PUTTING A HEAT SENSOR TO THE TEST
BY DON HERES
The ideas presented in this column are the expressed written views of the author and are not endorsed by Fire Engineering.
With the latest advance-ments in infrared imaging technology, today`s firefighters are seeing into the future. This technology may become as commonplace on fire apparatus as fog nozzles and rubber boots. However, the current cost of these units prohibits their deployment in sufficient numbers for some larger departments, and many smaller departments may never have the resources to acquire one.
Although thermal imaging`s use in search operations is indisputable, less expensive alternatives that use the same infrared technology, but in a different format, exist. Instead of converting infrared signals into expensive video images as the thermal imager does, the heat sensor in the alternative device converts the signals into sound. In video images, the brighter areas signify higher temperatures; heat sensor wands indicate higher temperature areas with louder sound. Moving the wand in a sweeping pattern allows firefighters to “hear” the location of the fire source.
During a recent training burn at an abandoned house, I used one of the newest heat sensor products available and assessed the usefulness of these heat sensors during fire attack and overhaul operations.
We used an old balloon-frame structure for the training exercise. Overhaul was critical if we were to save the structure for multiple burns. We used the heat sensor after each attack to reduce the delay after knockdown and to evaluate how the unit differentiates between residual burn and “hot spots.”
We found that the high residual heat left in the upper portions of the room immediately after knockdown created a noisy “heat interference” (similar to the “whiteout” effect in a thermal imager). However, hot objects such as embers or ceramic light fixtures were often discernable through the darkness of the smoke layer at the ceiling.
The lower areas of the room posed no problems. Sweeping the unit below the thermal layer left no doubt about where the fires had originated, because the temperature of the smoldering pallets and straw was substantially higher than the surrounding air temperature.
We also found that heat interference could be eliminated by delaying a scan of the ceiling area for a few moments to allow heat dissipation by passive, negative, or positive ventilation or simply by sweeping a fog stream across the ceiling. All of these methods allowed instructors to locate flame spread and hidden hot spots quickly.
While heat sensors are not considered attack tools, we tried the device in conjunction with our initial attacks. Realizing that the heat produced by a second-stage fire would rapidly fill a room, we wanted to see if there were methods that could assist the nozzleman in locating the seat of the fire in zero visibility.
We used a small, smoky fire in a rear bathroom. Since this was a very unscientific experiment, we simply asked the nozzleman to close his eyes, listen to the heat sensor as a guide, and sweep the area in front of him. By following the highest sound intensity, firefighters were able to locate the bathroom, find the fire (set in the bathtub), and extinguish it–all without the nozzleman`s opening his eyes.
These experiments were not performed under scientific conditions: They were not intended to produce data–only to determine the usefulness of an economical tool. We made several observations that proved interesting.
First, the unit is a useful attack tool during the early stages of a fire. It allowed firefighters to find and extinguish the fire rapidly.
Second, the unit allowed us to retain our acquired building because we could easily and effectively locate hot spots and hidden fires, thus eliminating rekindles.
Third, during our third operation, the unit was dropped: A firefighter slipped, and the unit was knocked hard against the floor. The sensor`s armored rubber housing prevented damage, and the unit continued to function throughout the day.
We found that for locating hidden fire and overhaul, the thermal scan units are effective, affordable firefighting tools.
DON HERES is a 17-year veteran of the fire service and a firefighter with the Clayton (NC) Fire Department. A North Carolina state-certified fire instructor and hazardous materials specialist, he is president of Hazard Risk Management Associates in Clayton, which provides OSHA and hazardous materials training.