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TOasea and 4shwH&* be reference-:

NATIONAL BUREAU OF STANDARDS REPORT

8172

RADIANT IGNITION OF

WALL FINISH MATERIALS IN A SMALL HOME

by

H. SHoub

and

E. W. Bender

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-12-10120 January 24, 1964 8172

RADIANT IGNITION OF

WALL FINISH MATERIALS IN A SMALL HOME

by

H. Shoub

and

E. W. Bender

IMPORTANT NOTICE NATIONAL BUREAU OF STAN

for use within the Government. Bel and review. For this reason, the pi whole or in part, is not authorizec Bureau of Standards, Washington

the Report has been specifically pre

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

recounting documents intended

ijected to additional evaluation

ting of this Report, either in

ffice of the Director, National

! Government agency for which

ss for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

RA ANT IGNITION OF WALL FINISH MATERIALS IN A

SMALL HOME

by

H. Shoub and E. W. Bender

ABSTRACT

Small-scale panels of different building

finish materials were exposed to a radiant heat

source to simulate the effect an overheated stove

or chimney may have on interior wall or ceiling

surfaces. Included in the tests were smoke

measurements, and a determination of temperatures

on the panel surfaces and at points in the room.

Some measurements were made of CO production, and

the presence of ignitable gases was checked. Tests

were also made with small masses of an insulating

material and with carbonized wood. Dense smoke was

produced in nearly all of the tests, and there was

indication that untenable conditions would be

quickly achieved in a living space even without

ignition of the surface finish material to active

flaming.

1. Introduction

In connection with a general program of investigating

several aspects of the behavior of building materials in fires,

tests were made to explore the ignition properties of certain

wall surface and finish materials when exposed to a radiant

heat source, such as might be furnished by an overheated stove

or chimney, or by the spreading heat of an accidental fire.

The tests were preliminary in nature, and severely limited

in scope by the short-term availability of the test structure.

Nevertheless, it was possible to conduct 14 tests of wall finish

materials, in which in addition to visual observation of smoke

and flaming, some smoke measurements were made, and temperatures

on the front and back of test specimens and at several points in

the room were determined. An effort was made to secure measurements of carbon monoxide concentration, and to determine, generally,

if gases in quantity to present a flash fire or explosion hazard,

or conversely, an inhibiting effect on combustion, could be produced

from building materials subjected to radiant heat. As part of the

investigation of the character of gas production, tests were also

made with stacks of fiberboard, representing masses of insulating

material, and with charcoal.
- 2 -

2. Description of Test Materials

A description of the specimens used in the tests is given in

Table 1. Flame spread measurements, determined by the radiant

panel method [l]— are included for a comparison of the performance

of the materials under the two methods of test.

Each of the lb test specimens subjected to radiant heat was in

the form of a panel, 3 ft square. Where required, the materials

were supported by a rigid backing.

The charcoal briquettes of Test 15 were a standard commercial

product. Approximately 12-1/2 lb were used in the trial. In Test

16 the wood fiber board? in 1/2-in. thick sheets, was arranged in a 1-ft cube. Also in this test, four stacks of fiberboard, each with

four 1-ft sq sheets, were used.

3. Test Method and Equipment

The tests were conducted in a small house (Fig. 1) on a rural

site. The brick veneer structure had a living space consisting of

four rooms on a single level, and an unfinished’ attic and basement,

the latter serving as the location of the several pieces of test

equipment used in the trials. The No. 2 bedroom, shown on the floor

plan of Fig. 2, was used as the test area. This room, approximately

10 by 10-1/2 ft, 8 ft high, had north and east exposures, each with

a 3 by 5 ft double hung wooden window. Weather tightness of the

windows was aided by the use of metal weather stripping, and further

by wooden storm sash fitted to the window frames. As its door was

kept closed during the tests, the closet shown on the plan did not

add directly to the volume of the room. Access to the room was

through a hallway door, opening inward.

In conducting the tests, the 3- by 3 “ft panels were mounted

near the outside corner on the east wall of the test room. Four

of the panels were placed against 1-5/8 in. thick furring strips

laid vertically against the plaster surface. In an effort to minimize damage to the structure, the remaining specimens, mostly in

the later tests, were affixed by screws directly to b- by 7-ft sheets

(two 1/2-in thicknesses) of asbestos millboard applied over 1-1/2 in.

furring strips. The two methods of attaching the panels are illustrated in Fig. 3, with Table 1 indicating the method applicable in

each test.

1/ Numbers in brackets refer to the list of references at the end

of this report.
3 -

An assembly of four electric oven-heating elements

placed in front of a 30- by 27-in. aluminum reflector

served as the source of radiant heat to which the

specimens were subjected. This assembly, shown in Fig. 4,

was movable, and was so positioned as to be centered

in front of and parallel to the test panel. All of the

tests were conducted with the heater at a distance of

6 in. from the face of the specimen. By means of a timing circuit, the heater could be operated at a full

or fractional duty cycle, which for many of the tests of

the series was approximately 50 percent with on and off

cycles of 5 sec. each. Excepting a trial in which the

cycle was changed in the course of a run, the remaining

tests were made with continuous pother to the heater.

Power consumption for the 50 percent cycle was 6.2 kw,

and for 100 percent duty 11.6 kw. On the basis of an

available measured radiant intensity at a point 24 in. normal

to the center of the heater, the effective blackbody temperatures were found to be 273°0 (523°F) for the 50 percent

duty cycle and 402°C (756°F) for the 100 percent cycle.

The radiant intensities at other points on a line parallel

to the heater surface and at 6 in. distance from it were

calculated, as shown in Fig. 5> using a geometric configuration factor [2]. The validity of this calculated curve is

indicated by the close correspondence of a curve similarly

calculated for the parallel traverse 18 in. from the heater

with one based on available experimental data taken with a calibrated radiometer at that distance. These curves are

also shown in Fig.7 5 * The minor variation occurring in the

two curves at 18 in. may possibly result from a slight

difference in the geometry of the heater used from that of

the symmetrical and uniform source assumed for the calculated

values

In tests 11 through 14, an effort was made to determine

the effect of a shield placed between the specimen and

heater. A 16 ga steel plate was mounted 1/2 in. in front

of the exposed face of the specimen. The spacing was

maintained by asbestos millboard strips at the bottom

and sides of the plate, the top being left open for
convection from the heated surface. The 1/2-in. separation of the specimen and shield was adopted as the

result of some studies which indicated that use of

greater separations did not add materially to the

reduction of temperature on the face of the specimen [3V

In these tests, as in the others, the distance from the

heater to the near side of the test panel was kept at 6 in.

Temperatures on the exposed and unexposed faces of

a specimen, as well as at various points and levels in

the test area were determined with thermocouples whose

response was recorded by a 12-point or a continuous

plotting electronic potentiometer.

In some of the tests, smoke measurements were made

with a meter operating on the response of a photoelectric cell with type S-A spectral characteristics, to

the obscuring effect of combustion products on a light

beam from a source b ft distant. The device is illustrated

In Fig. 6. A check of the output of the photometer showed

Its response to be linear within .1 percent. In use, the

mister was hung vertically with the window of the light

source about 12 In. below the center of the ceiling. Thus,

an integrated measure of transmission throughout a large

portion of the room height was achieved.

Carbon monoxide determinations were made in several

of the tests. For this purpose an MSA meter having a range of 0.005 to 0.15 percent CO was used. Pickup

tubes for the meter were at three locations in the room,

with samples drawn by a vacuum pump.

As a further check of -the possibility of combustible

gases being present in the distillation products of the

heated test panels, an Ignition system consisting of a pair of electrodes with 2>/b-±a, spacing was Installed at

a point 3 in. below the center of the ceiling. The
- 5

-

IgniLpr was energized at 10 -min intervals during the

test, through a high voltage transformer. To determine

the presence of a large volume of carbon dioxide in the

distillation products, or if the available oxygen was

otherwise depleted, a small lamp burning alcohol or

kerosene was placed near the center of the room at a height of 52 in. above the floor. Extinction of this

lamp would be an indication that the atmosphere of

the room would not support combustion. As visual

observation of the lamp was not always possible, a thermocouple was placed a short distance above the flame.

In Test 15, charcoal was placed in a 30-gal metal

container on 1/4-in hardware cloth mounted 2 in. above

the bottom. Air was introduced into the space beneath

the charcoal through a 1/4-in. tube. Ignition of the

charcoal was secured by a resistance wire heater passing

through the center of the mass. A similar arrangement was

used in Test 16, where a 1-ft cube of stacked wood fiberboard was used, except that there was no forced draft

in the container. In this test also, Ignition was attempted

at the center of the cube of insulating board. In addition, a pile of wood fiberboard 1 ft sq .and 2 In. thick

was placed on top of each of four 660 watt electric hot

plates. These small heaters were operated on the high

setting. In a similar test with an asbestos pad over the

heating element, a thermocouple placed between the pad

and heater indicated a temperature of 600°C at 70 min,

and a maximum of 635°C at approximately 2 hr. A somewhat

faster rise may be expected with fiberboard from the

contribution of its combustible content.

The period in which the tests were conducted was marked

by rather severe winter weather. Minimum, temperatures were

below freezing on nearly all test days, and there was a varying accumulation of snow, up to 18 in. at the midpoint

of the tests. The test house was located on an exposed site

with no hindrance to the almost continuous wind, which at a nearby weather station measured up to approximately 25 mph.
- 6 -

Despite the weather, however, the temperature within the

house was maintained in the range of 60 to 75°F at all

times. Forced hot air heat was supplied to the test room

except during times of actual test when the ducts were

sealed shut to prevent dispersion of smoke through the

entire structure. At such times, the door to the room was

also closed, and further sealed by wadding at the bottom.

The outside doors of the house were kept closed during the

tests, except that in a few instances, it was necessary that

they be opened in the latter part of a test to provide

ventilation.

In all of the tests, visual observations to the extent

allowed by the smoke in the room and condensation on the

glass, were made through a window. Carbon monoxide and smoke

indicating instruments were in the basement, as already

described. Here, too, were the controls for the radiant heat

source and the ignitor, as well as the recording potentiometer

used with the thermocouples.

The duration of the tests varied. Active flaming was

usually the criterion for ending a run. Where termination

occurred before the inception of flaming on the specimen,

the end point was usually defined as the time at which it

was estimated that all or most of the volatiles had been

distilled from the specimen. It was considered that further

flaming would not occur, or if it did, would represent the

ignition of only the carbonized remainder of the panel.

4. Results of Tests

The duration of the several tests is shown in Table 1,

together with an indication of whether or not termination

of a trial was brought about by the incidence of active

flaming. The table also gives the temperatures determined

from the thermocouple readings. Where a temperature

is shown as being more than 600°C, it indicates that the

actual temperature on a flaming specimen exceeded the top of

the scale of the recording potentiometer. Temperatures at

the floor and ceiling of the test room are included to give

some details of the temperature rise above the ambient

caused by the heat from the electric burners and from the

combustion of the specimen.
Table 1. Results of Tests

Specimen

Power Backing Spec. Temperature Max. Specimen Max. F oora Test Description of to and

p

/ Prior to Protection-7 Front Ignition Time to Test Temperature Tempera Ceilin^y

ture Tare a

r.

r o Specimens Heater Back Ignition Duration Front Back Flooch Index kw °c °C hr:min hr : min °C ! °C °c ”C is

1 • Hardboard; 1/b in; , Unfinished; 60 lb/ft-’ 5-2 b 386 37b 3

: 56 5:17 >600 | 572 ; 330 86 150

2. Cane fiberboard;

1/2 in.; factory-,

finisii; 18 lb/ft-' 6.2 a 260 158 0:55 0:55 -

1 560

: 13b 5b 83

3- Plywood, Exterior gr.; 1/2 .la.; 39- lb/ft3 6 • 2 a 25b 25b 5=10 7 : 2C 570 596 226 80 167

b. Laminated Paperboard;

3/0-in- ; Factory

finisii; primer;

3!/ lb/ft

5 .

a 270 96 0:35 0:35 >600 208

i

: 274 66 i 5- Laminated Paperboard • * 3/8-in. ; Primer andp

alkyd paint (500 ft /

j gal) 5.2 b 280 198 4:4 5 4:45 36b 238

| ibb 63 20

6

Acoustical tile; 1/2-in. ; Screwed on

|

| asbestos, millboard

Ko

17 lb/fC 6.2 b - - Ign. 5:00 222 166 8b 5b Lie

7. Polystyrene Wall tile;

4 -1/b xh-1/4x.068 in.; Cemented, on gypsum bd. No 65 lb/ftJ 6.2 Ign. 5:00 232 188 83 58 22-

Pj

- Wood veneer, cloth

bac.:ed; on 1/2-ln. gypsum board; Ho

52 lb/ft J 1

/

5.2 b - Ign. 2:25 250 126 76 l :3 77

Q . Vinyl coverd cloth

on 1/2-in gypsum bd.; No lb/ft3l/ 6.2 b - - Ign. 1:25 180 164 66 36 1C

10. hardboard; 1/b in.; ; Unfinished;

60 Ib/fto 11.6 a - - 0:23 0:23 - - i - 1; v n Hardboard; 1/b in.; Unfinished;

60 lb/f t> 11.6 c 418 228 1:05 3 = 15 5b 0 >600 120 58 ! 12. Laminated Paperboard; 6.2

3/6-in. jFactory finisl and

580

1 primer; bb 35 lb/ft3 11.6 c b6b 350 1:30 1:30 >600 110 | 13- Cane fiberboard; 1 l/2-in.; Factory,

finish; 13 lb/ftJ 6.2 c 150 0:25 1:00 >600 >600 90 | 5 ° ; 83

it. Plywood, Exterior, gr.; 1/2-in.; 39 lb/ftJ 11.6 c 308 230 0: b 1 0: 50 b60 >600

1 90 : 30 ; it/,* if. Ciiarcoal Briquettes;

b x 6-in. size; 12-1/2 lb _ _ Approx.

10:00 10:55

|

1 112 67

lo Wood Fiberboard;

1/2-in .; , Starch glaze;

20 Ib/fC

No I _ Ign. 10:45 115 1

L_

jJ i eurity of assembled finish material and backing

f air nacking; b - millboard backing; c - millboard backing with metal plate 1/2 in. in front of sjhv l matt. 3/ naove specimen

•_/ 2 ft above center of floor


NORTH

FIG.2- PLAN OF TEST HOUSE

HOUSE WAS BRICK VENEER OVER FIBERBOARD SHEATHING.

MINERAL WOOL BATS BETWEEN OUTSIDE WALL STUDS AND

CEILING JOISTS. INTERIOR WALLS GYPSUM LATHED AND

PLASTERED. ATTIC AND FULL BASEMENT UNFINISHED. NO.I

AND 2 BEDROOMS HAD 3'X 5' DOUBLE HUNG WOODEN WINDOWS

WITH FULL LENGTH WOODEN STORM SASH

OUTSIDE

BSMT.

EXIT
FIG.3- METHODS OF MOUNTING SPECIMENS
Fig

.

Radiant Heat Source
INTENSITY,

watts/cm

as

0.4 p-'

0.3

/ 6 DISTANCE

(CALCULATED)

\

\

\

\

SB DISTANCE

(MEASURED)

8 DISTANCE

(CALCULATED)

\

\

\

2 4 6 © SO 83 14 16

DISTANCE FROM PANEL CENTER .INCHES

18

F16.5- MEASURED AND CALCULATED RADIANT

INTENSI TIES 0NJE STJ3 PECIMEN

FO'R A HEATER INPUT OF 6.2 kw
'lg 6 Smoke Meter Housings for Light Source

Photo-Electric Cell (right)

(left) and
OPTICAL

DENSITY

PER

FOOT

OF

LIGHT

PATH

FIG. 7- SMOKE MEASUREMENTS AT

CENTER OF ROOM DURING TESTS

LIGHT

ABSORPTION!

100

M

INUS

TRANSMISSION)

,

PERCENT
h-CD< 2

LU22Ou

£L<

-J

Xom

in

Ixl uoa

UJo2<Hcno

s~CO

UJ

hco

UJ

cr3

I—<

cr

UJ

Q_

UJO

UJ

Q_

CO

UJ

h-Oo

cr

h~

co

UJ

I—

CDd

u_ oo

hcro

or

cl i

i—

rr *1X cc 5 o o

(/> 1“

CO3

“3

INOdd BONVlSia

NOTE!: X

INDICATES

THERMOCOUPLE

LOCATION
Table

2.

Smoke

Measurements

and

Observations

- 7

-

For these tests in which actual measurements were made,

values for smoke production are shown in Table 2. In the

absence of a standard for photoelectric smoke measurements, the

smoke concentrations have been reported on the basis of optical

density per fo’ot light path, " Cl/d)(log 10 100/T) where T is the

percent transmission, and d is the length of the light path in

feet. Optical density was used because it has a more nearly

linear relationship to smoke concentration than does absorption

or transmission. The smoke measuring apparatus was not available or not operative in some of the tests. For these, an

indication of visually observed smoke conditions is included.

Because of difficulties with the operation of the carbon

monoxide detection device, only scattered data are available

for this phase of the investigation. Representative readings

ranged from a low concentration of 0.04 percent CO in Test 12

to highs of 0.12 percent in Tests 11 and 14. The gas was also

detected in Test 13 where readings of 0.05 percent were observed

at two separate intervals. In Test 15 (charcoal briquettes),

the presence of some carbon monoxide was noted throughout most

of the trial, with a high meter reading of 0.11 to 0.12 perbent.

In none of the tests of the panels was any flashing of

combustible gases noted at the electrode ignitor, which was

periodically energized. However, in the test with the t /

charcoal briquettes, an ignition flash was observed to occur/

after about 8 hr. smoldering. The ignition was not of a force to cause damage to the structure, and was not sustained.

The small lamp, fueled with kerosene or alcohol, and

centrally located in the room, did not in any of the tests

indicate the presence of combustion inhibiting gases in a quantity sufficient to cause its extinction. Where extinction

of the lamp did occur, it was found to be due to fuel depletion in the later stages of a test of long duration.

In the two tests not involving panels, 15 with charcoal

briquettes and 16 using massed sheets of wood fiberboard, considerable smoke was produced from the materials which were

allowed to smolder after removal of the initiating heat. In

both cases the tests were continued for more than 10 hours.

Some flaming occurred in the charcoal hear the end of the

trial, but this was neither intense nor extensive. The wood

fiberboard appeared to smolder only, with no flaming detected

by visual observation or rise in temperature on an adjacent

thermocouple
5. Discussion of Results

Perhaps the most notable feature of the test was the very

large amount of smoke produced by the exposure, to a radiant heat

source, of only 9 ft^ of wall finish material, sometimes in a thin sheet, and never exceeding 1/2 in. in thickness. This smoke,

in a very few minutes, could fill and make untenable a room of

approximately 800 fto volume. The development of this smoke

condition, as indicated by the smoke meter readings in three of

the tests, is shown by the curves in Figure 7.

Correlation of the smoke output in these tests with the

smoke production during the radiant panel flame spread tests was

not always possible, nor could it be expected under the differing

bases and conditions of the two types of investigation. Smoke in

the radiant panel test is the product of more or less active

flaming of a specimen, and is measured as the weight or optical

density of a continuous particle deposit over a period of 15 min.

In the tests of this report, smoke measurements were made on the

output of a heated but not flaming surface, with light transmission observations only made periodically during the trial.

These differences in the characteristics measured could

account for the lack of correlation between the flame spread

smoke determination and that reported here for the vinyl cloth

(Test 9)* This material showed a high deposit of smoke particles

during flame spread test (second highest of those tested), but

ranked considerably better on the basis of smoke optical density

in the test room. The polystyrene tiles (Test 7) were not exposed

to radiation to the extent intended, as by 1-1/2 hr after the

start, most of them had buckled and fallen from their gypsum board

backing panel, and were thus no longer in the radiation field.

None of these tiles showed any evidence of ignition. The smoke

produced by this specimen apparently resulted from the exposure

of the tile adhesive and gypsum board backing.

In three of the tests, hardboard was the panel material.

For two of these (Tests 10 and 11) the radiant exposure was the

same at 11.6 kw heater input. There were differences in the

method of mounting, however, the panel of Test 10 being mounted

on furring strips and with no protection in front, that of

Test 11 flush against a millboard backing and with a metal plate

between the specimen and heat source.
- 9

- Although it would appear that lack of an air space behind the

specimen of Test 11 would increase the likelihood of early

ignition, the protection afforded by the presence of the steel

plate in front increased the time to ignition by a factor of

approximately three (23 min in Test 10, and 65 min in Test 11).

With the heater on 50 percent of the time (6.2 kw) , as in Test 1,

the time to ignition was increased to 3 hr 96 min, as compared

to 1 hr 5 min in Test 11, even though the similarly mounted

panel had no protective shield (Test 1). The shielding

capacity of the metal plate appears to be further exemplified

by a comparison of Tests 4 and 12. In Test 4, the laminated

paperboard was mounted on furring strips to give an air space

at the back. The specimen in Test 12 was applied to millboard

and had a metal shield 1/2 in. in front. The heating panel

was on 50 percent of the time in Test 4, and for the first

bO minutes of Test 12, after which it was changed to 100 percent

duty. The comparable Ignition times were 35 min in Test 4 and

1 hr 30 min in Test 12, with more than half of the latter time

at full radiant intensity.

This trend, however, appears to be contradicted in Tests 2

and 13-, where the former was mounted with an air space behind,

the latter having a millboard backing and the protective metal

shield in front. With a heater input of 6.2 kw in both tests,

the duration in Test 2 was 55 min as against 25 min in Test 13.

In the case of plywood, the metal plate appeared to offer little

protection against an increase in the intensity of the exposure.

An approximate 5-Wr duration to ignition at 50 percent exposure

(Test 3 ) was reduced to 4l min at 100 percent (Test 14) , notwithstanding the presence of the plate in the latter trial.

Although the extent of the protection provided by a steel plate

placed in front of the specimen is questionable, there is a possibility that, had it been feasible to mount the shield to

allow free vertical flow of air between it and the face of the

specimen, a greater protective effect would have resulted.

It was noted, also, that where the steel plate was interposed before the specimen, a greater temperature rise occurred

on the back surface of the specimen than on the front, Tests

11-14). This can be attributed to a self -heating phenomenon

on the back surface, which because of the insulating effect of

the millboard backing and the specimen itself, probably occured

at a faster rate than did the heating of the front surface

protected as it was by the metal shield.
10 -

The laminated paper board material of Test b showed

greatly improved resistance to ignition when treated with

single applications of primer and alkyd paint (Test 5)

•

The same phenomenon had been noted for this material, similarly

coated, when examined for flame spread properties by the

radiant panel method.

From the temperatures measured in the room during a test, it was noted that flaming of the specimen usually

resulted in greater temperature rises at the ceiling than

did prolonged heating, even in tests extending to 5 hrs.

In Tests 11-14 with the steel plate, however, the ultimate

ceiling temperature was only a little higher than that in

tests in which no flaming occurred, possibly due to an inhibiting effect on the flame through lack of oxygen caused

by the proximity of the plate to the burning surface. A plot

of isothermal lines in the room just prior to ignition of the

hardboard specimen in Test 11 is shown in Fig. 8.

6. Conclusions

It was apparent from the tests that many building finish

materials would give off smoke and acrid fumes when exposed

to a radiant heat source such as might result from an overheated stove, furnace, or chimney. The very large volume of

smoke produced by test panels of limited size indicates that,

even if only a small area of wall surface is exposed, a serious hazard may develop. The presence of carbon monoxide was

noted in the tests, and ignitable mixtures could be generated

by prolonged heating of carbonized wood.

The radiant heat source, as described, could also present

an ignition hazard, as many of the panel materials, after

varied exposure durations, were brought to a state of active

flaming. There was some evidence, however, that, by shielding

or for certain materials, by suitable surface application,

the inception of flaming may be considerably delayed, although

smoke production would not necessarily be curtailed.

An extension of the program of work reported here appears

to be warranted. If a suitable test structure could be made

available, it would be especially profitable to investigate

means of providing protection to structures that may be adjacent

to a heat source. Also, in light of the now recognized danger

from smoke and fumes, a project to determine what methods or

materials are required to mitigate this hazard may well be

instituted.
11

7« References

[1] A. F. Robertson, D. Gross and J. J. Loftus, A Method for

Measuring Surface Flammability of Materials Using a Radiant Energy Source, Proc., ASTM, Vol. 56, 1956,

pp. 1437-53.1

[2] D. C. Hamilton and W. R. Morgan, Radiant Energy Configuration Factors, NACA Technical Note 2836, Dec. 1952.

[3] D. I. Lawson, L. L. Fox and C. T. Webster, The Heating

of Panels by Flue Pipes, Fire Offices Committee, Fire

Research Special Report No. 1, London, HMSO, 1952.