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NATIONAL BUREAU OF STANDARDS REPORT 

10 320 


FIRE ENDURANCE TESTS OF UNPROTECTED WOOD-FLOOR 
CONSTRUCTIONS FOR SINGLE-FAMILY RESIDENCES 



U.S. DEPARTMENT OF COMMERCE 

NATIONAL BUREAU OF STANDARDS 


NATIONAL BUREAU OF STANDARDS 


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NATIONAL BUREAU OF STANDARDS REPORT 


NBS PROJECT 

4213461 


May 10, 1971 


NBS REPORT 

10 320 


FIRE ENDURANCE TESTS OF UNPROTECTED WOOD-FLOOR 
CONSTRUCTIONS FOR SINGLE-FAMILY RESIDENCES 


by 

B. C. Son 

Fire Research Section 
Building Research Division 
Institute for Applied Technology 
National Bureau of Standards 


Prepared for: 

U. S. Department of Housing and Urban Development 


IMPORTANT NOTICE 


NATIONAL BUREAU OF STAND 
for use within the Government. Befoi 
and review. For this reason, the pub 
whole or in part, is not authorized 
Bureau of Standards, Washington, D. 
the Report has been specifically prep 


Approved for public release by the 
director of the National Institute of 
Standards and Technology (NIST) 
on October 9, 2015 


'counting documents intended 
:cted to additional evaluation 
ng of this Report, either in 
ice of the Director, National 
Government agency for which 
. for its own use. 



U.S. DEPARTMENT OF COMMERCE 

NATIONAL BUREAU OF STANDARDS 


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FIRE ENDURANCE TESTS OF UNPROTECTED WOOD-FLOOR 
CONSTRUCTIONS FOR SINGLE-FAMILY RESIDENCES 


by 

B. C. Son 

Fire Research Section 
Building Research Division 


ABSTRACT 

Fire endurance tests were performed on two full-scale and 
12 small-^scale wood floor constructions. The fire endur- 
ance 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." The addition of 
carpeting with a hair pad delayed the time of "flame 
through" approximately 10 minutes. Time to "flame through" 
may be estimated from the thermal resistance of the 
construction. This may be modified by the effects of 
applied load or construction details such as gaps, joints, 
and penetrations. 


1 


TABLE OF CONTENTS 


page 

1.0 Introduction 1 

2.0 Preparation o£ Test Specimens 3 

2.1 Construction o£ Full Scale Test Specimens 3 

2.1.1 Specimen o£ Test #L-1 3 

2.1.2 Specimen Test #L-2 4 

2.2 Instrumentations o£ Full Scale Test 5 

2.2.1 Test #L-1 5 

2.2.2 Test #L-2 6 

2 . 3 Construction and Ins trumentation- Smal 1 

Scale Test Specimens 7 

3.0 Test Procedure 8 

3.1 Full Scale Tests 8 

3.2 Small Scale Test 9 

4.0 Test Results 10 

4.1 Full Scale Test 10 

4.1.1 Test #L-1 10 

4. 1.1.1 General Observations 10 

4.1.2 Test #L-2 11 

4. 1.2.1 General Observations 11 

4.2 Small Scale Tests 12 

4.2.1 Test #S-1 12 

4. 2. 1.1 General Observations 12 

4.2.2 Test #S-2 12 

4. 2. 2.1 General Observations 12 

4.2.3 Test #S-3 13 

4. 2. 3.1 General Observations 13 

4.2.4 Test #S-4 13 

4. 2. 4.1 General Observations 13 

4.2.5 Test #S-5 14 

4. 2. 5.1 General Observations 14 

4.2.6 Test #S-6 

4.2.6. 1 General Observations 


i i 


14 


4.2.7 


page 

Test #S-7 14 

4. 2. 7.1 General Observations 14 

4.2.8 Test #S-8 14 

4. 2. 8.1 General Observations 14 

4.2.9 Test #S-9 15 

4. 2. 9.1 General Observations 15 

4.2.10 Test #S-10 15 

4.2.10.1 General Observations 15 

4.2.11 Test #S-11 15 

4.2.11.1 General Observations 15 

4.2.12 Test #S-12 15 

4.2.12.1 General Observations 15 

4.2.13 Test Results on Small Scale Tests 16 

5.0 Summary of Results 17 

5.1 Comparison of the Results from the Full 

Scale and from Small Scale Tests. 17 

5.2 Effect of Carpeting 18 

5.3 Estimation of the Time of ’’Flame through.” 19 

5.4 Estimation of ’’Load Failure” by Excessive 

Deflection 19 

6.0 Conclusions 21 

7.0 References 22 

Appendix I 23 

Live Load Calculation 23 

Nomenclature 25 

Appendix II 26 

Log of Tests 26 

Test #L-1 26 

Observation During Test 26 

Smoke Development (Table 1) 27 

Deflection Measurements (Table 2) 28 


page 


Test #L-2 



29 

Observation 

During 

Test 

29 

Deflection Measurements (Table 3) 

30 

Test #S-1 



31 

Observation 

During 

Test 

31 

Test #S-2 



32 

Observation 

During 

Test 

32 

Test #S-3 



32 

Observation 

During 

Test 

32 

Test #S-4 



33 

Observation 

During 

Test 

33 

Test #S - 5 



33 

Observation 

During 

Test 

33 

Test #S-6 



34 

Observation 

During 

Test 

34 

Test #S-7 



34 

Observation 

During 

Test 

34 

Test #S-8 



35 

Observation 

During 

Test 

35 

Test #S-9 



35 

Observation 

During 

Test 

35 

Test #S-10 



36 

Observation 

During 

Test 

36 

Test #S-11 



36 

Observation 

During 

Test 

36 

Test #S-12 



37 

Observation 

During 

Test 

37 

4 Fire Endur; 

ance Times for Various Floor 



Constructions 38 

Table 5 Thermal Resistance o£ Various Floor 
Materials 
Figures 


39 


FIRE ENDURANCE TESTS OF UNPROTECTED WOOD-FLOOR 
CONSTRUCTIONS FOR SINGLE-FAMILY RESIDENCES 


by 

B. C. Son 

1.0 Introduction 

A series of ASTM Standard E119 fire tests were conducted 
to measure the fire endurance of wood floor constructions 
representative 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 
A.S.T.M. E119r69, for floors. Tests were run on both full- 
scale specimens (13 1/2 by 18 ft.) with structural load, and 
on small-scale specimens (2 by 2 ft.). 

These tests were carried out to study the relationship 
between the behavior of unprotected floors, over a basement 
or crawl space, and the "Guide Criteria" for Operation 
Breakthrough, Criterion A. 4. 1.1 of Volumes III and IV of 
the "Guide Criteria" states that the fire endurance of floors 
over a crawl space or basement should equal or exceed 10 
minutes . 

The constructions tested included several plywood subflooring 
and underlayment combinations and strip flooring directly 
on 2 X 8 or 2 X 10 nominal wood joists. The effect of carpet- 
ing was also examined. 

The fire endurance time was usually governed by excessive 
temperature rise on the unexposed surface of the wood floor. 
Failure by flame penetration (directly through the wood or 
at joints) and by excessive deflection (inability to sustain 
the applied load) followed shortly thereafter. 


1 


Small scale test in a nominal 2 ' x 2* furnace was also 
performed to investigate a much wider range of construc- 
tions 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. 

In the full-scale tests, the fire endurance time was 9 
minutes for a single layer 1/2 inch square edge plywood 
with blocked joints, and 10 minutes for a single layer of 
5/8 inch plywood with tongue and groove joints. It ranged 
from 9 minutes and 30 seconds to 25 minutes and 50 seconds 
in the small scale tests covering 12 different constructions. 


2 


2.0 Preparation of Test Specimens 


2.1 Construction of Full Scale Test Specimens 

2.1.1 Specimen of Test #L-1 

The floor was built into the 10 x 13 1/2 feet framed opening 
of the NBS Floor Test Furnace using nominal 2 x 10 inch 
Douglas Fir joists. The joists were air dried construction 
grade Douglas Fir. At the time of the test neither kiln 
dried lumber nor stress graded lumber was available in this 
area. The joists were spaced at intervals of 16 inches with 
a span of 13 1/2 feet. According to the FHA Minimum Property 
Standards (4) the maximum allowable span for 2x8 joists, 
on 16 in. centers, is 13 ft. Since the opening of the NBS 
Furnace is 13 ft. 6 in., the larger joist, nominal 2 x 10 , 
was used in test #L-1, In test #L-2 the more typical 
2x8 joist was used. The 2 x 10 inch solid bridging of the 
joists was spaced 5 feet apart and was staggered for direct 
nailing . 

The floor specimen, consisted of a layer of 1/2 inch thick 
grade A-C plywood subfloor and 1/2 inch, grade C-D plywood 
underlayment . The use of A-C plywood, compared to a lower 
grade, for the subfloor probably had no effect on the fire 
endurance. The subfloor was nailed with 8d coated nails 
spaced 10” apart, starting with a full sheet in the NW 
corner. The underlayment was nailed with 6d coated nails. 
Though this is not strictly in accordance with section 
817-4.3 of the FHA Minimum Property Standard (4), it is 
commonly used in house construction. Tliese Avere spaced 12” 
apart starting Avith a full sheet in the SE corner to pro- 
vide a pattern of staggered joints betAveen layers. Gypsum 
board protection was provided along the edges. 


3 


One half of the specimen was covered with nylon 501 carpet 
(weight 66.7 oz/yd^) over a hair pad underlayment , (weight 
33.5 oz/yd^) , while the other had no finish floor, as shown 
in Figure 1. Figure 2 shows the underside of the floor, 
including joists and solid bridging, furnace thermocouples, 
observation windows, and gas burners. Figure 3 is a gen- 
eral sketch of the large floor test furnace. 

To avoid overloading the joists, the lumber was assumed to be 
Rocky Mountain Region Douglas Fir. This has an allowable 
stress level of 1050 psi in bending according to Table III 
page 250 of the FHA Minimum Property Standards (4 ) . A load 
of 63.7 lbs/ ft ^ , calculated to produce a working s tress of 
1050 psi in bending at the extreme fibers of the j ois ts , was 
applied to the floor through four hydraulic j acks . 

2.1.2 Specimen Test #L-2 

The size of the floor and the layout of the j ois ts was the 
same as in test #L- 1 except that nominal 2x8 j ois ts were 
used instead of 2 x 10 ’s and s teel-X automatic steel bridg- 
ing was used along the longitudinal centerline ins tead of 
solid bridging. 

In this test , two types of s ingle- floor construction were 
tested. The floor was equally divided into two parts along 
the east-west center line . One consisted of a layer of 
1/2 inch thick plywood with a square edge j oint (interior 
grade , with exterior glue . In accordance with general 
practice , and with FHA Minimum Property Standards (4) 
requirements , the plywood was placed leaving a 1/16 " j oint 
spacing . The j oint was protected by nominal 2x3 inch 
blocking. The other area consisted of a layer of 5/8 inch 
thick plywood tongue and groove all 4 edges (underlayment 


4 


grade, sand finished, with exterior glue). Figure 4 shows 
a schematic picture of the floor. The floor was nailed 
with 8d common nails spaced 10” apart. 

In this test to study the effect of a more representative 
live load, the applied load was reduced to a nominal 20 psf 
(21 lbs per square foot actual) . This load, which was 
applied to the floor by the method used in test #L-1, repre- 
sented approximately 40 percent of the working stress of 
the joists (see Appendix I). 

The typical moisture contents of each material was measured, 
based on weight loss at 105°C; 10% for 5/8” thick tongue 
and groove plywood, 6% for 1/2” ’’Underlayment” plywood, 12% 
for 2 X 8” joist. 

2.2 Ins trumentation- 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 chromel -alumel (type K) thermocouples 
(.020 inch diameter wires) were placed on the top unexposed 
surface of the floor in such a way as to avoid contact witli 
the loading apparatus. These were placed under 0.4 in. thick 
standard asbestos pads. The distribution of the thermocouples 
is seen in figure 1. In addition, there were five thermo- 
couples located under the carpet at the quarter points and 
at the center. 

The temperatures of all the thermocouples were printed 
out at 2 minute intervals on a Data Logger. Tlie print out 


5 


was converted to punched cards for graphing by a Calcomp 
Plotter . 

Smoke meters with a 16 inch optical path were placed on 
the carpet 56 inches from the west end and 29 inches from 
the east-west center line in the carpeted area and at 
the diagonal opposite side over the bare area to measure 
the density of smoke accumulating above the two floor 
sections. The smoke meter consisted of a sheet metal canopy 
to collect the smoke and was 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 longitudinal center line. 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 cor- 
responding point on the floor during the test. 

2.2.2 Test #L-2 

The instrumentation was essentially the same as in the 
test #L-1, indicated in section 2.2.1, however no smoke 
measurements were made. The locations of the thermo- 
couples is shown in Figure 5. 


6 


2.3 Construction and Instrumentation- Small Scale 
Test Specimens 

Twelve small scale specimens 2 ' x 2* nominal (25" x 25" 
actual) were construction on 2 x 10" joists spaced on 16 
inch centers, similar to test #L-1. Joists and end block- 
ing are shown in Figure 6. The constructions and loadings 
are summarized in Table 4, The instrumentations consisted 
of 1 thermocouple at the center at middepth, 2 thermocouples 
on the wood surface and, whenever the specimen was covered 
with a rug, there were 2 thermocouples on the rug. When 
the joint was protected with a nominal 2 x 4 or 2 x 3 
blocking (as shown in Fig. 7) the thermocouple which was 
at the center was moved down on top of the blocking. 


7 


3.0 Test Procedure 


3.1 Full Scale Tests 

The load was applied eight minutes before the test started. 
The load, which is distributed through 36 steel channels, 

5 by 24 in, , approximates a uniform load. Details of allow- 
able live load calulation based on full design stress are 
given in Appendix I . 

The average temperature inside the furnace was measured by 
twelve protected thermocouples and was made to follow the 
standard A.S.T.M. E119-69 temperature- time curve by auto- 
matic control of the gas flow to the burners; which is shown 
in Figure 9. 

The fire endurance of a construction followed by criteria 
of failure designated by the A.S.T.M. £119^69: 

(a) The construction shall have sus tained the applied 
load during the fire endurance test without pas- 
sage of flame or gases hot enough to ignite cotton 
waste, for a period equal to that for which class- 
ification is desired. 

(b) Transmission of heat through the construction 
during the fire endurance that 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. 

All the following tests shall be regarded as successful if 
the above conditions are met. 


8 


3.2 Small Scale Test 


No load was applied to the floor in Test #S-1. But a load 
of 40 lbs. was applied to the floor at two locations by 
setting the weights on the floor 4” apart from the center 
along the longitudinal center line. 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 E119-69 temperature -time curve by automatic 
control of the gas flow to the burners. 


9 


4.0 Test Results 


Please refer to Appendix II for the log of tests. 

4.1 Full Scale Test 

4.1.1 Test #L-1 

4. 1.1.1 General Observations 

Flame pentration at the joint between the two sheets of 
plywood in the upper layer of the bare floor near the 
center was observed at 13min:30sec. The location where 
flaming occurred and the associated charred region is 
shown in Figure 10 . There was also a load failure , as 
evidence by the inability to maintain hydraulic pressure 
at llmin ; 38sec . 

The average temperature of the bare surface thermocouples 
was less than 75 °C when the test was terminated after 15 
minutes . On the carpet only one of the thermocouples 
exceeded 50 °C , with a reading of 80 °C . This thermocouple 
mi gh t have had a nail head directly underneath . The 
average temperatures of the bare floor and carpet are shown 
along with the average temperature beneath the carpet in 
Figure 11 . 

The smoke meter on the bare floor showed a sudden increas e 
in smoke at about 9 minutes , which was more than 4 minutes 
before ’’flame through” was noticed . The smoke level indi - 
cated by the meter over the carpet was appreciab ly lower . 
The transmission of the smoke meters is given in t ab 1 e 1 
Appendix II and Figure 12. 


10 


The deflection increased steadily as shown in Figure 13. Tlic 
deflection at the center of the floor was 6.5 inches at 11:38 
when the load could not be maintained. The deflections are 
tabulated in table 2 Appendix II. 

There were a few small scorch marks on the hair pad due 
to heat conduction through the nails. At some locations 
this continued into the burlap backing of the nylon 
carpet leaving scorch spots up to 1 inch in diameter. 

4.1.2 Test #L-2 

4. 1.2.1 General Observations 

Flames penetrated the 1/2’' plywood floor near the quarter 
point along the longitudinal center line between the blocked 
joints at llmin:00sec. About 50 seconds later flames 
were noticed along the tongue and groove joint near the 
center on the south west side. 

Figure 14 illustrates average temperature rises on the 
unexposed surface. The temperature failure was 9 minutes 
for the 1/2" plywood floor and 10 minutes for the 5/8" 
plywood floor. 

Figure 15 is the temperature history of tlie 6 specially 
arranged thermocouples. The slow rise in temperature of 
thermocouple C illustrates the effectiveness of the blocking 
in protecting the joint. 

The deflections are tabulated in table 3 Appentlix II and 
shown grapiiically in Figure 16. 


4.2 Small Scale Tests 


4.2.1 Test #S-1 

4. 2. 1.1 General Observations 

Some difficulties with the furnace control occured at the 
beginning of this test and so the furnace temperature- time 
curve was below the standard temperature- time curve (see 
Fig. 17). The corrected time of flame through, according 
to the correction formula stated in ASTM E119-69, was 
18min:10sec. This compares quite well with the 17min:21sec 
of test #S-2 which was a duplicate of #S- 1 excepting that 
a light load of 10 psf was applied to #S- 2 . 

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 bending 
and opening of the j oints . 

4.2.2 Test #S-2 

4 . 2 . 2 . 1 General Observations 

The rate of ’’burn through” was only one minute less than in 
Test #S - 1 . Since no bending was observed either upward or 
downward throughout the test, it is clear that this weight 
(10 psf) was not enough to produce downward bending . The 
difference of 1 minute between test #S- 1 and #S-2 is probab ly 
not significant . 


12 


4.2.3 Test ffS-7> 


• 4. 2. 3.1 General Ol^servat i ons 

The time to reach "Flame Through" was considerably decreased. 
As indicated in "Observation During Test" of test #S-2 it took 
about 4 minutes to produce a definite "flame through" after 
tlie subfloor burned out; but in tliis test it took only one- 
half a minute. 

The applied load did not appear to influence the behavior of 
the specimen unduly. This load, however, was used as a stan- 
dard procedure for the remaining small tests. 

The locations and shapes of "flame through" were rather 
localized along the joint, compared to previous tests, as 
shown in Figure 18. 

4.2.4 Test #S-4 

4. 2. 4.1 General Observations 

The "flame through" region covered a large portion of the 
floor and originated in the same area as in test #S-5. Tlie 
"flame through" in the test #S-3 was primarily througli tlie 
artificially open joint. In test #S- 4, the- fire burned a 
large hole all at once. The surface charred over a large 
area during the last 3 minutes 50 seconds of test and then 
the surface ignition suddenly took place over tlie char region. 
This was taken as the "flame through" time. 


13 


4.2.5 Test #S - 5 


4 . 2 . 5 . 1 General Observations 

’'Flame through” was also originated at tongue and groove 
joint (see Fig. 19). 

4.2.6 Test #S-6 

4. 2. 6.1 General Observations 

"Flame through” region was situated at the quarter points , 
i . e . , directly through the plywood and carpeting . 

The 2 X 4” blocking, besides protecting the joint thermal ly 
also acted like a stiffening beam and changed the pattern 
of the deflection from that in test #S-4 . Figures 20, 21 
and 22 show the pattern of deflection at 17.5 minutes and 
"flame through” ' at the north (left) ^ side , and the flaming 
regions , 


4.2.7 Test #S-7 

4. 2. 7.1 General Observations 

The "flame through” occurred in the s ame location as in 

Test #S-6 . 3- ■. c: 3 . 

: .i - ' 

- j ■'< f> ! i i . ^ ' 

4.2.8 Test #S-8 = • . . . 

4 . 2 . 8 . 1 General Observations 

The charring and "flame through” occurred in a s ame manner 
and location as in test #S-4 . 


14 


4.2.9 Test #S-9 


4. 2. 9.1 General Observations 

The '-flaiiie through’' occurred on the tongue and groove joint 
near the center. 

4.2.10 Test #S-10 

4.2.10.1 General Observations 

The ’‘flame through” and associated char region was located 
near the north-south quarter areas and not at the protected 
joint as in Test #S-7. 

4.2.11 Test #S-11 

4.2.11.1 General Observations 

The ’’flame through” region covered a large portion of the 
floor near the center and originated in the same area as in 
test #S-9 . 


4.2.12 Test #S-12 

4.2.12.1 General Observations 

The charring and ’’flame through” occurred in a same manner 
and location as in test #S-5. 


15 


4.2.13 Test Results on Small Scale Tests 


Figure 23 and 24 shows the temperature changes at half depth 
for the small scale tests. In Figure 24 the slope of curve 
7-1 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. 


16 


5.0 Summary of Results 


5.1 Comparison of the results from the full scale and 
from small scale tests. 

Experiments were carried out to measure the time of ’’flame 
through” of the different floor constructions subjected to 
the conditions of the standard fire endurance test. 

Structural failure of unprotected wood floors generally 
occures at approximately the same time as failure by exces- 
sive temperature rise or ’’flame through.” In test #L-1, 
the load to produce the design stress (63.7 psf live) on 
the nominal 2 by 10 joists, produced load failure at 11:38 
and ’’flame through” at 13:30. It was not possible to con- 
tinue the test to excessive temperature failure. To obtain 
a better measurement of temperature transmission failure, 
and to simulate a more representative live floor load, it 
was decided to use 20 psf for test #L-2. Temperature failure 
occurred between 9 and 10 minutes, ’’flame through” occurred 
between 11 and 12 minutes, and load failure occurred at 
13 minutes. No direct comparison is possible with the small 
scale tests since the joists were not loaded. 

It is believed, that, as the supporting joists in the full 
scale test are gradually destroyed by charring, cracks form 
at the extreme highly stressed fibers on the bottom surface. 
This increases the deflection and accelerates the rate of 
flame penetration through increased joint separations. There 
are differences in pressures in the large and small-scale 
furnaces which may also have an effect on the results . 


17 


As previously mentioned in test #S-3, the 1/8” fixed gap on 
the underlayment joint reduced the time of ’’flame through’' by 
4.5 minutes. For both the large scale and small scale tests 
the temperature rise on the unexposed surface was nearly the 
same. It may be that the artificial gap on small scale test 
#S-3 corresponded to the cracks made on the exposed surface 
due to the load in the full scale test #L-1. 


Furthermore, the time of ’’flame through” of the small scale 
test on the 5/8” plywood with tongue and groove joint or the 
1/2” plywood with square edge joint protected with 2” x 3” 
blocking are in agreement with those of the full scale test. 


Considering the criterion of temperature failure, it is inter- 
esting that the temperature failures were seen a few minutes 
earlier than the ’’flame through” failures in most cases. 

Table 4 includes different types of failure on various con- 
structions, loading conditions and total thermal resistance. 


Thermal resistance is calculated from a thickness and 
coefficient of thermal conductivity as follows : 


Thermal Resistance 


Thickness 

C o e f f i c 1 e n t o f t h e r m a 1^ C o n du c t i v i t y 


The thermal properties which form the basis for the computed 
thermal resistances (See Table 5) were obtained from a stand- 
ard reference source [2]. 

5.2 Effect of Carpeting 


It was obvious that the carpeting delayed the time of ’’flame 
through” by 8 to 12 minutes. Since the carpet itself did 


18 


not add any strength to the floor, there was not much 
difference in the deflections between the floor sections 
with or without carpet. 

5.3 Estimation of the time of "flame through." 

Figure 28 illustrates the influence of the thermal conduc- 
tivity of various materials on the time of "flame through" 
under free convection conditions and at room temperature. 

It is apparent that construction #4 (1/2" + 1/2" + 1/8" 
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 seen in figure 28, that 
emperically there is a linear relation between the thermal 
resistance and the "flame through" time. The slope is 
K = 0,133 (BTU/°F) . 

For instance, a 1/8" vinyl asbestos tile will add a thermal 
resistance (R) of 0.05 (HR °F/BTU) to the floor. The addi- 
tional 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" plywood with 2 x 3" blocking. Thus, the total time 
required for "flame through" on the floor construction of 
1/2" plywood with 2 x 3" blocking, finished with 1/8" vinyl 
asbestos tile can be estimated as 11.4 minutes. 

5.4 Estimation of "Load Failure" by Excessive 
Deflection 

There are no deflection requirements on ASTM E-119 to indicate 
"load failure." 


19 


Rased on a survey of laboratory fire endurance tests on reprt' 
sentative constructions, the requirement was proposetl tliat both 
a maximum Reflection D > aitd a maximum hourly deflection 

rate R > ^ 50 ^ be exceeded as an indication of load failure 
[3]. Taking L = 12’ lO'' as the span between supports and 
d = 9 5/8 in (0.80 ft) as the distance between the upper and 
lower extreme fibers of the critical fire exposed member 
(joist), load failure may be considered to have occurred at 
10:05 min in test #L-1, and with d = 7 5/8 in (0.64 ft), 
load failure may be considered to have occurred at 5:56 min. 
in test #L-2. 


20 


() . 0 Conclusions 


linrc wood floor constructions con form i n^.’. t(^ the I'llA Mininmn 
Property Standards (4) arc marginally able to meet a f i rt' 
endurance time requirement of 10 minutes. I’his includes 
single-floor plywood constructions 1/2 in. and 5/8 in. tliick. 
Strip flooring (25/32*’ softwood and 13/16” hardwood) directly 
over joists have a fire endurance time in the range of 10 to 
13 minutes. 

The addition of a separate finish floor sliould 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” 1/2” 

+ 1/8” gap + carpet) construction, which has total thermal 
resistance of 2.40 (HR °F/BTU) , is almost 4 times that for 
the (1/2” +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. 
This would be modified by the effects of the applied load 
or the gap size. 


21 


7.0 


REFERENCES 


1 . St andard Methods of Fire Tests of Building Cons true t iqii 
and Materi als , American Society for Testing and Materials 
Designation E 119-69. 

2. ’'Handbook of Fundamentals, Heating, Refrigerating, 
Ventilating and Air Conditioning” Published by ASHRAE , 
1967. 

3. J . V. Ryan and A. F . Robertson , "Proposed Cri teri a foi' 
Defining Load Failure of Beans, Floors, and Roof (T')n 

s tructions During Fire Test," Journal of R ese a rch of t i i o 
National Bureau of Sta nd ar ds^ - C . En gi n e (^i n g a n d 
Instrumentatio n , Vol. 63C, No, 2, Octolun'- f)oco]iibe r 19 SO. 

4 . "Minimum Property Standards For One 
FHA No. 300, U.S. Department of HUD, 


and Two L i v i ng_ ILOi t s 
F i 1 A , Ro V . J a n 1 1 .■ i r v 1 9 7 


22 


APPENDIX I 


LIVE LOAD CALCULATION 

Allowable design stress for Douglar fir construction grade 
joist with 2 X 10'' and 2 x 8” in cross-section on full scale 
test . 


According to the stress equations 


f = M 

iTc 


( 1 ) 


and 


M = 


WL' 


( 2 ) 


Allowable bending stress 


f|^ = 10 5 0 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) 


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


23 


1-roni liquation (2) 


^2 X 10 (Ib/ft) 

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) . 

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

Live load = Total allowable load - Dead load. 


Dead load = carpet 

1.0 

psf 

plywood (1’’ thick) 

3.0 

psf 

+ joist (2 X 10” cross-section) 

2.8 

psf 

total dead load 

6.8 

psf 


therefore , 

Live load/2 x 10 = 70.5 - 6.8 = 65. 7 (psf) 
Same manner 

'^^2 X 8 ^ 

Dead load = plywood (5/8 inch thick) 

= 1.87 psf 

therefore ^ 

Live load/2 x 8 = 52 - 1.87 = 50.1 (psf) 


24 


NOMENCLATURE 


M = Bending Moment 

f, = Bending Stress 

J/(’ = Section Modulus 

w = Load 

c = Half depth of joist 
Subscript 2 x 10 = 2 x 10 inch joist 
Subscript 2x8 =2x8 inch joist 


25 


APPENDIX II 


TEST #L-1 

LOG OF TESTS 


Observation During Test 


min : sec . 


1:00 

Joist ignited, crackling sounds, smoke escaping 
between joists and plywood deck around the edge 
o£ the floor. 

2:00 

Fire-exposed plywood surfaces all scorched. 

5:00 

Inside of furnace filled with smoke and flame. 
IVhole underside on fire. 

4 :00 

West side of fire-exposed plywood burned more 
than east side. 

5:00 

Smoke increasing through the cracks at the peri- 
meter, 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 


26 


Table 1 




TEST #L-1 

SMOKE DEVELOPMENT 





T ime 

Over plywood 

Over 

carpet 

min 

: sec , 

T(%)0. 

D.* 

T(% 

)O.D 

. * 


0 

:00 

100 

0 

100 


0 


1 

:00 

99.5 

0 

100 


0 


2 

:00 

99.5 

0 

99 


0 


3 

:00 

96 

0.01 

96. 

5 

0 . 

01 

4 

:00 

97.5 

0.01 

97. 

5 

0 . 

0.1 

5 

:00 

97 

0.01 

95. 

5 

0 . 

01 

6 

:00 

97,5 

0.01 

97. 

5 

0 . 

01 

7 

:00 

93.5 

0.037 

91. 

5 

0 . 

04 

8 

:00 

88 

0.053 

89 


0 . 

053 

9 

:00 

78 

0.1 

86. 

5 

0 . 

06 

10 

:00 

11.2 

0.93 

80 . 

5 

0 . 

09 

11 

;00 

4.5 

1.35 

78 


0 . 

1 

12 

:00 

12.4 

0.9 

72 


0 . 

"> 

12 

:30 

Readings discontinued 






*Over 16 in. optical path. 


27 


T ab 1 e 2 


TliST #L-1 Dl-FLECTION MEASUREMENTS 


Measurements of deflections were made at three 
points on the longitudinal center line: nt 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 
min : sec . 

.18 

.20 

.20 

1:00 

.20 

.20 

.20 

2:30 

.45 

.50 

.20 

5:00 

.6 

.75 

. 6 

6:00 

. 6 

.95 

.7 

7:00 

.9 

1.25 

.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 

'*7 

0 . ^ 


Load off (unable to maintain pressure) 


28 


TEST #L-2 

Observation During Test 


T ime 
min : sec . 


0:40 

Joist started flaming on the south side. 

1:00 

Joist started flaming on the north side. 

1:30 

Smoke on unexposed surface. 

3:00 

Large sheet of flames formed on under side 
of floor. 

4:00 

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

11:00 

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

11 :50 

"Flame through" on 5/8" plywood floor. 

13:00 

Load failure (floor broke through) . 


29 


Table 3 


T ime 
min : sec . 

0:00 

1:00 

2:00 

3:00 

4:00 

5:05 

7:00 

10:00 

12:00 

13:00 


TEST #L-2 DEFLECTION MEASUREMENTS 


N C 

0 1 

0 1.25 

0 1.5 

0 2 

1 2.5 

2.5 5 

4 8 

4 14 

7 18 

Wire broke 19 


S 

0.5 

1.0 

1.25 

1.5 

2 


3.5 


5 


9 


12 


30 


T]-:ST fts- \ 

Observations Huring 'best 


T line 
mill : sec . 


6:45 

Joists and exposed plywood surface ignited. 

10 : 20 

Tendency of center part of joint to bend upward 
due to thermal stress. Smoke coming out through 
j oint . 

18:00 

Fire inside furnace seen through the opening of 
joint . 

19:30 

Small fire coming through the joint. 

20:00 

Noticable difference in height between plywood 
sections at center of joint. 

21:43 

’’Flame through." 

(18:10) 

(Corrected time for flame through, see General 
Observations of test #S-1) . 


31 


TliST ^S-2 


Observations During Test 


T ime 

min : sec . 


1:00 

Inside the furnace was filled with flame and smoke 

1:20 

Joists started flaming. 

13:30 

Fire inside the furnace seen through the opening 
of the joint. (Subfloor burned through). 

14:00 

Along the edge of the joint, dehydration phe- 
nomena and black char appeared. 

17:21 
TEST #S-3 

’’Flame Through." 


Observations During Test 


T ime 
min : sec . 


1:10 

Joists started to burn. 

5:30 

Smoke from joint. 

12:15 

The furnace fire appeared through the gap. 
(Subfloor burned through) . 

12 :45 

"Flame Through." 


32 


T]- ST tfS-4 

Observations During Test 


T ime 
min : sec . 


1 :00 

Joist on fire 

7:00 

Gray smoke filtering through the carpet, and 
the center part of the unexposed surface was 
covered with moisture. 

14:00 

Fire reached under layment . (thermocouple indication) 

21:00 

Deflection due to the load was observed near center. 

22:00 

Black char on the carpet started to be formed. 

25:00 

Load was relaxed. (Could not sustain the weights). 

25 : 50 

'Tlame through.” 


TE ST #S-5 

Observations During Test 


T ime 
min : sec . 


1:00 

Joist started to burn. 

6:00 

Exposed surface under thick flame. 

9:00 

Smoke was noticed around T and G joint near 
the north end. At the same time its color 


became charcoal black, and sagging and open- 
ing at this joint was observed. 


33 


9:30 


The fire inside furnace was seen through the 
opening . 


10 ; 30 

Flame through” at the joints. The locations 
of ’’flame through” and openings at joints are 
seen in Figure 19. 


TEST_ #S-6 

Observations During Test 


Time 

min : sec . 


1:00 

Joist started to burn. 

8:00 

Gray smoke filtering through the carpet and 
moisture noted on the unexposed surface. 

14:50 

Black char on the carpet surface . An appre- 
ciable deflection was observed midway between 
dead center and north and south end , 

18:15 

’’Flame through . ” 


TjBST # S - 7 

Observations During Test 


T ime 

min : sec . 


1:06 

Ignition of j oist . 

7:00 

Smoke started to appear on unexposed surface . 

8:00 

The top surface became dark near north end . 

9 :25 

’’Flame through . ” 


34 


TliST #S -8 

Observations During Test 


T ime 

min : sec . 


1:05 

Joist ignited. 

6:15 

Appearance of gray smoke through the carpet 
at the middle of the joint. 

17:00 

Deflection occurring at center. 

19:10 

Formation of the char region near center of 


the carpet surface. 

20 : 20 

Deflection was severe. 

24:00 
TEST #S-9 

"Flame through" near center. 


Observations During Test 


T ime 
min : sec . 


1:00 

Ignition of joist. 

4:00 

Smoke was seen above tongue and groove joint. 

6:00 

Formation of dark char on the edge of the joint 


near center. 

9:40 

Flames were seen through the opening made on 
the joint. 

11 : 35 

"Flame through." 


35 


TEST A^"A^_ 

Observations During Test 


Time 
m i n : s e c , 


1:00 

Joist started to burn. 

7:40 

Char forming on the unexposed surface near 
north quarter area. 

10:25 

Fire inside furnace was seen throug the opening 
made where the char was formed. 

11:00 

’Tlame through.” 

TEST #S- 

■11 


Observations During Test 


Time 
min: sec . 


1:03 

Joist started to burn. 

7:00 

Gray smoke and moisture was observed on the 
unexposed surface near the center . 

15:00 

Black char forming . Deflection was noted . 

18:00 

Deflection severe . The charred region about 
three inches in diameter . 

19:20 

"Flame through . " 


36 


TEST #S-12 


Observations During Test 


Time 

min : sec , 


1:00 

Joist on fire. 

3:00 

Dehydration phenomena was clear on the edge of 
the wood. 

4:00 

Droplets of moisture were formed on top of the 
unexposed surface. 

10:30 

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

11:00 

The sagging resulted in a small opening. 

12:00 

Fire inside furnace was seen through the opening. 

13:21 

"Flame through" when the broken tongue existed. 

14:10 

"Flame through" at a normal joint. 


37 


FIRE ENDURANCE TIMES FOR VARIOUS FLOOR CONSTRUCTIONS 


H 





o 



00 

rr\ 


* Unable to maintain load application due to excessive rate of deflection 


T^iyj-__5 

THERMAL RESISTANCE OF VARIOUS FLOOR MATliRlALS 


MATERIAL 

DENSITY 

LB/FT^ 

CONDUCTIVITY 
BTU/MR FT °F 
K 

CONDUCTANCE THICKNESS 
BTU/HR °F INCH 

c L 

THERMAL 
RF.S I STANCE 
HR °F/BTU 
R 

OAK 

51,5 

1.2 

15/K) 

0 . b 5 

PINE 

34 

0.8 

25/32 

0.98 

PLYWOOD 


.80 

1/2 

0.02 

CARPET plus 
hair pad 



.8 

1.2 

VINYL 

asbestos tile 



20.0 1/8 

0.05 



R = L = 
K 

1/c 



39 



NYLON 501 CARPET 


UJ 




Fig, 1, Locations of Thermocouples and Smoke-Meters 



Fig. 2. Underside of the Floor Construction 



i 

I 


FIGURE 3. Section of the large floor-test furnace at NBS . 



METAL BRIDGING 


aOOMAld „3/l 


1 

J 


C9 

z 

o 

o 

J 

tn 


i 


aOOMAld .,8/Q 


o 

LJ 

o 

< 

£L 

COK 


3 

O 

u 



CM 

I 

hJ 


4J 

W 

cu 

H 


c 

c\3 

E 

U 

0) 

CL 

V'j 

J-l 

o 

o 

u, 


w 

;:3 

o 

M 

CLi 


TONGUE a GROOVE 



FIGURE 



FIGURE 6o Framing for Small Scale Specimen 



Figure 7 Location of Weights 
Test #S“3 



000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 


flVEKRGE FURNRCE TEMPERRTURE FOR TEST 475 C0I1PFIREO WITH STRNDRRO E119 


HI 



0 fiVERRGE FURNACE TEMPERATURE 
- standard El 19 


time (MINUTES) 


12 


14 15 


FIGURE 8 o 



Figure 9 Underside of Specimen in 
Test #S-6 




FIGURE 10, Char Region on Unexposed Surface after Test #L- 


60 

50 

40 

30 

20 

10 


fiVERRGE SURFftCE TEMPERRTURE RISES FOR PLYWOOD El O0R TEST 475 


4- UNDER THE CARPET 
® ON THE BARE FLOOR 
A ON THE CARPET 




X fe t 




r'j-- 1 

9 10 11 12 13 14 15 

TinE (niNUTES) 


FIGURE 11 


SMOKE DENSITY (OPTICAL DENSITY/FT) 



FIGURE 12, Smoke Density, Test #L-1 



FIGURE 13. Deflection Measurements Test #L-1 


TEMPERATURE (DEG C) 



FIGURE 14 


700 

650 

600 

550 

500 

450 

400 

350 

300 

250 

200 

150 

100 

50 


SPECIRL TEMPERRTURE RISES E0R TEST 477 


Symbols Symbols 
on graph in Figure 5 


X A 

5 B 


® C 


HUD PLYW00D EL00R 


t 


D 

E 



^ 5 ^ ^ ^ 5 To Vz 

TIME (MINUTES) 


i F 

* See Figure 9 for locations 



15 . 


DEFLECTION (IN) 



FIGURE 16, Deflection Measurements, Test #L-2 


000 . 

900. 

800. 

700. 

600 

500 

400 

300 

200 

100 

0 


RVERRGE FURNRCE TEMPERRTURES F0R TEST 1 C0MPRREO WITH STRNORRO E119 



0 PVERRGE FURNRCE TEMPERRTURE 
- STRNORRO El 19 


^ ^ 1~0 1*2 VI 16 Vs ^0 Vz ^ 

TINE (MINUTES) 


4 26 


FIGURE 17 



Fig, 18, Flame Through and Associated 
Char Region Test #S-3 



Fig, 19, Locations of Flame Through 
Openings at Joint (after 
removing load) Test #S-5 


WLl 




Fig, 21, Flame Through, Test ii^S-6 



Fig. 22 


Flaming Region Before 
Extinguishment, Text #S-6 


000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 


© 

< 

L 

I 


TEMPERfiTURE RISES RT HALF DEPTH FDR 2X2 TESTS 1-6 
1-1 

|~|First number indicates test number 

4- lSecond number indicates location of thermocoimle 

5- 1 (1: at the center at 1/2 depth) 



Fig« 23 


000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 


TErtPERRTURE RISES RT HRLF DEPTH F0R 2X2 TESTS 7-12 
^ 7-1 

^ Q J First number indicates test number 

a y— 1 

L 11-1 Second number indicates location or thermocouple 


’ 12-1 (1: at the center at 1/2 depth) 

/ 



TIMEtMINUTES) 


24 


1000 

900 

800 

700 

600 

500 

400 

300 

200 

Ic'j 

100 

0 


TEMPERfiTURE RISES 0N THE BRRE FL00R F0R TESTS 1-6 
A 1-2 
< 2-2 
^ 3-2 

L 5-2 
I 6-2 


First number indicates test number 


Second number indicates location of thormocoiin 1 o 
(2: on bare surface under carpet) 



o 25. 


1000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 


\ 




A 

s 

L 

1 


TEHPERRTURE RISES 0N THE BARE FL00R FOR TESTS 7-12 

7 - 2 

8 - 2 
9-2 

10-2 

11-2 


- 12-2 


First number indicates test number 

Second number indicates location of thermocouple 
(2: on bare surface under carpet) 


7 



10 12 14 16 18 20 

TIME! niNUTES) 


i;” 


26 


ig. 26 


000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 


-I- 

L 


TEMPERRTURE RISES 0N THE CARPET F0R THE 2X2 TESTS 
4-3 
6-3 
8-3 
1 1-3 


First number indicates test number 

Second number indicates location of thermocouple 
(3: on carpet) 


3 



Fig. 27. 


TIME TO FLAMETHROUGH (MIN) 


1 



0.5 I 1.5 2 2.5 

THERMAL RESISTANCE (HR®F/BTU) 


Fig 28 Thermal RESISTANCE of Floor Construction Vs F 1 ame L hrougl' 
T ime