Thermal imaging: breaking down the scan – Part 2

Optical view of a firefighter conducting a scan prior to the firefighters making entry for VES.

In Part 1 of our article, we discussed the importance of proper interpretation of the image along with understanding the key attributes of thermal imaging. We also discussed some ‘behavioural problems’ that occur during a scan such as failing to wipe the lens, standing up and scanning too quickly. Now we will address the actual process of conducting a scan with a thermal-imaging camera (TIC).

After teaching this curriculum internationally for many years, our stance has changed from the standard TIC educational recommendation regarding scanning techniques. The majority of TIC training in existence today advocates that firefighters should scan using the following method:

Scan high first
Scan the middle area second
Scan the lower area last

We have found this to be problematic and dangerous due to human behaviour under stressful situations. Even the most well-trained and experienced firefighters who follow this methodology have reported that they scanned high, saw the heat source and never recalled looking down. When asked if the TIC was in Low Sensitivity, they also could not recall if it was or not. In many incidents we have reviewed, this has contributed to near misses by firefighters failing to notice heat below them from fire in a basement area, failing to note the heat was travelling from below due to construction concerns (balloon frame construction, voids, knee walls, etc.). As shown in the photo, the Incident Commander noted an abnormal heat signature coming from a basement window hidden by shrubbery around the home. Therefore, we advocate that firefighters break their scan down into the following steps:

STEP ONE: Scan with their eyesight first! What does their training and experience tell them about what they are seeing? This will be explained from two viewpoints: the exterior size-up scan and the interior size-up scan.

Thermal Image of a basement window in low sensitivity mode indicative of high heat behind the window.

Exterior size-up view: Tactical 360

First, scan low: This allows firefighters to view areas of concern that are often hidden or missed on the exterior such as signs of a basement, down power lines and other hazards. Firefighters should look for crawl-space doors, basement doors/windows, crawl-space vents, areas where infrastructure pierces the exterior of the structure such as: utilities, dryer vents, condensation lines, HVAC systems, tankless water heaters, etc.

Second, scan middle height or area: The firefighter should scan the middle of the structure looking for thermal anomalies, areas of thermal bridging, specifically focusing on areas of higher heat transfer such as any openings in the structure: doors, windows, vents, gas fireplace direct venting systems, etc. Firefighters should note areas of higher heat in each division while comparing them to cold areas of the structure. This can indicate the possible fire location and the potential direction of fire spread. In certain cases, firefighters can locate the fire room through scanning of windows. Traditionally, firefighters have been taught that a TIC cannot see through glass. However, this is not completely accurate. As a TIC doesn’t see through the surface it does, however, pick up temperatures that are emitted from these surfaces and around them. By scanning the surface of newer windows, firefighters can see a cloudy effect that appears on their TIC due to the heat being transferred to the inert gases inside the double-paned windows.

Thermal images of a basement fire with heat signatures around the bottom of the structure and through single pane glass in the basement wall.

A thermal image of a house fire during size-up where the crawl space vents are showing high heat signatures indicative of fire beneath the floor.

A thermal image of a fire crew prior to making entry but detected thermal bridging (heat signatures around the door) where the insulation has failed showing abnormal heat signatures behind it.

Firefighters were taught that a TIC cannot see through glass. However, heat is transferred through the glass, its frame, and the insulation creating notable non-uniform patterns as shown on this window that can indicate a fire behind the window within close proximity.

Firefighters can also notice heat transfer or thermal bridging around the edges of window frames where the caulk and insulation fails quite quickly under fire conditions. And in older homes that consist of single-pane glass windows, the infrared energy is transferred through this medium allowing firefighters to view the heat signatures inside the room as shown in the lower photo.

Third, scan high or uppermost areas: As the firefighter scans the upper areas of the structure, they should note areas of heat loss/transfer such as gable vents, soffits, penetrations in the roof due to vents, solar panels, chimneys etc. All of these are areas for thermal bridging.

Firefighters should be aware that on a standard asphalt shingled roof, they can note the spacing of the roof joists and possible fire location underneath it due to heat transfer and temperature differences between the joists and the roof decking. As shown in the first photo, firefighters can deduce that this is a lightweight truss roof due to the spacing of the roof joists. A standard roof ladder is approximately 20in wide and fits between these joists indicating a 24in roof joist/truss spacing indicative of lightweight truss roof systems. However, this can be obstructed or blocked by solar loading if the roof has been in direct sunlight for a long period thereby producing a white image across the roof top.

Window photo with TIC view: This window is single pane glass which allows IR energy to pass through unlike newer Low E Glass which reflects most of the energy. A firefighter can clearly see the thermal cues of a fire within this room.

Thermal Image of a Roof line: Firefighters can assess an asphalt shingle roof for the following: roof joist spacing (indicative of light weight trusses vs legacy construction), thermal bridging of significant heat around gable vents, soffits, chimneys etc. and they can detect non-uniform heat signatures within the attic of a severe attic fire in many cases.

In obvious fire-involvement incidents, the TIC can provide an assessment of roof stability and level of fire involvement in the attic space as shown in the lower photo. However, a TIC should not be used as structural integrity diagnostic. It is NOT X-ray vision and areas of structural integrity loss may not be visible to the TIC or the naked eye.

In the next issue we will continue this article and explore the Interior Size-up Scan and look at why a firefighter should also continually assess the interior of a fire environment as they progress towards their desired objective.

For more information, go to www.insighttrainingllc.com