13Conceptual Design Phase

An Illustration of the PHA Method

13.1 Problem Definition

Background

ABC Chemicals has decided to proceed further with the VCM project. TheWhat-If Analysis performed during the R&D phase did not identify anyunmanageable hazards. Follow-up of the actions suggested in this review indicatedthat ABC had or could hire people to adequately deal with the hazards identified inthe VCM process. This information, combined with an encouraging marketingoutlook, convinced ABC management that the VCM project was viable.

ABC Chemicals has chosen their Anywhere, U.S.A. chlorine plant as the sitefor the proposed VCM plant. This chlorine plant, while very similar to Mr. Safety'sand Ms. Engineer's plant, is a different site from the one that was assumed to be thenew plant location during the R&D What-If Analysis. The Anywhere, U.S.A. sitewas chosen instead of the other ABC plant sites for several reasons:

• The nearest population center is small (compared to other ABCplant sites).

• This site is relatively near an ethylene supply pipeline.

• This site has ample property to accommodate the new plant.

Additional information concerning the VCM plant is available in this projectphase, including a tentative plant layout (Figure 13.1). ABC engineers have chosento locate the VCM plant in what was "buffer" property for the chlorine plant, eastof the existing unit. This site was chosen because (1) there is enough room toseparate the plant and the administrative offices, (2) ABC already owns the property,and (3) access to an ethylene supply is convenient.

With this new information in hand, the business team has decided anotherhazard evaluation is needed. While the business team wants to know about anyadditional hazards with the process, they also want the hazard evaluation to focus onthe suggested VCM plant siting. The business team recommends that Mr. Safetyagain lead this effort since he is familiar with the project and did an excellent job in

ANYVWERE U.S.A.POP. 20,500

RAILROAD

HIGHWAY

PROPOSEDNEWFACILmES

ABCCHEMICALS

ETHYLENEFEED

SYSTEM

VCMPLANT

FARMLAND(FIELDS)

OTHERINDUSTRIES

PREVAILINGWIND ADMINISTRATIVE

OFFICES

CHLORINEPLANT

PROPERTY LINE

NOT TO SCALEECHO RIVER

Figure 13.1 VCM plant layout.

the last review. Mr. Chemist, however, convinces the business team that a new pointof view is needed; therefore, Ms. Deal from the corporate process hazards analysisgroup is selected to lead this HE study.

Available Resources

The VCM plant has not yet been designed. However, engineering has providedMs. Deal with a preliminary plant layout (Figure 13.1). Engineering and R&D havealso provided the following:

• A preliminary list of raw materials, intermediate products, and finalproducts (Tkble 13.1)

• A preliminary list of major vessels in the plant (Tkble 13.2)• R&D reports on the VCM project• Previously collected literature on EDC and VCM• What-If Analysis results from the previous hazard evaluation• A preliminary list of the systems that will interface with the

Anywhere Chlorine plant

Tkble 13.1 Partial List of Materials in the VCM Plant

• Ethylene• Chlorine• Ethylene Bichloride• Vinyl Chloride Monomer• Hydrogen Chloride

• mter• Light Hydrocarbons• Heavy Hydrocarbons• Natural Gas

Tkble 13.2 Major Equipment in the VCM Plant

Equipment

Direct ChlorinationReactor

Compressor

Storage Spheres

Storage Tknk

Distillation Column

Accumulators

Furnace

Incinerator

Number

1

1

4

1

4

a

1

1

*Not yet determined.

Chemkalfc)

Chlorine, Ethylene

Ethylene

EDC, VCM

HQ Acid

EDC, VCM, HQ, DghtHydrocarbons, HeavyHydrocarbons

EDC, VCM, наEDC, VCM

Mixture

Wume

Large (Dquid)

Medium (Gas)

Large (Liquid)

Large (Liquid)

Large (Liquid/Gas)

Medium (Liquid)

Medium (Gas)

Medium (Gas)

Ms. Deal has also requested information on the Anywhere Chlorine plant Inparticular, she has asked for emergency procedures, safety equipment, and a list ofemergency shutdown interlocks for the plant. This information will be collected byan engineer at the Anywhere plant.

Selection of Hazard Evaluation Technique

The business team has left the selection of a hazard evaluation method up toMs. Deal. They have, however, requested that the What-If Analysis technique notbe chosen unless it is the only applicable method since it has been used once before.

Ms. Deal is familiar with most of the commonly used hazard evaluationmethods. Because the process is still not well defined, she quickly rules out HAZOPAnalysis, FMEA, Event Tfree Analysis, Fault TVee Analysis, Cause-ConsequenceAnalysis, and Human Reliability Analysis. She also eliminates Checklist Analysissince she does not have a good checklist to use. What-If Analysis is a possibility, butMs. Deal does not select it because it was previously used. Thus, the choice isnarrowed to Relative Ranking and PHA. At this point, the selection is a difficultjudgment call. Either method could be used; however, the PHA is better adapted toidentifying hazards than is the Relative Ranking method, and Ms. Deal is morefamiliar with PHA, so she chooses it.

Study Preparation

Ms. Deal has selected two additional employees of ABC to assist with the PHA.Mr. Dennis is a process hazard analyst with ABC who works in the corporateengineering division. He is chosen by Ms. Deal because he has some VCM andethylene experience with a previous employer. (Mr. Dennis was hired by ABC thispast year, in part because of the VCM project.) Mr. Dennis and Ms. Deal are in thesame working group within ABC Chemicals.

Mr. Scott, an experienced process engineer from the Anywhere Chlorine plant,is the other team member. Mr. Scott has worked in most of the units in the chlorineplant and is very familiar with the personnel; the operating, safety, and emergencypractices; and the layout of the Anywhere plant facility.

A business team member will not participate in the PHA. Tb ensure that thebusiness team's concerns are understood and that the PHA satisfies their objectives,Ms. Deal meets with Mr. Chemist to discuss these issues and to explain what thePHA will accomplish.

In preparation for the PHA, Ms. Deal sends a memo to Mr. Dennis and Mr.Scott announcing the PHA. Information in the memo includes: (1) the date, time(estimated to be one day), and location for the PHA, (2) a description of the PHAobjectives, and (3) copies of previous HE studies, R&D reports, and preliminaryengineering studies for PHA team members to review. A one-day meeting isscheduled at the Anywhere site for the PHA. (The Anywhere site is chosen becausethe business team is particularly concerned about siting issues, and neither Ms. Dealnor Mr. Dennis has seen the Anywhere plant)

Before the PHA meeting Ms. Deal will spend about a day reviewing theinformation on the VCM project. Based on this review she will formulate somequestions (Able 13.3) to ask during the PHA. She will also prepare some blankPHA forms to use in the team meeting.

ТЬЫе 133 Preliminary Questions for the Conceptual Design PHA

• How close is the nearest public neighbor to the Anywhere plant?The nearest industrial neighbor?

• What is due east of the plant? Due west? Due north? Due south?

• What emergency actions do you take in the event of a large chlorinerelease?

• Can the Echo River flooding threaten the plant site?

• What does the wind rose show for this location?

• What kinds of fire protection are available on-site? Off-site?

13.2 Analysis Description

The PHA study will involve the following tasks:

• A short tour of the Anywhere Chlorine plant and the proposedVCM site

• The PHA team meetings on the proposed VCM plant

• The review of the PHA results

Often, a tour of the area is not included in a PHA. However, since both Ms.Deal and Mr. Dennis are unfamiliar with the plant, a short tour (e.g., one-hour) isin order. During this tour (led by Mr. Scott), the team takes note of equipment andpersonnel locations at the existing chlorine plant and their proposed locations for theVCM plant. They also focus on what emergency equipment is available (e.g., gasalarms, fire monitors, hydrants) and where the equipment is located.

After the tour, the PHA team convenes in a plant conference room to beginthe analysis. Ms. Deal tells the others that the PHA will take the rest of the day,that breaks will be taken as needed, and that refreshments and lunch will be broughtin. Then, she briefly describes the PHA technique to the others, shows them thePHA table to be filled in during the review, explains the hazard category definitions,and reminds the team to think about secondary equipment damage and systeminteractions that may result from causes of hazardous situations (e.g., a crane bumpsinto a line and ruptures it, releasing a chemical that eventually explodes and rupturesa chemical storage tank). Ms. Deal also explains that to keep the PHA orderly shewill suggest a hazard and then move through the process from the front end to theback end, looking for causes, effects, and suggestions for improvements. Finally, Ms.Deal gives a brief overview of the VCM manufacturing process and then begins theanalysis.

The following is a brief excerpt from the PHA review.

Ms. Deal — Let's start with a toxic release as a hazard. Beginning withthe ethylene feed into the plant, what are some possiblecauses?

Mr. Dennis — Well, ethylene really isn't a toxic. It's much more anasphyxiant and a flammable hazard.

Ms. Deal — Okay. Let's consider some other toxics and come back tothose hazards later. What about the chlorine line to theVCM plant?

Mr. Scott — As I understand it, liquid chlorine will be piped to theVCM plant. [R&D determined that the chlorination reactionyield was higher using liquid chlorine.} A flange or gasketleak would release chlorine, but probably only smallamounts. A pipe rupture, say it's due to a crane accident,would release a lot of chlorine. Thermal expansion in ablocked-in line could also blow a gasket or valve packing,or cause the line to rupture.

Mr. Dennis — Perhaps we should suggest burying the line. That wouldremedy the crane problem.

Ms. Deal — Wait, guys. Let's get back on track. Before suggestingchanges, let's get an idea of how bad this situation wouldbe and what protective measures are provided.

Mr. Scott — Okay. Depending on wind direction, you could exposeseveral operators or the administrative building personnelto high chlorine concentrations. However, the likelysafeguards we would have in place include (1) fieldpersonnel equipped with respirators and self-containedbreathing apparatus (SCBAs) nearby, (2) safe havens inthe unit, (3) all welded and x-rayed piping, (4) expansionchambers on the piping, (5) chlorine gas detectors andalarms in the area, and (6) plant personnel trained torespond to a chlorine release. Should I go on?

Ms. Deal — What about public exposure?

Mr. Scott — The nearest residence is a mile-and-a-half due east. Ouremergency plans address this issue.

Ms. Deal — Do you see any special precautions we should take withthe chlorine feed line?

Mr. Scott — We need to make sure the line is empty if the VCM plantis down for any length of time.

Mr. Dennis — What about a line break? How will you isolate it?

Mr. Scott — We need positive shutoff valves, perhaps with some kindof interlock to trip when a line rupture occurs. By theway, the VCM plant people will also have to learn ouremergency procedures for chlorine releases and havepersonal protective equipment. Also, if the VCM plantsuddenly shuts down, we will need to make sure thechlorine plant can handle this shock.

Mr. Dennis

Mr. Scott

Ms. Deal

Mr. Scott

Mr. Dennis

Ms. Deal

Mr. Scott

Ms. Deal

Mr. Scott

Ms. Deal

Mr. Scott

Ms. Deal

Mr. Scott

Ms. Deal

Mr. Dennis

— What about burying the chlorine feed line?

— No, that's not a good idea. Little chlorine leaks tend tobecome big ones in a short time. We would rather be ableto see the pipe at all times and catch little leaks early.

— I've noted these things in the PHA table. Using thecategories I showed you at the start of this review, howwould you categorize a line leak and line rupture?

— Well, small chlorine leaks aren't uncommon and we haveno trouble with them. I'd say a leak is a category one. Arupture is pretty serious. I'd call it a four.

— I think that sounds reasonable.

— Okay, let's move on if there are no more ideas. [Pause.]The next major equipment item is the direct chlorinationreactor.

— Let me understand this thing. Liquid ethylene andchlorine are mixed together in this reactor to makeethylene dichloride. And the reaction is exothermic.

— That's right.

— Can it blow up?

— I don't know. I'm sure engineering will design a pressurerelief system for the worst credible case. Anyway, weshould assume it could, but we should also consult withthem concerning an appropriate design.

— How much chlorine does the reactor have in it? And atwhat temperature?

— The project is not far enough along to answer thosequestions. However, I believe it could be more than 10tons. Don't know about the temperature at all.

— If that reactor goes, you might expose Anywhere to a highconcentration of chlorine. About 15 years ago ABCmoved our storage tanks and rail yard to the west side ofPlant Road because they worried about a big chlorinerelease. This is definitely one of your category fourhazards. I think some study the environmental group didprompted this action. Anyway, it looks like thischlorination reactor may be in the same boat.

— What about safeguards?

— We don't know what the reactor will have yet. I'm surewe will put in appropriate interlocks to prevent a runaway.However, if a runaway isn't stopped, there will be a large

Mr. Scott

Ms. Deal

Mr. Dennis

Mr. Scott

Ms. Deal

chlorine and ethylene release. What about chlorine gasdetectors?

— The detectors are at select locations inside the chlorineplant. If the wind blows towards town, the detectors won'tsee the chlorine. If the rupture disk on the reactor burstor a relief valve lifted, we would probably hear it.

— So, do you suggest we move the VCM plant west of PlantRoad?

— I think we should have the environmental group model alarge chlorine release from the reactor and see what theoutcome is. If the public exposure is unacceptable, then Iagree we should move the plant west.

— I think we should just move the plant. The liquid chlorinepiping is already there, so there is no new risk from apipe rupture. The added distance helps protect the town.And our industrial neighbors to the west are betterprepared to respond to a gas release.

— If we move the plant west we will probably have to buymore land. I will note both of your points and leave it tothe business team to decide. Let's move on to the EDCstorage spheres. Can they contribute to a toxic release?

The discussions continue in this fashion until the team has reviewed all themajor equipment items for causes of toxic releases. Ms. Deal then redirects the PHAteam back to the beginning of the VCM process and focuses on causes of flammablereleases. The process is reviewed from front to back. The PHA team cycles throughthe VCM plant several times, each time looking for causes of new hazards (e.g.,decompositions, runaway reactions, cryogenic effects) and recommendations thataddress these hazards. (Note that other analysts might choose to identify all thehazards in one section of the plant and then move on to other plant sections tocomplete the PHA.)

At the end of the PHA review, Ms. Deal states that she will edit the PHAresults (tables) and send them to the team members for review in two weeks. Afterreceiving their comments she will send a report to the business team.

133 Discussion of Results

Tkble 13.4 lists an example of the PHA results. The table contains the hazardsconsidered, causes of these hazards, and suggestions for corrective actions andpreventive measures that ABC should consider. As with the earlier What- If Analysis,the PHA considered, but did not record, existing safeguards when evaluating hazards.Follow-up assignments for suggested corrective actions were not made either becausethe team did not have the authority or know the appropriate personnel to assign.Ms. Deal left this activity up to the business team.

TkWel3.4 Sample PHA Results for the VCM Plant Conceptual Design

Area: VCM Plant — Conceptual Design Page 1 of 27Drawing: Figure 13.1Meeting Date: 2/7/86Tfeam: Ms. Deal (Leader —ABC Process Hazards), Mr. Dennis (ABC Process Hazards), and Mr. Scott (ABC Anywhere Plant)

Corrective Action/ 1Preventive Measure

HazardOUegotf'Major Effect»CauseHazard

1. None

2a. Verify chlorine line isevacuated whenever theVCM plant is down forextended time

2b. Provide valves andinterlocks to positivelyisolate the line in the eventof a rupture

2c. Ttein VCM plant personnelto respond to chlorinereleases

2d. Equip VCM plantpersonnel with PPE forchlorine

2e. Do not bury chlorinepipeline

I

IV

1. Small chlorine releaseon-site

2. Large chlorine release,major on-site impact.Potential off-site impacts

1. Chlorine linegasket/packing leak

2. Chlorine line rupture (i.e.,vehicle accident, blocked-in line)

Tbric Release

За. Consider moving VCMplant west of Plant Road

3b. Perform dispersion studiesto assess off-site impact ofchlorine/EDC release dueto exotherm

3c. Verify reactor pressurerelief system can handle thisrelease

4. Minimize inventory ofchlorine/EDC in reactor

5. Verify the reactor pressurerelief system incinerator andscrubber are sized to handlethis release

6. Consider moving EDCsphere away from river

7a. Consider moving EDCsphere away from river

7b. Verify EDC (and othertanks) support structuredesigned to withstand floodconditions

IV

IV

Ш

IV

IV

3. Large chlorine/EDC/ethylene release.Depending on reactorsize/operating conditions,potential off-site impacts

4. Large chlorine/EDC/ethylene release.Depending on reactorsize/operating conditions,potential off-site impacts

5. Potential largeEDC/chlorine/ethylenerelease

6. Large release of EDC,potential off-site impact.Potential rivercontamination

7. Large release of EDC,potential off-site impact.Potential rivercontamination

3. Direct chlorinationreactor exotherm

4. Direct chlorinationreactor rupture

5. Direct chlorinationreactor relief valve lift

6. EDC storage sphererupture

7. Flood damages EDCsphere

Tbxic Release(cont'd)

"Hazard Category: I-negligible, II-marginal, Ш-critical, IV-catastrophic.

In addition to this PHA table, Ms. Deal will prepare a brief executive summaryand list everyone who participated in the PHA, as well as what was examined, andthe major findings. The results of the PHA proved very useful to the designers ofthe VCM plant, allowing them to correct inadequacies at an early phase of theproject.

13.4 Iblkm-Up

The PHA team's job is complete. The report submitted by this team hasseveral suggestions for improvements and some unresolved issues, which will beresolved by the business team. The business team is responsible for assigning theseissues to appropriate personnel and ensuring that each issue is resolved. Theimprovements, after review and approval by the business team, are passed on to theappropriate VCM project personnel within ABC Chemicals.

The suggestion of siting the VCM plant west of Plant Road requires immediateattention. If accepted, ABC must quickly begin purchasing land west of Plant Road.This action will increase the VCM project cost and may delay construction.However, siting the VCM plant to the east may increase the public risk. Thebusiness team requests an evaluation of the consequences of chlorine releasesassociated with the east site. However, ABC's process hazard group informs themthat too little is known about chemical inventories and process conditions at thisdesign stage to perform such an assessment. Based on Ms. Deal's review of the oldchlorine dispersion analysis studies done for the Anywhere plant (which she receivedtwo weeks after the PHA meeting), she tells the business team that significant off-siteeffects are possible if the VCM plant is located at the east site. Therefore, thebusiness team recommends the west site.

13.5 Conclusions and Observations

The PHA team developed several suggestions for addressing the hazardsidentified at the proposed VCM plant. Some of the more important suggestionswere as follows:

• Consider moving the VCM plant to the west side of Plant Road(this would depend on dispersion analysis results).

• Locate the EDC, VCM, and HC1 storage tanks away from EchoRiver (the team was concerned about flooding and releases intothe waterway).

• Minimize the inventory of EDC, VCM, and HC1 stored on-site.This will require some equipment changes to closely couple theunit operations.

• Modify plant emergency plans to address flammable releases (planttraffic could ignite such releases).

• Position the chlorine rail car spur so that a VCM polymerizationaccident will not precipitate a chlorine rail car rupture.

• Verify that the Anywhere plant firewater system has sufficientcapacity for the proposed VCM plant and is protected againstexplosions.

Several observations can be made concerning this PHA. They include thefollowing:

• No additional hazards (toxic materials, flammable materials, etc.)were identified. However, the proposed VCM plant might havecreated new hazards if it had been sited at another ABC facility,due to interactions between the proposed and existing plants.

• Many of the causes or consequences of hazardous situations arerelated to equipment location. Consequently, many of thesuggestions made involved moving equipment.

• Several new, specific hazardous situations (e.g., flooding, rail caraccidents) were identified that the R&D phase What-If Analysisdid not find. The previous What-If Analysis could not identifythese situations since information needed to find them (such assiting/plant layout) did not exist at the time the What-If Analysiswas performed.

• Experienced PHA team members were key to the success of thereview. In particular, Mr. Scott's recollection that large quantitiesof toxic materials were stored west of Plant Road (i.e., chlorinestorage) may save ABC from doing unnecessary siting work.

The time required to perform the PHA was not substantial, principally becausethe project is still in an early design phase. Tkble 13.5 summarizes the effortrequired for this PHA.

In summary, the PHA team identified many causes of hazardous situations thatthe VCM plant designers should consider when they lay out the new facility.Addressing these hazards now will result in a safer plant and, they hope, will helpABC avoid costly modifications in the future.

Tkble 13.5 PHA Staff Requirements for the Conceptual Design Phase

Personnel

Leader

Team Member6

Preparation (hr)

8

1

^Average per team member.

Evaluation (hr)

8

8

Documentation (hr)

12

2