rms report has been prepared

for information and record

''purposes and is not to be referenced

NATIONAL BUREAU OF STANDARDS REPORT

8947

A LABORATORY TEST FOR MEASURING SMOKE FROM BURNING MATERIALS

By

&

D. Gross

and

J.J. Loftus

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The 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 standards 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

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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

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

NBS PROJECT

42102-11-4212122

July 29, 1965

NBS REPORT

8947

A LABORATORY TEST FOR MEASURING SMOKE FROM BURNING MATERIALS

by

D. Gross

and

J.J. Loftus

IMPORTANT NOTICE NATIONAL BUREAU OF STA

for use within the Government. E and review. For this reason, the whole or in part, is not authom

Bureau of Standards, Washington

the Report has been specifically p

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

accounting documents intended

jbjected to additional evaluation

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

the Government agency for which

pies tor its own use. <nbj£>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

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.

A LABORATORY TEST FOR MEASURING SMOKE FROM BURNING MATERIALS

by

D*. Gross and JV 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 \ 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 ofoperating 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-f laming) 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.
- 2 -

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 Figs. 1 and 2, openings were provided to

accomodate a photometer (C & 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), and gas and air controls (S & 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 resistant 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

accomodate 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 beard 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 .G83 in. wall by 4-1/8 in. long stainless steel welded sanitary

tube (A), 180 grit polished inside ana 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 asbestoscovered 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. eircle.

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

.
-3-

The control system consists (Fig. 2) of a temperature controller (M) , two autotransformers (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

irradiance 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, approx. 2630 c 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 f loorwwere , , 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 singlestage vacuum photateebe

having an S-4 spectral snesit&vity response. This lens and stop combination

did not permit the receiver to register rays departing fsom parallel by more

than a few degrees, and reducdd to a negligible amount the effectoof the "beam

broadening" caused by smoke particles scattering light from the originaal

beam.

The phototube circuit load comprised theiinput resistance of the recorder

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 lighg transmission could be accommodated 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.
-4-

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. 3B) , the specimen surface l/^inch 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 (conforming to Fed. Spec. 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 stops

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

accurately positioned by placing it on the support bars and sliding the ra- diometer or another holder to the limit of its travel.

E . Radiometer

2

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 a:n 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 compressed 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 spraycoated 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 air-cooled

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 ealorimetrically 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 Co., Inc.

Waukegan, Illinios
-5-

Suggested Test Procedure

All specimens* prepared in the 3-by 3 inch 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 non -combustible base materials or being

tested for their inherent smoke contribution shall be applied to the

smooth surface of 1/4 inch 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 asbestos 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 correspond to the value

used for calibration. Adjust the controller temperature setting to produce

^ a millivolt output of the radiometer corresponding 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.
- 6

-

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 conditions in the chamber, making the

appropriate meter range changes. Clean the glass windows (ethyl alcohol

generally 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. It 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 meterial 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).

2

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.
- 7

-

The reduction in the light transmission caused by smoke in the photometer

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:

D

1L

(log

10

100

T

SncA L- where T is the percent transmission 3 ft.

path

.

is the length of the optical

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

(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)

.
6. References

D, Gross, J.J. Loftus, and R. Harris, "Wall Gladding Materials:

Smoke Production Measurements Under Simulated Fire Conditions"

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

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
Fig. 1 - Smoke Test Chamber

FIG. 2 - SMOKE CHAMBER ASSEMBLY

FIG. 3A-FURNACE SECTION

FIG.

3BFURNACE

SUPPORT

U38VWHD JO ON3 dJMOig

>

coo

o

cr

cr

Ixl CO

<rx

o

crUJ

CD ~ <r 0

X 5^

1 fe

< 3 2 X O h- to 2

o

FIG 4

-

PHOTOMETER

DETAILS

HOLES

(6)

V-|co

rO J 3V

_JLU

LlJ I-U)<O QO

cro<

t- -loo^

crUJ<

t-UJ

cruUJ

CLCD

_l 3 < 2

tCT)

FIG.

5-

DETAILS

OF

SPECIMEN

HOLDER

AND

PILOT

BURNER

U1<

fLUQ

crLU

hLU0O<

cr1 (X) d

0

0.5

1.0

1.5

2.0

2.5

3.0

IRRADIANCE

,

WATTS

/cm

2

FIG.7-

RADIOMETER

CALIBRATION

CURVE