Minimizing Off-Site Consequences of Anhydrous Ammonia Systems · the south, east, and west of the plant, but has a ... article was to closely examine its anhydrous ammonia storage

Minimizing Off-Site Consequencesof Anhydrous Ammonia SystemsFMC's manufacturing site for peroxygen chemicals was challenged to minimize off-siteconsequences for an anhydrous ammonia handling system in a cost-effective manner.

Several keys to the successful completion of this project are discussed.

John M. Rovison, A. A. Garcia, and Donald A. CollinsFMC Corporation, Tonawanda, NY 14150

Introduction

FMC's manufacturing site for peroxygen chem-icals resides primarily in an industrial zone tothe south, east, and west of the plant, but has a

residential area located just north of the plant site andleeward of the prevailing winds. Successfully meetingthe challenge to minimize off-site consequences for ananhydrous ammonia handling system in a cost-effec-tive manner required a systematic and multidiscipli-nary approach, using novel methods and standard toolsin innovative ways. Implementation of the projectcoincided with development of the sites' RiskManagement Plan (RMP) under the USEPA. Severalkeys to the successful completion of this project arediscussed. First, discussions with process safetyexperts were held to define the need for improving thepresent anhydrous ammonia handling system such thatmanagement support could be garnered despite thestrong process safety performance of the system as italready existed. Second, the program used an integrat-ed approach to define the project scope by: evaluatingthe effects or consequences of ammonia releases off-site; assigning probabilities to the potential failuremodes causing the releases; doing risk benefit analyseson the various options to mitigate those releases; andthen, selecting the optimal risk benefit option to

address the identified concerns. Finally, once the proj-ect was defined, it was then studied with a series ofprocess safety reviews to assess the changes, identifyissues, and address them prior to construction andinstallation. Upon completion of the project, FMC wasable to reduce the probability of any off-site conse-quence using cost-effective means to improve analready reliable process system.

Background

In the mid 1990s, several chemical sites within FMChad experienced a notable process incident which hadoff-site consequences. FMC took immediate actions torevisit its technologies applied to process hazardreviews, project review paths, and increased its focuson the potential effects on the communities surround-ing its operating facilities. This effort was in concertwith the U.S. EPA Risk Management Plan rule, whichwas to be effective in June of 1999 for listed chemicals.

The challenge for the plant site highlighted in thisarticle was to closely examine its anhydrous ammoniastorage and handling facility, also covered under theOSHA Process Safety Management (PSM) rule, anddetermine the most economical means for reducing off-site risk to the community. The benefits of expendingcapital on a system which had already met the compli-

AMMONIA TECHNICAL MANUAL 273 2001

ance requirements under PSM and had no off-site inci-dents over a 43-year operating history were unclear andhad to be presented to management such that theauthorization for spending could be rationalized. A sys-tematic approach to minimizing the effects of a poten-tial anhydrous ammonia leak was then developed andundertaken.

The key elements for the off-site effects study wereas follows: analysis of the storage and handling systemrelease scenarios with respect to quantity and storageor transfer devices; modeling each release scenario;determining the impact of each release scenario on thesurrounding community; and assigning probability datafor each type of release scenario (Deshotels andZimmerman, 1995). Once completed, a series of miti-gating designs, including a "Zero Risk" option wereformulated. Capital costs were estimated for each mit-igating design option and then compared using riskbenefit evaluations that measured the potential com-munity effects in financial terms. The optimal problemsolution was then selected and used to define the proj-ect scope. Operations input was sought to minimize theimpacts of daily operation. The strong statistical caseand loss avoidance in financial terms was used to pro-cure capital funding for the project. The end result wasan off-site risk reduction of nearly 50% with minimizedcapital employed once the project was fully imple-mented. Project implementation required several lev-els of process hazard reviews to address general designand control issues at both the conceptual and definedlevels. Upon completion of the installation, a thirdreview or pre-startup safety review was undertaken totrain operators and manufacturing engineers, as well aslook for installation errors and potential problems thatmay have been missed by the previous hazard reviews.The unit was then successfully started up without inci-dent.

Process description

In the base case, the site regularly received anhy-drous ammonia shipments by railcar delivery and off-loaded the material into two storage tanks connected bya series of common pipes. Unloading was accom-plished through the use of compression of ammoniavapors from the intended target tank into the railcar,

and then liquid transport through the railcars dip tube,a connecting hose, and ultimately the target tank viapiping. On occasion, truckload quantities are deliv-ered and unloaded through a dedicated truck unloadingstation and are accomplished similarly to the railunloading except that the compressor resides on thetruck itself. The tanks were protected with a series ofsafety devices and interlocks consistent with ANSIK61.1 (1989). Automated shutoff valves on the transferlines had been located distally on the hard piping andwould activate upon high ammonia levels detected bythe unloading station or around the storage tanks them-selves.

Ammonia was transferred to the consuming processby a -430 ft liquid handling pipeline by means of pres-surization. The pressurization on the tanks is accom-plished by maintaining heat input through controlledsteam heating into the tanks. Only one tank would beactively feeding the process at a given time with theother tank being used for inventory purposes or off-linefor scheduled preventive maintenance. Liquid ammo-nia entered a vaporizer with downstream flow con-trolled entry into the intended consumer process.Several additional process consumer lines tie into theammonia line downstream of the vaporizer which areactive on a regular, but nonperiodic basis.

Case Study

Fundamental studies

Initially, the whole ammonia storage and handlingsystem for the site was analyzed for potential worstcase releases and probable releases (Roberts andHandeman, 1986). Taken into account were the off-siteimpact areas, institutions (schools, hospitals, factories)potentially affected, and the residential population.Probabilities of wind direction were superimposed ontothe affected areas using wind rose data garnered fromthe local NOAA weather station. Modeling using thepopulation density, wind rose data, and concentrationlimits set forth by the USEPA using ERPG-3 (1,000ppm limits) was used to determine the potential fatali-ty estimates at 0.6% of the exposed assuming outdoorsexposure for the duration of the release. Scenariosincluded the content losses of each large vessel: railcar,large storage tank, and loss of a truck tank. This initial


Figure 1. Rolling average NH3 inventory.

screening was used to identify potential remediationcases and generate conceptual costs for each scenario.Operations data was also documented at this phasesuch as rolling inventory cycles for each of four storagescenarios: a base case with two storage tanks and rail-car delivery, a case with a small tank only and railcardelivery, a case with a large tank only and a tank truckdelivery, and, finally, a large tank with railcar delivery(Figure 1).

Ammonia consumption rates coupled with processlosses were also documented in anticipation of the "norisk" remediation case to be generated in the secondphase of the study. Each of seven remediation caseswere cost estimated and their potential operationalimpacts documented. Remediation devices or strate-gies developed at this point of the study included use ofalternative raw materials (0 risk options), railcarunloading pits, stone dikes, extra water nozzles, addi-tional ammonia sensors, swales, relocation of theprocess vaporizer (Bellinger et al., 1996), foam controlsystems, water spray "knockdown" systems, concretedikes, and added instrumentation. The various combi-nation of devices and strategies were matched to thevarious unloading cases and subsequent release scenar-ios. The site had six alternatives to sort through in addi-tion to the null case alternative. This preliminaryscreening provided data for a more deliberate approachto defining the project scope.

Detailed study

A consequence analysis was performed in two equip-ment sections. The first section detailed typical releas-es from different sized storage vessels under site spe-cific wind conditions and an assumed generic meteoro-logical stability class (D). The second section used thesame meteorological conditions, but was based onunloading incident history. Three types of incidents (1in. <j> leak until tank empty, catastrophic failure mod-eled as 4 in. <j) hole to vessel empty, and a leak thatempties the vessel in 10 min) were modeled for each offour vessels: small tank, large tank, railcar, and tanktruck. Surface roughness parameters for a rural areawere conservatively used as a default and an ambienttemperature of 65 °F was used. Endpoints for the dis-persion model were based again on the EmergencyPlanning Guidelines, level 3 (ERPG-3), and the ERPG-2 for ammonia. The data were then used to calculate theERPG-3 (1,000 ppm) distances and probability ofdeath from probit calculations at the given distances.The same exercise was repeated for the ERPG-2 (200ppm) exposure levels. This methodology was per-formed with the intention of identifying the effects ofinventory size on consequence zones, and is presentedin Tables 1 and 2.

A similar exercise was performed for various unload-ing scenarios, based on incident history, with hose fail-


Table 1. Distance to the Endpoint of Concern (ERPG-3)

ERPG-3 (1, 000 ppm)

1 in. leak from tank until empty

Probability 9.6xlO'5/yr

Catastrophic FailureW

Probability 9.7xlO'6/yr

10 min release of entire

contents. Prob= 6.9xlO"6/yr

Distance (Miles)Small tank (st)

0.4

(1.1%)

1.4

(0.3%)

0.8

(0.6%)

Large tank (It)

0.4

(2.5%)

1.4

(0.4%)

1.0

(0.6%)

Rail car (re)

0.4

(5.6%)

1.4

(0.5%)

1.2

(0.6%)

Tank truck (tt)

0.4

(0.9%)

1.4

(0.2%)

0.7

(0.6%)

Values in parenthesis are probability of death from probit calculation at given distance. Personnel are assumed to be outdoors andexposed for the duration of the release. Values below 1 % are extrapolated.(1) Treated as a 4 in. leak until tank is empty.

Table 2. Distance to the Endpoint of Concern (ERPG-2)

ERPG-2 (200 ppm)

1 in. leak from tank until empty

Catastrophic Failure^1)

10 min release of entirecontents.

Distance (Miles)

Small tank (st)

1.2

4.0

2.8

Large tank (It)

1.2

5.3

3.5

Rail car (re)

1.2

5.3

4.7

Tank truck (tt)

1.2

5.0(2)

2.2

(1) Treated as a 4 in. leak until tank is empty.(2) Larger distance due to dispersion modeling program quasi-instant, cloud treatment.

Table 3. Unloading Scenario Distance to the Endpoints of Concern

Unloading Scenario

Release from the 1 in. liquidunloading hose (rail car unloading)Release from the 1 in. liquidunloading hose (tank truck unloading)Release from the 1 in. liquid unloading line(reverse flow from tank only)Release from the 1 in. liquid unloading line(with forward and reverse flow release)Release from the 1 in. / 1.5 in. vapor returnlineRelease from the compressor in the vaporreturn line

Release Rate(Ib/s)

5.7

5.2

3.3

6.42.0

1.5

Distance to ERPG-3of 1,000 ppm (miles)

0.2

0.2

0.1

0.20.1

0.1

Distance to ERPG-2of 200 ppm (miles)

0.5

0.5

0.4

0.50.3

0.2


Table 4. Based on DNV's ARF Failure Rates for Onshore Process Equipment Except Where Indicated

Equipment Category

Vessels (/yr)

Loading/Unloading (/yr)

Flanges (/yr)

Process Piping (/m-yr)

Screwed Fittings (/yr)

Vaporizer (/yr)

Compressor (/yr)

Equipment

Storage Bullet

Rail CarTank TruckUnloading Hose(/yr) see note 1.

Flanges (<6 in.)Flanges (>6 in.)

1/2 in.

3/4 in.

l in.

1.5 in.2 in.

Threaded Joints,

see note 2.

Instrument Fittings

(<3/4 in.) see note 3

Shell-and-Tube

(Process Tube),

see note 4.

Reciprocating

5mm

3.70E-05

3.70E-053.70E-053.30E-02

4.00E-043.60E-04

3.60E-05

2.40E-05

1.70E-05

1.10E-05

7.50E-06

7.20E-04

9.20E-04

6.0E-06

n/a

25mm

9.60E-05

9.60E-059.60E-05n/a

n/a400E-05

n/a

n/a

n/a

n/a

n/a

n/a

n/a

1.5E-05

6.50E-03

100mm

9.70E-06

9.70E-069.70E-06n/a

n/an/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

1.7E-06

6.50E-04

Rupture

6.50E-06

6.50E-066.50E-06l.OOE-03

n/an/a

7.80E-07

1.10E-06

1.40E-06

1.50E-06

1.70E-06

2.00E-04

n/a

9.6E-07

max 4 in.

Total

1.49E-04

1.49E-041.49E-043.40E-02

4.00E-044.00E-04

3.68E-05

2.51E-05

1.84E-05

1.25E-05

9.20E-06

9.20E-04

9.20E-04

2.4E-05

7.15E-03

Notes:(1) Failure rates for hoses are generic hose failure frequencies from ARF tables.(2) No data are available on the screwed fittings. It is assumed that the failure rate for the small releases is twice that for a flange

(>6 in.) and the rupture rate is 5 times that for the large leak size for a flange (>6 in.). See also Lees Vol. 1 pp. 12/103-104.(3) Failure rate for screwed-on instrument fittings is assumed to be identical to total failure rates for threaded joints.(4) Failure rate for a vaporizer is based on the tube failure rates for a shell-and-tube type heat exchanger.


ures for both the railcar and tank truck unloading sys-tems, the liquid and vapor transfer piping to and fromthe tanks, and, finally, a line failure from the unloadingcompressor. The time frames used for these scenarioswas typically 13 min based on plant personnel responesto ammonia leaks except for the unloadinghoses that were modeled at 20 min (see Table 3). Inaddition, miscellaneous failures such as spurious liftsof a pressure relief valve (PRVs) or failure to functionwere documented.

A total of three remediation cases (Bellinger et al.,1996) were identified from the original seven that weredeveloped in the initial screening exercise:

• Base Case: Two storage bullets, jumbo railcar, andvaporizer located remotely from storage (at the time),the null alternative or "do nothing".

• Case 1: Use of aqua ammonia in place of anhydrousammonia.

• Case 2: Use of large storage bullet only, eliminatestorage tank not in use, tank truck receipts in place ofjumbo railcar, relocate vaporizer near to storage tank,add additional water fogging spray capability, and addadditional area sensors.

• Case 3: Continue rail car unloading, relocate vapor-izer near to storage tank, eliminate storage tank not inuse, add additional water fogging spray capability, addammonia area sensors, rebuild (fireproof) compressorshed and other system upgrades.

All of these design cases were compared againsteach other in a series of 22 comparative release scenar-ios using DNV ARF (Annual Rates of Failure, Table 4)failure rates for onshore process equipment to producea graphical representation of the frequency (yr ') of agiven number of fatalities or more in a year plotted log-arithmetrically against a number of deaths (N). Theresulting complimentary Fn curve is a plot in whichthere is the sum of probabilities of failures in terms ofthe frequency of the 22 scenarios tested resulting in Nfatalities (abscissa). Standardized performance curvesas put forth by DNV for existing plants (negligible andintolerable) are used as a comparative limit line for thebase case (Figure 2).

Societal risk Fn curves for a given facility show thefrequency and the expected number of fatalities foraccidents. Societal risk information is strongly depend-ent on the location of populated areas on- and off-site(offices, maintenance building, field engineers, and soon.) relative to the location and number of major haz-ards such as fires, explosions, and toxic releases. Oncea societal risk evaluation has been conducted for afacility and particular accidents have been identified asmajor contributors, it may be desirable to mitigate thesocietal risk to more acceptable levels by implementingone or more approaches.

The results of the other design cases are similarlyplotted for comparison sake. It should be noted that the

t.OOE-O» sas.

I .OOE-07 =jrm-^=

Numb« (N)

sr*-H<? !?r Emitting PlanU ****"**N«flKflible Tor (Existing '̂

Figure 2. Standard performance curves as a comparative limit line for the base case.


1 .ooE-02

1 .aoE-03

iit .OOE-04

1.00E-05

'S£

1 .OOE-06

1 .OOE-07

1.00E-1000

Number (N)

-BimeC«»« -*-C««e2

Figure 3. Other cases.

Figure 4. Data of number of fatalities per year for remedial design case under consideration.


most reduction in off-site risk occurs as the ordinalevalue migrates to the intersection of the x and y axes.The other cases are shown in Figure 3. Note that case1, the zero risk alternative, had a 100% risk reduction,and, therefore, did not plot.

The Fn exercise forces the team to look at theammonia release scenarios that are having the mostsignificant impact on the frequency analysis and thustake remedial action against the scenarios whichmigrate the respective design case curves away fromthe limit line (intolerable for existing plants, Figure 2).

Using the same data generated as part of the Fn exer-cise, the team then analyzes for the potential risk thereduction each design case presents relative to off-siteconsequence. This is termed the Societal Risk Index(SRI) and represents an unweighted expectation value.The risk index is calculated by taking the product ofaccident frequency and number of fatalities for each ofthe 22 release scenarios considered and then summingthis product for all accidents in the respective remedialdesign case. Mathematically

Unweighted Expectation Value = S/ (ƒ/* Nj)

In this equation, fi is the single accident frequency of

one of the 22 release scenarios considered and Nt is the

number of fatalities for each scenario. The interpreta-tion of unweighted expectation value is the expectednumber of fatalities per year for the remedial designcase under consideration. This data is presented inFigure 4.

Next the Risk Benefit Evaluation (RBE) was per-formed using NPV calculations. A value of $10M isused as a basis of expenditure to avoid a fatality. Case1 is used as the full annual loss value (a recovery orcost avoidance value) as it poses 0% societal risk and100% certainty and is $10M multiplied by the SRI pre-sented in the base case. Cases 2 and 3 represent 68%and 42%, respectively, of the potential risk reduction ofthe case 1 and are calculated similarly.

The maximum NPV (Net Present Value) is the annu-al loss value at a hurdle rate of 11.5% for an 11-yearproject life. The actual NPV is the maximum NPV dis-counted for effects by annual operating costs for eachoption over the course of the project life. The resultantRBE rating is then the actual NPV divided by the annu-al loss value. The results are presented in Table 5.

Table 5. RBE for Ammonia Release Mitigation Options

Description of Options

Base Case Continuation of current operations.!ase 1 Change to using aqueous ammonia; no anhydrous ammonia on-site.!ase 2 Change to tank truck receipt of anhydrous ammonia, relocate vaporizer near to tank, eliminate

storage tank not in use, eliminate rail receipts of anhydrous ammonia, add additional waterfogging spray capability and add ammonia area sensors.

Case 3 Continue to use railcar unloading, relocate vaporizer nearer to tank, eliminate (in place) storagetank not in use, add additional water fogging spray, and add additional ammonia sensors.Also install remotely activated isolation valves on inlet and outlet of rail car transfer hose.

Option Societal Risk Annual Loss Value Maximum NPV Initial Costs Operating Costs Actual NPV RBE ratingBase case 6.17E-03 $ - $ - $ - $ - $ - 0.00Casel 0 $ 61,700 $ 308,500 $ 503,000 $ 127,300 $ 3,940,000 63.86Case 2 1.99E-03 $ 41,800 $ 209,000 $ 150,000 $ 35,000 $ 1,680,000 40.19Case3 3.57E-03 $ 26,000 $ 130,000 $ 158,600 $ 35,000 $ 850,000 32.69

Notes:Maximum NPV is Annual Loss Value at 11.5% hurdle rate and 11 year project life.Actual NPV is Maximum NPV discounted for annual Operating Costs.RBE Rating = Actual NPV divided by Annual Loss Value.


Results and Discussion

The risks associated with the base case and threeproposed options for ammonia storage and transporta-tion is assessed in the study. The objective of the workis to provide a screening assessment of each option interms of societal risk and based on these results and arisk-benefit evaluation (RBE), to provide guidance onthe preferred option. The options were:

« Base Case: Two storage bullets, jumbo railcar andvaporizer located remotely from storage.

• Case 1: Use of aqua ammonia in place of anhydrousammonia.

• Case 2: Use of large storage bullet only, eliminatestorage tank not in use, tank truck receipts in place ofjumbo railcar, relocate vaporizer near to tank, add addi-tional water fogging spray capability, and add ammoniaarea sensors.

• Case 3: Continue railcar unloading, relocate vapor-izer near to tank, eliminate storage tank not in use, addadditional ammonia water fogging spray capability,add ammonia area sensors, rebuild (fireproof) com-pressor shed and other system upgrades.

During later reviews of these options, it was agreedthat water fogging spray capability was not a viablemitigation measure for ammonia releases such that thisfeature of Cases 2 and 3 was eliminated (Baldock,1980).

The most significant risk reduction is achieved byimplementation of the aqua ammonia case (Case 1).However, because of high capital requirements relativeto the other options considered, Case 1 is the leastdesirable in terms of RBE.

Compared to the base case, the Case 2 and 3 socie-tal risk are about half, and are essentially equal, giventhe coarse nature of the study. The main differencebetween these cases is that Case 2 tank truck risks aresomewhat lower than the Case 3 rail car risks due to ahigh failure rate for rail car hoses.

The shifting of transportation risks from the railroute to the road tanker route relative to Case 2 wasquestioned as to increasing the risk to the general pop-ulation in areas near the plant compared to continueduse of rail cars.

Although rail transportation generally is assumed tohave a safer record than road transportation of haz-

ardous goods (per tanker-mile), the difference is not sogreat that this can be applied as a general rule. In orderto make planning decisions on the basis of risk, it isnecessary to compare risks along specific routes. Inparticular, the following factors must be consideredwhen comparing rail vs. road tanker risks:

• Rail tankers carry larger inventories and will there-fore have a greater impact area if a major releaseoccurs.

• Rail tankers may be left in sidings during transit,which may expose nearby people to risk.

• Railcar accidents may occur in unpopulated areaswith no rail passengers involved, but there are normal-ly other road users involved in traffic accident scenar-ios.

• For any comparison of transportation risks, it mustbe decided whether the prime interest is risk to peoplein the local area (such as along a road or rail approachroutes) or whether exposure of people along the totaltransportation routes should be considered.

As most sites take custody of hazardous chemicalswhen the tankers enter company premises, releases enroute are not included in the RBE exercise.

The estimated risks for the base case and Cases 2 and3 are summarized in Figure 4. Risks are expressed associetal risk (estimated number of fatalities per year)and it is assumed that the societal risk for case 1 (aque-ous ammonia) would be zero. The risk values are high,but the absolute values should not be compared withrisk criteria as this is a coarse scale comparative riskexercise. Compared with the base case, the societal riskvalues for Cases 2 and 3 are about half, and are essen-tially equal, given the coarse scale nature of the riskquantification.

If the small storage bullet is discarded (isolated inplace, to be used only during PM of the main storagebullet, and done at essentially zero cost), about 14% ofthe Base Case risk is lost. The large storage bullet thendominates Case 2 risks. The main difference betweenCases 2 and 3 is that the rail car risks are higher thanthe tank truck risks and this is driven by the fact that arail car spends so much more time on-site, connectedup to the offloading system, compared with a tanktruck and that there exists a higher failure rate for railcar transfer hoses. Releases from all these (stationaryand transport) vessels are modeled as full inventories,


which is clearly pessimistic.After the initial risk analysis for the proposed reme-

dial design cases, several additional mitigation meth-ods were proposed to further lower the risk, especiallyfor Case 3. These options included:

(1) Installation of one additional ammonia sensoradjacent and downwind to the ammonia rail car-unloading area. This ammonia sensor was to alarm inthe control room.

(2) Installation of shutoff valves on the inlet and dis-charge sides of the railcar unloading hoses. The valveswere automatically actuated based on readings fromthe ammonia sensor system and can be remotely actu-ated by operators in a safe area located well away fromthe ammonia storage and unloading system (such asthe control room).

In the summary of RBE calculations for the variousoptions in Table 5 titled "Risk Results for AmmoniaRelease Mitigation Option," the far right column of thistable shows the RBE rating which is a metric for thecost effectiveness of each option. Case 3 has the lowestRBE rating and is therefore the most cost-effectiveoption.

The conclusions include two assumptions. First, themitigating effects of excess flow valves, emergencyisolation valves, or other BSD and emergency proce-dures that currently exist at the plant site are includedin the risk estimates. Second, as FMC formally takescustody of hazardous chemicals when tank cars or tanktrucks enter company premises, releases en route arenot included.

End Results

FMC's project execution guidelines required a multi-ple examination of the defined project scope to ensureminimized design oversights that could lead to processsafety issues. This process included a conceptual safe-ty review in which the changes were examined to deter-mine if adequate safeguards have been specified in theprocess design to detect, prevent, or mitigate releasesor other events involving releases of hazardous materi-als or energy. A provisional risk tier is provided usinga quantified risk assessment technique. The facility sit-ing aspects are examined during this phase of theprocess design. Regulatory impacts such as OSHAProcess Safety Management Standard (PSM) or EPA's

Risk Management Program (RMP) rule are also con-sidered.

At this point, the "What If' study is conducted andhazard scenarios on the preferred design are identified.A hazard scenario is defined as each combination of acause of a hazard together with its individual conse-quence. Each of the scenarios is risk ranked and deter-mines the provisional risk ranking that ultimatelydetermines the level of scrutiny that the project willentail during its life.

Once tiered, the project team is responsible foraddressing the concerns of the conceptual hazardreview, and then proceeds to more defined and in-depthhazard review studies, the number and depth of whichis determined by its provisional tiering in the concep-tual hazard review. The design for the project was"frozen" at this point and used as the basis for capitalrequests. Any design changes forthcoming in subse-quent reviews should be captured under the contin-gency of the capital request. It should be noted thatlarger capital projects, or projects being tiered moreseverely have an additional review prior to the "designfreeze".

This project underwent another detailed hazardsreview that included basic HAZOP studies, human fac-tors analysis, and a procedural review. Items uncoveredin this phase were addressed prior to startup and wereincluded during the actual construction phase withminimal impact on the capital spending.

A Pre-Startup Safety Review (PSSR) was conductedin which a check list of commonly encountered errorsor omissions is reviewed with operations, maintenance,installers, and the project leaders. This step is oftenused to close out open action items, aids in operatorand maintenance training, ensures final installation perdesign, and documents the instrumentation validationstep prior to the entry of hazardous chemicals into theprocess equipment. The process was then uneventfullystarted and was closely monitored for logic errors andoperability.

Conclusion

It was recommended that the truck unloading stationreceive some additional safeguards above and beyondthe original design intention of the project. This actionwas allowed because of the room left under the capital-


spending request of the original project and is current-ly proceeding. Once completed, a post startup safetyreview will be conducted to ensure that the changeshave not induced another unforeseen process safetyissue and that all "loose ends" of the project areaddressed.

Literature Cited

ANSI K61.1, "Safety Requirements for the Storageand Handling of Anhydrous Ammonia," AmericanNational Standards Institute (1989).

Baldock, P. J., "Accidental Releases of Ammonia: AnAnalysis of Reported Incidents," Loss Prevention,Vol. 13, pp. 35^0 (1980).

Bellinger, R. E. et al., "Inherently Safer ChemicalProcesses," CCPS AIChE, pp. 71-79 (1996).

Deshotels, R. and R. D. Zimmerman, Cost EffectiveRisk Assessment for Process Design, pp. 81-93,95-112, 131-147, and 214-219, McGraw-Hill, NewYork (1995).

Roberts, R.H., and S. E. Handeman, "MinimizeAmmonia Releases," Hydrocarbon Processing,(March 1986).


Documents

Minimizing Off-Site Consequences of Anhydrous Ammonia Systems · the south, east, and west of the plant, but has a ... article was to closely examine its anhydrous ammonia storage