RBI Consequence Analysis
Nature of RBI Consequence Analysis
 Coarse consequence analysis
 Intended for relative consequence measures
 Release rates and quantities calculated in
software
 Dispersion and consequences determined from
DNV software
Consequence Measures
Personnel
Injury
TOXIC AREA
FLAMMABLE AREA
Equipment
Damage
Phases of a Leak
1
2
Discharge
3
Ignition
(Flammables)
Dispersion
4
Consequence
high pressure
low pressure
ATMOSPHERE
A Leak Develops, With A
Defined Hole Size
EQUIPMENT
GAS
LIQUID
FLUID DISCHARGES THROUGH THE ORIFICE
Types of Effects from Releases
VCE
FLASH FIRE
FIREBALL
TOXIC EXPOSURE
SAFE DISPERSION
INSTANTANEOUS GAS
POOL FIRE
SAFE DISPERSION
INSTANTANEOUS LIQUID
VCE
FLASH FIRE
JET FIRE
TOXIC EXPOSURE
SAFE DISPERSION
CONTINUOUS GAS
JET FIRE
POOL FIRE
SAFE DISPERSION
CONTINUOUS LIQUID
Critical Factors in Consequence
Analysis
• TYPE of release
• PHASE in environment
• Discharge Rate/Mass
(pressure, volume)
• Duration, if toxic
What Causes an Undesirable
Consequence?
• HEAT from burning destroys equipment,
injures people
• PRESSURE WAVE from rapid burning
knocks down structures and people, causes
flying objects
• TOXIC cloud, for some duration, causes
toxic exposure injuries
Representative Hole Sizes
RBI approach tries to model full range of
leak/break sizes:
–1/4 inch
–1 inch
–4 inch
–rupture
RBI COMBINES ALL
FOUR HOLE SIZE
RESULTS INTO ONE
CONSEQUENCE
MEASURE
Program Settings
ESTABLISHES THE BASES FOR
CONSEQUENCE RESULTS
• Equipment Damage Area
• Potential Fatality Area
• Toxic Area
• Maximum
Consequence Calculation
Physical Properties
Process Information
Equipment Information
Calculate Release Rate or Release Mass
Assess Incident Outcome
Flammable
Effect Model
Toxic
Effect Model
Environmental
Effect Model
Financial Risk
Effect Model
Estimate
Consequences
(Sq. Ft.)
Estimate
Consequences
(Sq. Ft.)
Estimate
Consequences
($ Cost)
Estimate
Consequences
($ Loss)
Representative Fluids
 C1 - C2
 C3 - C5
 C6 - C8
 C9 - C12
 C13 - C16
 C17 - C25
 C25+
 hydrogen
 hydrogen sulfide
 hydrogen fluoride
 water
Pressure, Temperature
Inside Equipment
Total Mass Available
for Release
Release Rate
Determine
Type
CONTINUOUS
Use Flow Rate
INSTANTANEOUS
Use Total Mass
Determine
Final Phase
Determine
Final Phase
Continuous
Liquid
Release Duration
Continuous
Gas
Instantaneous
Liquid
Instantaneous
Gas
For the selected
TYPE and PHASE
Toxic Consequence
Flammable Consequence
Determining the Type of Release
Total Mass
Available
for Release
FIND THE TOTAL TIME
TO DEINVENTORY
Is the hole size
> 1/4 “
Release
Rate
NO
YES
Find the amount released in the
first 3 minutes
YES
Can more than 10,000
lbs. escape in the first
3 minutes?
INSTANTANEOUS
NO
CONTINUOUS
Assessing Post-Leak Response
 Rate the detection, isolation system
 Leak duration used in toxic calculation
Estimating Mass Available for Release
(Optional)
Inventory Group Approach
 Add together the masses of fluid for all of the vessels
 Add together the masses of each representative fluid in
each inventory group, regardless of phase
Release Mass Categories
< 100 lbs
Release resulting in less than the total
de-inventory of the equipment item being evaluated.
100 - 1,000 lbs
Release resulting in total de-inventory of the
equipment item being evaluated.
1,000 - 10,000 lbs
Release resulting in total de-inventory
of the equipment item being evaluated
plus one to ten other equipment items.
10,000 - 100,000 lbs
Release resulting in total de-inventory
of the equipment item being evaluated
plus ten or more other equipment items.
> 100,000 lbs
Release resulting in total de-inventory of the unit.
Detection System Rating Guide
Type of Detection System
Detection
Classification
Instrumentation designed specifically to detect
material losses by changes in operating
conditions (i.e., loss of pressure or flow) in the system.
A
Suitably located detectors to determine when the
material is present outside the pressure- containing envelope.
B
Visual detection, cameras, or detectors with
marginal coverage.
C
Isolation System Rating Guide
Type of Isolation System
Isolation
Classification
Isolation or shutdown systems activated directly
from process instrumentation or detectors, with
no operator intervention
A
Isolation or shutdown systems activated by
operators in the control room or other suitable
locations remote from the leak
B
Isolation dependent on manually-operated
valves
C
Special Case: Fluids Above AIT
• Fluids released at a temperature above AIT
are much more likely to ignite
• Treated conservatively in RBI
• P(ignition) = 1 for these cases
• Resulting outcome is fireball (instantaneous)
or jet fire (continuous)
Data Entry
• May be necessary to split large or
complex vessels into two pieces
different damage mechanisms
different fluid types
different fluid phases
nomenclature
Pressure and Temperature Entry
Pressure and
Temperature
Considerations
Column Top
•
•
Columns
Column Bottom
Use pressure for column half
Use average temperature that half
Pressure and Temperature Considerations
•
•
Use pressure for shell
Use average temperature across
inlet and outlet
Shell Side
•
•
Heat Exchanger
Tube Side
Use pressure for tubes
Use average temperature across
inlet and outlet
Pressure and Temperature Considerations
•
•
Pumps
Use outlet conditions for pressure
and temperature
Assume pump diameter is that of
inlet
Pressure and Temperature Considerations
•
•
Pipes, Furnaces, Other Vessels
Use pressure from process
Use average temperature across
inlet and outlet
Representative Fluid
• Must choose one fluid to represent all
fluids in an equipment
• May be necessary to split vessels that
have dramatically different fluids
Choosing a Representative Fluid
• Work with the fluid in the largest proportion, on
a mass basis
• Try to match molecular weight and normal
(atmospheric) boiling point
• Allowance is made in the software to input a
stream with some percent toxic
• Flammable consequences not very sensitive to
exact fluid match
Initial Fluid State
• Liquid or gas only
• Phase of fluid INSIDE EQUIPMENT
Determining the Final Phase
Phase of Fluid at
Steady-State
Operating Conditions
Phase of Fluid at
Steady-State Ambient
Conditions
Final Phase in
Consequence
Calculation
GAS
GAS
GAS
GAS
LIQUID
GAS
LIQUID
GAS
GAS, unless fluid
NBP is >80° F, then
LIQUID
LIQUID
LIQUID
LIQUID
Toxic Model
• Three choices
none
H2S
HF
• Input must be between 0 and 1
(i.e. 20 % = 0.20)
Estimating the Amount of Fluid
Available for Release
F
INVENTORY
GROUP
A
E
B
C
D
G
H
Assessing Post-Leak Response
• Rate the detection, isolation system
• Program will estimate duration of
leak, based on the BRD
• Duration used mainly in toxic
calculation
Adjustments for Detection and
Isolation
 Same as shown in BRD
 Adjustments based on ratings of isolation
and detection, only
 Fire water deluge, inventory blowdown
not credited
Adjustments for Detection and
Isolation Systems
Detection
Isolation
A
A
A or B
B
C
A
B
C
B
C
Release
Reduction
25%
20%
10%
15%
none
Consequence Results
• Maximum consequence will be used
• Program will display results from all three
consequence measures
• Only one of the three measures is used to
estimate consequence category - the one
selected at startup
Consequence Rating
Consequence Area
(sq. ft.)
0 - 10
10 - 100
100 - 1,000
1,000 - 10,000
>10,000
Consequence
Rating
A
B
C
D
E