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Each month, this column provides quick tips that help you and your firefighters learn how to use thermal imagers (TIs) more effectively. As we did in June, this month we will review a few potential drills that you can run in and around the firehouse to improve your image interpretation skills. These drills focus on the use of thermal imaging in hazmat.
Photo courtesy of Bullard
A thermal imager shows the presence of a material floating on water in the sink. Vegetable oil is excellent for use in this drill.
Drill 1: Hazmat Identification
Obviously, our taxpaying public would not appreciate it if we regularly practiced hazardous materials evolutions with toxic substances. However, you can practice hazmat evolutions in your firehouse with common foodstuffs.
Fill the kitchen sink with warm water, then pour a small amount of cooking oil into the water. This exercise will allow firefighters to practice seeing relative surface temperatures and determining the presence and flow of a material. For firefighters newer to thermal imaging, make the temperature difference significant to decrease the difficulty of identifying the product. For experienced members, especially those assigned to hazmat companies, try to make the water and oil temperatures closer to increase the difficulty of identifying the product.
After everyone has seen how lighter-than-water materials show on the water’s surface, refill the sink and pour milk or juice into it. This gives firefighters the opportunity to see how miscible or heavy materials rapidly disappear from the view of the TI. The effects of water can be reinforced as well by having one member immerse a hand in the sink, while the rest view it on the TI.
Drill 2: Hazmat and Emissivity
To most firefighters, emissivity is a foreign concept. Briefly, emissivity is the notion that all materials absorb heat and release heat at different rates. Think about the last time you baked a dish in the oven and had to cover it for part of the cooking time. Whether it was a glass or metal baking dish, you needed to wear oven mitts to remove it safely. However, you could pull the aluminum foil from the top of the dish with your bare fingertips. The dish and the aluminum foil were both exposed to the same oven temperatures, so they should be the same temperature. However, because aluminum foil does not absorb heat at the same rate as the baking dish, you can touch it without burning yourself.
Emissivity affects how materials appear on your TI. Your thermal imager is programmed to expect a certain emissivity level, with most units set to accurately read temperatures of objects with an emissivity reading similar to concrete or brick. When your TI views an item with an emissivity similar to aluminum foil, it does not know how to calculate its true relative temperature. As a result, certain materials (generally shiny metals) appear artificially cold on the TI display.
Photo courtesy of Bullard
Filling different containers with different temperatures of water helps firefighters learn proper image interpretation and how to identify product levels. Note that one container is empty.
To see the effect of emissivity on a thermal image, partially fill several containers with water. The containers should be made of different materials, such as plastic, glass and aluminum. Ask firefighters to view product levels in the containers by scanning them with the TI. This exercise shows how certain materials may hide heat differences better than other materials.
Next, place cold, warm and hot water in different containers to demonstrate which materials show product levels the best. To keep crewmembers on their toes, occasionally challenge them with an empty container to emphasize that firefighters cannot fool themselves into seeing product levels when none are present.
Drill 3: Hazmat Tracking