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Many operating staffs struggle with selecting the right flame detector to suit their specific application. Choosing the best device can improve fire detection and limit false alarms.
This article will help you determine the appropriate detector for your application by assessing factors such as field of view, fire size and sensitivity, and specialized hazards like hydrocarbon and hydrogen fires.
Detector Type
The fire detection system is one of the most important components in your facility’s fire protection plan. It is what initiates actions to protect your people, equipment, and environment by detecting a fire and communicating the necessary information to the fire alarm and suppression systems. However, fire detectors aren’t all created equally, and each can operate, perform, and detect different hazards in different ways. This makes choosing the right flame detector for your specific application a challenging task.
The basic function of a flame detector is to monitor radiation emitted from a flame. Depending on the design of the flame detector, it can respond to energy in the visible, infrared (IR), and ultraviolet (UV) spectrums. When a flame emits radiation in these ranges, it activates the detector’s sensor, which then converts that radiant intensity into a signal to initiate appropriate actions.
Typically, flame detectors are designed to detect the presence of hydrocarbon and hydrogen flames. In order to identify these types of flames, they must be capable of ignoring radiation emitted from other sources like sunlight, hot objects, and other inorganic materials.
To ensure that a flame detector is suitable for an application, users must evaluate the potential flame hazard and the environmental conditions in which it will operate. It is also critical to know the size of the protected space and its radiation characteristics, as these factors will determine the maximum field of view, detection range, and false alarm immunity required for a particular installation.
For example, visual flame imaging flame detectors use charged couple device (CCD) image sensors to scan and analyze live video images of a potential fire hazard. They are able to identify flames by the shapes and growth of their radiation, but they cannot detect invisible or near-invisible gases like hydrogen, so these detectors may not be well-suited for all applications.
UV/IR flame detectors integrate an optical UV and IR sensor into a single instrument that can detect both the UV and IR radiation emitted by a flame. This increases the overall false alarm immunity over either detector type alone, but it does limit fire detection to those sources that are both UV and IR-active.
Fuel Type
Detectors must be selected to suit the specific flame hazards being monitored. Each type of flame generates radiation at different wavelengths, and detectors use unique optical sensing attributes to differentiate the radiation emitted by fires from the surrounding environment. A variety of sensors are available to meet the needs of almost any process application, and the best option may be a combination of several types.
A few questions about the nature of your potential fire and the conditions you can expect at the site help you narrow down the selection process. The answers will guide you toward a model that can reliably sense and respond to the specific hazard.
For example, a plant that processes alcohol, gasoline, or jet fuels will require a sensor that can see through the dense smoke typically produced by these types of fires. This is best achieved by using a multi-spectrum infrared (MSIR) flame detector, which uses multiple infrared wavelengths to better distinguish flame-producing radiation from other sources such as sunlight, arc welding, or hot objects.
Other considerations include whether the process area will be indoors or outdoors and the degree of protection required. Most hazardous areas require continuous monitoring equipment to ensure that fires don’t occur in a way that could impact people or valuable assets. Flame detection systems are critical for this purpose, as they are capable of detecting fires before they can impact employees and equipment.
In addition, a flame detector’s ability to detect a fire in the presence of heavy smoke is an important feature for most applications. This is because smoke can interfere with a detector’s ability to distinguish between a fire and a background source, such as sunlight or arc welding.
The final factor that will influence the flame detector type you choose is its ability to reject false alarms. False fire alarms are more than just a nuisance; they reduce productivity and escalate costs. The more accurately a flame detector can discern between a real fire and the radiant energy emitted by sunlight, arc welding, hot objects, and other non-flame sources, the less likely it will be to falsely trigger an unwanted alarm.
Temperature Range
Flame detection plays a critical role in safeguarding personnel, equipment, and facilities in hazardous industries. Choosing the right detector depends on a number of factors, including detection range and FOV, sensitivity, false alarm rejection, environmental factors, and communication capabilities. Understanding the principles and technologies behind flame detection enables you to select the best detector for your application.
Detectors are activated by radiation emitted by a fire and convert that radiant energy into a voltage signal. Different types of sensors can be used to sense a wide spectrum of radiation, including ultraviolet (UV), infrared (IR), and multi-spectral infrared (MSIR).
The first and most important consideration when selecting a detector is that it accurately and reliably identifies flames. To do so, the National Fire Protection Association recommends that the device’s spectral response match the spectral emissions of the hazard to be detected.
UV flame detectors are a good option for general hydrocarbon and hydrogen fuel applications because they detect the spectral bands most commonly emitted by clean, solid fuels. However, they are less effective for detecting a vapor or liquid fire that uses a different fuel type.
Other types of optical flame detectors are available that offer improved sensitivity and better immunity to nuisance sources, such as sunlight, electrical discharges, arc welding, or hot objects. Optical flame detectors can also function well indoors or outdoors and can be used with various fuel types.
Most optical flame detectors provide a range of field-of-view (FOV) options that define the area covered by a single device, with center axis sensitivity defined as the maximum detection range for a specific fire size or type. Larger FOVs enable fewer devices to be used in a system, helping reduce installation and maintenance costs.
Other optical flame detectors, such as dual UV/IR and IR3 triple IR spectral bands, can compare threshold signals in multiple wavelength bands, minimizing the probability of false alarms by only activating when a flame is present in all three wavelengths. These detectors are often used in specialized applications, such as pyrolysis or hydrocarbon configurations, where a high-purity flame is required for operation.
False Alarm Rejection
Flame detectors are one of the most common devices used to monitor process areas for fire hazards. However, they are not all created equal – while all work to accomplish the same basic objective, each type operates, performs, and responds to particular hazards a bit differently. This can cause confusion for operating staff when selecting a device.
The best way to choose the right detector for a given application is to use an analysis of the specific fire risks and their causes. Then select a detector type that matches these characteristics. This will ensure that the device is able to effectively detect and respond to the specific fire risk without excessively increasing the chance of false alarms from non-fire phenomena.
Among the main factors to consider are detection range and field of view, response time, and the ability to communicate with other equipment through bidirectional communications protocols like HART. The sensitivity of a detector at varying angles is also important to determine the likelihood of false alarm rejection since the detector may be “blinded” by the reflection of sunlight or other sources of radiation from the wall of the building or other objects surrounding it.
Four primary optical flame-sensing technologies are available – UV, UV/IR, multi-spectrum infrared, and visual flame imaging. Each offers a different detection spectrum, field of view, and particular immunity to certain false alarm sources.
An easy-to-use flowchart is provided in the guide to help users select the correct detector for their application based on the characteristics of the potential fire risk and its cause. It is also recommended that a Detector Selection Table be used to record the main risks and all decisions and reasoning behind the chosen detection choice – both during system design and whenever changes to the detection are made.
Aside from the selection of a suitable detector type, it’s equally important to minimize false alarms through good plant design and maintenance practices. This includes ensuring that any equipment that could cause a fire in the area to be protected is properly maintained and located and that adequate safeguards are identified using engineering standards and established safety assessment methodologies like event tree and a layer of protection analysis.
