NATIONAL BUREAU OF STANDARDS REPORT

DEVELOPMENT OF A LABORATORY TEST

FOR

EVALUATION

OF THE

EFFECTIVENESS OF SMOKE SIGNALS

by

Ray Po Teele

Harry K» Hammond III

Photometry and Colorimetry Section

Optics and Metrology Division

Sponsored by

Testing and Development Division

United States Coast Guard

U. S. DEPARTMENT Of COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprinting, or reproduction of this report in any form, either in whole or in part, is prohibited

unless permission Is obtained in writing from theOffice of the Director, National Bureau of Standards, Washington

25, D, C, Such permission is not needed, however, by a Government agency for which a report has been specifically prepared if that agency wishes to reproduce additional copies of that particular report for its own use.

NBS PROJECT

1002-30-U82U July 1956

NBS REPORT

U792
<
lo INTRODUCTION

#

The United States Coast Guar'd has the duty of approving devices carried

on vessels as life-saving equipment,. One such device is a smoke signal for

daytime use*

The effectiveness of a smoke signal depends upon the opaqueness , color,

and duration of the smoke® The color of a smoke signal can be determined

satisfactorily by comparison with Minis ell color chips* However, the opaqueness of a smoke has been judged simply by observation and is therefore a matter of individual opinion* The present work was undertaken to devise a

laboratory method for evaluating the relative transmittance of the smoke

emitted by any signal, thereby evaluating its effectiveness*

Several manufacturing companies were invited to suggest methods of test

and to cooperate by supplying samples of signal smokes* The companies were?

Aerial Products, Inc., Kilgore, Inc. (International Signal Division), Superior

Signal Company, Inc*, and the Universal Match Corporation*

In addition to signals assumed to be acceptable, smoke signals known

to be defective in various ways were also supplied by the manufacturers*

Additional samples of various age and condition were supplied by the United

States Coast Guard*

The test method suggested by the manufacturers was essentially as follows

ignite the smoke signal in a large enclosure ; by a sampling technique, determine the volume of the smoke cloud, measire the optical density of a sample,

and thereby evaluate the effectiveness of tee signal. This suggested static

mk test method would require a relatively large enclosure. Also it would be

relatively difficult to determine the average smoke density. Furthermore,

the rate of smoke formation would be difficult to evaluate* These factors

together with cost and space considerations indicated the desirability of

developing a different type of test method*

2* TEST MEHDD

The test method selected for evaluating smoke signals was based on the

measurement of the transmittance of the smoke when drawn through a stack at

a known

( rate* The attenuation of a beam of light in tee stack and the lapse

of time * provided a measure of opaqueness and duration of tee smoke*

3o TEST APPARATUS

The test apparatus consisted of the followings a water tank with circulating tap water in which to float the smoke pot; a chemical hood, with

adequate air flow, in which the smoke is generated; an optical system installed in the exhaust stack; and a photometric system that together with

the optical system measures the transmittance of the exhausted smoke* A

Vel-O-Meter (Illinois Testing Laboratory) was used to measure tee intake

air velocity.
4

•
3d Hood

The general arrangement and dimensions of the hood are shown in Figure 1,

The sliding door of the hood was equipped with spacers to provide an inlet

of reproducible size, The essential dimensions are the inlet opening of one square foot area (approx, 27" x 5-1/2") at the bottom of the sliding door and

the exhaust stack diameter of 7-1/2 inches,. The exhaust blower produced an

average intake air velocity of 650 feet per minute* with or without the production of smoke

3o2 Optical System

On an extension of a diameter of tee stack are arranged an optical

system and a photoelectric receiver , The source* a 20-diopter collimating

lens* and a removable window are on one side of tee stack, On the other

side are* in order* a removable window* a 20-diopter lens forming an image

of the source* a 6,5 min circular stop in the focal plane of the lens* and

a phototube, This lens and stop combination permits the receiver to register

rays departing from parallel by plus or minus 3® 7 degrees.

The light source is a 6-8-voX t* 50-eandl@power marine service lamp*

trade number Xl81$.o The removable windows are provided to permit removal of

precipitated smoke particles , This optical system reduces to a negligible

amount the effect of "beam broadening" caused by smoke particles scattering

light from the original beam.

A glass tube installed earlier in the exhaust stack permitted visual

observation of the disiribution of the smoke and together with an examination of the smoke deposit on the tube surface indicated teat the distribution was sufficiently uniform for tee purpose, A metal tube was used for

all measurements.

Experience indicates that the windows need not be cleaned after each

signal. In fact the drift of tee 100 percent reading is less when smoke

from a previous deposit is allowed to remain,

3®3 Photometric System

The photometer was a Densic hron Densitometer (W, M, Welch Scientific

Co,)* equipped with a phototube having an S-l surface. The output was connected to a 10-ohm load resistor and a Brown recorder. The recording

instrument is a single variable* strip-chart recorder with Jj. l/2 second full

scale travel time.

ko TEST PROCEDURE

The voltage on the light source was adjusted together with the volume

control on the Densichron to produce a full scale deflection on tee recorder.

*
'

I
=3 “

The recorder driire was started, the smoke pot was ignited and placed in the

water tank in the hood, and the hood door was lowered onto the inlet spacers.

RESULTS

Figures 2 through $ are photocopies of representative chart records from

about 1$ smoke signals tested,, These records were made at a chart speed of

two inches per minute 0 Note that the pen moved from right to left across the

chart. Figures 2 and 3 are for smoke signals classed as "satisfactory" „ Note

that the transmittance is well below 20 percent throughout most of the smoke

emitting period. In Figure 2 the average transmittance for three minutes is

of the order of two percentf in Figure 3, five percent. Note also that at

least one minute is required after the initial appearance of smoke for the

signal to provide sufficient smoke to attenuate the beam appreciably.

Figures Ij. and $ are records of smoke signals classed as "inadequate** by

the cooperating manufacturer. Note from Figure k that the smoke started and

then nearly stopped twice before the steady rate became established. This

figure shows a smoke emitting period of about seven minutes, but the relatively high transmittance of 20 to $0 percent indicates that the smoke signal

would be inadequate. Figure $ indicates a similar signal performance but

shows a period of about 2 minutes when there was sufficient smoke to produce

less than 20 percent transmittal e@.

6. SUGGESTED DEFINITION FOR SATISFACTORY SMOKE SIGNAL

A satisfactory smoke signal, judging from the results of the measurements of the samples used in this report, might be defined as one that has

less than 20 percent transmittance for 3 minutes when measured with apparatus

operated as here described. The essential parameters of this apparatus are

a light path of 7 1/2", an optical system aperture of ± 3»7 degrees and an

entrance air flow of 65>0 cubic feet per minute. For other parameters the

transmittance, the duration, or both might be different.
.

1
USCQMM-NBS-DC

’-©3 iMSWfltfitMf NMOUB &U&.AB S««9 iMfclti A JOSTMl ON J.UVHO

1 '(\ ni aaiNitfrf r'V«l ' 03 IMINatlXCNI NMOUC SHI AO CC3I 1HDIWAW09 M-I0*8 OH i.¥VK3

USCOMM-NBS-DC