Myths vs. Reality in Thermal Imaging - Part I

Thermal imagers (TIs) are revolutionizing the fire industry, quickly becoming standard equipment sought by every department in the country. Every day, another fire department accepts the value of TIs and puts a camera into service. Despite the quick...


Thermal imagers (TIs) are revolutionizing the fire industry, quickly becoming standard equipment sought by every department in the country. Every day, another fire department accepts the value of TIs and puts a camera into service. Despite the quick adoption of thermal imaging, related technological and training issues have caused some resistance and confusion in the fire service. This multi-part article addresses some of the common misperceptions about thermal imaging technology and its uses, helping firefighters to better understand and apply it on the job.

Myth #1-Anything White on the TI Means a Fire or a Hotspot


Photo Courtesy Jonathan Bastian
In a 70?F room, a 50?F can of soda appears black because it is relatively cold, while a person with a skin temperature of 90?F appears bright white. The table and chairs are gray.

A fire department was called to a house that had been struck by lightning. On arrival, firefighters found an outlet with scorch marks around it. On their TI display, the FD members saw a white line running up the wall from the outlet. Taking this for an overheated electrical line behind the wall, the members quickly opened the wall from floor to ceiling, attempting to prevent damage from the hidden fire and to demonstrate the true value of their new tool. After opening the wall completely, the members discovered that the white line was caused by the hot water pipe running to the upstairs radiator. The FD mistook "white hot" to automatically mean "fire".

All thermal imagers detect and display relative differences in surface temperature. Modern TIs are extremely sensitive, recognizing temperature differences as little as 1/20th of a degree Celsius. As a result, "white" does not always mean "fire" or "hotspot." Image 1 shows a stable 70?F room. In it, a 50?F can of soda appears black because it is relatively cold, while a person with a skin temperature of 90?F appears bright white. The table and chairs are gray.

In a 100?F room, the can would still be black, but the table and chairs would be warmer than the person. As a result, the person would be light gray, and the table and chairs would display as white on the TI screen. The temperature of the can and the person would not change, but the person's relative temperature would change, thus the TI would display him differently.

Practical Application: When using the TI, remember that all temperature differences are relative. When looking for hotspots or investigating a possible fire, use additional techniques to verify questionable images. The back of a hand will help identify significant heat behind a wall, while a small inspection hole may help rule out smoldering wires. If verification is difficult, try comparing the item in question to similar items in the vicinity. For example, a "hot" roof may be caused by a smoldering attic fire or by the dark shingles that have been in the sun all day. Compare the questionable roof to a similar one next door to see if the heat patterns are alike.

Myth #2-Fire Victims Will Be Displayed In White


Photo Courtesy Jonathan Bastian
In this thermal image, firefighters are approaching a very hot door at a structure fire, which displays as white, while firefighters are displayed as dark gray.

This myth originated because many firefighters primarily operate thermal imagers in standard room temperature environments. As shown in Image 1, in normal environments, people are displayed as white because they are relatively hot. Unfortunately, many fire departments do not have regular access to live-fire environments. Consequently, much of their training occurs at room temperature, which gives the false impression that people will always be white on the TI display. In Image 2, firefighters are approaching a very hot door at a structure fire. Because the door is relatively hot, the firefighters in full turn out gear are relatively cool by comparison. Despite the fact it is 92?F outside, the firefighters are displayed in dark gray.

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