4fx/.eo

NATIONAL BUREAU OF STANDARDS REPORT

9056

PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period Ending December 31, 1965

by

J . V . Ryan

to

Federal Housing Administration

U.S. Department of Housing and Urban Development

Washington, D. C.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Th- National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards

Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference

Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Refer- ence Materials. Institute for Applied Technology. Building Research. Information Technology. Performance Test Development. Electronic Instrumentation. Textile and Apparel Technology Center. Technical Analysis.

Office of Weights and Measures. Office of Engineering Standards. Office of Invention and Innovation.

Office of Technical Resources. Clearinghouse for Federal Scientific and Technical Information.**

Central Radio Propagation Laboratory.* Ionospheric Telecommunications. Tropospheric Tele- communications. Space Environment Forecasting. Aeronomy.

* Located at Boulder, Colorado 80301. ** Located at 5285 Port Royal Road, Springfield, Virginia 22171.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

42100-12-4212405 February 23, 1966 9056

PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period Ending December 31, 1965

by

J. V. Ryan

Building Research Division

to

Federal Housing Administration

U.S„ Department of Housing and Urban Development

Washington, D. C.

IMPORTANT NOTICE NATIONAL BUREAU OF ST/

for use within the Government, and review. For this reason, the whole or in part, is not authori Bureau of Standards, Washingto

the Report has been specifically

Approved for public release by the

Director of the National Institute of

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

s accounting documents intended

subjected to additional evaluation

listing of this Report, either in Office of the Director, National

the Government agency for which

pies for its own use.

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
I
PERFORMANCE CHARACTERISTICS OF EXTERIOR WALLS

Progress Report for Period Ending December 31, 1965

By

J . V . Ryan

Building Research Division

1

.

INTRODUCTION

The objectives of this project are to adapt or develop test

methods and techniques for the measurement of the performance

characteristics of exterior walls, and to provide values obtained

by such tests when applied to representative walls. This project

was designed to bring under consideration all the characteristics

of exterior walls and to determine which are of importance. For

the latter, means of measurement are sought and values obtained.

These are expected to form the basis for decisions as to the levels

of performance against which to judge walls of various types.

2.

PROJECT PLAN

The plan of the project called for (1) an analysis of the

functions of exterior walls in order to develop a list of all

characteristics and the selection of those subject to physical

measurement, (2) review of existing test methods having potential

applicability, (3) testing of representative samples by these

methods, (4) development of additional test methods and apparatus

as needed, (5) measurement of the performance characteristics of

samples of representative wall systems by all the various methods,

and (6) where possible, suggest limiting values for each of the

significant wall performance characteristics subject to physical

measurement

.

3.

ACTIVITIES

The item number (1) under Project Plan was completed in an earlier period, except as review may be required in the light of

progress under the other items. Work has continued under items

(2) , (3) , and (4) and began under item (5) . This work is being

carried out in all but one of the Sections of the Building Research

Division

.

As a result of conferences among the Division staff engaged

in the project, and with staff of the Federal Housing Agency, a
set of six wall constructions were agreed upon for submission

to tests, per item (5) of the Project Plan: These are:

1. Framing : 2x4' s, common pine or fir, 16 in. o.c. with firestops near midheight.

Exterior : 1/2 in. insulating fiber sheathing

nailed to studs; 1 in. air space; single wythe

4 in. common face brick, with ties nailed to

framing (through sheathing)

.

Interior : single layer of 1/2 in. aluminum foil

backed gypsum wallboard, nailed to studs with joints

vertical, joints taped and cemented, nailheads cemented

two coats of self-sealing latex base paint.

2. Framing : same as 1 above.

Exterior : 1/2 in. insulating fiber sheathing nailed

to studs; 1x6 air-dried select wood drop siding nailed

through sheathing to studs; painted per MPS.

Interior : same as 1 above.

3. Exterior : 4 in. common face brick backed with 4 in.

cinder aggregate concrete block (3 oval hollow cores);

each set in mortar.

Interior : 1x2 wood furring, nailed vertically, at

16 in. o.c., with horizontal strips at top, bottom,

and midheight; drywall and paint as 1 above.

4. Sandwich wall (prefabricated) consisting of metal

exterior skin, hardboard interior skin, and foamed in

place plastic insulation to fill space between. Surface coatings (paint) as per normal production of the

manufacturer

.

5. Sandwich wall : same as 4 except hardboard skin on both faces.

6. Stressed skin, insulated, prefabricated.

For each of the above, enough material, or samples of prefabricated walls will be obtained in a single order to provide

specimens for all tests to be carried out.

2
3.1

Structural and Water Permeability

3.1.1 Racking Test

A racking-test frame has been assembled for applying diagonal

loads to 8 x 8 ft wall specimens in a horizontal position. Springloaded yokes for applying simulated floor and roof loads to the

wall are included in the equipment.

The decision to test the walls in a horizontal position instead of vertically was based on the results of trial tests on

a Type No. 2 wall specimen. When racking asymmetrical walls,

such as Type No. 2, there should be transverse restraint at the

top and bottom edge to prevent the wall from warping. For practical reasons it is easier to provide this restrain with the test

wall horizontal .

During our test development work the magnitude of the re- straint will be measured.

Recent NBS studies have indicated that the racking resistance

of load bearing walls is significantly affected by the vertical

loads imposed by roof and floor loads. The intention is to rack

test each wall type with three different vertical loading conditions. These superimposed vertical loads will be approximately

0, 0.5 and 1.0 of the calculated typical design load.

3.1.2 Dimensional Stability Test

The distortion of the test walls subjected to temperature

gradients will be measured in the air and water vapor transfer

chamber

.

3.1.3 Wind Load and Water Permeability Test

In addition to the trial wall described in the July-December

1964 Progress Report a Type No. 2 test wall has been tested in the

test chamber previously described. The reaction of both walls to

the 50 psf wind load was quite similar, with a center deflection

of about 0.5 in. No cracking or any other distress was noted.

Both walls behaved elastically with only a small amount of permenant set. The Type No. 2 wall was retested after the rain test.

The measured deflection of the damp wall was approximately 20%

less than the dry wall. This increase in stiffness was probably

due to the expansion of the wall frame and subsequent increase in

restraint around the perimeter.

3
The water permeability test indicated that both walls were fairly water tight. The test on the trial wall indicated that

about 15 hours of rain with a wind pressure of 10 psf would cause visible leakage on the interior. For the test on the Type No. 2 wall no visible water was noted on the interior until after 26

hours of continuous exposure. The through-wall leakage of the

trial wall was about 1 lb/hr for a wind pressure of 10 psf and

the rate increased rapidly with an increase in pressure.

The through-wall leakage of the Type No. 2 wall, although

visible, was never great enough to measure, with the pressure

at 10 psf. When the pressure was increased to 30 psf the leakage

increased to about 30 drops a minute for about 30 minutes and

then stopped. Subsequent increase in the pressure to 50 psf

caused a temporary leakage of about 2 drops of water per minute.

This leakage had practically ceased after about 10 minutes at

50 psf.

All indications were that the test wall of Type No. 2 was much more impermeable to wind driven rain than the trial wall.

The main difference between the two walls affecting the permeability

would seem to be the siding. The Type No. 2 wall was clad with wood

drop siding which was finished, after application, with 2 coats of

oil base paint (primer and finish) . The trial wall was clad with

a prefinished vinyl siding which could not be considered water

tight.

Examination of the walls after test revealed two facts.

These were:

1. That the use of interior grade plywood as sheathing

would not be satisfactory if the siding is not water

tight

.

2. The workmanship of the man who painted the siding of

the Type No. 2 wall was well above average because all

exposed surfaces had been well coated. This aboveaverage workmanship resulted in a well-sealed exterior

surface. For this reason a second Type No. 2 wall may

have to be tested for water permeability.

In order to arrive at some rational estimate of a reasonable

period of exposure for the water permeability test a study was made of the Weather Bureau records for Washington and Miami,

Florida. This was an hour-to-hour study of the records for 11

years. The data developed indicates that each year the Washington

- 4 -
area has a good chance of having a continuous rainy period of over 60 hours. The average rainfall during this period will

be less than 0.1-in. per hour. Also, the probable maximum

wind velocity (fastest mile) during this period would be only

about 20-mph (less than 2.5-psf pressure). For the Miami area the probable longest rain period each year is over 70 hours,

and the accompanying wind will reach a maximum of about 50-mph

(10-psf pressure). The probable rainfall is about double that

of the Washington area.

Originally it had been planned to use a rather short period

of exposure as the exposure conditions were judged to be rather

severe. The present thinking is that an exposure period of 72

hours is necessary, especially for constructions which have a buil t-in-reservior for collecting leakage through the exterior

surface

.

3.1.4 Compressive and Transverse Load Tests

The Type No. 2 wall has been tested using the compressive

and transverse load test procedures of ASTM E-72. These procedures have been found to be satisfactory. The ultimate compressive

load for the Type No. 2 wall was 10,500-lbs per lineal foot. Final

failure was due to the flexural fracture of two studs at knots,

although there was obvious differential movement between the

gypsum wallboard and the top and bottom plates.

3.2 Smoke Production

The apparatus for measurement of smoke production has been

completed and checked out on a number of specimens. However,

samples from the six walls described in paragraph 3. Activities,

had not been made available in time for results to be included

in this report. A detailed report on the apparatus is appended

to this report and will be circulated to other laboratories in

the fire research field. This is done to elicit the comments of

other professional fire researchers, since the apparatus is of a new design.

3.3 Air and Water Vapor Transfer

Construction of the environmental chambers to be used in

gathering data on the performance of exterior walls has been

completed. The chambers were constructed to provide enclosures

that are to be both air- and vapor-tight and to be capable of

maintaining air temperature and moisture content at a desired

level. The interior and exterior surfaces were covered with

5
a vapor barrier material in addition to using a special plywood

impregnated with a substance having a very low permeability.

The wall cavity was filled with urethane plastic foam for insulating value and airtightness. The insulation was foamed in

place after construction of the chambers and the vapor barrier

material was applied after the foaming operation. The chamber

to be used as a cold box is mounted in a fixed position and

the other chamber (the warm box) is mounted on casters and

can be moved away from the stationary chamber for insertion of

a test specimen which will be mounted in a support frame. The

frame is attached to an overhead trolley which can be moved to

position the specimen against the opening in the chambers.

Observation ports and doors are provided in each of the chambers.

Installation of the mechanical equipment (refrigeration system,

dehumidification system and flowmeters for infiltration measurements) is almost completed. Until the mechanical equipment is

ready other activities to ready the apparatus were carried on. Calibration of the chambers was made to determine if the chambers

leak and the amount of air leakage when specified pressures are maintained within the apparatus. Instrument racks were built

and instrumentation and controls for measuring the temperature,

humidity, pressure and air leakage were installed.

After installation of the mechanical equipment and the re- quired instrumentation, several dry runs will be made to check

out the apparatus. It is proposed that: (1) The air leakage be

determined at conditions (pressure differences across the wall

specimen) representing winds from 5 to 30 miles per hours, with

and without temperature variation of outdoor conditions; (2)

measurement be made of physical deflection, if any, caused by

thermal expansion or contraction; (3) determinations be made of

when and where condensation forms, by measurements at selected

points within the wall structure of relative humidity and temperature .

Preliminary test have been made to determine the amount and

location of the leakage through the chambers after installation

of instrumentation. Tests thus far have shown that the leakage

for the equivalent of a 30 mph wind is less than 1/2 cubic foot

per hour. Tests are also under way to determine the amount of

leakage that occurs at the joints where the specimen mounting

mask meets the steel support frame. A trial wall of 1/2-inch

plywood was constructed in the frame to simulate a wall having

no leaks, so that the leakage around the wall might be determined.

This amount of leakage will be eliminated or subtracted from the

leakage value of the specimen during the actual tests of infiltration. The chamber will be calibrated for leakage before each test.

6
The apparatus is instrumented to determine temperature,

relative humidities, and leakage air flows. Fifty thermocouples

are installed in the apparatus to give data on the temperature

conditions of the air in the chambers, at points within the wall

structure, and on the wall surfaces. Sixteen of the thermocouples

can be connected to a continuous recorder and the remaining thermocouples can be read through an indicator at desired intervals.

Twenty-four humidity sensing elements of the lithium chloride

type can be used to sample conditions of the chamber air and the

air within the wall structure. Control of the humidity is maintained by means of a humidity sensing device which causes humidification as necessary. Indications thus far have been that the

system for humidity control is quite adequate, giving control to

within one percent relative humidity. Eight of the elements can

be recorded continuously and the others can be monitored and

manually recorded through an indicator instrument. Two air

flow meters will be used to measure the amount of air that passes

into the chambers and through the wall specimen. One of the

meters, of 3 cfm capacity, has been calibrated and found accurate

to within 0.01 cfm.

The mechanical system, which is for the most part made up

of the refrigeration, humidifying, and dehumidifying systems is

in operation. A number of tests are scheduled for evaluating the

performance of the mechanical system and the degree of control

capabil ity

The refrigeration system is of the flooded coil type and has

the cooling coil housed directly in the conditioned space to re- duce penetrations of the chamber through which air might leak.

Liquid refrigerant, R-12, is circulated through the coil and re- turned to the flash chamber where, after expansion and heating,

the refrigerant is returned to the compressor in a continuous

cycle. Four blowers are used to move air across the large-surface

coil to provide better control of temperature. Circulation pattern

of the air in the chamber is designed so that the air flow will

not be directed against the wall specimen but parallel to it to

give more uniformity of pressure against the wall surface.

It is anticipated that three of the six selected wall speci- mens can be tested during the coming six months. A more optimistic

estimate at this time would be unrealistic since more tests must be

made on the test apparatus to determine its capability. Action has

been taken to retain the laboratory space at the present Washington

site for an additional six months (until January 1, 1967) to finish

the series of tests.

7
3.4 Weathering, Discoloration, Abrasion, etc.

The ability to predict the long-range performance of building

materials is, needless to say, very desirable. It is important

to assess, for instance, the durability of a paint when applied

to the exterior of a building, even though the expected lifetime

may be just a matter of a few years. It becomes even more important to evaluate the newer exterior siding materials with

respect to durability when it is considered that these materials

are now being sold with guarantees of up to 25 years. It is the

purpose of this report to describe some experiments, to evaluate

the data obtained, and to suggest conclusions concerning the

weatherability of some commercial samples of exterior residential

siding

.

3.4.1 Description of S amples

The materials used in this investigation were obtained from

manufacturers and local distributors and arrived with the various

abrasions and scratches received in transit. They were cut into

several 2-3/4 by 5-7/8 inch panels which were used in subsequent

tests. Thicknesses were determined with a micrometer; the paint

was removed, for this purpose, with paint remover. Table 1 lists

some of these figures and properties.

3 .4.2 Accelerated Weathering [l]

Two weatherometers were used to obtain data on the effects of

aging. One was an Atlas twin carbon-arc machine which was operated

on a 102-minute dry and 18-minute wet cycle. This instrument degrades samples via its rather strong ultraviolet emission and the

effects of periodic water sprays. The second machine, an Atlas xenon arc weatherometer , more closely simulates the solar radiation.

The water spray was not used with the xenon arc weatherometer.

3.4.3 Color, Gloss and Washability

Gloss readings were taken with a Hunter Precision Glossmeter,

with a specular reflectance of 60° [ 2 ]. Color readings were obtained with the Hunter Multipurpose Reflectometer [ 3 ]. The washability was determined using the Gardner Washability apparatus.

This instrument consists of an electric motor mounted on a flat

metal plate and a mechanism through which the motor imparts a reciprocating motion to a sponge, held in a metal box. A standard

soiling medium is applied to the test panel which is then placed

on the apparatus. A wet sponge, thoroughly rubbed with grit soap

is placed in the holder and is rubbed across the test panel for

a total of 35 cycles. Gloss and reflectance readings are taken

after completion of the test [ 4]. Values of gloss, color, and

washability were obtained before and after weathering in the twin

arc weatherometer. They are given in Table 2.

8
3.4.4

Abrasion Resistance

The abrasion resistance was determined jsing the NBS Jet

Abrader [ 5 ]. The instrument basically provides a source of

high speed abrasive particles which abrade the test specimen.

The end point is reached when the substrate is bared. The

time required to abrade through the specimen is a measure of

its relative abrasion resistance. Parameters such as distance

from test panel, speed of abrasive particles, angle of impingement, etc. are kept constant. Data for this test is given in

Table 3.

3.4.5 Fexibility

Flexibility is determined by bending samples of the sur- face film applied to flexible panels over 1/4 inch and 1/8 inch

cylindrical mandrels. The smallest diameter mandrel over which

a sample may be bent without causing cracks in the film is a measure of the film's flexibility [6], See Table 4.

3 .4.6 Repaintabil ity

Panels that were weathered 500 hours in the twin carbon arc weatherometer were coated, by brush, with a gray paint formulated

according to Federal Specification TT-P-102a. The painted panels were placed back in the weatherometer and removed after 100 hours

exposure. Adhesion was then determined by the knife test [ 7 ].

In this test a knife blade is used to cut through the film to the

substrate. Adhesion is measured qualitatively by the rupturing of

the surrounding area. The sidings that were factory painted gave

results indicating fair to good adhesion, i.e., the paint lifted

up in the form of a coil , with no shattering of the surrounding

surface. The plastic panels and polyester coated panel did less

well with slight shattering of the paint film. The Tedlar-coated

panels were poorest in this respect as extensive shattering of the

film occurred.

3.4.7 Chemi cal Analysis of Weathe ring

A chemical method for analyzing the extent of degradation was employed. This method, developed at NBS for degradation of plastics,

is a color reaction with a diamine, N ,N-dimethyl -p-phenyl enediamine

(DM.PDA) in a methonol -benzene solution: The amount of diamine re- acting with a sample is measured using absorption spectrophotometry

[8]. Results obtained are shown in Figure 1.

3.4.8 Heat Aging of Plastic Siding

It was found that samples I and J are heat sensitive and tend

to deform. At temperatures of 60°C both plastic samples soften

while at 100°C the panels cannot support their own weight.

9

3.4.9 Discussion

The difficulty of correlating any accelerated weathering

data with outdoor exposure is well known, as is the difficulty

in comparing results obtained with one weatherometer with that

of another [ 9 ]. In fact, exposures in different locations and

at different times of year can also have a pronounced effect on

the durability of coatings [lO]. However, certain general con- clusions can be drawn from inspection of Table 2. Gloss readings,

although low to start with, decreased in value with time in the

weatherometer. The values of L, the index of lightness, generally

decreases for the light colored samples and stays generally the same for the darker colored ones. The darkening of the light

colored samples is at least partially attributable to water

staining. Longer aging periods would be necessary to detect

significant differences between samples.

The flexibility does vary among the coatings and the Tedlar

coated panel survives this test best. No differences were noted

in this property after 500 hours of aging. However, it is doubtful

whether this is of much significance as a measure of potential

outdoor durability. Likewise, the abrasion resistance of Tedlar

is also bast. Bat here again, it would be premature to conclude

that the painted panels would fail in use due to their relatively

poor abrasion resistance. Repaintabil ity is, of course, a significant property and may greatly influence the choice of an exterior

siding. But in this case, the manufacturers may have recommendations

regarding repainting. The susceptabil ity of the plastic siding to

softening on heating may be significant in the long run because

this is a structural member and must at least support its own weight

Finally, it should be noted that a chemical colorimetric method

shows great promise as a predictor of degradation, as results show

up earlier in this method than in the standard gloss and color

changes

3.5 Impact Resistance

In considering the impact resistance to be expected from

house siding or cladding, the question is what kind of impact is

likely to be encountered in service. One of the causes of impact

damage is from baseballs, stones, and other missiles resulting

from children at play. In a previous report, it was hown that

a hard thrown baseball is comparable with respect to damage to

11
house siding to a steel ball, 1-3/4-inch in diameter, weighing

0.79 lb, dropped from a height of 10 feet. Another source of

damage is accidental striking with garden tools, etc. A third

source is hail damage, the incidence and severity of which depends on the locality. From a study of meteorological data,

it appears that a 10-foot drop with a 1-3/4-inch diameter steel

ball represents only about one-fourth the kinetic energy of a hailstone of the same diameter. However, the impact from this

drop is sufficient to damage most house siding. Hailstones

are not generally very hard frozen, even pure ice is much softer

than steel, and part of the energy of impact of hailstones is

undoubtedly dissipated in melting, plastic flow, and shattering.

Hence steel balls do not simulate hailstones very well. Investigators in South Africa have simulated hail damage by firing

ice balls from an air gun.

3.5.1 Tests on Whole Secti ons of House Siding

Various kinds of house siding or cladding were mounted in

the manner actually used in houses on a frame, 18- by 27-inches,

of 1/2-inch plywood, backed by 2- by 4-inch studs, 16 inches on centers. The frame was long enough for two or three 17-inch

lengths of siding, depending on the width of the material, and

was provided with retractable legs, so that the frame could be

placed at a 45° aogle as well as flat on the floor.

Some of the tests were performed at a 93° angle with the

frame resting flat on the floor, a steel ball being dropped

vertically through a guide tube. The frame was positioned so that the desired area would be struck by the ball, either a flat surface or the edge (butt or return) . The steel ball was 1-3/4 inch in diameter and weighed 0.79 pound. The results of

these tests are summarized in Table 5. Only qualitative visual

observations were made, with no measurements. Cement asbestos

shingle was tested above and below the line of overlap of

shingles instead of on the flat surface or the edge. This

material is apt to crack from impact above the line of overlap,

at a point where the shingle is unsupported. In supported areas,

as just below the overlap, it is resistant to impact. Vinyl

siding is apt to crack and split from impact at the edge or return but is highly resistant to impact on a flat surface.

Aluminum and wooden siding dent easily on impact and the edge

or butt is apt to become deformed. Plywood coated with Tedlar

is comparable to Douglas fir wooden siding. Hardboard coated

with polyester is very resistant to impact, the only effect

noted being a chipping of paint at the end of the butt due to

impact on the upper side.

- 12
The other tests were performed at a 45° angle with an impact dart as described in the American Standard Safety Code

for Safety Glazing Materials for Glazing Motor Vehicles Operating

on Land Highways, ASA Z26. 1-1950. In tests reported in Table 6,

a blunt tip was used for the dart, cylindrical in shape, the dart

and tip weighing 0.52 pound. In tests reported in Table 7, a pyramidal tip was used at the end of which was a steel ball, 1/8

inch in diameter. The weight of the dart and tip was 0.44 pound.

The dart was also dropped through the guide tube onto the desired

area of the mount. The blunt tipped dart had an effect on cement

asbestos similar to that of the steel ball. However, the dart

tended to scuff the material rather than produce slight dents,

as with the steel ball. The behavior with vinyl siding was also

similar except for more scuffing. With aluminum siding there

was also more scuffing and less deformation at the edge or butt.

Wooden siding and plywood coated with Tedlar tended to splinter

and crack on impact with the blunt tipped dart, as well as to

dent. With the dart, there was no tendency for hardboard coated

with polyester to chip paint at the end of the butt but this

material scuffed. Impact with the ball point dart failed to

crack cement asbestos shingle but produced scuffing. Behavior

with other materials was similar to that of the blunt tipped dart.

3.5.2 Tests on 6- by 8-inch Pi ec es of Siding Material

In these tests, 6- by 8-inch pieces of siding or cladding

material were mounted on plywood. In one type of mount, the

siding material rested flat on a 1/2-inch thick piece of plywood.

In the other type of mount, the siding material rested on two

pieces of plywood, 1/2-inch thick by 1- by 6-inches, fastened

to a 1/2-inch thick plywood backing, such that there was an un- supported span, 6 inches long by 6 inches wide. Either mount

could be placed flat on the floor for a 90° impact or at a 45°

angle on a wooden frame. The 1-3/4 inch diameter steel ball was dropped as close as possible to the center of each specimen.

Tests on specimens supported entirely by plywood are sum- marized in Table 8. The depth of the dents was measured with

a dial gauge, although accurate readings could not be obtained

with cement asbestos shingle, owing to the roughness and unevenness of the surface. In order to measure the depth of the dents

in aluminum siding, an area, about two inches square, was cut

around each dent and placed on a metal plate over a hole in the

plate slightly larger than the dent. This was then subjected

to pressure in a hydraulic press. The aluminum sheet was then

flat enough to provide a reference while backed by the metal

plate. Cement asbestos shingle was not cracked by this type

-13 -
of impact but was dented and scuffed. Aluminum, redwood, and

Southern yellow pine were dented about equally, while Douglas

fir siding, plywood coated with Tedlar and cement asbestos con- taining wood fibers were somewhat more resistant to denting.

Hardboard coated with polyester was undamaged except for slight

scuffing from impact at a 45° angle. Vinyl siding was not

affected at all by this type of impact test.

Tests on specimens supported at two ends, leaving 6- by 6-inch

unsupported span, are reported in Table 9. The impact from the

steel ball dropped only one foot at a 90° angle was sufficient to

crack cement asbestos shingle. A drop of 2 to 6 feet at a 45°

angle was required to crack the shingle. Cement asbestos siding

containing wood fibers was cracked by a 3-foot drop at 90° and by

a 6-foot drop at 45°. Aluminum siding was bent and dented, while

vinyl siding was not affected by a 10-foot drop.

3.5.3 Tests on 3- by 4-inch Pieces of Siding Material

This test was performed only on pieces of siding material

supported at two ends, leaving a 3- by 3-inch unsupported span.

Most siding materials were more vulnerable to this test than to

the preceding test on 6- by 8-inch pieces of material. Cement

asbestos shingle was cracked from a drop of only 6 inches and

cement asbestos containing wood fibers was cracked from a 1-foot

drop. Aluminum was bent and dented slightly from a 6- inch drop.

Again, vinyl siding was not affected by a 10-foot drop.

3.5.4 Effect of Temperature

Vinyl siding was found to be more brittle at 0° F than at 70° F

when tested according to ASTM D-746.

3.5.5 Discussion of Results

In evaluating house siding or cladding, it must be borne in

mind that the siding material is part of a system and the mode of

application must be considered. For example, it is important to

note whether there are unsupported areas which might be especially

vulnerable to impact. This is why tests were performed on unsupported as well as supported areas. The tests with 6- by 8- and

3- by 4-inch specimens were designed to isolate different features

of the systems and compare the characteristics of these features.

The Izod and Charpy tests are not suitable for all types of siding

materials and the test with steel ball and unsupported span provides sufficient information as to relative impact strength. The

14 -
test with steel ball and supported material provides information on hardness which is adequate for the purpose and cheaper

and more convenient than the conventional Rockwell test. Moreover, the steel ball test has been related to objects which

customarily damage house siding.

The same observations and measurements cannot be applied to all

siding materials because of their physical properties, such as the nature of the surface or the reaction of the material to

impact. Soft materials, such as wood and sheet aluminum are dented on impact and impact resistance can be stated in terms

of height of drop and depth of dent. However, unsupported

aluminum siding is bent out of shape to such an extent that

this masks the extent of denting. Brittle materials, such as cement asbestos shingle, are more apt to crack and impact re- sistance can usually be stated in terms of height of drop re- quired to crack the material. Impact produces other effects on cement asbestos, as some denting and scuffing, but since the

surface is rough and uneven, the depth of the dents cannot be

measured accurately.

Aside from the shape of dents produced by different shaped

missiles, the main difference between the results from impact

with the steel ball and the impact dart was that the dart cracked

and splintered wooden siding. Since hailstones are roughly

spherical in shape, the dart is even poorer than the steel ball

in simulating hail damage. The dart would roughly simulate damage

by garden tools, etc.

3.5.6 Recommendations

It seems likely that a continuation of this type of work will

result in a rating system based on the kind of impact tests described. The following is a preliminary rating system:

Drop a steel ball, 1-3/4 inch in diameter, weighing 0.79 lb.,

from a height of 3 feet at a 90° angle on a piece of siding 3-

by 4-inches, supported at two ends, so that there is an unsupported

span 3- by 3-inches. If the material cracks or shatters, it is

brittle and is in the class of cement asbestos shingle. If it

bends out of shape, it is flexible and soft, like aluminum siding.

Some siding might crack at low temperature (0° F) and establish

another class of material.

Drop the steel ball at a 90° angle from a height of 6 feet on

a piece of siding material supported by plywood. If there is a dent more than 10 mils deep, the material is soft, in the class

of wooden siding.

- 15
If the material survives these tests with no damage, it

should be considered to be in a superior class, as coated

Masonite, with respect to impact resistance.

It is unnecessary to test at a 45° angle as this merely

reduces the force on the siding due to less force vector acting on the surface and sliding of the missile due to low friction.

3.6 Heat Transfer

The heat transfer through exterior walls can be divided into

two different categories, the sum of which will give the total

heat transferred at a specific time. The first category covers

the steady-state effect, and includes the heat transferred by

means of a constant temperature difference between the mean

temperature of a weather cycle exterior to the wall and a con- stant temperature adjacent to the interior surface of the wall.

The steady-state effect is the best understood method of heat

transfer and is presently used for estimating the heat transfer

characteristics of exterior walls because only the thermal re- sistive effect of a wall need be computed (i.e., only the thermal

conductivities of the components of exterior walls and inside and

outside heat transfer coefficients need be known).

The second category includes heat transferred by means of

time-varying temperature fluctuations occurring in a weather

cycle, and according to the nature of the weather cycle, this

category can be termed either the transient or steady periodic

effect. The transient or steady periodic effect has not been

given widespread practical application in the past. Several reasons may be advanced for this; namely, the mathematical

solutions which include these effects are fairly complicated,

a representative weather cycle cannot be well-defined for a given locality, season, etc., and the thermal dif fusivities of

the components of an exterior wall must be known. The introduction of thermal diffusivity which is inversely proportional

to heat capacity gives a thermal capacitance to the exterior

wall which, when coupled with the thermal resistive effect,

determines the time-lag of the heat transfer rate at the interior

surface of a wall. The modulation of heat transfer rate at the

interior surface by the inherent thermal capacitances of the

components of a wall is governed by thermal response parameters.

For the purpose of the present investigation, the thermal

response parameters were termed "effective thermal conductance"

and "effective thermal diffusivity". The thermal response

parameters of a specific (nonhomogeneous) wall were set equal

to those of a homogeneous (one-material) wall of the same thickness which exhibited the same thermal response at its inner sur- face to an imposed temperature variation at its exterior surface.

16
A mathematical analysis was performed for the single homogeneous wall and the composite non-homogeneous wall consisting

of from two to four component materials. For a proposed experimental setup, it was decided to apply a simple sine-wave temperature variation of a given period on the exterior surface of a wall.

On the interior surface, a buffer material of known thermal properties

was proposed, with a constant temperature maintained at its exposed

surface. With these boundary conditions, the temperature as a function of time measured at the interface of the wall and buffer

enables calculation of the effective thermal response parameters.

The results of the mathematical analysis on some representative

s-'alls showed:

1. The thermal response parameters varied for a given wall

vith the period of a cycle. For very large periods the "effective

onductance" approached the steady-state conductance for the wall.

If it were possible to assign a representative period to weather

cycles, the thermal response parameters would have some meaning.

2. Positioning of the various components of a wall has con- siderable effect on the values of the thermal response parameters.

For example, placing a low thermal conductivity, low thermal heat

capacity material (insulating material) exterior to a high thermal

conductivity material (masonry) gives considerably different thermal response parameters than for the case where the materials are reversed in position.

3. The placing of a buffer which in itself has some heat

capacity effects has a deleterious effect on the determination of

the thermal response parameters. Further investigation for a proposed experimental setup will include replacing the present assumed

buffers by a buffer with a negligible heat capacity, i.e., an air

space and an interior panel maintained at a constant temperature.

It is concluded that because the periodicity of the exterior

surface temperature materially affects the thermal response parameters, attention must be given to selecting a period and waveform

for test measurements that will be reasonably representative for

walls in service, at least well enough for comparing different

walls. In brief, the task is to decide whether a simple sine-wave

of a suitable period can be taken as an acceptable approximation

to probable variations of building exterior surface temperatures

under use conditions, taking into account both air temperature

changes and solar heat absorption. If this can be answered

affirmatively, it will be feasible to develop a test method for

determining the dynamic thermal performance of walls under representative conditions.

- 17
4. REFERENCES

[1] Federal Test Method Std. No. 141, Method 6152.

[2] Federal Test Method Std. No. 141, Method 6101.

[ 3 ] ASTM Standards, Part 21, January 1965. D1260-55T, p. 241.

[ 4] Federal Test Method Std. No. 141, Method 6141.

[ 5 ] A. G. Roberts, ASTM Bulletin No. 244, February 1960, p. 43.

[6] Federal Test Method Std. No. 141, Method 6222.

[ 7 ] Federal Test Method Std. No. 141, Method 6304.

[8] V. E. Gray and J. R. Wright, J. Appl . Pol. Sci. _7 , 2161 (1963).

[ 9 ] L. J. Nowacki, Off. Dig., November 1962, p. 1191.

[l0] M. P. Morse, Off. Dig., June 1964, p. 695.

18
5 . TABLES

Table 1. Characteristics of Exterior Siding

Sample

Designation

Description Color Total Thickness

(mils)

Thicknes

Coating

A Tedlar film on aluminum White 25 2

B Painted aluminum White 23 1

C Painted aluminum White 24 1

D Textured painted aluminum Beige

(1) 30-35 ! (1>

E Painted aluminum Dark brown 24 1

F Painted aluminum Dark Gray 25 1

G Tedlar film on plywood White 355 2

H Painted galvanized steel White 21 1

T Solid plastic White 45 --

J Solid plastic Light green 50 --

K Polyester film on masonite White 395 2

L Painted cement asbestos Light green 150-200 (1)

1 (1)

(1) Because of textured finish, the figures are rough estimates.

- 19
Table

2.

60

Gloss

and L

Values

After

Aging

in

Twin

Arc

Weatherometer

and

After

Washability

Test £d

43 IT)

m 04m 00 o

co hJ 0 • • • . • cd CM 4) m cn 04 5 CO

Cl CO

00 n- 00 4) 04 CO

a> o 04 04

4J T-l • . • « • 0 4-t o

<30o

4)

CO

r-H on co o1-4 r^-

43 o 43 4> 00 43O CO ,-J • « . » • cd o 04 o m vD 3

cu co

Ci CO

00 00 00 4) CM CO

O

O 00 o 4i CM 00

4-1 r-1 . • . « • 0) O

MO o

T—l 04 in CM 00 LO o4

43

CO iJ

cd [2

C/3 Cl CO

cu o

4-1

H • 4-4 O

CO <JO

Ci o

33 4 O 43

lt> co ,_q cd 3

CL) CO C CO O O

4-1 r-4 CD O

PQOo

43

in 43 o m CM . • • • • • CO 00 s—)

r—1

00 00 00 00 43

00 00 <1" vr> CM

O . • . • » • 43 vO 00 CM

r—1 o 00 . o St

mO . • . • • • cn CO 03 T—1

<t CM 00 00 00 oo 4)

CM

O CM

O . • . • • 43 oo vD 00 CM

43

co hJ

cd 3 co C CO

O) o

4-) i—I • 4-1 O

co <30 c o

33 4 O 43

co >41 4 Cd 3

0) CO

Cl CO o o

4-1 .—I

cu o

moo4

43

COcd 3c

cu • 4-4

u

co <30 M O

43

43

CO

cd 3

a) co

Cl co o o

4-1 t-l <u O

eQOo

4>

43 o m o cn o O

O in

m

m CM in

m OO cn in

00 00 00 43 CM cn 00 00 00 00

CM CM oo On CM o 43 CM o

COm CM 00 43 03 r-. 00

r—1r-H r—1

43

mm o 43 43 >43 CM 43m o

CM in 43 CM

m cn 03 CM

m

00 00 00 43 CM cn 00 00 00 oo

«n 00m o m o 00 4 o

CM in cn o 4 4 00 00 00

rH r—l

O o 00 o 4 4 o in o 00

in cn 03 CM 1 1 4 4 o m

00 00 00 4 CM cn 00 00 03 00

cn CM 00 4 o o <t 4 o

cn r- cn l—1

rH r-*

T 1 1—1 i—i 1—1 o in o in o in in in o in 4 n- o in CM in in in cn in 4

00 00 03 4 CM cn 00 00 03 00 4 o in cn 03 in CM in in o

pH cn 4 CM oo o 00 00 03

pH rH pH «—1 < ca o Q w Ph o 53

M *1 t*3

O

4>O

CMO

co4)O

04O

044>O

04O

CM

t-J

20

63.5
Table 3. Abrasion Resistance

Sample

Designation

Time Required to Abrade

(Sec . )

A 58

B 3

C 3

D 2

E 2

F 2

G 51

H 1

I (a)

J (a)

K 8

L 2

(a) Test not applicable to these samples.

21
Table 4. Flexibility

Smallest Diameter

Sample Smallest Diam. Mandrel (inch) Mandrel (500 Hrs . ) (In)

A 1/8 1/8

B 1/8 Incipient Cracking 1/8 Incipient Cracking

C 1/8 Incipient Cracking 1/8 Incipient Cracking

D 1/4 1/4

E 1/4 1/4

F 1/8 Incipient Cracking 1/8 Incipient Cracking

G (a) (a)

H 1/4 1/4

I (a) (a)

J (a) (a)

K (a) (a)

L (a) (a)

(a) Test not applicable.

22
Table 5, Drop-Impact Tests at 90° Angle on Sections of House Siding Mounted

on an 18- by 27-inch Wooden Frane , using a 1-3/4-inch Diameter

Steel Ball. Weight of Ball 0.79 Pound.

Siding Material Tests on Flat Surface Tests on Butt or Edge

Height of

drop, ft. Visible Damage

Height of

drop, ft. Visible Damage

Aluminum 3 Noticeable dent

6 Deeper dent

10 Same but greater

effect

3 Dent; some deformation

6 Deep dent; considerable

deformation

10 Same but more

Cement Asbestos*

Brand A 3,6

10

None

Dent; long crack above overlap.

Brand B 3 3,6,10

Cracked on drop above overlap.

No damage on drops below overlap.

Hardboard coated with Polyester

10 None 3,6,10 Chipping of paint at

end of butt.

Plywood coated with Tedlar

3 Slight dent 3 6 Somewhat deeper dent 6

10 Noticeable dent 10

Slight dent

Deeper dent

Deep dent; deformation

Vinyl

Brand A 10 None

Brand B 10 None

6 None

10 Cracked; piece knocked off

5 No damage in 2 tests;

slight denting in 2 tests.

6 Dent in 1 test; crack,

split in another test.

10 Crack, split

Wood

Douglas fir 3,6 Slight dent

10 Deep dent

3,6 Slight dent

10 Dent, deformation

Redwood 3 Dent 3 Dent, deformation

Southern

fallow Pine 3,6 Slight dent

10 Deep dent

3,6 Slight dent

10 Dent, deformation

* Cement asbestos shingle was tested on areas above and below where shingles

overlap inste’ad of on the flat surface and on the butt.

23
Table 6. Drop-Impact Tests at 45° Angle on Sections of House Siding Mounted

on an 18- by 27- inch Wooden Frame, using a Blunt Tipped Dart.

Weight of Dart 0.52 pound.

Siding Material Tests on Flat Surface Tests on Butt or Edge

Height of Height of

drop, ft. Visible Damage drop, ft. Visible Damage

Aluminum 3 Scuffing; slight dent 3 Small dent; coating removed

6 Deep dent; scuffing 6 Fair sized dent; scuffing

Cement Asbestos*

Brand A 3,6 Slight scuffing

10 Scuffing; removal of coating; long crack above overlap c

Brand B 3 No damage above or below overlap

.

6 Scuffing

10 Scuffing; cracking above overlap

.

Hardboard coated with Polyester

3,6 Scuffing 3,6 Dart slipped and scuffed

lower panel.

Plywood coated with Tedlar

3 Scuffing 3 Scuffing; break in coating

6 Dent, break in coating 6 Dent, break in coating,

deformation

.

10 Deep dent, splintering of: 10 Deep dent, splintering,

plywood, peeling of coating peeling, deformation.

V ipy 1 Brand A 6 Scuffing 6 Scuffing

10 Scuffing 10 Noticeable dent.

Brand B 6 Scuffing 6 Scuffing

10 Considerable scuffing 10 Chipped off piece

Wood

Douglas fir 3,6, Progressively deeper 3,6, Denting, cracking,

10 dents 10 splintering

Redwood 3 Noticeable dent 3 Noticeable dent

6 Larger dent 6 Chipping, splintering

Southern 3,6, Progressively deeper 3,6, Denting, cracking,

Yellow Pine 10 dents 10 splintering

*Cement asbestos shingle was tested on areas above and below where shingles

overlap instead of on the flat surface and on the butt.

24
Table 7. Drop-Impact Tests at 45° Angle on Sections of House Siding Mounted

on an 18- by 27-inch Wooden Frame, using a Ball Point Dart.

Weight of Dart 0.44 pound.

Siding Material Tests on Flat Surface Tests on Butt or Edge

Height of Height of

drop, ft. Visible Damage drop, ft. Visible Damage

Aluminum 3 Dent, scuffing 3 Small dent; removed coating

6 Deep dent; scuffing 6 Scraped coating and slipped

Cement Asbestos*

Brand A 3 6,10

Slight scuffing

Definite scuffing

Brand B 3

6 No damage above or below

Scuffing

overlap

Hardboard coated

10 Scuffing; no cracking above

with Polyester

overlap

3 No damage 3 Slight scuffing

6 Scuffing

Plywood coated with Tedlar

6 Scuffing

3 Dent; peeling of coating 3 Dent; peeling of coating;

deformation

6 Deep , long dent 6 Chip, deformation

10 Deep dent, splintering,

long scuffed area

10 Small scuffed area with

some chipping.

Vinyl

i Brand A 6 Scuffing 6 Dent

10 Scuffing, long dent 10 Scuffing

Brand B 6 Scuffing 6 Scuffing

10 Long dent 10 Small chip

Wood

Douglas fir 3 Noticeable dent 3 Noticeable dent; split

Tedwood 3 Noticeable dent 3 Noticeable dent

6 More noticeable dent; some splintering.

6 More noticeable dent

Southern

Yellow Pine 3 Noticeable dent 3 Noticeable dent; split

* Cement asbestos shingle was tested on areas above and below where shingles

overlap instead of on the flat surface and on the butt.

25
Table 8- Drop-Impact Tests on 6- by 8-inch Pieces of House Siding Supported

on Plywood, using a 1-3/4-inch Diameter Steel Ball.

Siding Material Height of Angle Dimension of Dent

Drop, ft. of Drop Visible Damage Max

.

Max

.

diam. depth

in

.

mils

Aluminum 3 90° Dent 5/8 25

3 45° Dent 5/8 20

Cement Asbestos

Brand A 10 90° Dent; no cracking 18

6,10 45° Dent; no cracking 5 Brand B 3 90° Slight scuffing

6 90° Scuffing

10 90° Dent; crack part way across

3 45° None

6 45° Slight scuffing

10 45° Scuffing

Brand C 6 90° Dent 20

10 90 Noticeable dent 26

6 45° Slight dent

10 45° Slight dent 10

Cement Asbestos Containing Wood Fibers

3 90° Dent 9/16 10

6 90° Dent 9/16 22

10 90° Dent 13/16 44

3 45° Dent 7/16

6 45 Dent 1/2 5 10 45° Dent 5/8 15

Hardboard coated with Polyester

3,6,10 90° None

3,6 ,10 45° Slight scuffing

Plywood coated with Tedlar 0

3 90

o Dent 1/2 10

6 90

o Dent 3/4 20

3 45

o Dent 1/2 5 6 45 Dent 5/8 7

Vinyl - Brand A 10 90° None

10 45° None

Wood - Douglas fir 3 90° Dent 9/16 8

6 90° Dent 7/8 25

3 45° Dent 1/2 6

6 45° Dent 7/8 16

Redwood 3 90° Dent 1 30

6 90° Dent 1 48

3 45° Dent 5/8 15

6 45° Dent 5/8 27

Southern 3 90° Dent 3/4 22

Yellow Pine 6 90° Dent 3/4 40

3 o Dent 1/2 6

6 Dent 5/8 27

26
Table 9 . Drop-Impact Tests on 6 - by 8 -inch Pieces of House Siding,

Supported at Two Ends, 6 - by 6 -inch Unsupported Spans

Height of Angle

Siding Material Drop, ft. of Drop Visible Damage

Aluminum 3 vo 0

0

3 45°

Cement Asbestos

Brand A 1 90°

6 45°

Brand B 1/2 90°

1,2 90°

3 90°

1 45°

2 45°

3 45°

Brand C 1 90°

2 90°

1 45°

2 45°

0

3 45

6 45°

Cement Asbestos containing Wood Fibers

2 90°

3,6,10 90°

2 45°

, 0

3 45

6,10 45°

0

Vinyl - Brand A 10 90

10 45°

Dent; max. diam. 5/8 in.; max. depth 0.025 in.

Dent; max. diam. 5/8 in.; max. depth 0.020 in.

Crack all the way across Crack all the way across

None

Crack all the way through and across Broke in half

None

Fine crack all the way through

and across Crack all the way through and across

None

Cracked all the way across;

almost broke in half

None

Fine crack all the way across Crack all the way across Broke in half

None

Crack all the way through

None

Shallow dent; no crack

Crack all the way through

None

None

27
Table 10. Drop-Impact Tests at 90° Angle on 3- by 4-1/2-inch Pieces of House

Siding, Supported at Two Ends, 3- by 3-inch Unsupported Span.

Height of

Siding Material Drop, ft.

Aluminum 3, 6, 10

1 , 2 1/2

Cement Asbestos

Brand A 3, 6, 10

2

1 1/2

Cement Asbestos containing Wood Fibers

6, 10

2, 3

1 1/2

Vinyl - Brand B 6 , 10

Visible Damage

Bent and dented

Bent; slightly dented

Slightly bent; slightly dented

Shattered

Broken in center and one end

Cracked all the way across and through

Fine crack all the way across

Shattered

Cracked all the way across and through

Cracked all the way across; slight dent

Slight dent

None

28
6. APPENDIX

A LABORATORY TEST FOR MEASURING SMOKE FROM BURNING MATERIALS

By

D. Gross and J. J. Loftus

ABSTRACT

As a result of extended laboratory investigations

equipment has been assembled for quantitative measurement

of the smoke produced when material is burned or pyrolyzed

in a closed volume. This report provides the first complete

description of the equipment. It is presented at this time

to permit others, who so desire, to duplicate facilities

for their own use. A later report will be prepared describing

the work leading to development of the test method and reporting results obtained with a variety of building finish materials.

Al-
A LABORATORY TEST FOR MEASURING SMOKE FROM BURNING MATERIALS

by

D. Gross and J. J. Loftus

1. Introduction

In a previous report [ 1] , preliminary results were presented of the

smoke production characteristics of several materials within the Rohm and

Haas XP 2 Smoke Density Test Chamber [ 2 J. These results indicated that a small-scale laboratory test chamber appeared to be a useful and desirable

means for evaluating the smoke generation characteristics of materials

under simulated building fire conditions. This study has been extended

to establish test criteria and procedures which would permit simple,

reproducible and meaningful smoke measurements. An improved test chamber

has been designed and built for this purpose. This report gives a detailed

description of the chamber design and the test requirements on which it was based.

2. Requirements

The basic requirements for any laboratory test method are that it

be simple in concept and easy to operate, and that it yield realistic,

reproducible results based on sound principles. It should be relatively

insensitive to minor variables, but be capable of operating over a sufficiently wide range of conditions. In terms of smoke measurement,

the following conditions were considered appropriate:

A. The specimen be exposed and generate smoke from one surface only.

This simulates the usual case in accidental building fires, and

permits evaluation of the effectiveness of surface coatings in

reducing smoke.

B. The method be suitable for smoldering (non- flaming) as well as active flaming conditions.

C. Smoke and combustion products (including water vapor) result only

from specimen burning and not from the heat source.

D. The results be reported in units providing a measure of smoke

quantity and comparative obscuring power.

A2
3. Test Equipment

A . Chamber

The smoke chamber consists of a 16 ga . sheet metal box, 3 ft x 2 ft x 3 ft high. As shown in F ig . 1 and 2, openings were provided to accommodate a photometer (C 6c I) with a 3-ft vertical light path, power and signal lead wires, air and gas supply tubes, an exhaust blower and damper (B)

an aluminum foil blowout panel (D) , and a hinged door with a window (E)

The chamber is tightly closed and normally not ventilated during test. It

is supported on an angle iron frame (L) , on which are mounted the electric

(N, 0 6c P) , gas and air controls (S 6c Q) . A multi-range meter and timer,

or alternately, a recorder, are used for taking data.

The interior of the chamber and all parts used therein are either

anodized black or painted with a flat black paint which should be re- sistant to corrosive decomposition products.

B . Furnace and Control System

To provide a fairly uniform irradiance on the surface of the 3 by 3 in.

square specimen, an electrically-powered furnace with a 2-15/16 in. diameter opening is used. As shown in Fig. 3 A, a 525 watt type "End”

Silex heating element (D) is mounted within a 2-15/16 in. i.d. by 3-3/8 in.

o.d. by 1-5/8 in. long ceramic tube (C) , bored out to 3-1/32 in. i.d.,

5/8 in. deep, to accommodate the heating element. Behind the heating

element are mounted a 1/16 in. thick asbestos paper gasket (F) , three

1/16 in. stainless steel spacing washers (G) , and two 1/32 in. stainless

steel reflectors with 6 holes (H) and 3 holes (I), respectively. The

heating element assembly is centered with respect to the front 3/8 in.

asbestos board (B) , and the 3/8 in. asbestos board centering disk (J)

by means of a 6-32 stainless steel screw (E) , and the adjustment of the

nuts on the end of this screw provides the proper spacing of the furnace

components. Pyrex glass wool (W) is used to fill in the spaces in the

heating element assembly. Two spacing rings (K) of 3/8 in. asbestos

board, a rear cover (L) of 3/8 in. asbestos board, and a 4-in. o.d. by

,083 in. wall by 4-1/8 in. long stainless steel welded sanitary tube (A),

180 grit polished inside and outside, complete the furnace assembly.

Three sheet metal screws (M) , No. 6 by 1/2 in., are used around the

periphery at each end. Appropriate holes are provided in the centering

disk for asbestos-covered copper lead wires to the heating element and

in the rear cover for a motor base plug and six 1/2 in. ventilation holes

on a 2-1/2 in. dia. circle.

Although the materials and dimensions used are given in detail, they are

not considered critical, provided the construction can withstand continuous

operation and provided the geometry of the furnace opening is not materially

altered

- A3
The control system consists (Fig. 2) of a temperature controller (M)

,

two autotransformer s (P) , and a sensing thermocouple placed within and

close to the surface of the ceramic core of the furnace opening. The

temperature set point of the controller is arranged so that a radiometer,

placed at the same location as the specimen, will measure the prescribed

xrradiance level. The two autotransformers provide high and low voltage

levels (rather than on and off) , and can be adjusted to minimize power

fluctuations to the heating element.

C . Photometric System

The light path was arranged vertically to reduce errors in measurement

due to smoke stratification effects. The light source was a 30-watt. 120

volt, S-ll, Type BLC , film viewer lamp powered by a voltage regulating

transformer. It was mounted in a box (C, Fig. 2) extending above the top

of the smoke chamber, which contained, in order, the source, a 7-diopter

collimating lens and an adjustable metal finger. (See Fig. 4). A glass

window, gasketed for smoke-tightness, was mounted permanently in the ceiling of the chamber. The lamp was always operated at the same voltage (and

hence same color temperature, approximately 2630°K) , and adjustments of

the light intensity were made with the metal finger.

Another box (I, Fig. 2) containing the photometer was located directly

below the source and attached to the bottom of the smoke chamber. Below

a similarly mounted glass window in the chamber floor were, in order, a 7-diopter lens forming an image of the source, a 3/16 in. dia. circular

stop in the focal plane of the lens, and a 1P39 single-stage vacuum phototube having an S-4 spectral sensitivity response. This lens and stop com- bination did not permit the receiver to register rays departing from

parallel by more than a few degrees, and reduced to a negligible amount

the effect of the "beam broadening" caused by smoke particles scattering

light from the original beam.

The phototube circuit load comprised the input resistance of the re- corder and an adjustable load resistor arranged to provide a convenient

signal level. When the full-scale output for the clear, smoke-free condition was adjusted to 1 volt (using the metal finger and load resistor

adjustments), ten-fold reductions in light transmission could be accom- modated without appreciable loss in accuracy, by decade range changes of

the recorder down to 0.1 millivolts full scale. This permitted the recording of reliable optical densities of about 4, corresponding to transmission

values of .01 percent of the incident light. At the lowest levels of light

transmissions, a correction becomes necessary for the dark current of the

vacuum phototube, since this represents zero light transmission.

- A4
D . Specimen Holder

The 3x3 in. specimen is placed in a holder, Fig. 5, designed for

rapid positioning and for maintaining, by means of the furnace support

(Fig. 3 B) , the specimen surface 1 1/2 inches in front of, and parallel

to, the furnace opening. The furnace support also serves as a positioning mount for a radiometer. Fig. 6, which establishes the prescribed irradiance level at the specimen surface just prior to its exposure.

The stainless steel specimen holder is fabricated by bending and brazing

(or spot welding) to give a 2-9/16 in. square exposed area. The back,

edges, and front non-exposed surfaces of the specimen are covered with a single sheet of thin aluminum foil to prevent smoke passage at any but

the exposed specimen surface. Behind the specimen is placed a 3 x 3 x

1/2 in. thick sheet of asbestos millboard (confirming to Federal Specification HH-M-351) . A phosphor bronze spring and a steel pin are used to

maintain a snug assembly.

When the proper spacing (9-3/8 in.) is maintained between the spacing

tops of the furnace mount (Fig. 3 B) , the loaded specimen may be quickly

and accurately positioned by placing it on the support bars and sliding

the radiometer or another holder to the limit of its travel.

E. Radiometer

The desired irradiance level (2.5 w/cm^) at the specimen surface is

measured by means of a circular foil radiometer of the type described by

Gardon [3]. It is of simple construction, has a sufficiently rapid timeconstant and produces an emf, which is nearly proportional to the irradiance level. The use of a reflective heat shield, with aperture, on

the front of the radiometer, and a finned convector supplied with com- pressed air on the rear, help to maintain the radiometer body at a more constant temperature and to minimize effects due to variable convective

and radiative losses. The receiving surface was spray-coated with an infrared-absorbing black paint containing a silicone vehicle.* The

absorptivity of the paint to visible and infrared energy is approximately

0.93 to 0.95 for a film thickness of 1 mil.

Details of the radiometer construction are shown in Fig. 6. The aircooled radiometer was calibrated by placing it at suitable distances from

a radiant energy source and measuring its electrical output as a function

of the irradiance level, Fig. 7. The latter was determined calorimetrically by measuring the rate of temperature rise of a totally absorbing

copper disk of known weight, area and specific heat.

* Type 8 X 906 SICON Flat Black Paint, Midland Industrial Finishes Company,

Inc., Waukegan, Illinois.

- A5
4. Suggested Test Procedure

All specimens s prepared in the 3x3 in. size, should be predried

for 24 hours at 140°F and then conditioned to equilibrium with an ambient

of 73 ± 5°F and 50 ± 5 percent relative humidity. The specimen should be

representative of the material or assembly as intended for use and should

be prepared by the intended application procedures. Where the intended

application of a finish material is not specified, or may be any of

several, the finish material may be prepared for test as follows:

(a) Surface finish materials, in either liquid or sheet form,

including those intended to control and reduce the smoke

produced by supporting base materials, should be tested in

the assembly or assemblies proposed for use. In the absence

of specific information, the finish material should be

applied to the smooth surface of 1/4 in. thick tempered

hardboard using recommended (or practical) application

techniques and spreading rates.

(b) Liquid films, such as sealers, adhesives, etc., and other

materials intended for application to noncombustible base

materials or being tested for their inherent smoke contribution shall be applied to the smooth surface of 1/4 in.

thick asbestos cement board of 120 pcf density, using

recommended spreading rates.

(c) Materials intended for air-backed applications, such as suspended ceilings or hanging drapes, shall be mounted

in a specimen holder providing a 1/8 in. air space behind

the specimen. This may be accomplished by use of an as- bestos board back fitted with 1/8 in. thick, 1/4 in. wide

asbestos strips at the borders.

To perform a test, turn on the electrically-powered furnace and

associated controls. Place the radiometer in a specimen holder and position it in front of the furnace. Turn on the compressed air supply to

the radiometer convector and adjust the flow rate (or pressure) to cor- respond to the value used for calibration. Adjust the controller temperature setting to produce a millivolt output of the radiometer corres- ponding to an irradiance of 2.5 w/cm^ . Adjust the two autotransformers

to suitable voltage levels (approximately 70 and 90 volts) to minimize

cyclic variations in irradiance.

Turn on power to the photometer light source and the recording or indicating meter. Using the metal finger and load resistor adjustment,

set the output reading to full-scale on the 1-volt range. Verify the zero reading on the most sensitive range, and others if required, by

shorting the meter input.

- A6
Mount a preconditioned specimen in a cool specimen holder using a single sheet of aluminum foil along the back, edges, and front inside

surfaces of the specimen, taking care not to puncture the foil. Back

the specimen with a sheet of 1/2 inch asbestos millboard and assemble

into the holder snugly, using the spring and pin.

For non-flaming (smoldering) tests, place the loaded specimen holder

on the bar supports and slide it into position by displacing the radiometer.

Start the timer (or recorder chart) simultaneously. Turn off the air

supply to the radiometer and close the door. Record values of light

transmission versus time, making full-scale range changes (in decade

steps for maximum convenience) as appropriate. Observe and note any

characteristic smoking or burning patterns, the color and nature of the

smoke, etc. Continue until a minimum light transmission value is reached

or 15 minutes, which ever is lesser. Record the "dark current" light

transmission by switching off power to the photometer light source and

setting the recorder at a suitable high sensitivity. Verify the zero reading by shorting the meter input. Open the door a small amount and

turn on the exhaust fan to clear the chamber of smoke. Discard the

specimen and clear the chamber completely of smoke. With the photometer

light on, record the final light transmission value under clear air con- ditions in the chamber, making the appropriate meter range changes. Clean

the glass windows (ethyl alcohol generally is satisfactory) in preparation

for the succeeding test.

For tests employing pilot ignition, supply gas to the pilot burner

(see Fig. 5) at a rate of 200 Btu/hr (0.2 SCFH of natural gas, or equivalent). Ignite the horizontally oriented gas jet using an electrically powered platinum "hot wire". Swing the lighted pilot burner up to

impinge on the specimen surface when the loaded specimen holder displaces

the radiometer in front of the furnace. If the pilot burner is blown out

during a test, reignite it using the platinum hot wire. Proceed as before.

5. Test Results

The result of a smoke measurement test of a material is a curve of

optical density (per foot) versus time. The report of such a test should

also include the following:

(a) Identification of the material, including data such as density,

thickness, and type of base material (if used).

(b) Test conditions, including irradiance level (2.5 w/cm-),

flaming (pilot) or smoldering (no pilot) exposure, etc.

(c) Important visual observations of specimen, color and nature

of smoke, and test chamber conditions both during and after

test.

- A7
The reduction in the light transmission caused by smoke in the photo

meter light path is measured using a recorder or a meter and timer. The

transmission data is converted to optical density per foot using the

relation:

1 100

D = - ( log 10 — )

where T is the percent transmission and L = 3 ft is the length of the

optical path.

For each test, retain a record of (a) the "dark current" light trans

mission (with photometer light source off and recorder set at a suitably

high sensitivity), and (b) the final transmission value (after removing

specimen and clearing chamber of smoke)

.

- A8
6. References

r l] D. Gross, J. J. Loftus, and R. Harris, "Wall Cladding Materials:

Smoke Production Measurements Under Simulated Fire Conditions",

First Progress Report, NBS Report No. 8398, July 14, 1964.

[2] Anon., "A Method of Measuring Smoke Density", NFPA Quarterly, _57 pp 276-87, January 1964.

R. Gardon, "An Instrument for the Direct Measurement of Intense

Thermal Radiation", Rev. Sci. Inst., 24, pp 366-70, May 1953.

- A9 -

USCOMM-NBS -DC

Fig. 1 - Smoke Test Chamber
36

ro

\ :

j

FIG. 2-SMOKE CHAMBER ASSEMBLY
FIG.3A-FURNACE SECTION

FIG.

3BFURNACE

SUPPOR

yjQWVHO JO ON

U)o

O

O

LD

Ll

-

PHOTOMETER

DETAILS

HOLES

(6)

D V

cco

(_> DQZ

CCo

a.o

CD<

f—LUO

CCUJ

f—

LlJ oo<

cc! CD

C5

Li_

0

0.5

1.0

1.5

2.0

2.5

3.0

IRRADIANCE

,

WATTS/cm

2

FIG.

7

-

RADIOMETER

CALIBRATION

CURVE