Conse Anal MB

8/6/2019 Conse Anal MB

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Consequence AnalysisConsequence Analysis

AAPPI RecommendationsI Recommendations

Mieczysaw BorysiewiczMieczysaw Borysiewicz

Centrum Doskonaoci MANHAZCentrum Doskonaoci MANHAZ


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The consequences of releasing a hazardous

fluid are estimated in seven distinct steps:

a. Determining representative fluid and its

properties;

b. Selecting a set of hole sizes, to find the

possible range of consequences in the risk

calculation;c. Estimating the total amount of fluid available

for release;d. Estimating the potential release rate;


ADI RecommendationsADI Recommendations


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ADI RecommendationsADI Recommendationse. Defining the type of release, to determine

the method used for modeling the dispersionand consequence;

f. Selecting the final phase of the fluid, i.e., aliquid or a gas;

g. Evaluating the effect of post-leak response;h. Determining the area potentially affected by

the release, or the relative cost of the leakdue to down time or environmental clean up.


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Flammable consequence results are not highly

sensitive to the exact material selected, provided

the molecular weights are similar, because air

dispersion properties and heats of combustion aresimilar for all hydrocarbons with similar

molecular weights. This is particularly true for

straight chain alkanes, but becomes less true as

the materials become less saturated or aromatic.


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Pipe Hole Size SelectionPipe Hole Size Selection

Piping uses the standard four hole sizes: -inch, 1 - inch, 4 - inch, and rupture,

provided the diameter of the leak is less

than, or equal to, the diameter of the pipe

itself.


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Pressure VesselPressure Vessel

Hole Size SelectionHole Size SelectionPressure vessels assume the standard four hole sizes for allsizes and types of vessels. Equipment types included in this

general classification are: Vessel- standard pressure vessels such as KO drums,

accumulators, and reactors.

Filter- standard types of filters and strainers. Column - distillation columns, absorbers, strippers, etc.

Heat Exchanger Shell- shell side of reboilers,

condensers, heat exchangers. Heat Exchanger Tube - tube side of reboilers,

condensers, heat exchangers.

Fin/Fan Coolers - fin/fan - type heat exchangers.


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Hole Sizes Used in QuantitativeHole Sizes Used in Quantitative

RBI AnalysisRBI Analysis


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Pump Hole Size SelectionPump Hole Size Selection

Pumps are assumed to have three possible

hole sizes: - inch, 1-inch, and 4-inch. If

the suction line is less than 4 inches, the last

possible hole size will be the full suctionline diameter.


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Compressor Hole Size SelectionCompressor Hole Size Selection

Both centrifugal and reciprocatingcompressors use two hole sizes: 1-inch and

4-inch (or suction line full bore rupture,whichever is the smaller diameter).


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Atmospheric Storage Tank HoleAtmospheric Storage Tank Hole

Size SelectionSize SelectionAtmospheric storage tanks have unique

features requiring special hole sizes. They areusually surrounded by a berm, creating a

secondary containment area for leakage. The

floor of the tank may leak for extended periods

of time before detection, leading to underground

contamination.

A h i S k l


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RBI assumes that these tanks are at least partially

aboveground, and that the time to detect a leak is

dependent on detection methods. Because of the abovefeatures and limitations, the following hole sizes and

locations are assumed for atmospheric storage tanks:

a. - inch, 1- inch, and 4 - inch leaks from above-ground sides of the tank.

b. Tank rupture from the walls or from the floor,

provided the floor rupture can flow freely onto theground around the tank.

c. - inch and 1- inch leaks in the floor of an

atmospheric storage tank.

Atmospheric Storage Tank HoleAtmospheric Storage Tank Hole

Size SelectionSize Selection


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Liquid SystemsLiquid Systems

Examples of liquid systems may include:

The bottom half of a distillation column, its reboiler,

and the associated piping. An accumulator and its outlet piping.

A long feed pipeline.

A storage tank and its outlet piping. A series of heat exchangers and the associated piping.

Once the liquid piping and equipment groups areestablished, then add the inventories for each item to

obtain the group inventory. This liquid inventory would

be used for each equipment item modeled from thatgroup.


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Estimating The Release RateEstimating The Release Rate

a. Instantaneous - also called a puff release.

b. Continuous - also known as a plume release.

Release rates depend upon the physical

properties of the material, the initial phase, and theprocess conditions.

Determining The Type OfDetermining The Type


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Determining The Type OfDetermining The TypeReleaseRelease

D t i i Th Fi lD t i i Th Fi l


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Determining The FinalDetermining The Final

Phase Of The FluidPhase Of The Fluid

E l ti P tEvaluating Post L kLeak


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Evaluating PostEvaluating Post--LeakLeak

ResponseResponse

Approach To Evaluating Post-Leak Response

Two key parameters are determined in the post-leak response evaluation: release duration and

reduction of the spread of hazardous materials.

Release duration is a critical parameter in toxic andenvironmental consequence evaluations. Flammable

materials quickly reach steadystate concentrations,

therefore, duration is not a significant factor forflammables. Business interruption risks are estimated

directly from flammable consequence results so they,

too, are not highly sensitive to the leak duration.

Evaluating PostEvaluating Post LeakLeak


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For these reasons, different approaches are necessary

for evaluating the post-leak response for the 4 types

of consequences analyzed in RBI.Flammable Releases

For the release of flammable materials, isolation

valves serve to reduce the release rate or mass by a

specified amount, depending on the quality of these

systems.Toxic Releases

Release duration is estimated from the types of leak

detection and isolation systems.


ResponseResponse

Evaluating PostEvaluating Post LeakLeak


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Releases to the EnvironmentEnvironmental consequences are mitigated in two

ways: physical barriers act to contain leaks on-site,

and detection and isolation systems limit the duration

of the leak.

Assessing Post-Leak Response SystemsAll petrochemical processing plants have a variety of

mitigation systems that are designed to detect, isolate,

and reduce the effects of a release of hazardousmaterials. RBI has developed a simplified

methodology for assessing the effectiveness of

various types of mitigation systems.


ResponseResponse

Fl bl /E l iFl bl /E l i


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Flammable/ExplosiveFlammable/Explosive

ConsequencesConsequencesPotential release outcomes for flammable

materials are:

Safe Dispersion (SD).

Jet Fire (JF).

Vapor Cloud Explosion (VCE).

Flash Fire (FF).Fireball (BL).

Liquid Pool Fire (PF).

Fl bl CFlammable Consequence


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Flammable ConsequenceFlammable Consequence

Analysis ProcedureAnalysis ProcedureThe consequence results are derived using the following steps:

Step 1.Note the type of release and the phase of dispersion.

Step 2. Choose the appropriate table, based on the type of

release:

Table 7-8 for continuous type releases where autoignition is not likely.

Table 7-9 for instantaneous type releases where auto

ignition is not likely. Table 7-10 for continuous type releases where auto

ignition is likely.

Table 7-11 for instantaneous type releases where autoignition is likely.


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Analysis ProcedureAnalysis ProcedureThe consequence tables referred to in the above procedure

were derived using the following 3-step process:

Step 1. Predicting the probabilities of various outcomes

Step 2. Calculating the consequences for each type of

outcome.Step 3. Combining the consequences into a single

probability - weighted empirical equation.

Step 1 - Predicting Probabilities of Flammable

Outcomes


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Analysis ProcedureAnalysis ProcedureStep 2 - Calculating Consequences for EachOutcome

Equipment Damage Criteria:

Explosion Overpressure - 5 psig.Thermal Radiation - 12,000 BTU/hr-ft2 (jet

fire and pool fire).

Flash Fire - 25% of the area within the lower

flammability limits (LFL) of the cloud when

ignited.


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Analysis ProcedureAnalysis ProcedurePersonnel Fatality Criteria:

Explosion Overpressure - 5 psig.

Thermal Radiation - 4,000 BTU/hr-ft2 (jet fire,

fireball, and pool fire).

Flash Fire - the LFL limits of the cloud when

ignited.



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Analysis ProcedureAnalysis ProcedureThe consequence equations are presented in thefollowing form:

A = a x b

where

A = consequence area (ft2),

a,b = material and consequence dependent

constants,

x = release rate (lb/sec for continuous) or release

mass (lb for instantaneous).


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Assumptions andAssumptions and


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ppLimitationsLimitations

The consequence area does not reflect where the damage

occurs. Jet and pool fires tend to have damage areas localized

around the point of the release, but vapor cloud explosions

and flash fires may result in damage far from the releasepoint.

The use of a fixed set of conditions for meteorology and

release orientations is a great simplification over detailedconsequence calculations because these factors can have a

significant impact on the results.

The use of the standardized event trees for consequenceoutcomes and ignition probabilities is a limitation of the RBI

method. These factors are very site-specific, and the user

needs to realize that they are chosen to reflect representativeconditions for the petrochemical industry.

Toxic ConsequencesToxic Consequences


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Toxic ConsequencesToxic Consequences

Toxic fluids are similar to flammables in

that not all toxic releases result in a single type

of effect. On the other hand, some toxic

materials such as hydrogen sulfide (H2S) are

both toxic and flammable.

Scenario DevelopmentScenario Development


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Scenario DevelopmentScenario Development

The selection of scenarios follows the

methodology presented for flammable

consequences, using - inch, 1 - inch, 4 - inch

and rupture hole sizes.

Material ConcentrationMaterial Concentration


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Material Concentration

CutCut--OffOffAs a general rule, it is not necessary to

evaluate a toxic release if the concentration ofthe material within the equipment item is at or

below the IDLH (Immediately Dangerous to

Life or Health) value.

Release Rate/MassRelease Rate/Mass


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Release Rate/MassRelease Rate/Mass

For continuous releases, the discharge rate

should be calculated for flammable case.

Release DurationRelease Duration


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Release DurationRelease Duration

The duration of a release depends on the

following:

The inventory in the equipment item and

connected systems;

Time to detect and isolate;

Any response measures that may be taken.

Release DurationRelease Duration ContCont


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Release DurationRelease Duration ContCont..

For RBI, the maximum release duration is set at one

hour, for the following two reasons:

It is expected that the plants emergency

response personnel will employ a shutdown

procedure and initiate a combination ofmitigation measures to limit the duration of a

release.

The HF toxicity data used in estimating the

toxic dose effect are based on animal tests

ranging from 5 minutes to 60 minutes induration.

Toxic Impact CriteriaToxic Impact Criteria


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Toxic Impact CriteriaToxic Impact Criteria

For toxic vapor exposure, the probit (a shortened form

of probability unit) is represented as follows:

Pr = A + B ln (CNt)

where

Pr= a measure of the percentage of the populationthat sustains a certain level of harm,

C= concentration (ppm),

t= exposure duration (minutes),A,B,N = mathematical constants used to formulate

the probit equation, each toxic fluid has its own

A, B, and N.

Consequence EstimationConsequence Estimation


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Consequence EstimationConsequence Estimation

A consequence analysis tool was used for a

range of release rates and durations to obtain

graphs of toxic consequence areas. Release

durations of instantaneous (less than 3 minutes),

5 minutes (300 sec), 10 minutes (600 sec), 20minutes (1200 sec), 40 minutes (2400 sec), and 1

hour (3600 sec) were evaluated to obtain toxic

consequence areas for varying release rates.

Consequence AreaConsequence Area


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Consequence AreaConsequence Area ContCont..


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Ammonia/ChlorineAmmonia/Chlorine


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ModelingModeling

Ammonia/ChlorineAmmonia/Chlorine


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ModelingModelingFor instantaneous release cases, four

masses of ammonia and chlorine were modeled(10, 100, 1,000, and 10,000 lb), and the

relationship between inventory mass and are toprobit five was found to be:

A = 14.97 x

1.177

for chlorine, andA = 14.17 x0.9011 for ammonia.

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