Approved for public release by the / ^ Director of the National Institute of

Standards and Technology (NIST) d

on October 9, 2015.

NATIONAL BUREAU OF STANDARDS REPORT

6888

FIRES IN MODEL ROOMS

Results of Preliminary Experiments

Under an International Cooperative Program

by

D. Gross

D. Ward

H, Shoub

U. S. DEPARTMENT OF COMMERCE

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-11-10427 July 11, i960 6888

FIRES IN MODEL ROOMS

Results of Preliminary Experiments

Under an International Cooperative Program

by

D» Gross

D, Ward

H* Shoub

IMPORTANT NOTICE

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FIRES IN MODEL ROOMS

Results of Preliminary Experiments

Under an International Cooperative Program

by

D. Gross

D. Ward

H. Shoub

ABSTRACT

The results of a preliminary series of model

fire experiments performed under an international

cooperative program are reported. Three parameters

associated with the burning of a lattice-type fuel

bed in a model room enclosure were varied, namely,

the quantity of fuel, the dispersion or packing

arrangement of the fuel and the area of the window

opening. It was found that the area of the window

opening had the largest effect, particularly with

respect to the rate of weight loss of the fuel bed

and the radiation from the window. The peak temperatures measured at two points within the enclosure'

ranged from 890°C to 1025°C and were found to be

relatively unaffected by the range of parameters

investigated. An evaluation of several types of

thermal radiation detectors is included.

INTRODUCTION

In June 1959? a program for the systematic investigation

of the growth of fires in rooms using small-scale models was

suggested by the Joint Fire Research Organization (J.F.R.O.) of

the United Kingdom. [ll^The study took on an international character under the sponsorship of the Working Party on Fire Research

of the Conseil International du Batiment (C.I.B.), and with the

willingness of fire research laboratories in several countries

to participate. Since the Fire Protection Section had for some

time considered the need for engaging in model fire studies of

this type, these tests provided an ideal means of becoming

familiar with modelling techniques and instrumentation while at

1 Figures in brackets ..indicate the literature1 references at the

end of the report.
*
2

the same time participating in a planned cooperative program,

the results of which might not be otherwise obtainable. This

report describes the results of a preliminary series of experiments performed for the purpose of cross-checking results

and for establishing techniques on the basis of common experience among the various international participants.

2. EXPERIMENTAL PROCEDURE

2.1

Test Schedule

This series of tests was limited to a rectangular

compartment in which only three parameters were varied, namely,

the quantity of fuel, the dispersion or packing arrangement

of the fuel, and the area of the window opening. The schedule

of tests is listed in Table 1.

2.2

Test Compartment

The compartment was 1/2 meter wide by 1 meter long by

1/2 meter high, inside dimensions , and was constructed of

one layer of asbestos millboard of 1/2 in. thickness (density

/—' 1.0 g/cc). This material was used in place of the

suggested 3/8 in. thick "asbestos wood" material ( density

1.3

to 1.5 g/cc, thermal conductivity 7 to 9*10“^ cal sec

-1

cm“l°C“l) which was unavailable at the time of the tests.

The compartment was made with a detachable front panel containing a central window opening one-quarter of the box width

and extending from the floor to the ceiling.

2.3

Wood Cribs

The amount of fuel was 20 and 30 kg per square meter of

floor area or a fire load of 10 and 15 kg respectively. The

fuel consisted of wood sticks of square section arranged in

cribs with a lattice-type formation. The type of wood

suggested was spruce fir (white deal, abies excelsa) having

a density range of 0.*+5 to 0.55 g/cc. Since this species was

not commonly available, the wood used was Douglas Fir (Pseudotsuga) which has a similar nominal density range. The sticks

were smooth-sawed to 2-cm size and pre-assembled into cribs

using a urea resin adhesive, the weight of which never exceeded

1% of the crib weight. The length of the sticks parallel to

the long side of the compartment was 83.3 cm (5/8 meter) and

the length of those parallel to the short side was *+1.6 cm

(5/12 meter). The "dispersion of the fuel" represented the

- 3

-

open space between adjacent sticks in both horizonatal

dimensions expressed in terms of the stick width. The top

layer contained the necessary number of sticks and a portion

of a stick to yield the desired crib weight. The cribs were

conditioned to a constant weight of 10 and 15 kg in an atmosphere maintained at 65- 2°F and 65- 3%rh prior to test.

2.4- Ignition

The ignition of the crib was accomplished with the aid

of 1/2 in. by 1/2 in. by 83.3 cm long fiberboard wicks containing approximately 83 cc or about 1 cc of absorbed kerosene

per cm length. One wick was placed in each bottom interstice,

except that in the case of cribs constructed with "1" spacing,

the wick was omitted from the center interstice to prevent

interference with the lower thermocouple lead. The weight of

the fiberboard, not including the absorbed kerosene, was a

component of the total crib weight (10 or 15 kg).

2.5 Weight Measurements

The tests were performed near the center of a very large

and essentially draft-free room. The compartment was supported

over one sheet of asbestos millboard on an iron stand mounted

directly on a platform balance scale. Weighing was accomplished

by noting the time for balance after removing a small weight

increment. In tests 1 through 8, a simulated floor was constructed around the compartment at the front and sides in the

plane of the bottom surface of the compartment. The floor,

which was elevated about 28 in. , extended b feet in front and

3-1/2 feet at the sides of the compartment, and' served as a

convection baffle. In test 9 ? which duplicated test 1 in all

other .respects, the simulated floor was removed. Prior to

each test, a preliminary fire was used to remove absorbed

moisture from the compartment. The initial preliminary fire

also served to remove the small amount of organic material

contained in the asbestos millboard. Each test was started

as soon as possible after placing the crib in the compartment.

This was usually accomplished within 15 minutes after removal

from the conditioning room.

2.6 Instrumentation

Thermocouples, of 0.020 in. dia. chromel-alumel wire,

were used for measurement of the temperatures within the

compartment, and were replaced for each test. One thermocouple was placed at the intersection of diagonals on the

plan a quarter of the height (12.5 cm) below the ceiling

(ceiling thermocouple) and another the same distance above

the floor (floor thermocouple).

Measurement of the radiation from the windows was

made by means of both "copper disc" radiometers and an

enclosed radiometer. The copper disc radiometers, constructed from a published description 2 , were employed

in all nine tests whereas the enclosed radiometer 3 , supplied by the J.F.R.O., was used from test 3 on. The

copper disc radiometer actually consisted of a disc of

phosphor bronze 0.0159 in. thick and 1 in. in diameter to

one side of which chromel and constantan thermocouple leads

(0.0253 in. dia. wire) were silver soldered. Sodium silicate

adhesive was used to fasten a sheet of asbestos-base paper

(0.008 in. thick, 6.4-8 oz/yd2 ) to each face of the disc.

Each copper disc radiometer was calibrated, see Fig. 1, by

measurements using a copper slug calorimeter during exposure

to several intensity levels of an extended area radiant

energy source. For the intensity range of interest, the

calibration curves were similar to those published. For

the enclosed radiometer, the calibration curve furnished

with the instrument was used.

One copper disc radiometer was placed centrally 5 cm

above the top surface of the compartment and in the plane of

the window opening to indicate the potential ignition hazard

from flame radiation in an area above the burning compartment.

A second copper disc radiometer was placed 50 cm centrally in

front of the window and, in tests 3 to 9? the enclosed radiometer was placed adjacent to it.

3. Results

3.1 Weight Measurements

The weight-time records for all nine tests were plotted

for direct comparison in Fig. 2. The total starting weight

includes the weight of the kerosene primer. The curves consist essentially of three stages: a short period during which

- 5

-

the fire becomes established, the major period during which

the weight decreases linearly with time, and a slow decelerating period corresponding to glowing embers and ultimate

extinction. For the same initial crib weight, the most rapid

burning arrangement was the full window opening and "3 M spacing.

Table 2 lists the tests in order of decreasing rapidity and

tabulates the maximum rate of burning (i.e. the slope of the

straight line portion) directly and as a percent of the initial

crib weight.

3.2 Temperature Measurements

"Ceiling" and "floor" temperatures were automatically

recorded on multi-point potentiometer recorders and are shown

in Figs. 3 and 4. For convenience the data have also been

summarized in Tables 3 and 4. It may be noted that the

occurrence of the peak temperatures corresponds very closely

in almost every case to the termination of maximum combustion

and the beginning of the deceleration shown in Fig. 2.

3.3 Radiation Measurements

A record of the radiation intensities at the two

locations is shown in Figs. 5 and 6. Compensation was provided for cold junction temperatures. An initial peak in

several of the radiation curves at times less than ten

minutes may be considered as due in part to the burning of

the kerosene primer.

The curves of radiation from the window fall into two

general groups according to the area of the window opening.

The peak radiation for the tests employing the full window

opening ranged from 0.43 to 0.70 cal sec

-1 cm” 2 while the

range of maximum intensities for the one-quarter open window

was from 0.21 to 0.27 cal sec“ 2 cm

_ 2. Since the "flame"

copper disc radiometer was placed so as to indicate radiation

from flames emerging from the compartment, it experienced a considerably greater range of fluctuations. These test

results did not fall within distinct groups in the same

manner as the window radiation curves.

- 6 -

3.H- Flame Height

In addition to the measurements specifically requested.,

several additional measurements were made and visual observations recorded during the progress of each test.

Flame height measurements were made visually with

reference to a graduated rod placed along side the compartment and refer to the approximate maximum level of visible

flames whether part of the primary body of flaming or

separated from it. A typical record of flame height above

the base of the compartment (for test *+) is shown in Fig. 7«

The time at which the maximum flame height was observed for

this and the other tests was considerably earlier than the

time at which the maximum temperatures and radiation were

obtained.

Some note was also taken of the extent of flaming in

the window opening. The depth of flames measured below the

top of the window may be expressed conveniently as a fraction

of the total window or compartment height. The maximum flame

"depth" was found to be approximately one-quarter for all

the full window opening tests and about one-half for all the

quarter window opening tests and remained fairly constant

during the entire flaming period.

b. DISCUSSION

From a summary of the weight records, Table 2, it is

seen that very nearly the same maximum rate of burning,

expressed in kg/min, was obtained for both the 20 and 30

kg/mO loadings under the same conditions. The dispersion

of fuel had only a slight effect upon the maximum rate of

burning, ranging from 0 to 15 percent less with the "1"

spacing than with the "3 n spacing. The area of window

opening had the greatest effect upon the slope of the weighttime curve. The maximum rate of burning with the one-quarter

open window averaged approximately 40 percent less than the

comparable test with the full open window. The maximum rate

of burning when the compartment was tested without the simulated floor platform (test 9) was 21 percent greater than

that obtained when the floor platform was used (test 1),

indicating the strong dependence of the burning behavior on

the convection pattern at the window opening.

- 7

-

From the temperature records, it was found that varying

the quantity of fuel, the dispersion of the fuel and the

area of the window opening affected the duration of test hut

had very little effect upon the maximum temperatures reached.

The peak temperature range was 890 to 1025°C for the ceiling

temperatures and 910 to 1025°C for the floor temperatures.

However, the rate of temperature rise as well as the average

temperature level during the early stages was generally higher for the ceiling than for the floor thermocouples. A

comparison between the temperature histories of the ceiling

thermocouple and the temperature-time curve of a standard

fire test [4] , shows a general agreement up to about 25 to

30 minutes, at which time almost complete burnout had occurred

in about half the tests.

The area of the window opening had a pronounced influence

upon the radiation from the window, as seen in Fig. 5» This

was not the case with respect to radiation from the flames

extending above the compartment. With one exception, radiation from the window was generally greater with the "1"

spacing than with the "3" spacing. The tests with the greater

quantity of fuel did not result in a higher radiation level.

In connection with the fire model tests, evaluation of

thermal radiation detectors was considered. The requirements

of a good radiation detector for fire studies include mechanical

strength, reasonable cost, simplicity of operation, adequate

emf output and sensitivity to a substantial portion of the

thermal spectrum. In addition, the detector should be unaffected

by the extraneous effects of temperature and wind.

To evaluate the radiation detectors in terms of compensation for ambient temperature effects, a comparison test was

performed using a gas fired radiant energy surface combustor.

One copper disc radiometer, the enclosed radiometer and a

thermopile radiation detector fjom a commercial radiation

pyrometer were suddenly placed in a symmetrical pattern in

front of the '12 by 18 in. radiating surface. The latter detector consisted of a multiple- junction total radiation thermopile

with a wide-angle field of view and with a thin mica window

added at this laboratory. From the manufacturer's specifications, its rate of response was 98% within 2 seconds and

temperature compensation up to 250°F was achieved electrically

- 8 -

by means of a shunt nickel coil. The results of the comparison test are shown in Fig. 8, from which the following may

be noted:

(a) The response of the enclosed radiometer and of the

thermopile detector were comparable and considerably more

rapid than the copper disc radiometer.

(b) The emf output was greatest for the enclosed

radiometer and least for the thermopile detector. The low

output of the thermopile detector may be due to the relatively

short wave length cutoff of the laboratory-applied mica window.

(c) Whereas the emf output of the copper disc radiometer

was fairly steady over a period of 25 minutes, the emfs of

both the enclosed radiometer and the thermopile detector

decreased approximately 7 percent. Based upon other tests,

however, it should be noted that the unenclosed copper disc

radiometer is subject to significant output variations due to

ambient temperature, wind and shielding effects. The radiation records in Figs. 5 and 6 should be considered in terms

of these results.

The progress of flaming in all tests was from front to

rear. This is attributable to the ready access of air at the

open front. From the readings of thermocouples placed at the

floor level at positions one-quarter and three-quarters of

the compartment depth in test 9 ? the progress of flames

toward the rear was estimated to be on the order of 3.5 cm/min.

Whether a different pattern of flaming would be obtained with

ignition initiated solely at the center or at the rear of the

compartment should be explored.

REFERENCES

[1] D. I. Lawson, "International Co-operation in Modelling

Fires, A Suggested Programme", F.R.W.P./G.T.F.

No. 59/11 (U.K. ) , June 1959.

[2] C. T. Webster and M. J. Gregsten, "A Disc Type Radiometer", Instruments in Industry, J, No. 23, April 1956.

[3] J- H. McGuire and H. Wraight, "A Radiometer for Field

Use", F.R. Note No. 39V1959.

[b] American Society for Testing Materials, "Standard

Methods of Fire Tests of Building Construction and

Materials", ASTM Designation E 110-55®

USCOMM-NBS-DC

Table L. SCHEDULE OF TESTS

Test

No « Designation Amountof Fuel

Dispersion

of Fuel

Window

Opening

Remarks J

1 20- 3-1

kg/m^

20 3 spacing Full False Floor HLatfacm

2 30-1-i 30 1

" Quarter n

3 20-1-1 20 1

" Full M

30-1-1 30 1

" Full M

5 30-3-i 30 3

" Quarter It

6 20- 3-i 20 3

M Quarter II

7 20-l-i 20 1

" Quarter II

8 30-3-1 30 3

" Full II

9 20- 3-1 20 3

" Full No platform
*: N
Table 2. MAXIMUM RATE OF BURNING

10 kg Fuel Load 15 kg Fuel Load

Maximum rate Maximum rate

Test Designation of Burn ing lest Designation of Blirning

No * ke/miixx %/min No. kg/min %/min

9 20-3-1 0.580 0.0580

1 20-3-1 0.480 0.0480 8 30-3-1 0.470 0.0313

3 20-1-1 0.480 0.0480 4 30 - 1-1 0.445 0.0297

6 20-3-i 0.295 0.0295 5 30-3-i 0.305 0.0203

7 20-1-i 0.280 0.0280 2 30-1-i 0.255 0.0170

Table 3. CEILING TEMPERATURES

•Time

min

Test

1

Test

2

Test

3

Test

4

Test

5

Test

6

Test

7

Test

8

Test

9

S' o 20 20 20 20

/f\

20 20 20 20

2 625 135 200 300 1 405 300 445 525

if 660 235 530 500 No 460 520 500 600

6 685 405 760 650 490 625 550 675

8 690 470 750 650 Data 515 635 600 690

10 750 540 750 725 540 625 575 715

12 775 615 800 765 I 570 650 625 755

14 825 590 900 775 4/ 600 645 675 840

16 875 585 985 82 5 630 650 725 900

18 900 580 1000 850 490 655 675 780 895

20 890 575 1025 875 520 675 710 775 600

22 850 570 1020 900 540 740 740 830 500

24 700 565 900 935 580 770 780 840 465

26 5 65 575 645 975 595 790 820 880 405

28 480 590 575 985 600 825 875 890 365

30 4i5 630 490 990 625 840 890 800 285

35 275 662 4oo 950 660 895 945 505 135

40 175 725 330 805 75-5 700 985 425

45 810 275 650 845 620 775 350

50 850 465 920 575 640 225

55 890 390 850 595 l40

60 925 300 705 535

65 925 225 655 475

70 730 135 630

75 665 605

80 600 570

85 575

Max.

Temp. 900 925 1025 1000 920 935 985 890 900

Time 18 62 20 32 50 34 4o 28 16

Table 4. FLOOR TEMPERATURES

Time

min

1 2 3 4 5 6 7 8 9

0 20 20 20 20 T

20 20 20 20

2 115 50 45 25 1 75 200 100 160

4 160 85 245 75 No 95 300 115 215

6 205 125 685 115 130 400 135 285

8 •255 165 775 150 Data 190 450 180 450

10 525 215 825 215 » 250 480 205 675

12 830 290 850 275 390 550 315 8 75

l4 990 342 900 360 V 500 570 580 960

16 900 370 925 390 650 575 775 950

18 900 395 900 535 225 715 610 850 1000

20 850 420 925 575 250 775 640 910 950

22 850 535 975 610 275 950 690 900 825

24 750 455 965 695 300 800 725 860 710

26 600 465 910 755 320 925 820 930 625

28 520 475 855 835 350 910 880 975 500

30 415 525 830 925 400 875 875 925 385

35 150 575 850 930 560 890 940 600 125

40 75 700 700 915 800 865 870 425

45 875 600 930 805 840 850 350

50 910 865 900 655 830 180

55 845 795 850 805 105

60 820 705 875 730

65 880 590 900 675

70 880 280 840

75 815 790

80 722 720

85 670

Max sTkmp 1025 910 975 940 950 950 960 975 1000

Time l6i 50 22 36 46 22 36 28 18

RAD/ANT

INTENSITY

cal

sec

'1

cm'

/, 2S

N

t'00

0.75

O.SO

0.Z5

0

RAJ)/OH -.TER 8 \ /

^-RAD/OM rTER x>

^

0 5 /

0

/S 20 25

EMF OUTPUT /mi/

Figure 1. Calibration of Two Copper Disc Radiometers

TIME

m

/A

zores

Figure

3*

Ceiling

Temperatures

T/ME

toiMUTES

OOZ!

7~/ME

/*

/mutes

Figure

5*

Radiation

from

Window

«30

40

SO

T/ME

M/mc/TES

Figure

6-.,

Radiation

from

Flames

T/ME

/H/A/ures

0 /O 20 30 ^fo SO

TIME M/Ht/res

Flame Height - Measured above compartment base,

Test No. 4

Figure 7*

ft

T/ME

ai/a/utss

U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director THE NATIONAL BUREAU OF STANDARDS

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J