Suppression of Class C Fires

Transcription

1 Suppression of Class C Fires DEVELOPMENT OF A STANDARD PROCEDURE FOR THE EVALUATION OF THE PERFORMANCE OF CLEAN AGENTS March 23, 2007 Mark L. Robin, Ph.D., DuPont Fluoroproducts Bon Shaw and Brad Stilwell, Fike Corporation Presented at: Suppression & Detection Research & Applications (SUPDET 2007), March 6, 2007 Wyndham Orlando Resort, Orlando, Florida

2 2 Introduction: Class C Fire What is it? NFPA Class C Fires. Fires that involve energized electrical equipment. NFPA Class C Fires. Fires that involve energized electrical equipment where the electrical nonconductivity of the extinguishing media is of importance.

3 3 Class C Fire Why do we care? In some applications, power disconnection is highly undesirable because: Time = Money Downtime impact for a typical computing infrastructure is estimated to be $42,000 per hour

4 4 Downtime Impact per Minute Business Application Downtime Cost per Minute Supply Chain Management $11,000 e Commerce $10,000 Customer Service Center $3,700 ATM $3,500 Financial Management $1,500 Messaging $1,000 Infrastructure $700 Source: Alienan ROI Report, 2004

5 5 Class C Fires and Clean Agents NFPA 2001, 2004 edition Minimum design concentration for Class C hazards shall be at least that for Class A surface fire. Class A minimum design concentration equals 1.2 times the minimum extinguishing concentration determined by test as part of a listing program, where the listing program at a minimum must conform to UL 2127 or UL 2166.

6 6 Class C Fires and Clean Agents Report on Comments A2007 ROC Comment a (log #CC7) Minimum design concentration for Class C hazard shall be 1.6 times the Class A minimum extinguishing concentration Committee Action: Accept Substantiation: Laboratory testing indicates that the agent concentration required to extinguish a fire in energized electrical equipment typically increases with increased electrical power input.

7 7 ROC a: Implications For Class C hazards, the minimum design concentrations for all clean agents increased by 33% As a result, system costs increase by at least 33% Several clean agents basically eliminated from the market

8 8 Reality Check: Is Such Drastic Action Warranted? Q: Number of documented failures of any clean agent system to extinguish fires involving energized electrical equipment since the initial installation of clean agent systems approximately 15 years ago? A: Zero

9 9 Reality Check: Does laboratory testing warrant such a drastic change? Thirteen reports reviewed by NFPA 2001 Committee Energized Ni foil in an ethylene flame Energized Nichrome wire in a heptane flame Tests involving no electrically energized equipment Numerous reports on PMMA wrapped in Nichrome Conductive heating, ohmic heating, PC board failures (arc) Source: 3M, Modular Protection, Hughes Assoc., NIST

10 10 PMMA, Nichrome and Class C Hazards Typical Class C Hazards Telecommunications & EDP facilities Cables, electronic equipment Power Conduction Almost always copper Small percentage aluminum Not Nichrome Power Cable Insulation Majority PVC, FR-PVC, PE, HDPE Some Hypalon, XLPO Not PMMA

11 11 PMMA, Nichrome and Class C Hazards Nichrome wire Alloy of Ni and Cr High electrical resistance widely employed for resistive heating Never employed for power or data conduction Extremely corrosion resistance High mechanical strength at temperatures up to 2500 o F

12 12 Nichrome vs Copper Nichrome Copper Ni/Cr alloy Cu High mechanical strength Low mechanical strength Highly resistant to corrosion Low resistance to corrosion High electrical resistance Low electrical resistance Use: resistive heating Use: power and data conduction Max use T = 2000 o F Max use T = 1000 o F

13 13 Nichrome vs Copper Strength versus Temperature Tensile strength (psi) Nichrome 60/15 wire Hot Drawn Copper wire Temperature ( o F)

14 14 Overloaded Copper Wire 24 AWG Bare Copper Wire Current (A) Temperature ( F) Duration > 10 min > 10 min > 10 min min 3:23 5:13 6:02

15 15 Overloaded Copper Wire 24 AWG Jacketed Copper Wire Current (A) Temperature ( F) Duration > 10 min : : :10

16 16 Overloaded Bare Copper Wire AWG Current (A) Temperature ( F) Duration : : :07

17 17 Copper Wire Bare copper wire can withstand a 10-minute overcurrent only when the wire temperature is limited to 1000 o F Insulated copper wire can withstand a 10-minute overcurrent only when the wire temperature is limited to 700 o F Larger gauge wires require more current but behave similarly to smaller gauge wires at similar temperatures Stranded cables and single conductor cables behave similarly

18 18 Copper Wire Copper wire heated to o F is sustainable for 10 minutes ONLY if these temperatures are not exceeded anywhere along the length of wire Once copper wire is heated to above 700 o F, corrosion is accelerated, and this corrosion is the primary reason for failure at these temperatures

19 19 Nichrome, PMMA and Class C Fires PMMA/Nichrome studies Conducted at wire temperatures 1800 o F At 1800 o F, bare copper wire sustainable for < 10 seconds At 1800 o F, insulated copper wire sustainable for even less time These tests would be impossible to conduct with the conductor employed in 99.9% of all power transmission cables

20 20 PMMA Polymethylmethacrylate Lucite, Plexiglas Clear, shatterproof, excellent optical properties Hockey rink barriers Lenses, optical instruments, stop lights, auto lights Expensive Not employed for power conduction Combusts quantitatively to monomer

21 21 PMMA/Nichrome Wire Tests Not representative of real world hazard Materials NiCr not employed for power conduction PMMA not employed for insulation Conditions Cu wire able to withstand 1800 o F for < 10 s before failing

22 22 Conductive Heating Tests Hughes Associates Report Simulate overloaded connection 350 MCM Cu cable; PVC, Hypalon insulation Cable heated to 590 o F (310 o C); 1000 W ring heater Pilot flame ignition, 60 s preburn, system actuation 5 min soak with current applied McKenna, et al., 1998 HOTWC

23 23 Printed Wire Board Failure (Arc) Tests Hughes Associates Report Simulate PC board failure Test boards of FR-2 and FR-4 Parallel copper tracks Arc develops between tracks, travels along board After arc and flame travel 130 mm, actuate system McKenna, et al., 1998 HOTWC

24 24 Ohmic Heating Tests Hughes Associates Report Simulate overheated wire Wire mounted between Cu buses connected to a 600 A arc welder Butane flame pilot Bundled cable: Cables bundled around a central energized wire Preburn until flame judged to be well sustained McKenna, et al., 1998 HOTWC

25 25 Hughes Associates Report Testing on representative materials Conductive heating tests Printed wire board failure (arc) tests Ohmic heating tests Concluded that Fires initiated by and involving energized electrical circuits can be controlled by HFC-227ea at concentrations below 7% McKenna, et al., 1998 HOTWC

26 26 Modified Conductive Heating Tests Introduces continuous arc into conductive heating tests Poor Reproducibility Small flame at top of cable sometimes ignites vapors rising up sides of cable Flame sometimes disappears when enclosure sealed Difficult to determine point of extinguishment due in part to obscuration during discharge

27 27 Modified Conductive Heating Tests HFC-227ea Poor Reproducibility: KS-5482L28F cable 7.0% extinguished flame/reignition 8.0% no extinguishment/reignition 8.0% extinguished flame/no reignition 11.0% extinguished flame/reignition

28 28 Development of a Standard Class C Test Objectives Replicate real world scenario with materials choice and conditions Conservative Reproducible Simple to perform

29 29 Class C Test Protocol Replicate real word materials Conductor: Copper Insulation: PVC, PE, Hypalon, XLPO Replicate real world conditions But conservative (challenging) test

30 30 Class C Test Protocol Conditions Copper only able to withstand temperatures up to 1000 o F for extended periods Employ NiCr wire as ignition source and as heat source during preburn and soak periods Ignition: 1800 o F Preburn and soak: 1200 o F

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32 32 Shorter Pieces = Greater Challenge

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39 39 Test Procedure HFC-227ea, 6.25% v/v Ignition: Apply current corresponding to a wire temperature of 1800 o F At 30 s after ignition, reduce current to level corresponding to 1200 o F, and maintain this current through entire test After 60 s total preburn, activate system Examine for reignition during 10-minute soak period

40 40 Test Results Run Plastic Ignition (s) Preburn (s) Ext time from EOD (s) Reignition after soak? A1 ABS 0: NO A2 PP 0: NO A3 PP 0: NO A4 PMMA 0: NO A5 PVC NA 180 NA NO A6 PVC NA 600 NA NO A7 PVC NA 300 NA NO A8 HDPE 0: NO A9 PMMA 0: NO A10 ABS 0: NO A11 PP 0: NO A12 HDPE 0: NO A13 ABS 0: NO A14 PMMA 0: NO A15 HDPE 0: NO

41 41 Conclusions ROC a Field results do not justify ROC a The cited studies do not justify ROC a The results of the present study do not justify ROC a NITMAMs have been filed Previous studies Flawed in use of materials and conditions Flawed by reproducibility problems The one past test (HAI) employing realistic materials/conditions supports our conclusions

42 42 Conclusions: This Work Current Class A minimum design concentrations appear to be sufficient for the protection of Class C hazards The developed procedure is simple, challenging, and reproducible Suggest its use as a starting point for the development of a standard test

43 43 Future Work Additional plastics Additional agents Development of an arc test

44 Copyright 2007 DuPont. The DuPont Oval logo, DuPont, and The miracles of science are trademarks or registered trademarks of E.I. du Pont de Nemours and Company or its affiliates. All rights reserved. 03/07

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