NUREG/CR-2409

SAND81-7168

RP

Printed July 1982

:CONTRACTOR REPORT

Requirements for Establishing Detector

Siting Criteria in Fires Involving

Electrical Materials

John L. Boccio

Brookhaven National Laboratory

Upton, New York 11973

-Prepared by

Sandia National Laboratories

Albuquerque, New Mexico 87185 and Livermore, California 945!

for the United States Department of Energy

under Contract DE-AC04-76DP00789A•

50

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Sandia Laboratories

date: August 24, 1982 Albuquerque, New Mexico

Livermore. California

to: Distribution

from: Ruby C. Cochrell, 9400

subject: SAND81-7168, NUREG/CR-2409, "Requirements for Establishing

Detector Siting Criteria in Fires Involving Electrical

Materials"

During the printing process an error was made and the

title page inadvertently left out. Please correct your

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rcc/

enclosure

I

NUREG/CR-2409

SAND81-7168

RP

REQUIREMENTS FOR ESTABLISHING DETECTOR

SITING CRITERIA IN FIRES INVOLVING ELECTRICAL MATERIALS

August 1982

Sandia Project Officer: L. J. Klamerus

Prepared for

Sandia National Laboratories

Albuquerque, New Mexico 87185.

.operated by

Sandia Corporation

for the

US Department of Energy

Work performed under Sandia Contract No. 74-5093

Funded by

Division of Engineering Technology

Office of Nuclear Reactor Research

US Nuclear Regulatory Commission

Washington, DC 20555

Under Memorandum of Understanding DOE 40-550-75

NRC Fin No. A1010

A ii

/

ABSTRACT

Due to increased public awareness and regulatory actions, significant

strides have been made in the capabilities of fire technology as it applies to

fire detection systems. However, these advances in detector selection,

siting, reliability and approvals tests have not substantially addressed the

overall fire protection requirements within nuclear reactors.

This report emphasizes some of the basic requirements and considerations

needed for establishing siting criteria for early-warning detection of electrical cable fires. Recent research in electrical cable flammability and

damageability characteristics are discussed. Also current work in systemizing

detector siting criteria is also described.

Confirmatory tests linking assessment of electrical-cable damageability

with electrical cable fire detection is stressed.

iii
TABLE OF CONTENTS

Page

ABSTRACT ................................... . ................... ii i

LIST OF TABLES .... .. ..... ........ ..... .... .... ............ vi

LIST OF FIGURES ............................. ..................... vii

1.0 INTRODUCTION ....... ,......................................... ,.

2.0 FLAMMABILITY/DAMAGEABILITY/DETECTABILITY OF

ELECTRICAL CABLE FIRES- An-Overview ........................... 2

2.1 Categorization of Electrical Cable

Flammability Data ........................................ 3

2.2 Categorization of Electrical Cable

Damageabiliity ............................................... 4

2.3 Fire Detection/Cable Flammability Relationship ............... 17

2.4 Initial Convective Flow in Fire .............................. 22

2.5 Detection of Smoldering and Flaming Cable Fires .............. 26

2.6 Exposure Fire Hazards to Cable Trays ......................... 31

2.7 Summary ...................................................... 34

3.0 ELECTRICAL CABLE FIRES AND FIRE DETECTOR

ENVIRONMENTS - TEST PLAN ........................... o ...... *... 34

3.1 Scope .................... . .. ................ 9......... .. 34

3.2 General Considerations ........................................ 35 A

3.3 Specific Considerations ............. ......... 37

3.4 Measurement Considerations..., .. ... .................... 40

3.5 S m a y . . . . . . . . . . . . .. . . . . . . .. . . . . . .. 41

iv
TABLE OF CONTENTS (Cont'd.)

4.0 FINAL SUMMARY .... . ...... ....... ............ . .............

REFERENCES ............... ......................... .. . . . . .

Page

42

45

V
LIST OF TABLES

Table No. Title Page

1 Samples Used in Cable Flammability Study ................... 5

2 Piloted Ignition Parameters for

Cable Samples .................... ... .. .. ....... ..... 7

3 Critical Mass Loss Rate for Piloted Ignition in Normal Air ................................... 8

4 Heat Release Rate Per Unit Area and

Heat of Combustion for Flaming Fire

of Cable Samples in Normal Air at 60 kW/m 2 . ......... 9

5 Samples Used in Cable Damageability Study .................. 11

6 Insulation Degradation Parameters or Cable S a m p l e s , . . . . . -. . . . . . o.. . . . .. . . . . . . . . . . . . .. . . . . . 1 2

7 Ignition Parameters for Piloted and

Autoignition of Cables ................................... 13

8 Electrical Failure Parameters for Cables

Under Piloted Ignition Condition. ............ .. ...... 14

9 D/AT for the Combustion of Cable Samples in

Normal Air at 60 kW/m 2 ............. . . . . . . . . . . . . . . . . . . - 2 1

10 Detection Paramete rs.............. ............... 27

vi
LIST OF FIGURES

Figure No. Title Page

1 Laboratory scale combustibility apparatus ................ 6

2 Experimental determination of thermal degradation

energy and critical flux of thermal degradation

for PE/PVC cables ....................................... 15

3 Optical density per unit path length as a function

of fuel vapor mass concentration . ................... 20

4 Idealized heat release and fire growth rates ............. 24

5 Spacings of smoke detectors on a square array under

a flat extensive ceiling ............................... 28

6 Heat flux and gas temperature at ceiling versus time

from ignition... 32

7 Typical fire/detector sensitivity test room .............. 39

8 Qualitative relationship between time and damage

for different speeds of fire development and

average detection, reaction and fire-fighting

times ................................... ............ 43

vii
t
1.0 INTRODUCTION

Throughout the nuclear industry and cognizant regulatory body there has

been considerable responsive action relative to nuclear safety-related fire

protection and incorporating sound fire-protection principles in nuclearfacility design. New standards, new regulatory guides, and new criteria have

been promulgated since the fire at the Browns Ferry nuclear power station.

Basic fire protection guidance for nuclear power plants contained in

Branch Technical Position Auxiliary Power Conversion System Branch BTP APCSB

9.5-1, "Guidelines for Fire Protection for Nuclear Power Plants" and its attendant appendices, namely, Appendix A & R, mandate the need for early warning

fire-detection systems as part of a plant's general and specific fire protection requirements for assurances of performing a safe shutdown in the event of

a fire. However, recommended guidelines for the selection and installation of

early warning fire detection systems are currently based upon national standards and guides that do not realistically take into account a number of environmental and plant safety requirements that are unique to nuclear facilities.

Early-warning fire detector siting and selection must have fuller

accountability of:

(1) the environmental factors such as ventilation, room size/

configuration/congestion, background radiation on detector

response;

(2) the flammability characteristics of the types of combustibles

existing in nuclear power plants; and,

(3) the need to limit fire damage to systems required to achieve and

maintain safe shutdown conditions.

A prime common denominator in addressing the above three issues, in concert,

is the ability to prevent/detect fires involving electrical cables - a major

combustible within the plant and at the same time crucial in performing an

effective safe shutdown.

Recognizing early this unique dual characteristic of electrical cables,

significant contributions to the assessment of exposure fire hazards to electrical cable and cable tray installations have been made through EPRI- and

NRC-funded research programs that have included: 1) exposure fire characterization, 2) exposure fire environment within enclosures, and 3) preliminary

evaluation of the effectiveness of water, gas and/or baffle protection for

specific combination of cable type, tray configuration, and exposure fire.

1
Also, re~cent NBS- and UL-funded efforts have been expended in establishinq,.a*.more recancilable means of siting aerosol detectors, in establishing a

more cogent :set.of.stavdards' tests and in formulating a viable set of maintenance procedures that take Into account the environmental factors listed

above,

Notably in this connection is the series of studies by Factory Mutual

Research Corporation (FRRC), under EPRI sponsorship, investigating the characteristics of electrical cable fires( 1 , 2 ,

3 ,4) and their work done under NBS

sponsorship, in developing and In corrolating design information for detectors( 5 ) which has been summarized in a report prepared for the Fire Detection

Institute( 6 ). Much of this design data has been utilized in Reference 7 for

formulating an interim guide on detector-system assessments for nuclear power

plants. However, the design charts used have been noted to lack corroborative

evidence of detector spacing required for electrical cable fires.

Thus, it seems propitious at this stage in the state-of-the-art in: a)

the assessment of exposure fire hazards to cable trays and in b) the development of design information for aerosol detectors and detector sitin%,that confirmatory tests be undertaken linking these correlations and aerosol detector

siting criteria to flaming fires involving electrical cables. However, before

a test program can be scoped out, a brief review of the aforenoted work is

deemed warranted so that one may synthesize some of the aspects of fire detection analyses with electrical cable fire protection.

2.0 FLAMMABILITY/DAMAGEABILITY/DETECTABILITY OF ELECTRICAL CABLE FIRES -

An Overview

Specification of the required spacing of aerosol fire detectors generally requires that the following detection parameters be known: (1) the

growth rate of the fire, (2) the acceptable fire size at detection, and (3)

the response characteristics of the detectors to the particular aerosol generated. Determination of the growth rate of an electrical cable fire, or for

that matter the general flammability characteristics of electrical cables is

difficult because these cables, which are an integral part of today's power

generating facilities, are manufactured with various synthetic polymers,

plasticizers and flame-retardant additives.

2
Using a laboratory-scale combustibility apparatus, Tewarson(I)

attempts to categorize the flammability of electrical cables of various sizes,

...-- conductors and materials. The following section will discuss some-of the data

_' :-...'-.,extracted from this program and how it may be factored into the above three

requirements for detector spacing.

If electrical cables were considered simply as a combustible material,

its fire-hazard classification can be assessed from this information. But to

effect a safe-shutdown, one must also assess the damageability of cables that

are subjected to abnormal thermal environments such as a fire. Lee( 2 ) extends the work previously cited by formulating damageability indices under

varying thermal environments. Thus, quantifying cable damage potential

through these indices, which are also reviewed in this section, allows one to

appraise the possible acceptable fire size at detection.

However, in order to classify the various cables as to their total damage potential for a specific application, appraisals must be made of the effect of the environment on the potential hazard presented by a realistic fire

scenario in a facility. Newman and Hill( 4 ) consider fires from flammable

liquid spills as a realistic scenario and formulate a decision-making process,

which together with data on the flammability/damageability of electrical cable

from the laboratory-scale apparatus, may provide planners and engineers with

more rationale guidelines for cable selection, fire detection and protection.

Major highlights from this study are also discussed as well as how they would

factor into the above three requirements on detector siting.

Finally, this section also reviews briefly the corrolations formulated

by Heskestad and Delichatsios( 5 ) for evaluation of the initial convective

flow of idealistic fires and how this approach can be extended to generate

guidelines for detector spacing. Preliminary experimental work in extending

this approach to electrical cable fires, generated by Delichatsios( 3 ) is

also described herein.

2.1 Categorization of Electrical Cable Flammability Data

The present method for qualification of an electrical cable is the IEEE383 test for cable qualification. Although this test provides a single set of

3
fire source and cable conditions and is a "go or no go" test, categorization

of cables by Tewarson(l) under various radiant heat exposures with both

auto- and piloted-ignition indicated that cable damage varies with'radiant

heat source. Initially the objective had been to provide a laboratory test

basis for assessing cable-insulation damage on a comparative basis. Although

the experimental method has shown the damageability to be a complex phenomenon

depending on the oxides formed, the materials, the jacket material, the number

of conductors, it was found that there is a critical heat flux for damage and

that the cables are affected by the amount of energy applied above this level.

In this study, 22 types of cable samples (see Table 1) were'examined in

a test apparatus depicted in Figure 1. In this test procedure, small samples

(81 x 10- 4m2 ) of cables are subjected to different magnitudes of external,

radiant heat flux during which time measurements were made as to 1) time to

ignition (auto and piloted), 2) mass loss rate, 3) heat release rate, 4) rates

of generation of gaseous combustion products, and 5) optical transmission

through the evolving aerosol. With these measurements the combustibility

characteristics including ignition and flame spread behavior, (Table 2); critical mass loss rate for ignition, (Table 3); fire intesity in a changing

thermal environment and fire hazard in terms of heat release rate (Table 4)

can be determined. Details on applying global energy and mass balances

together with the measurements indicated, are described in the cited reference. These data suggest that polyethylene/polyvinylchloride cable (#5),

polyethylene-polypropylene/ chlorosulfonated polyethylene cable (#9) and

silicone cable(#22) samples represent "high, intermediate, and low fire

hazard based upon mass loss rate and heat release rate in the flaming fire".

.2.2 Categorization of Electrical Cable Damageability

Although electrical cable flammability data is considered crucial in

assessing the inherent fire hazard, factors other than insulation/jacket

degradation, ignition, fire growth, maximum burning, etc. must also be

considered critical to the safe operation of a facility where cables play such

an integral part of the entire system. These additional factors quantifying

cable Impairment which may occur before a fire is fully developed may be due

to the effect of changes in cable properties, such as insulation resistance,

4
Table 1

Samples Used in Cable Flammability Study *

Insulation/Jacket

Number Materials

I Low density PE

(1IW!), no Jacket

insulation/

Jacket Mate- Insulation Jacket Materials

Conductor Outer Cable rials (% of remaining as char (% of

No. Size Diameter total cable initial wt. of insulation/

(ANG) in. (a) weight Jacket materials)

Polyethylene (PE) /No Jacket

1 14 0.128(0.003) 23.9 0.10

IZEEZ-383

Rating

3

4

5

6

7

PE/PVC

WE/PVC

fl/Pvc

PE/PV

Polyethylene/Polyvinyl chloride (PE/PVC)

1 - 0.945(0.024) 15.6 21.9

1 12 0.164(0.004) 26.5 0.6

3 - 0.438(0.011) 49.9 20.8

5 - 0.748(0.019) 51.0 25.6

12 - 1.000(0.025) 57.8 24.4

Polyethylene, Polypropylene/Chlorosulfonated Polyethylene (PE, PP/Cl.S.PE)

s PzPP/cL. S'Pz 1 - 0.445(0.011) 23.2 41.6

(silicone o*

9 PRPP1FW.'S

10 P".PP/CL'S*P

11 PRPP/CI'S*I

12 PE ,PP/CL-S 'P

oAting)

S.PRb 1 6 0.368(0.009) 40.2 46.4

pt 1 12 0.192(0.005) 42.9 45.6

I1 5 14 0.6"8(0.017) 77.1 48.3

P1 2 16 0.426(0.011) 77.4 40.5

Crose-Linked Polyethylena/Crosa-Linked Poyethylene (XPE/XPZ)

3 12 0.458(0.012) 61.4 44.9

2 14 0.377(0.010) 73.5

Cross-Linked ltlyethyleno/Chlororulfonated Polyethylene (XDR/C€A*tS*)

4 16 0.360(0.009) 56.2 29.5

4 16 0.442(0.011) 62.1 31.0

Fail

Fail

Pass

Pas.

Pass

Pass

Pass

Pass

Pass

Pass

Pass

Pass

13

14

15

16

17

2

18

19

xPR/rmRnCb

rnz/DR

FUXP/cl~S.

DPE/c1-S-PR

XDE/Neo

DEZ/Neo

Cross Linked Polyethylene/Neoprene (xPE/Neo)

3 16 0.369(0.009) 73.2 43.9

7 12 0.630(0.016) 53.6

Polyethylee e, Nylon/Polyvinyl chloride, Nylon (PE, Ny/PVC , NY)

PC, Ny/PVC, NY

PR, Ny/PVC, NY

7

7

12

12

0.526(0.013)

0.520(0.013)

39.9

43.5

teflon

20 Teflon

21 Silicone, glass

braid

22 silicone, glass

braid/asbestos

34 - 0.516(0.013) 48.9 3.9

1 - 0.363(0.009)

9 14 0.875(0.0221

Silicone

34.0

-Pass

Pass 70. 5 59.4

aGeneric Class as given by the suppliera. Cable samples belonging to similar generic class may not be

similar because of different types and aunts of unknown additives in the cable samples.

bn - with fire retardat chmical

* From Reference (1)

5
Blower

Smoke Density

Measurement

4-.-

Gas

Analyzer

Exhaust Duct

* Smoke Analyzer

Thermocouples

r- Radiant Heaters

- Flux Gauge

Sample

02 - Analyzer_

Fig. 1. Laboratory scale combustibility apparatus. (From Ref. 1)

6
Table 2

PILOTED IGNITION PARAMETERS FOR CABLE SAMPLES *

a b,,b No. Cable Sample E eff o T IEEE-383

(kJ/m ) (kW/m2) (K) Ratingc

20 Teflon 8,696 43 933 Pass

Polyethylene (granular)d 3,744 19 761 NA

Polyvinyl chloride (granular)d 3,320 21, 780 NA

21 Silicone, glass braid 3,125 29 846

d

Polyethylene/25%C2.(granular)d 3,011 26 823 NA

Polyethylene/42%CZ (granular)d 1,969 22 789 NA

Polyethylene/36%Ct (granular) 1,891 26 823 NA

13 XPE/FRXPE 1,688 22 789 Pass

d

Polyethylene foam (rigid) 1,641 22 789 NA

16 XPE/Ck.S.PE 1,105 33 873 Pass

9 PE,PP/FRCL-S-PE 890 36 893 Pass

17 XPE/Neo 826 34 880 Pass

22 Silicone, glass braid/asbestos 778 14 70t Pass

Polyurethane foam (rigid)d 772 23 798 NA

4 PE/PVC 728 36 893 Fail

5 PE/PVC 347 22 789 Fail

aE is defined as the 'effective' energy associated with maintaining

flammable cable sample vapor/air mixture near the surface

b.,,

q or TS is defined as the critical heat flux or temperature at or below

which ignition cannot be achieved

CIEEE-383 rating as provided by the suppliers

dResearch samples, data from Ref. (8)

NA - Not applicable

* From Reference (1)

7
Table 3

CRITICAL MASS LOSS RATE FOR PILOTED IGNITION IN NORMAL AIRa *

Cable Sample

PE, PP/C-.S.PE (#11)

XPE/CP.-S.PE (#16)

FRXPE/Cl.-S.PE (#15)

PE, Ny/PVC, Ny (#18)

XPE/XPE (#13)

PE, PP/FR CL-S.PE (#9)

XPE/Neoprene (#17)

XPE/XPE (#14)

PE/PVC (#4)

Silicone, glass braid, asbestos (#22)

PE, PP/CY.-S.PE (#10)

Critical Mass Loss Rate 2

Per Unit Sample Area (g/m s)

2.6

2.9

3.3

3.4

3.7

4.0

4.3

4.4

4.4

4.5

4.8

aAverage peak values

PE,PP - polyethylene, polypropylene; C.SF.PE_-chlorosulfonated--polyethylene;-

XPE = crosslinked polyethylene, PE polyethylene; Ny m Nylon, PVC polyvinyl

chloride; FR - with fire retardant.

* From Reference (1)

8
Table 4

HEAT RELEASE RATE PER UNIT AREA AND HEAT OF COMBUSTION FOR FLAMING FIRE

OF CABLE SAMPLES IN NORMAL AIR AT 60 kW/m 2 a ,

IEEE Heat Release Rate Per

383 Unit Area (kW/m ) Heat of Combustion (kJ/g) Cable Sample Rating Actual Convective Radiative Actual Convective Radiative

Id PE (#1) 1NK 1071 398 673 31.3 11.6 19.7

PE/PVC (#5) Fail 589 325 264 24.0 13.0 11.0

XPE/FRXPE (#13) Pass 475 207 268 28.3 12.3 16.0

PE/PVC (#4) Fail 395 175 220 25.1 11.1 14.0

PE/PVC (#6) NK 359 228 131 22.0 14.0 8.0

XPE/Neoprene (#2) NK 354 166 188 12.6 5.9 6.7

PE,PP/Ct-S-PE (#12) Pass 345 131 214 17.4 6.6 10.8

PE/PVC (#3) NK 312 185 127 30.8 18.3 12.5

XPE/Neoprene (#17) Pass 302 144 158 10.3 4.9 5.4

PE, PP/C1oS-PE (#8) Pass 299 160 139 29.6 15.8 13.9

PE, PP/C1.S-PE (#11) Pass 271 172 99 26.8 17.0 9.8

FRXPE/CL-S-PE (#15) Pass 258 112 146 17.3 7.5 9.8

PE, Nylon/PVC, Nylon (*19) NK 231 120 110 9.2 4.8 4.4

PE, Nylon/PVC, Nylon (#18) NK 218 107 i1l 10.2 5.0 5.2

XPE/CltS-PE (#16) Pass 204 135 69 13.9 9.2 4.7

Silicone, glass braid, asbestos (#22) Pass 182 152 30 24.0 20.0 4.0

XPE/XPE (#14) Pass 178 107 71 12.5 7.5 5.0

PE,PP/CLoS-PE (#10) Pass 177 114 62 19.0 12.3 6.7

Silicone, glass braid (#21) NK 128 89 39 25.0 17.5 7.3

Teflon (020) Pass 98 82 16 3.2 2.7 0.4

aAverage peak values NK - Not known

* From Reference (1)
dielectric strength, and bending characteristics, upon heat flux exposure. Of

these stages, insulation/jacket degradation, ignition, and electrical integrity failure were chosen in a follow-on study( 2 ) by FMRC to represent cable

damage. In this study, also conducted in the laboratory-scale apparatus

alluded to above, the damage potential of these three processes is expressed

quantitatively by two parameters derived from experimental data, viz, the

critical flux which is the minimum external heat flux below which the damage

process will not occur and the critical energy which is the energy required to

effectively initiate the damage process. This energy is considered simply the

product of the available external heat flux and the time to initiate the

damage process. For control and power cables that are subjected to exp\osure

fires and which are required to effect a safe shutdown, consideration of these

times together with the necessary detector response time must be considered in

effecting an adequate, overall, fire detection system plan.

The following tables summarize the pertinent results from the cited

reference.

Fourteen different cable samples (Table 5) of five basic generic groups

were exposed to varying degrees of radiant heat flux (up to 70 kW/m 2 ) to

simulate the thermal environment of an exposure fire hazard. By recording the

amount of insulation/jacket material vaporized as a function of time during

the preignition phase, the degradation parameters as summarized in Table 6

were determined. Also, the times to ignition of the cable samples as functons of external heat flux under both piloted and non-piloted conditions were

used for the quantification of the ignition process as indicated in Table 7.

Additional tests were performed in the presence of a pilot flame (similar to

the piloted-ignition study) under varying thermal environments and with a

variable power source to energize the cable samples to 70V in each conductor.

The times to electrical shorting between conductors or to ground as functions

of heat flux were used for assessment of electrical integrity failure (Table

8).

Based upon this type of information and the two parameters defined

above, i.e., the critical energy and critical flux which is generated from

data typically plotted in Figure 2, three indicies comparatively relating the

damage process can be tabulated. These indices are respectively: the insulation degradation, the piloted ignition, and electrical failure indices

defined as follows:

10
Table 5

Samples Used in Cable Flammability Studya *

No.°

17

5

6

8

11

59

20

56

60

21

22

58

57

Insulation/Jacket Material

Conductor

No. Size (AWG)

Outer Cable

Diameter

in. (W)

XPE/Neopreneb

XPE/Neoprene

PE/PVCc

PE/PVC

EPR/Hypalond

EPR/Hypalon

EPR/Hypalon

Teflon/Teflon

Teflon/Teflon

Teflon/Teflon

Silicone (Glass

Silicone, Glass

Silicone, Glass

Silicone, Glass

7

3

12

16

3

5

1

5

7

0-~

'-4

Braid)

Braid/Asb. e

Braid/Asb.

Braid/Asb.

34

7

7

1

9

3

7

2

14

9

20

16

20

14

12

0.630

0.394

0.433

0.709

0.433

0.669

0.984

0.472

0.394

0.276

0.354

0.827

1.142

0.787

(0.016)

(0.010)

(0.011)

(0.018)

(0.011)

(0.017)

(0.025)

(0.012)

(0.010)

(0.007)

(0.009)

(0.021)

(0.029)

(0.020)

Insulation/Jacket

Material (% of

Total Cable Weight)

53.6

73.2

49.9

51.0

23.2

23.9

57.5

48.8

28.1

32.7

34.0

70.5

37.3

58.4)

IEEE-383

Rating

Pass

Fail

Pass

Pass

Pass

Pass

Cables Nos. 2, 5, 6, 8, 11, 17, 20, 21, and 22 are the same as those used in the previous study

b Cross-linked polyethylene insulation with Neoprene jacket cable.

c Polyethylene insulation with polyvinyl chloride jacket cable.

d Ethylene propylene rubber insulation with chlorosulfurated polyethylene jacket cable.

e Silicone rubber insulation with asbestos, glass braided jacket cable.

* From Reference (2)
Table 6

INSULATION DEGRADATION PARAMETERS OR CAi3LE SAMPLES *

No.

56

11

20

8

22

59

2

6

17

57

5

Cable Sample

Teflon/Teflon

EPR/Hypalon

Tetlon/Teflon

EPR/Hypalon

Silicone/Asbestos

EPR/Hypalon

XPE/Neoprene

PE/PVC

XPE/Neoprene

Silicone/Asbestos

PE/PVC

Critical

Energy of

Insulation

Degradation a

E id

(kJ/m2 )

9160

3390

3190

1792

1620

1420

1150

1000

900

760

530

Critical

Flux of

Degrada ion

(kW/m 2 )

16

6

18

11

18

19

24

18

22

21

18

Surface

Temperature

T c

S

(°C)

456

297

478

391

478

488

534

478

516

507

478

a E id is the critical energy of insulation degradation defined as the energy

required to initiate the insulation degradation process provided the available

heat flux exceeds the minimum requirement.

b.,b is the critical flux of degradation defined as the minimum heat flux

below which no significant insulation degradation can occur (see Section 3.1).

c T is the surface temperature calculated from 4"

qId"

* From Reference (2)

12
Table 7

.IGNITION PARAMETERS FOR PILOTED AND AUTOIGNITION OF CABLES *

Piloted Ignition Autoignition

Critical

Flux of

Piloted

Ignition

a E.o i,p

(No.)_.. (kJ/m2 )

Minimum

Flux for

Ignition

b

(kW/m2

Critical

Flux

Non-Piloted

Ignitionc

E.ig,n 2

(kJ/m

Minimum Difference

Flux for Piloted to

Non-Piloted Non-Piloted

Ignition Ignition

d .

ig,n

(kW/m ) (kW/m2 Sample

PE/PVC

PE/PVC

XPE/Neoprene

XPE/Neoprene

Silicone/

Asbestos

Silicone/

Asbestos

EPR/Hypalon

EPR/Hypalon

EPR/Hypalon

Teflon/Teflon

Teflon/Teflon

Teflon/Teflon

(5)

(6)

(2)

(17)

(22)

(57)

8)

(11)

(59)

(56)

(20)

(60)

460

690

1040

510

660

590

640

390

4680

'3011

18

23

21

27

26

23

23

27

24

40

6010

9480

11290

7180

3000

4420

f

f

f

f

f

5

15

4

18

31

27

NA

NA

NA

NA

NA

-13

-8

-17

-9

+ 5

+4

Eig,p is the critical energy of piloted ignition defined as the energy required to

carry out the ignition process by maintaining a flammable cable sample vapor/air

mixture near the surface provided the available heat flux exceeds the minimum

requirement.

b 4, is the critical flux of piloted ignition defined as the minimum flux below

which no ignition can occur.

c E. is the critical energy of non-piloted ignition defined the same as a.

d •g is the critical flux of non-piloted ignition defined the same as b.

ig, n

e A4" is the difference between gp and 4"

191p ig,n"

f no autoignition was observed at least up to 70 kW/m'.

* From Reference (2)

13
Table 8

ELECTRICAL FAILURE PARAMETERS FOR CABLES UNDER

PILOTED IGNITION CONDITION *

Critical Energy

of Electrical

Failure

E efa

(kJ/m2

Critical Flux

of Electrical

Failure %;f *.I b

(kW/m2

NA

Sample

Silicone/Asbestos

Silicone/Asbestos

Teflon/Teflon

EPR/Hypalon

EPR/Hypalon

XPE/Neoprene

EPR/Hypalon

PE/PVC

PE/PVC

XPE/Neoprene

(No.)

(22)

(58)

(56)

(59)

(11)

(2)

8)

(5)

6)

(17)

d

d

NA

NA

23,700 17

19,600

19,500

16,950

9,070

6,530

5,560

9

c

14

c

24

19

a E e is the critical energy of electrical failure defined as the energy-required ef

to break down the insulation to cause electrical shorting of the conductors

----provided the available heat -flux__exceeds. the minimum requirement -_

b qýf is the critical flux of electrical failure defined as the minimum heat flux

below which no electrical failure can occur.

c The critical flux of electrical failure cannot be determined for these cable

samples.

d 2 No electrical failure was observed at least up to 70 kW/m

* From Reference (2)

14
Z

Degadtion

• Energy, E id

c0 5--

iTi

Sepl

4- 4- 3 -/0

E

3-

S0

0o 10 20 40o Do SO soL 

External Heat Flux IkW/m 1

;•+Fig. 2. Experimental determination of thermal degradation energy and critical flux of thermal degradation for PE/PVC cables.

(From Reference 2)

15
IDI - 4i- Ji

P11 = ( - 4i'ý,p)/Eig~p

EF = e ef )fef

where:

IDI, PII, and EFI:

e"

Eid, E ig,p and Eef:

cid' , and %f

the combined damageability indices of the insulation degradation, piloted ignition and electrical failure processes

respectively (s- 1 ).

external heat flux (kW/m 2 ).

the critical energy of insulation degradation, piloted

ignition and electrical failure processes respectively

(kJ/m 2 ).

the critical flux of insulation degradation, piloted ignition and electrical failure processes respectively

(kJ/m2 ).

Ideally, from a detector siting point of view, these indices provide an

extremum value of time available for detector response for a given external

thermal condition such that the particular form of cable damage is minimized.

This study has indeed shown that the damage potential of a cable under

thermal exposures cannot be expressed by a single parameter but by a combination of parameters. Fortunately, interpretation of the test results indicate,

to some extent, that the critical flux values for each of the damage processes

studied all fall within a narrow range of values (around 20 kW/m 2 ); thus,

the critical energy is the predominant differentiator. Furthermore, amongst

the cables tested some did demonstrate low potential in all three damage processes with Teflon/Teflon rated highest; PE/PVC rated the lowest; and EPR/

Hypalon having a median rating. This ordering in the degree in cable damageability seems to be consistont with the ordering In the fire-hazard potential

previously discussed. As indicated in the cited references on cable flammability/damageability, cables of the same generic group do not necessarily

imply the same behavior under thermal exposure due to intrinsic differences in

manufacturing processes, construction type, number and size of conductors,

amount of additives as retardants and plasticizers, etc.

16
Accordingly, how this type of information can be factored into the overall detector siting/selection methodology requires a priori assessment of the

effect of the envirorunent on the potential hazards presented by exposure

fires. Detector threshold response must be part of the decision process which

considers the order of importance of the three electrical cable damage processes applicable to the particular facility. This information will provide, in

part, the necessary boundary condition or guidelines so that planners and engineers may select the appropriate cable and type of detector/protection

systems. How this type of information can be factored into the overall

decision-making process for detector-siting appraisal is discussed in the following sections.

2.3 Fire Detection/Cable Flammability Relationship

Data acquired from the FMRC laboratory-scale flammability apparatus in

delineating the combustibility characteristics of polymeric materials( 8 ) and

cables were subsequently used to derive pertinent information regarding aerosol detector response. The following briefly describes how this information

on smoke generation is evaluated.

Light obscuration by "smoke" is conventionally* expressed in terms of

optical density per unit path length, D,

D = (1/2-)ln (Io/I) (I)

where Z is the optical path length (m), and I/I0 is the fraction of light

transmitted through the "smoke." The light obscuration parameter of the aerosol can be expressed in terms of D and the mass-loss rate per unit volume of

the product-air mixture, i.e.,

D/(m'/VT) (2)

*Current research in "smoke" properties, their relationship with aerosol detector response, and development of standards tests indicates that measurement

of optical density alone is insufficient for classification of all generic

aerosol detectors.

17
where t is the light obscuration parameter (m2 /g); mn" is the mass loss rate

of the pyrolyzing/burning material per sample surface area (g/sm2 ); and VT

is the total volumetric flow rate of the product-air mixture through the apparatus per unit surface area of the material (m/s). Under actual bu'rrrtng condition this parameter will be related to initial buoyant plume velocity.

If the external heat flux, 4e, is sufficient to only pyrolyze then the

energy balance at the surface of the sample yields

" (-(3)

where L is the heat required to generate a unit mass of vapors (kJ/g) and

qrr is the surface re-radiation loss. For conditions where the sample is

burning the energy balance must account for the heat flux to the surface by

the flame, i.e.,

m= mb (4= + fc + 4r; qrr)/L (4)

where Wc, and qfr are respectively the convective and radiative components

from the flame to the cable sample. Measurements of the mass loss rate as a

function of external radiative heat flux allows one, as Tewarson describes, to

determine the other parameters. Ideally, qe would be the heat flux the

cable "sees" due to say an exposure fire; (qfc_ + q4r) would be the heat

flux the sample "sees" due to the burning of the samples' pyrolysis products;

qrr would be the amount of heat flux lost from the sample due to re-radiation

back into the environment. Note however, that conduction losses through the

actual burning configuration cannot be assessed from these laboratory-scale

tests. Thus with the mass-energy balance the optical density can be expressed

as:

D = (T/L)4 (5)

where n'" - '" for pyrolysis of this sample and q q + f + f r r

for combustion of the sample. From the above (and the test limitations), the

optical density, thus, depends on: (1) the thermal environment, (On- -rr);

(2) over- or under-ventilated environment, VT; (3) optical system and fraction of products responsible for light obscuration, T; and (4) the material,

18
t/L and q.rr The data on polymeric materials, as shown in Figure 3, suggest

that it may be possible to classify cable materials for T values based upon

their generic nature. For example, for cable #4 (see Table 1) which is

considered a highly chlorinated cable, the data from Reference 1 indicates

that at an external heat flux of 60 kW/m 2 applied to a sample of m!size

81(10)-4 m2 with an airflow rate of about 1.4(10)-3 m3 /s (thus VT =

1.4(10)-3/ 81(1O)-4 = 0.173 m/sec) the optical density is 5.5/m. From

Figure 3, with this value of D, the correlation for highly chlorinated

materials indicate that the quantity (1 /VT) (qn/L) is approximately 100;

thus, in'/L = 17.3 which is close to value of the average peak steady-state

value for mass loss rate (m"bý'•WL) of 15.8 that is recorded in Table 5-4

of Reference 1.

The question remains as to how one can relate this parameter, r, a

property measured at the burning/pyrolyzing source with those properties of

smoke normally ascribed to the "environment" just surrounding the detector.

For a plume rising in a quiescent environment, Heskestad( 9 ) notes that the

radial distribution of concentration of the products of combustion along the

ceiling of an enclosure is, except for scale, expected to be practicably identical to the radial distribution of excess enthalpy per unit mass of plume

fluid, cpAT, since both quantities are dispersed by the same turbulence

mechanism; i.e., cj/AT is a constant for the material where c, is the concentration of product, j, and AT is the gas temperature above ambient. Tewarson( 8 ) shows that indeed this is the case for over-ventilated fire conditions where the yield of the product, j, compared to that under stoichiometric

conditions is approximately constant. Under similar arguments then( 5 ,

8 ) the

ratio of the optical density per unit path length to gas temperature above

ambient, i.e., D/AT, is suggested to be a parameter for the evaluation of

response and spacing of fire detectors. This ratio has been analyzed in terms

of the properties of polymeric materials(B) and evaluated for various cable

samples( 1 ). Table 9 lists the results of the study on cable flammability

data under an imposed external heat flux of 60kW/m 2 . It is expected that

for flaming,, over-ventilated, fire conditions this ratio is a weak funttion of

external heat flux.

Heskestad and Delichatsios( 5 ) have used the ratio D/AT as a parameter

for the evaluation of the response and location of fire detectors in flaming

19
_ r PE/56% C j PS Foom

o4 PE/48% Pvc ',,4

0 Highly Chlorinotedl romatic

5-.0 Nonaromatic/Aroma tic,

Nonaromatic

o

0 0.o0 IoQO 1500 20o.0 250.0 300

(I/') (q /L)(g/m 3 )

Fig. 3. Optical density per unit path length as a function of

fuel vapor mass concentration; n = Ze + 4fs - qr

(From Reference 8)

20
Table 9

D/AT FOR THE COMBUSTION OF CABLE SAMPLES

IN NORMAL AIR AT 60 kW/m 2 a

Cable Sample

XPE/Neo (02)

PE, PP/CL-S.PE (#12)

FRXPE/CL-S*PE (015)

PVC (granular) b

PE/48%CL (granular) b

PE/36%C1 (granular)b

PE, NY/PVC, Ny (019)

XPE/Neo (*17)

PE, Ny/PVC, Ny (#18)

PE/25%CL (granular) b

PE/PVC (#4)

PE/PVC (#7)

PE/PVC (06)

Silicone, glass braid (#21)

XPE/XPE (013)

XPE/XPE (#14)

Silicone, glass braid/asbestos (#22)

XPE/CL*S*PE (*16)

U4PE (#l)

PE, PP/CL-S-PE (*#11)

PE/PVC (#3)

Nylon (granular)b

R4PE (granular)b

Teflon (020)

D(m-1

17.9

17.4

16.6

5.5

4.0

4.8

17.8

6.6

8.2

5.4

5.5

6.5

4.8

1.4

2.8

3.3

2.8

3.1

2.8

2.4

2.4

2A6

2.1

0.3

D/AT (iK)

0.647

0.630

0.563

0.550

0.395

0.387

0.357

0.294

0.269

0.250

0.185

0.166

0.160

0.133

0.127

0.126

0.125

0.107

0.082

0.080

0.069

0.062

0.039

0.013

Average peak values, D - in (I /1); L - optical path length (m),

I - optical transmission through air, I - optical transmission through the

mixture of products and air; AT - T d- T , T d gas temperature (K);

T - ambient temperature (K) ba

bResearch samples, data from Ref. 8

* From Reference (1)

21
fires. Basically the characteristic gas temperature rise at response is found

by dividing the optical density (e.g. 0.06m-1) by the measured respective

ratios of optical density to temperature rise found in the accompanying table.

From the information presented in this table, the range of characteristic

values of temperaturo rise at response would be from 1°C to 4.5%C if the optical density at response for all cables indicated is not larger than 0.06/m.

Detector spacing criteria, as described in Reference 5 and 6, is basically incorporating this characteristic temperature rise value with a fire

plume/horizontal ceiling gas-dynamic interaction model from which AT versus

radial extent along the ceiling can be predicted. Indeed a correlation of

this type, which is the basis for the spacing criteria presented in Reference

6 and 7 has been derived by Heskestad and Delichatsios(10) for steady and

parabolically growing fires. However, the detector siting design charts have

not, as yet, considered completely the thermal/particulate environment generated from burning electrical cables. Extension of this type of work with

electrical cable materials is one of the prime objectives of this report.

2.4 Initial Convective Flow in Fire

Heskestad and Delichatsios, under the auspices of the Fire Detection

Institute, have considered the physical modeling of the initial environment

generated by a fire in an enclosure that persists up to the time when recirculation of products of combustion begins to influence the further yield of

products. This is an important fire interval for fire detection problems

dealing with determining optimum spacing configurations of fire detectors.

Proposed modeling relations pertaining to idealized, yet realistic,

classes of unsteady fires and referred to as "power law" fires have been corroborated with experiments. These "power law" fires are by definition defined

as

Qc = actp (6)

which indicates that the convective heat release rate, Qc (watts) varies

with some power, p, of time, t, from ignition. For example, p=2, is often a

good representation of flaming and radially spreading fires in low fuel piles.

22
The coefficient, ac, determines the fire growth rate for a given power law

fire. For parabolic growing fires, p=2, as illustrated in Figure 4, the coefficient, ac, takes on the values of 4.44 (10)-2 kw/sec 2 for a "fast" fire

and & 79 (1O)-3 kw/sec 2 for a slow fire. These values reflect arbitrary

rate criteria but they do define within a practical range, the types of slowand fast-developing fires that might be expected from common burning materials. Also, since that release rate can be represented by the product of the

mass burning rate and the heat of combustion of the fuel, then the fire intensity coefficient, ac' is directly proportional to the heat of combustion of

the fuel.

Thus, fires can be sized by the rate of heat released, Qc- The detector site lOtatlon must be related to the size of the fire that one wishes

to detect. The size of the fire at threshold response, (Qcr), must reflect

the amount of damage equipment (see Sections 2.1 and 2.2) can sustain before

safety systems become impaired. Obviously, the smaller the critical fire or

conversely the larger the damageability indices for cables the more sophisticated will be the detection requirements. To have a detector system respond

before a fast developing fire grows to, say, 100 kw requires a idealistic

response time of approximately 50 secs (i.e. t = [(Qc)r/ac]l/2 =

[100/4.44(10)-211/2). Increasing the threshold fire size by an order of

magnitude indicates that the detector response time could be delayed by a

factor of 3.

Integrating Equation 6 with time and assuming that the only contribution

to the fire is from these hypothetical cables, the consumed cable material up

to detection can be determined, viz,

tr

mc (Qc)dt/Hc (7)

0

where Hc is the heat of combustion of the cable (J/gr), a value that can be

determined from small-scale tests (see Section 2.1). For a parabolically

growing fire the mass loss is

mc =(Qc)r] E 3 / 2 / 3qc 1 /2/H (8)

23
C11

u 200 400 600

TIME Isocl

Fig. 4. Idealized Heat Release and Fire Growth Rates.

(From Reference 6)

24
Data on the total mass loss of generic cables before electrical short

can also be used to determine approximately the range for early warning. The

question that must be answered is how this concept can be translated into

detector spacing. This requires knowledge of the dynamics of the fire plume

generated by the aforenoted, power law, transient fire within an enclosure.

Heskestad does provide scaling relationships relating plume temperature

rise and plume velocity as afunction of radial distances from the fire axis

and time with fire intensity and clearance distance between the ceiling and

the fire source as parameters.

Briefly, for fires growing with the second power of time explicit relations for a nondimensional temperature and velocity in the hottest layer under

large flat ceilings is given by

AT* it*-0.954(1+r/H)] / [0.188 + 0.313(r/H)]I 4/3 (9)

U*I(&T*)ll2 = 0.59(r/H)- 0 . 6 3 (10)

where the ( )* are nondimensional quantities defined as

A-2/5 T -1] -2/ A T * - A00 9 5H 3/5 AT (11)

= L* a H] -1/5 U (12)

t* Aac/H] 1/5 t (1 3)

where A = g/CpT.p. ; cp is the specific heat; p., T. are the ambient density

and temperature; g is gravity, and H is the clearance height between the ceiling and the combustible. These relations can be used to predict temperature

and velocity histories for arbitrary combinations of ceiling clearance and

fire growth rate.

This cited work of Heskestad and Delichatsios has been used, under the

auspices of the Fire Detection Institute, NBS, HUD, US. Bureau of Mines, Navy

Department and the Veterans Administration, to develop design siting information for aerosol and heat detectors( 6 ) once the detector/burning material

parameter, D/AT, is prescribed.

25
Before proceeding, it must be emphasized that this design information is

strictly applicable-to flaming, parabolically growing fires in quiescent

enclosures having smooth ceilings. Additional experimental corroboration is

required using cable material as combustibles.

2.5 Detection of Smoldering and Flaming Cable Fires

In accordance with the simple fire growth scenario presented previously,

the distribution of the smoke aerosol depends on the burning mode of the

material and its subsequent distribution within the enclosure. This latter

factor depends on room geometry and configuration and ambient conditions such

as temperature stratification and ventilation.

The three factors alluded to previously to specify the required spacing

of aerosol detectors for flaming fires in quiescent environments, namely,

* the response characteristics of detectors;

e the growth rate of the flaming fire; and,

* the acceptable fire size at detection

in accordance with the correlations previously sited were investigated by

Delichatsios( 3 ) using electrical cable material (Cable #17 in Table 1) as

the prime combustible. The effects of ceiling configuration and flow ventilation were also investigated within these preliminary tests in which two types

of commercially available smoke detectors were used. The sub-scale test

enclosure had a 2.44 m ceiling height with a length:width:height ratio of

5:0.5:1 (a corridor-type configuration).

The main conclusions drawn from this study indicate 1) that for these

preliminary tests the correlation presented previously are applicable to corridors involving burning electrical cables with no forced ventilation, 2) that

in still air smoldering fires larger than a size dictated by the ambient stratification within the enclosure can also be detected with spacing the same as

in flaming fires; and, finally, 3) that forced ventilation is still a study

area requiring additional testing.

26
Table 10 and Figure 5 summarize the spacing criteria developed for fires

involving the particular cable tested and for the particular detectors utilized using the corrolative approach previously described. For the tests,

however, the actual fire growth rate can be classified as "slow", f.e.,

•c-2.79(jo)- 3 kw/sec 2.

Thus, in practice, the following curves demonstrate how for a given detector and ceiling height, detectors can be spaced, S, so that for a fast or

slow burning fire releasing heat parabolically in time they should respond

when the fire reaches a stage where its rate of heat value release is QdPreviously discussed, the value of Qd chosen should be closely linked to the

damageability indices of heat Qd- The additional information required is

the gas temperature rise, ATr, at detector response which is a function of

the material burning and the installed detector. Similar charts as shown in

Figure 5 can be found in Reference 5 and 6 for combustibles other than electrical cables.

Table 10

DETECTION PARAMETERS *

Parabolic with Time Parabplic with Time

Flaming Cable Fire (10 W in 20 min) (100 W in 10 min)

(intensity) - slow fire - fast fire

Heat release at detection 104 W, 5 x 104W, 105W

Characteristic Smoke Detector 5-C, 10°C, 250C

Temperature Rise (ATr)

• From Reference (3)

27
201-

Slow fire

18- Fast fire

ATr 50C

16

EN

'N Od 10•

12 N1

NQd=5 x 101w

N-d- 1 l4W

0I23 4 5 6 7

Height Wm

Fig.L 5a. Spacings of smoke detectors on a square array under a flat

extensive ceiling: ATr = 50C.

(From Reference 3)

28
Slow fire

E

U)

Fost fire

14 ATr 1 OC

12-

8 N.

%, Od 10IOw

2 -" %4 d -5 x lO04w

Od =100w

q n w I n

C.

Height (in)

6 7

Fig. 5b. Spacings of smoke

extensive ceiling:

(From Reference 3)

detectors on a square array under a flat

ATr = 100C.

29
71-

Slow fire

E

Zl)

Fast fire

6[ ATr 25°C

5\

4-

Qd= s\ Qd=Ow

•,d s x 10 W

-0 2 3 4

Height ( m )

6 7

Fig. 5c. Spacings of smoke detectors on

extensive ceiling: ATr = 250C.

a square array under a flat i

(From Reference 3)

30
2.6 Exposure Fire Hazards to Cable Trays

The research programs described thus far have dealt with categorizing

cable flammability and damageability using small cable samples within

laboratory-scale and/or sub-scale enclosures. A first, and in our estimation,

notable step in incorporating these results into a quantitative assessment of

exposure fire hazards to full-scale cable tray configurations in a large scale

test enclosure has recently been completed( 4 ). The evaluation of exposure

fire hazards to cable trays has been conducted by an experimental test/

analytical program in the areas of (1) exposure fire categorization in open

environments, (2) exposure fire categorization within a sub-scale enclosure,

and (3) sprinkler and/or baffle protection requirements for cable trays within

a large-scale enclosure.

In this study, the time available for response to a particular exposure

fire hazard (a pool spill) is, reportably, predictable within certain limitations, from a combination of the following parameters:

* the enclosure ceiling height, floor area, and ventilation rate

e the location of cable tray

* the characteristic time constant and heat release rate of "pool" fire

* the maximum heat flux spatial distribution within the enclosure

* the critical heat flux for the particular cable type,.

The potential application of the enclosure fire tests is discussed in

great detail by Newman and Hill in the cited reference. An example of the use

of the data is also illustrated therein and repeated here as well. Illustrated in Figure (6) is the transient variation in "near ceiling" average heat

flux and temperature resulting from the burning of 80 liters of methanol fuel

in a 1.74 m pan located centrally on the floor of a-test enclosure having a

ceiling height of 4.57 m- and length-width-height proportions in this ratio

(L:W:H = 2:1:1). Forced ventilation provided 12 room changes/hour. Also

shown in this figure are:

1. istimates of the time at which a smoke detector would activate based

upon a prescribed value of temperature rise at detector response,

i.e. ATr as discussed by Heskestad & Delichatsios )(5) .3 

31
Smoke Detector Activation (3)

Activation (138 C Link)

2.5 1 V500

- C

Z 2-0 400E

10 • /• •,,• 200 E"

Onset of Cable Damage -E(2)

Human Response To

5 Fie Detection By 100 I// \•! mokeDetector

0 "20

0 60 120 t8O 240 300

Time From Ignition (s)

Fig. 6. Heat flux. and gas temperature at ceiling versus time from

ignition.

(From Reference 4)

32
2. The time for activation of a fusible' link sprinkler

3. The onset of cable damage (if a cable hý4 been located in the area

of the maurements) based upon the laboratory-scaled experiments of

Tewarson(1) or Lee

4. The time for manual response.

Detail evaluation of "exposure fire" test in open environment as well as

enclosures has lead to correlations relating the average heat flux with time,

vertical position, ventilation rate, pool spill characteristics, and floor

area. The following equation

r= (A/H2 ) {0.24 - (4.73) Vf/H 5/2 } (h/H) 1/ 2 (14)

correlates the maximum heat flux, qm, (kw/m 2 ) to be expected ,atr.anyp point,

h, (vertical height, m) in the enclosure with the enclosure ci~aracteristics,

namely, ceiling height, H, (m) and ventilation rate, Vf , (m3 /s) and fuel

spill characteristics, namely fuel heat release rate, 6r (kw/m 2 ) and.spill,

size, A, (i 2 ). Furthermore, a correlation of the instantaneous heat flux, 4"

normalized with respect to the aforenoted maximum heat flux, qm , is represented by the relation

q"/4m (h/H) 1 / 2 0.52 + 13 Vf/H5 /2 (t/r) 0.9 (15)

where T is a time constant that characterizes the time required for a pool of

a given combustible and size (in terms of diameter,-, .) .to r each the steadystate heat release rate, Q..

The above two correlations (one quasi-steady and the other time dependent), which can predict heat fluxes from an exposure fire within an enclosure

as a function of enclosure height, location of interest, within the enclosure,

ventilation rate, and exposure fire time and size, haveIbeen based-upon the

experimental observation of minimal horizontal variations in heat flux. As

such, although it is reported that these empirical correlations can eappIlied

directly to rooms of shape similar to the enclosure studied, i.e., r6oms with

length:width:height ratios of 2:1:1 care must be exercised in util;i zing these

correlations to other geometrically-shaped rooms. These limitations are

33
discussed further in the cited reference. It would.have been interesting,

however, if correlations tike the above could have been extended to include,

in addition to enclosure-room thermal environment, properties of smoke which

are directly attributable to detector response, viz. particle co'ncentration

and size.*

2.7 Summary

The previous discussions have briefly touched upon the most recent

relevant work involving electrical cable flammability, damageability, hazard

assessment and detection and, to some extent, indicates that evaluation of

exposure fire scenarios is a complex problem requiring many types of interrelated data. Indeed, the consolidation of these studies can provide planners

and engineers with useful information for formulating interim guidelines

needed for designing protective systems and assessing fire hazards to electrical cables in utility environments.

However, from a fire detection point of view, the very complex nature of

the properties of smoke and its transit, and the interrelationship between

these properties and detector response characteristics require further .xtension into these particular endeavors to obtain additional representative data

on the environmental characteristics of electrical cable fires considered

necessary for the design of ionization detector siting criteria and applications. These studies should initially involve detection of fires where the

only combustible present is the electrical cable.

3.0 ELECTRICAL CABLE FIRES AND FIRE DETECTOR ENVIRONMENTS - TEST PLAN

3.1 Scope

Regarding automatic fire detection, a prime consideration is the rate of

smoke movement from the fire source to the detector. Under a no-fire condition

air movement in a room or compartment is determined by forced convection for

heating and air conditioning purposes; by external winds, or by free corvec-

*It is also believed that correlations of this type together with cable

flammability and damageability indices can provide adequate guidelines for

safe separation distances once a design basis exposure fire is chosen.

34
tion attributed to heat sources. For very small (or incipient) fires, the

buoyancy effects of the fire heat are negligible and smoke will follow existing air circulation patterns. As the developing fire becomes larger, the hot

plume can have sufficient buoyant lift to reach'the ceiling and move radially

outward thereby creating a new air circulation pattern within the compartment.

It is possible also that temperature-induced stratification will alter this

type of smoke movement. For early detection of fires, these foregoing factors

are crucial in determining detector response.

A further consideration is the response characteristics of the automatic

detector to the particular smoke, (and hence the burning material) which can

vary with the time-dependent concentration and particle size of the smoke at

the detector. Other factors include the smoke velocity past the detector, its

orientation, its entry characteristics and its operating principle.

Indeed the problem of detector siting/response is highly complex but

fortunately both analytical and experimental progress, highlighted above, has

been made.

The purpose of this experimental program is, therefore, mainly confirmatory in nature in the sense that it should verify the sit.ing criteria previously established but, now, involving electrical cables as the prime combustible material.

The overall effort envisioned should be divided into three major phases

to assess the environment surrounding the fire detector, viz,

Phase 1: Effect of Fire Size, Ceiling Height and Cable Material

Phase 2: Effect of Fire Size, Ceiling Configuration and Cable Material

Phase 3: Effect of Fire Size, Room Volume and Ventilation.

3.2 General Considerations

The detectors involved in each of these phases should primarily be of

the ionization type since these types of detectors are normally 'found in

nuclear reactor utilities. In addition, the test should-be conducted and

measurements made so that optimum utilization of the results from the laboratory

and sub-scale experiments, that are discussed above, could be implemented.

35
For example, the electrical cable flammability tests(I) have indicated

that polyethylene/polyvtnylchloride cable, polyethylene-polypropylene/

chlorosulfonated polyethylene cable and silicone cable samples represent high,

intermediate and low fire hazarcba'sed upon mass loss and heat release ratesin

flaming fires. These types of cables are, in most respects, consistent with

the indices describing high, intermediate and low electrical failure

rating(2). These studies have also shown that for the types of cables

tested, the minimum external heat flux for the onset of the damage process is

approximately 20 kw/m 2 (;6345 BTU/hr.-ft. 2 ). As such, thermal exposure to

the electrical cables should be based upon this minimum value.

This brings to bear as to how to generate the electrical cable fire.

Measurements( 4 ) on an enclosure's thermal environment due to liquid spill

fires has been found to be 90-95% convective; the remaining attributable to

radiative heat transfer. One could then possibly use a liquid, such as acetone which produces negligible smoke as the external thermal source. Indeed,

this has been the case in the corridor-study( 3 ) described 6bove where lightextinction measurements were used to corrolate detector response. Since this

form of optical measurement methods can be used to measure particulates only

down to a few tenths of a micron range and since, in this study quantitative

evaluation of the response of ionization-type smoke detectors is desired which

can be sensitive to particles an order of magnitude smaller in size, it is

expected that the use of a flammable liquid, negligible smoke producing

notwithstanding, may give pre-mature indication of response to fires which are

not directly attributable to the burning of electrical cable material. Also,

possible condensation of water vapor on inherent dust may preclude, by the

same reasoning, the use of gas-ribbon burners. Consequently, radiating panels

are considered the likely candidate for supplying the external heat source.

Another factor which should be common to the overall test plan is the

size of the cable tray, cable configuration and load, and cable area subjected

to exposed heat flux. For consistency with past experiments in cable fires it

is anticipated that standard open ladder cable trays between 2.5 to 3 meters

in length be used with cables arranged in a,"figure eight" pattern. Size of

cable will then determine percent "fill." The length of cable tray subjected

to the external heat load should be a parameter of the test ranging from 10%

to 50% of the overall tray length.

36
Also, judging by the results of the laboratory-scale kits, external

radiative heat loads should be parametrically varied from between 20 kW to 70

kW per square meter of expose cable area. The cable tray structure should be

such that mass loss rate of the cable material could be monitored., Also, the

radiating panels should not duly interfere with the subsequent smoke movement.

3.3 Specific Considerations

Since the two major tasks for the Phase 1 program are to confirm recent

detector spacing as a function of 1) burning material and 2) ceiling height,

tests should be conducted in facilities that provide a rather large expanse of

unobstructed ceilings so that the ionization detectors chosen can be positioned at various radial locations from the center of the plume/ceiling

impingement point. Present thinking is three radial locations, viz, 20%, 50%,

100% of the ceiling height, where detector "boards" housing the various

ionization detectors can be mounted. The facility (or facilities) must also

provide sufficient flexibility so that ceiling height can be varied (eg. 3, 6,

9 m heights); sufficient volume so that any recirculation of products of

combustion due to the confining walls do not affect the subsequent readings;

and also provide a quiescent environment to the developing plume. For the

higher ceiling tests, any pre-test thermal stratification should be determined

and its effect on the developing plume assessed. Being confirmatory in

nature, the test plan, test execution, and measurements should follow closely

the procedure established in Reference 5 as well the improvements discussed

therein.

There is one major exception, however, and this has to do with the exclusive use of beam-type optical density meters for determining the requisite

smoke properties at the various detector locations. Present thinking (e.g.,

Reference 11) is that due to the complex nature of smoke, measuring instrumentation in detector standards tests, should react on only those properties of

smoke which affect the detector under tests. This implies that the standard

shall be based on similar operating principles as those of the detector.

Presently, a standard ionization chamber is available( 1 2 ) and should be

utilized in the test program. The analog signal from this device is directly

related to the product of smoke particle concentration, N, and mean particle

37
size, d p, - a combination of smoke-dependent parameter which also affects

commercial detectors output voltage. These tests may prove that instead of

corrolating the ratio D/AT one should attempt to correlate the ratio (Ndp)/AT

for purposes of establishing ionization detector siting criteria.

A typical fire test room along with ceiling-mounted instrumentation is

depicted in Figure 7 where the standard ionization measuring device, denoted

as MIC, is shown together with an optical beam density instrument. How the

output of this device can, with the use of an analytical representation of a

coagulating buoyant plume, be used to assess the relationship between fire

size and threshold response has been discussed by Boccio.( 1 3 )

It is believed also that use of a reference ionization instrument in

addition to an optical beam densitometer may provide the added information required for assessment of detector spacing under smoldering fire conditions

that had been lacking in previous experimental programs. Smoldering cable

fires can be generated using external radiative heat flux in the range of 16

to 24 kW/m 2 .

For the Phase 2 subprogram the prime objective is to confirm the siting

criteria for beamed ceilings.( 6 ) As such, the addition geometric parameter

that should be varied are beam depth, h, and beam spacing, L. Ratios of ceiling height to beam depth and beam spacing to beam depth should be consistent

with those typically found at reactor utilities. Also, the experimental work

cited in Reference 6 indicates that the presence of a "curtain" around the

test ceiling has a profound effect on the temperature field everywhere under

the ceiling except in the neighborhood of the plume/ceiling impingement region. However, unaccountability of walls or other obstructions have been reported to yield siting criteria that is conservative. As such, using a "freestanding" ceiling in Phase 1 and 2 sub-programs is considered satisfactory.

Since ventilation rate is the crucial parameter to be varied in the

Phase 3 subprogram, construction of a representative test enclosure must be

considered. With the idea of using and/or augmenting as much of the work on

cable flammability, damageability, and fire detection already reported, a test

cell with dimension and proportions (L:W:H = 2:1:1) used by Newman and Hill( 4 )

in their assessment of exposure fire hazards to cable trays should be considered. The reasons for such a configuration as discussed in Reference 4

38
Fig. 7. Typical fire/detector sensitivity test .room,

L:W:H = lOm:8m:4m

39
are: (1) any test results would be more or less representative of an actual

room (other than a corridor) in a utility, and (2) any test results can be

applied, through in-house modeling relationships,( 14 ) to typically-much

larger geometrically similar enclosures. This concept of applying the test

results for one size of enclosure to other different sizes is discussed more

fully in the cited reference along with its limitations.

Also, using a test enclosure of the aforenoted proportions, it would be

interesting to see if the correlations that have already been developed for

the heat buildup would lead to similar lines for correlating the aerosol

environment within the enclosure. That is, would the horizontally-averaged

value of the product of particle concentration and particle size (Ndp) scale

to the source value have the form:

(Ndp)/(Ndp)o - (A/H2 ) P(h/H)d lkl - k2 •/f/H 5/2 q

for lf < k1H5"A/k2 .

Ventilation rates, therefore, should also be similar, i.e., volumetric

throughput should be such as to provide 0, 6, and 12 enclosure room air

changes/hour. These are considered to be representative of the ventilation

extremes for typical room environments in utilities.

3.4 Measurement Considerations

For the Phase 1 and 2 subprograms instrumentation necessary for the

measurements of gas temperature, plume velocity, convective heat flux, smoke

parameters (optical density, oarticle number concentration and size or a combination thereof) should be concentrated along the ceiling in line with the

installed ionization detectors. Also, in order to determine the heat release

rate as a function of the externally-applied radiative flux means should also

be provided to measure mass-loss rate of burning material, at least, and also

oxygen depletion rate. The data of Tewarson(1) along with the mass depletion rate can be used to determine approximately the actual heat release rate.

40
A more realistic value would be obtained if in addition the oxygen depletion

rate was also measured since from these two measurements the actual heat of

combustion could also be determined. Assuming adiabatic conditions, the convective fraction of this heat release rate can be determined from the ceiling

measurements of temperature and velocity. Complete knowledge of the developing plume would require an inordinate amount of instrumentation which is

deemed to be unfeasible. As such pre-test planning should consider the best

location for the limited number of instrumentation that may be considered

adequate.

For Phase 3, the added complexion of forced ventilation requires, in

addition to ceiling-mounted and fire source instrumentation, additional instrumentation (temperature, smoke, etc.) stations mounted vertically through

the test enclosures to probe the local environment within the enclosure. In

Reference 4, five instrumentation stations within room enclosure of surface

area 27m2 was deemed sufficient. Accordingly, the ratio of instrumentation

stations per unit floor area should be approximately one station per 5 square

meters. The actual number and vertical location of probes mounted at each

station should be part of the pre-test plan.

Measurement of detector response along with the aforenoted variables

would then supply the necessary preliminary data to: (1) confirm existing

correlations (when applicable), (2) augment these correlations, and (3)

provide additional data for detector siting criteria not already established.

3.5 Summary

This section has discussed in rather broad terms a three-phase confirmatory test program concerned with evaluating the performance of fire-detection

systems within nuclear facility type environments. It should provide data

which can be used with recent state-of-the-art advances in detection systems

and cable damageability to establish a basis for a guide for detector selection and siting criteria. Detector siting criteria involve complex and highly

'coupled physical phenomena. This report, as such, has only delved into three

of these broad areas, namely ceiling height, ceiling configuration, and ventilation, needed for assessing detector performance within a thermal environ41
ment generated by flaming electrical cables. An effective, comprehensive program requires-a viable combination of detector standards tests together with

environmental "fire" tests such as those which have been described.

Specific details of the overall test plan, especially the specific type

of measuring instrumentation, gas-dynamic probes, etc. and the associated data

reduction procedures necessary to determine the requisite parameters to confirm and/or augment existing correlations for detector siting criteria have

not been discussed. Addressing these particular issues now is not considered

crucial for meeting the immediate objectives of this report.

4.0 FINAL SUMMARY

Although the capabilities of technology, as it applies to fire detection systems, have made significant strides due to increased public awareness

and regulatory actions, these advances in detector selection, siting, reliability, and approval tests have not substantially addressed the fireprotection requirements within nuclear reactors.

In particular, this report has stressed some of the basic requirements

and considerations needed for establishing siting criteria for ionization detectors. Particular emphasis has been placed in establishing or confirming

siting criteria for early warning detection of electrical cable fires.

An overall fire surveillance plan, typified in Figure 8, necessitates

consideration of many factorswhich integrate technology and personnel in the

decision chain. To properly design the detection phase of the overall system

requires a more deterministic appraisal of electrical cable fire development

and growth, the degree of damageability that electrical cable trays can sustain before impairing operation of safe-shutdown systems, and therefore, the

time necessary for detector alarm.

Each of these factors involve highly complex and coupled fluid-dynamic

and chemical-kinetic phenomena and, as such, detailed knowledge of all the

physical ingredients and their interactions is beyond the capability-of analysis.

42
I I I (.)tO 11tO2 1103 t04 105t 1 Itj t$ 4 t5 + •""with Theoreticaldcountsoof fire-fighting flm

IIrdeo | . registration riot recommended L L L •Automatic L extinuihiftg ayptem

-•%._ • necmallry depending upon

Incident Star Incipient forty warning Stan of Reaction Stan of Decisin: strt of 1n11i111 As Il Turo,-Q

OTli-e hosel before detector RS chock * of o___- celin Re o - E__erg__nt: rescue Ind Hill- m o ir m o Fife detecion d -totll file - clno of 14 chick signaml -" presslain fighl-n d@W- dIecet

by dutector pearsonrocn chock b* pulhh-b•tlton. ophra,* n ment tom Ftlonwing fore depenlin+e~lt

Ti-e point 101 -- 19 -- gint I I II iI--2 '12 t I -- t| 3 131 13--14 t4-

Time require- I - I unknown -- ca. 2 mnn -- to . 4 "'1". - to .i 3 min. tol. $i1

lime requitotan l Igl ... I1 - | min. co €.I ORION. elf€i. 12,

Detection choe0 Reaction, assembly and fite-figlitngl phls*

•RS chock = Rise&

Fig. 8. Qualitative relationship between time and damage for different speeds

of fire development and average detection, reaction and fire-fighting times. (From Reference 15)
However, laboratory-scaled and sub-scale tests discussed, which attempt

to quantify I'1 elctrical cable flammability and damageability characteristics, together with 2) modelling and testing the initial convective flow of

fire, both in sub-scale and full-scale facilities, will provide the necessary

ground work In effecting an adequate set of guidelines for early warning fire

detecti on systems.

By presenting an overview of this recent research, this report describes

a set of confirmatory tests where the results of electrical fire development

and growth are coupled with the parameters needed to assess detector response

so that existing detector-siting criteria may be appraised.

The information acquired will help provide planners and engineers with

adequate guidelines to select appropriate cables and-type of detection protection systems, thus improving safety within the facility.

44
REFERENCES

1. Tewarson, A., Lee, J.L., and Pion, R.F., "Categorization of Cable Flammability Parameters," EPRI NP-1200, October 1979.

2. Lee, J.L., "A Study of Damageability of Electrical Cables in Simulated

Fire Environments," EPRI Report, EPRI NP-1767, March 1981.

3. Delichatsios, M.A., "Categorization of Cable Flammability: Detection of

Smoldering and Flaming Cable Fires," EPRI Report, EPRI NP-1630, November

1980.

4. Newman, J.S., and Hill, J.P., "Assessment of Exposure Fire Hazards to

Cable Trays," EPRI Report, NP-1675, June 1980.

5. Heskestad, G., and Delichatsios, M.A., "Environments of Fire Detectors -

Phase 1: Effect of Fire Size, Ceiling Height, and Material, Volume 2

Analysis," NBS-GCR-77-95, July 1977.

6. Benjamin, I.A., "Detector Response in Large Buildings," Joint NBS-SFPA

Workshop on "Engineering Applications of Fire Technology," NBS, Gaithersburg, Maryland, April 16-18, 1980.

7. Boccio, J.L., Asp, I., and Hall, R.E., "Acceptance and Verification for

Early Warning Fire Detection Systems (Interim Guide)," NUREG/CR-1798, May

1980.

8. Tewarson, A.,."Physio-Chemical and Combustion/Pyrolysis Properties of

Polymeric Materials," FMRC Technical Report RC80-T-79, November 1980.

9. Heskestad, G., "Pressure Profiles Generated by Fire Plumes Impacting on

Horizontal Ceilings," FMRC Technical Report, RC80-T-54, August 1980.

10. Heskestad, G., and Delichatsios, M.A., "The Initial Convective Flow in

Fire," Seventeenth (International/Symposium Combustion) The Combustion

Institute, pp. 1113-1122, 1978. Also FMRC Report No. RC79-T-2, January

1979.

11. Bukowski, R.W., "Smoke Measurements in Large and Small Scale Fire Testings," National Bureau of Standards Report NBSIR-78-1502, October 1978.

12. Scheidweiler, A., "The Ionization Chamber As A Smoke Dependent Resistance," NFPA Fire Technology, May 1976.

13. Boccio, J.L., "Ionization Detector Response in a Coagulating Buoyant

Plume," Brookhaven National Laboratory Report, BNL-NUREG-29449, March

1981.

14. Heskestad, G., "Modeling of Enclosure Fires," Fourteenth Symposium

(International) on Combustion, The Combustion Institute, pp. 1021-1030,

August 1972.

15.. Ruggli, M. and Daetwyler, F., "Cerberus Alarm Concept" Cerberus, Ltd.,

Mannedorf, Switzerland.

45

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