NBSIR 73-166

Fire Endurance Test of an

Interdweiling Double Wall Construction

of Paper Honeycomb and Gypsum

Board

B. C. Son

Center for Building Technology

Institute for Applied Teclinology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington. D. C. 20410

NBSIR 73-166

FIRE ENDURANCE TEST OF AN

INTERDWELLING DOUBLE WALL CONSTRUCTION

OF PAPER HONEYCOMB AND GYPSUM

BOARD

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Final Report

Prepared for Office of Research and Technology

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 Test of an Interdwelling Double Wall

Construction of Paper Honeycomb and Gypsum Board

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

ABSTRACT

As a part of the evaluation of a housing system proposed under

Operation BREAKTHROUGH, a fire endurance test was performed at the

National Bureau of Standards on a double wall assembly intended as an

interdwelling separation for single family attached housing. Each wall

of the assembly contained a core of paper honeycomb surfaced on both

sides with glass fabric impregnated with polyester resin, and protective

layers of gypsum board.

The test method was generally in accordance with the requirements

of ASTM E 119, Fire Tests of Building Construction and Materials. The

applied live load was 636 plf on each panel and the results of this test

are valid only for walls of similar construction loaded at or below the

stress levels developed by this loading.

The fire endurance of the first (fire-exposed) wall panel was

65 min:30 sec, based on flame penetration through cracks and openings

formed on the back face of the first wall. The overall fire resistance

i
of the double wall assembly was 79 minutes when pieces of the structural

glass fabric of the front face of the second wall were observed falling

into the furnace.

Key Words: Fire endurance; fire test; flame penetration; glass reinforce

plastic; housing systems; interdwelling wall; modular

construction; Operation BREAKTHROUGH; paper honeycomb;

structural panel

ii
TABLE OF CONTENTS

Page

ABSTRACT i

1 . 0 INTRODUCTION 1

2.0 CONSTRUCTION . 1

3.0 TEST METHOD MD EgUIPMENT 2

4.0 TEST EVALUATION 4

5.0 TEST RESULTS 4

6.0 DISCUSSION • 5

TABLE I 7 APPENDIX I SI Conversion Units 9

iii
-
1.0 INTRODUCTION

A standard fire endurance test was conducted at the National Bureau

of Standards to measure the fire performance of a double wall for use as

a loadbearing interdwelling separation for single family attached housing.

The work was sponsored by the Department of Housing and Urban Development

under its Operation BREAKTHROUGH program. The test method was generally

in accordance with the requirements of ASTM E 119^^, Standard Method of

Fire Tests of Building Construction and Materials.

The double wall, which is required to be a fire barrier between two

adjacent modules, was constructed of two identical parallel walls separated

by a 2-3/4 in. air space. Each wall panel consisted of a paper honeycomb

core surfaced on both sides with glass fabric impregnated with polyester

resin, and one sheet of adhesively bonded gypsum board. The test was

conducted to determine the fire endurance characteristics of this innovative construction, especially the behavior of the paper core and the

possible burning or loosening of the adhesive.

2.0 CONSTRUCTION

The double wall assembly, as shown in Figure 1, consisted of two

identical, 16 ft. wide x 8 ft. high panels. These were placed parallel

to each other and separated by a 2-3/4 in. air space. The honeycomb

core was flame retardant treated paper 3 in. thick. The core was placed

between skins of glass fiber-reinforced polyester (GRP) sheets composed

of 5 X 4 count, 20 oz. , 0.04 in. thick woven glass fiber roving impregnated

with polyester resin. The gypsum board was type X, 5/8 in. thick and was

—^ Standard Methods of Fire Tests of Building Construction and Materials , American Society &r Testing and Materials, available at 1916 Race St.,

Philadelphia, Pa. 19103.

1
adhesively bonded to each face of the structural core with a polyesterbase adhesive containing one percent asbestos fiber. The edges of each

panel were finished with 3 in. thick x 3 in. wide laminated plywood closeout pieces. The surface of each wall facing the air space was finished

with sprayed polyester resin containing chopped glass fibers (0.001

0.002 in. dia. x 1/2 in. long). All joints between the gypsum boards

were taped and filled with plaster joint compound. The joints on the

unexposed and exposed gypsum board layers were not staggered. Each

8 ft high panel weighed approximately 10 plf.

3.0 TEST METHOD AND EQUIPMENT

The wall assembly was built into the 16 ft. by 10 ft. loading frame

of the NBS wall testing furnace. Since the height of the test specimen

was less than the 10 ft high opening of the wall furnace frame, it was

necessary to close in the space between the specimen and the frame.

A filler piece (2 x 16 ft), which was placed below the specimen, was

expected to have sufficient fire endurance and rigidity during the test.

The instrumentation consisted of thermocouples, deflection measuring devices and loading equipment. A total of 33 thermocouples were used;

nine thermocouples inside each of the wall panels, six in the air space

between the two wall panels and nine on the unexposed surface. The

surface thermocouples were placed under standard 6 x 6 x 0.4 in. thick

felted asbestos pads. See Figures 1 and 2 for the locations of the

thermocouples. Figure 3 shows the unexposed surface of the specimen,

the connections of the thermocouples and the loading equipment before the

test started. The temperatures of the thermocouples were printed out at
1 minute intervals on a data logger from which they were punched onto

cards for processing and plotting by computer. Figure 4 is a schematic

drawing of the wall testing furnace with a typical specimen in place.

A stationary deflection wire was strung horizontally at the center

height of the specimen and 3-1/4 in. from the surface. The variations

of the distance from the wire to the wall surface were measured periodically during the test.

Five minutes before the test started the prescribed live load of

636 plf (plus 10 plf dead load) was applied to each panel independently

through four hydraulic jacks.

The temperature inside the furnace was measured by 12 protected

thermocouples and followed the standard ASTM E 119 temperature-time

curve by manual control of the gas flow to the burners. The furnace

temperatures are shown in Figure 5.

The pressure measurement within the furnace was made with a disk

type probe mounted perpendicular to the upward flow of gases in the furnace

and connected to a differential pressure transducer with tubing. The

probe consisted of 1/8 in. inside diameter stainless steel tubing attached

to the edge of a 1-1/8 in. diameter flat metal disk having a rounded

edge and connected to a small hole in the center of the disk. The test

was run with the furnace neutral pressure point located at the one-third

height of the specimen above the bottom of the specimen.

3
4.0 'I'l'lS'l' VALUATION

The fire endurance of a construction according to ASTM E-119 is

established by the time required to reach the first occurrence of one

of the criteria of failure, which are:

1. Inability to sustain the applied load.

2. Passage of flame or gas through the structure to the unexposed

surface hot enough to ignite cotton waste.

3. A temperature rise of 250 degrees F (139 degreesC) average,

or 325 degrees F (181 degrees C) at one point, above the

initial temperature on the unexposed surface.

It should be noted that there are no established fire endurance

criteria in ASTM E 119 for individually loaded double walls typical of

modular construction. However, it is evident that structural failure

of one wall may immediately endanger the structural capacity of the

second wall. Also, flame penetration of one wall may immediately endanger the structural capacity of the second wall, and initiate the

spread of fire to one or more adjacent modules through the common air

space.

5.0 TEST RESULTS

A complete log of test observations is given in Table I. The

average temperature rise of the unexposed surface was 48 degrees C

(118 degrees F) and the maximum temperature rise was 70 degrees C

(158 degrees F) at the test time of 1 hr. 30 min. as shown in Figure 6 .

The temperature profile across the wall assembly is shown in

Figure 7. After 2 3 min. , when delamination of the paper honeycomb core

of the exposed wall was occurring, the temperature of the thermocouples

4
placed in the C position of the exposed wall panel started to rise more

quickly than those in the A or B position. This may be because the

thermocouples in the C position were touched by the flame generated from

the burning of the paper honeycomb.

Failure of the first (fire exposed) wall occurred at 62 min. The

mode of failure was by flame-through at the cracks and openings on the

back face of the first wall. Because of variation of the furnace exposure

from that prescribed, the failure time of the first wall was corrected

to be 65 min. 30 sec, in accordance with the standard correction

formula in ASTM E 119 based on the comparison of the areas under the

actual time temperature curve and the standard curve.

Structural failure was assumed to have occurred at 76 min. with

the observed collapse of the interior face of the second (unexposed) wall.

The corrected time of the overall failure was 79 min. 15 sec.

The maximum wall deflection measured during the test was less than

1/4 in.

6.0 DISCUSSION

Although the test assembly continued to support the applied load

during the test there was indication that the load was probably carried

by the 3 in. x 3 in. laminated plywood closeout pieces at the edges of

the panel. Due to the loading arrangement used, the rigid filler piece

transmitted the load primarily to the closeout pieces which were only

slightly scorched during the test. This arrangement does not represent

the distributed load conditions that would normally be Imposed on the

supporting walls of a module. In actual construction the closeout pieces

would be spaced about 30 feet apart with most of the double wall load

5
applied between the edge pieces. Under more representative loading

conditions it is not known if the assembly could sustain the load for

as long as 79 minutes

The wall assembly constructed of a paper honeycomb sandwich with

resin-impregnated woven fiber glass and gypsum board faces was symmetrical

so that if the opposite side had been exposed to the fire it would have

probably provided the same fire endurance.
Log of

TABLE I

Test Observations

Time Observations

MinrSec

0:00 Start of test.

1:00 Paper on the fire exposed surface layer of gypsum board

started to burn at the north side and then spread over

the surface.

4:00 Completion of the burning of the paper surface.

5:30 Spackle dropping off at the joints.

17:30 Flame on the bottom of the middle joint.

18:00 Pieces of gypsum board from the_raiddle of the third board

from the north end falling into the furnace. The paper

honeycomb has ignited.

22:00 First joint from the north end flaming inside the furnace.

Figure 7 is a picture taken through the observation window,

showing flames from the paper honeycomb core and glassreinforced plastic skin coming through the opened joint.

25:00 Smoke observed at the bottom of the unexposed surface.

Strong odor of burning polyester resin.

29:00 All joints opening up on the exposed side. Considerable

flaming inside furnace over full width of the first (exposed)

wall.

31:20 Smoke from the top of the north end of the unexposed surface.

32:00 Big pieces of gypsum board on the front face of the first

wall fell into the furnace leaving a large hole.

38:00 Collapse of 2/3 of the front face of the first wall. Figure

8 shows woven glass pieces hanging down on the ASTM furnace

thermocouples and flaming from the hole in the face of the

wall

* To identify the location of an occurrence, the two ends of the assembly

are differentiated according to their orientation.

7
Time

Min: Sec

Observations

40:00 Doors and windows in test building opened. (Observers

experiencing throat and eye irritation.)

61:00 Paper honeycomb of the first wall was mostly consumed

or falling into the furnace.

62:00 Cracks and openings were observed on the backface of

(65:30''O the first wall.

67:00 Backface of the first wall started to fall down.

70:00 ; Loose pieces of gypsum board on the backface of the

first wall dropping. Observers were able to see the

newly exposed face of the second (unexposed) wall.

76:00 ' Big hole formed at the middle front face of the second

(79:15'>'«') wall. Pieces of the structural glass fabric of the

front face observed falling into the furnace.

85:00 A few cracks noticed on the unexposed surface of the

second wall

90:00 . Paper honeycomb of the second wall panel was either

consumed or delaminated.

93:40 Load Off. End of Test (Figure 9 shows the fire side

of the wall assembly right after it was removed from

the furnace .

* Corrected time to failure in accordance with the formula given in

paragraph 5(c) of ASTM E 119.

8
APPENDIX I

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 readings 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

Mas s

1 pound = 0.45 kilograms

Force

1 kip = 4448 newton

Stress

1 psf = 47.88 newton /meters

Temperature

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

9
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Figure 3 The unexposed surface of the

specimen and thermocouple connections

before the test started.
SECTION LONGITUDINAL SECTION HALF ELEVATION

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' SCALE

FIGURE 4. DETAILS OF WALL-TESTING FURNACE,

A, FURNACE chamber; B, BURNERS; C , THERMOCOUPLE PROTECTION TUBES; D, PIT FOR DEBRIS',

E, OBSERVATION WINDOWS; F, AIR INLETS; G, FLUE OUTLETS AND DAMPERS; H, FIREBRICK

FURNACE LINING! I, REINFORCED CONCRETE FURNACE SHELL, K,GAS COCKS; L, CONTROL VALVE. M, LADDERS AND PLATFORMS TO OBSERVATION WINDOWSi N, MOVABLE FIREPROOFED TEST

frame; 0, LOADING BEAM; P, HYDRAULIC JACKS, Q.TEST WALL, R, ASBESTOS FELTED PADS

COVERING THERMOCOUPLES ON UNEXPOSED SURFACE OF TEST WALL.

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Locatiofi9 (Refet fig«r^ 2)

Position A of Expbs^d wei 1 pan^l

Position B of Exposed wall panel

Position C of Exposed wall panel

Air Space

Position A of miexposerl wall panell

Position B of unexposed Xv-all pane

Position C of unexposed wall pane'

unexposed surfa<

Figure 7. TEMPERATUPvE RISE ACROSS WALL ASSEMBLY

0 iho

16
X7
II
(I

FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 2. Gov't Accession

No. NBSIR 73-166

3. Recipient's Accession No.

4. TITl F ^ND SIIRTITI F Fire Endurance Test of an Tnterdwelling Double Wall

Construction of Paper Honeycomb and Gypsum Board

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Byung Chan Son

3. Performing Organization

NBSIR 73-166

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4600442

11. Contract/Grant No. IAA-H-16-70

12. Sponsoring Organization Name and Address

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

6. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) As a part of the evaluation of a housing system proposed under Operation BREAKTHROUGH,

a fire endurance test was performed at the National Bureau of Standards on a double

wall assembly intended as an interdwelling separation for single family attached

housing. Each wall of the assembly contained a core of paper honeycomb surfaced on both sides with glass fabric impregnated with polyester resin, and protective layers

of gypsum board.

The test method was generally in accordance with the requirements of ASTM E 119, Fire

Tests of Building Construction and Materials. The applied live load was 636 plf on each panel and the results of this test are valid only for walls of similar construction loaded at or below the stress levels developed by this loading.

The fire endurance of the first (fire-exposed) wall panel was 65 min:30 sec, based

on flame penetration through cracks and openings formed on the back face of the

first wall. The overall fire resistance of the double wall assembly was 79 minutes

when pieces of the structural glass fabric of the front face of the second wall

were observed falling into the furnace.

17. KEY WORDS (Alphabetical order, separated by semicolons) Fire endurance; fire test; flame penetration;

glass reinforced plastic; housing systems; interdwelling wall; modular construction;

Operation BREAKTHROUGH; paper honeycomb; structural panel

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UNCL ASSIFIED

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22. Price

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