NBSIR 73-263

Fire Endurance Tests of Unprotected

Wood-Floor Constructions for

Single-Family Residences

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards Washington, D. C. 20234

July 1973

Final Report

Prepared for Office of Policy Development and Research

Department of Housing and Urban Development

Washington. D. C. 20410

NBSIR 73-263

FIRE ENDURANCE TESTS OF UNPROTECTED

WOOD-FLOOR CONSTRUCTIONS FOR

SINGLE-FAMILY RESIDENCES

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards Washington, D. C. 20234

July 1973

Final Report

Prepared for Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

FIRE ENDURANCE TESTS OF UNPROTECTED WOOD-FLOOR

CONSTRUCTIONS FOR SINGLE-FAMILY RESIDENCES

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

! ABSTRACT

Fire endurance tests were performed on two full-scale and twelve

small scale wood floor constructions. The fire endurance ratings on

unfinished wood joist and plywood subfloor constructions varied from 10

to 13 minutes and were mainly determined by the time to "flame through."

In small-scale tests, the addition of carpeting with a hair pad delayed

the time of "flame through" approximately 8 minutes. Time, to "flame

through" may be estimated from the thermal resistance of the construction,

and may be modified by the effects of applied load or construction

details such as gaps, joints, and penetrations.

Key Words: Fire endurance; fire test; flame through; full scale; housing;

Operation BREAKTHROUGH; single family residence; small scale;

thermal resistance; wood floor; wood joist

i
TABLE OF CONTENTS

Page

1.0 INTRODUCTION 1

2.0 PREPARATION OF TEST SPECIMENS 3

2.1 Construction of Full Scale Test Specimen 3

2.1.1 Specimen of Test //L-l 3

2.1.2 Specimen Test //L-2 4

2.2 Instrumentations of Full Scale Test 5 2.2.1 Test //L-1 5

2.2.2 Test //L-2 6

2.3 Construction and Instrumentation-Small Scale

Test Specimen 6

3.0 TEST PROCEDURE 8

3.1 Full Scale Test 8

3.2 Small Scale Test 8

3.3 Fire Endurance Criteria 8

4.0 TEST RESULTS. ......... ^ . 10

4.1 General Observations of Full Scale Test 10

4.1.1 Test #L-1 10

4.1.2 Test //L-2 11

4.2 General Observations of Small Scale Tests 11

4.2.1 Test //S-1 11

4.2.2 Test //S-2 12

4.2.3 Test #S-3 12

4.2.4 Test //S-4 13

4.2.5 Test //S-5 13

4.2.6 Test //S-6 13

4.2.7 Test //S-7 14

4.2.8 Test //S-8 14

: 4.2.9 Test //S-9 14

4.2.10 Test //S-10 14

4.2.11 Test //S-11 14

4.2.12 Test //S-12 15

. ' 4.2.13 Test Results on Small Scale Tests 15

5.0 SUMMARY OF RESULTS 16

5.1 Comparison of the Results From the Full Scale

and From Small Scale Tests 16

5.2 Effect of Carpeting 17

5.3 Estimation of the Time of "Flame Through" 18

6.0 CONCLUSION 19

7 . 0 REFERENCES 20

ii
Page

APPENDIX I Table 1, Fire Endurance Times for Various Floor

Construction 21

Table 2, Test //L-1, Smoke Development 22

Table 3, Test #L-1, Deflection Measurements 23

Table A, Test //L-2, Deflection Measurements 24

Table 5, Thermal Resistance of Various Floor Material . . 25

APPENDIX II

Live Load Calculations 26

Nomenclature 27

APPENDIX III

Log of Observations During Test * 28

Test #L-1 28

Test #L-2 29

Test #S-1 , 29

Test //S-2 30

Test #S-3 30

Test #S-4 30

Test #S-5 31

Test #S-6 31

Test //S-7 31

Test #S-8 32

Test //S-9 32

Test //S-10 32

Test 33

Test //S-12 33

FIGURES

APPENDIX IV

SI Conversion Units 60

iii

1.0 INTRODUCTION

A series of fire tests were conducted to measure the fire endurance

of wood floor constructions representiative of those used in single family

residences. The fire exposure followed the requirements of the Standard

Methods of Fire Tests of Building Constructions and Materials ASTM

[1]-/

E 119-70 for floors. Tests were run on both full-scale specimens

(13-1/2 ft. by 18 ft.) with superimposed loads and on small-scale

specimens (2 ft. by 2 ft. nominal) loaded with "dead" weight to

restrain the specimens.

The assemblies tested included several plywood subflooring and

2/ underlayment combinations and strip flooring directly on 2 x 8 or 2 x 10—

wood joists. The effect of carpeting was also examined.

The fire endurance time was generally governed by excessive temperature rise on the unexposed surface of the wood floor. Failure by flame

through (directly through the wood or at joints) as well as the inability

to sustain the applied load followed shortly thereafter.

Small scale tests were also performed in a nominal 2 ft. x 2 ft.

furnace to investigate a much wider range of constructions than could

be tested full scale. To the extent that thermal effects principally

determine fire behavior, it should be possible to predict the results

of full scale tests from those of small scale tests.

— Numbers in brackets refer to reference given at the end of the report.

2/— All sizes of wood members in the test hereafter are given as nominal

sizes in inches in accordance with SPR 16-53 ' '

1
In the full-scale tests, the fire endurance time was 11 min:38 sec

by load failure for two layers of 1/2 in. plywood with or without carpeting (2 X 10 joists at 16 in. centers), and 9 minutes by temperature

failure for a single layer 1/2 in. square edge plywood with blocked

joints, and 10 minutes by temperature failure for a single layer of 5/8

in. plywood with tongue and groove joints (2x8 joists at 16 in. centers).

In the small scale tests covering 12 different constructions, fire

endurance ranged from 9 min:30 sec to 25 min:50 sec.

2
2.0 PREPARATION OF TEST SPECIMENS

2.1 Construction of Full Scale Test Specimens

2.1.1 Specimen of Test //L-1

The assembly was built into the 18 ft. x 13 ft. -6 in. framed opening

of the National Bureau of Standards (NBS) Floor Test Furnace. The specimen

consisted of air dried 2 x 10 construction grade Douglas Fir joists spaced

at 16 in. on center on a span of 13 ft. -6 in. Solid 2 x 10 bridging of

the joists was spaced 5 feet apart and was staggered for direct nailing.

Flooring material, as shown in figure 1, consisted of 1/2 in. thick grade

C-D plywood subfloor and 1/2 in. grade A-C plywood underlayment . The

plywood grades indicated here were in conformance with U.S. Product

Standard, PS 1-66. The subfloor was nailed with 8d coated nails spaced

6 in. on center along the edges and 10 in. along the intermediate joists,

starting with a full sheet in the NW corner. Underlayment was nailed with

6d coated nails spaced at 12 in. on center starting with a full sheet in

the SE corner to provide a pattern of staggered joints between layers.

Though the nailing was not strictly in accordance with the FHA Minimum

[3] Property Standards (MPS) , it is commonly used in the house construction.

In conformance with general practice and according to FHA-MPS requirements, a 1/16 in. spacing was allowed at the plywood joints.

The perimeter of the specimen was simply supported along the edges

of the furnace. Gypsum board protection was provided along the edges.

As shown in figure 1, one half of the specimen was covered with

2 nylon 501 carpet (weight 66.7 oz/yd ), while the other half, designated

as "bare", had no finish floor. Figure 2 shows the underside of the

3
floor, including joists and solid bridging, furnace thermocouples,

observation windows, and gas burners. Figure 3 is a general sketch of

the large floor test furnace.

The lumber used for the joists was Rocky Mountain Region Douglas

Fir which has an allowable stress level of 1050 pounds per square inch

2 (psi) in bending. A load of 63.7 lbs/ft , calculated to produce a

working stress of 1050 psi in bending at the extreme fibers of the

joists, was applied to the floor through four hydraulic jacks.

' }"''] 2.1.2 Specimen of Test //l-2

The size of the floor and the layout of the joists were the same as

in test //L-1 except that 2x8 joists were used instead of 2 x 10 's and

steel automatic adjustable bridging was used along the longitudinal

centerline instead of solid wood bridging.

Two types of combined subf loor-underlayment construction were used.

The floor was equally divided into two parts along the east-west center

line as shown in figure 4. One area consisted of a layer of 1/2 in. thick

plywood (interior A-C grade with exterior glue) vjith a square edge joints

protected by 2 x 3 blocking placed in line for toe nailing. The other

area consisted of a layer of 5/8 in. thick plywood tongue and groove

joints at all edges (underlayment grade, sand finished, with exterior

glue). The floor was nailed with 8d common nails spaced 10 in. on center.

In this test the applied load was reduced to a nominal 20 psf (21

psf actual) to study the effect of a more representative live load. This

4
load, which was applied to the floor by the method used in test //L-1,

represented approximately 38 percent of the working stress of the joists

(see Appendix II).

The typical moisture content of each material, based on a measured

weight loss at 105°C was (a) 10% for 5/8 in. thick tongue and groove

plywood, (b) 6% for 1/2 in. plywood, (c) 12% for 2x8 joist.

2.2 Instrumentation-Full Scale Test

2.2.1 Test //L-1

The instrumentation consisted of thermocouples, floor deflection

indicators, smoke meters and a motion picture camera. Eighteen ChromelAlumel (type K, .020 in. diameter wire) thermocouples were placed on

the top (unexposed surface) of the floor under 0.4 in. thick 6x6 in.

felted asbestos pads in such a way as to avoid contact with the steel

loading apparatus. In addition, five thermocouples were located under

the carpet at the quarter points and at the center of the carpeted area.

The distribution of the thermocouples is shown in figure 1.

The temperatures of all the thermocouples were printed out at 2

minute intervals on a Data Logger and then converted to punched cards

for graphing by a Calcomp Plotter.

Smoke meters with a 16 in. optical path were used to measure the

density of smoke accumulating above the two floor sections. They were

placed on the carpet 59 in. from the west edge and 28 in. from the eastwest centerline in the carpeted area and approximately at the diagonal

opposite side over the bare area. The smoke meter consisted of a sheet

metal canopy to collect the smoke arranged with a light source on one
side and a vacuum phototube on the other side. An opening was provided

at the bottom for air inlet and holes were provided in the top for the

controlled discharge of the smoky air.

The deflection indicators consisted of wires attached to nails

placed at three points; at the quarter points and midway along the

north-south centerline (see figure 1) . The wires were terminated with

small weights which kept them taut. Indicating riders were attached to

the wires where they passed over a vertical scale just above the small

weights. Each rider indicated the amount of movement at the corresponding point on the floor during the test.

: 2.2.2 Test i^L-2

The instrumentation was essentially the same as in the test #L-1,

except no smoke measurements were made. The location of the thermocouples is shown in figure 5.

2.3 Construction and Instrumentation-Small

Scale Test Specimens

Twelve (#S-1 through #S-12) small scale tests were performed on 2 ft.

X 2 ft. nominal (25 in. x 25 in. actual) specimens constructed of 2 x 10

joists spaced 16 in. on centers with various combinations of flooring

material. Specimen configuration is shown in figure 6 and the constructions

and loadings are summarized in Table 1, Appendix I. Joints of the underlayment and sub floor were perpendicular and met at the midpoint. In

tests #S-1 and //S-2 a 1/16 in. spacing was allowed at the plywood joints

as in the large scale tests. Since it was not possible to apply enough

load on the small scale specimen to produce the equivalent stress levels

as on the large scale specimen, in tests //S-3, //S-4, ifS-6 , //S-7, #S-8 and

6
//S-10 the plywood joint spacing was set at 1/8 in. This simulated

more closely the cracks observed in the plywood during the large-scale

test due to the applied load. Joist and end blocking details are shown

in figure 6.

Thermocouples were placed in the following manner: 1 thermocouple

at mid-depth of the center, 2 thermocouples on the unexposed wood

surface and, where applicable, there were 2 thermocouples on the rug.

When the joint was protected with a2x4or2x3 blocking as shown

in figure 7 the thermocouple at the center was moved to Che top of the

blocking.

7
3.0 TEST PROCEDURE

3.1 Full Scale Test

Load was applied eight minutes prior to the start of test with 35

steel channels, 5 in. x 24 in, which approximated a uniform load. Details

of the allowable live load calculation based on full design stress are

given in Appendix II.

The average temperature inside the furnace was measured by twelve

protected thermocouples and was made to follow the standard ASTM

E119-70 temperature-time curve by automatic control of the gas flow to

the burners, which is shown in figure 8.

3.2 Small Scale Test

Test specimen #S-1 was not loaded during the fire test. A load of

40 lbs. (10 psf) was applied to specimen #S-2 at two locations by setting

weights 4 in. each side of the longitudinal centerline. The load was

increased from 40 lbs. to 240 lbs. by putting four 60 lbs. weights at

four locations in Test #S-3 through Test #S-12 as shown in figure 9.

Four protected thermocouples were used to measure the average temperature inside the furnace which was made to follow the ASTM Standard E119-

70 temperature-time curve by automatic control of the gas flow to the

burner.

3.3 Fire Endurance Criteria

The fire endurance of a construction defined by the criteria of

failure designated by ASTM E119-70 is as follows:

8
(a) The construction shall have sustained the applied load

during the fire endurance test without passage of flame

or gases hot enough to ignite cotton waste, for a period

equal to that for which classification is desired.

(b) Transmission of heat through the construction during the

fire endurance test shall not raise the average temperature

on its unexposed surface more than 250°F (139°C) or 325°F

(181°C) at one point, above its initial temperature.

9
4.0 TEST RESULTS

4.1 General Observations of Full Scale Test

A log of observation made during the test is given in Appendix III.

, 4.1.1 Test #L-1

Flame penetration near the center at the joint between the two sheets

of plywood in the upper layer of the "bare" floor was observed at 13 min:

30 sec. The location where flaming occurred and the associated charred

region is shown in figure 10. There was also a load failure, as evidenced

by the inability to maintain hydraulic pressure at 11 min: 38 sec.

The average temperature rise of the surface thermocouples on the

"bare" floor was less than 75°C when the test was terminated after 15

minutes. A single thermocouple on the carpet exceeded a 50°C rise,

with a reading of 80°C indicating that it may have been directly over

a nailhead. The average temperatures of the "bare" floor and the

carpet-finished floor are shown along with the average temperature

beneath the carpet in figure 11.

The smoke meter on the "bare" floor showed a sudden increase in

smoke at about 9 minutes, which was more than 4 minutes before "flame

through" was noticed. The smoke level indicated by the meter over the

carpet-finished floor was considerably less. Smoke meter transmission

is given in Table 2, Appendix I and figure 12.

The deflection increased steadily to 6.5 in. at 11 min: 38 sec when

the load could not be maintained as shown in figure 13. Deflections

are tabulated in Table 3, Appendix I.

10
There was a few small scorch marks on the hair pad due to heat

conduction through the nails. This continued into the burlap backing of

the nylon carpet at several locations leaving scorch spots up to 1 inch

in diameter.

4.1.2 Test //L-2

Flames penetrated the 1/2 in. plywood floor near the quarter point

along the longitudinal centerline between the blocked joints at 11 min.

Flames were noticed along the tongue and groove joint near the center

on the southwest side about 50 seconds later.

Figure 14 illustrates average temperature rises on the unexposed

surface. Temperature failure occurred at 9 min. for the 1/2 in. plywood

floor and 10 min. for the 5/8 in. plywood floor.

Figure 15 is the temperature history of six specially arranged

thermocouples (see figure 5). The slow rise in temperature of thermocouple C illustrates the effectiveness of the blocking in protecting

the joint.

The deflections are tabulated in Table 4, Appendix I and shown

graphically in figure 16. The deflection increased rapidly and the

floor broke through at 13 min.

4.2 General Observations of Small Scale Tests

A log of observations made during the test is given in Appendix III.

4.2.1 Test //S-1

Some difficulty with the furnace control was experienced at the

beginning of this test causing the furnace temperature-time curve to be

below the standard temperature-time curve (see figure 17). Flame through

occurred at 21 min: 43 sec. The corrected time of flame through, according

11
to the correction formula stated in ASTM E119-70 based on the comparison

of the areas under the actual time-temperature curve and the standard

curve, was 18 min:10 sec.

The corrected time to flame through was 5 minutes longer than in

the full scale test. The probable reason for this difference was that

no load was applied to produce downward bending and opening of the

joints. During the test the center part of the joint tended to bend

upward due to thermal stress.

, 4.2.2 Test //S-2

The flame through occurred at 17 min:21 sec. This compares quite

well with the corresponding time of 18 min:10 sec in test #S-1 considering

that a light load of 10 psf was applied in test #S-2. No bending was

observed either upward or downward throughout this test.

'

' ' A. 2. 3 Test

The time 12 min:45 sec. to reach flame through was considerably decreased compared to test //S-2. As indicated in the test observations, it

took about four minutes to produce a definite flame through after the

subfloor burned out in test //S-2 but only one half a minute in test //S-3.

The flame through was primarily through the 1/8 in. joint separation

provided in the construction.

The applied load did not appear to unduly influence the behavior

of the specimen. This load, however, was used as a standard condition

for the remaining small scale tests.

The location of flame through was rather localized along the joint

in test //S-3, compared to previous tests, as shown in Figure 18.

12
4.2.4 Test //S-4

The flame through region covered a large portion of the floor and

originated in the same area as in test //S-3. In test //S-4 the fire

burned a large hole all at once. The unexposed surface of the carpeted

floor charred over a large area during the last 3 min:50 sec of test and

then surface ignition suddenly took place over the char region at 25 mint

50 sec of test time. This was taken as the flame through time. Deflection

due to the load vas observed near the center after 21 min of test time.

4.2.5 Test //S-5

The tongue and groove joint started to char and open up at 9 min

followed by flame through near the north quarter point at 10 min: 30 sec

of test time (see figure 19).

4.2.6 Test #S-6

The flame through (surface ignition) region was situated at the

quarter points, i.e., directly through the plywood and carpeting, not

at the joint.

The 2x4 blocking, besides protecting the joint thermally also

acted like a stiffening beam and changed the pattern of the deflection

and the flame through from that in test //S-4. Figures 20, 21 and 22

show the pattern of deflection at 17 min:30 sec and the flame through at

18 min:15 sec near the north quarter point and the flaming regions before

extinguishment, respectively.

13
4.2.7 Test #S-7

The flame through occurred at 9 min:25 sec near the north quarter

point, not at the protected joint, as in Test //S-6. However, the flame

through occurred earlier since there was no carpet to provide additional

thermal resistance.

' r 4.2.8 Test J/S-8

Deflection and charring near the center of the carpeted unexposed

surface was observed at 17 min and 19 min : 10 sec, respectively. The

flame through (surface ignition) occurred near the center at 24 min

in the same manner and location as in test #S-4.

' . 4.2.9 Test #S-9

The tongue and groove joint started to char and open up near the

center at 6 min. The flame through occurred near the center at 11 min:

35 sec .

: : . :

4.2.10 Test y/S-10

The flame through occurred at 11 min : 35 sec near the north-south

quarter areas and not at the protected joint. The pattern of the

deflection and the flame through was similar to test //S-6.

4.2.11 Test #S-11

Deflection and charring on the unexposed surface of the carpeted

floor was observed at 15 min of test time. The flame through (surface

ignition) took place over a large portion of the floor at 19 min:20

sec.

14
4.2.12 Test //S-12

During construction of the specimen //S-12 a small piece (1 in. long)

of tongue and groove was broken at the north end joint. Sagging and

charring occurred at the joint with the broken tongue at 10 min : 30 sec

which is 1 min earlier than at the undamaged joints.

The flame through at the joint with the broken tongue and at an

undamaged joint near the center occurred at 13 min:21 sec and 14 min:10

sec, respectively.

4.2.13 Temperature Readings on Small Scale Tests

Figures 23 and 24 show the temperature changes at half depth for

the small scale tests. In figure 24 the slope of curve 7 is flatter

than the others, which is explained by the blocking under the joint

protecting the joint from the fire.

The temperature changes on the bare floor and on the carpet surface

are shown in Figures 25, 26 and 27. The temperature failure due to the

average temperature rise of 139°C on the unexposed surface occurred a

few minutes (1-7 minutes) earlier than the failure by flame through.

These are shown in Table 1 of Appendix I.

15
5.0 SUMMARY OF RESULTS

5.1 Comparison of the Results from the

Full Scale and Small Scale Tests

Experiments were carried out to measure the time of fire endurance

of the different floor constructions subjected to the conditions of

the standard fire endurance test, ASTM E 119-70.

In loaded full-scale fire tests on unprotected wood floors, structural

failure generally occurs at approximately the same time as excessive

temperature rise or "flame through". In test #L-1 under the load, which

produced the design stress (63.7 psf live) on the 2 x 10 joists, the

load failure by inability to sustain the applied load occurred at 11 min:

38 sec and "flame through" at 13 min: 30 sec. It was not possible to

continue the test to achieve failure due to excessive temperature rise on

the unexposed surface. To obtain a better measurement of temperature

transmission failure, and to simulate a more representative floor live load,

in test y/L-2 with 2x8 joists the load was reduced to 20 psf. Load

failure occurred at 13 min, temperature failure occurred between 9 and

10 minutes, and flame through occurred between 11 and 12 minutes.

It is believed that, as the supporting joists in the full scale

test are destroyed by charring, cracks form at the highly stressed

extreme fibers on the bottom surface. This increases the deflection

and accelerates the rate of flame penetration through increased joint

separations.

As previously mentioned in test #S-3, the 1/8 in. fixed gap on the

underlayment joint reduced the time of "flame through" by 4.5 minutes.

For both the large scale and small scale test, the temperature rise on

the unexposed surface was nearly the same. It may be that the gap

16
built in during construction of the small scale test specimen //S-3

corresponded to the cracks made on the exposed surface due to the load

in the full scale test //L-1.

It is noticed that the time of flame through of the small scale tests

on the 5/8 in. plywood with tongue and groove joint (Test //S-9) or the

1/2 in. plywood with square edge joint protected with 2x3 blocking

(Test #S-10) are in agreement with those of the full scale test (Test /'L-2)

Considering the criterion of temperature failure, it is interesting

that the temperature failures occurred a few minutes earlier than the

"flame through" failures in most cases. Table 1 of Appendix I summarizes

the different types of failure on the various constructions , the loading

conditions and the total thermal resistance.

Thermal resistance is calculated from the thickness and coefficient

of thermal conductivity as follows:

^, -, . Thickness

Thermal Resistance = 7;—7-7-:—: —7—;rr z—^—-——:—r—

Coefficient of Thermal Conductivity

The thermal properties which form the basis for the computed thermal

resistance (see Table 5 of Appendix I) were obtained from a standard

reference source . ''^

5.2 Effect of Carpeting

In the small scale tests (#S-4, -6 and -8), it was obvious that the

carpeting delayed the time of "flame through" and temperature failure

by 8 to 12 minutes. In the large scale test (Test #L-1) , the carpet

itself did not add any strength to the floor as evidenced by the slight

difference in the deflections between the floor sections with or without

carpet (see figure 13).
5.3 Estimation of the Time of "Flame Through"

Figure 28 illustrates the influence of the thermal conductivity of

various materials on the time of "flame through" under free convection

conditions and at room temperature. It is apparent that construction

//S-4 (1/2 in. plywood + 1/2 in. plywood + 1/8 in. gap + carpet) has the

largest value of thermal resistance and requires the longest time for the

flame to penetrate through the floor. It can be also seen in figure 28,

that empirically there is a linear relation between the thermal resistance

and the "flame through" time. The developed slope K is 0.133 (BTU/°F)

For instance, a 1/8 in. vinyl asbestos tile will add a thermal

resistance (R) of 0.05 (HR °F/BTU) to the floor. The additional time

for the flame to pass through the tile with a resistance of R = 0.05

(HR °F/BTU) will be 24 seconds. The flame through time of 11 minutes was

observed by experiment on 1/2 in. plywood with 2x3 blocking (test #1-2

and //S-10) . Thus, the total time required for "flame through" on the

floor construction of 1/2 in. plywood with 2x3 blocking, finished with

1/8 in. vinyl asbestos tile can be estimated as 11 min:2A sec.

18
6.0 CONCLUSION

Bare wood floor constructions conforming to the FHA Minimum

Property Standards are able to meet a fire endurance time requirement of 10 minutes measured according to the ASTM E-119 Standard..

This includes single-floor plywood constructions 1/2 in. and 5/8 in.

thick. Strip flooring (25/32 in. softwood and 13/16 in. hardwood)

directly over joists have a fire endurance time in the range of 10 to

13 minutes.

The addition of a separate finish floor should increase the fire

endurance time by an amount dependent on its additional thermal

resistance. This is estimated to be approximately 1/2 minute for

1/8 in. vinyl asbestos tile to approximately 10 minutes for carpeting

over a hair pad.

For example, the time of flame through for the (1/2 in. plywood +

1/2 in. plywood + 1/8 in. gap + carpet) construction, which has total

thermal resistance of 2.40 (HR °F/BTU), is almost A times that for the

(1/2 in. plywood +2x4 blocking) construction with total thermal

resistance of 0.62 (HR °F/BTU)

The total thermal resistance of the floor construction can be used

as a factor for estimation of "flame through" time. Further study

would be necessary to determine the effects of the applied load or the

gap size.

19
REFERENCES

Standard Methods of Fire Tests of Building Construction and Materials

American Society for Testing and Materials Designation E119-70.

Simplified Practice Recommendations 16-53, Lumber, American Standards

for Softwood Lumber , U.S. Department of Commerce, Washington, D.C.,

January 1953.

Minimum Property Standards For One and Two Living Units , FHA No. 300,

U.S. Department of HUD, FHA, Rev. January 1970.

"Handbook of Fundamentals, Heating, Refrigerating, Ventilating and

Air Conditioning " Published by ASHRAE, 1967.

20
H

M o W J.

I

< U-l Q

00

.+ — o

rH O

.+ 3

oo^ T3O + O

00 ^

C .-I

OO 4J r4 (U OQ Q.

: m

u

X

r T3 +—H 60

a

+ n)00

— O ^ O

.+ S

- >

CM —

00 WOO ^-^^

o o ^ M O M O a

+ Oi

•H O

00 iH>-«t! in —

U cq

w

zoH

O

g

H

COO

o

CSo

o

J

21
Table 2

TEST //L-1 SMOKE DEVELOPMENT

Time

min : sec

0:00

1 :00

2:00

3:00

4:00

5:00

6:00

7 :00

8:00

9:00

10:00

11:00

12 :00

12:30

Over Plywood

T(%) O.D

Over Carpet

T(%) O.D

100

99.5

99.5

96

97.5

97

97.5

93.5

88

78

11.2

4.5

12.4

0

0

0

0.01

0.01

0.01

0.01

0.037

0.053

0.01

0. 93

1. 35

0.9

100

ICQ

99

96.5

97.5

95.5

97.5

91.5

89

86.5

80.5

78

72

0

0

0

0.01

0.01

0.01

0.01

0.04

0.053

0.06

0.09

0.1

0.2

Readings discontinued

T(%) : Measured transmission percentage from smoke meter

O.D: Optical density converted from T(%)

22
Table 3

TEST #L-1 DEFLECTION MEASUREMENTS

Measurements of deflections were made at three points on the longitudinal center line; at the North (N) and South

(S) quarter points, and at dead center (C) . Readings in

inches

N C S

Before load 0 0 0

After load 0.18 0.20 0.20

min:sec.

1:00 0.20 0.20 0.20

2:30 0.45 0.50 0.20

5:00 0.6 0.75 0.6

6:00 0.6 0.95 0.7

7:00 0.9 1.25 0.9

8:00 1.1 1.6 1.1

9:00 1.5 2.3 1.5

10:00 1.8 3.0 1.8

10:30 2.1 3.6 2.1

11:10 2.4 4.5 2.8

11:38 2.7 6.5 3.3

Load off (unable to maintain pressure)

23
Table 4

TEST //L-2 DEFLECTION MEASUREMENTS

(Reading in inches)

Time

min : sec

0:00

1:00

2 :00

3:00

4:00

5:05

7:00

10:00

12:00

13:00

N

0

0

0

0

1

2.5

4

4

7

Wire broke

1

1.25

1.5

2

2.5

5

8

14

18

19

0.5

1.0

1.25

1.5

2

3.5

5

9

12

24
Table 5

THERMAL RESISTANCE OF VARIOUS FLOOR MATERIAL [4 ]

THERMAL

MATERIAL

DENSITY

LB/FT^

CONDUCTIVITY

BTU/HR FT °F

K

CONDUCTANCE

BTU/HR °F

c

THICKNESS

INCH

L

RESISTANCE

HR °F/BTU

R

Oak 51.5 1.2 13/16 0.65

Pine 34 0.8 25/32 0.98

Plywood .80 1/2 0.62

Carpet plus

hair pad

.8 1.2

Vinyl

asbestos

tile

20.0 1/8 0.05

R = ^ = 1/c

25
APPENDIX II

: Live Load Calculations

Allowable design stress for Douglas fir construction grade joist

with 2 X 10 and 2x8 in. cross-section on full scale test.

According to the stress equations

M

and , 2

Allowable bending stress

f^= 1050 psi

Section modulus

I/C = 24.44 (in^) for 2 x 10 joist

I/C = 15.23 (in^) for 2 x 8 joist

From Equation [1]

^2 X 10 " ^^^^ ^ 24.44 = 25,700 (Ib-in) = 2140 (Ib-ft)

From Equation [2] -

= 8 (2140) ^ ^ X 10 (13.52)2 y^-u UD/rt;

Above value is for unit length on the joist. Therefore, the working

load corresponding to unit area can be converted by multiplying by the

factor (12/16).

^2 X 10 " ^^'^ ^ 12/16 = 70.5 (psf)

Live load = Total allowable load - Dead load

26
therefore

,

Same manner

therefore

,

Dead load = carpet 1.0 psf

Two layers of plywood (1" thick) 3.0 psf

+ joist (2 X 10 cross-section) 2.8 psf

total dead load 6.8 psf

Live load/2 x 10 = 70.5 - 6.8 = 63.7 (psf)

W_ „ = 58.3 psf 2x8 ^

Dead load » plywood (5/8 Inch thick)

= 1.87 psf

Live load/2 x 8 = 58.3 = 1.87 = 56.43 (psf)

NOMENCLATURE

M = Bending Moment

f, = Bending Stress

b

l/C = Section Modulus

w = Load

c = Half depth of joist

Subscript 2 x 10 = 2 x 10 joist

Subscript 2x8 =2x8 joist

27
APPENDIX III

Log of Observations During Test

Test #L-1

mln:sec.

1:00 Joist Ignited, crackling sounds, smoke escaping between

joists and plywood deck around the edge of the floor.

2:00 Fire-exposed plywood surfaces all scorched.

3:00 Inside of furnace filled with smoke and flame. Whole

underside on fire.

4:00 West side of fire-exposed pljrwood burned more than east

side.

5:00 Smoke increasing through the cracks at the perimeter, but

no smoke directly from upper surface.

8:00 Crackling sounds were more severe.

10:00 Appreciable smoke around T/C //8 pad on bare floor.

11:38 "Load Failure" (could not sustain hydraulic load).

12:30 Load off. At least 2 joists were broken.

13:30 Flame through at joint.

15:00 Gas off. END OF TEST

28
Test #L-2

Time

min:sec.

0:40

1:00

1:30

3:00

4:00

11:00

11:50

13:00

Test #S-1

6:45

10:20

18:00

19:30

20:00

21:43

(18:10)

Joist started flaming on the south side.

Joist started flaming on the north side.

Smoke on unexposed surface.

Large sheet of flames formed on under side of floor.

Formation of black char at a few spots on the top surface.

"Flame through" on 1/2 in. plywood floor.

"Flame through" on 5/8 in. pljrwood floor.

Load failure (floor broke through)

Joists and exposed plywood surface ignited.

Tendency of center part of joint to bend upward due to

thermal stress. Smoke coming out through joint.

Fire inside furnace seen through the opening of joint.

Small fire coming through the joint

Noticable difference in height between plywood sections

at center of joint.

"Flame through."

(Corrected time for flame through, see General Observations

of test #S-1).

29
Test //S-2

Time

min : sec

1:00

1:20

13:30

14:00

'

17:21

Test //S-3

1:10

5:30

12:15

12:45

Test //S-4

1:00

7:00

14:00

21:00

22 :00

25:00

25:50

Inside the furnace was filled with flame and smoke.

Joists started flaming.

Fire inside the furnace seen through the opening of the

joint. (Subfloor burned through).

Along the edge of the joint, dehydration phenomena and

black char appeared.

"Flame Through".

Joists started to burn.

Smoke from joint.

The furnace fire appeared through the gap. (Subfloor

burned through)

"Flame Through".

Joist on fire .-: -.

Gray smoke filtering through the carpet, and the center

part of the unexposed surface was covered with moisture.

Fire reached underlayment . (Thermocouple indication)

Deflection due to the load was observed near center.

Black Char on the carpet started to be formed.

Load was relaxed. (Could not sustain the weights)

"Flame through".

30
Test #S-5

Time

min :sec.

1:00

6:00

9:00

9:30

10:30

Test #S-6

1:00

8:00

14:50

18:15

Test #S-7

1:06

7:00

8:00

9:25

Joist started to burn.

Exposed surface under thick flame.

Smoke was noticed around T and G joint near the north end.

At the same time its color became charcoal black, and sagging and opening at this joint was observed.

The fire inside furnace was seen through the opening.

"Flame through at the joints. The locations of "flame

through" and openings at joints are seen in Figure 19.

Joist started to burn.

Gray smoke filtering through the carpet and moisture noted

on the unexposed surface.

Black char on the carpet surface. An appreciable deflection was observed midway between dead center and north and

south end.

"Flame through".

Ignition of joist.

Smoke started to appear on unexposed surface.

The top surface became dark near north end.

"Flame through."

31
Test //S-8

Time

mi n : s e c

1 :05

6:15

17:00

19:10

20:20

24:00

Test //S-9

1:00

4:00

6:00

9:40

11:35

Test //S-10

1:00

7:40

10:25

11:00

Joist ignited. •

Appearance of gray smoke through the carpet at the middle

of the joint.

Deflection occurring at center.

Formation of the char region near center of the carpet

surface

Deflection was severe.

"Flame through" near center.

Ignition of joist.

Smoke was seen above tongue and groove joint.

Formation of dark char on the edge of the joint near center

,

Flames were seen through the opening made on the joint.

"Flame through.

Joist started to burn.

Char forming on the unexposed

area.

Fire inside furnace was seen

the char was formed.

"Flame through."

surface near north quarter

through the opening made where

32
Test //S-11

Time

min : sec

1:03

7:00

15:00

18:00

19:20

Test #S-12

1:00

3:00

4:00

10:30

11:00

12:00

13:21

14:10

Joist started to burn.

Gray smoke and moisture was observed on the unexposed

surface near the center.

Black char forming. Deflection was noted.

Deflection severe. The charred region about three inches

in diameter.

"Flame through."

Joist on fire.

Dehydration phenomena was clear on the edge of the wood.

Droplets of moisture was formed on top of the unexposed

surface.

Sagging was observed near north end where tongue was broken during construction.

The sagging resulted in a small opening.

Fire inside furnace was seen through the opening.

"Flame through" where the broken tongue existed.

"Flame through" at a normal joint near center.

33
I-UJ

Ql UJ oz\ 1 -

1/2"

(UNDERLAY -

1/2

(SUBFLOO

—^ 11 \ t 5

Q.<X o

UJ I

CO

)-l VSI<uoc

CO

(U I—I a3O

CJoE

>-i <u H

cauo

•H

ft,

34
35

I J

aOOMAld „z/\ —

z

:^o

o

-J

f

ill o

<a.

3O

LtJ >O

o

•J

+J

CO(U H

u-(oc

o

<ua.

COu

oo

iH

1^

(U>^00

•H

|X4

37

39
Figure 7 Underside of Specimen

Test #S-6

40
1000_,

900_

800_

TIME (niNUTES)

FIGURE 8 , Average Furnace Temperature for #L-1 Compared with Standard E119

41
Figure 9 Location of Weights

Test //S-3

42
43
FICUFE :U Average Surface Temperature Rises on Bare Plywood Floor,

Under the Carpet, and on the Carpet (Test //L-1)

44
o OVER BARE FLOOR

X OVER CARPET AREA

5 10

TIME(MIN)

FIGURE 12. Smoke Density, Test #L-1

A5
. I- It

TIME{MiN)

1''K;1IR1': I.J. Deflection Measurements Test y^L-l

46
700

650.

600_

550_

500.

450.

* on 5/6' plywood

4 on i/V plywood

400J

k \ S \ \ \^ H ^"2 ^1 TIME (rilNUTES)

FIGURE 14. Average Temperature Rises for Test #L-2

47
700_

650

600_

550_

o

UJ

CD

UJ

cr

or

(jj

250

1 50-

Syinbols Symhols

on graph in Figure 5 X

AA

R

8 C

t D

F

See Figure

0 1 I I h r~ 9

TIME (niNUTESJ

10 II 12

I' lciiRls ]

•'-', Temperature Rises of Special Thermocouples For Test #L-2

48
TIME (MiN)

FIGURE 16. Deflection Measurements, Test #L-2

49
1000_

900_

0 i 4 I 6 10 yZ ^6 1^ ^0 £2 ^4 26

TIME (niNUTES)

FIGURE 17. Average Furnace Temperatures for Test //S-1 Compared with

Standard E 119

50
Fig, 19. Locations of Flame Through

Openings at Joint (after

removing load) Test #S-5

51
Fig. 20 Smoke at 17.5 min. Test #S-6
Fig, 22, Flaming Region Before

Extinguishment, Text #S-6

53
Fig„ 23 Temperature Rises at Half Depth For 2X2 Tests #S-1 - 5 54
1000_

TIME( MINUTES )

Fig. IL^ Temperature Rises at Half Depth For 2X2 Tests #S-7 - 12
('iK„ 2 5. Temperature Rises on the Bare Floor for Tests #S-1 - 6

56
1000.,

^ 9 Number indicates test number.

E 10

TlnE( niNUTES)

Fig. 26. Temperature Rises on the Bare Surface Under Carpet for Tests 7-12

57
FiK- 27. Temperature Rises on the Carpet for the 2X2 Tests

58
X

e)

IDO

(TX

O

I-UJ

26-

24-

22-

20-

18-

16-

14-

12-

10-

8-

6-

4-

2-

o SMALL SCALE TEST

X LARGE SCALE TEST

J. 0.5 I 1.9 2 2.5

THERMAL RESISTANCE (HR*»F/BTU)

Fig 28 Thorni.)) RESISTANCE of Floor Construction Vs ] T ime

59
Appendix IV

SI Conversion Units

In view of present accepted practice in this country in this

technological area, common US units of measurement have been used throughout this paper. In recognition of the position of the United States as

a signatory to the General Conference on Weights and Measurements which

gave official status to the metric SI system of units in 1960, we assist

readers interested in making use of the coherent system of SI units by

giving conversion factors applicable to US units used in this paper.

Length

1 in = 0.0254 meter

1 ft = 0.3048 meter

Mass ; . ",•„,.

1 lb = 0.45 kilogram

Stress .

2 1 psf = 47.88 newton/meter

2

1 psi = 0.332 newton/meter

1 plf = 13.49 newton/meter

Temperature

Temperature in "F = 9/5 (temperature in °C) + 32°F

60
FORM NBS-114A (1-71)

t II. r.r^^T. r.r- COMM. j 1. PIM'.MC ATION o;^ Kl-;rOKT NO.

LHi^fX I Nu b iR /j>' Zoj

t'/C/v'r. .'cccs.oion I 3. Kccipi cru' o .\cccssion .\'o.

4. 'ilTLt AND i-UbllTLE

Fire Endurance Tests of Ui.-iprotectod Wood-Floor CcnstrucLions

for Single-'Faniily Residences

7. AUTHOIUS)

B. C. Son

9. PLRFORMINC;- ORGANIZATION NAMK AND ADDKHSS

J AT 10 N A 1 . Fa: R L: A 1 1 OF ST A N D R \) S DEPARTMi-NT OF CO.MMFRCE

WASHINGTON, D.C. 20234

12. Sponsoring Org.iniz.ition Name and Address

Department of Housing and Urban Development

Washington, D.C. 20410

5. Publication Date July 1973

6. Performing Or^ianiz: tion C-.. 'r

8. Pcrfornung Orjjar. i?..Ui ir: NBSIR 73-263

10. Project/Task/ Work l.'nii :.o. 4600461

11. Contract/Grant \'o. IAA-H-16-70

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

1 5. SU P PL E .\! E N T A R Y N OT E S This is a revision of N13S-10320

16. AB.STR.ACT (A .""OO-word or less factual summary of rr.ost significant infoimation. If document includes a significant

bibliography or literature survey, mention it here.)

Fire endurance tests were performed on two full-scale and twelve small scale v.'ood floor constructions. The fire endurance ratings on unfinished v/ood joist and

plyvjood subtloor constructions varied from 10 to 13 minutes and were mainly

determined by the time to "flame through." In small-scale tests, the addition

of carpeting with a hair pad delayed the time of "flame through" approximately 8

minutes. Tim.e to "flame through" may be estimated from the thermal resistance

of the construction, and may be modified by the effects or applied load or construction details such as gaps, joints, and penetrations.

17. KEY WORDS 'Alphabetical order, separated !>/ - ^m irt/i,-n s) Fire cudu ratTciT^f ire tcst; flavae tTiroagr; ; full scale; housing; Operaticu lREAKTI'ROUGK ; single family residence; small scale;

j thermal resistance; wood floor; aogg joist I 18. AVAIl.AHllJ l Y .STA I E.MENT

F^' UNEIMI l Ei^.

i\' NTIS,

jl9. SI-:CUK1TY {.I. ASS

(THIS Ri,Pv)R 1

i ' : i .\S:';i' ir' D

21. NO. OF PAGES

7 0