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Flame and Gas Detection Handbook

ICEweb acknowleges the submission of this fire and gas technical handbook by AMPAC INDUSTRIES

 CONTENTS 

1.0 Introduction
2.0 Flame detectors

2.1 Infrared Single Frequency Flame Detectors
2.2 Multi Spectrum Flame Detectors
2.3 Ultraviolet Flame Detectors
2.4 Ultraviolet / Infrared Flame Detectors
2.5 What Do I Connect A Flame Detector To?
2.6 Flame Detector Installation
2.7 Flame Detector Selection

3.0 Gas detectors

3.1 Catalytic Gas Detectors
3.2 Infrared Gas Detectors
3.3 Electrochemical Gas Detectors
3.4 What Do I Connect A Gas Detector To?
3.5 Gas Detector Installation
3.6 Gas Detector Selection

1.0 INTRODUCTION

The purpose of this handbook is to provide information on the various types of flame and gas detectors available.

Although Ampac has created the handbook, and represents Det-Tronics, it does not relate specifically to our products and it is intended to be used as a guide for all manufacturers’ equipment and systems.

It should be noted that the information is to be used as a reference only and that when specifying equipment for a project, it is best to consult with the end user and the manufacturer to ensure the most appropriate equipment is selected.

Additional copies of the handbook are available on request, as are in house presentations, or just call one of our customer service offices for more information.

HEAD OFFICE
PERTH MELBOURNE BRISBANE SYDNEY
AMPAC INDUSTRIES P/L AMPAC INDUSTRIES P/L AMPAC INDUSTRIES P/L AMPAC INDUSTRIES P/L
97 WALTERS DRIVE 422 JOHNSTON STREET UNIT 3/121 KERRY ROAD UNIT 4/33 NYRANG ST
OSBORNE PARK ABBOTSFORD ARCHERFIELD LIDCOMBE
WESTERN AUSTRALIA 6017 VICTORIA 3067 QUEENSLAND 4108 NSW 2141
PH: 61 (08) 9242 3333 PH: 61 (03) 9416 4111 PH: 61 (07) 3216 6654 PH: 61 (02) 9648 4933
FAX: 61 (08) 9242 3334 FAX: 61 (03) 9416 4227 FAX: 61 (07) 3216 7498 FAX: 61 (02) 9648 4932

Email: info@ampac-ind.com.au

Website: www.ampac-ind.com.au

We acknowledge Jim Russell, Principal Instrument Engineer for Woodside Energy Perth Western Australia and Mark Sutherland, Product Manager for Detector Electronics Corporation for their assistance in creating this handbook.

2.0 FLAME DETECTORS

Most fire detection technology focuses on detecting heat, smoke (particle matter) or flame (light) – the three major characteristics of fire. All of these characteristics also have benign sources other than fire, such as heat from steam pipes, particle matter from aerosols, and light from the sun. Other factors further confound the process of fire detection by masking the characteristic of interest, such as air temperature, and air movement. In addition, smoke and heat from fires can dissipate too rapidly or accumulate too slowly for effective detection. In contrast, because flame detectors are optical devices, they can respond to flames in less than a second. This optical quality also limits the flame detector as not all fires have a flame. As with any type of detection method its use must match the environment and the risk within the environment.

Typical applications for optical flame detectors are;

Examples of actual installations are;

There are three types of flame detectors currently available. They are Infrared (IR), Ultraviolet (UV), and a combination of UV and IR. The spectrum below shows the relationship between these frequencies and visible light.

2.1 INFRARED SINGLE FREQUENCY FLAME DETECTORS

Infrared detectors have been available for many years, however, it has only been in recent times that technology has allowed for stable, accurate detection to occur. There are two types of Infrared detectors, single frequency and multi spectrum.

The basic principle of operation for a single frequency IR detector is;

The detector is sensitive to a narrow band of radiation around the 4.4 micron range which is a predominant emission band for hydrocarbon fuelled fires. Additionally, the sun’s radiation at this band is absorbed by the earth’s atmosphere, making the IR flame detector solar blind. Single frequency detectors use a pyroelectric sensor, which responds to changes in IR radiation intensity. In addition they incorporate a low frequency band pass filter, which limits their response to those frequencies that are characteristic of a flickering fire. In response to a fire signal from the sensor, electronic circuitry in the detector generates an output signal.

Strengths of the single frequency IR detector are;

Limitations of the single frequency IR detector are;

2.2 INFRARED MULTI SPECTRUM FLAME DETECTORS

The basic principle of operation for a multi spectrum IR detector is;

The detector has three sensors, each sensitive to a different frequency of radiation. The IR radiation emitted by a typical hydrocarbon fire is more intense at the wavelength accepted by one sensor than the other two. Electronic circuitry in the detector translates the difference in intensity of the three sensors to a ratio, that along with a synchronous flicker must be present before a fire signal is produced. This allows the detector to reject high intensity flickering black body radiation sources since these sources will not meet the proper ratio criteria.

Strengths of the multi spectrum IR detector are;

Limitations of multi spectrum IR detector are;

IR detectors are sensitive to most hydrocarbon fires (liquids, gases, and solids). Fires such as burning metals, ammonia, hydrogen and sulphur do not emit significant amounts of IR in the detector's sensitivity range to activate an alarm. IR detectors are suitable for applications where hydrocarbon fires are likely to occur and high concentrations of airborne contaminants and / or UV radiation sources may be present. The detector should be used with caution when the presence of hot objects and the potential for ice build up on the detector are likely.

2.3 ULTRAVIOLET FLAME DETECTORS

A UV detector uses a sensor tube that detects radiation emitted in the 1000 to 3000 angstrom (one ten billionth of a metre) range. It is important to note that ultraviolet radiation from the sun that reaches earth starts at 2800 angstrom. If the detector's sensor has a wide range then it will be triggered by the sun’s rays, which means it is only suitable for indoor use. There are sensors available with a range of 1800 to 2500 angstroms. Virtually all fires emit radiation in this band, while the sun’s radiation at this band is absorbed by the earth’s atmosphere. The result is that the UV flame detector is solar blind. The implication of this feature is that the detector can be used indoors and outdoors. In response to UV radiation from a flame that falls within the narrow band, the sensor generates a series of pulses that are converted by the detector electronics into an alarm output.

Strengths of the UV detector are;