Search & Rescue Magazine, May 2003
Thermal Imagers in Rural and Urban Rescue
By Jonathan Bastian
Introduction
First responders usually think of thermal imagers (TIs) as tools for
structural fire. The obvious benefits of this technology in fire suppression
and structural rescue have catapulted thermal imaging from obscurity
to fast-paced adoption in the fire service. The Federal Emergency Management
Agency estimates that 25 percent of all US fire departments have acquired
at least one TI over the past decade.
The immense benefits of thermal imaging for non-fire search and rescue are not as well known, but the applications are just as dramatic and far-reaching. The major benefit of TIs in search and rescue stem from the fact that the technology offers first responders the ability to improve and speed their efforts in incidents where their eyes don’t give them the information they need. From the most active urban departments to relatively inactive rural departments, a number of rescue situations can be positively impacted by the timely and effective use of a TI.
What is a TI?
Prior to understanding how a TI is helpful to rescuers, it is beneficial to understand exactly what a TI is and what it does. Briefly, a TI is a device that detects relative differences in surface temperature. These relative differences in temperature are converted into an electronic signal and shown on a video screen for the user to see. Modern fire service thermal imagers are sensitive to 0.05° C.
Functionally, the sensor in the TI is similar to the human eye. The TI’s sensor (called a focal plane array, or FPA) and the eye are both receivers; they receive energy and convert it into an image for our brains to interpret. The eye senses wavelengths of energy called “visible light,” while the FPA senses wavelengths of heat energy called “infrared.”
Different wavelengths of energy have different properties, similar to radio frequencies. While light energy passes easily through windows, it does not pass through dark plastic bags (which are high in silicone content). Eyes looking through a window will see what is behind the window, while eyes looking at a plastic bag will see only the color of the bag, not what is behind the bag. Silicone is somewhat transparent to infrared energy, so a TI will identify surface temperatures behind the plastic bag. Glass, however, is not transparent to infrared. For the most part, glass reflects infrared energy and thermal signatures. Photos 1 and 2 demonstrate how light and infrared behave differently.
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Photo 1: Silicone is somewhat transparent to infrared, so a thermal imager identifies surface temperatures behind a plastic bag. Photo courtesy of Bullard.
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Photo 2: Glass is not transparent to infrared, but it is transparent to light. The thermal image shows the reflection of the user. Photo courtesy of Bullard.
Besides the rare transparent material, the human eye and the TI do not
“see” through most materials. Drywall, concrete, steel, wood,
paneling, plaster, blankets, doors, sofas and the like are not transparent
to visible light or infrared. For the most part, the human eye and the
TI “see” only what is on the surface--colors for the eye,
temperature differences for the TI.
Motor Vehicle Accidents
One of the most common non-fire rescues is the everyday MVA. While a
TI will not help treat a patient, the proactive fire department may
use the technology to help find the patient. Rural fire departments
could use a TI to confront the difficulty of not only finding patients,
but also finding vehicles involved in an accident. Because the TI senses
infrared energy, which humans normally detect as heat, it can often
assist in incidents where rescuers’ eyes fail them.
High speed MVAs occur in both rural and urban settings. When vehicles travel at high speeds, the risk of occupant ejection greatly increases because of the kinetic energy that transfers to the occupants of the vehicles. When such an incident occurs in daylight, it usually is not difficult to find all of the occupants. At night, however, the same task can be immensely challenging. Victims who are ejected dozens of yards from the vehicle can be out of range of scene lights or can be covered in dense brush. While the rescuer’s lights may not penetrate far enough to find an ejected patient, his or her heat may radiate far enough to be seen on the screen of a TI. Similarly, while brush may camouflage the presence of an ejected patient, the patient’s heat signature could be visible to the TI.
For example, one Sunday night in October 2002, the Mariemont (Ohio) Fire Department responded mutual aid to assist with an auto accident with entrapment. Firefighters were advised en route that the operator of the vehicle was not in the vehicle, but somewhere at the bottom of a 30-foot ravine. Two firefighters used a TI to sweep the woods and creek bottom. Within minutes they identified an unknown heat source on the side of the hill, approximately 175 feet from the vehicle. They found a young woman, covered in mud and wedged in some tree roots, conscious but disoriented. She had crawled away from her vehicle, in the opposite direction of the crews that were searching for her. Firefighters estimate the search could have taken hours if they hadn’t used the thermal imager to identify her location.
The TI may also help rescuers determine how many people were in a vehicle prior to the accident by showing residual heat left on the seats. For example, if the TI shows that the front two seats exhibit heat impressions, yet the rear seats do not, emergency services personnel probably have only two victims. Rescuers may still benefit from a quick scene search, because the absence of additional heat signatures should not be considered as definitive proof that all victims have been discovered. For example, heat signatures would not be left behind by a small child who had been riding in an adult’s lap, or by a heavily clothed passenger whose body heat hadn’t been transmitted to the seat.
Lost or Missing Persons
MVAs are not the only types of incidents in which thermal imagers can be useful in locating people. In urban areas, the TI may assist in the search for lost children or walk-aways from long-term care facilities. Because the TI displays differences in surface temperatures, the likelihood of success is greater when there is a more significant temperature difference between the environment and the missing person. These conditions also increase the effective range of the TI.
Rural rescuers may be called up to find children lost in a cornfield or adults who become lost during recreational activities. Searching for children lost in agricultural fields may require an elevated viewing position, as may be achieved by using an aerial ladder. Because the heat of the child may be blocked by the rows of leaves and stalks, an overhead view may allow more of the person’s heat to reach the TI.
One rescue in Vashon Island, Washington, was impacted dramatically by the use of thermal imaging. On a September night in 2000, a report came in that two adults on personal water crafts were lost in heavy rain and choppy waters, along the south end of Colvos Passage. In addition to its own boat, the Coast Guard asked the Des Moines Fire Department and Vashon Island Fire and Rescue to join the search. The skiers were found unhurt on a dark beach within 15 minutes after the VIFR’s 16-foot inflatable rescue boat was launched. The TI its crew carried, in service for only two days at the time, saved what could have been many hours of hazardous exposure in the stormy water for the boat crews, in addition to limiting the exposure of the two stranded people. By using the TI, the rescue team was able to stay close to shore rather than going out in the middle of the channel to conduct the search.
Confined Space
Whether involving a worker trapped in a silo eight miles from town, or a technician stuck in telephone vault under Michigan Avenue, confined space rescue poses significant challenges. By definition, confined spaces have limited access points, so they may also have limited ambient light. Thermal imaging is an ideal option whenever visible light is limited in effectiveness.
Thermal imagers give the rescuer several advantages in confined spaces.
First, infrared energy may penetrate the atmosphere of the confined
space better than rescuers’ searchlights. Smokey, steamy or dust-filled
environments can render even the strongest flashlights ineffective.
Because the TI senses infrared, it will perform in most of these situations.
As a result, rescuers can properly evaluate the environmental conditions
within the confined space as well as the condition of the trapped individual.
Second, rescuers can use the TI to evaluate any extraordinary safety
concerns in the confined space, such as energized electrical equipment.
While the human eye might detect the location of a motor housing, the
TI can detect that the housing is still warm because electricity is
flowing through it. Wires and cables, nearly invisible to the eye and
a flashlight, could show up as white threads across a TI display, warning
of entanglement hazards prior to entry.
In short, the TI can help provide the rescuers with additional information so that the team can properly prepare itself for the intricacies of the upcoming rescue.
Other Technical Rescues
The reality is that the use of thermal imaging is restricted mostly by the user’s imagination and creativity. As long as one understands and respects the principles of thermal imaging and infrared radiation, the TI can be applied in a number of scenarios. Other possible uses include:
During swift-water rescue at night, verifying the number of victims stranded on an island or on the roof of a vehicle.
During water rescues following suicide attempts, checking the shoreline for tracks of cold water on the warm ground to determine if the “jumper” may have self-rescued.
During wilderness rescues at night, using the TI to help choose the least obstructed path to the patient and then to the recovery point.
During collapse rescues, examining void spaces for potential victims who may be covered with a camouflaging layer of dust.
In fact, in November 2001, the Bollivar County Volunteer Fire Department responded to a house struck by a late-night tornado in Skene, Mississippi. The house was literally removed from its foundation before being torn apart, leaving a seven-year old child missing. Firefighters initially used flashlights to attempt to find the missing boy. Two industrious members of the department grabbed their TI, and shortly thereafter discovered a heat source that seemed out-of-place. The unconscious boy had been pinned beneath a thin section of drywall and his body heat was heating the drywall just enough for the TI to discern a relative difference in temperature. The search for the critically injured boy was completed in less than 30 minutes, instead of lasting through the night. Because the boy had several skull fractures and a bruised lung, the time saved undoubtedly contributed to the positive outcome of his treatment and rehabilitation.
Conclusion
While fire departments have adopted thermal imaging primarily because
of the tremendous benefits it brings to firefighting, it is clear that
there are numerous applications for TIs outside of structure fires.
A number of EMS, search, rescue and technical rescue incidents could
benefit from prompt, efficient use of a thermal imager. In fact, for
any incident in which the human eye cannot gather all the desired information,
a thermal imager may well be the tool to provide the additional data
required.
Use your TI often, wisely and safely.