Common misconceptions of thermal imaging use – Myths versus Facts

The fire service has been using thermal imaging cameras successfully since the 1990’s. Many lives have been saved through the tactical use of thermal imaging cameras (TIC). And since the first implementation of these devices they have been greatly improved and their overall cost has been dramatically reduced making them more readily available to the fire service.

However, the education and training on TIC’s has not been updated nor has it been the primary focus for the fire service. This is exemplified in many fire departments as they will have newer apparatus, newer SCBA’s (BA’s), and PPE but they will still be using 15-20 year old antiquated TIC’s. The difference in old thermal imaging technology and newer current models is quite staggering and as shown in the adjacent photo by Max Fire Box comparing a 20 year old TIC versus a 2 year old TIC the image clarity. This can be compared to viewing a black and white television versus a modern day LED High Definition TV. Traditionally, the view of the fire environment has been an optical one. Firefighters have been taught to read the building, read the smoke, and judge the IDLH environment based on what they see with the naked eye and to rely on feeling the heat as a measurement of thermal severity. This tactical measurement leaves out an unseen critical perspective known as thermal data. Thermal radiation is one of the fundamental methods of heat transfer which firefighters cannot see. This lack of understanding and in many cases a total absence of training has created an education gap that leaves many firefighters literally in the dark with a device that they don’t know how to fully use properly that could potentially save their lives, save their citizens lives, and enhance their overall fire ground effectiveness.

In this article we will address some of the misconceptions or “myths” of fire service thermal imaging use. The term fire service thermal imager or TIC will be used as there are many different types of thermal imaging cameras for use outside of the fire service that have various capabilities that firefighters currently do not use or have training on as of yet. We will address these issues with factual, evidence based data, and these references can be found at the end of the article for further reading and review in the works cited section.

Myth: “I don’t need a fire service thermal imaging camera to tell me how hot it is; I will wait until my ears are burning or pencil the ceiling to measure the heat.”

Firefighters are taught many valuable concepts and skills as they progress throughout their career. Unfortunately, many of us (including myself) were never taught to measure heat correctly. For example, NFPA 1971: The Standard on Protective Ensembles for Structural Firefighting and Proximity Firefighting requires that all firefighter PPE (coats, pants, gloves, and hoods) to be tested to perform and certified to a certain value known as TPP or thermal protective performance (NFPA 1971 p.64). This data originated from Alice Stoll’s work which is now known as the Stoll Curve. This data was used to measure all of the variables that were required to produce a second degree burn on a human victim. This testing was done in the 50’s and 60’s on US Sailors. Her work is now the basis for the thermal protective performance ratings in NFPA certified firefighting garments or PPE (Oberon p.1). The minimum requirement is 35 which provides 17.5 seconds of thermal protection until the wearer receives a second degree burn. At first this seems very ingenious, but we as firefighters have used this protection to our own demise as the humanist Huxley stated so eloquently “what science has actually done has provided improved means to rather deteriorated ends.”

Firefighters in today’s modern environment are so well encapsulated that by the time they feel painful heat sensations their PPE is saturated with heat energy. Once their PPE is saturated or full, the heat energy begins to transfer to the firefighters flesh. When a firefighter feels bee sting like sensations of pain that force them to withdraw or drives them to the floor this is known as Alarm Time. This is the amount of time between feeling pain and actually suffering a burn. When this occurs, firefighters are about to be burned as their skin is at or approaching 130 degrees Fahrenheit (54 degrees Celsius). This is the temperature that the Stoll Curve found that a second degree burn occurs in a human victim. Her work also proved that if the skin temperature continues to rise, then at 140 degrees Fahrenheit (or 60 Celsius), the human body’s pain receptors are turned off! Also, in the FEMSA manual which is included with every piece of firefighter PPE sold in the US and Canada the following quote can be found: “If your protective ensemble comes in contact with a hot environment or a hot object, you may be burned beneath your protective ensemble with no warning or no damage to the protective ensemble. Be constantly alert to the possibility of exposure to a hot environment, hot objects or other hazards” (FEMSA p.2-4). Therefore, to use the human body as a thermometer in today’s fire environment with modern advancements in PPE is to be forced into a reactive defensive posture that may be too late for a firefighter to respond, withdrawal, or cool the environment before they are burned or killed. It is imperative that firefighters understand thermal severity through the eyes of a Fire Service TIC to “see the heat” and not wait until they “feel the heat.”

Myth-Isn’t thermal imaging just point, shoot, and read the temperature? Why do firefighters need in-depth training on this device?

Another misconception encountered when teaching firefighters on how to properly use a fire service TIC is overcoming the tendency to read the spot temperature which is temperature reading in the lower right hand corner of the display or screen. First and foremost, firefighters need to understand that fire service thermal imaging cameras are NOT thermometers. This numerical reading of the temperature is a small measurement of a 12” area that calibrated to +/- 3 degrees Celsius IF the TIC is within its proper distance to the target AND without any atmospheric attenuation that may affect its measurement. This measurement is known as an “apparent temperature” which are an approximates or estimates that falls within certain variables. When the fire service TIC is calibrated it is done so by measuring a temperature on a target at a preset distance with no smoke, fire, moisture that would interfere with the measurement. And in the instruction manual of every fire service thermal imaging camera, the following words can be found in regard to relying on the spot temperature: “Do not use temperature readings as exact measurements.” However, on the fire ground and in a fire, there are many variables that can cause this measurement to be far from correct. These variables are many and are not limited to the following:

• Proper Distance to the Target: Fire Service TIC’s Distance to Spot Ratio accuracy vary and are as low as 10:1 (10 feet away measuring a 1 foot square) to as high as 900:1 (900 feet away and measuring a 1 foot square).
• Emissivity: One of the most important variables in temperature measurement is Emissivity. Emissivity is an objects ability to emit heat. Emissivity ratings are defined as fraction of energy (rated between zero and one) in comparison to a perfect black surface which has an emissivity value of 1.

A TIC detects thermal radiance from solid surfaces and from gases that radiate in the 8-14 micron spectral range. Emissivity affects the radiation in a way that can make the surface or gas appear to be a temperature that is different than it actually is. In general, surfaces that are black and rough in surface texture tend to have a high emissivity’s and surfaces that are shiny/smooth have lower emissivity’s. This is exemplified in the adjacent photo of the Max Fire Box after a fire behavior demonstration burn. The sides of the box are made of diamond plating (a very shiny material with low emissivity) which causes the TIC to read the reflected apparent temperature which is the ambient temperature around it which is incorrect. Some other variables that will affect a Fire Service TIC’s measurement are listed below:

• Wind-Winds as low as 3 miles per hour can cut temperature measurements by 50%.
• Moisture: Long Wave Infrared Energy can be blocked or dissipated as it moves through steam. Environments with sprinkler heads flowing or high moisture content may limit or block the TIC’s ability to measure or see. The lens of the TIC may become obscured with moisture preventing it from working properly.
• Optical density of the smoke: The thicker the smoke in a fire due to particulates, lack of ventilation, and the type of material burning can absorb more energy between the target and the fire service TIC which can limit the range and effectiveness of certain fire service thermal imaging cameras. In the NIST Research paper it was found that heavier smoke conditions 160×120 resolution Thermal Imaging Cameras reduces the contrast transfer function (CTF) which is the ability to discern finite details between different temperatures of objects at a distance (NIST p.41).

Myth: A Thermal Imaging Camera can read smoke or gas temperatures.

There are many types of thermal imaging cameras available today and some of them can read gas temperatures which are known as optical gas imaging cameras. However, fire service thermal imaging cameras do not read gases nor accurately read smoke temperatures. This is due to the following:

• Emissivity: Fire Service TIC’s measure heat from surfaces that fall in the emissivity range of .95 to .97. There are only three known gases that fall into this range which are ethane, ethylene oxide, and hydrogen cyanide.
• Different Range of the Infrared Spectrum: Fire Service TIC’s see or detect Long Wave Infrared Energy which falls into the spectral range of 7-14 microns. A micron is a millionth of a meter. Many gases fall into the spectral range of UV light, Short Wave Infrared (SWIR) and Mid Wave Infrared (MWIR). A Fire Service TIC does not detect infrared energy within these ranges.

Firefighters are encouraged to view the environment knowing that what the TIC is showing them is heat signatures from services and convection currents coming from those surfaces.

Myth: All TIC’s are the same:

To believe such a statement can ultimately cost the department by an improper purchase and can lead to firefighter injuries or deaths. In the NIST research paper the following statement was made in regard to image quality “It should be emphasized that the TIC optical system, electronic processing, and display quality make large contributions to overall image quality” (NIST p.36). Each fire service TIC that is produced today uses a variety of detectors, different electronic processing, and some are even using interpolation which is a form of image enhancement that allows the firefighter to see more detail than ever before.

In addition to this there are predominately two major types of fire service TIC’s available today: Situational Awareness TIC’s & Decision Making TIC’s. Both are necessary and useful in their proper context but to use a situational awareness TIC for a decision making TIC will ultimately lead the end user to a very dangerous and disappointing conclusion. What is the difference between the two types of fire service TIC’s? A situational awareness TIC can be simply described as a single purpose unit designed to prevent firefighter disorientation. They are generally smaller in size (can be hand-held, Facepiece mounted, or SCBA integrated). They are generally lower resolution and have a slower processor speed of refresh rate. A decision making TIC is can be described as one that meets the following criteria: High resolution (minimum of 320×240 pixels), Fast Refresh Rate (at least 30 Hertz), 3.5” viewfinder or display screen, and a High Dynamic Range (from zero degrees Fahrenheit to 1200 degrees Fahrenheit/650 degrees Celsius).

What does this mean to the end user or firefighter? First, lower resolution fire service TIC’s have very short ranges of visibility and measurement (generally 7-10 feet or 2-4 meters). Secondly, they typically have a lower distance to spot ratio which means they are only able to accurately measure or determine a heat source at a relatively close distance such as 10 feet away which limits the firefighters tactical decision making abilities. Thirdly, they tend to have a slower processor speed or refresh rate. Some are as low as 9 Hertz. One hertz is one frame per second. The human eye sees at 27 Hertz. Therefore, the NFPA 1801 minimum for refresh rate or processor speed is 25 Hertz. This is why we do not recommend purchasing a TIC less than 25-27 Hertz. TIC’s that have a refresh rate less than this rate will trail or lag when scanning which can cause the firefighter to miss large areas as the TIC will shutter to catch up. As the TIC shutters or NUC’s (non-uniformity correction) it briefly “closes its eyes” by the process of an electronic shutter that fires in front of the lens allowing the pixels on the detector to be wiped clean and a new image is formed as the pixels receive new infrared heat signatures. In a 9 Hertz fire service TIC, the time it takes to perform this operation can cause firefighters to miss valuable information. For example, some situational awareness fire service TIC’s take 3-5 seconds when they encounter large heat signatures as the TIC switches from High Sensitivity to Low Sensitivity.

In my tenure in the fire service, I have seldom encountered a patient firefighter in an environment where every second counts nor do they have the luxury of time. This is why these lower refresh rates are not optimal nor practical for use as decision making TIC’s. But why would an organization or department try to use a situational awareness TIC improperly you might ask? Because they don’t know what they don’t know and for budgetary reasons. A smooth salesperson who shows them that they can buy a TIC for every firefighter for $1000 dollars versus the cost of one high resolution decision making TIC can be 5X’s this amount or higher can sway the buyer quite easily. We have read articles across the US and Canada where departments have disposed of their hand held fire service TIC’s and replaced them with lower cost, low resolution, situational awareness TIC’s. They have even made public statements that their firefighters are now better prepared. This is an illusion of superiority created by a lack of education and unethical salesmanship. However, Situational Awareness TIC’s are extremely important to firefighters and if a fire department can afford to outfit every firefighter with one, they will find that their firefighters will be safer by preventing firefighter disorientation. They are not meant nor designed to replace a high resolution, faster refresh rate, higher dynamic range decision making TIC.

Myth-Fire Service TIC’s show colorization when it is too hot!

Studying numerous models of fire service TIC’s and working diligently to stay up to date and knowledgeable on new technologies as they emerge onto the market is a constant battle. Thus, many firefighters are not educated on the fact that colorization of the thermal environment and their associated temperatures are not universal across

TIC manufacturers. For example, the majority of fire service TIC’s (with the exception of a few) do not show colorization until the TIC switches to Low Sensitivity Temperature Mode. Unfortunately, when fire service TIC’s switch to low sensitivity and at what temperature they begin to show color is not standardized nor universal. NFPA 1801 states that a fire service TIC shall follow the TI Basic color format which progresses from hot to cold in the following color progression: black, gray, white, yellow, orange, red. Unfortunately, no two manufacturers are alike in regard to color temperature correlation.

For example, the following fire service TIC’s show colorization in low sensitivity temperature mode at the following temperatures:

• MSA 6000: Yellow Colorization appears at 1000 Degrees Fahrenheit/538 Degrees Celsius in Low Sensitivity Temperature Mode
• Drager UCF series (6000-9000 models): Yellow colorization appears at 572 Degrees Fahrenheit/300 Degrees Celsius in Low Sensitivity Temperature Mode.
• Bullard (all models): Yellow colorization begins at 500 degrees Fahrenheit/260 Degrees Celsius in Low Sensitivity Temperature Mode.
• FLIR (K2-K65 Models): Yellow colorization begins at 300 degrees Fahrenheit/148 Degrees Celsius in Low Sensitivity Temperature Mode
• Leader 3.3 Model: Yellow colorization appears at 392 Degrees Fahrenheit/200 Degrees Celsius
• Argus: Yellow colorization appears at 300 Degrees Fahrenheit/148 Degrees Celsius.
• Scott X380 Models: This model has Tri Mode Temperature Sensitivity and breaks the overall temperature range into three spans (High, Medium, and Low Sensitivity). Each Temperature Sensitivity Mode has a different color temperature correlation.

In conclusion, this is only five of numerous myths or misconceptions about fire service TIC’s that we have encountered in our travels. We encourage the reader to learn their specific brand of TIC, how to properly interpret the image, and to attend as much training on fire ground application with their TIC as they can so they will be better prepared for the challenges of the modern fire ground.

For more information, go to www.insighttrainingllc.com

References

1. Amon, Francine. Bryner, Nelson. Hamins, Anthony. Lock, Andrew (2008). NIST Technical Note 1499 Performance Metrics for Fire Fighting Thermal Imaging Cameras – Small- and Full-Scale Experiments. NIST pp 36, 41.
2. FEMSA Manual (2015). Fire & Emergency Manufacturers Services Organization Inc. www.femsa.org. p. 2-4
3. NFPA (2018). NFPA 1971 Standard on Protective Ensembles for Structural Fire Fighting and Proximity Firefighting. NFPA. Section 8.1 Thermal Protective Performance Test. P.64.
4. Oberon Company (2005). Understanding the Stoll Curve. Oberon. Pg.1 Retrieved from: http://ebooks.bharathuniv.ac.in/gdlc1/gdlc1/Engineering%20Merged%20Library%20v3.0/GDLC/Understanding%20the%20Stoll%20Curve%20(3569)/Understanding%20the%20Stoll%20Curve%20-%20GDLC.pdf