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This month, the column will examine a two-part question from a firefighter in California. He asks, One of our companies used its thermal imager at what turned out to be a fatal fire. During search operations, they couldn't find the victim, even though he was lying on the couch that was on fire. Then, when training in the fire station, we found that we couldn't see a "victim" hiding in a bed. Is our TI malfunctioning or are we doing something wrong?
This is an interesting question because it touches on several different topics. The answers also demonstrate how important it is to regularly train with the thermal imager (TI) and ensure that all members using it understand how it performs. As we examine the questions at hand, we have to return to the very basics of what a thermal imager does. Remember, despite its high-tech performance, the thermal imager itself isn't very smart. In fact, all it can do is show you different levels of heat by creating a black and white image. Big differences in heat are displayed in white and black; small differences in heat are displayed in varying shades of gray.
The key is to remember that the TI doesn't identify anything other than heat levels. The user (that's you) has to interpret the image to determine what the TI is showing. For example, the imager doesn't identify a doorway; it merely identifies the temperature differences that indicate the shape of a doorway and the firefighter has to "read" the TI as displaying a doorway. So, for a TI to be effective, we need two components: temperature differences and user interpretation.
The Victim on the Couch
Let's examine our firefighter's first problem: the inability to locate a victim lying on a couch that is on fire. The thermal imager displays an image based on temperature differences. As a result, if the couch is on fire and the victim lying on it is on fire, there will be little temperature difference between the two. Also, intense fires, such as those caused by burning polyurethane, can overwhelm the infrared detector in the TI. When the detector is overwhelmed, it has no option but to display everything in white (or on some imagers, red). This is technically called "saturation." Many Tis, when they are saturated, lose clarity in the saturated area. Therefore, when the couch and victim are both on fire, they are essentially equal to the TI. They both show as white, and therefore blend together.
In short, when the victim is essentially the same temperature as his background, it will be much more difficult to identify him on the TI. Remember, the TI doesn't identify the victim - it just shows the temperature differences. You have to interpret the picture to "see" a victim.
The Victim in the Bed
Training with the TI around the firehouse is a great way to gain experience with image interpretation. The bunk room can also help simulate the challenges we face when searching bedrooms in a house. The complications here are actually fewer than in a real search.
Again, the TI is displaying temperature differences. What is the purpose of blankets and sheets on a bed? Obviously, to hold in the sleeping person's body heat to keep him warm. If the bed linens are holding in the person's heat, then that heat is not escaping out to the TI. Depending on the number and thickness of the layers, a person on a bed may be easy to detect or nearly impossible.
If the person is a child, the complications are compounded. We have a smaller heat source that is generally covered by even more blankets than an adult. Additionally, parents frequently insist that kids wear pajamasâ€¦and in the winter, these can be full-body suits that would make Arctic explorers envious. This doesn't even take into account a child hiding under a bed, behind a blanket or dust ruffle, or behind stuffed animals. Your standard policy should be to search every bed by hand, regardless of what your TI may indicate.