A UNITO STATES DEPARTMENT OF COMMERCE

PUBLICATION NBS TECHNICAL NOTE 757

The Smoke Density Chamber Method

For Evaluating

The Potential Smoke Generation

Of Building Materials

U.S. IEPARTMENT

OF

COMMERCE

National

Bureau

of Standards

The Smoke Density Chamber Method

For Evaluating the Potential Smoke

Generation of Building Materials

T. G. Lee

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards Washington, D.C. 20234

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of

transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

40* 0F o .

Ku of

**

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary

NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director,

Issued January 1973
National Bureau of Standards Technical Note 757

Nat. Bur. Stand. (U.S.), Tech. Note 757, 20 pages (Jan. 1973) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.46:757). Price 45 cents.
THE SMOKE DENSITY CHAMBER METHOD FOR EVALUATING

THE POTENTIAL SMOKE GENERATION OF EUILDING MATERIALS

T. G. Lee

The paper reviews the Smoke Density Chamber Test

Method and illustrates its use and application to

assess smoke generation of building materials in

fire situations. It shows how test results may

ai3 the Fire Services and code authorities in

evaluating and reducing the potential lightobscuration hazard of smoke in buildings. An

example is given for calculating visibility in

a simplified fire situation involving material

of known smoke generation. The smoke generation of

some common interior finish and construction

materials are given.

Key words: Building Codes; building materials; fire;

Fire Services; smoke; smoke density chamber; smoke

generation; test method; visibility.
The Smoke Density Chamber Method for Evaluating

The Potential Smoke Generation of Building Materials

1. Introduction

There is a well known adage, "where there's smoke, there's fire." Fire

is one of the foremost causes of accidental injury and we suffer the

consequences of its by-product, smoke.

Statistics show that "smoke inhalation" and "asphyxiation" rather than

burn injury cause a majority of the fire fatalities in this country. It

is not accurately known how many people are trapped by decreased visibility due to dense smoke and who eventually succumb to the direct effects

of fire and smoke in the immediate vicinity of the fire. Smoke can also

cause apprehension, panic, or even death to occupants in other parts of

a building because of smoke movement induced by natural convection or by

mechanical ventilating systems. Furthermore, property losses are greatly

increased because smoke also impedes fire fighting efforts. A smoke

logged building often requires venting, in order to clear out smoke and

hot gases. This generally increases the fire severity, but allows the

fire fighting to be accomplished more effectively. The extent of these

difficulties depends on the amount and rate of smoke generation in a given

fire.

The increased use of plastics in coatings insulations, furnishings, and

other materials of construction has changed the type and volume of smoke

2
generated and thereby broadened the fire problem. Chemical treatments

or retardants added to reduce flammability of material may also increase

the smoke generated in a fire.

One way to reduce problems associated with smoke is to provide reliable

and meaningful information on the smoke generation of common materials.

Such data may then be used by building designers, owners, or code

officials in selecting materials of construction and furnishings at

various levels of risk. For example in certain locations where smoke is

critical such as in shafts, heating plant rooms and enclosures, exitways,

duct linings, and filters in air conditioning systems, material of low

smoke potential may be selected.

We have come to understand the concept and the application of fire load ^

in the design of fire resistive walls, columns, and floors. We should

now begin thinking in terms of a smoke load *1 so that a rational building

design will allow control of smoke by automatic venting, dilution, and/or

shaft (i.e. stair and elevator shaft) pressurization in high rise buildings,

Fire load: the total heat which could be liberated by the complete

burnout of combustible materials in a prescribed area. Commonly

expressed in terms of weight of combustibles per square foot of floor area in a compartment on the basis of a calorific value of 8000 Btu/lb,

2 Smoke load: the total smoke which could be liberated by the com- bustion of furnishings and finish materials in a compartment under

prescribed exposure conditions. It may be based on the summation of

the product of specific optical densities and the area of smoke

producing materials associated with a given volume. The specific

optical densities are determined by measurements of sample specimens

in the standardized Smoke Density Chamber.
At the present time very little meaningful data on quantitative smoke

production are available to those who wish to design low-risk facilities

such as nursing homes.

2. Requirements of a Meaningful Test Method

To date, smoke requirements have been used only sparingly; this is due

partly to a lack of knowledge on how to apply smoke limitations, and

partly to a lack of a meaningful test method. The need for a quantitative

means for smoke measurement, based on flaming and nonflaming modes of

exposure was clearly apparent to fire research workers, in both government and private organizations.

The Smoke Density Chamber meets all the following essential requirements

of a good laboratory test method for measuring smoke generation of

materials:

1. It must give relevant and useful results. Exposure

conditions in the test should simulate important and

typical parameters experienced in a real fire. For

example, the amount and rate of smoke generation for

most materials depends on whether the specimen is

exposed to flame or just radiant heating.

2. The method must provide reliable and quantitative

results. The degree of reproducibility (among

laboratories) and repeatability (within a laboratory)
of the test results, determined by interlaboratory

evaluations of the test method, must be acceptable.

3. The method must provide a continuous scale of

measure and have sufficient resolution to cover the

common materials. It should be capable of measuring

the total smoke generated as well as the amount

released over a specified time period.

4. The result must be understandable to various user

groups (Fire Service, code official, architect,

engineer, etc.) and fit the concept of performance

criteria in building code enforcement. A building

designer should be able to use the data to design

for the possible smoke load. He should, for example,

be able to select a material with moderate potential

smoke generation to cover small parts of a room (or its

furnishings), and a material of very low potential

smoke in the rest of the room; so that the total smoke

generation does not exceed some agreed upon limit.

3. The Test Method, Reliability, and Limitation

3.1 The Test Method

The test method, using the Smoke Density Chamber, was developed in 1966

by the Fire Research Section at the National Bureau of Standards (NBS)

for the measurement of smoke potential of solid materials. [1] Several

The original work was supported by the Federal Housing Administration

as part of a technical study of test methods and performance criteria

for wall systems.
TABLE 1

Smoke Generation of Selected Specimens

Thickness Density Smoke (Dm) Specimens inch lb/ft 3 oz/yd Non-Flam. Flaming

Wall & Ceiling Material

Asbestos Cement Board 0.187 125 Gypsum Board (unfinish, paper) 0.375 51 35 10 Plywood 0.17 32 305 45 Fiber Board 0.5 16 230 75 PVC Veneer on Gypsum 0.5 51 109 110 (Veneer) (0.01)

Flooring

Red Oak Flooring 0.75 39 505 300 Vinyl Asbestos Tile 0.062 93 240 325 Polyamide (aromatic) carpet 0.22 49 175 105 Nylon (foam backing) carpet 0.39 86 310 270 Acrylic carpet 0.375 82 470 220

Polymer Sheet

Polyvinyl Chloride 0.01 87 100 Polyvinyl Chloride 0.015 87 210 Polyvinyl Chloride 0.03 87 120 430 Acrylonitrile-Butadiene-Styrene .022 66 188 Acrylonitrile-Butadiene-Styrene .032 66 220 450 Glass Reinforced Polyester .110 48 420 720

Wood

Elm 0.05 40 150 35 Elm 0.125 40 270 Elm 0.185 40 390 65 Elm 0.24 40 510

Insulation

Glass Fiber Insulation 1.0 3.5 25 25 Polystyrene Foam (Rigid) 1.0 1.8 25 390
of the early applications of the Smoke Density Chamber were the measurement of smoke produced by aircraft interior finish materials [1] and the

effect of ventilation on the smoke produced by wood and plastic materials

[2]. References [3] and [4] give the complete theory, construction

details and the test method procedures of the Smoke Density Chamber. The

3 Chamber is an 18 ft closed cabinet in which a specimen three inches

square is supported vertically in a holder and is exposed to heat under

one of two conditions, designated as "flaming" or "nonf laming" (smoldering)

The thickness and mounting of the test specimens should match the end use

(installation) thickness and mounting. For each specimen, the combustion

generated smoke accumulates within the chamber and the reduction of

light transmission during the test is reported in terms of optical

density of the smoke. The principle of smoke measurement in the chamber

is based on application of the law of light absorption through solid or

liquid aerosols commonly referred to as the Beer-Lambert Law [3].

Optical density is the single measurement most characteristic of a

"quantity of smoke." The data from the chamber gives both the maximum

optical density and the rate of increase in optical density during the

test. To simplify use of the test results, however, only the maximum

optical density, D , may be used to estimate the potential smoke

generation of materials in building fires. The range of the instrument

is between and 800 units which adequately covers the D levels for m

most building finish materials.

Table 1 shows the maximum specific optical density of some common

materials under flaming and nonflaming exposure conditions. In general,

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specimens from wood products gave higher smoke values under the nonflaming than under the flaming exposure condition while for solid

plastic materials, the reverse was true.

Although not a part of the smoke density measurement and not discussed

in this paper, the Smoke Density Chamber can also be used for the

simultaneous measurement of the concentration of potentially toxic gases

and vapors

.

3.2 Reliability

The reproducibility of the test result from one laboratory to another

compares favorably with other fire test methods. Several interested

laboratories constructed their own chambers based on the published

drawings and used the method to measure the smoke produced by a variety

of materials [5,6]. This led, in 1970, to the production of a commercial

version of the chamber incorporating a number of refinements by the

American Instrument Company (AMINCO)

.

Twenty-two laboratories (18 with identical AMINCO chambers, four with

"home-made" chambers) have participated in an inter-laboratory evaluation

of the method involving eight common building materials under the prescribed flaming and nonf laming exposure conditions [4], Several

recommendations for procedural changes by the participants were accepted

and are included in the latest test method standard; see Appendix II,

NBS Technical Note 708 [4]. Table 2 shows a summary of these results
including supplemental flaming tests by twelve laboratories. The

median reproducibility (among laboratories) for a variety of materials

under the two exposure conditions was on the order of 8%.

Two standard reference materials to check the performance of the chamber

are available from the Office of Standard Reference Materials, National

Bureau of Standards.

3.3 Limitations

This test, in common with some other fire tests, does not measure an

inherent property or "smoke characteristic" of a material; what the test

does measure is the light obscuration characteristic of smoke generated

by a particular material or assembly (of prescribed density, thickness,

moisture content, etc.) under two stipulated conditions of fire exposure.

At the present time, it is not possible to predict smoke production from

a specimen without testing. For a solid uniform material, the smoke

generated increases proportionally with thickness up to a certain

thickness depending on its density and thermal properties. Specimens

submitted for testing should be identical in all respects including

thickness to that to be used in the field. The test specimen holder

can handle specimens up to one inch thick.

4. How to Use the Data to Estimate Relative Smoke Hazard

In practical situations where no information is available on the disposition of interior finish material in the building, D may be used to

10
estimate the comparative light-obscuration hazard of smoke from burning

different specimens. A simple specification, for example, could require

that the surface finish materials of a room or other space not exceed

a value of D based on the average of flaming and nonflaming exposure

conditions, or alternately based on the higher value. However, to be

accurate, information on the volume of the room or building, and the

size, and type of the material should be used by designers to calculate

the potential smoke load. Consideration should also be given to the

effect of air dilution in the room or building as a basis of estimating

possible smoke levels in the event of fire.

The maximum optical density D is a property of the particular specimen,

its thickness and type of backing. If the identical material were to be

similar exposed in a room, visibility, through the smoke generated in

that room neglecting eye irritation, may be estimated from data

based on the laboratory tests. To do this, we take into account the

three geometrical factors affecting smoke density:

the exposed area of material producing smoke, (A)

Greater area, more smoke;

- the volume of the room in which the smoke is accumulating (V)

- Greater volume, lower density (concentration);

the length of vision path (L)

Greater length, reduced visibility.

11
The estimated density of smoke (D/L) in a room can be calculated from

the (D ) value in the test chamber by the following equation:

D/L = D x A/V Equation (1) m

The relation between visual distance and smoke density is determined

experimentally. Figure 1 is based on data from Jin [7] for smoke of

various types. It represents the visual threshold response for several

observers situated outside the room viewing through a window either a

back-lighted sign or a side illuminated placard. These results show

that for a given smoke density, the visual distance is affected

primarily by the brightness of the sign and only slightly by the

color of the smoke, burning conditions and type of material used. However, other studies have indicated variability in the relationship between

visual distance and smoke density as summarized in the review by McGuire

et al [8]. All of this work has ignored the irritant and lachrymatic

effect that the smoke may have on an occupant located within the room.

The following example shows how data from the Smoke Density Chamber

may be used to estimate the visibility in a hypothetical situation.

3 2 It is desired to estimate the visibility in a 3200 ft room where a 32 ft

area of material is exposed to fire over its entire surface and is the

only material producing smoke. A test specimen of thickness identical

to that of the panel is tested in the Smoke Density Chamber and . the

measured maximum specific optical density (D ) is 100.

12
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\ \ 80 Lux illumination _ \

Illuminated Placard x 40 Lux illumination

J I I

I I

1.3 2 3 4 6 8 10 15 20 30 40 60

VISUAL DISTANCE, ft.

Fig. 1. Smoke Density and Visual Threshold of Signs Based on Data Ref. [7].

13
Substituting these numbers in equation (1) , the smoke concentration

(optical density per unit length) in the room will be:

D/L = 100 x 32/3200 = 1.0 per foot

Though experimental data on visibility in the 1.0 optical density per

foot range was not given by Jin, extrapolation of the curves in Figure 1,

(for illustration purposes) may be used to estimate visibility. D/L = 1.0

corresponds to a visual distance of only 3.5 ft for a back lighted (exit)

sign under a typical light level of 80 lux* (without smoke) and 1.3 ft

for a side illuminated placard under a light level of 40 lux.

However if the smoke were diluted from the room by natural convection

due to stack effect or by a forced air ventilating system into the whole

3 building with a volume of 45,000 ft , the smoke concentration assuming

no losses will be:

D/L = 100 x 32/45,000 = .071 per foot

From Figure 1, D/L = .071 corresponds to a threshold visual distance of

about 50 ft for the back lighted (exit) sign and about 18 ft for the side

illuminated placard under the same lighting conditions.

5. How the Smoke Density Chamber Can Aid

the Fire Services and Building Code Officials

The Fire Services in various jurisdictions have realized the critical

nature of the problem of smoke in high density public occupancy buildings

* NFPA No. 101-1970 standard for exit sign calls for a minimum of 5 footcandle or approximately 54 lux on the illuminated surface.

14
such as nursing homes, apartment buildings, and hotels. Some jurisdictions have enacted ordinances for its control. The Smoke Density

Chamber is offered as a tool to evaluate the potential smoke generation

which may occur in a room, a corridor, or a building caused by either

surface finishes or by contents.

A test method based on the use of the Smoke Density Chamber has been

submitted to ASTM for consideration and possible promulgation as a

voluntary standard. At the present time over 70 chambers of the commercial type are being used by industrial, research and testing

laboratories in this country and abroad. The following commercial

testing laboratories have reported that they can provide the test

service for the public:

American Instrument Company

Silver Spring, Maryland 20910

Underwriters' Laboratories, Inc. Northbrook, Illinois 60062

Southwest Research Institute

San Antonio, Texas 78228

U. S. Testing Company

Hoboken, New Jersey 07030

6. Summary and Conclusion

The Smoke Density Chamber is a method for the measurement of the smoke

generation of materials based on common fire exposure situations. A

large number of industrial and government research laboratories have

used the method to develop information on the smoke generation of a

wide variety of materials. Tests are also being performed by several

15
commercial testing laboratories. Reduction of visibility by smoke

without consideration of its irritant effect may be calculated based on

the results of laboratory tests. The precision of the method has been

determined by inter-laboratory evaluation using typical materials.

Standard reference materials are available for the test calibration.

The concept of the Smoke Density Chamber method is proposed as a suitable

first step in evaluating the production of smoke and as a basis for

future code requirements. Limitation on the use of materials on the basis

of smoke production or smoke load in building may vary, however, depending

on fire experience, type of occupancy, level of risk, and type of built-in

protection used. These factors should be considered in any requirement

to be established.

16
7. References

[1] Gross, Loftus, Lee, and Gray, "Smoke and Gases Produced by Burning

Aircraft Interior Materials," NES Building Science Series BSS 18,

1969.

[2] Gaskill, "Smoke Development in Polymers During Pyrolysis of

Combustion," Journal of Fire and Flammability , 1_, pp. 183-216, 1970.

[3] Gross, Loftus, and Robertson, "A Method for Measuring Smoke from

Burning Materials," ASTM Special Technical Publication STP 422, 1967,

[4] Lee, T. G. , "Interlaboratory Evaluation of Smoke Density Chamber,"

NBS Technical Note 708, December 1971.

[5] Brenden, J. J., "Usefulness of a New Method for Measuring Smoke

Yield from Wood Species and Panel Products," Forest Product Journal

21, pp. 23-28, 1971.

[6] Gaskill and Veith, "Smoke Opacity from Certain Woods and Plastics,"

Fire Technology, 4_, pp. 185-195, 1968.

[7] Jin, T., "Visibility Through Fire Smoke," Report of Fire Research

Institute of Japan 31 33 (1971).

[8] McGuire, Tamura, and Wilson, "Factors in Controlling Smoke in High

Buildings," ASHRAE Symposium: Fire Hazards in Building, pp. 8-13,

January 1970.

• U. S. GOVERNMENT PRINTING OFFICE : 1973—511-322/146

17
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-757

2. Gov't Accession No.3. Recipient's Accession No.

4. TITLE AND SUBTITLE The Smoke Density Chamber Method for Evaluating the

Potential Smoke Generation of Building Materials

5. Publication Date January 1973

6. Performing Organization Code

7. AUTHOR(S) g. Performing Organization T. G. Lee

10. Project/Task/Work Unit No. 9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Gtant No.

12. Sponsoring Organization Name and Address Same as 913. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) The paper reviews the Smoke Density Chamber Test

Method and illustrates its use and application to

assess smoke generation of building materia3-S in

fire situations. It shows how test results may

aid the Fire Services and code authorities in

evaluating and reducing the potential lightobscuration hazrrd of smoke in buildings. An

example is given for calculating visibility In

a simplified fire situation involving material

of known smoke generation. The smoke generation of

some common interior finish and construction materials are given.

"7. KEY WORDS (Alphabetical order, separated by semicolons) . , , . Building materials; fire', fire

services; smokej smoke density chamber; smoke potential; test method;

visibility.

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