NATIONAL BUREAU OF STANDARDS REPORT

6531

EXTINGUISHMENT EFFECTIVENESS

OF

SOME POWDERED MATERIALS ON HYDROCARBON FIRES

by

T. G. Lee and A. F. Robertson

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

upe pDAirrT

1002-12-104-21 September 8, 1959

EXTINGUISHMENT EFFECTIVENESS

of

SOME POWDERED MATERIALS ON HYDROCARBON

by

T. G. Lee and A. F. Robertson

for

Bureau of Ships

Department of the Navy

Code 538

Index Number NS-183-001

IMPORTANT NOTICE

NATIONAL BUREAU OF STANDAr

intended for use yvithin the Goverr

to additional evaluation and review,

listing of this Report, either in who

the Office of the Director, National however, by the Government agenc

to reproduce additional copies for

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBS REPORT

6531

FIRES

s accounting documents

published it is subjected

uction, or open-literature obtained in writing from

jermission is not needed, ed if that agency wishes

EXTINGUISHMENT EFFECTIVENESS

of

SOME POWDERED MATERIALS ON HYDROCARBON FIRES

•ABSTRACT

Laboratory methods are described for evaluating the effectiveness

of powdered materials in extinguishing liquid hydrocarbon fires. These

methods employ fire models 1 1/8- , 6-, and 22 3/A-in. diameter together

with special equipment for controlled application of powder to the model

fires o Extinguishment effectiveness was measured in terms of the minimum application rate required for extinction. The methods described

were used to evaluate four different powdered materials of controlled

particle sizes. Four additional materials were studied with the small

model alone. The extinguishment effectiveness of the powders tested

was found to depend upon (1) chemical nature (2) specific surface, and

(3) particle size of the powder. On a surface-area basis, the most

effective materials studied , potassium oxalate monohydrate and potassium

iodide, were about four and two-and-one-half times, respectively as

effective as sodium bicarbonate, the commonly used extinguishing agent.

The relative effectiveness of different powders did not change

appreciably from one fire model to another. For a given powder and

method of application, minimum application rate (surface-area basis),

required for extinction of diffusion fires appears to be nearly proportional to the liquid burning rate of the fire model. Limited extinguishment data on large-scale fires of other workers seems to confirm the

usefulness of the model method for evaluating powder effectiveness.

1. INTRODUCTION

In the search for a better understanding of the mechanism of action

of powder-type extinguishing agents when used on burning liquids, a method has been needed to evaluate the effectiveness of various powders.

This paper describes methods that have been developed for such evaluation,

and presents results on several powdered agents, some of which were found

superior to the powders now commonly used.

Following recent expiration of the patent rights covering dry chemical

extinguishers, devices of this type havef because of their relatively high

efficiency, found increasing use for control of flammable liquid fires.

The extinguishing agent commonly used consists of about 96-98 per cent

sodium bicarbonate in the form of a crystalline powder (0 to 50 micron

2

particle size), and a coating agent to improve free flow. It is discharged from containers varying in size from 2 to 1000-lb capacity by

means of a compressed gas.

A review of literature in the field of combustion and flame extinction indicates the possibility of improving the effectiveness of powdered

extinguishing agents <, Although the mechanism by which powders extinguish

flames is not well understood, it apparently involves breaking of chemical

chain reactions by ions, and quenching by cold surfaces, as well as

possible inerting by gases formed through decomposition. The ability of

alkali halides to suppress gas explosions and to change the explosionlimit pressures of hydrogen-oxygen reaction has been studied by Hinshelwood and Willbourn. /l,2/*. Work by Jorissen, Snidders, and Vink/

-//,

and more recently by Dolan and Dempster/""47, on ignition and explosion

suppression of the methane-air system showed that the specific chemical

nature as well as the specific surface of_the salt determines its effectiveness® Duffaisse, LeBras, and German/ /7, observed wide variations

in salt effectiveness on small flames burning on premixed gases.

Excellent reviews of the problem with literature compilations are given

by Fryburg and by Friedman and Levy/7,7 & 8/. In general, the alkali

salts with low decomposition temperatures were the most effective of

those reported for inhibiting combustion reactions.

If these conclusions are applicable to full-scale (greater than 9 ft 2

) gasoline fires, an improvement in the effectiveness of the present-day dry

chemical (NaHCC^) extinguisher by a factor of four or five is a distinct

possibility. However, in extinguishing large-scale, free-burning liquid

hydrocarbon fires, numerous factors are involved that do not appear in

small flames burning premixed gases. For example, the problem of dispersing the powder and maintaining a sufficient concentration of powder in

the flame zone is a critical one. No studies are available on the influence of such factors as chemical composition, particle size, discharge

rate, and nozzle shape on extinction effectiveness. Nozzle shape of

recent portable extinguisher models vary from a circular opening to a long, narrow slit, from diverging discharge to straight stream, depending,

apparently, only on preference of the manufacturer.

McCamy, Shoub, and Lee/

-/7have reported the use of salts other than

NaHC03 on field-scale fires. They indicate, qualitatively, that for a heptane fire burning on a 4 x 4- ft area, particle size and dispersibility

of the powders influence their effectivenessj_ The powders used were

mainly inert and poorly dispersible. Neill/107, recently reported that

KHCO3 is about twice as effective as Dry Chemical (NaHC03)on 3 ft square fires

when applied at minimum critical rates. For fires up to 10ft square with

powder application at a given constant rate, the same order of effectiveness held for extinguishment on an area basis.

*Figures in brackets indicate literature reference at the end of this text.

- 3

-

Obviously, only a slight improvement in extinguisher effectiveness

may provide the difference between success and failure in controlling a

fire. Thus, a reliable laboratory method is needed to measure the

extinguishment effectiveness of powders and to evaluate the factors upon

which this effectiveness is based. A good method should be^small-scale

one but should give reproducible results that can be correlated with those

of much larger fires. The methods described in this paper appear to meet

these requirements. These involve the extinguishing of liquid heptane fire

models of 1 .1/8- , 6-, and 22 3/4-in. diameter.

A measure of the effectiveness of any extinguishing agent can be

obtained from (1) the minimum rate of application required to extinguish a

standard fire, or (2) the time required for extinction under a given rate

of application to a standard fire. The first method forms the basis of

reporting efficiency here although both types of measurements were made.

2. MATERIALS INVESTIGATED

Table 1 lists the powdered materials that were tested and the preparatory treatment they received. All powder samples, with the exception of

glass beads and dry chemical, were made from reagent-grade chemicals by

grinding in a pebble mill. Two per cent of zinc stearate was added before

grinding to most samples to improve their free-flow properties and to

reduce moisture absorption. The powders were separated into fairly narrow

fractions according to particle size by sieving and air elutriation. Beyond

this, no definite tolerance was placed on particle size distribution.

Measurement of particle size distribution of some samples by microscopic

method showed that the cutoff was sharp on the large particle side of the

distribution curve. Mean particle size was measured with a Fisher Subsieve

Sizer based on the air permeability principle. The glass beads used were

spherical and had a very narrow particle-size distribution.

3. EXPERIMENTAL PROCEDURES

3.1 One-inch Diameter Fire Model

The procedure used with the 1 1/8-in. diameter fire model was simple

in principle and required only about 0.5g of powder for each run. Powder

was dispersed in the air at a controlled rate while a small diffusion flame,

supported by n-heptane liquid in a cup, was slowly introduced into the

freely falling powder stream. Various rates of powder discharge were used

to determine the minimum effective rate that would cause extinction.

Figure 1 shows the essential features of the apparatus. The dispenser

consisted of a cylinder containing a stainless steel screen at mid-height

to support the powder. The rate of discharge of powder was controlled by

adjusting the amplitude of an electromechanical vibrator. A brass cup with

an inside diameter of 1 1/8 in. was used as a burner. In use, the cup contained 1.0 ml of n-heptane floated on 3»0 ml of water, with fuel surface

initially about 1/32 in. below the rim.

- 4 -

The burner was placed on a flat carriage which moved at a uniform

velocity of 1.9 in. /sec toward the powder stream. An identical but

empty cup was placed on the carriage 2 in. ahead of the burner cup.

The weight of powder collected in this cup served as a measure of discharge rate. A recording densitometer monitored the discharge stream

for variation in the rate of discharge® The entire apparatus was enclosed in a draft-free cabinet. The fuel was ignited by a spark discharge and the flame was allowed to burn 35 sec before the carriage

moved it into contact with the falling powder stream. At leas^’ 20 runs

were made with each powder sample.

3.2 Six-Inch Diameter Fire Model

For the 6-in. diameter fire model, powder was propelled by air into

a flame burning in a circular, stationary pan (Fig. 2). The powder dispenser involved use of a serrated rotor within a housing. Powder was

fed to the jnoving rotor from a hopper at the top of the housing. A

high-pressure stream of air directed through the bottom of the housing

stripped the powder from the rotor serrations and carried it out through

a nozzle. The powder discharge rate was governed by the speed of the

rotor. In this way, uniform, reproducible discharge rates were obtained.

A solenoid-operated powder diverter, through which the powder was

removed by means of a vacuum system, was used to limit the duration

of powder application and was found necessary to reduce the effect of

starting and stopping transients. Timing was controlled by a clock-driven

stepping switch.

For the purpose of measuring the rate of powder discharge, the

diverter was fitted with a cellulose filter thimble and used to collect

powder for a measured period of 2 to 3 sec. The average discharge rate

for a given dispenser speed was then calculated from the weight of powder

collected in the filter and the time period of collection.

The flame was supported by 30 ml of n-heptane floating on water in

a brass cup having an inside diameter of 6 in. A 12-in. diameter horizontal flange attached to the rim of this container was found desirable

in stabilizing the flame. A distance of 1/8- in. was left between the

fuel surface and the top of the flange. The flame was allowed to burn

for 45 sec before the powder was applied.

Compressed air at a flow rate of about 1 ft^/min was used to propel

the powder. The powder was first discharged into the diverter for about

3 sec’ before it was directed into the fire. The distance from the

nozzle to the center of the pan was l4.5 in*.

The powder was aimed parallel to and slightly above the surface of

the pan and flange. The nozzle provided a horizontally flat and diverging

discharge pattern. The cross section of discharge was about 6 in. wide

and 1 in. thick at the reagion near the fire. In reporting powder

- 5

-

application rates for the two large fire models no correction has been

made for powder which did not enter the fire zone during application.

During each series of runs the discharge rate was varied stepwise

from one run to the next and the time for extinction was determined in

each case. As the discharge rate was decreased, the extinction time

increased until a minimum discharge rate was obtained, below which

extinction did not occur. Extinction time was taken as the period between

arrival of powder at the flame and the time when the flame had decayed to

20 per cent of its initial value as recorded by a lead sulphide infrared

detector located behind the fire.

3*3 Twenty-three Inch Diameter Fire Model

The apparatus and procedure for the 22 3A-in. diameter fire model

were similar to those used with the 6-in. model except:

$ (1) The distance from the nozzle to the center of the fire was 36 in.

(2) The air flow rate was about 7 ft-Vmin providing a discharge

cross section of about 26 x 4 in. at the center and above the

fuel pan.

(3) A flange of 37 in. diameter was used around the top of the fuel

pan.

(4) A freeboard of 1/2-in. was used above the fuel surface.

(5) Three hundred ml of practical heptanes (Eastman Kodak P-2215)

was used as the fuel.

(6) A preburn period of 30 seconds was used.

Figure 3 shows the equipment being used for extinguishment of this

large fire model. The photometers were not being used when this photograph was made.

4, RESULTS

4.1 One- Inch Diameter Model

Figure 4 presents data on minimum rate of powder application for

extinguishment of the smallest fire model by various powders as related

to mean particle size. Each point is plotted as a cross in which the

vertical line represents the region of overlap where both extinction and

non-extinction results occurred during the 20 runs. All runs at discharge

pates above the top of the vertical line resulted in extinction^^&ift nonextihctjLons occurred belch/ ifhe lower end of the line-,. The point at which

the horizontal and vertical lines intersect indicates the best value for

the minimum effective rate as determined by a statistical formula developed

by C. S. McCamy /Il7.

- 6 -

This formula may be stated as follows:

Wm

= a + —2— (b-a) 111 x+y

where

x = H (Wn

-a)

,

a<Wn <b

y

= hJL- 1 (b-We ), a<We <b

and, Wm = minimum effective rate

^e = rate at which extinction occurred

wn = rate at which non-extinction occurred

a = rate at or below which there were no extinctions

b = rate at or above which there were no non-extinctions

j = number of non-extinctions in interval between a and b

k = number of extinctions in interval between a and b

The values of a and b were experimentally determined and, in this case,

were based upon 20 runs. All data were on a weight basis.

Hird and Gregsten/l27have shown that extinguishment behavior of

NaHCOo powders of different sizes may be largely correlated when presented

in terms of surface area of the powder particles. Accordingly, the curves

of Figure have been converted to a surface area basis on the assumption

that the particles are spherical in shape and the Fisher Subsieve Sizer

measurements are applicable. The resulting curves are presented in

Figure 5«

It will be evident on inspection of this figure that properties

other than surface area are important in determining effectiveness of the

powders used. During the experiments it was observed that particles on

the order of 5 micron or less were lifted by the hot gases above the

fuel and in some instances this effect prevented extinguishment from

taking place. The differences observed between the NaHC03 and "dry

chemical" curves may be a result of dispersibility and particle shape

differences perhaps resulting from different preparation techniques/137.

Figure 6 shows the effectiveness of mixtures of 22-u glass beads

and 8-p potassium oxalate monohydrate at various weight ratios. The

experimental results are plotted as crosses in which the horizontal and

vertical lines have the same significance as in Figure 4. These plotted

results may be compared with the curve shown, which was calculated from

the minimum effective extinguishment rate for 100 per cent 8-^a oxalate

on the assumption that the glass beads have no effect in extinguishing

the fire. (Thus, for example, the calculated minimum effective rate

for the 50-50 mixture is twice that for the 100 per cent oxalate).

These results seem indicative that an inert carrier with larger mass

could be used to introduce a finely divided and chemically effective

agent into the desired zone of the flame. Due to surface forces, the

fine particles adhere firmly to the carrier, at least prior to its

introduction into the flame. The higher momentum acquired by the much

larger mass of the carrier would be able to overcome the buoyant forces

created by upward draft above the combustion zone.
• .
- 7

-

4.2 Six and Twenty-three Inch Diameter Fire Models

Figures 7 and 8 show the time to extinguishment as a function of

application rate expressed on a surface-area basis. Various powders were

used in these tests with 6-in. and 23-in. model fires. To avoid overcrowding, the plotted points in Figure 7 are shown only for the sodium

bicarbonate curve. In general, these data seem similar to those of

Hird and Gregsten /T27 and show that for a given powder, extinction

time increases as the discharge rate decreases. Eventually, the point

of non-extinction is reached. At very high discharge rates it appears

that the extinction time approaches a constant.

Table 2 presents summary results for the three fire model studies

and each of the four powders tested. The results are presented in terms

of minimum powder application rate on a surface-area basis, as well as

in relative application rates with reference to NaHC 03 as a reference

material. Also shown is the fuel burning rate for each of the fires

used. This latter shows fuel consumption rates roughly 60 per cent of

those reported by Blinov and Khudiakov Zl47 for gasoline burning in

deep fuel pans. Whetn minimum NaHCCh application rates are divided by

fuel consumption rates, the quotient is found to vary by a factor of

2.7 over the very wide range of fire sizes.

5. DISCUSSION

The results show that the fire extinguishing effectiveness of the

powders tested depends on the physical and chemical nature of the powder.

Thus, potassium oxalate monohydrate was more effective than sodium

bicarbonate or potassium bicarbonate in all three models; and potassium

iodide was about 2.5 times as effective as sodium bicarbonate in the

two larger models on surface-area basis. However, the relative effectiveness appears to be somewhat influenced by method of powder application.

It was also found that, within a limited range of particle sizes,

extinguishment effectiveness is a function of specific surface of the

powder. For particles of smaller or greater size, buoyant or gravitational forces may limit their introduction and retention in the flame

zone.

Figure 5 shows that, for a given powder, an optimum range of particle

sizes exists for which the minimum powder application rate is effective

for control of the 1 1/8 in. fire model. This range is between 15 and

20 microns for many of the powders tested. Although sufficient data were

not obtained to confirm the existence of this behavior in the larger fires,

a somewhat similar effect should be assumed. In this 1 1/8 in. model,

powder particles approach the flame at or below the terminal velocity of

free fall. Hence, the extinguishing behavior of the powders may be more

sensitive to particle size, shape, and density than in the other models

8

where powder was propelled into the fire. The higher density of KI for

example, appears to improve its effectiveness in this model. As particle

size increases above the optimum, residence time in the flame zone

shortens, the surfaces may not attain the decomposition temperature, and/or

the total heat absorbed is less, thus lowering the efficiency. The

generally flat shape of the potassium oxalate curve over a wide particle

size range and for the smallest fire model may provide an indication of

more rapid extinguishment action than achieved with bicarbonate salts.

One method of overcoming the poor physical behavior of fine powders

is to employ a carrier to introduce a very finely divided yet chemically

effective material into the flame zone. Reference to Figures b and 6

shows that a mixture consisting of glass beads and only 8 per cent 8-u

potassium oxalate could be considered equivalent to the normally used

22~u dry chemical. Besides increasing effectiveness, proper use of a

carrier may reduce toxicity hazards.

Figures 7 and 8 provide a good illustration of the need for use of

minimum application rates in measuring relative effectiveness of different

agents. Thus, it would be difficult to distinguish between effectiveness

of different powders in the field if high discharge rates were used which

resulted in extinguishment times being close to the minimum shown in

these figures.

Individual points on Figures 7 and 8, and vertical lines on Figures 4

and 6 indicate the magnitude of the error. Since the methods developed

are primarily for comparative evaluation, no ^analysis of error was made.

However, the discharge reproducibility of the rotor dispenser, as

measured at the nozzle, was within 3 per cent for all free-flowing powders used.

Table 2 presents results on the ratio of NaHCCb application rate

to fuel combustion rate. Similar results for the other powders could

have been presented. While this ratio does not appear to be a constant,

the range within which it varies is on the order of 2.7 for all the

powders studied. It thus becomes evident that in spite of the very wide

range of fire sizes and powder application rates used there appears to be

no drastic change in the character of the fire or the mechanism of

extinguishment. It thus appears that the minimum powder application rate

required for extinguishment is roughly proportional to the rate of fuel

consumption.

This latter fact may perhaps be more clearly illustrated by the data

shown in Figure 9» Here the extent to which the burning rate curve is

parallel to the minimum application rate data served to indicate the

degree of proportionality.

- 9

-

In considering these results, it should be remembered that different techniques were used for powder application. For the 1 1/8-in.

model, powder was applied to the flame under a condition of free fall.

For the 6-in. and 23-in. models, powder particles were carried by a

propelling air stream, discharged from a fixed nozzle. For the 3-ft

square pan indoor, and the 10-ft square outdoor gasoline fire, Neill/lO/

used an especially adapted commercial extinguisher and attacked the

fire manually by sweepingr from side to side. Hird and Gregsten/l27

used a fixed nozzle to cover the fire area together with a modified comr

mercial extinguisher. Their fire was supplied by a 1 1/2-in. layer

of gasoline in a 3-ft square pan involving a 1/2-in. freeboard.

Neill's results on extinguishment of gasoline fires shown in

Figure 9 seem to present a reasonable extrapolation of our results.

In plotting these data it was assumed that they could be shown as applicable to fires on circular pans having an equivalent surface area.

Neill/l07 did not mention specific surface in his paper, but found,

later, that the NaHCC>3 powder had 1750 cm2 /gr /T27. Specific surface

for the KHCO

3 was assumed to be the same on the basis of his results of

sieve analysis. The extent of agreement between the two sets of results

is encouraging especially when consideration is given to the differences

in powder application techniques and the many other variables involved.

The higher application rates apparently required for Hird and

Gregsten's experiments may have resulted from the need to cool the

2 l72 in. rim of the fuel container below the flash temperature of the

fuel air vapors.

The methods described have been shown to be effective in evaluation

of different powder extinguishing agents when applied to flammable

liquid fires. It is not known to what extent these measurement techniques will be applicable to very large fires although the work of Neill

seems to indicate the possibility of such use. For study of second

order effect, variables such as air velocity, powder concentration and

particle size distribution must be more closely controlled than was

possible in the work described.

6 . SUMMARY

Laboratory methods have been developed to evaluate the fire extinguishment effectiveness of powdered materials. These methods

employed 1 1/8-in. , 6-in. , and 22 3A-in. fire models resembling the

free burning of a liquid hydrocarbon. Dispensers which permitted controlled application of powder to the fire were designed and used for

the evaluation.
—

-
10

The extinguishment effectiveness of various materials was determined by measuring the minimum rate of powder application required for

extinction. The effectiveness of a powder was found to depend on

(1) the chemical nature, (2) the specific surface and (3) particle size

of the powder.

The most effective material studied was potassium oxalate monohydrate. It was about four times more effective than sodium bicarbonate

of optimum particle size, the commonly used extinguishing agent. On a surface-area basis, when using the 1 1/8-in. fire model, particle sizes

between 15- and 20-^u were generally most efficient.

There was found to be a correlation close to proportionality between fuel burning rate in a model and the minimum powder discharge

rate required to extinguish it. Limited extinguishment data on largescale fires of other workers seems to confirm the usefulness of the

model method for evaluating powder effectiveness.

ACKNOWLEDGMENT

The work reported here was made possible by financial support from

the U. S. Navy, Bureau of Ships.

- 11

REFERENCES

1. Hinshelwood, C, N. , Proc. Roy. Soc., London, A 188, 1-9 (1946),

"The More Recent Work on the Reaction Between Hydrogen and Oxygen."

2. Willbourn, A, S., and Hinshelwood, C. N. , Proc. Roy. Soc. London,

A 185, 376-80 (1946), "The Mechanism of the Hydrogen- Oxygen

Reaction. III. The Influence of Salts,"

3. Jorissen, W. P., Snidders, H. G. , and Vink, H. J. , Rec. Trav. Chim.

22 957-962 (195-0).

5,

Dolan, J. E., and Dempster, P. B. , J. Appl. Chem. , 2> 510-517 (1955)*

"The Suppression of Methane-Air Ignition by Fine Powders."

5. Dufraisse, C., LeBras, J., and German, M. , Compt. rend., 235, 164-7

(1953) • "Extinguishing Powers of Powders in Flames and Explosions."

6. Fryburg, G., NACA Technical Note 2102. May 1950, "Review of Literature Pertinent to Fire Extinguishing Agents and to Basic Mechanism

Involved in Their Action."

7. Friedman, R., Levy, J. B, , Wright Air Development Command, Technical

Report 58-568, Jan. 1957, Wright-Patterson Air Force Base, Ohio,

"“Survey of Fundamental Knowledge of Mechanism of Action of FlameExtinguishing Agents."

8. Friedmpn, R. , Levy, J. B, , Wright Air Development Command,. Technical

Report 56-568 Supplement I, September 1958 Wright Patterson Air Force

Base, Ohio, "Survey of Fundamental Knowldedge of Mechanism of Action

of Flame Extinguishing Agents: First Supplementary Report."

9. McCamy, C. S. , Shoub, H. , and Lee, T, G. Sixth Symposium (International)

on Combustion, Rheinhold Pub. Co. New York 1957*

10.

Neill, R. R. , Naval Research Laboratory Report 5183, Aug. 21, 1958,

"The Hydrocarbon Flame Extinguishing Efficiencies of Sodium and

Potassium Bicarbonate Powders."

LI, McCamy, C. S. , private communication.

L2. Hird, D. , Gregsten, M. J. , Fire Protection Review, November 1956.

12

13. Scheichl, L., VFDB Zeitschrift V6N3, 111-112 1957 Arten, Wirkungesweise und Anwendungsgrenzen von Trockenloschpulver (Types, Mode of

Action and Limits of Applicability of Dry Fire-Extinguishing Powder).

£-.?viy

lb, Blivov, V.l. and Khudiakov,/vAkademiia Nauk, SSSR Doklady V113, 109^-7,

1957 (Certain Laws Governing Diffusive Burning of Liquids).

15. Neill, R. R. private communication.

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CO £ P P £ P 0

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cd 0 0 0 o o 0

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TABLE

2.

Minimum

Effective

Rates

of

Powder

Application

and

Rates

of

Fuel

Consumption

for

Various

Fire

Sizes

and

Powder

Types

in

Average

Size

Range

of

6-12

Microns

Eho

SC •H o o P

•H •H

a P POP a

cd

O cd

p ro PO PO PO PO

B o o U) a o o o o o

IB P Eh o 1—1 r—1 1—1 1—1 1—1 CD cd H O \ P B a O 1—1 X X X X X

cd

p

PC i—1

to 1—1

PO PO

CD » * » » • P CO 1—1

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B 1—1

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po

CD -P

rtS PC o

C\J oOB o^ -J ob

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CM BB

PO oo

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po ooBB

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CM

p

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a o a •H • • *

cd

B i—1 NO CM o

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Data

shown

are

for

20-yb_p

article

size

powders

**

Data

from

reference

/!§./

bO •H

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for

evaluating

the

fire

extinction

efficiency

of

powders

using

the

1

1/8-in.

fire

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infrared

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RATE

OF

FUEL

CONSUMPTION,

ml/sec

Fig. 9« Bate of fuel consumption and minimum rate of powder application

for extinction of fires of different diametersRATE

OF

POWDER

APPLICATION,

cm

/sec

U.S. DEPARTMENT OF COMMERCE

FmlnicW II. Mueller, Seerelury NATIONAL 1IUREAU OF STANDARDS

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

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

laboratories in 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 and Electronics. Resistance and Reactance. Electron Devices. • Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic Technology.

Length. Engineering Metrology. Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances. Mechanics. Sound. , Mechanical Instruments. Fluid Mechanics. Engineering Mechanics, Mass and Scale. Capacity, Density, and Fluid Meters. 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.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering.* Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction.

; Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earlh'Rclalionshipa. VII F Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic, Propagation.

Radio Propagat ion Engineering. Data Reduction Instrumentation. Modulation Systems. Radio Noise,

tropospheric Measurements. Tropospheric Analysis. Radio Systems Application Engineering. RadioMeteorology. Lower Atmosphere Physics.

Rudio Standards. High Frequency Electrical Standards. Ratlin Broadcast Service. High Frequency lm-

• pcdancc Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Communication and Systems. Low Frequency and Very Low Frequency Research. High fre- quency and Very High frequency Research. Ultra High Frequency and Super High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.