Fire Detectors – Flame Detectors


Fire Detectors – Flame Detectors

A flame detector is an optical sensory device that is designed to detect flames. Early detection has a significant impact on a successful fire fighting effort. It is reliable in a harsh environment where smoke or heat detectors cannot be installed, as they will be continually be triggered in such environments.

Oxygen, heat, and fuel combine to form a chemical reaction which produces fire. When the reaction occurs, ultraviolet and infrared rays are emitted. Flame detectors are special sensors that can effectively detect the radiation emitted by flame. They are designed to effortlessly differentiate the difference between a live flame and a false alarm.

The way and manner a flame detector will respond to fire depends on how it was installed. Some models are embedded with special alarms, others can deactivate a fuel line (natural gas and propane line), and some can activate a fire suppression system.

In industrial furnaces, they are used for evaluation purposes and to accurately determine if the furnace is working well. In this application, they take no further action beyond notifying the control system.

A flame detector can respond more accurately and faster than heat and smoke detector due to the special mechanisms it uses to detect flames.

The following article will explain how flame detectors work, unveil the various types of flame detectors and their application and answer some important questions about flame detectors.

Light spectrums

To get a clear picture of how flame detectors work, you first have to have basic knowledge of light spectrums.

Light spectrums are wavelengths. The eyes can only see a wavelength of 350 to 790nm. However, there are some wavelengths that are invisible to the human eyes. These invisible wavelengths can be detected by a working flame detector. The sensor on them detects the amount of ambient light absorbed within a particular wavelength and triggers an alarm if enough light is sensed by the device.

The working principle of a flame detector

Flame detectors are special devices designed to quickly detect common fuel like kerosene, jet fuel, hydrogen, LNG/LPG, textile, sulfur, solvents, diesel, gasoline, alcohols, textiles and wood.
That can effectively distinguish between radiation from hot objects, sunlight, welding, lighting, and other non-flame sources. A false alarm causes a drastic increase in cost and productivity loss.

The flame detector comprises an electromagnetic radiation receiver and a small electronic circuit. They are triggered when they receive electromagnetic radiation from a well-defined wavelength according to the infrared spectrum. Most advanced flame detectors models have a view of about 120°.

The IR detector can easily detect flicking IR radiation ranging from 1 to 15 Hz. The device use flicker techniques to do this. It can operate through oil, dust, water vapor, or ice. Some models of IR flame detectors can respond to the lights emitted by hydrocarbon flames.

Below are some key applications of fire detectors:

  • Agriculture power plants and pharmaceuticals.
  • Fume cupboard – MDF factories.
  • Generators and storage tanks.
  • Domestic heating systems.
  • Gas fuelled cookers.
  • Printing – tunnels and spray booths.
  • Engine rooms and engine test facilities.
  • Furnaces.
  • Industrial heating and drying systems.
  • Aircrafts hangers.
  • High voltage equipment and clothing dryers.
  • Oil refineries and industrial gas.

Types of flame detectors

Industries involved in processing, transporting of flammable materials, manufacturing and commercial centers rely on flame sensory systems for safety. At the core of them is a very important component- the flame detector. Flame detectors are specially designed to detect heat and send information to a control board. After with an alarm is triggered or a fire suppressing system is activated.

There are different types of flame detectors available on the market today, some of the common types are described below.

Ultraviolet flame detectors

UV flame detectors work by detecting the Ultra violet rays emitted at the ignition of a fire. They can detect explosions and fires within 4 to 5 milliseconds. Most times, they are programmed to delay for 3 to 5 seconds to minimize false alarms which can be triggered by UV sources like welding, sunlight, radiation, and lightning. UV detectors operate with wavelengths shorter than 300nm to reduce the effect of natural background radiation. The only downside of this device is that they are overly sensitive to halogen light and welding, therefore they are usually installed indoors.

Near IR array

Near IR array flame detectors, which are also known as visual flame detectors, use advanced flame recognition technology to confirm fire by carefully analyzing near infrared radiation known as CCD (charged-coupled device).

A near IR sensor can effectively monitor a flame without much hindrance form water vapor and water. The device relies on pyroelectric sensors and pixel array sensory monitoring system to detect even a flicking flame.

They are divided into different ranges:

  • Short wavelength IR (1.4-3µm).
  • Near IR (0.75-1.4µm).
  • Long wavelength IR (8-15 µm).
  • Far IR (15-1,000 µm).
  • Mid-wavelength IR (3-8 µm).

Infrared detectors

Wideband or infrared detectors are designed to monitor the IR spectral band for certain patterns given off by hot or burning gasses. These are accurately sensed using a high-tech TIC (Thermal imaging camera). False alarms can be caused by background thermal radiation or by other hot surfaces in the area. Water or vapor on the detector’s lens will reduce the accuracy of the device, as will exposure to sunlight.

The device has a special frequency range of 4.3 to 4.4µm, which is somewhat similar to the frequency of CO2. During the burning of hydrocarbons, heat and CO2 is released. The energy released by the hot CO2 resonates with the frequency of the device. The sensitivity of IR detectors is reduced by sunlight.

The detector is made to distinguish between a false alarm that can be caused by heat radiation from hot machinery and a live flame. The device is embedded with a special infrared detector that uses algorithms to effectively suppress the effect of blackbody or background radiation.

One disadvantage of infrared detector is that they are unresponsive when used in open areas or exposed to the elements. They are better used indoors, where they are less likely to be interrupted by water vapor.

Infrared thermal cameras

IR thermal cameras are designed to detect heat. They are embedded with a special algorithm that enables them to accurately detect hot-spots and flames within an area. They are can be used in a dark environment, indoors and outdoors.

UV/IR

These detectors are sensitive to IR and UV wavelengths and can accurately detect flames by comparing the signal of both ranges. This helps to significantly reduce false alarms.

IR3 flame detection

IR3 detectors are designed to compare 3 wavelength bands within an Infrared spectral region and their ratio to one another. For example, when one of the sensors monitors a 4.4-micrometer range, the other sensors could be monitoring wavelengths below or above 4.4. The device is designed this way so that it can accurately distinguish between actual flames emitted by Co2 and non-flame IR sources. This ultimately makes the device immune to false alarms and super effective in detecting fires.

IR3 detector can easily pick up or detect 0.1m2 gasoline fire at 65 meters in less than 10 seconds. Like other IR detectors, they are susceptible to water and water vapor.

Most IR detectors are made to ignore background IR radiation, which is present in every environment. They are designed to quickly detect a sudden change in sources of radiation. Unlike UV/ IR and IR detectors that are prone to false alarms when exposed to the rapid-changing patterns of non- flammable radiation, IR3 detectors are immune or less sensitive to false alarms.

IR/ IR flame detection

IR/IR detector can effectively compare the signal in two different IR ranges. Most times one of the sensors is focused on 4.4 micrometer Co2, while the other sensor is focused on Co2 emissions in non-carbon based fuels like hydrogen.

Visible sensors

This device is designed to use a special light to identify smoke and flames. Unfortunately, visible sensors, which look like a camera, can be blinded or covered by humans or by heavy smoke. It is also possible for the device to mix infrared information with light information, which will reduce the odds of a false alarm being triggered. A good example of the visible sensors is the corona camera. In this equipment, the visible image information is mixed with the information of the ultraviolet camera embedded in the device.

Video

A closed-circuit television can be used to detect wavelengths between 0.4 and 0.7µm. Thick fog and heavy smoke can drastically reduce the effective range of this device because they depend on visible spectrums to operate.

Thermocouple flame detection

Thermocouples are sophisticated devices that are used exclusively for closely monitoring flame presence in combustible heating sources like gas cookers. They are mostly used to cut off the supply of fuel in the event of a fire to prevent the accumulation of unburned fuel. These sensors can also measure heat and are commonly used to accurately determine the absence of flame as well as to verify the presence of an active flame.

Why flame detectors are reliable

Flame detection systems are important in every industry. When they are combined with an emergency response system and a fire detection system, the odds of a business or facility suffering large-scale property damage and loss of lives will be drastically reduced.

The main function of a flame detection system, regardless of its type and working principle is to warn the occupant of a building or structure of a fire on time so that occupants can evacuate on time and alert the fire brigade.

This is possible because fire detection systems have sensitive electronic sensors that can easily detect flames. Flame detectors are so effective in detecting flames before they get out of hand because they use a line of sight sensors. This means that the flame detection system can identify the visible light, infrared light and ultraviolet lights emitted by flames during combustion.
If a flame detection device detects any other type of light that comes from a fire, it will trigger an alarm.

Where to install a flame detector

Whether you own a large factory or a small manufacturing plant, it is likely going to be difficult for you to determine the right place to install a flame detector in your building.

Below are some key areas to install them:

  • Any location where smoke and heat are evolved, fire detectors cannot be installed.
  • Outdoor areas that are prone to heavy winds can make it difficult for smoke and heat detectors to work properly.
  • Warehouses with very high ceilings.
  • Any location where paint cans, petrochemical products, and fuel are stored.
  • Flame detectors should never be installed in hallways and storage rooms. Once key areas like this catch on fire, it will be difficult to prevent the loss of lives and preserve property.

More importantly, you need to have your flame detectors and other fire detection device in your building maintained and tested on a regular basis. Always remember that dirt and dust can negatively affect the sensitive sensors in flame detectors, smoke detectors, and heat detectors.

Reliability of your fire detection devices is crucial to maintaining fire and life safety. If there is a small chance that a combustible material might come in contact with an active heat source in your facility, then you need fire detection systems installed.

Pros of flame detection systems

Flame detectors are reliable and can be used in hostile environments like fuel loading platforms, aircraft maintenance facilities, and mines to name a few. They are also suitable for areas where smoke detectors or another type of detector cannot be installed.

Flame detectors FAQ

Q: How can I tell if my flame detector is working well?

A: There is a special flame tester unit on the market that can help you determine if your detector is in a perfect working condition. It is advised that when testing your detector, you test with the same range and signal strength every time to accurately gauge the effectiveness of the device.

Q: What should I do if the LED in my flame detector is not ON?

A: Switch off the device and turn it on again. It may be that the LED has been moved from position. Check your wiring carefully to see if everything is properly connected. If the amber LED is not on, there is a possibility that the unit is faulty.

Q: How often should I test my detector device?

A: It is best you test your flame detector device annually- this can vary depending on the regulation and local law and the site requirement.

Q: Can flame detectors work from behind screen or glass?

A: Yes. IR3 and IR2 flame detector can operate through mist and dust without a decline in their performance.

Q: How many flame detectors should I install?

A: To accurately determine the number of flame detectors to install in your work environment, you must consider the following factors:

  • Know your fire risks – Does your work environment contain flammable substances? The risks in your environment will determine the number flame detector device you need to ensure that your property is fully protected.
  • Model – Learn about the various models of flame detectors to figure out the one that will suit your work environment.
  • Your measurement – The size of the area you want to protect is surely going to affect the number of flame detector units you need to install.

Final note

Whether you own an oil or gas engineering company or a facility where flame liquids and solids are stored, it is important that you follow precautionary measures to keep your working environment risk-free. The best way to do that is to install flame detectors. Since all flame detectors may not be suitable for your work environment, it is wise that you learn as much as you can about the various flame detectors that are available so that you can narrow down the one that will suit the unique needs of your work environment.

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