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What's The Best Type of Flame Detection?

What's The Best Type of Flame Detection?

Posted by Claire Allcock on 27th Feb 2020

With a wide range of environments, you need a flame detection system that’s as unique as your workplace. But how do you know which flame detector is right for you?

How Flame Detectors Work

Heat, smoke and flame (light) are the three characteristics of fire that flame sensors used to detect. However, there are some instances where the fire maybe a little more difficult to detect.

Heat can come from steam escaping pipes, smoke from aerosols, and light from the sun — leading to false alarms. Other environmental factors like air temperature and movement can make detection even more difficult. If that wasn’t enough, smoke dissipating too rapidly or accumulating too slowly can inhibit detection.

Flame detectors are optical instruments — they can detect flames in less than a second, but there are a lot of factors which can be potentially life-threatening if your detectors cannot do their job effectively. This shows you just how important it is to get the right flame detection system for your work environment.

What Environments Need Flame Detection?

While this is pretty self-explanatory — wherever there is a risk of fire — there are some important characteristics of an environment that would lend themselves to needing flame detection:

  • Highly combustible materials are present.
  • There is a need for an instant response to fire.
  • Unsupervised areas need automated fire protection
  • There is a large capital investment to protect.

Once you have determined that you need a flame detection system, the next steps are understanding the different types, and what detectors would meet your needs.

IR Single Frequency Flame Detectors

The technology used in single frequency IR flame detectors has been around for years, but recent innovations mean that detection is much more stable and accurate than before, making them a viable choice for many more environments.

These flame detectors use a pyroelectric sensor, responding to changes in IR intensity around the 4.4 micron range. This is the predominant emission band for hydrocarbon-fuelled fires, making them perfect for detecting them. Single frequency IR detectors also include a low-frequency band-pass filter, which limits the sensor to frequencies that would occur in the presence of a flickering flame.

Fires involving burning metals, ammonia and sulfur do not emit the right frequency of infrared, so the sensor would not be able to detect them.

While these detectors are solar blind (meaning the suns radiation does not affect readings) and relatively immune to optical contaminants like dirt, dust and oil, they are susceptible to rain, ice and water vapour inhibiting detection.

IR Multi-Spectrum Flame Detectors

Multi-spectrum flame detectors contain three sensors, which detect at different frequencies of IR radiation.

One sensor is more attuned to the IR radiation emitted from a typical hydrocarbon fire compared to the other two. The system will then translate that difference in intensity of the three sensors into a ratio; only when this occurs along with the IR radiation from a flickering flame will an alarm be sounded by the system.

This makes the multi-spectrum flame detector almost immune to false alarms, as proper ratio criteria must be present. However, the downside to this is that response time can be longer than with single frequency detectors.

UV Flame Detectors

Ultraviolet flame detectors use a sensor tube to detect radiation within 1000–3000 angstrom. If a flame is detected within this range, the detector will generate pulses which are interpreted by the system to sound the alarm.

It’s important to note that the sun’s radiation to the Earth falls at around 2800 angstrom, meaning that it can be picked up by the sensor and provide false readings. For this reason, UV flame detectors are available with a range of 1800–2500, making the detector solar-blind and can, therefore, be used inside or outside.

Most fires fall within this smaller band, meaning that UV detection systems can respond to hydrocarbon, hydrogen and metal fires, with a short process making for faster response times. Depending on the range of your sensors, UV detectors may respond to welding, lightening, and x-rays, so it’s important to factor these into your workplace considerations.

UV/IR Flame Detectors

A UV/IR flame detector consists of both a UV and a single frequency IR detector within one unit. While both sensors still behave in the same way as their individual counterparts, the system is connected to process information from both sensors, reducing the potential for false alarms.

Because of this extra layer of detection, the sun’s radiation, welding, lightening, x-rays and sparks will not affect the readings, although some gases will inhibit detection.

The UV/IR flame detection system is suitable for environments where the potential for hydrocarbon fires is high, and other sources of radiation are present (such as being outside, or welding).

When choosing the right type of flame detection for you, it’s important to note your environment and any specific requirements. Think about potential contaminants, activities or safety considerations that need to be assessed. DSA Suppliers can guide you through the process with our years of experience – just get in touch with us to get started.