Review of Fire Detection Technologies for Autonomous Robotic Fire Suppression Systems (ARFSS)

Selecting the right fire detection technology for your needs can be critically important to save lives and property.

FlameRanger, the world’s most advanced autonomous robotic fire suppression system (ARFSS), can work with them all.

So what should you choose, and what should you consider?

With so many fire detection technologies on the market, it can be a bit daunting to determine the right detector, or combination of detectors, for your needs.

Here, we present and compare our thoughts and opinions about the most common detection technologies on the market that can be used for autonomous fire fighting systems.

The aim of this article is to provide general information and considerations when selecting the right detection technology for your needs. Of course, each customer must use his own judgement and ensure that his choice is approved in the local jurisdiction and by his fire safety engineer. We hope this helps convey a sense of the pro’s and con’s to consider and discuss with your local professional agents.

Pro’s & Con’s of Fire Detection Technologies

Below, we present a brief description of the primary fire detection technologies on the market and their advantages and disadvantages. All of the following technologies can also be used by autonomous robotic fire suppression systems, such as the FlameRanger™ by Unifire AB of Sweden. While other detection technologies exist and can also be considered for autonomous systems, the technologies discussed below are the most widely adopted for commercial uses.

Flame Detectors

How Flame Detectors Work

Flame Detectors detect actual visible flames within their field of view by using a variety of methods that analyze the light emitted in various wavelengths from a flame. Perhaps the most reliable of flame detectors are called Triple-IR (abbreviated IR3). IR3 detectors have three separate detectors, each of which detects a different wavelength of light, and the detector analyzes and compares them and their ratios to better rule out false alarms.

Learn more about flame detectors at:

Advantages of Flame Detectors

Flame detectors are a well established technology, which are reliable & very fast acting. They do not respond to heat or smoke. Rather, they look for the tell-tale wavelengths of light emitted by flames of the types of fires we want to fight, while ignoring other sources of light. Flame detectors tend to have a very low susceptibility to false alarms. This makes them a very reliable detection technology for detecting actual fires the moment they break out.

Another significant advantage, when using a flame detector that can provide the flame’s coordinates, is that the FlameRanger autonomous robotic fire suppression system (ARFSS) can determine the exact three-dimensional (3D) size and position of the fire and track it in real time, and suppress it dynamically even as it moves, shrinks or develops.

Disadvantages of Flame Detectors

Because flame detectors only detect and react to visible flame, and unlike some of the technologies discussed below, they do not provide an early warning of a heat buildup, nor can the detect smoke, nor can they detect reflections of flame when the flame is hidden from direct view of the detector. This may be a disadvantage, or an advantage, depending on the application.

Another possible disadvantage to consider is the fact that most flame detectors currently on the market are unable to provide the location (coordinates) of the flame they detect. When it comes to autonomous robotic fire suppression systems, this means the robotic nozzle cannot accurately target the fire, but must suppress the entire area within the view of the detector. Fortunately, there is at least one detector on the market that can provide accurate location data of the detected fire (or fires).

Conclusions About Flame Detectors

Flame detectors, and particularly triple-IR (IR3) flame detectors, are generally a very fast and reliable way to detect a fire as soon as it breaks out in the detector’s view. They are highly resistant to false alarms, and they are not triggered by smoke or hot objects, which can be either an advantage or a disadvantage, depending on your risk and requirements.

Thermal Imaging Cameras

How Thermal Imaging Cameras Work

Thermal imaging camera systems detect heat in the infrared wavelengths. They can accurately read the temperatures of all surfaces within their field of view. The cameras themselves are typically connected to a computer that reads the data from the camera and displays it on a video monitor. Software allows the user to set numerous parameters, including pre-alarms at any desired temperature or change in temperature in a certain amount of time, alarms in certain areas of the field of view, and to ignore areas that are known to have hot objects you don’t want triggering an alarm.

Learn more about thermal imaging at:

Advantages of Thermal Imaging Cameras

Quality thermal imaging camera systems are very good at providing early detection of a possible fire, even before it has broken out or before it is visible as flame (such as when it is smoldering under the surface). They typically react very quickly and with fairly high resolution.

Their ability to give an early warning is one of the primary advantage of thermal imaging cameras. They are very flexible in their ability to set alarms to the customer’s needs and site conditions. They also allow a human operator to see on a video monitor the heat of objects in the room, making it very easy and intuitive to see potential problems as they develop, and also to signal trouble quickly as it develops.

Typically, these systems can also provide location information that can be used by an autonomous robotic fire suppression system in order to guide a robotic nozzle to suppress the fire or heat buildup.

Disadvantages of Thermal Imaging Cameras

The primary disadvantage of thermal imaging cameras for detecting fire is that they are more susceptible to false alarms than flame detectors, especially outdoors and in environments with other machinery and hot items.

The reason for this is that they detect heat / temperature. Any source of heat that reaches the alarm thresholds may therefore raise an alarm. This can include things like hot machinery, hot vehicle engines and exhaust and other sources that may not actually be the kind of threat you wish to suppress. When an alarm is triggered by a benign source like this, it is called a “false alarm”, even though the system did exactly what it was supposed to do – raise an alarm due to a defined heat signature.

As a result, environments that regularly have heat sources that may trigger the thermal imaging camera system’s alarm—such as waste and recycling storage areas where tractors and vehicles are regularly working to move materials—may experience fairly frequent false alarms. This can not only be frustrating, but may lead to ignoring alarms that may in fact be a fire, or turning off the system, rending it useless. When used with an autonomous robotic fire suppression system, a false alarm will commence fire suppression, which could be dangerous if the water or foam stream is aimed where people may be working.

It is important to point out, however, that modern thermal imaging systems generally feature increasingly-sophisticated algorithms that seek to reduce false alarms by ignoring things like moving heat signatures, such as those generated by a moving vehicle’s engine, etc. Also, they do allow known hot spots in their field of view to be ignored (or “masked”) so that they won’t cause an alarm.

Conclusions About Thermal Imaging Cameras

Thermal imaging cameras are a great option for early warning of high temperatures or a rapid heat buildup. False alarms may occur, particularly in areas where there are other heat sources, such as hot vehicles, hot lamps, etc. Care must be taken to mask known hot objects and to avoid false alarms that could result in possible danger from reaction by an autonomous robotic fire suppression system.

Video Analytics

How Video Analytics Works

Video analytics systems use advanced algorithms and computing to analyze regular visible video feed from a high definition video camera. This technology is used for many industries. In the fire detection industry, the video analysis is designed to detect, among other things, flames and smoke and sometimes reflections of flames.

Learn more about video analytics at:

Advantages of Video Analytics Systems

Video analytics systems can typically use any standard video camera feed. A frequently deployed option also allows the recording of the video feed they are analyzing, which can later be reviewed and analyzed after a fire event. They are also able to display the smoke and/or fire they detect on a video monitor for an operator so that she may respond appropriately.

Video analytics systems are also able to provide the coordinates of the fire and/or smoke. These coordinates can be used both by on-site crew to know where the problem is, but also can be used to autonomously aim the robotic nozzle of an autonomous robotic fire suppression system (ARFSS).

Disadvantages of Video Analytics Systems

Video analytics systems can be susceptible to false alarms, and they are typically slower to react than flame detectors or thermal imaging systems (≈10-20 seconds longer). They are not appropriate in all environments, such as where the sun, bright reflections or other flickering objects (such as tarps or flags flapping in the wind) are likely to trigger false alarms. Dust, steam and exhaust may also trigger a false alarm, as they can be difficult for these systems to distinguish from smoke.

As with thermal imaging camera systems, however, false alarms are reduced by “masking” (ignoring) known problematic objects, and also by means of ever-advancing algorithms that seek to ignore moving objects and other known sources of false alarms.

Conclusions about Video Analytics Systems

In the right environments, particularly in relatively static ones with little wind, dust and/or flashing objects, video analytics can be a very good technology for detecting smoke, fire and even reflections of fire. They can display this information for crew, provide alarms and warnings, and can also send the alarm and location data to an ARFSS. Careful consideration must be given to ensure that false alarms will be kept to a minimum.

Hybrid Thermal Imaging & Video Analytics Systems

How Hybrid Thermal Imaging & Video Analytics Systems Work

These detectors represent a relatively new and emerging class of fire detection technology.

Hybrid thermal imaging and video analytics systems combine both a thermal imaging system and a video camera with video analytics technology. Unifire calls this class of detectors Hybrid Thermal Imaging & Video Analytics.

The theory behind these systems is that they can provide three separate indicators of a fire: from the thermal imaging system, 1) a customized temperature pre-alarm and alarm; and, from the thermal imaging system, 2) the presence of a flame, and 3) the presence of smoke.

These three separate sources of data can be used by an autonomous robotic fire suppression system in any desired combination. For example, autonomous suppression may be programmed to commenced if, and only if, the detector detects: A) a flame detected by the video analytics, and B) a temperature at the same location with a temperature of over 100℃; and irrespective of whether the video analytics detected smoke. Any combination of the three channels can be used, and such logic would depend on the customer’s facility and conditions.

Advantages of Hybrid Thermal Imaging / Video Analytics Detectors

Hybrid thermal imaging and video analytics fire detectors are designed to provide fire detection that is less susceptible to false alarms than either of the respective technologies on its own. They seek to achieve this by allowing a conditional response, such as to trigger an alarm only if a certain temperature is measured AND the video analytics sees smoke and/or fire. In this way, the technologies act as a cross-check on each other, such as to ignore a hot temperature if no flame is visible to the video analytics, and vice versa.

Unifire believes that this technology may be intriguing and promising, and we are currently testing this technology for integration with the FlameRanger ARFSS. We do remain guarded, however, as to the actual susceptibility to false alarms in practice, as discussed in the disadvantages, below.

Disadvantages of Hybrid Thermal Imaging / Video Analytics Detectors

Not being a true flame detector, false alarms still remain a possibility. In theory, the risk of false alarms should be reduced as compared with either of the respective technologies on its own.

But, take for example, the fact that it is often the case that sources that are hot (and which would therefore raise a heat alarm from the thermal imaging part of the system) may also emit smoke, such as a moving vehicle and its exhaust. A system designed to detect heat and smoke may still trigger an alarm from a benign object, such as a moving vehicle. Moreover, dust may also possibly be recognized by the video analytics as smoke, so a hot spot, combined with dust in the air, may trigger a false alarm in some circumstances.

Conclusions About Hybrid Thermal Imaging & Video Analytics Detectors

For us, the jury remains out, as we ourselves have little data or experience from users of this technology in order to opine as to their efficacy or susceptibility to false alarms. The concept is certainly intriguing, and could provide a rapid and reliable means of detecting fire in the right circumstances, particular as this technology matures. In practice, however, it is too early for us to opine whether in fact these hybrid systems are a good choice. We are keen to test and explore this technology further and we are in the process of doing so.

Fiber-Optic Linear Heat Detectors

How Fiber-Optic Linear Heat Detectors Work

Fiber-optic linear heat detection systems pass light through a fiber-optic cable and, by using advanced computing technology that analyzes the light signals running through the cable, can reliably detect and locate heat buildups anywhere along the cable.

Advantages of Fiber-Optic Linear Heat Detectors

Fiber-optic linear heat detection systems have a very low susceptibility to false alarms. They also can be very economical to install, particularly for large areas, because the fiber-optic cable itself is relatively inexpensive. These systems can provide continuous fire detection along the entire sensor cable length of up to 10 kilometers. They are also very low-maintenance and well suited for very harsh environments, including nuclear radiation. They are also immune to EMC and RFI, and are inherently safe in explosive environments.

Disadvantages of Fiber-Optic Linear Heat Detectors

The primary disadvantage to fiber-optic linear heat detection is their relatively slow reaction time and relatively low accuracy of locating the fire. Before an alarm is triggered, heat must build up and heat the cable sufficiently to detect the fire. Moreover, the fire itself may be located near, but not exactly at, the location of the cable heat build-up, resulting in imprecise information as to the exact location of the fire. While this technology may be appropriate in some autonomous robotic fire suppression (ARFSS) systems like the FlameRanger, generally the faster-acting technologies listed above are preferable.

Conclusions About Fiber-Optic Linear Heat Detectors

Fiber-optic linear heat detectors can be a cost-effective way to detect heat build-ups and fires, particularly over long distances. Of all of the technologies discussed in this article, however, they are by far the slowest to react and have a fairly imprecise (although perhaps sufficient) ability to locate the exact source of the fire. When it comes to successful fire fighting, including autonomous robotic fire suppression systems, reducing to an absolute minimum the time to detect and begin suppressing a fire is critically important. The faster you can put water on a fire, the better. For this reason, fiber-optic linear heat detection systems are the least attractive for most installation types, but could still be very useful in the right situation when the other detection technologies discussed above are impracticable.

Further Factors to Consider when Choosing an Autonomous Robotic Fire Suppression System

The various fire detection technologies, and even different brands and models within each technology class, may result in varying ways for an autonomous robotic fire suppression system to locate and target the fire. ARFS systems may be able to use a combination of detection technologies and techniques of aiming the robotic nozzle.

Be sure to ask your ARFSS supplier questions to understand how the system detects, aims, commences and ceases suppression, how great are the risks of false alarms, etc.

Questions to consider asking include:

  • What type of fire detection technology is used for my system?
  • What can I expect in terms of false alarms from the selected fire detectors, particularly given the environment of the location where the system will be installed.
  • How does the system locate the fire, and how accurately?
  • How does the system aim the robotic nozzle (or monitor) at the fire?
  • Does it aim the water or foam stream straight at the fire, without moving, or does it also oscillate around the fire to prevent spreading? How has that response been determined, and has it been tested? If so, what are the results?
  • Does the system adjust the nozzle tip’s spray pattern, such as changing to a fog pattern for fires near the robotic nozzle (or monitor), and a jet stream for fires farther away?
  • How accurate is the system’s ability to aim?
  • How does the system stay calibrated?
  • Does the robotic nozzle (or monitor) use brushless motors, which are more accurate and do not require re-calibration over time?
  • How does the system know when to shut off the water or foam supply (i.e., close the valve or shut off the pump)?
  • Has the system been tested by a third party? If so, which, and can you share results, reports or video?
  • Can a human operator take manual remote control of the robotic nozzle at any time, regardless of whether the system has detected a fire? If so, what types of controllers can be used?
  • Can the system provide a pre-alarm to alert crew of a possible fire, before the system responds autonomously?

Concluding Remarks

Autonomous Robotic Fire Suppression Systems are rapidly advancing, and are ever-more capable of working with a wide variety of fire detection technologies and brands and models.

Every fire detection technology has advantages and disadvantages inherent in the technology itself, and irrespective of the quality of the product. We hope this article provides some helpful guidance and suggestions in determining which fire detection technology is right for you.

For more information about Unifire’s FlameRanger system and how it uses the various detection technologies, contact Unifire at sales @

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