Flame Detectors are used to detect the fire hazards and run fire alarm using fire security and surveillance systems. Among the several types of flame detectors, Optical flame detectors are popular. Optical flame detector is a detector that uses optical sensors to detect flames. There are also ionisation flame detectors, which use current flow in the flame to detect flame presence, and thermocouple flame detectors. Optical flame detectors are used Wherever highly combustible materials are involved, Where there is a need for instantaneous response to flame, and Wherever unsupervised areas require automated fire protection.

Most fire detection technology focuses on detecting heat, smoke (particle matter) or flame (light) – the three major characteristics of fire. 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.

Types of Flame Detector Sensors

  • Ultraviolet (UV) Flame Detector Sensors – Ultraviolet (UV) detectors work with wavelengths shorter than 300 nm. These detectors detect fires and explosions within 3–4 milliseconds due to the UV radiation emitted at the instant of their ignition. False alarms can be triggered by UV sources such as lightning, arc welding, radiation, and sunlight. In order to reduce false alarm a time delay of 2-3 seconds is often included in the UV Flame detector design.
  • Infrared (IR) Flame Detector Sensors – Infrared (IR) flame detectors work within the infrared spectral band. Hot gases emit a specific spectral pattern in the infrared region, which can be sensed with a thermal imaging camera (TIC) a type of thermographic camera. False alarms can be caused by other hot surfaces and background thermal radiation in the area as well as blinding from water and solar energy. A typical frequency where single frequency IR flame detector is sensitive is in the 4.4 micrometre range. Typical response time is 3-5 seconds.
    • Single-Frequency Infrared (IR) Flame Detector
    • MultiSpectrum Infrared (IR) Flame Detector
  • Near Infrared (IR) Flame Detector Sensors
  • Ultraviolet-Infrared (UV-IR) Flame Detector Sensors – UV and IR flame detectors compare the threshold signal in two ranges in “AND” configuration and their ratio to each other to confirm the fire signal and minimize false alarms.
  • Dual-Infrared (IR-IR) Flame Detector Sensors – Dual IR (IR/IR) flame detectors compare the threshold signal in two infrared ranges.
  • Tripple-Infrared (IR-IR-IR) Flame Detector Sensors – Triple IR flame detectors compare three specific wavelength bands within the IR spectral region and their ratio to each other to reliably detect flames while attempting to reduce false alarms.
  • Visible Image Sensor Flame Detector – In some detectors a sensor for visible radiation is added to the design in order to be able to discriminate against false alarms better or improve the detection range. Example: UV/IR/vis, IR/IR/vis, IR/IR/IR/vis flame detectors.
  • CCTV Camera Video Flame Detector – Closed-circuit television or a web camera can be used for video detection (wavelength between 0.4 and 0.7 µm). Like humans, the camera can be blinded by smoke or fog.
  • Ionization Current Flame Detector – The intense ionization within the body of a flame can be measured by means of the current which will flow when a voltage is applied. This current can be used to verify flame presence and quality. They are normally used in large industrial process gas heaters and are connected to the flame control system and act as both the flame quality monitor and the “flame failure device”.
  • Thermocouple Flame Detector – Thermocouples are used extensively for monitoring flame presence in combustion heating systems and gas cookers. They are commonly used as the “flame failure device” to cut off the supply of fuel if the flame fails.