChlorine Feed Line Example

What if the line is contaminated with oil during maintenance?What if the nitrogen header pressure regulator fails?Is the chlorine tank rated for full vacuum?What if there is a leak in the line during a night transfer operation?Have previous chlorine release incidents in industry been reviewed?Does this equipment meet the recommendations of the Chlorine Institute?Are there any sampling or drain points at the low spots in the pipeline?Has the correct metallurgy been specified for this equipment?If inert material-lined piping is being used, how will its integrity be periodicallytested?

• What emergency notification systems exist for alerting the community?

6.7 Hazard and Operabflity Analysis

Technical Approach

The Hazard and Operability (HAZOP) Analysistechnique is based on the principle that severalexperts with different backgrounds can interact in acreative, systematic fashion and identify moreproblems when working together than when workingseparately and combining their results. Although theHAZOP Analysis technique was originally developedfor evaluation of a new design or technology, it isapplicable to almost all phases of a process's lifetime.

The essence of the HAZOP Analysis approachis to review process drawings and/or procedures in aseries of meetings, during which a multidisciplinary team uses a prescribed protocolto methodically evaluate the significance of deviations from the normal designintention. Imperial Chemical Industries (ICI) originally defined the HAZOPAnalysis technique to require that HAZOP studies be performed by aninterdisciplinary team.1'3 Thus, while it is passible for one person to use the HAZOPAnalysis thought process, such a study cannot be called a HAZOP Analysis* Therefore,the HAZOP Analysis technique is distinctively different ftomwhile the other approaches can be performed by sin^ analysts (ahhou^ in fnost(^ise^it is better to use an interdisciplinary team), HAZOP Analysis, by definition, must beperformed by a team of individuals with the specific, necessary skills.

The primary advantage of the brainstorming associated with HAZOP Analysisis that it stimulates creativity and generates new ideas. This creativity results fromthe interaction of a team with diverse backgrounds. Consequently, the success of thestudy requires that all participants freely express their views, but participants shouldrefrain from criticizing each other to avoid stifling the creative process. This creativeapproach combined with the use of a systematic protocol for examining hazardoussituations helps improve the thoroughness of the study.

The HAZOP study focuses on specific points of the process or operation called"study nodes," process sections, or operating steps. One at a tiine, the HAZOPteam examines each section or step for potentially hazardous process deviations thatare derived from a set of established guide words. One purpose of the guide wordsis to ensure that all relevant deviations of process parameters are evaluated.Sometimes, teams consider a fairly large number of deviations (i.e., up to 10 to 20)for each section or step and identify their potential causes and consequences.Normally, all of the deviations for a given section or step are analyzed by the teambefore it proceeds further.

HAZOP Analysis studies can be performed on new projects as well as onexisting facilities.4"6 For new projects, it is best to conduct a HAZOP Analysis whenthe process design is fairly firm. Normally, the system P&IDs are available so theteam can formulate meaningful answers to the questions raised in the HAZOPAnalysis process. Also, it is still possible to change the design without incurringmajor costs. However, HAZOP Analysis studies can also be performed at earlierstages of a process lifetime as long as the team members have adequate processdocumentation and knowledge upon which to base their analysis. But a HAZOPanalysis performed at this early stage should not be a substitute for a thoroughdesign review.

Although the basic HAZOP Analysis approach is well established, the way thatit is employed may vary from organization to organization. Tkble 6.13 lists terms anddefinitions that are commonly used in HAZOP Analysis. The guide words shown inTkble 6.14 are the original ones developed by ICI for use in a HAZOP study and areapplied to process parameters such as those shown in Tkble 6.15. Someorganizations have modified this list to be specific to their operations and to guideteams more quickly to the areas where significant process safety problems may exist.Other organizations have created specialized lists of guide words or specificdeviations for analyzing batch operations and procedural steps.4

In the original ICI approach, each guide word is combined with relevant processparameters and applied at each point (study node, process section, or operating step)in the process that is being examined. The following is an example of creatingdeviations using guide words and process parameters:

Guide Words Parameter Deviation

NO + FLOW = NO FLOW

MORE + PRESSURE = HIGHPRESSURE

AS WELL AS + ONE PHASE = TWO PHASE

OTHER + OPERATION = MAINTENANCETHAN

Guide words are applied to both the more general parameters (e.g., react, mix)and the more specific parameters (e.g., pressure, temperature). With the generalparameters, it is not unusual to have more than one deviation from the applicationof one guide word. For example, "more reaction" could mean either that a reactiontakes place at a faster rate, or that a greater quantity of product results. On the

ТЬЫебЛЗ Common HAZQP Analysis Terminology

'Rrm

Process Sections (orStudy Nodes)

Operating Steps

Intention

Guide Words

Process Parameter

Deviations

Causes

Consequences

Safeguards

Actions (orRecommendations)

Definition

Sections of equipment with definite boundaries (e.g., a tinebetween two vessels) within which process parameters areinvestigated for deviations. The locations on P&IDs at which theprocess parameters are investigated for deviations (e.g., reactor)

Discrete actions in a batch process or a procedure analyzed by aHAZOP analysis team. May be manual, automatic, or software-implemented actions. The deviations applied to each step aresomewhat different than the ones used for a continuous process

Definition of how the plant is expected to operate in the absenceof deviations. Tbkes a number of forms and can be eitherdescriptive or diagrammatic (e.g., process description, flowsheets,line diagrams, P&IDs)

Simple words that are used to qualify or quantify the designintention and to guide and stimulate the brainstorming process foridentifying process hazards

Physical or chemical property associated with the process.Includes general items such as reaction, mixing, concentration, pH,and specific items such as temperature, pressure, phase, and flow

Departures from the design intention that are discovered bysystematically applying the guide words to process parameters(flow, pressure, etc.) resulting in a list for the team to review (noflow, high pressure, etc.) for each process section, learns oftensupplement their list of deviations with ad hoc items

Reasons why deviations might occur. Once a deviation has beenshown to have a credible cause, it can be treated as a meaningfuldeviation. These causes can be hardware failures, human errors,unanticipated process states (e.g., change of composition), externaldisruptions (e.g., loss of power), etc.

Results of deviations (e.g., release of toxic materials). Normally,the team assumes active protection systems fail to work. Minorconsequences, unrelated to the study objective, are not considered

Engineered systems or administrative controls designed to preventthe causes or mitigate the consequences of deviations (e.g., processalarms, interlocks, procedures)

Suggestions for design changes, procedural changes, or areas forfurther study (e.g., adding a redundant pressure alarm or reversingthe sequence of two operating steps)

Tkble6.15 Common НА2ЮР Analysis Process Parameters

Flow

Pressure

Temperature

Level

Time

Composition

рнSpeed

Frequency

Viscosity

Voltage

Information

Mixing

Addition

Separation

Reaction

other hand, some combinations of guide words and parameter will yield no sensibledeviation (e.g., "as well as" with "pressure").

With the specific parameters, some modification of the guide words may benecessary. In addition, analysts often find that some potential deviations areirrelevant because of a physical limitation. For example, if temperature parametersare being considered, the guide words "more11 or "less" may be the onlypossibilities.

The following are other useful alternative interpretations of the original guidewords:

• Sooner or later for "other than" when considering time

• Where else for "other than" when considering position, sources, ordestination

• Higher and lower for "more" and "less" when considering levels,temperature, or pressure

When dealing with a design intention involving a complex set of interrelatedplant parameters (e.g., temperature, reaction rate, composition, and pressure), it maybe better to apply the whole sequence of guide words to each parameter individuallythan to apply each guide word across all of the parameters as a group. Also, when

lkble 6.14 Original HAZOP Analysis Guide Words and Meanings

Guide Wards

No

Less

More

Part Of

As Well As

Reverse

Other Than

Meaning

Negation of the Design Intent

Quantitative Decrease

Quantitative Increase

Qualitative Decrease

Qualitative Increase

Logical Opposite of the Intent

Complete Substitution

applying the guide words to an operating instruction (e.g., procedural step), it maybe more useful to apply the sequence of guide words to each word or phraseseparately, starting with the key part that describes the activity. These parts of thesentence usually are related to some impact on the process parameters. RH example,in the procedural step The operator starts flow A when pressure В is reached," theguide words would be applied to:

• Starts flow A (no, more, less, etc.)

• When pressure В is reached (sooner, later, etc.)

The guide-word-based HAZOP Analysis method is the originally definedHAZOP Analysis technique. However, several variations of this basic method havebeen developed. These variations will be discussed later in this section (HAZOPAnalysis Variations). In many situations, these variations may be more effective thanthe original guide-word approach.

Analysis Procedure

The concepts presented above are put into practice in the following steps: (1)preparing for the review, (2) performing the review, and (3) documenting the results.Figure 6.4 illustrates the concept of the HAZOP Analysis technique. It is importantto recognize that some of these steps can take place concurrently. For example, insome cases the team may review the design, record the findings, and perform follow-up over the same period of several weeks or months. Nonetheless, the steps arediscussed separately as though they are executed one at a time.

Preparing for the Review. Chapter 2 describes the various tasks that HE teamleaders must perform to prepare for HE studies. This section amplifies some of

AttitudeMeetingLeadership

Preparation

HAZOPReview

•&Team

Knowledge/'Experience

Team's HAZOPExperience

Information forstudy (P&IDs, PFDs)

Table

Documentation Follow-up

Figure 6.4 Overview of the HAZOP analysis technique.

Deviation Causes Consequences Safeguards Action

these items because of their importance to the success of a HAZOP Analysis study.The amount of preparation depends upon the size and complexity of the processbeing analyzed.

Define the purpose, objectives, and scope of the study. The purpose, objectives,and scope of the study should be made as explicit as possible. The objectivesare normally set by the person who is responsible for the plant or project; thisperson is assisted by the HAZOP study leader. It is important that peoplework together to provide the proper direction and focus for the study. It isalso important to define what specific consequences are to be considered. Fbrexample, a HAZOP study might be conducted to determine where to build aplant to have the minimal impact on public safety. In this case, the HAZOPstudy should focus on deviations that result in off-site effects.

Select the team. The HE team leader should ensure the availability of anadequately sized and skilled HAZOP team. A HAZOP team, at a minimum,should consist of a leader, a scribe, and two other individuals who have anunderstanding of the design and operation of the subject process. Ideally, theteam consists of five to seven members, although a smaller team could besufficient for a simpler, less hazardous plant. If the team is too large, thegroup approach will be difficult. On the other hand, if the group is too small,it may lack the breadth of knowledge needed to assure thoroughness. Section2.4 provides more detail on team composition.

Obtain the necessary data. Typically, the data consist of various drawings in theform of P&IDs, flowsheets, and plant layout schematics. Additionally, theremay be operating instructions, instrument sequence control charts, logicdiagrams, and computer programs. Occasionally, there may be plant manualsand equipment manufacturers' manuals. Important drawings and data shouldbe provided to HAZOP team members well before the meetings.

Convert the data into a suitable form and plan the study sequence. The amountof work required in this stage depends on the type of process. With continuousprocesses, preparation can be minimal. Study nodes or process sections maybe identified before the meetings using up-to-date flowsheets and P&IDs.Sufficient copies of each drawing should be available for team members to seeduring the meeting(s).

Sometimes, team leaders may also develop a preliminary list of deviations tobe considered in the meeting and prepare a worksheet on which to record theteam's responses. However, the leader should avoid using a previouslyassembled list as the "only" deviations to be considered. This could stifle thecreative synergism of the team when identifying process hazards and couldresult in missing some hazardous deviations due to complacency. It is to beexpected that, due to the learning process that accompanies the study, somechanges will be made as the study progresses.

With batch processes, preparation is usually more extensive, primarily due tothe more complicated operations and procedures (e.g., heat the reactor in step

3, cool the reactor in step 8). Analyzing procedures is a large part of theHAZOP study for batch processes. In some circumstances (e.g., when two ormore batches of material are being processed at the same time), it may benecessary to prepare a display indicating the status of each vessel at each stepof the process. If operators are physically involved in the process (e.g., incharging vessels rather than simply controlling the process), their activitiesshould be represented by flow charts.

Tb make sure that the team approaches the plant and its operationmethodically, the leader will usually prepare a plan before the study begins.This means the team leader must spend some time before the meetings todetermine the "best" study sequence, based on how the specific plant isoperated.

Arrange the necessary meeting?. Once the data and drawings have beenassembled, the team leader is in a position to plan the review meetings. Thefirst requirement is to estimate the meeting time needed for the study. As ageneral rule, each process section or study node will take an average of 20-30minutes. For example, a vessel with two inlets, two exits, and a vent shouldtake about three hours. Thus, a leader can estimate the HAZOP meeting timerequired by considering the number of process sections or nodes. Another wayto make a rough estimate is to allow about two to three hours for each majorpiece of equipment. Fifteen minutes should also be allowed for each simpleverbal statement in operating procedures, such as "switch on pump," "motorstarts,19 or "pump starts.19 After estimating the meeting time required, theteam leader can arrange the review meetings. Ideally, each session should lastno more than four to six hours (preferably in the morning). Longer sessionsare undesirable because the team's effectiveness usually begins to diminish. Inextreme cases, sessions may be held on consecutive days with longer hours, butsuch a program should be attempted only in exceptional circumstances (e.g.,when team members are from out of town and cannot travel to the meeting siteevery day).

With large projects, one team may not be able to analyze all of the subjectprocesses within the allotted time; it may be necessary to use several teams andteam leaders (one of the team leaders should act as a coordinator). Thecoordinator will divide the processes into logical sets, allocate portions of theprocess to different teams, and prepare schedules for the study as a whole.

Performing the Review. The HAZOP Analysis technique requires that aprocess drawing or procedure be divided into study nodes, process sections, oroperating steps and that the hazards of the process be addressed using the guidewords. Figure 6.5 illustrates the typical flow of activities in a HAZOP meeting. Asthe team applies all of the relevant guide words to each process section or step, theyrecord either (1) the deviation with its causes, consequences, safeguards, and actions,or (2) the need for more complete information to evaluate the deviation. Ashazardous situations are detected, the team leader should make sure that everyoneunderstands them. As mentioned in Chapter 2, it is important for the HAZOP team

Select aprocess section or

operating step

Explain design intentionof the process section

or operating step

Repeat for allprocess sections

or operating steps

Select aprocess variable

or task

Repeat for allprocess variables

or tasks

Apply guide word toprocess variable or

task to developmeaningful deviation

Repeat forall guide

words

Develop action items

Examine consequencesassociated with deviation(assuming all protection

fails)

List possiblecauses of deviation

Assess acceptability ofrisk based on

consequences, causes,and protection

Identify existingsafeguards to

prevent deviation

Figure 6.5 HAZOP analysis method flow diagram.

leader to control the degree of problem solving that occurs during the teammeetings. Tb minimize inappropriate problem solving, the leader can:

• Complete the study of one process deviation and associatedsuggested actions before proceeding to the next deviation

• Evaluate all hazards associated with a process section beforeconsidering suggested actions for improving safety

In practice, HAZOP leaders should strike a compromise, allowing the teamenough time to consider solutions that are easy to resolve, yet not allowing the teamto spend too much time "designing solutions." It may not be appropriate, or evenpossible, for a team to find a solution during a meeting. On the other hand, if thesolution is straightforward, a specific recommendation should be recordedimmediately. Tb ensure effective meetings, the team leader must keep several factorsin mind: (1) do not compete with the members; (2) take care to listen to all of themembers; (3) during meetings, do not permit anyone to be put on the defensive; and(4) keep the energy level high by taking breaks as needed.

Although the team leader will have prepared for the study, the HAZOPtechnique may expose gaps in the available plant operating information or in theknowledge of the team members. Sometimes calling a specialist for information onsome aspect of plant operation or deciding to postpone certain parts of the study toobtain more information may be necessary.

Documenting the Results. The recording process is an important part of theHAZOP study. The person assigned to scribe the meetings must be able to distillthe pertinent results from the myriad of conversations that occur during themeetings. It is impossible to manually record all that is said during the meetings, yetit is very important that all important ideas are preserved. Some analysts may decideto minimize their documentation effort by not pursuing (and not documenting) thecauses of deviations for which there are no significant safety consequences. It maybe helpful to have the team members review the final report and reconvene for areport review meeting. Reviewing key issues will often fine-tune the findings anduncover other problems. Normally, the results of HAZOP meetings are recorded ina tabular format (Tkble 6.16); however, action items may be recorded separately.

Tkble6.16 Typical Format for a HAZOP Analysis Worksheet

Tbam: Drawing NumberMeeting Date: Revision Number

ItemNo. Deviation Causes Consequences Safeguards Actions

Study node, process section, or operating step description

Definition of design intention

Anticipated Work Products

A HAZOP study can be documented in a number of ways. Recording themeeting results in tabular form preserves the team's evaluations in a detailed manner.HAZOP analysis documentation may include: (1) a brief process description; (2) alist of drawings or procedures covered; (3) the names, affiliations, and attendancedates of the team members; (4) a brief description of the way the HAZOP techniquewas used; (5) the HAZOP meeting notes; and (6) a list of potential safetyimprovements (action items) for management consideration. If less detaileddocumentation is selected, only a description of the action items is created. Chapter7 provides additional information concerning analysis follow-up considerations.

Computer Software Aids

The following are commercially available software programs specificallydesigned to perform HAZOP Analysis studies:

CAHAZOP(NUS Corporation, San Diego, California)

HAZOP-PC(Primatech, Inc., Columbus, Ohio)

HAZOPtimizer(A D. Little, Cambridge, Massachusetts)

HAZSEC(Tfechnica, Inc., Columbus, Ohio)

HAZTEK(Westinghouse Electric Corp., Pittsburgh, Pennsylvania)

LEADER(JBF Associates, Inc., Knoxville, Tfennessee)

SAFEPLAN(Du Pont, Westlake Village, California)

Standard word processing and spreadsheet software programs can also aid analystsin documenting the results of HAZOP Analysis studies.

HAZOP Analysis Variations

As mentioned at the beginning of this section, the original guide-word-basedHAZOP approach was developed by ICI. Over the years many organizations havemodified the approach to suit their special needs.8 Also, a number of novelimprovements have been suggested, and some are in routine practice. These variousindustry-, company-, or facility-specific approaches may be quite appropriate in theapplications for which they are intended. The purpose of this section is to outline

relatively common variations of the HAZOP Analysis technique that preserve theessential elements of the original approach.

There are two basic variations of the guide-word HAZOP Analysis approach:

• Different ways to identify deviations for consideration by theHAZOP team

• Different ways to document the HAZOP team meeting results

Other variations involving ways of ranking the HAZOP results also exist. However,these are not discussed here; see Section 7.1 concerning alternatives for prioritizingthe results of HE studies. The following sections outline several alternatives thatorganizations are using in each of the two categories listed above.

Identifying Relevant Process Deviations. One of the strengths of the guide-word approach is its ability to exhaustively identify process deviations for each studynode, process section, or operating step. Systematically applying the various guidewords to a complete list of process parameters in a "brute force" fashion can leadto the development of an overwhelming list of deviations for the team to evaluate.The advantage of this approach is that an inexperienced HAZOP leader and teamcan be fairly confident that they have considered all of the ways that a process canmalfunction. The disadvantage is that an experienced team may be burdened by thisrigorous, yet ponderous, approach if many of the guide-word-based deviations leadto "dead ends" from a hazard significance standpoint.

Ttoo alternatives have emerged through practice as efficient ways for relativelyexperienced leaders and teams to generate the list of deviations they consider foreach study node, process section, or operating step: the library-based approach andthe knowledge-based approach. Both variations seek to increase the efficiency of theteam meetings by minimizing the time spent in identifying the causes, effects, andsafeguards of deviations that would obviously not result in an effect of interest.

The library-based approach is the most closely related alternative to the originalguide-word approach. Before the HAZOP team meeting, the HAZOP leader orscribe should survey a standard library of potential deviations to determine whichones are relevant for each node, section, or step. Each node, section, or step usuallyfocuses on a major piece of equipment. Depending upon the type of equipmentinvolved (e.g., reactor, column, pump, tank, piping, heat exchanger), some potentialdeviations will not be relevant. For example, high level in a normally liquid-filledvessel would not be expected to create any significant hazard.

In addition, depending upon how skilled the HAZOP leader or scribe is atdividing the process into nodes or sections, some hazardous deviations may beomitted from consideration if the analyst believes that evaluating upstream ordownstream sections will identify these effects. For example, consider three processsections involving a feed line, a set of redundant centrifugal pumps, and a dischargeline leading to a reactor. There is nothing gained by a team considering "HighFlow," or other such deviations in the pump section if this same deviation and itseffects have been considered elsewhere. The location of the effect of "High Row"would normally be at the reactor. Since there are no credibly different causes andeffects of "High Flow" in the pump section itself, time can be saved if the team does

not have to reconsider the causes and effects of deviations in sections that areotherwise identified in upstream or downstream sections.

Tkble 6.17 is an example of a library that HAZOP leaders and scribes could useto select relevant deviations of interest before the HAZOP meetings.9 Using thisapproach can save as much as 20% to 50% in meeting time, depending upon thespecific process, hazards of interest, and types of equipment involved. However,analysts choosing this variation should recognize the potential for inadvertentlymissing some deviations because the team did not help create the library.

Tkbte6.17 Example Library of Relevant Deviations for Process Section Types

Deviation

High flow

Low/no flow

High level

Low level

High interface

Low interface

High pressure

Low pressure

High temperature

Low temperature

High concentration

Low concentration

Reverse/misdirectedflow

Tiibe leak

Tiibe rupture

Leak

Rupture

Column

X

X

X

X

X

X

X

X

X

X

Process Section "type?

Tknk/Vessel

X

X

X

X

X

X

X

X

X

X

X

X

Line

X

X

X

X

X

X

X

X

X

X

X

HeatFxrtiangei^

X

X

X

X

Рипф*

X

X

flThis library was developed for a specific strategy for defining process sections. Readersare cautioned not to blindly use this typical library or any other library without carefullyreviewing it for relevance and completeness.

^This library assumes that other deviations (e.g., low flow, high temperature) areconsidered when examining the line downstream of these equipment items.

The knowledge-based approach is a specialization of the guide-word HAZOPAnalysis in which the guide words are supplemented or partially replaced by both theteam's knowledge and specific checklists. This knowledge base is used to comparethe design to well-established basic design practices that have been developed anddocumented from previous plant experience. The implicit premise of this version ofthe HAZOP Analysis technique is that the organization has extensive designstandards that the team members are familiar with. An important advantage of thismethod is that the lessons learned over many years of experience are incorporatedinto the company's practices and are available for use at all stages in the plant'sdesign and construction. Thus, the knowledge-based HAZOP Analysis study canhelp ensure that the company's practices, and therefore its experience, have indeedbeen incorporated in the design.

Comparing a process design to codes and practices will generate additionalquestions that are different from the guide-word HAZOP Analysis deviations. Forexample, questions might be:

• "Shouldn't the design be like...?"

• "Will the proposed design change control the hazard so that therisk of operating the process does not increase?"

As a more specific example, consider the discharge from a centrifugal pump.The guide-word HAZOP approach would apply the guide word "Reverse* to identifythe need for a check valve. The knowledge-based HAZOP approach might alsoidentify the need for a check valve because an actual problem was experienced withreverse flow, and the use of check valves on a centrifugal pump discharge has beenadopted as a standard practice.

Sometimes a checklist can be used to help a team develop deviations for aparticular study. Appendix В contains a comprehensive checklist that readers can useto supplement their knowledge when leading a HAZOP team.

It is also important to note that the experience-based checklists used in thisvariation of HAZOP may be of little value compared to the guide-word approachwhen portions of the process involve major changes in equipment technology orinvolve new chemistry.

Documentation Options. Many organizations have developed specialized waysof documenting the results of a HAZOP analysis team meeting. The following area few of the more common variations known to the authors.

Deviadon-by^deviation HAZOP table. In the deviation-by-deviation (DBD)approach, all causes, consequences, safeguards, and actions are related to aparticular deviation. However, no correlation between individual causes,consequences, and safeguards for that deviation is expressed. Thus, all causeslisted for a deviation do not necessarily result in all of the listed consequences,and specific cause/consequence/safeguard/action relationships are not explicitlyidentified. For example, high steam flow and external fire may both cause hightemperature, but a sprinkler system is only an effective safeguard against thefire. Documenting a table using the DBD approach assumes that thecorrelation(s) among causes, consequences, safeguards, and actions can be

inferred by anyone reading the HAZOP table. The DBD documentationapproach is widely used because the table construction requires less time andits length is greatly reduced compared with the approach discussed below.

Cause-by-cause HAZOP table. In the cause-by-cause (CBC) approach, the tableexplicitly correlates the consequences, safeguards, and actions to each particularcause of a deviation. A team may identify as many causes of a deviation as areappropriate, and every cause will have an independent set of consequences andsafeguards related to it. For example, consider the deviation Mpump leak." Ifthe first cause of that deviation is seal failure, the table would list allconsequences, safeguards, and actions related to seal failures. The team wouldthen proceed to the next cause, which might be pump casing flange failure.Thus, by its very nature, CBC is more precise in the treatment of data thanDBD. And CBC may reduce ambiguity in some instances. For example, amalfunctioning level controller may cause high level, but that same levelcontroller may be a safeguard against high feed flow causing high level.Displaying the same item as both a cause and a safeguard, as in DBD, may beconfusing. So if data for a particular table are potentially confusing, or ifpersonal or company needs require that explicit safeguards be clearly definedfor each cause, an HE team should consider using CBC for its documentationapproach.

Exception-only HAZOP table. In this approach, the table includes only thosedeviations for which the team believes there are credible causes and significanteffects. The advantage of this approach is that the resulting HAZOP meetingtime and table length are greatly reduced. A major disadvantage is that it isalmost impossible to audit such an analysis for completeness. This is especiallyimportant if the report could be subject to the scrutiny of a regulatory agency.The exception-only approach can be used with either the DBD or CBC format.

Action item-only HAZOP table. This variation is considered to be the minimaldocumentation acceptable from a HAZOP study. In this case, only thesuggestions that a team makes for safety improvements are recorded. Theseaction items can then be passed on for risk management decision makingpurposes. The advantage of this variation is that it can save meeting time anddocumentation time outside the meeting since no detailed table is prepared asa result of the team meetings. The disadvantage is that there is nodocumentation to audit the analysis for quality assurance or other purposes.

Example

Using the DAP reaction system presented in the Checklist Analysis example,a guide-word HAZOP study is performed to address personnel hazards. The DAPprocess schematic is repeated here as Figure 6.6; readers should refer to Section 6.2for the description of the DAP process. The team leader applies the guide words tothe process parameters. A sample guide word application is presented for thephosphoric acid solution line to the DAP reactor.

Figure 6.6 DAP process schematic for HAZOP analysis example.

Process Section: Phosphoric Acid Feed Line to the DAP Reactor

Design Intention: Feed phosphoric acid at a controlled rate to the DAP Reactor

Guide Word: No Process Parameter Flow

Deviation: No Flow

Consequences: (1) Excess ammonia in the reactor, leading to...

(2) Unreacted ammonia in the DAP storage tank, withsubsequent...

(3) Release of unreacted ammonia from the DAP storagetank to the enclosed work area

(4) Loss of DAP production

Causes: (1) No feed material in the phosphoric acid storage tank

(2) Flow indicator/controller fails high

(3) Operator sets the flow controller too low

(4) Phosphoric acid control valve В fails closed

(5) Plugging of the line

(6) Leak or rupture of the line

UNLOADINGSTATIONS

AMMONIASOLUTIONSTORAGE

TANK

DAPREACTOR ENCLOSEDWORKAREA

DAPSTORAGETANK LOADING

STATIONS

OUTDOORS

UNLOADINGSTATIONS

PHOSPHORICACD

STORAGETANK

Safeguards: (1) Periodic maintenance of valve В

Actions: (1) Consider adding an alarm/shutdown of the system forlow phosphoric acid flow to the reactor

(2) Ensure that periodic maintenance and inspection forvalve В are adequate

(3) Consider using a closed tank for DAP storage

This process is repeated with other combinations of guide words and processparameters for each section of the design. Every process section is evaluated, andthe relevant information is recorded in a HAZOP study table. The resultingHAZOP study table, showing only a few selected sections and deviations, is presentedin Tkble 6.18.

References

1. Hazard and Operability Studies, Process Safety Report 2, Imperial ChemicalIndustries Limited, London, 1974.

2. A Guide to Hazard and Operability Studies, Chemical Industries Association,Alembic House, London, 1977.

3. R. E. Knowlton, Hazard and Operability Studies, The Guide Word Approach,Chemetics International Company, Vancouver, British Columbia, 1981.


5. "Use of Hazard and Operability Studies in Process Analysis," AIChE TodaySeries, American Institute of Chemical Engineers, New York, 1985.

6. L. Theodore et al., Accident and Emergency Management, (ISBN 0-471-61911-6),John Wiley & Sons, Inc., New York, 1989.

7. W. E. Bridges et al., "Integrating Human Reliability Analysis with ProcessHazard Evaluations," International Conference on Hazard Identification andRisk Analysis, Human Factors and Human Reliability in Process Safety, Centerfor Chemical Process Safety, Orlando, FL, January, 1992.

8. K. A. Ford and W. H. Brown, "Innovative Applications of the HAZOPTfechnique," presented at the AIChE Spring National Meeting, Orlando, March1990.

9. Technical Specifications for Performing a HAZOP Analysis, JBF Associates, Inc.,Knoxville, TN, 1990.

Tkble 6.18 Sample Pages from the HAZOP Analysis Tkble for the DAP Process Example

Team: HAZOP Tfeam #3Meeting Date: 6/27/81

ItemNo. Deviation

Drawing Number 70-OBP-57100Revision Number. 3

Causes Consequences Safeguards Actions

1.0 Vessel - Ammonia solution storage tank. Safely contain ammonia feed at ambient temperature and pressure (dwg:Figure 6.6)

1.1 High level Unloadingammonia from theunloading stationwithout adequatespace in theammonia storagetank

Ammonia storagetank level indicatorfails low

Potential release ofammonia to theatmosphere

Level indicator onthe storage tank

Ammonia storagetank relief valve tothe atmosphere

Review ammoniaunloadingprocedures toensure adequatespace in the storagetank beforeunloading

Consider sendingthe relief valvedischarge to ascrubber

Consider adding anindependent highlevel alarm for theammonia storagetank

Team: HAZOP Team #3Meeting Date: 6/27/81

ItemNo. Deviation

Drawing Number 70-OBP-57100Revision Number 3

Causes Consequences Safeguards Action

2.0 Line - Ammonia feed line to the DAP reactor. Deliver ammonia to reactor at у gpm and z psig(dwg: Figure 6.6)

2.1 High flow Ammonia feed linecontrol valve Afails open

Flow indicator failslow

Operator setsammonia flow ratetoo high

Unreactedammonia carryoverto the DAPstorage tank andrelease to the workarea

Periodicmaintenance ofvalve A

Ammonia detectorand alarm

Consider adding analarm/shutdown ofthe system for highammonia flow tothe reactor

Ensure periodicmaintenance andinspection forvalve A is adequate

Ensure adequateventilation exists forenclosed work areaand/or considerusing an enclosedDAP storage tank

Table 6.18 (cont'd)

Team: HAZOP Tbam #3Meeting Date: 6/27/81

ItemNo.

2.9

Deviation

Leak


Causes

Corrosion

Erosion

External impacts

Gasket andpacking failures

Maintenanceerrors

Consequences

Small continuousleak of ammonia tothe enclosed workarea

Safeguards

Periodicmaintenance of line

Periodic inspectiontours by operator inthe DAP processarea

Action

Ensure adequateventilation exists forenclosed work area


ItemNa Deviation

Drawing Number. 70-OBP-57100Revision Number: 3

Causes Consequences Safeguards Actions

3.0 Vessel - Phosphoric acid solution storage tank. Safely contain acid feed at ambient temperature and pressure(dwg: Figure 6.6)

3.7 Lowconcentrationof phosphoric

acid

Low phosphoricacid concentrationsupplied by thevendor

Error in chargingphosphoric acid tothe supply tank

Unreactedammonia in thereactor carriedover to the DAPstorage tank andreleased to theenclosed work area

Acid unloading andtransfer procedure


Ensure existence ofadequate materialhandling andreceivingprocedures andlabeling

Consider verifyingthe phosphoric addconcentration in thestorage tank beforeoperation


Table 6Л 8 (cont'd)


ItemNo. Deviation

Drawing Number: 70-OBP-57100Revision Number: 3

Games Consequences Safeguard* Action*

4.0 Line - Phosphoric acid feed line to the DAP reactor. Deliver acid feed to reactor at a rate of x gpm and у psig(dwg: Figure 6.6)

4.2 Low/noflow*

No feed materialin the phosphoricacid storage tank

Flow indicator failshigh

Operator setsphosphoric acidflow rate too low

Phosphoric acidfeed line controlvalve В fails closed

Plugging of line

Leak or rupture ofline


Periodicmaintenance ofvalve В


Consider adding analarm/shutdown ofthe system for lowphosphoric acidflow to the reactor

Ensure periodicmaintenance andinspection for valveВ is adequate


"These deviations were discussed separately but were combined in this table.

learn: HAZOP Team #3Meeting Date: 6/27/81

ItemNo.

5.10

Deviation

Drawing Number 70-OBP-57100Revision Number: 3

Causes Consequences Safeguard» Action*

5.0 Vessel - DAP reactor. Contain the reaction at x °C and у psig (dwg: Figure 6.6)

Loss ofagitation

Agitator motorfoils

Agitatormechanical linkagefoils

Operator fails toactivate theagitator



Consider adding analarm/shutdown ofthe system for lossof agitation in thereactor


Table 6Л 8 (cont'd)


ItemNo. Deviation


Causes Consequences Safeguards Action

6.0 Line - DAP reactor outlet line to the DAP storage tank. Deliver product flow at у gpm and x prig(dwg: Figure 6.6)

6.3 Reverse/mis-directed flow

No credible causes No significanteffects

7.0 Vessel - DAP storage tank. Store DAP product at ambient temperature and pressure (dwg: Figure 6.6)

7.1 High level Excess flow fromthe reactor

No flow to theloading stations

Operabilityproblems causedby overfilling theDAP storage tankto the enclosedarea (DAP doesnot pose an acutehazard topersonnel)

Operatorobservation of theDAP storage tanklevel

Consider adding ahigh level alarm forthe DAP storagetank

Consider providinga dike around thestorage tank

Next Page

Documents

References - ftp.feq.ufu.brftp.feq.ufu.br/Luis_Claudio/Books/E-Books/Safety/GUIDELINES_Hazar… · the HE team leader assembles a qualified team, determines the physical and analytical