NATIONAL BUREAU OF STANDARDS REPORT

6319

ROUND ROBIN FLAME SPREAD TESTS

BY THE RADIANT PANEL TEST METHOD

by

D» Gross

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BIJREAIJ OF STANDARDS

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SfHATIONAL BUREAU OF STANDARDS REPORT

MB* BROiCCT

1002-20-^875

MBS REPORT

February 24, 1959 6319

ROUND ROBIN FLAME SPREAD TESTS

BY THE RADIANT PANEL TEST METHOD

by

D. Gross

for

Tri-Service Building Materials Investigation Committee

IMPORTANT NOTICE

NATIONAL BUREAU Of

intended for use within 1 to additional evaluation 1 listing of this Reporti eltl the Ofttce of the Director however, hy the Governm

to reproduce additional c

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

or progress accounting documents

is formally published it is subjected

ting, reproduction, or openditerature

irmisslon Is obtained In writing from

. C. Such permission is not needed,

caiiy prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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ROUND ROBIN FLAME SPREAD TESTS

BY THE RADIANT PANEL TEST METHOD,

ABSTRACT

A report is presented of the first interlaboratory

comparison of flame spread measurements as determined by

the radiant panel test method. A total of eight laboratories

including National Bureau of Standards made measurements on

four acoustical tile materials provided by ASTM Committee C-20.

Analysis of the results indicate that the precision of the

measurements within laboratories was similar but that considerable systematic bias was observed between different

laboratories. These biases were such that the participating

laboratories yielded flame spread indices which were generally

lower than those measured by NBS, Subsequent checks on radiation pyrometers and radiation measuring techniques used by

five of the seven participating laboratories indicate that the

radiant panel energy output level used by these laboratories

was lower than that intended. Although other differences were

observed between the test methods used and the results obtained

at the various laboratories the primary cause of the biases

observed appears to have resulted from the use of uncalibrated

radiation pyrometers.

INTRODUCTION

A program to evaluate the degree of correlation between

results of flame spread test methods was undertaken by Subcommittee II of ASTM Committee C-20 on Acoustical Materials.

The Task Group authorized a series of round robin tests to be

conducted by laboratories employing the radiant panel flame

spread test method^ to supplement similar round robin tests

by laboratories employing the tunnel method for flame spread

rating (E 84-50T) and the eight-foot tunnel test method of

Forest Products Laboratory.

The Task Group made available to the National Bureau of

Standards approximately 4o tiles of each of the four acoustical

materials tested in the tunnel round robin study. The four

materials for the radiant panel round robin series were received at NBS on September 9? 1958 and sent out to seven

participating laboratories on October 3, 1958. The materials

were identified only by the code letters "W" , "X" , "Y” and "Z"

with no reference to appearance, characteristics or manufacturer.

2

PARTICIPANTS

All private and commercial laboratories which were known

to have installed the radiant panel flame spread test equipment at the time, were contacted and all agreed to participate in the round robin study. In addition to NBS, the

following laboratories participated:

Benjamin Foster Company

^635 W. Girard Avenue

Philadelphia 31 ? Pa.

Curtiss-Wright Corporation

Research Division

Quehanna, Pa.

E. I. duPont de Nemours & Co.

Engineering Test Center

Wilmington 98? Del.

Johns -Manville Products Corp.

Research Center

Manville, N. J.

The Lubrizol Corporation

Cleveland 17 ? Ohio

National Gypsum Company

1650 Military Road

Buffalo 17? N. Y.

United States Testing Co., Inc.

1^15 Park Avenue

Hoboken, N. J.

TEST PROCEDURE

The study reported was purposely carried out prior to any

cross checks between laboratories. In many instances the equipment had been assembled, installed and adjusted without detailed

discussions or visits to NBS in connection with this equipment.

In a few instances visits had been made to NBS for the purpose

of clarifying some test procedure details. In only one instance

had one of the participating laboratories been furnished two

specimens each of three materials together with the flame

spread index as determined at NBS.
'J-^. I
- 3

-

Details of the test procedure used in the radiant panel

round robin were specified in a preliminary draft of a proposed Federal Standard for surface flammability entitled

"Suggested Method for Flame-Spread Classification of Materials"

copies of which were distributed to the participants* The

outlined procedures were considered to be sufficiently detailed

to permit testing under controlled and reproducible conditions*

However, a certain amount of reasonable discretion on the part

of individual operators and laboratories was inevitable in the

manual test procedures*

The prescribed procedure for the conditioning of specimens

prior to test consisted of pre-drying for 2k hours at l60F

followed by conditioning to equilibrium at 73 ±, 5F and 50 + 5^

relative humidity. This procedure, which reduces differences

in moisture content resulting from approaching the equilibrium

condition from a high or from a low moisture level, was suggested

by Mr* R* H* Neisel of Johns-Manville Corp*

RESULTS

The results of the tests are summarized in the following

tables* To maintain the confidential nature of each laboratory's results, code letter identification has been given to

all participating laboratories other than NBS. Individual and

average flame spread index values are given in Table lA and

the corresponding flame spread and heat evolution factors in

Table IB* Moisture content and smoke data are listed in Table II*

Some characteristics of the individual test apparatus are indicated in Table III from which may be noted the wide variety of

gas types, BTU content, hours of operation, etc*

ANALYSIS OF RESULTS

A. Statistical

Analysis of previous data at NBS has shown that, in general,

for low values of the flame spread index (below 10 - 15 ), the

indicated variability expressed as a coefficient of variation

is not a representative measure of the precision of the experiment* It was considered that the inclusion of material "X" in

a statistical analysis of the interlaboratory results would not

add any useful information and the analysis is therefore based

upon eight laboratories and materials "W"

,

"Y" and "Z" only.
; 'a cting x

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Assuming that the standard deviation is proportional to

the mean2, the logarithms of the flame spread index values are

used in the analysis » Figure 1 is a graph showing the flame

spread index for each laboratory plotted against the average

flame spread index for all laboratories on logarithmic coordinates o It is evident that laboratories tend to be consistently

lower or consistently higher than the average values for all

laboratories o Numerical analysis further confirms the existence

of systematic bias which could result from shortcomings in

specification of the test procedure ^ from individual modifications

in the test procedure, or from different operating conditions o The

latter effect will be discussed in detail in the next section^

Excepting for material "X'% the intralaboratory precisions of the

laboratories as measured by the standard deviations of the replicated tests, are of similar magnitude and equivalent to an average

coefficient of variation of approximately 20^ o These results are

in line with statistical experience which shows that laboratories

usually vary considerably in their biases and vary relatively

little in their individual precisions

o

B. Experimental Bias

None of the remarks received from the individuals performing

the tests at the various laboratories Indicated that the contents

of the test specification were either overly vague or unduly

restrictive o Although the test specification was closely followed

in most particulars, some deviations- were notedo A large portion

of the experimental bias appears to have been Introduced by

differences in the callbra.tions of radiation pyrometers used for

monitoring the energy output of the radiant panel o Five laboratories procured identical model radiation pyrometers from the

same manufacturer with the implied understanding that they were

calibrated instrumentSo A comparison of h of these pyrometers

subsequent to the test program showed that this was not the caseo

Since NBS and laboratory F are the only laboratories known to have

performed their own pyrometer calibrations, the other laboratories

were actually operating with, uncalibrated instrumentSo It should

be noted, however, that laboratory F performed its calibration at

a temperature considerably above 670^0 and without use of a blackbody source o Table IV lists the measured millivolt readings

corresponding to a blackbody temperature of 670° C for those pyrometers subsequently ca.li.brated at NBS; the millivolt readings used

by laboratories C, D, E, and F also given for comparisono In each

case use of the assumed millivolt reading resulted, in operation of

the radiant panel at an energy output level corresponding directly

to the bias in the results o It was further determined that laboratory A, in employing a narrow angle pyrometer and sighting on the

hotter portio.n of the lower .half of the panel was also operating

its panel at a considerably lower energy output than that specifiedo

- 5

-

DISCUSSION

A more detailed investigation of the method for standardization of the radiant panel energy output leads to several

necessary considerations <> These involve the spectral transmittance characteristics of the radiation pyrometer lens or

window and the emittance characteristics of the radiant panel

itself

o

In order to evaluate the effect of the radiation pyrometer

optics, a series of measurements were made using a radiation

pyrometer with a calcium fluoride lens as well as this instrument

with assorted windov;s placed in front of it» The results are

shown in Table Vo The differences observed between the readings

obtained while sighting at a blackbody source and those obtained

while sighting at the radiant panel source were small o Although

this is an indication that the overall emittance of this radiant

panel is fairly high, no information was available on the spectral distribution of emittance or on the variability to be

expected between different radia.nt panels o For this reason,

several computations were performed based on the assumption

that the radiant panel emits energy as a grey body, ioO.., one

whose emittance is less than one and is Independent of wave

lengtho Taking the average wave length cut-offs for fused silica

and calcium fluoride as 3»8 and 9-5 microns, respectively,

Figure 2 shows the percent energy emitted as a function of emittance for two lens-type radiation pyrometers. If the emittance

of the panel were lower in the near infrared region (below ^ microns), as some information indicates it may be, these

differences would be further magnified.

It should be noted that the thermal detector of a radiation

pyrometer with a calcium fluoride lens "sees" 89^ of the energy

emitted by a blackbody at 670“C whereas one with a fused silica

lens or window "sees" only kOfo of this energy. In addition, the

droop of the calcium fluoride curve with respect to emittance is

much less pronounced than the fused silica curve. Thus, a radiation pyrometer with high transmission in the infrared appears to

have significant advantages for standardization of the radiant

panel output.

SUMMARY

A series of round robin tests v;ere performed by eight

laboratories equipped with the radiant panel flame spread test

equipment as authorized by Subcommittee II of ASTM Committee C-20

on Acoustical Materials. The test equipment was installed in the

other seven laboratories from the published descriptions of the

apparatus and with little or no prior checking or material testing.

There was considerable variation among the laboratories in the type

and heating value of the gas supplied to the radiant panel, in

the type of instrumentation used, in the hours of operating experience prior to this series of tests, etc. Some deviations

from the test specifications distributed to the participating

laboratories were observed.

The test results are given in Table I. Analysis of the

results Indicates the existence of systematic experimental bias as

shown by consistently low or consistently high flame spread index

values by individual laboratories relative to the overall averages.

Subsequent investigation revealed that differences in the calibrations of the radiation pyrometers used to monitor the energy

output of the radiant panel accounted for a large portion of this

systematic bias. The extent to which a laboratory's results were

low bore a direct relationship to the low energy output at v/hich

its radiant panel operated and necessarily to the difference

between the calibrated and assumed readings of its radiation

pyrometer. The intralaboratory precisions vjere found to be of

similar magnitude and v/ere equivalent to an average coefficient of

variation of approximately 20^.

Analysis shows that a radiation pyrometer with high transmission

in the infrared has advantages for standardization of the radiant

panel output. The necessity for calibration of the radiation pyrometer has been demonstrated. Under energy output conditions established

by means of a calibrated radiation pyrometer and by close following

of the test specifications, improved interlaboratory agreement may

be expected.

ACKNWLEDGEMENT

The participation of the National Bureau of Standards in this

study was supported by funds furnished by the Department of Defense

in connection with the establishment of a Federal Standard for

surface flammability. The study was made possible through the

splendid cooperation of the many individuals who performed and

directed the testing at the participating laboratories. The aid

of Mr. H. H. Ku in the statistical interpretation of the test results

is gratefully acknowledged.
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REFERENCES

1. "A Method For Measuring Surface Flammability of

Materials Using a Radiant Energy Source” , by

A. F. Robertson, D. Gross and J. Loftus, Proc.

ASTM, 56, 1^37-1^53, 1956.

2. "Flame Spread Properties of Building Finish Materials",

by D. Gross and J. Loftus, Bull. ASTM 230, 56-60, 1958

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TABLE I. Radiant Panel Round Robin Test Results

A, Flame Spread Index

Laboratory

Specimen

KBS A B C D E

. F G

Average

All

Laboratories

W , 171 H[B5

!^7 179 185 167 384 329 346 248

klh 192 194 149 372 330 274 180

*+02 167 191 185 357 335 365 213

398 180 220 166 331 _329 519 206

W Average w “T5o 198 ~T6B 361 iH 376 'ToS . 279 ...

X 1.2 4.8 6.15

0

1.5 19.0 10.6 N* 10.4

k-.O 4.2 1.92 0 12.8 2.8 N* 9.0

1.1 7.2 5,84 0.52 7.3 13.0 N*

L2.0 9.0 4.25 0 6.3 8.4 N+ 24

X Average 4.6 6,._3 4.54 'o'.'4 11 ._3 8.7 N+ 21.1 7.1

28 43

106 45 63 28 Il4 74 93 48

Y 83 4o 30 91 69 101 58

99 33 49 30 Il4 65 147 55

86 33 62 28 ... , 77 70 _ 170 . 57 . Y Average 94-.. 38 56 .. 29 99 70.:, _ 128 . ...5.2 .._ 71

16 93

34 26 26 18 49 49 21 37

33 22.5 19 18 44 45 50 44

50 17 27 20 50 4o 36 52

. 29 18.2 29 21 .. .36... 31

Z Average -3.6 20.9 - 25 19 45 41 _36 -5l._ .34

*N Negative value. Taken as zero in computing averages

TABLE

Average

all

Laboratories

Fs

C

21.9

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TABLE II. Moisture Content and Smoke Evolution Data

Laboratory

NBS A B* C D F. + * F G

"W" Moisture

content, $

Smoke . me 8.0 7.8 4.95 8.0 5.2 6.6

0.0 0.4 1.9 0.1 .... 0.1 0 . 2 ^ 0 .^ "X" Moisture

content, %

Smoke . me 2.2 2.6 1.36 2.0 1.4 1.53

0.0 0.1 .... 0.2 .... 0.1 .... 0.0

"Y" Moisture

content, %

Smoke, me 7.2 6.9 4.53 6.7 5.0 4.49

0.4 0.3 0.6 0.5 .... 0.3 0.2 0.9

"Z" Moisture

content, %

Smoke . me 7.2 7.3 3.60 5.4 4.2 4.250.1 0.2 0.7 0.6 0.5 0.1 0.3

Note: Moisture content is expressed as a percentage of the oven-dry weight.

* Conditioned at relative humidity.

** Conditioned at room temperature and humidity.

All others conditioned at 50 + 5 ^ relative humidity.

TABLE III. Operating Characteristics of Test Apparatus

Laboratorv

NBS A B C D E F G Date placed in

operation

T955 Feb.

1957

May

1957

Jan.

1958

Aug.

1958

Sept

1957

. Jan.

1957

Oct.

1958

Total hours of

operation, approx. 2000 80 200 100 100 500 8

Type of gas supplied

to radiant panel

Mfgd

Natural plus

natural

PropanePropanePropaneCity Illuminating

Natural

plus

artificial

Heating value of

gas BTU/ft8 1050 b04 2400 2336 .2550 750 604 900

Stack calibration

constant jg, deg Fmin/BTU ^

0.92 1.1 0.90 0.97 0.7 0.77 0.97 0.9

Radiation pyrometer a b c a a a a a Method of calibration of pyrometer NBS MFR MFR + + * + *

Hood above apparatus ? Yes No • • • • Yes Yes Yes Yes Yes

a. Calcium fluoride lens

b. Fused silica lens

c. Fused silica window

* Procured on the basis of pre-calibration but found as a result of

this study to be uncalibrated.
'4

,1
TABLB; JV, Compai'lson Betv/een Headings of

Identical Model Radiation Pyroinetei'o

Laboratory Reading of Radiation Pyromete r-Blackbody at 670'^

C

r

! Measured at NBS ! Assumed

1 NBS

j

i

2 c, b 3 inv + ^ 2.b3 rnv

1 c 1 5.25 i 3.05

”

1 3.20 ( 3.03

1 E 1 3.5-3 , 3.03

F , 2.09 I

1

i

2.4 * +

* Actual reading with special oxterisiori tube was 1.95 mv. Based on (non-blackbody )callbratlon at 730°C with special extension tube.

TABLE V. Effect of Lens and Window Materials

on Readings of Radiation Pyrometer r

Radiation i Receiver

j

Nominal

Wave Length

Cut-off

Radiation Pyrometer Readings

|

Energy Received from

Blackbody

at 670c

Blackbody

at 670C

Radiant Panel j Normal

Operation + 1 Microns mv mv Watt/ Percm2 cent

Total (Theoretical

)

00 — -- 4.49 100

Calcium Fluoride Lens 9.5 1.952 1.952 3.99 89

Calcium Fluoride Lens

Plus Vycor (96^ Fused

Silica) Window 3.8 0.793 0.784 1.80 40

Calcium Fluoride Lens

Plus Crystalline

Quartz Window 0.73'+ 0.724

Calcium Fluoride Lens

Plus Pyrex Window 2.7 0.338 0.352

* Adjusted to temperature such that radiant output as measured by

radiation pyrometer corresponds to that of a blackbody at 670'-'’C.

FLAME

SPREAD

INDEXINDIVIDUAL

LABORATORY

AVERAGE FLAME SPREAD INDEX- ALL LABORATORIES

FIG. I -FLAME SPREAD INDEX OF INDIVIDUAL LABORATORY

VS AVERAGE FLAME SPREAD INDEX FOR ALL LABORATORIES
I

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ta-' :1S. >1
F1G.2-ENERGY EMITTED BY A GREY BODY

BASED ON CALIBRATIONS BY TWO LENS-TYPE RADIATION PYROMETERS MAINTAINING SAME OUTPUT INDICATIONS AS FROM

BLACK BODY AT 670‘*C

tl. S. DEPARTMENT OF COMMERCE

Lpwi« Ij. Sprrftnry

NATIONAI, HDUFAU OF STANl)AFM)S

A. V, Astlil, Dirrctor THE IVATMl'XAE BlinEAlJ OE STAlV«»Alt.B>S

The scope of activities of the National Bureau of Slarulnrcls at its headquarters in Wasliiiif'lon,

f). C., find its major laboratories in Botdder, Colo., is suf^pesled in the following listing of the divisions and sections engaged in technical w«)rk. In general, each seelion eorri<!s out sj)eeializ('<i research, development, and engineering in the field indieaterl by its title. A brief 'description of

the activities, and of tbe resultant publications, appears on the inside front cover. WASHINGTON, H. C.

nnil KInntrmiiESt. Resistanee and Reactance. Electron Devices. Electrical In- struments. Magnetic Mcasitrcmenls. Dielectrics.. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat* Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research.

Atomic and Radiation Rliysics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic I‘hysics. Neutron Physics. Radiation Theory.

Radioactivity. X-rays. High Energy Radiation. Nucleonic Instrumentation. Radiological

Equipment. ' ClaOinlstry. Organic (ioatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical

Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

^OclianicSo Sound, Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Organic and Mnicrini^^. Rubber. Textiles. Paper. Leather. Testing and

Specifications. Polymer Structure. Plastics. Dental Research.

HSctnllurgy. Thermal Metallurgy, Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral l*roductSe Engineering Ceramics. Class. Refractories, Enameled Metals. Concreting

Materials, Constitution and Microstructure.

Illlllding TecllUfl>logy« Structural Engineering, Fire Protection. Air Conditioning, Heating,

and Refrigeration, Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer.

Aj|t|>liod Mallirmatics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Hala Rrocrssing SEAC Engineering Group. Components and Teehniques. Digital

Circuitry. Digital Systems. Anolog Systems. Application Engineering.

® Office of Basic Instrumentation. ® Office of Weights and Measures. RHIimUR, COLORAHO

Cl*yO|^onic Ln^iiiOBM’in^. Cryogenic Eipiipment. Cryogenic Proccs.ses. P.'opcrtics of Materials. Gas Liquefaction.

Radio I*i‘0|»a]^ai.ion Upper Atmosphere Rc.search. lonosiiherij Research. Regular Propagation Services. Sun-Earth Relationship,-. VIII' Research, lonosplieric Gommuniealion

Systems.

Radio BVO|lil|4af ion Dala Redm'lion InsIrmiKmlalion. Modulation Sy.-lems.

Navigation Systems. Radio Noise;. Troposphcrii; Measurements, 'rropospherie Analysis. Radio

Systems Application EngifH;oring. Radio-M(;l(;orology.

Radio SiaildardN. High Ere(|(K;n(;y EI(M:lrieal Slamlanls. Ra<lio Rroadeasl Service. High

Fre(|ueney Impedunce Slamlaid.s. i'ileeli oni(; Galihralion Center. Mieruwase Physics. Miero\\ave

Circuit .Standards,
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