NBSIR 76-1040

Points of View in Testing

Flame Detectors

M. Schnell

Verband der Sachversicherer, e. V.

Cologne, West Germany

Translated for:

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1976

Final Report

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 76-1040

POINTS OF VIEW IN TESTING

FLAME DETECTORS

M. Schnell

Verband der Sachversicherer, e. V.

Cologne, West Germany

Translated for:

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1976

Final Report

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science end Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

PREFACE

This report is a translation of a paper prepared by M. Schnell and presented by him at the

Seventh International Seminar on Problems in Automatic Fire Detection held in Aachen, Germany, on

March 5-6, 1975. The Seminar was sponsored by

the Institute for Electrical Communications Engineering in Aachen in conjunction with the Gesamthochschule in Duisburg.

This translation has been prepared to disseminate useful information on a need-to-know basis

and is not an original work of the Center for Fire

Research.

We express our appreciation to the author,

Mr. M. Schnell for his permission and assistance in

making this information available.

We also express our appreciation to the Joint

Publication Research Service, Arlington, Virginia,

who provided the translation of the original paper.

Richard G. Bright

Program for Fire Detection

and Control Systems

Center for Fire Research

CONTENTS

Page

PREFACE iii

LIST OF FIGURES vi

Abstract 1

1. INTRODUCTION 1

2. BASIC TESTING 2

3. TRIAL TESTING 3

4. TESTING TECHNOLOGY 6

4.1. Directional Dependence 10

4.2. Glare 11

4.3. Trial Test 11

5. CONCLUSIONS 11

6. REFERENCES 12

v
LIST OF FIGURES

Page

Figure 1. Emission Spectrum of a Wood Fire 14

Figure 2. Emission Spectrum of an Alcohol Fire and

of an Alocholbenzene Fire 15

Figure 3. Interfering Radiation Spectrum 16

Figure 4. Infrared Radiation Detector — Test

Apparatus 17

Figure 5. Infrared Radiation Detector — Test

Apparatus 18

Figure 6. Infrared Radiation Detector — Test

Apparatus 18

vi
POINTS OF VIEW IN TESTING FLAME DETECTORS

M. Schnell 1

Abstract

The general principles for type testing the

fire detectors which are already in use in the

assessment of heat and smoke detectors are summarized. These include the so-called basic tests

and the trial tests. The trial tests were intended

to include all test fires in order to ensure comparability of tested fire detectors. Additional

test fires are proposed which are intended to

permit differentiated comparison of flame detectors between one another. The main problem in

assessing the performance of flame detectors during environmental influences is the selection of

a suitable radiation source for reproducibly simulating the characteristic "flame." The requirements that this radiation source must fulfill

are dealt with and various realizations involved

are discussed. The practical testing of infrared

flame detectors to the basic tests is described.

In addition, a suggested test apparatus for ultraviolet flame detectors is dealt with.

Key words: Detection; fire detectors; flame

detectors; heat detectors; infrared detectors;

smoke detectors; testing; ultraviolet detectors.

1. INTRODUCTION

In various national and international panels, suggestions for suitable testing of automatic fire detectors have

been discussed for many years. In practice, only heat detectors and smoke detectors have hitherto been considered. This

work has in the meantime more or less reached its terminus.

For many years, however, automatic fire detectors have

also been utilized in practice, which address other fire

characteristics, such as, for example, changes in air humidity, air turbulence, or flame radiation. Among these types

of fire detectors, the most important group is represented by

flame radiation detectors. Their utilization has proven

At the time this paper was presented, Mr. Schnell was at

the Gesamthochschule , Duisburg, Germany.

1
suitable in various applications. The need soon arose to

set requirements for radiation detectors, similar to those

for smoke and heat detectors — requirements which can be

checked in the laboratory as easily as possible.

To improve understanding, the essential viewpoints in

testing heat and smoke detectors shall here be reviewed.

2. BASIC TESTING

The requirements and the associated test methods can be

divided into two groups. In one group, the influence of

deleterious environmental influences, occurring in practice

on the detector, are checked. This first group is called

basic test. Here, in most cases, the procedure is as follows:

The automatic fire detector to be tested is exposed

to a simulated increasing fire characteristic. A

measurable physical quantity which characterizes

this fire characteristic is recorded. The measured

value at the time the detector is triggered, the socalled threshold value, is recorded; then the automatic fire detector to be tested is subjected to a

certain environmental stress. Next, the threshold

value is again measured and tested according to the

above method, to see whether, and to what extent, it

has changed.

Very high requirements must be made with respect to the

reproducibility of the simulated fire characteristic and

with respect to the reliability of the measurement devices

used. Only thus can it be reliably determined that differing

measured values are based on changes in the test sample and

not on changes of the measuring devices. To meet these

requirements, which are obvious in themselves, is often quite

difficult. The importance of this problem becomes clear, for

example, in measuring the "smoke density" in testing smoke

detectors. Here, the concept "smoke density" is deliberately

not specified more closely. Smoke can only be completely

described by measuring many (at least 6) parameters. But at

this time, it is not yet possible to measure all these parameters continuously and simultaneously. As a rule, only two

measuring processes are simultaneously utilized.

It is improbable that the same results are attained for

different experiments, when simultaneous measurements, using

two different methods, are made on practically occurring

smokes, even though essential smoke parameters are different.

2
Of course, the assumption that this is improbable is

justified when the measuring range, in which the used

measurement devices operate reliably, and their behavior

under temperature changes and higher flow velocities are

known

.

In the second group, four of the fire detectors to be

tested are exposed to real test fires, and their behavior

is checked. This group of tests is called trial test.

3. TRIAL TESTING

In principle, all types of fire detectors are exposed

to the same test fires, to make possible comparison of the

sensitivity to different types of fires between different

types of detection.

The following five types of fires are under discussion

and have already been used for several years — at least in

Germany, and according to my knowledge also in Switzerland:

1. Open wood-burning fire (loosely stacked, dried

small beechwood sticks)

2. Smoldering fire (smoldering of several small,

dried beechwood sticks on a heating plate —

no flames)

3. Synthetics fire (polyurethane — soft foam

mats without fire inhibiting additives)

4. Diesel fuel fire

5. Alcohol fuel fire

Each fire is carried out in three steps, i.e. with different

amounts of fuel material, which increases with the step

number

.

3
Type of Test Fire Amount of Fuel Material Fuel Material

1. Open woodburning fire

0.75 1.5 3.0 kg Beechwood

10 x 20 x 250 mm 3

2 . Smoldering

fire

3 6 12 pieces 10 x 20 x 50 mm 3

3. Synthetics

fire

1 2 3 mats Polyurethanesoft foam mats

20 x 400 x 500 mm

4. Diesel fuel

fire

15

25

25

50

40

100

g

cm z Diesel fuel

(surface)

5. Alcohol fuel

fire

1.2

1100

1.6

1500

2.0

1900

kg

cm 2

Alcohol fuel

C 2 H 5 OH (surface)

The result of the trial test is recorded in a calibration

table. That means whether, and at what step, and at which

type of fire a detection ensemble has been triggered is

shown in tabular form.

Such calibration tables can, for example, look like this:

Type of Fire Classification

I II III

1. Open wood-burning fire - X

2. Smoldering fire X - -

3. Synthetics fire - X -

4. Diesel oil fire - X -

5. Fuel alcohol fire - - -

(Typical result for a smoke detector)

4
Type of Fire Classification

I II III

1. Open wood-burning fire X -

2. Smoldering fire -

3. Synthetics fire X -

4. Diesel oil fire - X

5. Fuel alcohol fire X

(Typical result for an infrared radiation detector)

A cross at test fire No. 1, Step I, means that all four

samples of a certain detector type triggered for the smallest

amounts of fuel material. The suitability table which is to

be prepared for all types of automatic fire detectors is an

important aid in choosing the correct type of fire detector

in projecting automatic fire detection systems.

To conclude this general survey, all tests will once

again be summarized in tabular form:

1. Switch-on

2. Reproducibility

3. Directional Dependence

4 . Sample Scatter

5. Electric Energy Supply

a) Long-term fluctuations

b) Noise Voltages

6. Wind Dependence (only smoke detectors)

7 . Temperature Dependence

a) High Temperatures

b) Low Temperatures

8 . Glare (only optical smoke detectors and

radiation detectors)

9. Moisture Requirement

10. Vibration

11. Mechanical Shock

12. Mechanical Impact

13. Corrosion (S0 2 and H 2 S — atmosphere)

14. Dust (only smoke detectors)

15. Trial Test (5 test fires)

5
In the first 4 tests, the fire detectors are examined

for direct deficiencies in mechanical construction and

electrical circuitry. In tests 5 through 14, the influence

of disruptive environmental influences are investigated.

Finally, with test 15, sensitivity is tested and the suitability table is produced.

After this general survey concerning testing methodology

in general, the special testing technology for radiation

detectors will now be addressed more closely.

First of all, the most important types of radiation

detectors will be mentioned:

1. The radiation itself and the time behavior of

the radiation is monitored in one definite wavelength band in the infrared region. The detector

triggers when infrared radiation occurs for

a definite time, and if it fluctuates with a

characteristic frequency ("flicker").

2. Radiation is monitored in two wavelength ranges

(one range in the visible and one in the infrared, or both in the infrared) . The detector

triggers when the radiation intensities in the

two ranges have a ratio typical for flames.

3. Like 2, but the time behavior is additionally

evaluated.

4. The light-sensitive element of the radiation

detector is a switching tube, to which electric

voltage is applied, and which triggers when

ultraviolet radiation occurs in the range of

about 0.22 ym to about 0.28 ym. To increase

reliability against mis-triggering, the tubes

are generally connected to an impulse voltage,

so that, when the tube is triggered, it immediately turns off again at the end of a voltage

impulse

.

Only when a certain number of triggers per unit

time is reached, does the radiation detector

itself trigger.

4. TESTING TECHNOLOGY

The problem now is to find a suitable measuring and

test apparatus with which the triggering threshold of the

detectors can be measured in the basic test, for example,

before and after an environmental stress. It was originally

6
planned to test all types of radiation detectors, that is

ultraviolet and infrared radiation detectors, with one

apparatus. However, this idea again, had to be abandoned

for the following reasons:

1. The basic difference in the mode of action

between ultraviolet and infrared radiation

detectors

.

2. Constancy of the radiation must be able to be

continuously monitored during the experiments.

This presents great difficulties because, in

the ultraviolet region of interest (0.2... 0.3

ym) , the radiative powers differ by orders of

magnitude from those in the infrared region of

interest (0.8... 10 ym) . No receiver exists

which is capable of measuring with sufficient

accuracy in both regions simultaneously.

3. Finding a reproducible laboratory flame, which

emits constant radiative power in both regions

at the same time, poses difficulties.

Because of the wider distribution of infrared radiation

detectors, the principal endeavor has first of all been concerned with the development of testing technology for such

detectors.

Let us consider the emission spectra of flames where

hydrocarbons are principally burned (figures 1 and 2)

.

The similarity of the spectra is very conspicuous. The

emphatic peak at 4.4 ym which belongs to a C0 2 — resonance

line, is especially characteristic.

If emission spectra of artificial radiation sources are

considered, such as incandescent lamps, heating bodies, etc.,

an entirely different course results. The emission spectrum

of a black body is here shown (figure 3) as representative

for such radiation sources.

It is just these characteristic differences that are

utilized by many infrared radiation detectors to improve

reliability against false alarms. Therefore, it is immediately clear that, for example, a black body simulator cannot cause such detectors to trigger, and is therefore not

suitable to simulate the fire characteristic "flame radiation."

According to this insight, the problem is to develop a

suitable laboratory flame based on hydrocarbons. This flame

should be reproducible with sufficient accuracy relative to

constancy of emission and time behavior. The radiative

7
power of a flame can in principle be controlled by controlling the supply of fuel. But not so its time behavior. Flickering is co-determined by external influences, such as, for

example, air motion in the laboratory.

The problem can be solved by using a laboratory flame

whose radiation is constant in time: a flame, therefore,

which does not flicker. The "flicker," which is required

for triggering most detectors, is generated by a chopper

disk in the ray path between flame and detector.

Here in the Institute, a device has been used for several

years, which operates with a non-flickering methane flame

(figures 4 through 6)

.

An aperture system, a chopper disk, and several control

devices are built into a stable metal chassis. The burner

system is solidly connected with the chassis. The entire

device is mounted on an optic bench. Since the flame is to

burn very quietly, two tubes are fastened to the burning

chamber, which result in laminar gas flow. The vertical pressure tube in front of the combustion chamber generally prevents flickering caused by turbulent environmental air, and

gives an even flow of surrounding air through the two apertures in the combustion chamber. The fuel gas is brought in

through a tube which lies concentrically in the air supply

tube. By moving the gas supply tube and by changing the

through-flow of gas, the flicker of the flame can be minimized.

The combustion chamber block is water-cooled through drilled

channels, so that any heat radiation from hot metal worth

speaking of is generally prevented.

Originally, the device was operated with natural gas

from the city supply. But it turned out that pressure pulses,

which are unavoidable in the gas line, produced too strong

a flicker of the flame. It was further determined that the

composition of natural gas is not always the same, so that

the reproducibility of the flame emission spectrum could not

always be guaranteed.

For this reason, methane from a pressurized bottle was

chosen as fuel gas. The gas is brought to the burner through

a pressure reduction valve, a pneumatic flow control, and a

flow metering device.

Immediately in front of the combustion chamber, there

is an adjustable hole aperture, through which part of the

flame radiation can exit. Before the aperture there is a

perforated disk, driven by an electric motor, by means of

which chopping frequencies of about 1 Hz to 30 Hz can be set.

The chopper frequency is sensed by a photocell and is indicated digitally.

8
Since the sensitivity of radiation detectors is not to

be measured with the device, but only relative changes in

trigger threshold, precise knowledge of the spectral distribution of the emission spectrum is not required. It is sufficient when all infrared radiation detectors under test can

reliably be made to trigger.

The dependence of the radiation density on the distance

between radiation source and receiver is measured with a

silicon photodiode, a PbS photoresistor , and a radiation

thermoelement. This dependence can be described by the

following formula:

d>y = ———— • 6

r

Y o

Here symbols have the following meaning:

<(> Radiation flow recorded by the receiver

d> Radiation flow measured in a reference

o plane in front of the device

r Distance between receiver and radiation

source

r Distance of the reference plane from the

o , . . . ^ radiation source.

Through this relation, relative changes in the triggering

threshold of detectors can be determined by determining the

distance differences. By slightly changing the gas flow,

the residual flicker of the flame can be minimized to about

1% of the mean value of the radiation intensity. Experiments

have shown that, with this residual flicker, commercial radiation detectors are not brought to trigger.

The constancy of the radiation source is checked with

the PbS photoresistor. Within a time interval of 4 hours,

the maximum deviations that occurred were 2.5%.

With a heat-up time of at least 20 minutes each time,

the radiation intensity can be reproduced without new corrections with an accuracy of 2.5%.

Naturally, the radiation intensity can at any time be

monitored during the experiment by means of the PbS photoresistance and, should circumstances so require, can be readjusted by small changes in the gas flow. The device was

tested with various commercial radiation detectors. The

maximum distances between the detectors and the flame were

9
determined, where triggering just barely occurred. After

several hours and days, these distances were determined anew,

whereby the detectors were exposed to no special stresses in

the meantime

.

The maximum distances for which triggering just barely

occurred then corresponded to a sensitivity change of about

0.5%, which lies within the accuracy of measurement.

For practical tests from the "basic test" group, the

detector under test is mounted on a stand so that the lightsensitive part is at the height of the aperture opening of

the measuring apparatus. In addition, the detector can be

rotated about the stand axis. The angle of rotation and the

distance to the burner flame can be read.

The chopper frequency for which the radiation detector

under test has maximum sensitivity is set at the measuring

apparatus. The detector is first pushed so near the aperture opening that it certainly triggers. The triggering

time required for this is noted. Then the detector is pushed

so far away from the aperture opening that it no longer triggers. Then the radiation detector is pushed closer to the

aperture opening step-by-step. At each step, one waits for

three times the previously measured triggering time. The

point is determined at which the detector triggers three

times, one after the other. As a control, a position is

sought, which lies as close as possible behind this "triggering point," at which the detector does not trigger. The

step sizes should amount to 1/2 cm to 2 cm, depending on the

distance from the radiation source.

The entire procedure should be begun at the earliest 15

minutes after connection to the supply voltage and should be

concluded at the latest after another 15 minutes, since the

sensitivity of some light detectors can still change even

after several hours.

Special requirements hold for the following tests,

because of the physical peculiarities of radiation detectors.

4.1. Directional Dependence

The triggering thresholds are determined in a range of

angular openings of 120°; i.e., a radiation detector should

meet the still-to-be-formulated requirement for the triggering threshold within a range of opening angles of 120°.

10
4.2. Glare

Glare from foreign radiation can shift the operating

point of photoelectric construction elements into a nonlinear region, which would entail reduction of sensitivity.

The following types of glare are proposed:

1. One-hour irradiation with a circular fluorescent lamp (32 watts) at a distance of 30 cm

2. One-hour irradiation with two incandescent

lamps (25 watts each) at a distance of 30 cm.

Both interfering radiation sources are connected to

alternating voltage. During the glare exposure, the detectors should not trigger. During and after each glare exposure, the triggering threshold of the detector is again

measured

.

The remaining tests of the "basic tests" do not differ

essentially from those for smoke and heat detectors. The

triggering threshold of the detectors is measured before and

during or after each stress. The change in the value of the

triggering threshold may not exceed a certain value. The

permissible value for the relative change must be set when

more test experience has been accumulated. We consider a

factor of two suitable as the maximum permissible change for

the present time.

In addition to the five proposed test fires, a fire is

also to be introduced which is specific to the radiation

detector. The purpose of this additional fire is to see

whether fires can still be detected at great distances. A

methyl alcohol test fire (burning surface 2000 to 3000 cm2

) is proposed, to be detected at a horizontal distance of 15 m.

The proposed requirements and tests for infrared radiation detectors in our opinion allow the opportunity of objective evaluation of a type of fire detector which is in many

cases a good supplement for a classical fire detection system.

In some applications, radiation detectors are the only usable

type of fire detector because of special circumstances.

4.3. Trial Test

5. CONCLUSIONS

11
Because of the completely different functional principle

of ultraviolet radiation detectors (no consideration of the

temporal behavior of flames, no evaluation of certain peculiarities in the flame emission spectrum) , the use of laboratory flames can be dispensed within simulating the ultraviolet flame radiation as a fire characteristic.

Experiments which promise success were performed by us.

Here, mercury vapor lamps were used as radiation sources.

The 0.2537 ym emission line is filtered out through an optical interference filter and is attenuated. The radiation is

measured with a photomultiplier that is sensitive only in

the ultraviolet.

The current through the mercury vapor lamp is adjustable.

A linear increase of the radiative power of the 0.2537 ym

emission line is achieved through a function generator, which

prescribes a long linear rise of the should-value . The photomultiplier serves as an is-value sensor. Radiative power is

increased until the detector under test triggers. With this

method it is possible to measure triggering thresholds for

ultraviolet radiation detectors. For the rest, the same procedure can be used as for infrared radiation detectors. The

entire procedure is still in the experimental stage and is

not yet suitable for running-type tests for ultraviolet radiation detectors.

6 . REFERENCES

[1] Kirsch, W. , Toward a Determination of Wavelength

Ranges in the Infrared Range, Suitable for Automatic

Fire Detection, Dissertation, T. H. Aachen (1970)

.

[2] Pfenning, D. B. , Radiative Transfer from Laminar

Diffusion Flames, Dissertation, University of Oklahoma

(1970).

[3] Kirsch, W. , Temperature Radiation as a Characteristic

of Starting Fires, Research Report of the Province

Nordrhein-Westf alen No. 2217, West German Publisher

Opladen (1972).

[4] Kirsch, W. and Portscht, R. , Temperature Radiation as

Characteristic of Starting Fires, Research Report of

the Province Nordrhein-Westfalen No. 2136, West German

Publisher Opladen (1970)

.

12
[5] Portscht, R. , Concerning the Time Behavior of Temperature Radiation as Characteristic of a Fire, Dissertation, T. H. Aachen (1970)

[6] Luck, H. and Portscht, R. , A Testing Scheme for Automatic Fire Detection Systems, VFDB-Zeitschrift 17,

No. 2, 37 (1968).

13
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25cmx25cm

4)

Enfernung Strahlungsquelle-Empfdnger: 930cm

1.5 2,5 3 3,5 4 4,5

5) Wellenldnge X

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Figure 1. Emission Spectrum of a Wood Fire,

(According to Kirsch)

1. Spectral Radiation Flow

2. Fuel Material: Fir Wood Sticks

3. Burning Surface: 25 cm x 25 cm

4. Radiation Source — Detector Distance:

930 cm

5. Wavelength

14
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4)

Entfernung Strahlungsquelle-Empfdnger: 930cm

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a

30

c

3

25

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15

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um Brennmaterial : Brennspiritus 95%

Benzol ^ 5 V.

brennende Oberflache 26cm» 26cm

Entfernung Strahlungsquelle- Empfanger: 930cm

2.5 5)

3 3,5 4 4,5 Wellenldnge X —

5(im

Figure 2. Emission Spectrum of an Alcohol Fire and of an

Alcoholbenzene Fire (According to Kirsch)

1. Spectral Radiation Flow

2. Fuel Material: Methyl Alcohol

3. Burning Surface: 26 cm x 26 cm

4. Radiation Source — Detector Distance: 9 30 cm

5. Wavelength

6. Fuel Material: Methyl Alcohol 95% Benzene 5%

15
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Figure 3. Interfering Radiation Spectrum / (According to Kirsch)

1. Spectral Irradiation Intensity

2. Radiation Source: Black Body at a

Distance of 15.4 m from the Detector

3. Wavelength

16
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2) Optische Bank

7) Aufsetzplatte

Lampe 8)

Luftzufuhr

9)

saustritt 12)

Photodiode 13)

Gaszufuhr 14)

Figure 4. Infrared Radiation Detector — Test Apparatus

1. PbS Photoresistor

2. Optic Bench

3. Aperture Mounting

4 . Perforated Disk

5. Mounting for Motor with Height Adjustment

6. Drive Motor for Perforated Disk

7. Mounting Plate

8 . Lamp

9 . Air Intake

10. Water-Cooled Combustion Chamber

11. Pressure Tube

12. Gas Exit

13. Photo Diode

14. Gas Intake

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NBS-1 14A (REV. 7-73)

U.S DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1040

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

POINTS OF VIEW IN TESTING FLAME DETECTORS

5. Publication Date May 1976

6. Performing Organization Code

7. AUTHOR(S)

M. Schnell

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. 492-8677

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 tactual summary ol most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

The general principles for type testing the fire detectors which are

already in use in the assessment of heat and smoke detectors are

summarized. These include the so-called basic tests and the trial

tests. The trial tests were intended to include all test fires in

order to ensure comparability of tested fire detectors. Additional

test fires are proposed which are intended to permit differentiated

comparison of flame detectors between one another. The main problem

in assessing the performance of flame detectors during environmental

influences is the selection of a suitable radiation source for

reproducibly simulating the characteristic "flame." The requirements

that this radiation source must fulfill are dealt with and various

realizations involved are discussed. The practical testing of infrared

flame detectors to the basic tests is described. In addition, a

suggested test apparatus for ultraviolet flame detectors is dealt with.

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 semicolons)

Detection; fire detectors; flame detectors; heat detectors; infrared

detectors; smoke detectors; testing; ultraviolet detectors.

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