ccps an aiche technology alliancerisk analysis screening tools (rast) overview / demonstration march...

CCPSCenter for Chemical Process Safety

An AIChE Technology Alliance Risk Analysis Screening Tools (RAST) Overview / Demonstration

March 20, 2019 Slide - 1

Risk Analysis Screening Tools (RAST)

Case Study – DPC Industries


An AIChE Technology Alliance

DPC Enterprises – Chorine Release

Festus, Missouri

August 14, 2002




Case Study – DPC IndustriesHazard Identification and Risk Analysis (HIRA) Study

What are the Hazards?

What can go Wrong?

How Bad could it Be?

How Oftenmight it

Happen?

Is the Risk Tolerable?

Identify Chemical

and ProcessHazards

Estimate Frequency

Analyze Consequences

AnalyzeRisk

IdentifyAdditional Safeguards as Needed

DevelopScenarios

Identify Equipment

or Activity to be Analyzed

Manage Barriers

for Life Cycle of Facility

We begin the study by Identifying the Equipment or Activity for which we intend to perform

an analysis. RAST uses the operation of a specific equipment item containing a specific

chemical or chemical mixture to define the activity. For example, the operation of a storage

tank, a reactor, a piping network, etc. Inputs are chemical data, equipment designinformation, operating conditions, and plant layout.





Process DescriptionWe have been asked to perform a HIRA study of a chlorine repackaging facility. The DPC Enterprises

facility in Festus Missouri repackages chlorine from railcars into smaller containers. DPC captures

chlorine vented from these operations in one of two caustic scrubbers that also produce household

bleach for sale as a byproduct.

The chlorine repackaging operation involves the following:

• Connecting a 90-ton (180,000 pounds) chlorine tank car to one of three unloading stations.

• Transferring liquid chlorine from the tank car through the process piping system to filling stations.

• Loading the filled 150-pound cylinders and 1-ton containers onto trucks for distribution.

• Cleaning and preparing empty cylinders and containers for reuse.

In addition to repackaging chlorine, the Festus facility also runs a continuous bleach manufacturing

process. We will start with the chlorine railcar unloading operation

This is an illustrative example and does not reflect a thorough or complete study.





Process DescriptionTank cars are brought into the facility through a

rail spur along the northwest corner of the site. A

storage area located on the eastern side of the

repackaging building contains several bulk

storage tanks of sodium hydroxide (caustic soda),

bleach, and wastewater. The three chlorine tank

car unloading stations are located along the

northern side of the repackaging building.

Pad air is used to help push the liquid chlorine

out of the tank car into the plant piping. An

eduction pipe is used to unload liquid material. It

is a long steel pipe attached to the liquid valve

and extends to the bottom of the tank car.





Process DescriptionEach unloading station is equipped with three chlorine transfer hoses, each approximately 11 feet in

length and 1 inch in diameter. The chlorine system is designed to shut off accidental releases

utilizing chlorine detectors and automatic air-actuated ball valves. These valves may be activated

either automatically or manually by pressing one of several Emergency Shut Dow buttons located

throughout the facility. Hoses remain pressurized to approximately 8 bar (115 psig) throughout

normal operations although flow is stopped during breaks and lunch.






We will start by entering information for chlorine rail car. At some point, we may decide to

include other equipment associated with the facility in the study.

One the Main Menu, enter the equipment identification as the Chlorine Rail Car, equipment

type as Tank Truck/Rail Car/Tote and location as Outdoors.

Chemical Data – RAST requires a chemical or chemical mixture that is representative of the

hazards. RAST does not perform time-dependent or location-dependent composition

changes (such as within a reactor or distillation column). In this example, we will merely

enter chlorine as the chemical.



Import from Previous Study

Merge Data from Another Study into this Study

Update Previously Saved Information

Access LOPA Workbook from Scenario Results

Update Notes and Comments for Entire Workbook

Select Default Units: Study File: Copy of Risk Analysis Screening Tool.xlsm

Session Date: Participants:

Equipment Identification =

Equipment Type =

Equipment Location =

Data Entry Status or Notes:

Plant Section or Sub-Area:

P&ID Number:

Min

Complete

RAST

Input Data Sufficient to Proceed with Analysis

Input Information

Tank Truck/Rail Car/Tote

Outdoors

Chlorine Rail Car

Evaluations and Reports

Risk Analysis Screening Tools (V 2)Latest Revision Date 3/02/19

Import from RAST File

Equipment Parameter Input

Chemical Data Input

Reaction Input and Evaluation

Fire & Explosion Index / Chemical Exposure Index

English Units SI Units

Relief Effluent Screening

Scenario Identification

Check Inputs

Save Inputs toEquipment Table

Go to Equipment Table >

Process Conditions Input

Plant Layout Input

Hazards & Consequences

LOPA Menu >

Clear Input

Update Scenarios for Equipment Loaded

Input Guidance Information

CLEAR EVERYTHING IN WORKBOOK

Pool Fire Evaluation

Merge Data from Another File

Go to Workbook Notes >

Go to Revision Log >

Go To Scenario Results >

Go To Instructions >>


Enter Equipment Identification,

Equipment Type and Location


Case Study – DPC InstrustriesBegin by entering

information on the

Main Menu worksheet.

Start with the Chlorine

Rail Car.





Chemical Data

The chemical name is

entered as chlorine and the

weight fraction as 1.0

The operating pressure was

entered as 8 barg and the

operating temperature is

entered at 25 C. That that

units may be changed such

as an operating pressure of

115 psig and operating

temperature of 77 F.

Chemical Data Input

Equipment Identification: 25 C

Equipment Type: 8 bar

Location: 30.4 C

Key Chemical: Reference:

Chemical Comments:

Reg. Agency Considers Toxic? Yes

ERPG-3 Values, LC1, LC50, and/or Categories for Aquatic Toxicity or Dermal Toxicity must be entered

Chlorine 1.000 1.000 1.0000 70.91 3 20

Sum = 1.00 Vapor Mixture Properties: 70.9 3.0 20.0

Mixture azeotrope? No

Melting Point = -101 deg C

Flash Point = deg C

Est Mixture Flash Point =

1 Not “Sustained Burning”?

AutoIgnition Temperature = deg C

Ease of Ignition =

Fuel Reactivity =

Dermal Toxicity =

Aquatic Toxicity =

Model as a single Pseudo-Chemical? Mixture NFPA Flammability = 0

Mixture NFPA Health = 4

Reactivity Category =

Mixture NFPA Reactivity = 0

Estimated Boiling Point = -34.0 C Liquid Conductivity = Non-Conductive

Vapor Pressure at Operating Temp = 7.709 atm

Liquid Density at Operating Temp = 1.38 gm/ml

Liq Heat Capacity at Op Temp = 0.25

Liq Heat Capacity at Boiling Point = 0.22 micron

Heat of Vaporization at Op Temp = 60 micron

Heat of Vaporization at Boiling Point = 69 mJoule

Boiling Point at Relief Set or MAWP = 79.5 C

Boiling Point at Burst Pressure = 119.4 C

From the above vapor composition: Estimated 1 hour LC 1 74.3 ppm Estimated 1 hour LC 50 404.3 ppm

State Mol Weight ERPG-2 (ppm) ERPG-3 (ppm) LFL (vol %) Flash Pt (C )

Pad Gas Properties Vapor 29

Heat Transfer Fluid

High Viscous Material (for F&EI)?

Mixture Properties

Wt Fraction

Feed

Molecular

Weight

Second Liq

Phase

Relative

Volatility

Wt Fraction

Vapor

User ValuesMixture

Estimates

ERPG-3 (ppm)ERPG-2 (ppm) LFL (vol %)

Liquid

Operating Temperature =

Chlorine

Chlorine Rail Car

Outdoors


Second Liq

Phase

Chemicals (the first chemical listed is the 'key'

chemical)

Wt Fraction

Feed

Saturation Temperature =

Physical State =

Operating Pressure (gauge) =

Solids Mean Particle Size =

cal/gmDust Min Ignition Energy =

Name

Dust-flammable hybrid?

Particle Size at 10% Fraction =

Solids Bulk Density >160 g/liter (>10 lb/ft3)?

Summary of Chemical Properties

cal/gm C

Standard Mixture (the key chemical has been

defined as a mixture)

Dust CharacteristicsDust/Solids Hazard Class =

Go To Process Conditions >Save All Input to Equipment TableEnter New Chemical Clear Input

<< Go To Main Menu

Go To Plant Layout >

Show Chemical Details Hide Chemical Details

Go To Equipment Input >

Saturation temperature is

displayed and physical

state as “liquid”

RAST allows up to 5

components.

Chemical details may

be shown or hidden

The operating pressure

and temperature



Equipment Input

Equipment Identification:

Equipment Type:

Location:

17300 gal Pipe Length = m

375 psi Piping Vulnerable to Damage?

Apply Screwed Connection Penalty?

C

C

1 in Pump Type =

Seal or Containment Type =

Remote Start Pump?

43965 kg Pump Automated Suction or Discharge?

kg Estimated User Entry

Pump Volume (including piping to block valves), liter 0.3

Pump Surface (including piping to block valves), m2 0.06

Kwatt

Equipment or Piping Connection =

76 sq m

sq m Replacement Cost & Business Loss

m Drum Oven Volume = cu m

mm High Speed Rotating Equipment?

Bellows or Expansion Joint Used?

Sight Glass Used?

Relief Device Identification

Relief Type =

Relief Discharges to:

Relief Set Pressure (gauge) = bar

sq m Relief Size (equiv. diameter) = mm

Kwatt /sq m C Relief Design Actual Flow Rate = kg/min

C Release Pipe Diameter = mm

bar Release Elevation m

Closest Distance From Relief to Elevated Work Area = m

Heat Transfer Fluid Name = Furthest Distance from Relief to Elevated Work Area = m

Elevation of Nearest Work Area = m

Enter Distances from Relief Location ONLY if Different from Equipment Location

mm Relief Distance to Property Limit or Fence Line = m

Relief Distance to Occupied Bldg 1 or Area = m

sq m Relief Distance to Center of Occ Bldg 1 = m

Kwatt /sq m C Occ Bldg 2 in Same Wind Direction for Relief?

C Relief Distance to Occupied Bldg 2 = m

Relief Distance to Center of Occ Bldg 2 = m

Piping Parameters

Pump / Agitator Parameters

MAWP (gauge) =

Equipment Description

The tank car was a U.S. Department of Transportation (DOT) 105J500W specification car.

Equipment Volume =


Equipment Parameters

Full Vacuum Rated?

Estimated High Temperature Failure =

Estimated Embrittlement Temperature =

Equipment Elevation to Surface =

Drain Valve Size

Chlorine Rail Car

Outdoors

Susceptible to Vibration Fatigue?

Motor Power =

User Equipment Max. Wetted Area =

Heat Transfer Fluid State =

Vessel/Tank Parameters

Material of Construction

Internal Corrosive or Stress Cracking Potential?

Equipment Mass =

Number of Flanges or Nozzles =

Nozzle or Pipe Size =

Estimated Equip Mass based on C. Steel

Other Equipment Parameters

Transportation Equipment or Piping Parameters

Tube Failure Release to Atmosphere?

Hose

Insulation

Estimated Equipment Max Wetted Area =

Heating Fluid Temperature =

Heating Transfer Area =

Tracing ?

Vessel/Tank Geometry?

Insulation Heat Reduction Factor =

Warning: Operating Pressure Greater than Relief Set Pressure

Low Pressure Tank with Weak Seam Roof?

Coolant Temperature =

Conductive Dip Pipe or Bottom Fill?

Cooling Transfer Area =

Tube (or Leak) Diameter =

Quantity Hot Oil Handled (for F&E) =

Cooling Overall U =

Number of Tubes =

Relief Device Parameters

Heat Transfer Parameters

Heating Overall U =

Heat Transfer Fluid Pressure (gauge) =

Vessel/Tank Considered as "Storage"?

Clear InputSave Input to Equipment Table< Go To Chemical Data

<< Go To Main Menu Go To Process Conditions Input >

Go To Plant Layout >

Go To Reaction Input >



Equipment Input

A chorine rail car contains a

maximum of 82000 kg chlorine

(90 m3 or 17300 gal). The

maximum allowable working

pressure is 26 barg or 375 psig.

Liquid connections are 1 inch.

The equipment volume

and maximum allowable

working pressure

A largest “working” nozzle

of 1 inch is entered

A connection type of “Hose”

is also entered.





Process ConditionsThe maximum flowrate to the

railcar is zero as railcars are

only unloaded at this facility.

A 0.9 maximum fill fraction is

entered as the rail car is

received approximately 90% full

(versus the default 80% if the

entry is blank).

The default ambient

temperature of 25 C has been

assumed (based on no entry for

ambient temperature).

Process Conditions Input


Equipment Type:

Location:

Ambient Temperature = Operating Temperature = 25 C

Inventory Limit (blank is unlimited) = kg Operating Pressure (gauge) = 8 bar

Liquid Head within Equipment, Dh = m Physical State =

Limiting Maximum Fill Fraction = 0.9 Saturation Temperature = 30.4 C

Limiting Minimum Fill Fraction = Contained Mass = 81592 kg

Maximum Feed Press (gauge) = bar Maximum Contained Mass = 90658 kg

Maximum Feed or Flow Rate = 0 kg/min Inventory for Reference = 90658 kg

Maximum Feed Temperature = C

Type of Feed (Batch or Continuous)

Non-Ignitable Atmosphere Maintained?

Potential for Aerosol or Mist?

Pad Gas Name = Percent of Time in Operation =

Max Pad Gas Pressure (gauge)= bar

Maximum Pad Gas Rate = kg/min

Downstream Pressure (gauge) = bar

Maximum Back Flow Rate = kg/min

Equipment Vents to .. =

Use Time-based Release for Equipment Rupture? sec

Chlorine Rail Car


Process Description

The rail cars are only unloaded such that the maximum fill

rate is zero.

Process/Operating Conditions

Outdoors

Summary for Chlorine

Frequent Turnaround or Cleanout?

Operating Procedures

Liquid

Review Date:

Review of Operating Procedures for

Selected Equipment Item by:

Centralized Ventilation Shut-Off Bldg 1?

Centralized Ventilation Shut-Off Bldg 2?

Clear InputSave Input to Equipment Table< Go To Chemical Data

Go To Plant Layout ><< Go To Main Menu

< Go To Equipment Input

Go To Reaction Input >





Site LayoutIn addition to the site office building 50 m

south of the rail car station (~ 5 occupants),

various businesses and residential areas

surround the DPC Festus facility:

• Blue Fountain residential mobile home

park, consisting of about 100 homes, is

approximately 100 m southwest.

• Goodwin Brothers Construction and

Intermodal Tire Retreading are located

about 100 to 200 m to the east, separated

from DPC by Highway 61. Each business

has about 18 full-time employees.

• Interstate 55 is located less than 0.5 mile

to the east Approximately 500 m

Railcar Station



2E-4 people/m2

Residential homes

on very large plots

5E-5 people/m2

Rural homes/farms


Site Layout

March 20, 2019 Slide - 12Approximately 500 m

RAST allows for entry of two offsite

populated areas referred to as Zone 1

and beyond Zone 1. Zone 1 begins at

the “Distance to Property Limit”

extends to “Distance to End of Zone 1”

on the Plant Layout worksheet.

A free software program, MARPLOT

(from the US EPA), may be used to

determine population density in the

United State. Outside the US or

where data is not available from

MARPLOT, the following pictures give

an idea of offsite population density.

Examples of Sparsely populated areas



3E-4 people/m2

Mobile Homes (upper

end of Moderate)

1.5E-3 people/m2

Typical suburban

residential area

5E-3 people/m2

Multifamily dwellings –

multi-story apartments

closely spaced

4E-3 people/m2

Multifamily dwellings

– 2 story apartments

and duplexes

4E-3 people/m2

Very closely spaced

single family dwellings

Examples of Moderately populated areas Examples of Densely populated areas



Site Layout





Site LayoutThe Blue Fountain mobile home park

(noted as Zone 1) is located adjacent to

the DPC property and extends to

approximately 500 m from the rail car

station. The population density is higher

than a typical residential area at roughly

0.003 people/m2. The region beyond

the mobile home park (in the same wind

direction) denoted as beyond Zone 1 is

rural with a very low population density

(maybe 0.00005 people/m2).

The site office and offsite businesses

are entered as occupied buildings.

Plant Layout Input


Equipment Type:

Location:

Distance to Property Limit or Fence Line = 100 m Occupied Building 1 Name =

Furthest Distance to Fence Line ( > 100 m ) = m Distance to Occupied Bldg 1 or Area = 50 m

Max. Onsite Outdoor Population Density people/m2 Elevation of Occ Bldg 1 Ventilation Inlet = m

Personnel Routinely in Immediate Area? Yes Distance to Center of Occupied Bldg 1 = m

Distance to end of Offsite Zone 1 500 m Occupied Bldg Type =

Offsite Population Density within Zone 1 0.003 people/m2 Occupied Bldg Ventilation Rate = changes/hr

Offsite Population Density Beyond Zone 1 0.0001 people/m2 Number of Building Occupants = 5

Effective Egress from Work Area? Occ Bldg 2 in Same Wind Direction? No

Access for Emergency Services? Occupied Building 2 Name =

Degree of Equipment Congestion in Area? Distance to Occupied Bldg 2 200 m

Containment or Dike Surface Area = sq m Elevation of Occ Bldg 2 Ventilation Inlet = m

Consider Dike or Bund Failure for Vessel Rupture? Distance to Center of Occ Bldg2 = m

Credit Fire Heat Adsorption for Drainage/Indirect? Occupied Bldg 2 Type =

Distance to Nearest Fired Equipment = Occupied Bldg 2 Ventilation Rate = changes/hr

Quantity of "Other" Flammables in Immediate Area kg Number of Occupants Bldg 2 = 30

Quantity of Flammables in Adjacent Area kg

Adjacent Containment or Dike Surface Area = sq m

Automated EBVs to limit spill quantity?

Spills to Soil Require Remediation?

Potential for Water Contamination?

Enclosed Process Volume = cu m High Population Downstream of Facility?

Enclosed Process Ventilation = changes/hr

No. Enclosed Area Personnel =

Note that Environmental Scenarios are Excluded

Enclosed Process Area Data

Occupied Building DataLocation Information

Environmental Inputs

Goodwin Bothers/Intermodal Tire

Site Office

Chlorine Rail Car


Outdoors

Layout Description

Clear InputSave Input to Equipment Table< Go To Process Conditions

Go To Reaction Input ><< Go To Main Menu

< Go To Equipment Input

< Go To Chemical Data






Input Data for an Equipment Item

stored in one row by Equipment Tag

Retrieve Information for an Equipment

Item by selecting any cell in the desired

row and entering Load Selected

Select Save Inputs to Equipment Table (blue macro button). All Input Information

will be stored in the Equipment Table in a single row identified by a unique Equipment

Identification or Tag.




Risk Matrix


To understand the Consequence

Severity and Tolerable Frequency, the

values for key Study Parameters and a

Risk Matrix may be viewed on the

Workbook Notes worksheet. These

values may be updated on hidden

worksheets and should reflect the

company’s specific risk criteria.

For this case study, the Risk Matrix

(right) has been used. The Human

Harm criteria is based on an estimated

number of people severely impacted

(severe injury including fatality).

2 3 4 5 6 7

Description Human Harm Environment Business Loss 10^-2/year 10^-3/year 10^-4/year 10^-5/year 10^-6/year 10^-7/year

Reportable Incident to Environmental Agency OR

< 10 kg Very Toxic to Waterway OR < 100 kg NFPA-H4 to Soil

< 100 kg Toxic to Waterway OR < 1000 kg NFPA-H3 to Soil

< 1000 kg Harmful to Waterway OR < 10000 kg NFPA-H2 to Soil

Environmental Contamination Confined to Site OR




Environmental Contamination of Local Groundwater OR




Incident Requiring Significant Off-Site Remediation OR



> 100000 kg Harmful to Waterway OR > 100000 kg NFPA-H2 to Soil

Incident with Significant National Media Attention OR


> 100000 kg Toxic to Waterway OR > 1000000 kg NFPA-H3 to Soil

Acceptable

Tolerable - Offsite

Tolerable - Onsite

Unacceptable

Low

Con

sequ

ence

Hig

h

Con

sequ

ence

Low

Frequency

High

Frequency

Consequence Severity Description Frequency

Severity Level-1

Minor Injury On-site

(or < 0.01 Person Severely Impacted On-site)

Potential for Adverse Local Publicity

Property Damage and

Business Loss < $50M2 Orange Yellow

Green

Green

Yellow> 10 People Severely Impacted On-site

> 1 Person Severely Impacted Off-site

Property Damage and

Business Loss > $50 MM6 Red

Red Red Orange Yellow GreenSeverity Level-41 to 10 People Severely Impacted On-site

0.1 to 1 People Severely Impacted Off-site

Property Damage and

Business Loss $5 MM to

$50 MM

Legend

6

Yellow Green GreenSeverity Level-2

Major Injury On-site

(or 0.01 to 0.1 Person Severely Impacted On-site)

Public Required to Shelter Indoors

(or Minor Injury Off-site)

Property Damage and

Business Loss $50 M to

$500 M

3 Red

Red Orange Yellow GreenSeverity Level-3

Potential Fatality On-site

(or 0.1 to 1 Person Severely Impacted On-site)

or Potential Major Injury Off-site

Property Damage and

Business Loss $5 MM to

$50 MM

4 Red

Severity Level-5

6

Red Orange

5 Red

Risk Matrix: Risk = Consequence Severity times Frequency

Red Red

Green Green Green Green

Orange





Suggested Scenarios for Rail Car

HAZOP Node: HAZOP Design IntentPlant Section =

Equipment Type = Tank Truck/Rail

Car/ToteEquipment Tag = Chlorine Rail Car

LOPA Menu Filters:

Scenario Type Scenario CommentsParameters and

DeviationInitiating Event (Cause) Initiating Event Description Loss Event Outcome

Off

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Damage from Movement

Spill caused by Truck or car

movement while transfer is in

progress

Flow-Loss of

Containment3rd Party Intervention Driver inadvertantly moves truck or car Full Bore Hole Size Leak

Off-Site Toxic Release, On-Site

Toxic Release, Toxic Infiltration6 5 6

Drain or Vent Valve OpenDrain or Vent Valve left open following

loading/unloading or batch transfer

Flow-Loss of

Containment

Human Failure Action more than once

per quarter

Operator leaves Drain or Vent Open

following unloading or clean-outDrain or Vent Leak



Hose or Loading Arm ConnectionSpill associated with improper

connection of hose or loading arm

Flow-Loss of

Containment

Human Failure Action more than once

per quarter

Operator fails to ensure a proper connection

before starting material transferGasket Failure



Piping or Equipment Leak - Full

Bore

Assessment Excludes Mechanical

Integrity Scenarios

Flow-Loss of

ContainmentUnloading/Loading Hose Failure Failure of Hose from fatigue,etc. Full Bore Hole Size Leak



Excessive Heat Input - Heat

Transfer

No Heating Media Temperature was

notedPressure-High BPCS Instrument Loop Failure Failure of Flow Control

Criteria for Triggering Incidents Not

Met

Excessive Pad Gas Pressure

Maximum Pad Gas Pressure Does

Not Exceed the Maximum Allowable

Working Pressure or Relief Set

Pressure

Flow-High Regulator FailureRegulator Fails causing high flow or

pressure


Met

Overfill, Overflow, or Backflow

Overfill or Backflow of liquid with spill

rate equal to the feed rate to a

maximum quantity of the available

inventory minus contained mass

Level-High or Flow-

BackflowBPCS Instrument Loop Failure

Failure of Level Indication with continued

addition of material


Met

Pad Gas Compression

Maximum Feed or Downstream

Pressure does not exceed the

Maximum Allowable Working

Pressure or Relief Set Pressure

Pressure-High BPCS Instrument Loop Failure Failure of Pressure ControlCriteria for Triggering Incidents Not

Met

Vacuum Damage Equipment is rated for Full Vacuum Pressure-LowHuman Failure Action more than once

per quarter

Operator leaves valves closed allowing

vacuum during emptying of equipment


Met

Potential Outcome / Tolerable Frequency Factors

Suggested Scenarios from the RAST Library

Scenarios in gray were

considered but are excluded for

reason noted

Scenarios with NO IPL's Required will NOT be reported.Mechanical Integrity Scenarios will NOT be reported

Chlorine Rail Car is a Tank Truck/Rail Car/Tote containing Chlorine that operates at

25 C and 8 bar. The volume is 18000 gal with a maximum allowable working

pressure of 375 psi. The maximum feed or flow rate is 0 kg/min.

Off

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On

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Update Go To Scenario Results ><< Go To Main Menu

Create UserScenario

Note that Mechanical Integrity (Residual Failures) have been excluded for the listing based on entering “Yes” to

“Exclude MI Scenarios?” on the LOPA Menu worksheet.





Suggested Scenarios for the Rail Car

❑ Review the suggested list of scenarios. Do these represent what you

would expect for a rail car unloading operation?

❑ Are there scenarios that have been “screened out” (shown in gray) that

should be considered?

❑ Are there scenarios missing? (Possibly similar scenarios with different

Initiating Events)

❑ Do you agree with the “worst” Consequence (Tolerable Frequency

Factor) for the scenario listed?





Consequence AnalysisRAST Version 2

Release Location Outdoors

Airborne Quantity Summary:

Release Temperature, C 25.0 Factor Probability

Release Pressure, barg 8.000

Physical State at Release Conditions Liquid

Heat Input, Kcal/min

Equivalent Hole Size, cm 2.540

Release Rate, Kg/sec 5.75

Release Duration, min 60.00

Spray Distance, m 14.0

Flash + Aerosol Evaporation Fraction 0.784

Estimated Aerosol Droplet Diameter, micron 99

Pool Area, sq m 55.9

Estimated Pool Temperature, C -34.4

Maximum Pool Evaporation Rate, kg/sec 1.9973

Total Airborne Rate, kg/sec 6.50

Total Airborne Quantity, Kg 19821.4

Airborne Quantity Composition:

Mole Fraction Chlorine 1.000

Mole Fraction Pad Gas (at Mw = 29)

ERPG-2 for Vapor Composition, ppm by volume 3.2

ERPG-3 for Vapor Composition, ppm by volume 21.2

LC-50 Concentration, ppm by volume 775.7

One-hour ERPG-3 for Vapor Composition, ppm by volume 20.0

One-hour LC-1 Concentration, ppm by volume 74.3

LFL for Vapor Composition, % by volume

Dispersion Summary (Atmospheric Stability Class D with 3 m/sec wind except as noted):

Max Distance to Time-Scaled ERPG-2, m 3428.0

Max Distance to Time-Scaled ERPG-3, m 1327.6

Max Distance to 1% Lethality for 1.5 F weather, m 2717.0

Max Distance to Estimated LC-50 Concentration, m 219.7

Max Distance to Flash Fire Impact or 0.5 LFL, m

Maximum Ground Elevation Concentration, ppm 1000000.0

Concentration at Distance to Fence Line, ppm 3731.7

Concentration at Distance to Unrestricted Work Area, ppm 1000000.0

Concentration within Occupied Bldg 1, ppm 6798.3

Concentration within Occupied Bldg 2, ppm 430.9

Concentration within Enclosed Process Area, ppm

Conc within Enclosed Process Area w/Ventilation, ppm

Potential Toxic

Impact within

Occupied Building

(Indoor Conc > one-

Prob of Exposure (proximity based)

Fence Line

Concentration

Exceeds ERPG-2

On-Site Toxic POE

Flash Fire POE

Physical Explosion POE

Chemical Exposure POE

CONSEQUENCE SUMMARY Date:

Full Bore Pipe or Nozzle LeakLoss Event for: Tank Truck/Rail Car/Tote; Chlorine Rail Car

Containing Chlorine :

Ground or Work Area

Exceeds Multiple of

LFL or Time-Scaled

ERPG-3

with Personnel in Immediate Area

For the Rail Car, select Full Bore

Pipe or Nozzle Leak as the Loss

Event. This provides a “worst”

Consequence for a total hose failure.

The distance to ERPG-2 is estimated

in RAST to be more than 3400 m or

2.1 miles. Adjusting for the actual

1.5 m/sec wind speed at the time of

the incident, the distance to ERPG-2

would have been estimated at 3.0

miles which is in close agreement

with CPB modeling of 3.7 miles.

The leak rate estimated by CSB was

approximately 2 kg/sec, somewhat

less than a full bore failure..

The actual wind speed was nearly 1.5

m/sec. Wind speed, atmospheric

stability, and surface roughness are

Administrative Parameters that may be

adjusted on hidden worksheets.



RAST Version 2

Explosion Summary:

VCE or Building Explosion Energy, kcal

VCE or Building Explosion Distance to 1 psi Overpressure, m

Maximum Distance to LFL Concentration, m

Blast Overpressure at Center of Occupied Building 1, psi 0.0

Blast Overpressure at Center of Occupied Building 2, psi 0.0

Distance to Severe Thermal Radiation Impact, m

Rupture Explosion Energy, kcal

Distance to Direct Blast Impact (10 psi), m

Maximum Fragment Range, m

Rupture Distance to 1 psi Overpressure, m

Rupture Overpressure at Center of Occupied Building 1, psi 0.0

Rupture Overpressure at Center of Occupied Building 2, psi 0.0

Incident Outcome and Consequence Summary:

6

Onsite Toxic Impact based on Distance to LC-50 Concentration of 220 m Yes 5

Outdoor Toxic Exposure Duration 600 sec

Onsite Flash Fire Impact based on Distance to 0.5 LFL Concentration of 0 m NA

Chemical Exposure based on Dermal or Thermal Hazards and Spray Distance of 14 m NA

Onsite Direct Blast Impact based on Distance to 10 psi of 0 m

Onsite Thermal Radation Impact based on Distance from Fireball of 0 m

Occupied Building Toxic Impact Yes 6

Number of Potential Serious Impacts for Building 1: 5 people

Number of Potential Serious Impacts for Building 2: 15.8 people

Occupied Building Impact from Vapor Cloud Explosion No NA



Occupied Building Physical Explosion Impact No



Environmental Impact: NA

Estimated Number of

People Impacted

Probability of Ignition (POI)

Probability of Explosion (POX)

LOPA Tolerable Frequency

Factors Based On

CONSEQUENCE SUMMARY Date:

Full Bore Pipe or Nozzle LeakLoss Event for: Tank Truck/Rail Car/Tote; Chlorine Rail Car

Containing Chlorine :

Impact Assessment with Personnel routinely in the immediate

area

Exceeds Threshold

Criteria

YesOffsite Toxic Impact based on Toxic Integration Method and 100 m to Fence Line



Consequence Analysis

The number of people severely impacted

(likely fatalities) within the occupied

buildings is significant depending on any

evasive actions that many have been taken.

The estimated number of severely

impacted people (potential fatalities) is

greater than 10 for either the offsite

occupied businesses or the trailer park.

Fortunately the wind was away from the

trailer park (and most residents were at

work rather than home) and personnel

within the site office and nearby

occupied buildings were able to

evacuate quickly.

In the actual incident, there were no

fatalities but 63 people sought medical

attention and hundreds sheltered in

place for up to four hours.

The number of people severely impacted is

highly inaccurate and represents a “worst”

case assuming no effective evasive actions

or effective safeguards.



A simplification in RAST is wind

direction toward the highest population.

This is quite reasonable in Risk Analysis

where the wind direction is unknown.

In the actual incident, the wind direction

was toward the east southeast rather

than southwest toward the trailer park or

directly toward the nearby businesses.

Wind Direction represents a key

difference between estimates for Risk

Analysis versus Incident Investigation.



Consequence Analysis

REPORT NO. 2002-04-I-MO , US Chemical Safety Board

Figure 6. Aerial view of DPC Festus facility and surrounding area.

Release Point –

Rail Spot # 3

3 mile radius to ERPG-

2 concentration

Estimated Cloud

plume in RAST



Scenario Definition

Protection

Gap

Scenario /

Cross Ref

Description of Undesired ConsequenceLOPA Tolerable Frequency Factor

(chemicals, quantity involved,

and basis for calculations)

Initiating Event Probability of Ignition Probability of Exposure

(Presence Factor)

Time at Risk or Other

Enabling Factor

New

Instrumented

Protection

Credits

Taken

IPL Status? -->

Safety

AnalysisTolerable Frequency Factor 6 Unloading/Loading Hose Failure

5 1 6 1 0 0

12.01

Failure of Hose from fatigue,etc.

Tank Truck/Rail Car/Tote, Chlorine Rail Car, is involved

in a Piping or Equipment Leak - Full Bore event

resulting in a Full Bore Hole Size Leak with

subsequent 19800 kg airborne release of Chlorine at

an airborne release rate of 390 kg/min.

This incident could result in an Off-Site

Toxic Release at a Distance to ERPG-2

Concentration (HD2) of 3430 m which

exceeds Distance to the Fence Line of 100

m with the potential for Severity Level-5

< Back to Scenario Results

+

Expand All Collapse All

> Human Error ++ +> Possible IPLs



Risk Analysis / Layers of Protection Analysis (LOPA)

The initial Initiating Event description

may be modified by the study team to

more clearly describe what happened

Select Loss Event Piping or

Equipment – Full Bore with

Incident Outcome of Off-Site Toxic

for analysis in LOPA (“Yes”), then

select LOPA Worksheet






A time at risk enabling condition of the leak occurring only during a 2000 hour operation per 8760

hour year may be appropriate as the hoses are checked daily for leaks. A conditional modifier for

personnel presence to represent that most trailer park occupants are not present during weekdays

may also be appropriate. The combination of these factors could reduce the scenario frequency or

severity of consequences by a factor of 10 depending on company specific protocol.

Scenario Definition

Protection

Gap

Scenario /

Cross Ref

Description of Undesired ConsequenceLOPA Tolerable Frequency Factor

(chemicals, quantity involved,

and basis for calculations)

Initiating Event Probability of Ignition Probability of Exposure

(Presence Factor)

Time at Risk or Other

Enabling Factor

New

Instrumented

Protection

Credits

Taken

IPL Status? -->

Safety

AnalysisTolerable Frequency Factor 6 Unloading/Loading Hose Failure

USER DEFINED Enabling

Factor = 1

1 1 6 1 0 0 1

12.01

Failure of Hose from fatigue,etc.

Tank Truck/Rail Car/Tote, Chlorine Rail Car, is involved

in a Piping or Equipment Leak - Full Bore event

resulting in a Full Bore Hole Size Leak with

subsequent 19800 kg airborne release of Chlorine at

an airborne release rate of 390 kg/min.

This incident could result in an Off-Site

Toxic Release at a Distance to ERPG-2

Concentration (HD2) of 3430 m which

exceeds Distance to the Fence Line of 100

m with the potential for Severity Level-5

The hose is leak checked

prior to each use such that a

time at risk may be

appropriate. 2000 hours use

per year operation of 8760

hours or 23% of time. As the

greatest risk is likely the

trailer park, greater than

40% of residents are not

home during repackaging

operation. Total factor 0.4

< Back to Scenario Results

+

Expand All Collapse All

> Human Error ++ +> Possible IPLs






The existing safeguards may not have been sufficient for managing this scenario to a tolerable risk

level. The chlorine sensor system is shared between the BPCS alarm and a SIL-2 SIS interlock but

may not have been designed to this level of reliability. The block valves could be operated manually

or via an emergency shutdown “button” but may be the same values for both the BPCS and the SIL-2

SIS and not be sufficiently reliable. Finally, the Excess Flow Valve may not effective as it addresses

leaks less than 15000 lb/hour for which there remains a significant consequence severity.

BPCS Control or

Human Response

to Alarm

BPCS Control or

Human Response

to Alarm

SIS Function A SIS Function BPressure Relief Device SRPS 1 SRPS 2 SRPS 3

Human Response to

Abnormal Condition Alarm >

1/4 hr to respond

SIS - SIL 2

1 2

Excess flow valve closes at

15,000 lb/hour chlorine flow.

However leak rate of less than

15,000 lb/hour is not likely

sufficient to reduce the

consequence by one severity

level (or 0.1)

Notes / Comments Issues to Resolve

Operator responds to audible

alarm from chlorine detectors

at 5 ppm and closes a manual

valve.

Chlorine detectors close

automated block valves when

the concentration reachess 10

ppm.

Not Allowed

+ + + +





Case Study – DPC IndustriesRisk Analysis and Incident Investigation often use similar methods to better

understand the scenario. Risk Analysis “anticipates” what could go wrong

and what the potential consequences may be. For Incident Investigation, the

Incident Outcome and Consequences are known in addition to the actual

weather conditions and wind direction.

For the Chlorine Rail Car, RAST did suggest hose failure as one of many

scenarios to consider. RAST also recognized that an Off-Site Toxic Impact

could be a feasible Incident Outcome for this loss event. RAST was

conservative in estimating the number of people severely impacted as actual

wind direction was not toward the highest population. However, the “order of

magnitude” estimate of consequences seems reasonable.



Questions?


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