NATIONAL BUREAU OF STANDARDS REPORT

2310

EXTINGUISHMENT EFFICIENCY OF SOME POWDERS

ON GASOLINE FIRES

by

Te G. Lee

and

H. Shoub

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, S^retary

NATIONAL BUREAU OF STANDARDS

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-10-1030 March 2 , 1953 2310

EXTINGUISHMENT EFFICIENCY OF SOl^ POWDERS

ON GASOLINE FIRES

by

T» Go Lee

and

Ho Shoub

The publication, reprli

unless permission Isob 25iD,C, Suchpermli

tally prepared If that

Approved for public release by the

, TWT • IT X r lards, Washington Director of the National Institute ot ^ t hat boon tpocin- Standards and Technology (NIST) ^ for its own use. on October 9, 2015.
"

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'•1, ' ,>!*•';« j’;'- 1" .'4:’, 4’r,''' t''' '^H'' :
EXTINGUISHMENT EFFICIENCY OF SOME POWDERS

ON GASOLINE FIRES

ABSTRACT

Extinguishment efficiency of 12 common

powders on gasoline fires were determined

by visual observations. Tests consisted of

discharging 2 to 2.5 pounds of powder at a

rate of O.h to 0.5 Ib/sec into by 4-ft

,

free-surface , gasoline fires. Several pow~

ders tested were able to extinguish the fire.

Free flowing, 325 mesh NaHCO^ and KHCO^ had

the highest extinguishment efficiency.

Extinguishment efficiency seemed to

depend primarily on particle size and powder dispersibility. The nature of the

powder itself showed some influence on its

behavior as an extinguishing agent.

1. INTRODUCTION

The advent of dry-chemical powder fire extinguishers

into the market and their outstanding effectiveness on

gasoline fires have stimulated discussions as to the mechanism by which they operate. An early and still advanced

theory attributed their effectiveness to the process of

an inerting-gas effect (1 )? (2 )

,

it held that the CO2 and

H2O gases released from the decomposition of the powder

particles (NaHCO^) as a result of heating in the fire,

would inert the atmosphere in and around the fire. The

momentarily suspended particles in the fire together with

the expanding inert gases released by the particles, would

effectively block further diffusion of oxygen to the

flammable vapor.
- 2 ~

That theory was challenged recently on the ground that

the transit time of particles passing through the fire was

insufficient to allow them to reach their decomposition ternperature of 270° c3 )lhe actual percentage of decomposition

of NaHC03 discharged from a dry-chemical extinguisher onto

a free-surface gasoline fire, using established fire-fighting

methods, was recently measured here. The decomposed powder

was found to be less than of the discharged powder.

Others have obtained an average of 20^ decomposition. Even

assuming total decomposition, the inert gases released by

NaHC03 would be only one-tenth as much as that required to

extinguish a given fire by use of conventional CO 2 extinguishers. Both the cooling and inerting effect have been

considered as the mechanism in the conventional COp extlnguisner.

One of the other possible theories which might explain

the effectiveness of this extinguishing material is based on

the radiant-heat absorption and scattering characteristics

of the powder. It emphasized the fact that the surface area

of the powder exceeds 1000 ft^/lb. ^5) With continuous powder

application to a fire, a point may be reached where all combustible gases are cooled below their ignition temperature.

In addition to the cooling effect, the powder would greatly

reduce the radiant heat transfer from the burning gas downward to the fuel surface, thus reducing the evaporation rate.

Another possible reason for the effectiveness may result

from a negative catalytic effect. Sodium bicarbonate may be

considered as a salt of high chain-breaking efficiency. Such

a powder is likely to inhibit the chain-branching reaction of

hydrocarbon combustion by adsorbing the intermediate products.

Experimental data are needed on this point.

In view of the above theories and the lack of published

data on the subject, it was felt that preliminary experiments

should be performed with various commonly available powders.

Undoubtedly, variables such as particle concentration, unit

surface area, size-distribution, adsorptlvlty , thermal properties, etc. would influence , the final fire-extinguishing

property of a powder. The relative importance of each of.

these factors could not be studied in detail in the work described. It appeared, however, that qualitative information

of value might be obtained by a comparison of the efficiency

of some common powders in gasoline-fire extinguishment.
" 3

2. APPARATUS AND METHOD

A practical approach to the tests was made by simulating

actual fire-fighting conditions. The tests consisted of discharging 2 to 2.5 lb of a given powder at a 4- x 4-ft freesurface gasoline fire. The powder was propelled from a

cylinder pressurized with inert gas. The comparative extinguishment efficiency and characteristics of each powder were

evaluated during three separate runs.

2.1 Powders

The choice of powders was dictated by consideration of

one or more outstanding physical properties of each powder.

As examples, the characteristics of high heat capacity and

low decomposition temperature of borax; the dark surface

color of cement and fire clay; the hard and smooth surface

of Si 02 as compared to the soft and irregular surfaces of

talc particles; the high internal surface area of the activated Na2

C 0 ^^°^ against the high external surface. area of

the MgCO^; the inertness of Si 02 i the fine and free flowing

quality of commercial dry chemical, etc., were reasons for

their selection.

The ih powders tested were of sizes ranging from 200 to

hOO mesh. It was realized that particle size, hence surface

area, was likely to be of particular importance in radiant

heat adsorption, but in this preliminary survey, it seemed

impractical to standardize all powders to a uniform size.

However, some grinding was done to bring all powders within

the range of sizes used. The particle sizes mentioned mean

that over 85^ of the particles passed that particular mesh

screen.

The weight of each powder charge varied from 2 to 2.5 lb

depending on the bulk density of the powder. On some low den

sity powders, slight packing was needed to bring the charge

up to 2 lb.

2.2 Fire Extinguisher

A commercial stored-pressure , dry-chemical fire extinguisher of nominal 2.5 lb capacity was used hor these tests.

Through the use of a removable discharge nozzle, the gas

inlet could be adapted for either charging or discharging

purposes. The effective opening of the discharge nozzle was'
_ 4 «

0»0l5 in^. Dry nitrogen at a pressure of 350 Ib/in'O gage was

used to pressurize the cylinder The average discharge rate

for the various powders varied over the range of Ooh to 0.5

Ib/sec.

2o3 Fire

A slightly indented x 4-ft flat, concrete, surface

basin held the 5/8 gallon of .leaded-gasoline which served as

the fuel for the test fire. The test, powder was applied at

the end of a 5“sec pre-burn period. ’ This 5“sec period was

designed to standardize the initial warm-up period and permit

an approach to the maximum combustion rate prior to extinguishment. The burning rate of free sur|“ace gasoline was

e.stimated to be about 0.009 lb/ft2/sec. An effort was made

by the operator to keep the discharging operation uniform for

all tests. The method consisted of aiming the discharge nozzle

at the base of the fire and advancing slowly while sweeping

from one side to the other.

3. TEST OBSERVATIONS

In performing tests with the various powders, three performance characteristics were noted?

t' 1. Was the fire extinguished?

2. Dispersibility, of discharged powder.

3. Efficiency of fire extinguishment.

The first of these required only a positive or negative list-,

ing. The two other characteristics were evaluated in qualitative manner by visual observation and classification as

A,B, or C. The letter "A" was used for high efficiency or

dispersion and the letter "C" was used to designate the

poorest performance.

Dispersibility of the powder was defined as the percentage of the total number of particles which were suspended as

individual particles without adhering to others. Its determination was based on visual observations during use of the

extinguisher.

Extinguishment efficiency was based on the time rate of

extinguishment or the extent to which flames were suppressed.

It was evaluated by two observers.
" 5 "

'4. RESULTS MD DISCUSSION

The results of these tests are presented in table 1» In

this table the various powders are arranged in order of apparent effectivenesso Factors considered in order of importance

were, was fire extinguished, efficiency of extinguishment, and

dispersibility of the powder^ Three separate tests were performed on each of the powders mentionedo In most, cases the

powder performed in. a very similar manner during each of the

tests o In cases where extinguishment was not accomplished,

all the available powder had been discharged without extinguishing the fire»

The results seem to demonstrate that both fine particle

size and good dispersibility are required for extinguishment

of fires^ The fact that both borax and silica were effective

in extinguishment tends to confirm the belief that release of

carbon dioxide from, the dry chemical has little effect on performance of the powders o The heat capacity of the powder, also

seems to be relatively unimportant, as evidenced by the relative performance of borax and dry chemical, although the

slightly inferior behavior of the decomposed dry chemical prevents any definite conclusions being drawn on the importance

of heat capacity of the powder

The value of good dispersibility is demonstrated by the

' commercial grade of NaHC 03 tested both in the dried and undried

states o The dried powder was effective in extinguishing the

fire while the untreated material was ineffective, being judged

as one of the poorest powders tested® The importance of maintaining a particular particle size w), (8) for optimum dispersion was neglected in this particular study®

During the performance of these preliminary tests, it has

become evident that further work of this nature will be greatly

aided by development of a more' easily controlled- standard fire

and a regulated method of powder . applicationo Measurements of

efficiency and dispersion must also be placed on a quantitative

basis to permit more accurate evaluation of relative behavior

of the different powders®
Table lo Extinguishment Efficiency

NOo Powder^ Treatment

Special Characteristics

1 KHCO3 2% zinc s tears Decomposes at I6OC

4 ground in fine particles

2 Dry Chem. Free-flowing

3 Borax 2% zinc

decomposes at 270C

High heat capacity

4 Na2C03*

stearate -8H2O at 60c

Activated; high

5 70% Na2C03

int. surface area

Mixture had better

6

30% Mg2C03

50% 832003 Dried at 120C

flow than Mg2C03

7

50^ Cement

60^ Si02 Dry Chem® and Mixture had better

40^ Na2C03 Si02j 280c 3hr flow than Si02

8 30^ S102 Same as No, 7

9

70% Na2C03

Na2C03** Same as No. 4

10 NaHC03 Same as No.

6

poor

11 Silica 2% zinc

dispersibility

Inert, hard and

12 Borax (Na2Bl4_0'^ ° IOH2O

)

stearate

Same as No. 11

irregular surface

Particle sizes are

13 Plaster (CaS0)+“-^H20)

larger than No.

3

-iH20 at 16'3C

14 Portland Cement Same as No.

6

Dark gray color

15 Talc Soft surface

16 Fire Clay Low heat conduct.

17 Silica Dried at 15OC

light gray color

18 NaHC03 Same as NodO

19 Silica

1) Powders were either technical or commercial grade®

2) Approximate heat required to raise the temperature of the

powder from l8c to 300C including heat of decomposition

where appropriate. Numbers in parentheses do not include

heat of decomposition.

3) In this table both efficiency and dispersibility increase

in order from C to A.
of -'Powders Tested

No

Density

. Bulk Real

Heat .3 Absorp.

AHS8C-30 0C

Size

Mesh

Effi»

^3

Fire

Out?

gm/cc cal/gm

1 1.3 2.2 238(59) <325 A A-f Yes

2 1.2 2.2 250(68) 325 A A Yes

3 0.62 1.7 462(108) <325 A A Yes

4 .58 2.5 79 <325 A B Yes

5 . 51 72 325 A B Yes

6 . 85 68 325 B B Yes

7 .71 67 >325 B B Yes

8 e 65 74 325 B B Yes

9 .1+9 2.5 79 <200 B B Yes

10 ,84 250 (68) 200 B C Yes

11 .91 2.6 60 400est B C Yes

12 .55 1.7 462(108) <200 A B No

13 .83 1.3 61(58) 400est B B No

14 1.0 3.1 58 >325 0 B No

15 ,56 2.8 66 Impalp. C B No

16 1.3 3.0 63 200 A 0 No

17 '.‘91 2.6 60 400est B 0 No

l8 .84 2.2 250(68

)

200 C C No

19 .91 2,6 60 400est C C No

4) Dry chemical refers to a commercial extinguisher powder

containing 95+^ NaHCO:; 9 * All Na2C03 used was derived from decomposed dry chemical

except No. 9 . Dry chemical was kept at 270--2750 for

3 hrs.

** Derived from untreated NaHC03.
5o CONCLUSIONS

The following conclusions seem justified from the results

of the preliminary work descrihed;

lo Powders other than sodium bicarbonate are very

effective as dry chemical flre-extinguishing

material

c

2e Powders that do not release carbon dioxide on exposure

to heat are effective fire-extinguishing materials

o

Preliminary evidence indicates that the heat capacity

of the powder is not of controlling importance in

determining its value as a fire extinguisher^

REFERENCES

(1) Crosby, Fiske and Foster, Handbook of Fire Protection,

tenth edition (19^8 )j National Fire Protection Assoc®

(2) We Fo O'Connor, Safety Engineering, Oct® 19^9°

(3) Ce B. White, Blazes, March-April 1950? American-LaFranceFoamite Corp® , Elmira, New Yorko

(4) Jo Ho Burgoyne, L® L® Katan, J® F® Richardson, Journ-o of

Insto of Petroleum, Vol® 35? No® 312 (1949)°

(5) Mo Dallavalle, Micromeritics , 1948 ed®

,

Pitman Pub®

Corp®

(6) Jo Ho Burgoyne and L® L® Katan, Journ® of the Insto of

Petroleum, Vol® 33, No® 279 (1947)

o

(7) A® Ko Mo Andreasen, Hofman-Bang and N® H® Rasmussen,

Kolloidzeitso , Vol® 86, 70 (1939)°

(8) So Jo Gregg, Surface Chemistry of Solids, 1951? Reinholc

Pub® Corp®, New York®
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 hy Congress in Public Law 619, 1950.

These include the development and maintenance of the national standards of

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presents summary and preliminary reports on work in progress; and Basic Radio

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Information on the Bureau’s puhhcations can he found in NBS Circular 460,

Puhhcations of the National Bureau of Standards ($1.00). Information on caUbration services and fees can be foimd in NBS Circular 483, Testing by the National

Bureau of Standards (25 cents). Both are available from the Government Bruiting Office. Inquiries regarding the Bureau’s reports and puhhcations should be

addressed to the Office of Scientific Puhhcations, National Bureau of Standards,

Washington 25, D. C.

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 PuhUc Law 619, 1950.

These include the development and maintenance of the national standards of

measurement and the provision of means and methods for making measmrements

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 appUed research, development, engineering, iustrumentation, 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 fisting of divisions and sections on the inside of the

front cover. Reports and Publications

The results of the Bmreau’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 Bmeau of Standards ($1.00). Information on cali- bration 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 Bruiting 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.
NBS