designing a safer process plants

7/29/2019 Designing a Safer Process Plants

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Many individuals and organi-zations have made impor-tant contributions to the cre-ation of inherently safer (IS)

products, processes and process plants[1–3]. A brief survey of successful casehistories shows that most reportedapplications relied on only a few of the core IS principles. This paper em-

phasizes the opportunities presentedby three particular — and often-over-looked — possibilities for inherentlysafer processes.

The methods proposed here ensureintegration of IS methods beginning with process conception and continu-ing through process plant engineering design. Particular emphasis is givento matching the IS principles with thestate of the project. For example, sub-stitution is best applied during prod-uct and process research, while limita-

tion of effects is most effective during plot plan layout and equipment ar-rangement.

The chemical process industries(CPI) face the challenge of working with processes and products thatpresent many hazards, such asthe following:•Themanufactureoffuelsuses and

produces products that burn withsignificant energy release

•Certain basic chemicals, such asmineral acids and halogens are toxicand/or corrosive

•Many manufacturing processes ei-ther release or require significant

energy transfer to achieve chemicaltransformation

•Somemanufacturingprocessespro-duce benign products but requirehazardous chemical intermediatesin their manufacture

For these reasons, rigorous processand product safety practices must beused throughout the lifecycle of pro-

cess plants and must be applied totheir associated raw materials andproducts. In recent years, this hasled to major efforts in green chemis-try and engineering to develop prod-ucts, manufacturing processes, andplants that are safer for both peopleand the environment.

Before green chemistry and engi-neering achieved prominence, therewere pioneering insights in the de-sign of safer process plants. Early ap-proaches to safer processes often em-

ployed additional instrumentation andprocedures. These measures were oftenhelpful and necessary, but instrumen-tation and operators can fail, especiallywhen faced with complexity.

Trevor Kletz [1] recognized that“What you don’t have can’t leak”, whenhe first proposed the concept of theinherently safer chemical processesin 1977. His approach placed an em-phasis on the inherent nature of theprocess. Since then, important relatedconcepts such as product design forsafety and safer products, process andplant lifecycles have also advanced.

Creation of IS processes has been the

objectives of a number of creative individuals and organizations since Kletz’spath finding proposal, with many no-table successes.

Complete coverage of the entire prod-uct/process/plant lifecycle is needed toassure optimum health, safety and en-

vironmental performance of a chemi-

cal enterprise.This article focuses on how to en-

sure maximum incorporation of ISprocesses into the creation of a pro-cess plant by beginning at the productand process research stages and con-cluding with the detailed design. Noeffort is made to address the applica-tion of inherently safer principles be-yond plant design, although these arealso important.

Layers of protectionThe classical onion diagram (Figure1) illustrates the safety layers thattechnical professionals throughout

Feature Report

44 ChemiCal engineering www.Che.Com april 2011

Engineering Practice

Victor H. Edwards, P.E., Aker Solutions

1. Process design

3. Critical alarms, operator supervisionand manual intervention

4. Automatic action safety-instrumentedsystems (SIS) or ESD

5. Physical protection (relief devices)

6. Physical protection (dikes)

7. Plant emergency response

8. Community emergency response

2. Basic controls, process alarms andoperator supervision

12

3

4

5

6

7

8

Designing

SaferProcess Plants

Several often-overlooked strategies

to increase inherent safety are discussed here

FIGURE 1. Shown here are sometypical layers o protection that can beemployed in a modern process plant [ 4].At the core is an inherently sae processdesign. Moving outward rom the core,

the proposed options move through thespectrum rom inherent to passive toactive to procedural or administrativecontrols, which are considered to beprogressively less reliable



the CPI use to prevent process plantincidents. This diagram helps to ex-plain the following four basic processrisk-management strategies: Inher-ent, passive, active, and procedural oradministrative Inherent safety is at the core of theonion — the process design. A processthat cannot have a major fire, explo-sion or toxic release is inherently saferthan one that could if one or more lay-ers of protection were to fail. Passive safety layers represent the

addition of such safety features as a dike or a blast wall. Because passivelayers of protection require no activeintervention by a human or by a ma-chine, they are deemed more reliablethan active layers of protection orprocedural layers of protection. None-theless, the ability to make an explo-sion impossible — when possible — isclearly better than trying to mitigatethe effects of a potential explosion byadding a blast wall. Active layers of protection repre-

sent such features as the basic processcontrol system, a safety-instrumentedsystem, and mechanical interlocks. Procedural or administrativesafety layers are generally consideredto be the least reliable and include op-erating procedures and operator inter-

vention. Depending on the site-specifichazard, procedural or administrativecontrols may be entirely appropriate.

In general, the preferred ranking of methods to control process risks isshown below:

Inherent > passive > active > proce-dural or administrative

Basic conceptsInherently safer process concepts aresummarized below [1]:•Substitution•Minimizationorintensification•Moderationorattenuation•Simplification•Limitationof(hazardous)effects•Avoidingknock-oneffects•Makingincorrectassemblyimpossible•Makestatusclear•Toleranceoferror•Easeofcontrol

• Administrative controls or proce-dures

In 2007, the Center for ChemicalProcess Safety (CCPS) of the Ameri-can Institute of Chemical Engineers(AIChE) concluded that these elevenbasic concepts could be reduced to thefollowing four principles [ 2]:• Minimize• Substitute

• Moderate• Moderate and simplify

This more concise set of principles

makes IS practices simpler to under-stand and easier to apply. The excel-lent new CCPS book (2009) goes on todistinguish between first-order andsecond-order IS:•First-order IS efforts change the

chemistry of a process•Second-order IS effortschange the

process variables As can be seen by a survey of the pro-cess safety literature, most publishedwork has applied one or more of thefirst four concepts of the eleven citedby Kletz and Amyotte [1] For thisreason, this article emphasizes threeother promising concepts.

Often-overlooked IS conceptsThree underutilized IS concepts arepresented here and illustrated withexamples:

1. Hybridization or transforma-tion. One relatively new IS concept isbased on the recent innovative workby Chen [5] who reports an inherentlysafer process for the partial oxidationof cyclohexane. Partial oxidation pro-cesses often involve hazardous condi-tions, as illustrated by the Flixborough,England, tragedy in 1974 — whichkilled 28 people, destroyed a plant, ledto new process safety regulations, andinspired Trevor Kletz to propose hisinherently safer design concept. The

Flixborough plant carried out liquid-phase oxidation of large inventories of hot cyclohexane in large pressurized

vessels. When containment was lost, alarge flammable vapor cloud formed,ignited, and exploded with devastating effect(Figure2,fromMannan[6]).

The traditional cyclohexane-oxida-tion process to produce a mixture of cy-clohexanone and cyclohexanol (K/A oilor ketone/alcohol oil) was operated atlow conversion rates (typically 3–5%)to avoid formation of unwanted byprod-

ucts. The K/A oil was subsequently con- verted into adipic acid and caprolactamfor the production of nylon.

Oxidation of cyclohexane with airinstead of oxygen is common practiceto reduce risks of transition from apartial oxidation reaction to an un-controlled deflagration in bubblesor in the vapor space in the reactor.Low conversions and reactionrates led to large inventories of liquidcyclohexane.

During systematic research on the

flammability and deflagration haz-ards of cyclohexane, air and oxygenmixtures, Chen [5] discovered that theaddition of a small amount of water— which is inert and does not par-ticipate in the reaction — helped toinert the otherwise flammable vapors.Cyclohexane and water are known toform minimum-boiling azeotropes.The increase in the vapor pressure of the cyclohexane/water liquid resultsfrom the increased vapor pressure of the water. The water vapor inerts the

vapor mixture by lowering the upperflammable limit of the vapor [5].Chen’s work suggests that it will be

ChemiCal engineering www.Che.Com april 2011 45

FIGURE 2. The Flixborough tragedy ushered in a new era in process saety [6]





safe and practical to use pure oxygenfor cyclohexane oxidation. Benefits in-clude both IS operation and improvedproductivity. They also suggest that

this approach could be extended tosafer processes for partial oxidation of other liquid hydrocarbons using pureoxygen.

Chen’s approach is a first-order ISprocess innovation because it changesthe chemistry of the gas phase in agas-liquid reaction and prevents theunwanted side reaction of combustionfrom occurring in the gas phase.

Although reference [5] did not claimto have demonstrated a new IS con-cept, Chen’s work is different from the

classical definition of the Substituteprinciple because the same reactants,chemical reactions, and products areinvolved. If the name Substitute werebroadened to names such as Changein Chemistry or Hybridize, then itcould be lumped in with the many suc-cessful applications that are possiblewhen using the Substitute concept.

Chen’s innovation permits rapid cy-clohexane oxidation at lower tempera-tures and pressures, and could thusbe said to be an example of the inher-

ently safer principle Moderate. How-ever, Chen’s approach enables moremoderate conditions by narrowing theflammability limits through the addi-tion of a new component, water. It isthus an example of supplementationor hybridization.

Although not proposed by Chen [5]himself, his work suggests that theremay be many other opportunitiesfor transformation or hybridizationof other potentially hazardous reac-tions to make them inherently safer.

Although water would be high on any-one’s list as a potentially transform-ing additive, it probably will not helpmany potentially hazardous reactions.However, there are many other chemi-cals that may be inert to the reactionand thus also be capable of inerting the

vapor phase involved in an otherwisereactive liquid-vapor reaction. For in-stance, there are many examples of azeotropic mixtures in the literatureand there are many compounds thatcould prove inert to oxidation reac-tions (such as, certain halocarbons).

Applications are not limited topartial oxidation with air or oxygen;

other oxidations includechlorination and bromi-nation reactions, for ex-ample. And there may be

other examples of vapor-liquid reactions, such ashydrogenation reactions,where addition of a newchemical could improvethe safety of the process.

Addition of an ad-ditional compound to areaction mixture to min-imize hazardous reac-tions may add complexity to the puri-fication process, but it may be justifiedby the increased safety.

Chen’s [5] paper on cyclohexaneoxidation illustrates transformationor hybridization, in which the basicchemistry is maintained, but the ad-dition of another chemical componenttransforms a potentially hazardous re-action process into a much safer one. 2. Create a robust process to sta-

bilize or ensure dynamic stability.Not all process designs are inherentlystable, and if the process design is to besafe, the process engineer must ensuredynamic stability as well as ensuring

that the steady-state mass and energybalances are achieved. A number of processes exist that have narrow safe-operating limits but have been madestable by the addition of control sys-tems. Dynamic stability and controlof chemical processes has been exten-sively studied [7 ].

Designing the process to be moreinherently stable to process upsetswith and without control systems isclearly inherently safer, although thisprinciple is not addressed in most dis-

cussions of IS. The IS principle Ease of Control has usually been interpretedto mean a process with a control sys-tem that the operator can understandclearly and manage effectively.

CCPS briefly mentions the advan-tages of designing processes that areinherently more stable or robust [ 2]:

“It is inherently safer to developprocesses with wide operating limitsthat are less sensitive to variations inthe operating parameters...Sometimesthis type of process is referred to as aforgiving or robust process.”

Designing a robust process increasesinherent safety by imposing a change

in the process variables and is a formof Moderate, a second-order inherentlysafer design.

CCPS [ 2] also cites the work of LuybenandHendershot[8] that high-lights how minimization or intensifi-cation in a reaction system that is in-tended to improve process safety maylead to less robust processes with theopposite effect.

I propose here that Stabilize or En-sure Dynamic Stability be added tothe list of IS concepts to be sure thatit is not overlooked in the quest for in-herently safer processes.

Application of some of the other IS

principles can adversely affect the dy-namic stability of a process. For exam-ple, reduced liquid inventories ( Mini-

mize) in a distillation train make theprocess inherently safer from one per-spective because the smaller processinventory decreases the consequencesof loss of containment. However, thesmaller inventory also shortens theresponse time of the distillation sys-tem to process upsets, increasing therisk that the basic control system willnot be able to restore the distillation

system to the desired operating condi-tions and avoid a potentially unsafeoperating condition and/or an un-scheduled process shutdown [ 2].

Chemical reactors carrying outexothermic chemical reactions areperhaps the best known examples of processes that can be dynamicallyunstable. Harriott [9] provides the il-lustration of an irreversible first-orderchemical reaction being conducted ina continuous-flow, stirred-tank reactor(CSTR). Figure 3 shows the heat-gen-eration rate by the chemical reactionas a function of reactor temperature.Heat-generation rates are low at low

Reactor temperature

A

C

D

Qout

Qout

Qout

12

Heat removed

Qheat generated

3

BE

B t u / h

FIGURE 3. Heat-generation (Qheat generated ) and heat-removal (QOut ) rates as a unction o reactor temperatureor three dierent heat-removal designs [9]. Heat gen-eration is equal to heat removal at points A, C, D, E, andB, so steady state operation is possible. However, thereactor is not stable at point D without the addition ocontrols or a modifcation o the design



ChemiCal engineering www.Che.Com april 2011 47

temperatures, but as temperatureincreases, the reaction rate increasesrapidly because of the exponentialdependence of the reaction rate co-efficient on temperature. At higherreactor temperatures, the shrinking concentration of reactant (due to con-

version to product) reduces the reac-tion rate and partially overcomes thestill-increasing reaction-rate coeffi-cient. The heat-generation rate even-

tually reaches a constant maximum value when the reaction has reachedcomplete conversion.

Figure 3 also shows three differentstraight lines for the heat-removalrate from the reactor for three differ-ent reactor-cooling-system designs. Toachieve a steady-state energy balance,the rate of heat generation (Qheat gen-

erated) by the chemical reaction mustequal the rate of heat removal (Qout)by the reactor cooling system. Thatenergy balance occurs when the heat

generation curve intersects the heatremoval curve (where Qheat generated

= Qout). In Figure 3, the three differ-ent heat-removal-rate lines intersectthe reactor heat generation rate curveat five points. At four of these points( A, B, C, E), the steady-state energybalance solution is stable. At each of these points, if there is an increase intemperature, the rate of heat removalincreases more rapidly than the rateof heat generation by the reaction andthe reactor temperature tends to re-

turn to the desired operating point.Similarly, if the temperature dropsslightly at one of these four operating conditions, the rate of heat removaldecreases more than the rate of heatgeneration by the reactor and the tem-perature trends back up to the desiredoperating condition.

In contrast, point D in Figure 3 is aninherently unstable operating condi-tion even though the steady state rateof heat generation by the reactor equalsthe rate of heat removal by the reactorcooling system. At point D, an increasein reactor temperature increases therate of heat generation by the reactor

more than it increases the rate of heatremoval by the reactor cooling system,so the reactor temperature increasesmore instead of cooling back to the de-sired operating point.

This further increase in reactor tem-perature then leads to an even largerrate of heat generation rate by thereactor and additional heating of thereactor. Without any effective controlactions, the reactor temperature will

tend to increase to point E in Figure 3before it stabilizes.

Similarly, in Figure 3 a decrease inreactor temperature at point D couldeventually lead to the reactor temper-ature and conversion dropping back topoint C.

Clearly, of the three reactor cooling-system designs represented by thethree straight lines in Figure 3, thereactor cooling system represented byline CDE is the least desirable froma dynamic-stability perspective. Ad-

dition of an effective control systemmight be able to provide dynamic sta-bility — but at the cost of installationand maintenance of the control sys-tem and at the cost of residual risk if the control system fails.

Another example of potentialsources of process instability resultsfrom efforts to improve energy effi-ciencies in distillation trains throughheat integration. In these cases, thefeed to a column may be preheatedby the bottoms product of a second

downstream column. This may in-crease the risk of process upsets dueto increased interactions between thetwo columns.

While avoidance of add-on controlshas always been a goal of inherentlysafer design, achievement of that goalhas seldom mentioned the conceptsof Ensure dynamic stability or Stabi-lize as tools of the process engineer. Itshould be considered when consider-ing other means to assure inherentlysafer processes during process design.The process engineer should workclosely with the control systems engi-neer to address the dynamic stability

of both the uncontrolled process andthe controlled process to ensure a ro-bust process. 3. Limit hazardous effects duringconceptual and detailed engineer-

ing. David Clark published a seminalpaper [10] on the limitation of effectswhen siting and designing processplants. He reminds us that there is astrong, non-linear decrease of fire, ex-plosion, and toxic effects with separa-

tion distance. Comparatively small de-creases in separation distance have amajor effect, while larger increases inseparation offer diminishing returns.Methods,suchastheDowFireand

Explosion Index [11] and the DowChemical Exposure Index [12, 13], pro-

vide quantitative screening estimatesof the hazards from various parts of achemical process. Other indices havebeen developed and evaluated to per-form a similar objective to the Dow in-dices [1, 2, 14]. These screening tools

can identify those parts of a processwhere increased separation distancesare needed to limit potential escala-tion of an incident.

In one typical plant design, a 10%increase in separation distances forall units increases total plant invest-ment cost by only 3%. Similarly, dou-bling the separation distance for ahazardous unit representing 10% of the investment cost of the plant wouldcost only 3% more. Because of the non-linear effect of separation distance,

doubling the separation distance for ahazardous unit could reduce explosionoverpressures on the adjacent unitsby a factor of four or more.

The strong decrease in hazardouseffects with modest increases in sepa-ration distances will often more than

justify increased capital cost.Spacing also offers important ben-

efits in crane and other maintenanceaccess, ergonomic advantages anddecreased risk of incident escalation.Future plant expansions or processimprovements are also facilitated, al-though expansions that decrease spac-ing may increase hazardous effects.

Tools for InherenTly safer Process PlanT DesIgn

• Processhazardsreviews• Chemicalinteractionmatrices• DowFireandExplosionIndexand

ChemicalExposureIndex • Fire,explosionandtoxic-release

consequencemodelingandriskassessments

• Layerofprotectionanalysis• Spacingtablesforunitsandfor

processequipment

• Dynamicprocesssimulation

• Inherentsafetyanalysis

• Periodicdesignreviewsduringproductandprocessresearch,developmentanddesign

• Reviewsofplantsiting,plotplan,equipmentarrangementand3-Dcomputermodels

• Occupiedbuildingevaluationanddesign

• Areaelectricalclassification• Safetyintegritylevelassessments

andsafetyinstrumentedsystems• Humanfactorsreviews• Ergonomicsreviews• Safetycasedevelopment • Thedesignprocessitself





Applying different IS principles As discussed, the different IS prin-ciples are best applied at differentstages of the process plant timeline.

Although IS checklists are often usedat the screening process hazards anal-ysis (PHA) level, much more is neededthroughout the development and de-sign of a process plant.

For example, Substitute is bestdone during the product and processresearch phases before significantinvestments of time and resources ina particular product and process aremade. Hybridize or Transform is bestdone during process research and de-

velopment, as is Moderate.

Minimize, Simplify, and Error tol- erance have the best result when ap-plied during the process development,conceptual design and detail designphases. Stabilize or Ensure Dynamic

Stability is also best done during de-sign development.

Limitation of effects, which is closelyrelated to passive protection, has itsgreatest impact during developmentof the plot plan and equipment ar-rangement.

IS processes and plants As mentioned previously, the CCPS [2]defines two levels of inherent safety:• First-order inherent safety results

from changes in the chemistry of aprocess that reduces the hazardsof the chemicals used or produced.

Substitute or Hybridize efforts lead

to first-order inherent safety• Second-order inherent safety results

from changes in the process vari-ables. Examples include Minimize,

Simplify and Stabilize the opera-tions.

It is also helpful to distinguish be-tween IS processes and IS plants.Even when hazards cannot beeliminated from the chemistry of the process, the plant using the po-tentially hazardous process can bemade inherently safer through ju-

dicious design.Note also that even with IS process

chemistry, it is essential to employIS principles during the process andplant design to ensure an IS plant.

Tools for IS plant designThere are a number of tools availableto aid in designing process plants thatare inherently safer (Box, p. 18). Al-though inherently safer reviews are a

valuable tool for identifying opportu-nities for improvement, it is important

to keep the principles of inherentlysafer in mind throughout the designprocess. n

Edited by Suzanne Shelley

AcknowledgmentsI gratefully acknowledge the process safety in-sights from my colleagues at Aker Solutions andat the leading operating companies whose facili-ties we have helped to design, from ProfessorsSamMannan,TrevorKletz,RonDarby,Harry

WestandtheMaryKayO’ConnorProcessSafetyCenter atTexas A & MUniversity, and frommany others in the community of process safetyprofessionals. The financial support of Aker So-lutions is also appreciated.

Author Victor H. Edwards, P.E., is director of process safetyfor Aker Solutions Ameri-cas Inc., (3010 BriarparkDrive, Houston, TX 77042;Phone: 713-270-2817;Fax: 713-270-3195; Émail:

[email protected]). In his 28 years with

Aker, Edwards’ experienceincludes process engineering,safety management and pro-

cess, biochemical and environmental technolo-gies. He has received numerous accolades in theareas of safety and environmental engineering,including five DuPont awards, and has contrib-uted extensively to the engineering literature.His earlier experience includes assistant pro-fessor of chemicalengineering atCornellUni- versity, an assignment at the National ScienceFoundation,pharmaceuticalresearchatMerck,alternate energy research at United EnergyResources,visitingprofessoratRiceUniversityand process engineering at Fluor Corp. EdwardsearnedhisB.A.Ch.EfromRiceUniversityandhisPh.D.inchemicalengineeringfromtheUni-

versity of California at Berkeley. A registeredprofessional engineer in Texas, he is an AIChEFellow, and a member of ACS, AAAS, NFPA,NSPE, and the N.Y. Academy of Sciences.

References1. Kletz, Trevor A., and Amyotte, Paul, “Process

Plants – a Handbook of Inherently Safer De-sign,” 2nd Ed., Taylor and Francis, Philadel-phia, PA, 2010.

2. Center for Chemical Process Safety (CCPS),“Inherently Safer Chemical Processes – A LifeCycleApproach,”2ndEd.,AIChE,New

York, NY, 2009.3. Hendershot, Dennis C., An overview of inher-

ently safer design, Process Safety Progress, Vol. 25, No. 2, 98–107, June 2006.

4. Dowell, III,ArthurM., Layerof protectionanalysis and inherently safer processes, Pro-cess Safety Progress, Vol. 18, No. 4, 214–220,Winter 1999.

5. Chen, Jenq-Renn, An inherently safer processof cyclohexane oxidation using pure oxygen –

An example of how better process safety leadsto better productivity, Process Safety Progress, Vol.23,No.1,72–81,March2004.

6. Mannan,Sam,Ed.,“Lee’sLossPreventioninthe Process Industries,” 3rd Ed., Elsevier But-terworthHeinemann,Oxford,U.K.,2005.

7. Edgar, Thomas F., and others, Process Control,Section 8 in “Perry’s Chemical Engineers Hand-book,” 8th Edition, Don W. Green, Editor-in-Chief,McGraw-HillBook,NewYork,NY,2008.

8. Luyben, W.L., and Hendershot, D.C., “Dy-namic disadvantages of intensification in

inherently safer process design,” Industrial Engineering Chemistry Research, Vol. 43, No.2 (2004) cited in CCPS, 2009.

9. Harriott,Peter,“ProcessControl,”McGraw-Hill, New York, NY, 1964.

10. Clark, David G., Applying the ‘limitation of ef-fects’ inherently safer processing strategy whensiting and designing facilities, Process Safety

Progress, Vol. 27, No. 2, 121–130, June 2008.11. “Dow’s Fire and Explosion Index Hazard Clas-

sification Guide”, 7th Ed., American Instituteof Chemical Engineers, New York, NY, 1994.

12. “Dow’s Chemical Exposure Index Guide”, American Institute of Chemical Engineers,New York, NY, 1994.

13.Suardin, Jaffee, Mannan, M. Sam, andEl-

Halwagi,Mahmoud,TheintegrationofDow’sFire and Explosion Index (F&EI) into processdesign and optimization to achieve inherentlysafer design, Journal of Loss Prevention in the

Process Industries, Vol. 20, pp. 79–90, 2007.14. Khan, Faisal I., and Amyotte, Paul R., How

to make inherent safety practice a reality,Canadian Journal of Chemical Engineering,

Vol. 81, No. 2, 2–16, February 2003.

Additional suggested reading 1. Edwards, David, Editorial – Special Topic

Issue – Inherent safety – Are we too safe forinherent safety?, “Process Safety and Envi-ronmental Protection – Transactions of theInstitution of Chemical Engineers Part B,”

Vol. 81, No. B6, 399–400, November 2003.2. Englund,StanleyM.,Inherentlysaferplants:

Practical applications, Process Safety Prog-

ress, Vol. 14, No. 1, 63–70, January 1995.3. French, Raymond W., Williams, Donald D., andWixom, Everett D., Inherent safety, health, andenvironmental (SHE) reviews, Process Safety

Progress, Vol. 15, No. 1, 48–51, Spring 1996.

4. Gupta, J.R., and Edwards, D.W., Inherentlysafer design — Present and future, “ProcessSafety and Environmental Protection — Trans-actions of the Institution of Chemical EngineersPartB,”Vol.80,115–125,May2002.

5. Gupta,J.R.,Hendershot,D.C.,andMannan,M.S.,Therealcostofprocesssafety—Aclearcase for inherent safety, “Process Safety andEnvironmental Protection – Transactions of the Institution of Chemical Engineers PartB,” Vol. 81, No. B6, 406–413, November 2003.

6. Hendershot, Dennis C., et al., Implementing in-herently safer design in an existing plant, Process Safety Progress,Vol.25,No.1,52–57,March2006.

7. Kletz, Trevor A., Inherently safer design: Thegrowth of an idea, Process Safety Progress,

Vol. 15, No. 1, 5–8, Spring 1996.8. Lutz,WilliamK.,Takechemistryandphys-

ics into consideration in all phases of chemi-cal plant design, Process Safety Progress, Vol.14, No. 3, 153–160, July 1995.

9. Lutz,WilliamK.,Advancinginherentsafetyinto methodology, Process Safety Progress,

Vol. 16, No. 2, 86–88, Summer 1997.10.Maxwell,GaryR.Edwards,VictorH.,Robert-

son,Mark,andShah,Kamal,Assuringprocesssafety in the transfer of hydrogen cyanide man-ufacturing technology, Journal of Hazardous

Materials, Vol. 142, pp. 677–684, June 2007.11.Overton,Timand King,GeorgeM., Inher-

ently safer technology: An evolutionary ap-

proach, Process Safety Progress, Vol. 25, No.2, 116–119, June 2006.12. Study, Karen, A real-llife example of choosing an

inherently safer process option, Process Safety Progress, Vol. 25, No. 4, 274–279, December 2006.

Note: This article is based on a paper presentedattheMaryKayO’ConnorInternationalSym-posium,TexasA&MUniversity,October27-28,2009.

designing a safer process plants

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