NATIONAL BUREAU OF STANDARDS REPORT

2541

SIMULATED USE TESTS OF SUBSTITUTE DUCT MATERIALS

by

O. N. McDorman

P. R. Achenbach

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

1003 -20-1014 June 3, 1953 2541

SIMULATED USE TESTS OF SUBSTITUTE DUCT MATERIALS

by

O. N* MeDorman

P, R. Achenbach

to

Office of the Housing Administrator

Housing and Home Finance Agency

Washington, D. C.

The publication, reprln

unless permission isobt

25, D. C, Such permls

cal ly prepared If that

Approved for public release by the

,a "' 15 proh,d,,ea

, l

. . c lards, Washington Director of the National Institute ot ,t has been specin- Standards and Technology (NIST) for lt8 own use on October 9, 2015.
CO*.
SIMULATED USE TESTS OF SUBSTITUTE DUCT MATERIALS

Abstract

Simulated use tests were made of substitute duct materials

to determine mold growth, water absorption, delamination

upon alternate heating and cooling, weight and dimensional

changes during exposure to high humidity, deformation and

deterioration at elevated temperatures, odor generation,

and damage from dropping. Some deformation measurements

were made on light gage metal ducts for comparison. The

temperatures produced in a high-temperature forced warm " air heating system during full-load and runaway operation

of a coal furnace were also measured. These data and other

data reported in NBS Report 1947 were used to develop

criteria for substitute duct materials on flame spread,

deformation at elevated temperatures, penetration of flame,

rigidity, deterioration, odor, and practicability of joints

and fittings.

I. INTRODUCTION

At the request of the Housing and Home Finance Agency a study

was made to determine criteria for selecting suitable materials to

be used as substitutes for metal ducts in warm air heating systems.

To assist in setting proper limits on the physical characteristics

for such materials similated use tests were made of some commercial

materials, certain measurements were made on metal ducts now commonly used for warm air heating systems', and temperature studies

were made in a typical high temperature forced warm air heating

system to determine what temperatures would be reached in the ducts

if the blower stopped running while the dampers were wide open on

a coal furnace.

Tests to determine mold growth, water absorption, delamaination

upon alternate heating and cooling, and weight and dimensional changes

during exposure to high humidity were made on two commercial materials.

In addition, a test to determine deformation and deterioration at

elevated temperatures, an odor test, and a dropping test were made

on one of these two materials.

The results of certain fire hazard tests on these same two commercial materials are described in a separate report (NBS Report

1947 entitled Fire Hazard Tests of Substitute Duct Materials]

.

Measurements of the deflection of light gage galvanized iron and

aluminum ducts comparable to the lightest that are now permitted

by NBFU Pamphlet No* 90 for warm air heating systems in residences

were made when four-foot sections were simply supported at each end.
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The criteria recommended for evaluating substitute duct

materials are listed and discussed in NBS Report #2540*

II* TEST MATERIALS

Substitute materials made available for test in connection

with this investigation were:

(a) Several l£ foot lengths of Sonoair duct manufactured by the

Sonoco Products Co., Hartsville, South Carolina. This

material was a laminated fiber duct having an inside diameter of £ inches and an outside diameter of £-7/16 inches.

The cellulose plies of this duct were spirally wound and

cemented together with an organic binder. The inside and

outside surfaces of the duct were coated with paraffin.

(b) Several sheets of Sal-Mo No. 77 Ductboard manufactured by

the Sail Mountain Co., Hamilton, Ohio. This material was

an admixture of asbestos and other materials. The sheets

measured 33 inches by 4$ inches and were l/£-inch thick.

Galvanized iron ducts of U. S. Gage. No. 30 and aluminum ducts

of B&S Gage No. 26 were studied for deflection when supported at

4-foot intervals.

III. TESTS

A. Water Absorption

Specimens of the Sonoair duct and the Sal-Mo ductboard were

tested for absorption of water during immersion.

(a) Sonoair duct.

All test pieces that were used in this phase of the study

were circular cross sections of the duct, 3 inches high, £-7/16

inches outer diameter and £ inches inner diameter.

The edges of the test pieces were treated with wax in order to

render them impermeable to water, which allowed the water to come

in contact only with the inner and outer surfaces of the duct

material. The following table is a summary of the results obtained

when test pieces at room temperature were submerged in water of

room temperature after having undergone a pre-conditioning period

at 200°F. All the tests were run in duplicate, test piece numbers

1 and 2.
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Table 1

II

1

HI

I

II

II

II

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II

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fl

R

PERCENT ABSORPTION OF WATER BY SONOAIR DUCT

Length of Pre= Percent Gain in Weight Due to the

Conditioning Absorption of Water during Immersion Periods

Period at 200°F 4 hours 8 hours 24 hours

hours 1 2 Avg : 1 2 Avg : 1 2 Avg

0 27.1 35.4 31.2! 44 * 6 57.2 50.

9

:

. 100.1 95.5 97.8

2 15.2 22.8 19.0: 21.9 30.3 26.1: 49.2 64 .O 560.6

8 24.0 15.9 20 . 0 : 33.6 21.5 27 . 6 : 73.0 56.8 64.9

24 8.8 9.3 9 . 0 : 12.6 11.0 11 . 8 : 32.7 28.9 30.8

The results in Table 1 indicate that heating the specimens to 200°F

before immersion decreased the water absorption. In most cases this

effect was progressive for preheating periods up to 24 hours.

A test was conducted to determine whether the water was being

absorbed through the inner or outer surface of the Sonoair duct.

The lower end of the specimen was sealed with aluminum foil, which

restricted water contact to the outer surface. The water level

was maintained at a height of 2-3/4 inches. The test was made at

room temperature with these observations;

Table 2

Hours of Immersion Weight of Specimen

0 186 .

8

grams

4 187.7

7 188.2

24 189.5

The results indicate that only a small amount of water was absorbed by the outer surface and that most of the absorption indicated by the data in Table 1 occurred through the inside surfaces.

(b) Sal-Mo Ductboard.

Eight specimens measuring approximately 8-1/4 inches by

8-1/4 inches by 1/8 inch thick were used. The edges of the specimens were coated with wax so the water was in contact with only

the two large surfaces. A summary of the results in Table 3 shows

that preheating the specimens had practically no effect on the

amount of water absorbed and that only a small amount of water

was absorbed after the first 4 hours of immersion.

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Table 3

PERCENT ABSORPTION OF WATER BY SAL MO DUCT

Length of Pre- Percent Gain in Weight Due to the

Conditioning Absorption of Water during Immersion Periods

Period at 200°F 4 hours 3 hours 24 hours

hours 1 2 Avg : 1 2 Avg : 1 2 Avg

0 5^.6 59.4 59.0: 61.2 62.2 61.7: 63.0 63.3 63.2

2 53.3 59.3 59.0: 61.8 62.2 62 . 0 : 67.6 63.3 63.2

8 62.5 64 .O 63 . 2 : 64.3 66.3 65.3: 67.3 70.5 63.9

24 61.6 59.4 60 . 5 : 63 .6 61.5 62.5: 67.3 64.7 66 .

0

B. Effect of High Humidityla) Sonoair Duct.

Two specimens of duct 3 inches long were subjected to a relative humidity of 100% at a temperature of 7o°F for 21 days. Dimensions and weight were observed at intervals during the test periods.

The results in Table 4 show small changes in length and thickness of

the specimens during 21 days and an average gain in weight of 1 $

percent

.

Height

.

inches

Table 4

Thicknessi. inches Weight

,

grams

Exposure Specimen Specimen Specimen Specimen Specimen Specimen

Days 1 2 1 2 1 2

0 3 , 3 , 7/32 7/32 163.3 162.0

7 3 - 1/32 3 - 1/32 s/32 8/32 132.2 130.2

14 3

- 1/32 3 - 1/32 9/32 8/32 133.2 137.6

21 3 -1/32 3 - 1/32 9/32 8/32 192.6 190.6

(b) Sal-Mo Ductboard.

Two specimens of this ductobard about 3 inches square were

subjected to a relative humidity of 100% at a temperature of 76°F

for 14 days. Dimensions and weight were observed at intervals during

the test period. The results in Table 5 show that the width and

length increased l/l6 inch during the test period whereas the average increase in weight was 11.5 percent.

- 5 -

Table 5

Length, inches

Exposure Spec, Spec,

Days 1 2

Width , inches

Spec. Spec.

1 2

Thickness , inches Weights, grams

Spec. 12Spec. Spec. 12Spec.

0 8- 1/4 8- 3/16

7 8- 5/16 8- 1/4

14 8- 5/16 8- 1/4

8- 1/4 8- 3/16 1/8

8- 5/16 8- 1/4 1/8

8- 5/16 8- 1/4 1/8

i/a 128.3 123 o 5

i/a 140.1 134*7

1/8 142.5 138.2

C. Delamination during Alternate Heating and Cooling.

(a) Sonoair Duct.

Two test pieces of duct material were alternately heated

for 2 hours at 200°F and then chilled for 2 hours at about 40°F in

a refrigerator. There was no evidence of any change at the end of

the first cycle. At the end of the second cycle a delamination of

1-1/2 inches in length was observed in the outer ply of the spirallywounded paper. Five additional cycles resulted in no further structural change.

The test was repeated under the same conditions except that

the specimen was cooled to room temperature. Similar results were

observed.

(b) Sal-Mo Ductboard.

Two test pieces were alternately heated for 2 hours at 200°F

and then chilled for 2 hours at about 40°F in a refrigerator. There

was no evidence of any delamination or breakdown after seven cycles.

The test was repeated under the same conditions except that the

specimen was cooled to room temperature. Similar results were observed.

D. Mildew Resistance Tests.

Mildew resistance tests were made on five specimens of Sal-Mo

ductboard, identified as samples A and B, and five specimens of

Sonoair duct, identified as samples C and D, by the Organic and

Fibrous Materials Division. The test procedure used, the test results observed, and the conclusions reached are contained in the

following report. Fig. 1 is a photograph of one specimen of each

sample of the duct materials and the cardboard sample used as a

control taken at the conclusion of the 14 day test period. There

was no apparent difference between the five specimens in any one

of the four samples tested.
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Procedure

Specimen . Four samples, consisting of five specimens for

each sample, were submitted for the microbiological test for

mildew resistance. Samples rt A

Tt and TT B

TT were asbestos and cotton

measuring 2" x 6

n with Tt A

tT heated at 100°C for 120 hours. Samples

rr C" and Tt D" were cellulosic ply duct dipped in paraffin measuring

2” x 6" with ,T C

n heated at 100°C for 120 hours. One control of

untreated cardboard was inoculated to test the viability of the

organism.

Culture medium. The substrate was an agar medium containing all of the growth requirements for Chaetomiurn globosum except carbon which the organism got through the breakdown of the

cellulose found in the fibers. The medium was as follows:

Agar 10.00 g

Sodium nitrate 3° 00 g

Dipotassium phosphate 1.00 g

Magnesium sulfate 0.25 g Potassium chloride 0.25 g

Distilled water - to make 1000.00 ml

Forty milliters of the above medium were dispensed into

each of twenty-one 16 oz. French square bottles having screw caps

with fiber glass filters in the tops. These bottles were then

autoclaved for 20 minutes at 121°C, 15 lbs pressure and then each

laid on its side until the agar had cooled and hardened.

Inoculum. 1. Organism - Chaetomiurn globosum, culture

A'TCC 1042.4.

2. Scrapings from a 10-cm Petri dish surface of

a ripe fruiting culture of Chaetomiurn globosum was added to 100

ml of sterile distilled water. The transfer was made with a flamed

platinum wire loop. The spore clusters were squeezed against the

sides of the flask until the spores went into suspension.

Method

.

The specimens and control previously described were

laid flat on the substrate in the bottles and each inoculated with

2 ml of the inoculum which was evenly distributed over the surface

of the specimens. They were then incubated for a period of 14

days at 29°C ($4.2°F) at approximately 90$ relative humidity.

- 7

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Observations

:

Growth

Sample Specimen Treatment Mycelial Reproductive

A 1 Heated 100°C Heavy (1) Slight (3)

Asbestos 2 for 120 hr. Heavy (1) Slight (3)

3 Heavy (1) Slight (3)

4 Heavy (1) Slight (3)

5 Heavy (1) Slight (3)

B 1 Unheated Heavy (1) Slight (3)

Asbestos 2

* Heavy (1) Slight (3)

3 Heavy (1) Slight (3)

4 Heavv (1) Slight (3)

5 Heavy (1) Slight (3)

C 1 Heated 100°C Slight (5) Moderate (3) (4)

Ply Duct 2 for 120 hr. Slight (5) Moderate (3) (4)

Paraffin 3 Slight (5) Moderate ( 3 ) (4)

Dipped 4 Slight (5) Moderate (3) (4)

5 Slight (5) Moderate ( 3 ) ( 4

)

D 1 Unheated None Slight (2) (4)

Ply Duct 2 None Slight (2)(4)

Paraffin 3 None Slight ( 2 ) (4

)

Dipped 4 None Slight (2)(4)

5 None Slight (2) (4)

Control 1 Untreated Moderate Heavy

Cardboard

Note. 1. (1) designates heavy mycelial growth.

2. (2) designates good growth on edges

.

3. (3) designates sparse growth 'on surface.

4. ( 4

)

designates reproductive growth on surface and sides.

5. (5) designates mycelial growth on sides.

Conclusion

.

The observed results indicate a general lack of resistance to mold by the organic substitute duct. This is especially

true of the asbestos samples ,T A

TT and rt B

Tt where ,f B

Tt

, the unheated

sample, showed equally as much mycelial and reproductive growth

as "A”. Samples ,f C

rt and n D

tT differed to a slight degree in the

amount of visible growth present, where rt C’T , the heated sample,

showed the greatest amount. It is reasonable to assume in the

case of ”0” and "Dn that during the process of heating, the

paraffin on n C

TT was broken-down or melted, leaving it susceptible

to attack by the organism.
. III . III*
For the most part, growth on f, C

tr and f, DrT was reproductive

which occurred on the edges and between the layers of duct. This

may indicate that the paraffin did not penetrate the sample completely.

Upon testing the residual strength by breaking the specimens

in the hands, sample tT D

n was the only one which showed any remaining strength comparable to the untreated samples and that was extremely little.

E. Dropping Test.

(a) Sonoair Duct.

Tests were made to simulate rough treatment of ducts which

might occur during shipment or delivery to a construction site

prior to installation. Specimens were dropped from a height of

4 feet to simulate falling from the tailgate of a freight truck.

Four-foot sections were dropped in such a manner that a concrete

pavement was struck flat and at angles of 45° and 90°. Specimens were also dropped upon cinder block and wooden members. At

the conclusion of these tests the ducts were considered to be in

usable condition. The specimen dropped on the edge of a cement

block was not punctured and collars of the same material still

fitted properly.

F. Deformation at Elevated Temperatures.

(a) Sonoair Duct.

Test apparatus was constructed in which the specimen

duct could be exposed to air temperatures simulating those expected during normal or abnormal operation of a forced warm air

heating system.

A recirculating forced warm air heating system was used for

the first part of the test. This system consisted of a blower of

400 cfm capacity, an electric heater mounted in a metal duct, a 4-foot specimen of the $-inch Sonoair duct, and enough galvanized

pipe and elbows to make a closed circuit. The temperature of the

warm air at the center of the specimen duct was measured by means

of a 4-junction averaging thermocouple. A temperature of 200°F

was maintained at this point b^^ thermostatic control. Several

tests were conducted, the longest for a period of 7 hours. No

sagging of the duct along its axis or change in shape of its cross

section could, be observed by means of a steel straight edge. The

duct was removed from the apparatus and examined internally. No

evidence of discoloration or delamination was apparent.

The second part of the test was conducted with still air.

A 4-foot specimen of Sonoair duct was attached to the electric

heater in a vertical position. Temperatures were observed by
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two thermocouples. One was located in air at midheight in the

duct. The second was sealed into the duct wall one inch from

the edge adjacent to the heat source. The specimen was subjected to a temperature of approximately 400°F for one hour. Smoke

appeared at a temperature of approximately 3$0°F. It persisted

for about 5 minutes. During the remainder of the tests no additional smoke was observed. The test was repeated with a duct

covered with a double thickness of rock wool batts. A temperature of 400°F was maintained for 3 hours. The results were similar. At the conclusion of the test the duct, in our opinion,

would be considered serviceable although the duct was darkened

considerably during the tests at 400°F.

G. Odor Test.

The Sonoair duct emitted no strong odor at a temperature

of 250°F.

H. Deformation of Metal Ducts.

Two rectangular metal ducts were constructed for these tests.

One was formed of galvanized iron No. 30 gauge U. S. and the

second was made of 24 S aluminum alloy No. 26 gauge B & S.

The dimensions of the galvanized iron duct were about 11-1/2

inches by 13-1/2 inches whereas the aluminum duct was approximately 12 inches square. The aluminum specimen represented the largest

duct that could be made of 26 gauge aluminum and still comply with

the requirements of NBFU Pamphlet No. 90 for installation of warm

air heating ducts. The galvanized iron duct should have been made

of 23 gauge material to comply with NBFU Pamphlet No. 90.

The principal dimensions of the duct openings were measured

with the specimens unsupported while standing vertically, one

opening resting on the floor. The ducts were then supported in

a horizontal position by two 2-inch boards spaced 4^-inches apart.

The dimensions of the openings were measured under all possible

oritentat ions

.

The maximum dimensional changes observed were galvanized

iron, 3/16 inch or 1.6% and aluminum, 1/4 inch or 2.0^. There was

no visible sagging of either duct at the middle of the 4-foot span.

Table 6

SECTIONAL DIMENSIONS OF METAL DUCTS, INCHES

Duct Position Deformation

Duct Vertical Horizontal in

Material on Floor Max

.

Min. Horizontal Position

galv. iron

galv. iron

13-1/2

11-3/8

13-9/16

n-3/8

13-7/16

11-3/16

± 1/16

+ 3/16 , -0

aluminum

aluminum

12 - 3/3

12-1/4

12-1/2

12-9/32

12-5/16

12.0

+l/8,

+1/32

,

-1/16

-1/4

I. Temperatures in Warm Air Heating Systems

.

A replica of an actual warm air heating system used in some

FHA-insured houses in Newport News, Virginia, was built to determine the temperatures attained in ductwork and on surrounding wood

members under normal full-load operation and under abnormal operating conditions. The system consisted of a coal-burning furnace

with l$-inch combustion chamber, a circulating blower, a warm air

plenum on top of the furnace, an elbow to connect the plenum to the

supply duct, and 6 feet of horizontal metal supply duct. The furnace and supply duct are shown in Fig. 2 and the blower and return

duct connection to the furnace are shown in Fig. 3<> The horizontal

duct was framed with nominal 2-by 2-inch wood members spaced a minimum of 1-inch from the metal duct preparatory to furring the

duct into the ceiling. The wood framing and the ceiling joists

can be seen in Fig. 2, 4, 5, and 6 from several sides of the furnace. Fig. 7 is a photograph of the furnace and duct system after

application of plasterboard to the wood frame and ceiling joists.

Only six feet of metal duct was used because a substitute duct

material was to be used beyond this point, and because information on the temperatures attained in the first six feet of duct

were of special importance in this investigation.

Thermocouples were used to measure air temperatures in the

supply and return system, metal temperatures of the supply duct,

temperatures of wood framing around the supply duct and the temperatures of the flue gases, furnace dome, and furnace jacket near

the top. Temperatures were observed at the several stations during four-hour test periods at each of six test conditions. The

furnace was operated with the flue gas temperature maintained at

about 900°F by damper control and with the dampers wide open for

each of three conditions of air circulation; namely, a blower air

delivery of 350 cfm, gravity circulation of air through the system

with the blower stopped, and with the warm air outlet covered and

the blower stopped.

* A high volatile bituminous coal was used for these tests to

obtain high combustion rates and long flames in the combustion

chamber. The furnace was equipped with about 15 feet of vertical

chimney without a stack damper. At the beginning of each test

with a runaway fire the furnace was refilled with fuel and the

dampers were left wide open while burning the entire charge.

A summary of the principal temperatures observed during these

tests is contained in Table 7. The temperatures summarized are

the maximum temperatures that occurred during each test condition.

The furnace burned from 10 to 12 lb. of coal per hour during

Tests 1-3, inclusive and from 20 to 25 lb. of coal per hour during

Tests 4-6, inclusive. The following significant results are shown

in Table 7:

*r

NBS

DTn

FIG

saN

FIG, 6

L

L

FIG. 7

Table 7

SUMMARY OF RESULTS

TEMPERATURES IN A REPLICA FURNACE AND DUCT SYSTEM

DURING FULL LOAD AND RUNAWAY CONDITIONS

Test No. 1 2 3 4 5 6

Nominal Stack Temp.,°F 900 900 900 Max. Max. Max.

Blower Operation On Off Off On Off Off

Warm Air Supply Outlet Open Open Closed Open Open Closed

Flue Gas Temp. a °F 931 910 913 1470 1525 1175

Jacket Temp. 12” from Top,°F 333 407 370 363 563 652

Furnace Dome Temp. °F 904 335 305 1032 1156 1160

Air Temperatures

Furnace Plenum °F 296 430 530 325 643 783

Horizontal Supply Duct

Entrance °F 277 440 431 305 592 716

Midpoint °F 270 403 365 297 533 601

Outlet °F 269 414 363 295 533 532

Cold Air Return °F 36 37 35 33 90 90

Metal Temp.

Top of Plenum °F 330 452 442 444 636 637

Duct Entrance, Top °F 251 314 332 230 4!2 448

Duct Midpoint, Top °F 242 305 303 264 343b 420

Duct Outlet, Top °F 231 270 272 252 362 368

Wood Framing Temp.

Bottom of Ceiling Joist

near Duct Entrance, °F 192 230 256 220 317 325

Bottom of Ceiling Joist

at Duct Outlet, °F 133 219 230 209 296 289

Top of 2”x2 TT near Duct

entrance, °F 130 192 214 194 242 279 c

Top of 2

Tt x2” at blank end

of Duct, °F 200 243 260 203 344 335

Adjacent Face of 2

Tt x4 T? at

blank end of Duct, °F 135 221 243 220 295 319

a l 8 inches from smoke cellar.

^Thermocouple loose during this test.

cFire started near this thermocouple station on 2x2-inch

member between plenum and duct 20 min. after refiring.
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(a) With the blower running the maximum air temperature in the

horizontal duct was 305 °F, the maximum metal temperature

in the horizontal duct was 2$0°F, and the highest temperature observed on the wood framing was 220°F in Test 4 with

a runaway fire. At the outlet end of the 6-ft. metal duct

the air temperature was 295°F and the metal duct temperature

was 252°F on the top side.

(b) With gravity circulation of air through the system ignition

of the wood was imminent after one firing cycle with a runaway fire, as shoxvn in Test 5. Under these conditions the

maximum air temperature observed in the 6-ft horizontal duct

was 592°F, the maximum metal temperature observed on this

duct was 412°F, and the highest temperature observed on the

wood framing was 344°F, At the outlet end of the 6-ft metal

duct the air temperature was 53$°F and the metal duct temperature was 362°F on the top side.

(c) When the warm air supply outlet was closed (actually covered

with a tight sheet metal cover) as in Test 6, ignition of the

wood occurred within 20 minutes after refiring the furnace.

Test 6 followed immediately after Test 5 without cooling of

the system. The test data indicate that ignition would

probably have occurred almost as soon if the conditions of

Test 5 had been continued for another firing cycle. Ignition

originated on the 2x2-inch framing member located between the

top of the plenum and the bottom of the elbow connecting the

plenum and overhead duct. Presumably, this member was at a higher temperature than those stations at which thermocouples

were located. The fire in the wood members was extinguished

as quickly as possible and the test was terminated. Fig. 3

is a photograph of the charred ceiling joists as .viewed from

above. In this view the plywood sheets that covered the ceiling joists 6n the upper side are propped up to reveal the

burned joists. The stick at the right holding up the plywood

is resting on the metal duct.

The air temperatures and metal temperatures in the plenum and

duct were appreciably higher during the brief duration of Test

6 than during Test 5, but the temperatures on the wood framing

were higher at some stations in Test 6 and lower at others

than for Test 5«

V.' DISCUSSION AND CONCLUSIONS

The above tests provide information on the characteristics

of substitute duct materials which should be considered in developing criteria on water absorption, effect of high humidity,

delamination on alternate heating and cooling, mildew resistance,

FIG

12

resistance to damage from handling, deformation at elevated

temperature, and odor. Criteria were not developed for all

of these characteristics because some were considered unnecessary and others could not be made sufficiently definitive with

present testing procedures.

The tests made with a forced warm air heating system employing a coal-fired furnace and a supply duct system furred

into the ceiling construction showed that a 1-inch spacing of

wood members from the heating duct was not enough -to prevent

ignition when the furnace was operated with the dampers wide

open and the circulation of air was restricted by blower failure or damper closure. These tests also provide information

on the temperatures that £an occur in the duct system and on

the metal and wood surfaces near the furnace during such abnormal conditions.

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.