Reading a Commercial Structure with a Thermal Imager

Sept. 10, 2007
The usefulness of a TI in size-up can be affected by the type of construction.

September's Firehouse Magazine article discusses how a thermal imager (TI) can help at a commercial building, especially in size up. The usefulness of a TI in size-up can be affected by the type of construction. Online, we'll examine how different types of construction can mask what is happening inside the structure. Type III construction is addressed in the magazine article; the remainder will be addressed here.

Type V

This wood-frame construction is probably the lightest weight construction. The fact that it is wood probably helps keep us, as firefighters, from getting overly confident inside these buildings. We know they will burn - it's just a matter of time. Because there is usually little mass in the overall construction, the effects of a fire are transmitted rapidly to the exterior walls. As a result, the outside surfaces of the structure heat up quickly in response to where the fire is inside the building.

Type IV

The heavy timber construction of days past is probably the most durable. The thick timbers, as well as the millions of bricks, have the ability to absorb a tremendous amount of fire and heat. In fact, I once worked in such a building that had sustained significant fire damage in 1944 - some of the timbers still had charring on them, but had been painted over. These buildings, frequently mills or old warehouses, will generally hide much of the fire from a TI on the outside. Because the fire must heat so much mass, it generally does not impact that outside surface of the building. As such, a TI will rarely show the advancement of a fire inside a Type IV structure.

Type II and I

These structures tend to be high rises, although they are not exclusively high rises. These types of buildings may be coated in materials that are very reflective of infrared energy, such as polished steel or mirrored glass. As such, reading the effects of a fire can be nearly impossible. Many of these buildings, while heavier than a Type III, are still much lighter than a Type IV. As such, if the exterior shell allows, an active fire may transfer heat to the exterior of the building, allowing a TI to "see" what the heat signature looks like and where the fire may be headed. Keep in mind that the exterior material will probably be the biggest hindrance to reading what is happening inside the building.


Lighter weight construction will be more likely to show the impact and travel of an active fire. The exterior material will impact the "readability" of the heat signature, as certain reflective materials may mask the interior conditions. By bringing your TI with you on fire planning exercises, as well as inspections, you can gain practice evaluating and interpreting thermal images from the various types of construction. As always, when working outside, don't discount the effects of the sun on your thermal image.

Be safe.

Jonathan Bastian is a Thermal Imaging Specialist for Bullard. He is certified as a thermal imaging instructor by the Law Enforcement Thermographers' Association (LETA). He is also the author of the FD Training Network "FireNotes" book, Thermal Imaging for the Fire Service. Bastian served 12 years on the North Park, IL, Fire Department, including the last three as a captain. He has taught classes on thermal imaging, rapid intervention teams and search and rescue operations. He is currently a police officer in Lexington, Kentucky. If you have questions about thermal imaging, please send them to [email protected].

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