Ammonia Barging Risk Assessment

An integrated risk assessment program of DuPont's ammoniabarging operations utilizes such tools as HAZOP, HAZAN,dispersion, and consequence analysis. These tools, which reducethe risk effectively, can be applied to preventing exposure to othertoxic or flammable materials.

James R. ThompsonE.I. DuPont de Nemours & Co., Victoria, TX

Geoffrey Kaiser, John Brooks, Michael Check, and Thomas McKelveyNUS Corporation, Gaithersburg, MD

Anil Raj and William GreinerBrown & Root, Houston, TX

The purpose of this paper is to describe anintegrated set of risk management tools thatcan be effectively used to perform in-depthreviews of operations in which hazardousmaterials are handled and transported.These tools can be used to establish thecurrent safety level of the operation andhelp identify changes in design and/or main-tenance and operating procedures that canenhance safety even further. This papercontains a discussion of these risk manage-ment techniques, along with an applicationto a spec i f i c examp l e : E . I . OuPont deNemours' ammonia barging operations.

The first step in such a risk manage-ment procedure is to perform a hazards iden-tification analysis using, for example, theHazard and Operability (HAZOP) team review.This technique serves to identify what cango wrong with the operation and acts as ascreening procedure that enables the team todetermine which potential accident scenariosare of sufficient concern and are suffi-ciently complex to warrant a quantitativeanalysis. The HAZOP can also be used in itsown right, without resorting to quantitativeprocedures, to identify recommendations thatw i l l make some of the scenarios less likelyto occur or less severe in result.

The second stepquantitative analysis in

consists of atwo parts. The

G. Kaiser la currently at Science Applications International Corp.McLean, Va.

J. Brooks is currently at Davey-McKee, Chicago, II.I. HcKelvey is currently at Arthur D. Little, Inc., Cambridge, «a.

first is a determination of the frequencyof each accident scenario, using HazardsAnalysis (HAZAN). In general, HAZANconsists of the development and thequantification of fault trees. The secondquantitative analysis is a dispersion andimpact calculation that determines, for eachaccident scenario and for a range of weatherconditions and wind directions, themagn i tude of the consequences.

The complete analysis of the operation(HAZOP, HAZAN and consequence analysis)leads to a detailed understanding of equip-ment and operator responses under accidentconditions. From this understanding, it ispossible to identify those changes indesign, maintenance or operating procedures,or training that w i l l further enhance thesafety of the operation. Each of the inte-grated set of risk management tools andtheir benefits is discussed in more detailbeIow.

The set of techniques mentioned abovewas applied to a detailed risk assessment ofDuPont's ammonia barging network. The studywas initiated by DuPont in order to gain abetter understanding of the level of safetyin these operations and to identify anyimprovements that might be made, and wasperformed jointly by DuPont and NUSCorporation covering the following ammoniabarging operations:

I Barge loading and unloading at Beaumont(Texas)

I Barge unloading at Victoria (Texas)

1 Barge unloading at other sites (Extrapo-lated from Victoria results), and

t Barges in transit along the followingroutes :

Beaumont - Victoria (Texas)IntracoastaI Waterway

v ia the

Orleans Area - Belle (West Virgin-via the Mississippi, Ohio and

Newi a)Kanawha Rivers

* New Orleans Area - Seneca (Illinois)via the Mississippi River and Illinoiswaterway

* New Orleans Area - Memphis (Tennessee)via the Mississippi River.

These routes cover most of the ton-miles ofammonia transportation over DuPont's bargingnetwork. Note that, since the completion ofthis study, DuPont has ceased to operate theSeneca route.

The study revealed that DuPont's ammoniabarging operations are already very safe.For example, the estimated chance that anymember of the public or any worker (otherthan those working in the immediate vicinityof a barge) might be exposed to a concentra-t i on exceed i ng the LCB0 (potent i a I Iy fata Iconcentration) is essentially zero duringloading and unloading and only one in twentythousand per year during transit. Based onaverage national accident statistics, therisk from barging ammonia for the populationalong DuPont's ammonia transportation routesis estimated to be:

R 0.000005 % of the risk of fatalities fromautomobile accidents

1 0.000033 % of the risk of fatalities fromfires

i 0.000050 % of the risk of fatalities fromdrown i ng.

The chance of exceeding the IDLH (ImmediatelyDangerous to Life and Health) concentrationfor that same population is about one in twohundred per year, which is also low comparedto the risk of death from "natural" causes(exposure to IDLH concentrations of ammoniai s NOT potent 'tally I etha I, a I though i t maycause temporary impairment or permanentdamage).

As expected, an additional benefit ofthis study was that it identified areas whereDuPont could most effectively make itsammonia operations even safer. In addition,areas in which future studies could be madewere identified.

METHODOLOGY

The main elements of a typical riskmanagement study of a hazardous materialstransportation operation are:

1 HAZOPstudy

I HAZAN

(Hazard & Operability)

(Hazards Analysis) ofscenarios identified in the HAZOP

Dispersion,ana lysis

impact and risk

Col Iisionbarges

damage analysis for

Hazards and Operability (HAZOP) Review

The HAZOP is a procedure that has beendescribed in, for example, the recentlypublished "Guidelines for Hazard EvaluationProcedures" (I). There are also variationson the basic line-by-line technique such asthe qualitative fault tree procedure that isdescr i bed i n reference (2).

The approach taken is to form a multi-discipli nary team to identify hazard andoperability problems by searching fordeviations from the design intent. To thisend the team follows a systematic series ofguidewords or questions, developed fromexperience, that ensure that the wholeoperation is thoroughly examined to determinewhat can go wrong. A typical team consistsof six persons. There is a "chairman" who isexpert in the HAZOP technique and a recording"secretary". The remainder of the team ismade up of such persons as the operationmanager, an operator, a process supervisor,an electrical engineer or a maintenanceengineer.

The utility of the HAZOP procedure isthat, by assembling a team consisting both ofexperts in the technique and of those who arefamiliar in detail with the operation,concerns can be systematically identified.The careful recording of concerns andrecommendations then ensures that they arebrought to the attention of management andaddressed.

A well performed HAZOP has the followingoutcomes :

I Identification of the accidentsequences that could lead toinjury to the workers or to thepublic, or to severe economicconsequences.

i Development of recommendations fordesign or procedural changes thatw i l l prevent the occurrence ofthese severe accidents, or reducetheir probability of occurrence,or reduce the severity of theconsequences. These recommen-dations are each recorded as"action items".

I Identification of the accidentsequences that are so complex, orso frequent, or which have suchsevere consequences that a quan-titative hazards analysis and/ordispersion and consequence analy-sis is desireable. Thus, a HAZOPis an effective screening tech-nique leading to efficient HAZANand consequence analysis.

I Identification of the causes ofpotential upsets to the systemthat can result in reduced yield,unanticipated downtime, equip-ment failures, etc., leading toless economical operation of theplant.

I Identification of changes in theplant design or procedures thatw i l l improve the efficient opera-tion of the unit under considera-tion, and the recording of thesechanges as "action items".

Hazards Analysis

The accident scenarios identified duringthe HAZOP as requiring quantitativeexamination are subsequently analyzed indetail in order to determine the predictedfrequency of release, which can be obtainedfor each accident scenario by applying thetechniques of Hazards Analysis (HAZAN). Insome cases, fault tree analyses are carriedout. Event trees may also be used, althoughthis did not prove to be necessary in thespecific DuPont example.

The fault tree approach is wellestablished (1,3) and has ? long history of

applications in the chemical processenvironment (4). It breaks down an undesiredevent into causes that are well understood -for example, combinations of basic equipmentfailures and operating errors. The keys tosuccessful use of a fault tree are:

1 Assuring that the fault tree is completeand takes into account al I of the eventsto describe the scenario logically.

I Using "good" basic event data for theprobability of equipment failures andhuman errors.

1 Comparing the predicted values withexperience to help avoid errors.

The best source of equipment failuredata is from plant specific records. Wherethese data are sparse, they can be supple-mented by data from a generic data bank. TheCenter for Chemical Plant Safety of the AIChEis currently compiling a bank of equipmentfailure data, provided mainly by its U.S.sponsor companies.

There are also techniques forquantifying probabilities of human error.One such that was developed specifically foruse in the chemical process environment isthe TESEO (Tecnica Empirica Stima Error iOperator i) method (5). The technique is usedto quantify the probability of any givenhuman error taking account of the degree ofstress, the training and knowledge of theoperator, the degree of anxiety generated bythe situation and environment and ergonomics.References to other human reliabilitytechniques may be found in (1) .

In gênerai, HAZAN gives insights intohow the operation behaves during accidentsand leads to the identification of changes indesign, and/or operating procedures that w i l lreduce the frequency of occurrence oface i dents.

Dispersion, Impact and Risk Analysis

Most accidental releases of toxic orflammable vapors from operations that handlehazardous materials are denser than thesurrounding atmosphere, so that appropriateheavy vapor dispersion codes must be used.There are several possible codes available(6). For this study, two codes were used:DPLUMFand NUDENZ.

DPLUME was recently developed at NUS.It considers a continuous release of a

buoyant or heavier-than-air release from anarea source and is suitable for the modelingof continuous spillages of ammonia ontowater. DPLUME is based on the model of Oomset al. (7) for the dispersion of plumes fromstacks. It treats both heavy and buoyantplumes, including some considerations onplume rise derived from the well known workof Br i ggs (8) . For the purposes of th i sstudy, DPLUME was customized for the case ofammonia evaporating from water pools by usingthe empirical correlations of Raj et al. (9)to establish input boundary conditions (seebelow for further discussion). This observa-tion illustrates a general point about dis-persion modeling in the context of riskassessment; generally, there is no "blackbox" that can easily be used. The mode ofrelease determines the type of dispersionmodel that should be used.

NUDENZ was developed by NUS based onDENZ (10), a code developed at the UnitedKingdom Atomic Energy Authority's Safety andReliability Directorate, and is a code whichmodels the instantaneous release of aheavier-than-air puff. DENZ has beenextensively used in the European context,particularly to help UK industry satisfy therequirements of the Seveso Directive, whichmandates the establishment of a safety case(11). It has a I so been va l i dated aga i nst theThorney Island experiments (12). Thosereaders who wish to study further the circum-stances in which ammonia and air can formheavy mixtures should consult reference (13).

As noted above, one of the most criticalparts of a dispersion analysis is to properlycharacterize the "source term", which, foran atmospheric dispersion model, consists ofthe specification of input parameters such asthe mass rate of vaporization, the area ofthe evaporating spill, the initial density,the initial upward momentum flux and soforth. For example, many of the releasesconsidered in this study were spillages ofliquid refrigerated ammonia onto water;experimental results are available from whichto specify the characteristics for the sourceterm in these cases (9). Other scenariosconsisted of releases of vapor throughvalves, for which standard calculations areavai(able.

The dispersion models then calculate theconcentrations of toxic or flammable vapor asa function of downwind distance. Thesecalculations can then be combined withinformation on the health effects of toxicvapors or the effects of vapor cloud fires

and explosions to calculate the magnitude ofthe consequences. One example is the numberof people exposed to at or above the LCE0 orIDLH concentration levels of a toxic plume.

In order to impart realism to theanalysis, a model of protective actions canbe included at this stage. One simple modelassumes that the bulk of the people (approx-imately 85%) w i l l be indoors and that, as aresult, the average concentration w i l l beconsiderably reduced relative to thatexperienced by people outside. The modelused to calculate the rate of concentrationbuildup inside is described in Reference(14). The precise degree of concentrationand dosage reduction depends on the releasescenario, weather conditions and assumptionsabout how long people remain inside after thecloud has passed by. Reductions by factorsof five or ten are typical for ten-minutereleases, and typically result in largereductions in the number of people exposed atthe LC60 and IDLH concentration levels.

Finally, the results of the dispersioncalculations and the HAZAN are integrated toform an estimate of risk. This risk is inthe form of frequency (f) versus number (N)plots, where N is the magnitude of the con-sequences (number of people exposed). For agiven value of N, the frequency f is thepredicted number of times per year with whicha given value of N is equaled or exceeded.This is a common way of presenting theresults of studies of the risks associatedwith the manufacture, storage or transporta-tion of hazardous materials (15).

In the same way as described above forthe HAZAN, the dispersion, impact and riskanalysis leads to insights that in turn leadto identification of ways of reducing thepredicted frequency of occurrence of an acci-dent sequence and/or the magnitude of itsconsequences.

Collision Damage Analysis

In the specific example considered inthis study, it was necessary to perform ananalysis of the consequences of collisionswith other vessels of various sizes andcharacteristics and with the support pylonsof bridges in order to determine whatrelative velocity is necessary to cause therupture of an ammonia tank. Three methods ofcollision analysis were chosen for use inthis study: a) the M i norsky method (16),which is applicable to high energycollisions; b) the Van Mater-Jones method

(17), which is a modification of the Minorskymethod for low energy collisions and c) theRosenbIatt method (18), a somewhat morecomplex technique for low energy colli-sions. These methods were chosen on thebasis of a review (17) of 226 papers dealingwith the analysis of collisions.

In addition, a damaged stabilityanalysis was carried out to determine thefinal draft, trim and heel of a barge undervarious damaged conditions. In the specificexample, it was determined that the bargesare unlikely to sink as a result of acol Iision.

AMMONIA gARQINQ STUDY

The techniques described above wereapplied to DuPont's ammonia barging net-work. As mentioned earlier, the study wasinitiated by DuPont and carried out jointlyby DuPont and NUS. The various tasks thatwere performed and the flow of the study areshown on Figure 1. The purposes of the studywere as fol lows:

a) to determine the level of riskassociated with each of the oper-ations

b) to recommend potential improve-ments in design or operatingprocedures i n order to reduce therisks

c) to identify further worthwhilestudies, if any.

HAZOP of Ammonia Operations and Barges

A team made up of DuPont and NUSpersonnel conducted a HAZOP review of theammonia unloading facilities at Victoria, theloading facilities at Beaumont and one of thebarges. There were two major outcomes ofthis HAZOP:

First, a number of HAZOP "action" itemswere identified. These action items weredeveloped from concerns identified by theHAZOP team and resulted in recommendationsfor follow-up. For example, the two bargesused on the Beaumont-Victoria route, known asEIDC 56 and 57, had been recently purchasedby DuPont (they had previously been leased)and there was a question about the adequacyof the asbestos gaskets in the ammonia pipingon the barges. This stemmed from the factsthat (1) DuPont normally uses spiral-woundgaskets in ammonia service and (2) two small

leaks had occurred on valve bonnet asbestosgaskets on the barges. The "action item"recommended that the existing gasket mate-rials be reviewed for adequacy and, if nec-essary, a suitable replacement be selected.The resultant action was that DuPont replacedthe asbestos gaskets on EIDC 56 and 57 withspiral-wound gaskets to improve gasketreliability. In a similar fashion, sixteenrecommendations which required some follow-upwere identified by the DuPont/NUS team.

Second, a number of potential accidentalammonia scenarios during loading, unloadingor in transit were identified for furtherquantitative study. These scenarios includedsuch things as leaks, equipment failure,human error, barge collisions andcatastrophic failures.

HAZAN of Selected Scenarios

The scenarios identified for quantita-tive study were analyzed using the methods ofHazards Analysis. Fault trees were drawn andquantified in part using site- and barge-spec i f i c data suppIi ed by DuPont suppIementedby, where appropriate, generic data. DuPonthas a compilation of such generic dataavailable for internal use (19).

In addition to equipment failure data,it was also necessary to quantify thefrequency of barge collisions with othervessels and with structures such as thesupport pylons of bridges. This was done byusing data specific to DuPont's network andavailable in reports from the U.S. CoastGuard (20) and the Corps of Engineers (21).The TESEO method (5) was used to quantifyhuman failure probabilities.

The outcome of the HAZAN was the pre-dicted frequency for each accident scenario.

Dispersion, Consequence and Risk Analyses

As described in the foregoing, the sce-narios that were selected in the HAZOP forquantitative study were analyzed using thedispersion codes DPLUME and NUDENZ. In orderto do this, several data sets had to becomp i Ied:

a) Meteorological Data

The dispersion codes that were used forthe analysis required joint frequencydistributions; that is, the probability thatthe wind w i l l blow towards a specifieddirection, given that the windspeed lies in a

specifTed range and gîven the atmosphericstability category. Discussions withexperienced meteorologists led to theconclusion that data from the following wouldadequately represent the meteorologicalconditions which would be encountered enroute or at the loading and unloadingfacilities; Galveston, Baton Rouge, GrandGulf (near Vicksburg), St. Louis, Peoria,Paducah, Cincinnati and Charleston, WestVirginia.

b) Population Data

Fixed site population data were providedby DuPont for Victoria, Beaumont, Memphis,Seneca and Belle out to a distance of fivemiles. These data were processed into a formsuitable for input to the dispersion codes,namely into elements of a grid defined by thesixteen wind directions of the jointfrequency distribution and circles of radii0.5, I, 1.5, 2, 2.5, 3, 4 and 5 miles. Forthe purposes of the analysis, the people ineach grid element were assumed to beuniformly spread along a circle lying halfwaybetween the inner and outer radii.

For accidental releases of ammoniaduring transit, a uniform populationdistribution was assumed with the populationdensity being equal to that of the mostdensely populated county or city on each sideof the waterway. Each route was then dividedinto sections with the population density invarious ranges, and the length of thesections corresponding to each density rangewas calculated.

c) Health Effects of Ammonia

This set had to do with thetoxicology of ammonia. Experienced NUSindustrial hygienists reviewed the availablereferences on the health effects of ammoniainhalation. They then assembled the alreadyexisting data into curves of the levels ofconcentration as a function of exposure timefor health effects equivalent to those causedby the Immediately Dangerous to Life andHealth (IDLH) concentration and the LC50,which is a potentially fatal concentration(fatal to 50% of the animals exposed) ofammon i a.

The outcome of the dispersion, impactand risk analysis was two sets of f-N lines,one for the number of people exposed toconcentrations exceeding the LCE0 and one forthe number of people exposed to concentra-tions exceeding the IDLH.

Resu Its

As mentioned earlier, the results of thestudy showed that DuPont's barging operationsare very safe in terms of normally acceptedmeasures of risk of exposure to its employeesand to the public. The only identifiedaccident scenario which could potentiallycause fatalities would occur as a result of abarge tank rupture following a collisionwhile in transit. The risks associated withthis scenario were found to be very low,indicating that DuPont did not need to modifyor replace the existing barges. However,there are some potential modifications thatcould be made to barges to further enhancethe safety of the operations (if the timecomes when DuPont decides to build newammonia barges). These potentialmodifications were suggested by the collisiondamage analysis:

One of the striking features of thedeterministic collision damage analysis isthat, for a small number of collision loca-tions (which represent between 5 and 10% ofthe perimeter of the barge), a collisionspeed of less than 0.2 knots can possiblycause an ammonia tank rupture. This wouldoccur if a colliding vessel makes contact ata point at which the impact would be directlytransmitted to the tank support saddle. Onemodification worth studying, then, is to seeif the tank saddles can be structurally modi-fied to decouple them from the existing side-shells. Other possible modifications whichwould decrease the chance of release during acollision include longitudinally dividing thewing tanks or f i l l i n g them with a "honeycomb"structure to absorb more energy. It was sug-gested that DuPont might want to study thefeasibility of these concepts, including anydisadvantages which may arise (e.g., makingit more difficult to scuttle a barge for hur-ricane protection).

Marine arm or marine arm hose failurewas also a concern in the HAZOP, but theHAZAN showed that it was only a moderatecontributor to risk. In the unlikely eventof a marine arm failure, some of the peoplenearby may be exposed to concentrations ofammonia above the IDLH level. To furtherenhance safety, DuPont has installed marinearms with emergency release couplings and/or"breakaway cable" shutdown systems at severals i tes.

Another potential area for improvementwhich was identified at Victoria was mooringeffectiveness, which directly affects the

possibility of marine arm failure. In orderto improve effectiveness, DuPont has nowinstalled additional dolphins at Victoria, isusing additional and stronger mooring ropesand is upgrading its hurricane mooringfacilities and procedures.

As mentioned earlier, gasket failureemerged as a risk contributor in the HAZOPand HAZAN. DuPont has addressed this issueby installing spiral-wound gaskets on theEIDC 56 and 57 barges, and gasket replacementis planned for all barges. The use of thesegaskets should reduce the frequency of gasketfa i l ure by at I east two orders of magn i tude.The rate of release of ammonia through anyplausible failure in a spiral-wound gasketought also to be lower than the rate used inthe study, although this was not explicitlyaddressed in the study. Overall, the newgaskets should ensure that gasket failurebecomes a negligible contributor to risk.

Overfilling the ammonia barges whileloading or unloading did not emerge as asignificant risk contributor. However, ifsuch an event were to take place, a number ofpeople could be exposed above the IDLH level.Therefore, it was recommended that DuPontconsider installing high level switches onthe barges appropriately connected to the on-shore and on-barge shutdown systems. It wasalso suggested that the replacement of thecurrent type of barge tank level gauges beconsidered due to their significant failurerate.

The information described above encom-passes the major recommendations. Table 1summarizes these recommendations and othersof low priority.

CONCLUSION

As mentioned earlier, the study hasshown that DuPont's ammonia barging opera-tions are already very safe. The study reaf-firmed the safety position and pointed outareas where DuPont could further enhance thesafety of its barg ing operations.

In addition, some potentially majorscenarios were found to be small or zero con-tributors to risk: (i) The damaged stabilityanalysis showed that it is extremely unlikelythat a barge w i l l sink after a collision, sothat an ammonia release from a sunken bargedoes not contribute to the risks and (ii)Loss of refrigeration (for a sufficient timeto cause the relief valves to vent) isextremely unlikely.

Since the completion of this study inAugust of 1987, DuPont has taken severalsteps in response to the recommendations:

I A hydraulically-operated marine arm withposition switches, an "Emergency ReleaseCoupling", and ammonia detection has beeninstalled at Victoria. An electronic"breakaway" shutdown system has beeninsta I led at Bel le.

I Revisions to upgrade the barge mooringfacilities at Victoria for normal opera-tions and in case of a hurricane have beencompIeted.

I Gasket upgrading and other preventivemaintenance has been performed on a l lbarges.

The maintenance oftation has beenfailure rates.

the barge instrumen-improved to reduce

1 Relief valves with higher set pressureshave been installed on several barges.

I Other lower-priority recommendations fromthe study are s t i l l being addressed.

This study has shown the value of usingan integrated set of risk management tools tothoroughly analyze the risk involved in ahazardous material distribution system and toimplement those changes which w i l l mosteffectively reduce the risk involved. Thesetechniques can be applied to other toxic orflammable materials where potential exposureto employees and/or to the public is aconcern.

LITERATURE CITED

1. "Gui de Iines for Hazard Evaluation Proce-dures", Center for Chemical Process Safe-ty of the American Institute of ChemicalEngineers, New York, 1985.

2. McKelvey, T.C., "Hazards Inductive andDeductive Evaluation (HIDE)", Paper 56ain the National Meeting of the AmericanInstitute of Chemical Engineers, Boston,Summer 1986.

3. W.E. Vesely et al., "Fault Tree Hand-book", NUREG-0492, United States NuclearRegulatory Commission, Washington DC,1981.

4. G.J. Powers and F.C. Tompkins, "FaultTree Systems for Chemical Processes",

AIChE Journal 20, 1974.

5. G.C. Bello and V. Co lumbari, ReliabilityEngineering l (1980) pp 3 et seq.

6. S.R. Hanna and P.J. Drivas, "Guidelinesfor Use of Vapor Cloud DispersionModels", Center for Chemical ProcessSafety of the American Institute ofChemical Engineers, New York, 1987.

7. Li Xiao-Yun, H. Lei j dens and G. Ooms, "AnExperimental Verification of a Theoreti-cal Model for the Dispersion of a StackPlume Heavier then Air", AtmosphericEnvironment 20 (1986) 1087-1094; G.Ooms, A.P. Mahieu and F. Zelis, "ThePlume Path of Vent Gases Heavier thanAir", First International Symposium onLoss Prevention and Safety Promotion inthe Process Industries, The Hague, May1974.

8. G.A. Briggs, "Plume Rise Buoyancy EffectsAtmospheric Science and Power Product-ion", DOE/TIC-27601 (1984) 327-366.

9. Raj, P.K., Hagopian, J. and Kal el kar,A.S., "Prediction of Hazards of Spills ofAnhydrous Ammonia Onto Water", CG-D-74-74, Prepared for the U.S. Coast Guard byArthur D.. Little, Inc., Cambridge, MA,1974.

10. Fryer, L.S. and Kaiser, G.D., "DENZ - AComputer Program for the Calculation ofthe Dispersion of Dense Toxic or Explo-s i ve Gases i n the Atmosphere", Un i tedKingdom Atomic Energy Authority ReportSRD R152, 1979.

11. R.P. Pape and C. Nussey, "A BasicApproach for the Analysis of Risks fromMajor Toxic Hazards", in The Assessmentand Control of Major Hazards, I.Chem ESymposium Series 93 (1985), 367-388,Pergamon Press.

12. R.D. Fitzpatrick and C. Nussey, "GroundLevel Concentration Contours for theThorney Island Phase I Trials and aComparison with the DENZ Model", Pro-ceedings of the Second Symposium on HeavyGas Dispersion Trials at Thorney Island,Sheffield, 1986.

13. Kaiser, G.D., "A Review of Models forPredicting the Dispersion of Ammonia inthe Atmosphere", Plant/Operations Pro-gress, January 1989.

14.

15.

18.

19.

Davis, P.C. and Purdy, G., "Toxic GasRisk Assessments - the Effect of BeingIndoors", in Proceedings of the UKInstitution of Chemical Engineers'Symposium, "Refinement of Estimates ofthe Consequences of Heavy Toxic VaporReleases", Manchester, UK, 1986.

Blokker, E.F., Lans, H.J.D. andMeppelder, F., "Evaluation of Risks As-sociated with Process Industries in theRijnmond Area - A Pilot Study", Proc. 3rdInternational Loss Preventi on Symposium,Basel (Sept. 1980).

16.

17.

Minorsky, V.W., "An Analysis of ShipCollisions with Reference to theProtection of Nuclear Power Plants",Journal of Ship Research, October 1959.

Van Mater, P.R., Gianotti, J.G., Jones,N. and Geralis, P., "Critical Evaluationof Low-Energy Ship Collision-DamageTheories and Design Methodologies", ShipStructure Committee, Project SR-1237,U.S. Coast Guard Contract No. DOT-CG-63738-A, July 1978.

United States Coast Guard, "Evaluation ofTanker Structures in Collision", M.Rosenblatt and Son, Inc. and UnitedStates Steel Corporation, Report No.2087-15, U.S. Coast Guard Contract No.DOT-CG-10, 605A, November 1973.

E.I. DuPont de Nemours, Inc., "Guide forFault Tree Analysis", Volume 1, Section6.2, Issued by the Safety and ProtectionDivision, Employee Relations Department,Wilmington, DE 19898.

20. United States Coast Guard, 1979-83,"Statistics of Casualties".

21. Corps of Engineers, "Waterborne Commerceof the United States", Calendar Year1984, Part 5, National Summaries, WRSC-WCUS-84-5.

James R. Thompson»1

Thomas McKelvey

Table 1. Recommendations from ammonia barging study.

Scenarios

Marine arm or hosefailure

Gasket failure

Ammonia tankrelease followingcollision

Tank overfilling

Several scenarios

Several scenarios

Refrigeration

Recommendations

(a) Study mooring strategy at Victoria(already being done by DuPont)

(b) Study feasibility of installation of strain-sensitive marine arm(already being done by DuPont)

Review materials of construction of gasketsand replace if necessary(already being done by DuPont}

(a) Study feasibility of decoupling saddles fromexisting sideshells

(b) Study potential modifications to barge toreduce probability of release - e.g., fillwing tanks with honeycomb

(a) Automatic shutdown of pumping by high levelswitches in the tanks

(b) Replace current tank level gauges with a morereliable type

(c) Install an on-shore integrating flow meterfor loading operations

Protect manual cable trip system frominadvertent actuation by passers-by

Review operator training for routineoperations carried out during loading andunloading

'(a) Install relief valves with higher setpressures on EIDC 53, 54, 55 barges

(b) Add redundant tank pressure gauge on eachbarge tank

HAZOParProject B«at Victoria

Collision StatisticsFrom Literature

idoH

It— •" oC

/£

IAZOP Actionemsefinition ofOccidentSequences

StatisticalAnalysis ofCollisions

Information fromDuPont onDocking Facilities

HAZANofSequences atDockingFaculties

KEY:

o Identification ofRisk DominantSequences

o MakeRecommendations

Figure 1. Ammonia barging risk analysis.

9

DISCUSSIONBILL HOOKEY, Chevron Chemical: You have a lotof preemptive-type material in there and have sensorsto detect leaks. Do you have any water spray systemsto knock down a nuisance cloud or something largerthan that?

J.R. THOMPSON, Good point. We gave a lot ofconsideration to that sometime ago, maybe two yearsago. I got from Max Appl some pictures of a setup,which his company has on a rail car spot. We talkedabout that at length regarding our system. In ourparticular configuration it is difficult to do anything interms of water spray there, because it is such a smallarea that so much of the potential exposure area is outon the barge. Because it is difficult to have some kindof effective water spray system that could cover all thecontingencies and we only have one person on the bargeand one on shore who also take care of all

other systems, we decided not to try to do anythinglike that in our case. I could see how it can be appliedin other cases where it would be a little easier to getat your ammonia leak and separate it from the people.We, however, do not have a lot of people, and therewas a great difficulty with most of our stuff being offthe shore. The question we faced was "what to do withit." Of course, I am familiar with some ships with watersprays, but it would be difficult to do anything cost-effective, since this barge is a much smaller vessel. Idon't think, however, that any of those slides showedour fairly new fire control system which has five spraytowers which can spray water or foam. We unloadflammables in this barge dock area, and thought we mightbe able to swing those because they can go up anddown and sideways and may operate just as well asa water curtain-type system. But, I think there still arecases for which it can be effectively applied.

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