MBS

Pubii • cations

NAT L INST. OF STAND & TECH R.I.C.

A 1 1 1 0 4 E375flb

NBSIR 78-1502

Smoke Measurements in Large

and Small Scale Fire Testing

Richard W. Bukowski

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

October 1978

Final Report

100 s department of commerce

I

I U 56 ITIONAL BUREAU OF STANDARDS

78-1502 -

SSaftonal Bureau of Sfandarte APR 1? 1971

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NBSIR 78-1502

SMOKE MEASUREMENTS IN LARGE

AND SMALL SCALE FIRE TESTING

Richard W. Bukowski

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

October 1978

Final Report

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director
.

,
CONTENTS

T Page

LIST OF FIGURES iv

Abstract 1

1. THE NEED FOR COMPARABLE MEASUREMENTS OF SMOKE 1

2. THEORY OF OPTICAL MEASUREMENTS 3

3. CURRENT PHOTOMETER DESIGNS 5

4. PROTOTYPE PHOTOMETER: DESIGN DESCRIPTION AND DISCUSSION ... 8

5. THE NEED FOR A REFERENCE IONIZATION CHAMBER 12

6. FUTURE NEEDS 14

7. REFERENCES 16

iii
LIST OF FIGURES

Page

Figure 1. NBS extinction beam photometer and six-channel

control 18

Figure 2. Light scattering and extinction by a particle 19

Figure 3. Theory of optical smoke measurements 20

Figure 4. Typical photometer design 21

Figure 5. Variation of optical density with wavelength for

typical black and white smokes 22

Figure 6. NBS extinction beam photometer light source 23

Figure 7. NBS extinction beam photometer receiver 24

Figure 8. Typical schematic - two—channel amplifier 25

Figure 9. Circuit for converting percent transmittance to

optical density or optical density per unit length . . 26

Figure 10. Test results - photometer calibration with neutral

density filters 27

Figure 11. Relative sensitivity of various detection principles

for constant mass concentration 28

Figure 12. Reference ionization chamber based on a commercial

detector 29

Figure 13. Hosemann reference ionization chamber 30

Figure 14. The separated ionization chamber 31

Figure 15. The Cerberus measuring ionization chamber 32

Figure 16. Mie scattering by polydisperse spheres compared with

diffraction, refraction, and reflection as a function

of scattering angle 33

Figure 17. The Sinnott-Gravatt multiple scattering instrument . . 34

Figure 18. Japanese computer fire tests-success percentages ... 35

IV
SMOKE MEASUREMENTS IN LARGE AND SMALL SCALE FIRE TESTING

Richard W. Bukowski

Abstract

The extinction beam photometer is the most widely

used instrument for taking smoke measurements in fire

testing. Most existing designs were found to be inaccurate and unreliable for measurements where smoke

detection performance is evaluated due to the low

levels of smoke present at activation. Accordingly,

a new extinction beam photometer design was developed

which will provide the stability and accuracy necessary for these measurements. The paper describes the new design and proposes its adoption as an industry

standard

.

The paper also discusses the need for a reference

ionization chamber instrument and a reference measurement which relates to gas sensing fire detectors.

Key words: Fire testing; ionization chamber; light

extinction; light scattering; Mie scattering; Rayleigh

scattering; smoke measurements.

1. THE NEED FOR COMPARABLE MEASUREMENTS OF SMOKE

As demonstrated by the old saying "where there's smoke there's

fire," the interrelationship between smoke and fire has always been

recognized. As pertains to safety to life, smoke is also recognized

as perhaps the most important by-product of a fire; since reduction of

visibility and associated panic is the most common and earliest occurring factor which prevents people involved in a fire from escaping the

fire area. Of course, eye irritation from smoke is an important factor

1
in visibility which cannot be measured by these instruments. Thus, the

relationship between these measurements and human visibility are only

valid for non-irritating smokes or where a self-contained breathing

apparatus with full face mask is used.

The importance of smoke measurements in fire testing has greatly

increased since the development of the smoke detector as a fire protection device. The phenomenal increase in the use of smoke detectors over

the last few years, especially in residential applications, has resulted

in a large increase in the number of people making smoke measurements in

research, product development, and product testing and approval.

The level of sophistication of the smoke aerosol measurements depends

on the amount of detail one needs in terms of the smoke properties. If,

for example, one were interested in the size distributions of a variety

of smokes, one might use an electrical aerosol analyzer, a cascade impactor, an optical particle counter, and/or a condensation nuclei counter.

These are sophisticated, expensive instruments requiring some care in

operation as well as expertise in reducing the data. Such instruments

are not the concern of this paper; instead, the interest is in inexpensive, reliable smoke measurements that provide some measure of the

smoke hazard. The primary measurement technique described here is the

measurement of light attenuation.

Since, on the surface, the measurement of smoke by the attenuation

of light appears to be rather straightforward, most people making these

measurements build their own photometers. There are as many different

designs as there are people building them, and often these designs make

only minimal attempts to take into account the well-defined theory of

light attenuation by aerosols.

Since fire itself is an extremely complex physical and chemical

phenomenon, a vast amount of data are necessary to attempt to understand

the burning process. Of necessity, this data comes from many different

sources, so measurements of the various parameters of fire must be

2
comparable among these sources. The only way to achieve this comparability is to minimize the number of variables in instrument design which

can affect the measurements. For this reason, NBS has developed a reference extinction beam photometer for smoke measurements. This photometer

and a six-channel amplifier are shown in figure 1.

2. THEORY OF OPTICAL MEASUREMENTS

The theories defining the attenuation of a beam of light by suspended

aerosol particulates have been fairly well defined since the late 19th and

early 20th centuries. Theories by such familiar names as Lambert-Beer

,

Mie, and Rayleigh clearly define the extinction phenomena. The following

represents a simplified discussion of these theories.

The extinction phenomenon is simply the removal or attenuation of

light in a transmitted beam by a suspension of particles. As shown in

figure 2, a suspension of particles will always remove light from an illuminating beam by scattering, and also by absorption if the particles

are made of absorbing material. The amount of light removed from the

illuminating beam is a function of the optical characteristics of the

particle, the number of particles, the size of the particles, and the

wavelength of the light. The extinction beam photometer measures only

the reduction in transmitted light, independent of whether it is reduced

by absorption and/or scattering. For dark, large spherical particle

smokes where absorption predominates, the Lambert-Beer law governing

the extinction phenomenon can be expressed by the formula: [1]^

exp (-4* M tK/A) (1)

is the transmittance (ratio of the transmitted

to the incident light flux)

M ( 1— i k) is the complex refractive index

o

where

M =

Numbers in brackets refer to the references at the end of this paper.

3
t = is the path length through the aerosol

K = is the absorption coefficient

X = is the wavelength

Since, for other than very black smokes, the absorption coefficient

of most smoke particulates is low, the primary phenomenon controlling

the extinction of light in most smoke measurements is scattering. Let

us now discuss the factors which govern the scattering phenomena.

Scattering of light by particulates is strongly affected by the

relationship between the light wavelength and the particle diameter.

Figure 3 shows particle size ranges for the three scattering regions

encountered in smoke aerosol measurements for visible light [2]. For

particles whose diameter is one order of magnitude smaller than the

wavelength or less, the scattering phenomena is defined by Rayleigh.

For very small, nonabsorbing, spherical particles (k=0) , where scattering is entirely in the Rayleigh region, the Lambert-Beer law can be

written in the form: [3]

fj

= exp

o

! TT 5

(j 6

3 A

4 (—) \M2 +2/ Nt ( 2 )

where

d is the particle diameter

M is the index of refraction

N is the particle number concentration

In the Rayleigh scattering regime the scattering efficiency is

directly proportional to the sixth power of the particle diameter and

inversely proportional to the fourth power of the wavelength. It is

because of this fourth order wavelength dependence that optical smoke

measurement devices using visible light will not respond to particles

below a few tenths micron. The use of longer wavelength light in the

red or infrared regions such as from lasers or light emitting diodes

further reduces the efficiency of scattering in the Rayleigh region.

4
For particles whose diameter is greater than one order of magnitude

larger (actually this boundary varies from 4A to 100A as a function of

refractive index, but is generally from 4A to 20A for most smokes) than

the wavelength of the incident light (in the Bricard region), the scattering efficiency approaches a limit of two, not one as one might think.

The reason this is so is because of diffraction effects at the edges of

the particle. That is, a large particle removes from the beam twice the

amount of light intercepted by its geometric area. The geometric cross- sectional area of the particle blocks one unit of light, and a portion

of the beam not intercepted by the sphere forms a plane wave front from

which a region corresponding to the cross-sectional area of the sphere

is missing. The diffraction pattern within the shadow area of the particle results in the loss of the second unit of light from the beam. The

intensity distribution of the light within this diffraction pattern depends

on the shape of the perimeter and size of the particle relative to the

wavelength of the light and is independent of composition, refractive

index, or the reflective nature of the surface. The total amount of

energy appearing in the diffraction pattern is equal to the energy of the

beam intercepted by the geometric cross section of the particle.

Mie theory explains the phenomena of scattering taking place where

the particle diameter and wavelength of light are of the same order of

magnitude. Expressions for scattering and extinction in the Mie region

are obtained by solving Maxwell's equations for the regions inside and

outside the sphere and are found to be a function of the particle diameter and complex index of refraction alone. Due to the complexity of

the governing equations, the calculations must be carried out numerically

with the results tabulated for specific values of refractive index.

3. CURRENT PHOTOMETER DESIGNS

Most photometers used for smoke density measurement employ the same basic design, represented in figure 4. They use a light source (usually

a tungsten filament lamp) in a direct optical line with a light-receiving

5
element. The light source and receiver are rigidly mounted some known

distance apart and are enclosed in a darkened testing chamber or shielded

in some way to reduce the influence of ambient light.

The light source is normally operated from a highly stable, constant

voltage source at somewhat less than rated voltage. The output of the

cell is normally monitored with a high quality meter of proper impedance

so as to operate the cell within its linear range.

In most cases the photometer is adjusted at the beginning of each

test so that the meter reading is some specific value. This facilitates

the use of a chart for conversion to whatever smoke density units are being used without having to calculate the values each time. This adjustment is normally made by varying the voltage applied to the lamp, and is

a major source of error in design and operation.

Adjusting the voltage across the lamp changes the filament color

temperature and thus changes the wavelength distribution of the light

being produced. Since light scattering intensity is an exponential function of the wavelength of the light, this results in major variations in

the readings obtained under different voltages even when using the same photometer. In order to eliminate variations in readings from a single

photometer or variations between photometers it is imperative that tungsten filament light sources be operated at the same filament color temperature. Figure 5 shows the variation in apparent optical density with

changing light wavelength (using an adjustable monochromatic source) for

white and black smokes (at constant particle concentration) as developed

at the British Fire Research Station [4]. Trr‘om this data, a change in

wavelength from 1.0 ym to 1.5 urn to 1.5 urn results in a 50% reduction in

apparent optical density for white smoke and a 30% reduction for black

smoke. This difference is reasonable since the extinction reading for

white smoke would be more dependent on scattering and the reading for

black smoke would be more dependent on absorption.

6
Another method of assuring a constant wavelength light would be to use an essentially monochromatic source, such as a light-emitting diode,

laser, or a tungsten filament lamp with an optical filter passing one frequency. Because of their very low light output, light emitting diodes can only be used in very short path lengths (a few inches) . Lasers produce

sufficient light output, but cost prohibits their use where a large number

of photometers are necessary and would prohibit their use in large scale

testing where damage to the laser would be possible fron the test fire.

Thus, the only practical solutions would be operation with white light

at a constant color temperature or use of monochromatic light.

Since the intensity of the light source cannot be adjusted to a specific starting point without changing the filament color temperature,

the sensitivity adjustment should be made by controlling the output of

the light receiving element. This can easily be done by adjusting the

gain of an amplifier in the output circuit. The use of a linear amplifier

would be necessary in this case.

While operation of the light source at a reduced voltage is

advantageous in increasing lamp life, it is imperative that the lamp be

operated with direct current since reduced voltage alternating current

applied to a tungsten filament lamp results in filament notching, which

can actually reduce life. In addition to reducing life, this notching

effect can result in a change in the light wavelength output due to the

creation of "hot spots" on the filament.

The light source and receiver used should be matched for spectral

response and the receiver should be operated in the linear region of its

response curve. The light beam should be highly collimated and should

be as small in diameter as possible to reduce the effect of multiple scattering, especially in side lobes. The light receiver should be designed

with lenses so as to have as narrow a viewing angle as possible, which

will reduce the effect of ambient light. Where high ambient light levels

are unavoidable, chopping techniques can be used to make the output

insensitive to the ambient signal. Care must also be taken to eliminate

7
lamp filament projection on the light receiver, which produces nonlinearities in the output. This reduction in accuracy is caused by the

filament projection causing dark areas on the receiver during clear

conditions which gradually disappear as the light is diffused through

the smoke.

4. PROTOTYPE PHOTOMETER: DESIGN DESCRIPTION AND DISCUSSION

Once the problems with existing photometers had been identified,

modifications were undertaken to eliminate these problems. This has

resulted in the following design.

The light source selected is a number 1810 lamp with a T-3/4 bulb

and a miniature bayonet base. This lamp is rated 6.3 volts, 0.40 amps,

1.5 candela, 3000 hour life. The lamp is mounted behind a +20 diopter,

double convex collimating lens and is focused to produce maximum light

on the receiver. The lamp is operated at 5 volts dc (which gives a 2425°K color temperature), [5], regulated by use of a 7805, series pass

regulator mounted at the lamp. The regulator is mounted at the lamp so

as to reduce variations in voltage due to cable length. A photograph

of the light end of the instrument is figure 6.

The light receiver chosen is a 1P39 phototube (with a filter to

correct its spectral response to the standard CIE curve for the human

eye response peaking at 550 NM) mounted just ahead of the focal point

of a +10 diopter plano-convex lens. The inside of the housing containing the phototube is painted optical black to minimize internal

reflections. Figure 7 shows the instrument receiver.

A typical two-channel amplifier schematic is shown in figure 8.

The output of the phototube is connected by means of a shielded cable

to a FET input, linear, operational power amplifier (40 J) which is

operated as a current to voltage converter with an adjustable gain of

approximately 10 6

. The control panel contains a zero, and coarse and

fine span adjustments. The zeroing is done with the operational

8
amplifier null connection. The coarse and fine span adjustment consists

of two potentiometers in series serving as the feedback resistance of the

amplifier. A 10-turn potentiometer was selected for the fine adjust to

reduce adjustment criticality.

The system is designed to provide an adjusted 1.000 volt signal in

clear air conditions. While higher voltages can be obtained if desired,

increasing the gain of the operational amplifier results in increased

effect of ambient light on the reading.

While the use of 1.000 volt reference signal will give an output

in percent transmittance over the beam path length, it is sometimes more convenient to have an output directly in the final engineering units,

such as optical density. For this purpose a second amplifier stage may

be added using a commercially available Log ratio amplifier. The

schematic for this amplifier stage is shown in figure 9.

The voltage transfer equation for this circuit is:

where

:

e out - LOG

t

'ref

e sm

(3)

e = circuit output voltage in proper

engineering units

e^

e £ = set to the clear air photometer voltage

e

g ^

= output of the photometer amp.

t = conversion circuit gain set to equal the

reciprocal of the path length by eq . 4

Comparing this with the equations for optical density, it can be seen that the photometer output is converted directly to optical density

per unit length or unit optical density (where t = l) . For optical density where t/1, a fixed value resistor (R^) is used. The value of

resistance is calculated from:

9
16.7 (1/t) - 1 (Kft) (4)

where t is the beam path length in the desired units. For unit optical

density (or where t=l) the lv/decade pin is connected to the output pin.

To use the circuit, the output of the smoke meter amplifier is

connected to the e terminals and e .. is set to 1.000 volts (or whatever

sm ref

reference voltage is used) . The output (e ) is then in the proper engineering units. The Log ratio module is calibrated using the calibrate

potentiometer and a neutral density filter of known optical density.

It has been found that once the lamps have been "burned in" for

approximately 24 hours, they need only be warmed up for approximately

one hour to obtain stable operation. Full-scale output variation appears

to be less than +1 millivolt per volt.

Three photometers of one meter length and a three-channel amplifier

using this design were built for evaluation. The meters were calibrated

using gelatin (Wratten) filters in the range of 0.1 to 1.0 optical density. Tests showed that all three meters read precisely the same with

each filter when placed in the same position along the one meter length.

The results for the calibration are shown in figure 10. The stability

of the system allows its use without drift error to one millivolt accuracy. This results in accurate measurements to within +0.0004 optical

density per meter (due to the low output variation)

.

In working with the initial prototypes, it was found necessary to use a shielded cable between the control and the phototube when running

cable lengths over about one meter. This is due to the high impedance

of the phototube and the high amplifier gain.

It was also found necessary to operate the lamp circuit from a pure

dc supply which never drops lower than 10 volts. Although the series

pass regulator would give rough regulation from a full-wave-rectified,

unfiltered power supply, the switching times of the regulator were so

10
short that whenever the supply fell below 10 volts dc, regulation was

lost and an imperceptible flicker was obtained which caused instability

in the output. This should be avoided either by operating from a pure

dc supply or using a capacitor smoothed, full-wave-rectified supply of

a high enough voltage such that the circuit output voltage never falls

below 10 volts. Since the regulators are capable of handling an input

voltage as high as 35 volts dc, a 28 volt, full-wave-rectified supply

with a large smoothing capacitor is capable of operating the system

satisfactorily.

The 200-volt bias supply for the phototubes does not require as critical a regulation as the lamp supply. It is necessary, however, to use a fairly large smoothing capacitor to minimize ripple which injects

a 60 Hz noise in the amplifier output. The effect of this noise may be

significant if the output device does not have a 60 Hz rejection filter.

The phototube also has the advantage of more thermal stability than

any other type of receiving device. The 1P39 is rated as stable to temperatures as high as 70°C. Above this temperature the output increases

sharply, doubling every 3 to 5°C [6], At about 190°C, the cathode begins

to decompose by driving off cesium. This decomposition is only partially

reversible, so any tube which may have exceeded 190°C should be replaced.

Keeping the 1P39 below 70°C can be accomplished in several ways,

depending on the peak expected temperature and exposure time. For short

exposures, insulation of the receiver box will slow the heat transfer

enough to maintain the tube below the critical temperature. For higher

peak temperatures or longer exposure times, purging the receiver box

with cool air or nitrogen may be necessary. If you are unsure of your

methods, it is good practice to place a thermocouple on the rear of the

tube to indicate the time at which the tube has exceeded its critical

temperature. Readings taken after this point should be disregarded.

If a silicon cell is used as a receiver, it must be operated into

an effective short circuit to maintain thermal stability. Where long

11
cable runs are made, this would necessitate use of a preamplifier in

the receiver box. The critical temperature for the cell and amplifier

must then be determined, and similar steps must be taken to keep the

receiver temperature below this value.

A particular advantage to the design proposed above is that the

entire photometer (exclusive of control) can be built at moderate cost.

Thus, it is no great concern if one of these photometers is destroyed

during a full-scale test. This allows positioning of the photometer in

the most advantageous locations without concern for its protection.

An additional point about this particular design is that the light source chosen, when operated at 5 volts, has an estimated life of nearly

five years [7]. Thus it is possible to let the lamps run continuously

without worry of burning out bulbs.

5. THE NEED FOR A REFERENCE IONIZATION CHAMBER

As was stated earlier, optical measurement methods can be used to

measure particulates only down to the few tenths micron range, due primarily to the fourth order dependence on the particle diameter to wavelength ratio. In tests where the smoke measurement is only being used

to approximate vision obscuration and thus the potential for escape

through the fire or smoke filled areas, these light extinction measurements are sufficient. If, however, quantitative evaluation of the

response of ionization type smoke detectors is desired, smoke measurements down at least one more order of magnitude in particle diameter are necessary. This is true simply because changes in the numbers of particles in the 0.01 to 0.1 micron range would grossly affect the ionization

detector response without resulting in significant changes in the reading

of the photometer. The recognition of this fact has resulted in the

development of a number of instruments using ionization chamber sensors

to make measurements in this lower size range. The theoretical relative

sensitivity of scattering, extinction, and ionization chambers as a function of particle size for constant mass concentration is given in

figure 11 [8]

12
Many manufacturers of ionization type smoke detectors have produced

units with analog output signals which can be read on meters. One such

device is shown in figure 12. While these devices all give relative

readings, they typically relate well only to the exact detector from

which they are made. The reason for this is that the sensing chambers

in commercially produced detectors are optimized for cost and ease of

manufacture, and are not designed to perform strictly according to ionization theory. Such critical design parameters as electrode spacing,

chamber volume, source strength, uniformity of ionization and electric

fields, and effects of outside air currents are not, and cannot be, as closely controlled as is necessary in a measuring instrument, due to

cost considerations. Thus, these devices are not acceptable as precision

laboratory instruments.

Because of these facts, several attempts have been made to design

reference instruments. The first such instrument which we have identified

was designed by Dr. Hosemann at Aacher University [9] and is shown in

figure 13. While Dr. Hosemann and his colleague Dr. Krause have had

good results with this chamber, attempts to reproduce it have not been so successful. In fact, critical alignment of internal parts has resulted

in a situation where, when disassembled for cleaning, Dr. Krause must personally reassemble and calibrate the chamber to get it to operate properly.

Mr. Peter Burry at the British Fire Research Station at Borehamwood,

England developed a chamber commonly known as the separated charge chamber

[10]. A schematic representation of this chamber is shown in figure 14.

While he found that his chamber was reproducible and noncritical in assembly, experimentation showed that its inherent sensitivity was much too

high. This resulted in a total loss of chamber current at particle con- centration levels below those normally encountered in detector testing.

This chamber is now being used for measuring particulate concentrations

of air pollution and background particle levels in non-fire situations.

These problems with the earlier two reference chambers led

Dr. Andreus Scheidweiler of Cerberus AG in Mannedorf, Switzerland to

13
develop a third instrument, shown in figure 15. Early results of tests

conducted with this instrument seem to indicate that the problems of the

earlier two have been solved. The instrument is reproducible and non- critical and will operate properly at particulate concentrations normally

encountered in smoke detector testing. Copies of this instrument have

been purchased by Krause at Aachen, Burry at Borehamwood, and ourselves;

and it is currently being evaluated as to its suitability as a reference

instrument. At this point we feel that this device shows great promise,

but we are not yet ready to propose its adoption as an industry standard.

Details of the operation of this device are given in reference 11, a paper by Dr. Scheidweiler

.

6 . FUTURE NEEDS

Use of a reference ionization chamber in conjunction with a reference

extinction beam photometer will allow a fairly good approximation of mass median particle size and number concentration, and should allow good quantitative correlation to the operation of most smoke detectors. Therefore,

using these two instruments in concert gives much more information than

either one alone. The question arises as to whether the use of additional

instruments is advisable. There is one other important parameter of the

particulate cloud relating to photoelectric detectors which these two

instruments do not quantify. This is the angular scattering intensity

(at a given angle). Figure 16, for example, shows such an angular scattering intensity distribution for polydisperse spheres with a refractive

index of 1.33 [12] and compares the distribution predicted by Mie theory

to the sum of the diffraction, refraction and reflection components.

Photoelectric detectors look at the light scattered from the smoke

particles at a specific angle. With the extinction beam photometer light

scattered at any angle does not reach the receiver. As the refractive

index of an aerosol changes, the intensity at any given angle can change

without affecting the total scattered light and thus not affect the photometer. Therefore, it is theoretically possible to expose a photoelectric detector to smokes from two different sources which give the same reading on both the extinction beam photometer and ionization chamber

14
but cause different results in the detector response. Even though this

is theoretically possible, photoelectric detectors, in general, do seem

to correlate well to the extinction beam photometer for most cases. It

is hoped that this effect is not important enough to warrant the addition of scattering readings as these would have to be taken at the exact

angle used by the detector optics. Since scattering angles in commercially available detectors vary from 90° to less than 27° from forward,

this would involve a multiplicity of readings and greatly increase the

complexity of the instrument. Such an instrument has been developed at

the National Bureau of Standards for research on smoke aerosol

characteristics and is shown in figure 17.

One possible future need might be a reference gas detector. In the

last few years, gas sensing fire detectors have been proposed. While

current units do not seem to be suitable for general applications, there

is some evidence that they may be quite effective in some special applications, such as detecting fires in electronic equipment. Figure 18

summarizes the results of tests of three types of fire detectors in com- puters in Japan [13]. This figure gives success percentages for ionization, photoelectric, and gas detectors located inside a computer, in the

subfloor, and on the ceiling of a test room. A number of computer fire

simulations were conducted, and success was defined as detection occurring

before an error was generated in the computer program due to the fire.

Newer gas detection principles, or better information on application of

existing principles such as these Japanese tests, may result in more general acceptance of gas sensing fire detectors. One of the biggest

stumbling blocks, however, is the lack of general information on gaseous

species and concentrations in fire testing. Without this information it

is impossible to determine what gases and what concentrations of these

gases must be detected for satisfactory performance. Thus, if an instrument such as a total hydrocarbon analyzer were added to the instrumentation of many full-scale fire tests, relative data could be obtained which

may demonstrate certain areas of application in which gas sensing fire

detectors could be used.

15
In conclusion, it is felt that the rapidly growing amount of large

and small scale fire testing being conducted in this and other countries

could be of much greater overall benefit if standardized instrumentation

were used which allows proper comparison of tesfs conducted by different

parties. Such comparisons would alleviate the need for duplicate testing

and allow a much more rapid attainment of an understanding of the fire

phenomena

7. REFERENCES

[1] Hodkinson , J. R • 9 The optical measurement of aerosols, Aerosol

Science

edited by C. N. Davies, Academic Press

London

1966,

Chap. 10, 290.

[2] Hodkinson , J. R • 9 The optical measurement of aerosols. Aerosol

Science, edited by C. N. Davies, Academic Press

London

1966,

Chap. 10, 316.

[3] Cadle, Richard D. , The Measurement of Airborne Particles,

John Wiley and Sons

1975, Chap. 4, 236.

[4] Fire Research, Annual Report of the British Fire Research

Station

1971, 63.

[5] G. E. Miniature Lamp Division, private communication.

[6] Kissinger, G. D. , RCA Electronic Components, Phototube

Applications Section, private communication.

[7] G. E. Miniature Lamp Catalog 3-6253, Revised 12/72, A.

[8] Purt, G., Specific fire risk factors and their significance

for automatic fire detection, Fourth International Fire

Protection Seminar, Zurich, 1973.

16
[9]

Hosemann, J. P., Considerations in testing smoke detectors,

Symposium on Problems of Automatic Fire Detection, 1971

Aachen Conference, Aachen, Germany, Oct. 4-6, 1971.

[10] Burry, P., The separated ionization chamber, Proceedings of the

Symposium on Fire Detection for Life Safety, National Academy

of Sciences, 1977.

[11] Scheidweiler , A., The ionization chamber as a smoke dependent

resistance, NFPA Fire Technology, May 1976.

[12] Hodkinson, J. R. , The optical measurement of aerosols. Aerosol

Science, edited by C. N. Davies, Academic Press, London, 1966,

Chap. 10, 325.

[13] Report of computer fire tests. Joint Group on Computer Fire

Protection, J. of the Japanese Association of Fire Science and

Engineering, Vol. 24, No. 3, 1974 (In Japanese; English translation available from the author. of this paper)

.

17
18

Figure

1.

NBS

extinction

beam

photometer

and

six—

channel

control
a*

-AAA/VVVVNr 53

- — o

* A A A A

®

'll

19

Figure

2.

Light

scattering

and

extinction

by

a

particle
20

Figure

3.

Theory

of

optical

smoke

measurement
light

shield-.

21

Figure

4.

Typical

photometer

design
OPTICAL

DENSITY

PER

METRE

WAVE LENGTH - Mm

Figure 5. Variation of optical density with wavelength

for typical black and white smokes

22
23

Figure

6.

NBS

extinction

beam

photometer

light
24

Figure

7.

NBS

extinction

beam

photometer

receiver
ZERO

2.5k

OC

111 Q

BEo

o

111 oc

cc

LUQ

BEo

o

Ul

QC

25

Figure

8.

Typical

schematic

-

two—

channel

amplifier
TELEDYNE

PHILBRIC&

4366

OR

4367

H3o >mT

cc3

CM

CM >

inT“+

LUI-<

cc

00<o

26

Figure

9.

Circuit

for

converting

percent

transmittance

to

opticaldensity

or

optical

density

per

unit

length
PHOTOMETER

CALIBRATION

i

1

. -

] /

•

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CO

C/> i.i +-»

C\l

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o—

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s 2 S

cr

• 2 o1 -4

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o * *' • . • . CO

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00

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s

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o

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as

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r

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o o

too

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m

03

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in

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03

00

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• *• <0• 00

• O• o o o o oo -

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00

>c

27

Figure

10.

Test

results

-

photometer

calibration

with

neutral

density

filters
I

_o

.—_* Czi. G2) tSu ©

s

eg

o

£'

CO

*© B CT*.

i E

.s

65 GS ©

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o

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28

PARTICLE

DIAMETER
29

Figure

12.

Reference

ionization

chamber

based

on
30

Figure

13.

Hosemann

reference

ionization

chamber
31

Figure

14.

The

separated

ionization

chamber
I

32

Figure

15.

The

Cerberus

measuring

ionization

chamber
Mie

theory

Diffraction+Refraction+Ref

lection o

o

o

CO

o

CSJ

O

LU

cs

C3

oo

|o) z

l + |©l

l

l 1N3IDIJJ303 UISN31NI Q3M311V3S

33

Figure

16.

Mie

scattering

by

polydisperse

spheres

compared

with

diffraction,

refraction,

and

reflection

as

a

function

of

scattering

angle
34

Figure

17.

The

Sinnott-Gravatt

multiple

scattering

instrument
00

ON CEILING

CD

40

30

10

25

100

0

53

63

32

o

mo

o

LU

UNDER FLOOR

CD

30

10

10

100

100

50

63

42

26

LU

LU CD CD LO CO m in

NSIDE ACHIN - 60 100 79 — 60 0 37

to

QC

o

UJ

Q_

Z O 00

LU —I LkJ

SN0I1V001

3dlJ

C3

aT

35

Figure

18.

Japanese

computer

fire

tests-success

percentages
NBS-I 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 78- 15022. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

SMOKE MEASUREMENTS IN LARGE AND SMALL SCALE FIRE TESTING

5. Publication Date October 1978

6. Performing Organization Code

7. AUTHOR

{£j

) charci Bukowski

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4928677 (7528677)

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9

13. Type of Report & Period Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The extinction beam photometer is the most widely used instrument for taking

smoke measurements in fire testing. Most existing designs were found to be

inaccurate and unreliable for measurements where smoke detection performance

is evaluated due to the low levels of smoke present at activation. Accordingly, a new extinction beam photometer design was developed which will

provide the stability and accuracy necessary for these measurements. The

paper describes the new design and proposes its adoption as an industry

standard.

The paper also discusses the need for a reference ionization chamber instrument

and a reference measurement which relates to gas sensing fire detectors.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name, separated by sem, colons)

ppre ; ionization chamber; light extinction; light

scattering; Mie scattering; Rayleigh scattering; smoke measurements.

18. AVAILABILITY FT1 Unlimited 19. SECURITY CLASS

(THIS REPORT)

| For Official Distribution. Do Not Release to NT1S

UNCL ASSIFIED

1 Order From Sup. of Doc., U.S. Government Printing Office 20. SECURITY CLASS

Washington. D.C. 20402. SD Cat. No. 03 (THIS PAGE)

[X ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151 UNCLASSIFIED

21. NO. OF PAGES

22. Price

USCOMM-DC 29042-P74
im

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