Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

NATIONAL BUREAU OF STANDARDS REPORT

7327

PRELIMINARY RESULTS

of

EXPERIMENTAL FIRES IN ENCLOSURES

by

Daniel Gross

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publ ications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published iti Outside Journals 1950 to 1959) ($2 .25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-11-10122 August 23, 1961 7327

PRELIMINARY RESULTS

of

EXPERIMENTAL FIRES IN ENCLOSURES

by

Daniel Gross

IMPORTANT NOTICE

NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents

Intended for use within the Government, Before material in the reports Is formally published It Is subjected

to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature

listing of this Report, either In whole or In part, Is not authorbed unless permission Is obtained In writing from

the Office of tho Director, National Bureau of Standards, Washington 25, D. C. Such permission Is not needed,

however, by the Government agency for which the Report has been specifically prepared If that agency wishes

tf* reproduce additional copies for Its own use.

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PRELIMINARY RESULTS

of

EXPERIMENTAL FIRES IN ENCLOSURES

by

Daniel Gross

ABSTRACT

Preliminary results are presented of experimental studies of the burning of fuel within small

enclosure models. It was found that on decreasing

the size of the ventilation opening in the wall of

such an enclosure, not only is the burning rate

varied, but on reaching a critical opening size,

the character of the combustion reaction appears to

be abruptly modified in such a manner as to discontinuously increase the rate of combustion.

Further reductions of opening size result in further

orderly reductions of combustion rate.

Tests have been conducted in which cribs of fiberboard have

been burned in enclosures and the effect on the rate of burning

of the size, shape and position of windows studied. The majority

of tests were performed using a single full width (horizontal) or

full height (vertical) centrally located window in an insulated

steel box. Several tests with off-center and dual-opening windows

were also made. Fiberboard was used because of its rapid flaming

characters tics and the crib was constructed so that the spacing

between sticks was three times the stick width. The test was

started by igniting kerosene-soaked wicks placed In the openings

of the bottom row of sticks. The crib was supported about 3 stick

widths above the enclosure floor and was located between the center

and rear of the box. Weight-time data was obtained by use of a platform balance scale on which the entire assembly was mounted at

least 1/2 meter above the floor level. The rate of burning was

taken as ‘the mean rate of weight loss from 80 to ^ 0% of the original

crib weight. Temperatures were measured at several locations within

the box by means of bare, unshielded No. 24 gage (0.020 in.) chromelalumel thermocouples.
2

The results are summarized in Fig. 1 for a box 50 by 50 by

100 cm and in Fig. 2 for a box approximately 15 by 15 by 30 cm.

Tests are planned for an enclosure approximately 150 by 150 by

300 cm.* It may be observed that for each enclosure, a limiting

value of A /H~ was reached beyond which the window no longer

limited and the rate of burning had a constant value equal (very

nearly) to the rate of burning of the crib in the open. This

point corresponded for the 50 cm box to about 5

% of the box

width for a central vertical window and 60% for a central

horizontal window.

A characteristic transition region was found for each

enclosure in which the data line for small window openings was

shifted upward. The data for this line has been extended to

include extremely small openings where an essentially pyrolytic

reaction was occurring with the absence of visible flaming.

In such cases, repeated and prolonged ignition was required tp

elevate the enclosure temperature to that required for sustaining the pyrolysis.

It is possible to interpret the results in terms of a simple analysis of wood-burning such as that presented by

Kawagoe [l]. From the basic chemistry of cellulose burning

and consideration of fluid flow through an opening, the fuel

combustion rate W was shown to be a function of the coefficient

of discharge C, the opening area A, the effective height of

the opening H, the temperature difference between the enclosure

and the surroundings, and the volume of exhaust gas per unit

weight of fuel G, as fol

G is a function of the temperature in the box T, the

fraction of complete combustion x and the amount of excess air n. The location of the neutral zone determines the effective height

of the opening.

For window openings greater than that at the transition

point, the temperature was practically constant (see Figs. 1

and 2) and there was apparently sufficient (excess) air for

complete combustion. However, for window openings at or below

the transition point, the pattern of burning changed and the

mean temperature within the enclosure decreased with the window

opening. The slope of the line encompassing data below the

transition point adjusted to unity when_the temperature difference correction was applied to the A/H product for the 50 cm box.

G

*Data for two horizontalwindows located at top and bottom

are also included, using for H the full height of the box.
- 3

-

Changes observed during the tests with small window

openings could bring about a considerably lower exhaust gas

volume G compared to those tests with greater window openings*

Below the transition point, the deficiency of air prevented

the maintenance of complete combustion within the crib and

flaming was shifted from within the crib to predominantly in

front of or behind the crib. The flames were also observed

to oscillate or to pulsate strongly between the window and

the crib, sometimes burning exclusively at the window opening.

The imperfect combustion also changed the composition of the

exhaust products. These changes, which were observed at and

below the transition point, serve to reduce the value of G

significantly. Actual measurements of the velocity at the

opening and the changes in exhaust gas composition are planned.

References

[l] Kawagoe, K. Fire Behavior in Rooms, Building Research

Institute Report No. 27, Ministry of Construction, Tokyo,

Japan, Sept. 1958.

USCOMM-NBS-DC
'
FIG, / RATE OF &URN//V

G AlVd TF/VlPER ATC/R

B , SO CM BOX

/NtT/AL Cfc'B tvf-tGHT S/SO <3
RATE Or BUZH/NQ ANb TEMPERATURE , /5 CM Box . //V/T/AL CR/B MSIGHT 2 6 S G

FIG. 2
U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover.

WASHINGTON, D.C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length, Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic 'Physics. Equation of State. Statistical Physics,

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standar Refer- ence Materials. Applied Analytical Research.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Organic and Fibrous Materials. Rubber, Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics. Electrolysis and Metal Deposition.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Crystal Growth. Physical

Properties. Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Bata Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems. Analog Systems,

Applications Engineering.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services. Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research.

Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency ana Time Interval Standards. Electronic Calibration Center. Millimeter-Wave Research,

Microwave Circuit Standards. Radio Systems. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research.

Navigation Systems.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.
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