Thermal Imaging Training Series: Tactical TIC use is not a thermometer
With the recent release of the UL Fire Attack Study, we have received numerous questions about the reliability of TIC use in the fire environment. After reviewing the very short section on thermal imaging in their report there are several common statements that were already known in regards to thermal imaging that firefighters may not been aware of it but our curriculum teaches. The following quote comes from page 167 of the report:
“Further, the sensors in the thermal imagers are designed for a range of wavelengths which allow them to “see” though a variety of hot gases and vapors. As a result if the thermal imager is aimed at a hot wall, it will display an estimated temperature of that hot wall based on the radiant heat flux being emitted from the wall and the assumed emissivity. If gases of a higher temperature are located between the wall and the thermal imager, it is possible that the thermal imager will not “see” them. As a result, a firefighter could be in contact with gas temperatures that are hotter than those displayed by the thermal imager.
*For the reasons above, thermal imagers are considered unreliable thermometers.”*
In our training, we advocate that firefighters understand that fire service TIC’s only “see” a certain wavelength of Infrared Energy (more specifically LWIR which is typically 7-14 microns) and within this spectrum and within the preset emissivity of a fire service TIC there are only three gases that are visible for the fire service TIC: ethane, ethylene, and Hydrogen Cyanide. Fire service TIC’s do not see gas temperatures or accurately represent all of the temperatures of the gases within a fire compartment. However, they do provide a diagnostic tool from strictly a qualitative perspective. For example, every fire service TIC manual states:
That fire service TIC’s read “apparent temperatures” which are estimates based on a preset emissivity (which is .95 in most fire service TIC’s). These apparent temperatures are to be used from a qualitative perspective and not from a specific numeric value as in quantitative thermography. To quote NIST technical note 1499 p.14 it states: “While temperature measurements provide useful information in a fire situation, the accuracy of the measurement is not as critical as it might be in other TIC applications.” In other words, firefighting thermal imaging use is known as qualitative thermography and not quantitative thermography. We are not viewing exact temperature measurements (as their are too many variables to calculate in a dynamic fire environment simultaneously to be exact) but we are looking for anomalies or things that are warning signs of threats that may harm us.￼
Fire Service Tic’s are not thermometers and were never intended to be even though to be certified as NFPA 1801 compliant the TIC does have to accurately measure a temperature from a preset distance. As this photo/slide indicates, fire service TIC’s are designed to “see” the environment from a perspective of seeing the heat, and not from reading the spot temperature measurement. As you can see in the photo, where the firefighter’s head is located is clearly hotter than 87 degrees. And with the knowledge of knowing these are “apparent temperatures” a firefighter would be wise to see that an apparent temperature reading of over 500 degrees Fahrenheit is indicative of gas temperatures of much higher than this as the UL report does accurately state in one of several charts that shows the actual temperatures in the environment compared to the TIC reading.
If we stopped here, we would all be inclined to stop using the TIC from a tactical perspective but several variables were not addressed in the testing of the TIC compared to the actual measurements taken. First the type of TIC was not listed in regards to the following:
* Distance to Spot Ratio: What size of target can it accurately measure from what distance
* Field of View: The TIC’s were placed on the floor and measured only what was within their field of view which is typically very narrow.
* Thermal Sensitivity: The report states the difference in visibility with the TIC in different scenarios based on ventilation but fails to address that the TIC’s thermal sensitivity partly determines how clearly the image will be defined in more uniform temperature environments such as closer to the floor. In general the higher the number the TIC is rated in degrees milliKelvin the less detail the TIC will produce in uniform temperature environments.
* Pixel Ratio/Sensitivity Change: Most fire service TIC’s have two temperature modes: high and low sensitivity. This is based on the amount of heat within the detectors field of view. As the human eye has to constrict the pupil to adjust for a bright light the aperture of the optic lens must also constrict to see larger amounts of heat without causing the detector to saturate. Their is no set standard that states that at a certain percentage of the pixels are heated to over 300 degrees that the detector must switch to Low Sensitivity mode. Why is this important? Because if your detector is 76, 800 pixels (320×240) and the detector requires 32% of the pixels to be 300 degrees for it to switch to low sensitivity; a firefighter will have to be that much closer to the target for the sensitivity to change and colorization to engage indicating they are in thermally severe environment. Some fire service TIC’s only require one pixel to change which allows for greater detail and faster decision making.
Firefighters need to be aware that the fire environment is far hotter than the TIC is showing but as the video we have attached to this link shows, a well trained firefighter would read the big picture (or the color palette) and see the thermal cues that need to be mitigated before moving forward. Make no mistake, a TIC is a tool but the biggest limitations to the fire service in regards to thermal imaging currently are the following:
* An uneducated user
* Incorrect information being shared
* Low resolution/Low refresh rate TIC’s that are being sold to firefighters instead of high resolution/high refresh rate decision making TIC’s
In closing, please know that there is an abundance of knowledge out there in regard to thermal imaging. And currently, the fire service hasn’t even scratched the service on how we can truly use it to our advantage. But until, every homeowner equips their structures with thermocouples and data fed to our mask along with optical gas imaging cameras we must be intelligently aggressive to know that every tool has a limitation but we can make smarter decisions by knowing our environment.
Thanks for your passion and dedication,
Instructor Andy Starnes