A S H RA E J O U R N A L

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The following article was published in ASHRAE Journal, February 1998. © Copyright 1998 American Society of Heating, Refrigerating and Air-Conditioning Engineers,Inc. It is presented for educational purposes only. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE.

Applying Process Hazard AnalysisTo Laboratory HVAC Design

By John O. Varley, P.E.Member ASHRAE

he chemical and oil processing industries have operatedunder self-regulated “best practice,” including the use of

process hazard analysis (PHA) techniques, for several years.The Occupational Safety and Health Administration (OSHA)authored a federal mandate, the Process Safety Management(PSM) of Highly Hazardous Chemicals...1 (29 CFR § 1910.119)in 1992, which provides regulatory motivation for engineers toapply PHA techniques to new or revised processes. Althoughlaboratory facilities using hazardous materials are excludedfrom this law, the procedures and guidelines listed in it provideexcellent guidance for the design and operation of these facili-ties. Regardless of the nature of the hazards (chemical or biolog-ical) contained in a laboratory, the engineers and operationspersonnel responsible for laboratory design, construction andmaintenance can benefit by using PHA methods.

Several guidelines exist for the design and maintenance oflaboratory facilities. For example, regulatory requirements forlaboratories using hazardous chemicals are summarized inOccupational Exposure to Chemicals in Laboratories 2 (29CFR § 1910.1450). In addition, federal mandates exist for non-clinical and pharmaceutical laboratories3,4 (21 CFR § 58, 21CFR § 211). Finally, several industry guidelines andstandards5,6,7,8 (ASHRAE, 1995; NRC, 1981; NFPA, 1996;ANSI/AIHA,1992) are available for laboratory HVAC design.These tools offer prudent guidance for the design and opera-tion of laboratories; but none of them specify the deliberatemethods of evaluating design listed in the PSM rule. Althoughnot intended to be used as a design tool, PHA offers designersa systematic approach to engineering for safety. This articlewill review PHA requirements, offer ideas to apply them toHVAC system design and operation, and relate the benefits oftheir use.

PHA Method OverviewProcess hazard analysis is the study of a facility, process,

building, service or operation carried out to ensure that hazardsare identified, understood and properly controlled. A varietyof PHA methods are available, including:

• Hazard and Operability (HAZOP) Studies.• “What If” analysis.• Failure modes and effects analysis.• Fault tree analysis.• Event tree analysis.• Cause-consequence analysis.• Human error analysis.A more detailed overview of these approaches can be found

in the literature9 (AICHE, 1985). In this article, the HAZOPmethod is reviewed9,10 (AICHE, 1985; Larkin, 1996).

HAZOP is only part of the total hazard study of a new orrevised process. A typical hazard study consists of severalphases:

1. This phase is performed during the initial and prelimi-nary engineering stage of project development. Its purpose isto ensure that the project, the process and related processingmaterials are understood. This study will result in a cursoryunderstanding of the safety, health and environmental issuesassociated with the project. It plays an important role inenabling management to make key policy decisions and estab-lishing rapport among the project team members. Upon com-pletion of flow diagrams and general equipment layoutssignificant hazards, their possible causes and protective mea-sures to meet relevant criteria, are identified.

2. This phase is performed after detailed process and instru-mentation diagrams (P&IDs) have been generated. It isintended to identify hazards or obstacles to operability thatcould arise from deviations in the design intent. In this phasethe HAZOP method is applied.

3. The post-construction phase consists of several steps: pro-cess commissioning, review of safety, health and environmentalprotection, and documentation verification. The purpose of thecommissioning process is to verify that the building and/or pro-cess has been built to the intended design and that actions fromthe previous hazard studies have been completed. Next, safety,employee health and environmental protection on the site arereviewed for conformance with corporate and legislativerequirements. Finally, all documentation associated with the

About the Author

John O. Varley, P.E., is a consulting engineer located in BrayVillage, Ohio. He is a member of ASHRAE TC 9.10, LaboratorySystems. Varley has a Bachelor of Science in Mechanical Engi-neering from the University of Akron, Akron, Ohio, and a Mas-ter of Science in Chemical Engineering from Cleveland StateUniversity, Cleveland, Ohio.

TGuide Words Meaning

No Design intent is not achieved.

Less Result is less than the design intent.

More Result is more than the design intent.

Part of Result is qualitatively less than the design intent.

As well as Result is in addition to the design intent.

Reverse Result is the opposite of the design intent.

Other than Complete substitution for design intent.

Table 1: HAZOP guide words.

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project is reviewed andincorporated into theoperation of the facility.

Using a team-ori-ented approach that“brainstorms” potentialproblems with a design,the HAZOP methodevaluates process haz-ards and identifiespotential operabilityissues. It achieves itsresults by applyingguide words to specificpoints (or nodes) in thedesign.

The HAZOP studyrequires basic informa-tion prior to commence-ment including apreliminary process andinstrumentation diagram(P&ID), material datasafety sheets (MSDS)and preliminary operat-ing procedures. Theproject manager typi-cally drives the HAZOPprocess by assemblingthe data, establishing theschedule and identifyingthe team members.Team membershipshould include a trainedHAZOP team leader, ascribe to record theresults of the study, rele-vant operating personneland the project manager.

The team meetingsbegin after the processor facility has beendivided into its discretenodes. Under the tute-lage of the study leader, the team identi-fies the design intent of each node andthen applies guide words (Table 1) toreview the process.

The use of guide words prompts dis-covery of deviations from the designintent. The team then discusses the con-sequences and causes, suggests recom-mendations and records results. Theresults are recorded. An example of thisprocess is discussed later in this article.

Applying HAZOPRegardless of the nature of work

housed in a laboratory (industrial, aca-demic or institutional), it will contain the

same materials as a hazardous chemicalor biochemical process facility, but insmaller and more varied quantities.Therefore, the hazards within the labora-tory facility can be as severe as a processfacility, as seen in recent catastrophicaccidents11,12,13 (Dowdy, 1995; Lhotka,1995; Reed, 1996). Further, the HVACsystem associated with the laboratory isa primary means of hazard mitigation.This suggests that application of theHAZOP method is a logical extension ofthe design process. Although a literaturesearch uncovered discussion of riskassessment14 (West, 1978) for laborato-ries, no work was found on the applica-

tion of process hazard analysis methodsto laboratory design.

Prior to the HAZOP session, thedesign team will have gathered the fol-lowing information:

• The airflow and instrumentation di-agram (AF&ID). This drawing is similarto the P&ID described earlier and pro-vides the basis for the structure of theHAZOP (Figure 1).

• Relevant material data safety sheets(MSDS).

• Preliminary equipment list.• Sequence of operations for the con-

trol system.

L A B O RA T O R Y

DA

LAB MODULE

OUTSIDE AIR

AIR HANDLING UNIT

M

DA

OA

TE

MA

PT

SP

EXHAUST FAN

HWSHWR

FTEA

T

GEADA

DAEOAEA

FTFV

DA

SA

Legend:

XX

YY InstrumentUse

T Temperature sensorEOA Exhaust outside airEA Exhaust airFT Flow transmitterFV Face velocity

DA Damper actuatorGEA General exhaust airTE Temperature elementMA Makeup airPT Pressure transmitterSA Supply airSP Static pressure

ControlVolume ofNode

LAB MODULE

OUTSIDE AIR

AIR HANDLING UNIT

M

DA

OA

TE

MA

PTSP

EXHAUST FAN

HWSHWR

FT

EA

T

GEA

DA

DA

EOA

DA

EA

FT

FV

DA

SA

NODE 3

NODE 6-EXHAUST MANIFOLD

NODE 1

NODE 5

NODE 2

NODE 4

Figure 1: Sample AF&ID.

Figure 2: Breakdown of AF&ID into nodes.

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The project manager (owner’s repre-sentative) will then assemble the studyteam. The team members should consistof the following:

• The hazard study team leader.• Scribe.• The local safety and health manager.• Commissioning manager.• Facilities representative.• The affected lab users.• The engineer.• The project manager.The meeting membership (with the

exception of the hazard study leader andscribe) should be composed of individu-als who have working knowledge of theproposed system. For example, the por-tion of the study involving mechanicalspace should involve facilities person-nel. On the other hand, the study of oper-ations within the lab module shouldinvolve lab personnel. Typically, execu-tive management is excluded from haz-ard study meetings.

Prior to the meeting, the project man-ager and engineer will reduce the airflowand instrumentation diagram into itsnodes (Figure 2). This will allow theteam to focus on discrete parts of theprocess to simplify the discussion.

The study team participants shouldallow ample time to complete the study.Although time requirements vary accord-ing to the complexity of the drawings, atypical rule-of- thumb is to allow thirtyminutes per node. Common nodes canreceive a cursory study, thereby eliminat-ing some labor. In addition, the deliberatequality of the study will require manybreaks in the meeting. To maintain a high

caliber of discussion, the meetings shouldnot extend to a point where team mem-bers can no longer concentrate. Four hourmeetings seem to provide optimal results.This discussion suggests that the effortassociated with a rigorous HAZOPshould not be underestimated. As a result,the study team leadership must receivethe support of executive management.This will provide positive reinforcementto the team membership to contribute therequisite time for this endeavor.

The effort of documenting the studycan be significantly reduced by usingsoftware readily available on the market.Other meeting tools, such as an over-head projector, can also improve discus-sion and productivity.

With team and tools assembled at themeeting place, the actual process ofHAZOP begins. Following the HAZOPguide word method, each node is evalu-ated for possible deviations to the designintent. The study depicted in Table 2involves the design of a manifolded VAVexhaust system. The node illustrated here(Node 1 of Figure 2) includes a fumehood, fume hood sensor, controller andexhaust valve. The design intent, as deter-mined by the team, is to provide a hood toenclose weigh-up and mixing operations,and solvent cleaning of lab apparatus.

The study leader must ensure that allnodes are identified and discussed duringthe session. The project manager is respon-sible for responding to all recommenda-tions (sometimes referred to as findings).

Although the HAZOP method is ide-ally suited for evaluation of AF&IDs, itcan also be used to review building con-

struction practices. In addition, the otheraforementioned PHA techniques mayoffer expedient and effective approachesto the analysis of the process and building.

Conclusion Process Hazard Analysis enhances the

opportunity to create inherently safedesigns by identifying alternatives to pro-cessing, raw materials used in processing,construction materials and procedures. Inaddition, PHA forces the design team torigorously analyze their design assump-tions and clearly document the intent oftheir design. Although design improve-ments generated by PHA significantlylower the hazards of the process, the iden-tification of procedural and educationalrequirements for the design may provideeven greater benefits. As seen in the ear-lier example, these needs are identifiedand resolved. Thus, the PHA process cansignificantly reduce the hazards createdby human error.

By using a multi-discipline team, thesestudies tend to identify design improve-ments. Although HAZOP requires anexpenditure of time and money, it canresult in even greater savings in first costsand operating costs by improving the sys-tem design. As a result, processes thathave been evaluated using PHA are inher-ently more value-driven than thosedesigns that ignore the technique. Further,PHA reduces costly additions to a projectduring construction by enhancing com-munication among team members duringconceptual and preliminary engineering.

Finally, the process expedites thecommissioning and turn-over phase of aproject. Operating personnel involved

Guide Word Deviation Causes Consequences Recommendations

No No Flow VAV Valve failure, block-age, power failure

Chemical exposure 1. Evaluate failure modes of VAV valve.

Less Less Flow Same as no. Hoods all open at the same time.

Chemical exposure 2. Establish procedure for low flow situation.

Reverse Reverse flow Fan Failure Chemical exposure 3. Establish procedure for this failure.4. Evaluate failure mode of damper.5. Minimize leakage areas in duct.6. Explore possibility of installing LEL detectors.7. Investigate whether explosion venting for the duct

should be installed.

Late Late valve action Slow controller response Same as no 8. Establish procedure to verify hood performance prior to use.

9. Establish appropriate controller response time.

As well as Spill in hood as well as normal hazards

Spill Chemical exposure, fire and explosion hazard

10. Establish procedure for clean-up.12. Investigate installing emergency devices in hood and

room.13. Establish emergency response procedure for incident in

hood or outside of hood.

Table 2: HAZOP example.

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with the study receive early training rel-ative to the design. This results in ahigher degree of involvement by theusers of the design and ultimately greater“buy-in.” In addition, the HAZOP pro-vides complete documentation of thedesign intent of the process, therebyfacilitating the commissioning of controlloops and other operations.References

1. American Institute of Chemical Engi-neers, Guidelines for Hazard Evaluation Pro-cedures, New York, NY, 1985.

2. ANSI/AIHA, Standard Z 9.5-92, Labo-ratory Ventilation, American IndustrialHygiene Association, Fairfax, VA, 1992.

3. ASHRAE, Laboratory Systems, Chap-ter 13, Applications Handbook, 1995.

4. Code of Federal Regulations, “CurrentGood Manufacturing Practice for FinishedPharmaceuticals,” 21 CFR § 211.

5. Code of Federal Regulations, “GoodLaboratory Practice for Non-clinical Labora-tory Studies,” 21 CFR § 58.

6. Code of Federal Regulations, “Occupa-tional Exposure to Chemicals in Laborato-ries,” 29 CFR §1910.1450.

7. Code of Federal Regulations, “ProcessSafety Management of Highly HazardousChemicals,” 29 CFR § 1910.119.

8. Dowdy, Zachary R., “Chemical Explo-sion Burns Two Lab Technicians,” BostonGlobe, p. 24, col 3, Aug. 30, 1995.

9. Larkin, Felim, “HAZOP Study fromTheory to Practice,” Process Engineering,vol 27, p. 26-7, March 1996.

10. Lhotka, William C., “Technician Suc-cumbs to Blast Injuries,” St. Louis-Dispatch,Sec. D, p. 12, col. 1, Sep. 17, 1995.

11. National Research Council, PrudentPractices for Handling Hazardous Chemi-cals in Laboratories, National AcademyPress, Washington, D.C., 1981.

12. NFPA, Standard 45, Fire Protection forLaboratories Using Chemicals, National FireProtection Association, Quincy, MA, 1996.

13. Reed, Mack, “Firm Agrees to RecordFine in Fatal Blast,” Los Angeles Times, Sec.A, p. 3, col.5, April 9, 1996.

14. West, D., “Assessment of Risk in theResearch Laboratory: A Basis for FacilityDesign,” ASHRAE Transactions, Vol. 84,Part 1B, 1978.

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