Fireproofing Critical Electrical & Instrumentation Kris Thorsteinsson
E & I Thermal Damage Criteria Radiant Heat Flux &/or Temperature Damage or failure threshold criteria can be specified as either:
temperature of a hot gas layer or fire plume, or
radiant heat flux from the luminous flame and/or smoky zones of a fire
The following four (4) slides show:
Structural Steel Thermal Damage Criteria (one table)
E & I Cables Thermal Damage Criteria (three tables)
Conclusion – cables are more vulnerable than steel to temperature and radiant heat flux:
Cables are damageable at < 12.5 kW/m2 vs. steel > 37.5 kW/m2,
Cables are damageable at approx. 250°C / 480°F vs. steel @ 538°C/1000°F
The next two (2) slides show results of pool fire modeling of a hexane spill:
6 m diameter spill with 2 m/s wind;
17.2 m diameter API 521 fire with little wind
Conclusion – fire hazard zones for cables extend further horizontally and vertically than for structural steel
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Steel Thermal Damage Criteria Radiant Heat Flux &/or Temperature Structural Steel Thermal Damage Threshold Criteria Equipment Type
Radiant Heat Criteria***
process equipment and 37.5 kW/m2 (3.3 Btu/ft2-s) steel beams uninsulated steel 35-37.5 kW/m2 (3.1-3.3 columns & beams Btu/ft2-s)* steel structures & 37.5 kW/m2 (3.3 Btu/ft2-s) equipment process equipment
Exposed Temperature Criteria***
references
(60 min. exposure)
Alderman 2007
593°C (1100°F)*
Barry 2003 Technica 1988
37.5 kW/m2 (3.3 Btu/ft2-s)
process equipment & 44 kW/m2 (3.9 Btu/ft2-s) vessels steel members 50 kW/m2 (4.4 Btu/ft2-s)** theoretical maximum steel members design 25 kW/m2 (2.2 Btu/ft2-s)** w/ safety factor
BS 5908 IP 1993 540°C (1000°F)**
EPC 2007
410°C (770°F)**
EPC 2007 Robertson 1976 / Wells 1980
storage tanks
37.8 kW/m2 (3.3 Btu/ft2-s)
pipe / riser / process vessel rupture
37.5 kW/m2 (3.3 Btu/ft2-s)
(60 min. exposure)
DNV 2009
steel beam yield
37.5 kW/m2 (3.3 Btu/ft2-s)
(60 min. exposure)
DNV 2009
steel beam collapse
37.5 kW/m2 (3.3 Btu/ft2-s)
(120 min. exposure)
DNV 2009
Notes *10-15 minute exposure time ** Indefinite exposure time *** Consider time to damage
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E & I Cables Thermal Damage Criteria Radiant Heat Flux &/or Temperature E & I Thermal Damage Threshold Criteria Equipment Type
Radiant Heat Criteria***
Exposed Temperature Criteria***
references
205°C (400°F) EPRI 2010 thermoplastic cables* 6 kW/m2 (0.5 Btu/ft2-s) 2 2 330°C (625°F) EPRI 2010 thermoset cables* 11 kW/m (1.0 Btu/ft -s) 2 2 65°C (150°F) EPRI 2010 electronics 3 kW/m (0.25 Btu/ft -s) Flamtrol XLPE, 12 385-388°C (725-730°F) EPRI 2010 AWG, I/C, 600 V** plastic-insulated and Mecklenburgh 1985 12 kW/m2 (1.1 Btu/ft2-s) 120-140°C (250-285°F) clad E&I cables plastic tubing melting, Technica 1988 / CCPS 12.5 kW/m2 (1.1 Btu/ft2-s) wood ignition 2000 severe damage to Robertson 1976 / Wells 12.6 kW/m2 (1.1 Btu/ft2-s) property & cables 1980 electrical failure non130°C (265°F) Sandia 1983 8 kW/m2 (0.7 Btu/ft2-s) qualified cable electrical failure IEEE 250°C (480°F) Sandia 1983 18 kW/m2 (1.6 Btu/ft2-s) 383 qualified cable plastic cable insulation 18-20 kW/m2 (10 min. exposure) Barry 2003 degrades (1.6-1.8 Btu/ft2-s) PE and PVC-insulated (2 -20 min. exposure) 250°C (480°F) NUREG 1805 cable failure threshold Notes *No credit for conduit for delaying onset of damage * No credit for fire retardant coating or rating for delaying onset of damage ** Plant-specific or product -specific data may be used if appropriate basis is provided *** Consider time to damage - EPRI 2010 values use 19 minutes, Sandia 60 min.
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Thermoset Cables (e.g. XLPE, XLPO, flame retardant) Thermal Damage Criteria NUREG 1805 - Fire Dynamics Tools
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Thermoplastic Cables (e.g. PE, PVC, non-flame retardant) Thermal Damage Criteria NUREG 1805 - Fire Dynamics Tools
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Pool Fire Radiant Heat Levels Fire 6.0 m Dia. Radiant Heat Levels from 6 m Diameter Pool Fire - 2m/s Wind Speed 20
Convection Thermal Effects Above Fire not Modeled
Height above Pool Fire Base (m)
15
Electrical Cable Vulnerability Hexane Fire
Steel Vulnerability Hexane Fire
37.5 kW/m2 @ 56 kW/m2 Hexane
10
12.5 kW/m2 @ 56 kW/m2 Hexane
5
Draft Radiant Heat Modeling K. Thorsteinsson
6 m dia pool fire 0 0
5
10
15
20
Distance from Pool Fire Centre (m)
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Pool Fire Radiant Heat Levels API 521 Size Fire 17.2 m Dia. Radiant Heat Levels from API 521 Pool Fire 17.2 m Equiv. Dia. - 0.1m/s Wind Speed Convection Thermal Effects Above Fire not Modeled
35
Electrical Cable Vulnerability Hexane Fire
Height above Pool Fire Base (m)
30
37.5 kW/m2 @ 56 kW/m2 Hexane
25
20
12.5 kW/m2 @ 56 kW/m2 Hexane
15
Steel Vulnerability Hexane Fire 10
Draft Radiant Heat Modeling K. Thorsteinsson
5
17.2 m dia pool fire 0 0
5
10
15
20
25
30
Distance from Pool Fire Centre (m)
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Common Radiant Heat Flux Damage Criteria Protected / Unprotected Atmos. Tankage - 32 / 8 kW/m2
Process Equipment – 38 - 44 kW/m2
Vegetation –
Process Buildings –
10 kW/m2 LPG Storage –
25 kW/m2
22 kW/m2
Operator Response < 60 sec – 6.3 kW/m2 Prolonged Operator Response – 4.7 kW/m2
Combustible Structures – 10 kW/m2
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Control & Inst –
Property Lines & Roadways –
12.5 kW/m2
5 kW/m2
Electrical Equipment / Cables – 12.5 kW/m2
Fireproofing Critical E & I
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References
EPRI 2010 - Methods for Applying Fire Risk Analysis to Fire Scenarios (MARIAFIRES)-2008 – NUREG/CP-0194, EPRI 2010
Mecklenburgh 1985 - Process Plant Layout - JC Mecklenburgh, IChemE / Wiley, 1985
Technica 1988 - Techniques for Assessing Industrial Hazards - A Manual - Technica / World Bank, 1988
Wells 1980 - Safety in Process Plant Design, GL Wells, IChemE / Wiley, 1980
Robertson 1976 - Spacing in Chemical Plant Design Against Loss by Fire, R Robertson, IChemE Symp Series 47, 1976
CCPS 2000 - Guidelines for Chemical Process Quantitative Risk Analysis, 2nd Ed., AIChE CCPS, 2000
NUREG 1983 - Investigation of Twenty-Foot Separation Distance as a Fire Protection Method as Specified in 10CFR50, App R, NUREG/CR-3192, Sandia, 1983
NUREG 1805 - Fire Dynamics Tools - Quantitative Fire hazard Analysis Methods for the US Nuclear Regulatory Commission Fire Protection Inspection Program (NUREG 1805), 2004
Alderman 2007 - Risk Assessment in the Oil and Gas Energy Industry, JA Alderman, Fire Protection Engineering, 2007
Barry 2003 - Fire Exposure Profile Modeling; Some Threshold Damage Limit (TDL) Data, TF Barry, Fire Risk Forum, 2003
BS 5908 - Fire and Explosion Precautions at Premises Handling Flammable Gases, Liquids and Dusts, BS 5908-1, BSI, 1990
IP 1993 - Fire Precautions at Petroleum Refineries and Bulk Storage Installations, Institute of Petroleum IP Part 19, 1993
EPC 2007 - Engineering Instructions for Passive Fire Protection, EPC Firm Process Safety Group, 2007
DNV 2009 - Case Study of Rapid Blowdown on Offshore Platform, DNV / BP, 2009
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