Depressurization in fire
Breaking fallacies about API 521 15min to 50% rule.
Muhammad Saim
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Introduction
Muhammad Saim, is a Technical Safety & Loss
Prevention Engineering Consultant with more than
20 years’ experience in E&P, Chemical and Energy
sector.
Saim is working as a consultant since 2014,
previously he had worked with PDO, BP & Engro
Corporation.
Experienced in QRA, Fire, Explosion and Toxic
Hazard Management, Buildings Risk Assessment,
Hazard Analysis and Risk Assessment studies, HAZID,
HAZOP, SIL, SIMOPS, Bow-Ties etc.
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
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Introduction
Process Safety Management
Implementation Assistance & Audit
Qualitative Risk Assessments
HAZID, HAZOP, LOPA, SIMOPS, Bow-ties
Quantitative Risk Assessments
QRA, Buildings Risk Assessments
Fire, Explosion & Toxic Hazard Management
Fire Protection Engineering, F&G Detectors 3D
Mapping, Fire Pre-Plans, Escape, Evacuation
and Rescue Analysis, Emergency Systems
Survivability Analysis
Process Safety Engineering
Hazardous Area Classification, SIL Verification
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Introduction
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Poll 1
Emergency depressurization/blow-down system are
designed to depressurize
A. to 50% of Design Pressure in 15 min
B. to 100 Psi (690Kpa) in 15min
C. at rates determined based on scenario analysis
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Emergency depressurization scenarios?
Emergency depressurization is needed due to one or
more of the following reasons:
1. To reduce failure potential of pressure vessels
due to heat (exposed to external fire)
2. Reducing fuel to fire (for jet fire control)
3. Others – e.g. runaway reactions
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1- Pressure vessels protection
“
a vapor depressuring system should have adequate
capacity to permit reduction of the vessel stress to a
level at which stress rupture is not of immediate
concern” API 521 - 4.6.6
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
1- Pressure vessels protection
Pipe & Vessel Stress, ƒ(P) << UTS, ƒ(1/T)
100
90 Material UTS
(decreases with increasing temperature)
80
70
Pipe Stress and UTS
60 Rupture
50
40
30
20
10
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41
Time-Temperature
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
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1- Pressure vessels protection
Pipe & Vessel Stress, ƒ(P) << UTS, ƒ(1/T)
100
Material UTS
90
(decreases with increasing temperature)
80
Pipe Stress and UTS
70
Rupture
60
50
Pipe Stress, ƒ(P)
40
30
20
10
0
1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142
Time (Temperature) in fire
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
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1- Pressure vessels protection
Pipe & Vessel Stress, ƒ(P) << UTS, ƒ(1/T)
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
1- Pressure vessels protection – Jet Fire Case
Depressurization rate for Jet Fire???
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Types of fires
• Open pool fire: 50 kW/m2 to 150 kW/m2
(15,850 Btu/h·ft2 to 47,550 Btu/h·ft2).
• Confined pool fire: 100 kW/m2 to 250 kW/m2
(31,700 Btu/h·ft2 to 79,250 Btu/h·ft2).
• Jet fire: 100 kW/m2 to 400 kW/m2
(31,700 Btu/h·ft2 to 126,800 Btu/h·ft2).
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
1- Pressure vessels protection – Jet Fire Case
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2- Reducing fuel to fire (for jet fire control)
• Isolation and depressurization is most effective tool against jet fires
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Estimated Time to Failure
CCPS Guidelines for Fire Protection in Chemical, Petrochemical, and Hydrocarbon Processing Facilities
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2- Reducing fuel to fire (for jet fire control)
OP: 1000 Psig
Initial flame length 10m
(25mm hole) : 23m
Pipe rack
Flare Header
Flare Stack
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
2- Reducing fuel to fire (for jet fire control)
Internal Pressure vs Flame Length
1200 25
23
22 Flame length, m
1016 21 Pressure, Psig
1000
19 20
18
17
800 16
15
14 15
13
12
Psig 600 11 meter
11
10
486 9 10
437
400 393
354
319
287
258
232 5
200
0 0
Depressurization Time
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
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Estimated Time to Failure
CCPS Guidelines for Fire Protection in Chemical, Petrochemical, and Hydrocarbon Processing Facilities
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
2- Reducing fuel to fire (for jet fire control)
Internal Pressure vs Flame Length
1200 25
23
22 Flame length, m
1016 21 Pressure, Psig
1000
19 20
18
17
800 16
15
14 15
13
12
Psig 600 11 meter
11
10
486 9 10
437
400 393
354
319
287
258
232 5
200
0 0
Depressurization Time
Time available for depressurization: 3 – 4 min
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2- Reducing fuel to fire (for jet fire control)
Internal Pressure vs Flame Length
1200 25
23 23 23 23 23 23 23 23 23
22 Flame length, m
1016 1016 1016 21 Pressure, Psig
1000 19 20
914 18
17
800 823 16
15
Time for fire detection and initiation 740 14 15
666 13
of isolation and blowdown 12
Psig 600 600 11 meter
11
540 10
486 9 10
437
400 393
354
319
287
258
2325
200
0 0
Depressurization Time
TD+I + T BD = 3 ~ 4 min
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Time for fire detection and initiation of Blow down
• Fire detector which auto triggers ESD & BD: 75sec – 120sec
• Fire detector with initiation of remote ESD & BD by operator: 5 ~ 10
minutes
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2- Reducing fuel to fire (for jet fire control)
Internal Pressure vs Flame Length
1200 25
23 23 23 23 23 23 23 23 23
22 Flame length, m
1016 1016 1016 21 Pressure, Psig
1000 19 20
914 18
17
800 823 16
15
Time for fire detection and initiation 740 14 15
666 13
of isolation and blowdown 12
Psig 600 600 11 meter
11
540 10
486 9 10
437
400 393
354
319
287
258
2325
200
0 0
Depressurization Time
TD+I + T BD = 3 ~ 4 min
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
1- Pressure vessels protection
Pipe & Vessel Stress, ƒ(P) << UTS, ƒ(1/T)
Depressurization rate: (15 – TD+I) minutes to
50% of DP
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1- Pressure vessels protection – Jet Fire Case
TD+I + TD
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Poll 2
Question: What is fire detection philosophy at your plant?
A. Automatic shutdown & Blow-down upon fire detection 2ooN
B. Fire detection and initiation of remote shutdown and blow-down by
operator in control room
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
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Cautions – fast blow-down
Relief header capacity
Low temperature/brittle fracture
High Velocities/internals damage
Depressurization in Fire Muhammad.Saim@shepherdrisk.com
Fire Escalation Control
Active &
Fire
passive fire
detection &
protection response
Relief
Layout & system
Spacing size
Fire
protection
philosophy
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Thank you for listening
Questions?
Muhammad.Saim@shepherdrisk.com
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