What is a Flame Detector and How Does it Work?

What is a Flame Detector? 

A flame detector is a type of sensor that can detect and respond to the presence of a flame. These detectors have the ability to identify smokeless liquid and smoke that can create open fire. For example, in boiler furnaces flame detectors are widely used, as a flame detector can detect heat, smoke, and fire. These devices can also detect fire according to the air temperature and air movement. The flame detectors use Ultraviolet (UV) or Infra-Red (IR) technology to identify flames meaning they can alert to flames in less than a second. The flame detector would respond to the detection of a flame according to its installation, it could for example sound an alarm, deactivate the fuel line, or even activate a fire suppression system. 

Where would you find these Detectors? 

  • Industrial warehouses
  • Chemical production plants 
  • Chemical stores 
  • Petrol storage and pump stations 
  • Arc welding workshops 
  • Power plants 
  • Transformer stations 
  • Underground tunnels 
  • Motor testbeds 
  • Wood stores 

What are the Components of a Flame Monitoring System and does it work?

The major component of a flame detector system is the detector itself. It comprises of photoelectric detective circuits, signal conditioning circuits, microprocessor systems, I/O circuits, and wind cooling systems. The sensors in the flame detector will detect the radiation that is sent by the flame, the photoelectric converts the radiant intensity signal of the flame to a relevant voltage signal and this signal would be processed in a single chip microcomputer and converted into a desired output. 

How many types of Flame Detectors are there and how do they work? 

There are 3 different types of flame detector: Ultra-Violet, Infra-Red and a combination of them both Ultra-Violet-Infra-Red 

Ultra-Violet (UV) 

This type of flame detector works by detecting the UV radiation at the point of ignition. Almost entirely all fires emit UV radiations, so in case of the flame, the sensor would become aware of it and produce a series of the pulses that are converted by detector electronics into an alarm output.  

There are advantages and disadvantages of a UV detector. Advantages of UV detector include High-speed response, the ability to respond to hydrocarbon, hydrogen, and metal fires. On the other hand, the disadvantages of UV detectors include responding to welding at long range, and they may also respond to lightning, sparks, etc. 

Infra-Red (IR) 

The infra-red flame detector works by checking the infrared spectral band for certain ornamentation that hot gases release. However, this type of device requires a flickering motion of the flame. The IR radiation may not only be emitted by flames, but may also be radiated from ovens, lamps, etc. Therefore, there is a higher risk for a false alarm 

UV-IR 

This type of detector is capable to detect both the UV and IR radiations, so it possesses both the UV and IR sensor. The two sensors individually operate the same as those described, but supplementary both circuitry processes signals are present due to there being both sensors. Consequently, the combined detector has better false alarm rejection capability than the individual UV or IR detector. 

Although there are advantages and disadvantages of UV/IR flame detector. Advantages include High-speed response and are immune to the false alarm. On the other hand, the disadvantages of UV/IR flame detector include the issue that it cannot be used for non-carbon fires as well as only being able to detect fires that emits both the UV/IR radiation not individually.  

Are any products available? 

The FGard IR3 delivers superior performance in the detection of hydrocarbon fires. The device utilises the latest IR flame detection algorithms to ensure maximum false alarm immunity. The detector has been independently tested to demonstrate it can detect a hydrocarbon fuel pan fire at nearly 200 feet in less than 5 seconds. The FGuard IR3 has a multi spectrum IR allowing for 60 metre flame detection range. That can detect all Hydrocarbon fires with no condensation forming on the window, improving reliability and performance across temperature. This product has fast detection time responding in less than 5 seconds to 0.1m² fire at 60 metres.  

Crowcon offers a range of infra-red (IR) and ultra-violet (UV) based flame detectors for quickly detecting flames at a distance. Depending on model, this includes a variety of gas and fuel fires including those generated from hydrocarbons, hydrogen, metals, inorganic and hydroxyl sources.

You won’t find Crowcon sensors sleeping on the job

MOS (metal oxide semiconductor) sensors have been seen as one of the most recent solutions for tackling detection of hydrogen sulphide (H2S) in fluctuating temperatures from up to 50°C down to the mid-twenties, as well as humid climates such as the Middle East.

However, users and gas detection professionals have realised MOS sensors are not the most reliable detection technology. This blog covers why this technology can prove difficult to maintain and what issues users can face.

One of the major drawbacks of the technology is the liability of the sensor “going to sleep” when it doesn’t encounter gas for a period of time. Of course, this is a huge safety risk for workers in the area… no-one wants to face a gas detector that ultimately doesn’t detect gas.

MOS sensors require a heater to equalise, enabling them to produce a consistent reading. However, when initially switched on, the heater takes time to warm up, causing a significant delay between turning on the sensors and it responding to hazardous gas. MOS manufacturers therefore recommend users to allow the sensor to equilibrate for 24-48 hours before calibration. Some users may find this a hinderance for production, as well as extended time for servicing and maintenance.

The heater delay isn’t the only problem. It uses a lot of power which poses an additional issue of dramatic changes of temperature in the DC power cable, causing changes in voltage as the detector head and inaccuracies in gas level reading. 

As its metal oxide semiconductor name suggests, the sensors are based around semiconductors which are recognised to drift with changes in humidity- something that is not ideal for the humid Middle Eastern climate. In other industries, semiconductors are often encased in epoxy resin to avoid this, however in a gas sensor this coating would the gas detection mechanism as the gas couldn’t reach the semiconductor. The device is also open to the acidic environment created by the local sand in the Middle East, effecting conductivity and accuracy of gas read-out.

Another significant safety implication of a MOS sensor is that with output at near-zero levels of H2S can be false alarms. Often the sensor is used with a level of “zero suppression” at the control panel. This means that the control panel may show a zero read-out for some time after levels of H2S have begun to rise. This late registering of low-level gas presence can then delay the warning of a serious gas leak, opportunity for evacuation and the extreme risk of lives.

MOS sensors excel in reacting quickly to H2S, therefore the need for a sinter counteracts this benefit. Due to H2S being a “sticky” gas, it is able to be adsorbed onto surfaces including those of sinters, in result slowing down the rate at which gas reaches the detection surface.

To tackle the drawbacks of MOS sensors, we’ve revisited and improved on the electrochemical technology with our new High Temperature (HT) H2S sensor for XgardIQ. The new developments of our sensor allow operation of up to 70°C at 0-95%rh- a significant difference against other manufacturers claiming detection of up to 60°C, especially under the harsh Middle Eastern environments.

Our new HT H2S sensor has been proven to be a reliable and resilient solution for the detection of H2S at high temperatures- a solution that doesn’t fall asleep on the job!

Click here for more information on our new High Temperature (HT) H2S sensor for XgardIQ.

Explosion hazards in inerted tanks and how to avoid them

Hydrogen sulphide (H2S) is known for being extremely toxic, as well as highly corrosive. In an inerted tank environment, it poses an additional and serious hazard combustion which, it is suspected, has been the cause of serious explosions in the past.

Hydrogen sulphide can be present in %vol levels in “sour” oil or gas. Fuel can also be turned ‘sour’ by the action of sulphate-reducing bacteria found in sea water, often present in cargo holds of tankers. It is therefore important to continue to monitor the level of H2S, as it can change, particularly at sea. This H2S can increase the likelihood of a fire if the situation is not properly managed.

Tanks are generally lined with iron (sometimes zinc-coated). Iron rusts, creating iron oxide (FeO). In an inerted headspace of a tank, iron oxide can react with H2S to form iron sulphide (FeS). Iron sulphide is a pyrophore; which means that it can spontaneously ignite in the presence of oxygen

Excluding the elements of fire

A tank full of oil or gas is an obvious fire hazard under the right circumstances. The three elements of fire are fuel, oxygen and an ignition source. Without these three things, a fire can’t start. Air is around 21% oxygen. Therefore, a common means to control the risk of a fire in a tank is to remove as much air as possible by flushing the air out of the tank with an inert gas, such as nitrogen or carbon dioxide. During tank unloading, care is taken that fuel is replaced with inert gas rather than air. This removes the oxygen and prevents fire starting.

By definition, there is not enough oxygen in an inerted environment for a fire to start. But at some point, air will have to be let into the tank – for maintenance staff to safety enter, for example. There is now the chance for the three elements of fire coming together. How is it to be controlled?

  • Oxygen has to be allowed in
  • There may be present FeS, which the oxygen will cause to spark
  • The element that can be controlled is fuel.

If all the fuel has been removed and the combination of air and FeS causes a spark, it can’t do any harm.

Monitoring the elements

From the above, it is obvious how important it is to keep track of all the elements that could cause a fire in these fuel tanks. Oxygen and fuel can be directly monitored using an appropriate gas detector, like Gas-Pro TK. Designed for these specialist environments, Gas-Pro TK automatically copes with measuring a tank full of gas (measured in %vol) and a tank nearly empty of gas (measured in %LEL). Gas-Pro TK can tell you when oxygen levels are low enough to be safe to load fuel or high enough for staff to safely enter the tank. Another important use for Gas-Pro TK is to monitor for H2S, to allow you judge the likely presence of the pryophore, iron sulphide.

Servicing for safety… A visit to the oil refinery

Working in the office makes it easy to focus on the individual tasks and get detached from how our products are making a difference to people’s lives. One of our customers was kind enough to facilitate an onsite visit so that Andrea (our Halma Future Leader on a marketing placement) could see first-hand how our products are used and who the end users are. This meant a visit to an oil refinery to see where our Crowcon portable gas detectors are used.


“The main thing that surprised me was the sheer size of the site. The oil refinery was very spaced out and it took us 10 minutes to walk from the entrance of the site to where the Crowcon engineer’s based. The engineers and employees around different parts of the refinery wore Hi Vis jackets, big safety boots, hard hats and all appeared to have personal gas detectors. During a quick site tour, I learned the products of the oil refinery are not limited to gas or petrol, but also tar, asphalt, lubricants, washing up liquid, paraffin wax and much more.

The products are all stored in big containers with pipes all over the site. Most of the products are highly flammable which explains the big focus on safety. In the distance, there were a few dome shaped containers which are pressurised vessels. If one of them were to explode, it would have a 10 mile blast radius. Suddenly I had the urge to leave and drive about 10 miles.

Crowcon’s engineer base was full of orange T4s, Gas-Pros as well as an army of “Daleks”, I mean Detectives, awaiting calibration and service. While the harshness of this industrial environment was evident from their appearance, they were otherwise in good working order, and the service engineer worked through the devices quickly.

The end users think of them as a simple device they have to wear to do their job, and they like the simplicity and reliability of Crowcon devices. The Detectives get thrown around and Gas-Pros are almost black is comparison to the usual orange, which just showcases how important the robustness of our devices is. The dangers of this working environment are not generally a big concern to the users, this is everyday life to them. Our devices help ensure they go home after a tough shift. Ensuring the devices are functioning properly is down to the service engineers, and they need to think for the users to ensure that the devices are being used properly.

Seeing Crowcon’s devices being used and the number of times someone enquired if the devices are calibrated and ready to go back into action, highlighted just how important use of portables as part of the safety regime  is considered. “Quality” and “robust” is how users describe Crowcon products and even though they may now treat them like the life saving devices they are, the devices are regularly used and valued. They make a very flammable and dangerous environment a safer place to be.”

Facts on Fixed Detection

Optimal placement of fixed gas detectors requires thorough risk assessment. This short video highlights some of the questions you need to ask before buying or installing a fixed system at your plant or site.

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Celebrating 45 years of Gas Detection with photography!

Yes that’s right – Crowcon is another year wiser making our business 45 years old. From the humble beginning of gas engineers wanting to improve the safety of their workplace, to today, where our detectors are used in 100’s of applications across tens of thousands of sites worldwide, one thing remains; our focus on Saving Lives!

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The simple steps to looking after your gas detection equipment this winter.

Gas detectors are there to save your life, whether it is a fixed system or a portable detector, keeping them well maintained is an important part of ownership.

Our guest blogger this week, Julian, has put together simple steps to ensure your gas detector is up for the job as and when it’s required.

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