Flying 500 feet above the Blind Trail Complex wildfire, just south of the Grand Teton National Forest in Jackson, Wyo., Mark Gamroth trained his infrared thermal imaging camera on the miles of burned-out forestland below him. For two weeks straight, Gamroth, of Infrared Inc., Reno, Nev., searched for bright white hotspots through his viewfinder that would indicate escaped sparks and smoldering fires that could rekindle and grow into raging fires. He was able to see these hidden dangers, which would have been impossible with the naked eye, with the help of a technology that is growing in importance in wildland firefighting.

Thermal imaging cameras, first used in the military, are helping firefighters see through smoke, darkness, thick foliage and less-than-ideal weather conditions. Though the technology has been used in wildland firefighting since the mid-1970s, firefighters are relying on it even more. Today, thermal imaging cameras are easier to use and more portable, affordable and prevalent in the field.

Thermal imaging in action

Summer 2000 proved to be one of the most active wildland fire seasons in the United States in recent memory, with 90,674 fires burning over 7 million acres. The majority of the fires occurred in 10 western states: Idaho, Montana, Wyoming, Utah, Nevada, Arizona, New Mexico, Washington and Oregon. As the fires spread and spanned larger distances, some more than hundreds of miles, firefighters turned to thermal imaging cameras to help them more effectively gather intelligence to manage the blazes and their aftermath. Hundreds of hand-held cameras were used to scan vast distances from helicopters and high ground locations, and while walking and driving along the perimeter of the fires.

Increased issues of liability in urban interface fires have fueled the use of thermal imaging cameras to track the perimeter of a fire. This past summer, thermal imaging systems proved to be an invaluable tool in monitoring wildland fires in the Bitterroot Valley, south of Missoula, Mont. The valley was ringed by wildfires and was the site of intense firefighting. Firefighters relied on thermal imaging systems to help predict the fire's path, which helped them send in appropriate resources to protect people and homes. They also used them during the mop-up period to locate any smoldering fires and determine that the fires were completely out before moving on to other areas.

Thermal imaging is particularly helpful in gathering strategic information on the fire's behavior to develop more effective ways to combat it and deploy firefighting resources. Fire migrates depending on fuel sources and oxygen and can change direction instantly because of wind. Thermal imaging helps the command center monitor the fire's perimeter, which can be difficult to track in heavy smoke. Firefighters routinely scan both sides of the perimeter with thermal imaging cameras to watch for flare-ups or sparks and embers that can travel hundreds of feet with the wind and jump over the established perimeter of the fire to fresh fuel sources.

“It's very dangerous for ground crews when fires jump or flashover,” says Glenn Hogan of Western Sensor Inc., Hayden, Idaho, who introduced thermal imaging to wildland firefighting and who sells and services thermal imaging cameras. “Thermal imaging systems can be a lifesaver to crews caught in these situations to help them find escape routes out of the fire through heavy smoke.”

Because thermal imaging detects subtle temperature differences and not just fire, it can be used to locate items with a “colder” temperature signature, such as water. In heavy smoke, when it may be difficult to find natural resources, it can be used to locate water supplies.

“Thermal imaging can also help firefighters understand the topography of the area and determine natural drainage paths and influences of melting snow, which can help break a fire's path,” Hogan says. On the fire perimeter, ground crews use thermal imaging systems to scan earthen berms, which are created by turning over and building up dirt mounds to cut off the fire's fuel supply, to check for excess heat in the ground material that could signal a smoldering fire.

Though thermal imaging cameras are easy to use and can be operated by firefighters without formal ir training, the quality of the data and interpretation improves with the skill and experience of the operator. “Not all white spots on the thermal image are fires,” Hogan explains. “Sometimes it can be the reflection from an aluminum can or another object. Skilled operators know how to shut down the sensitivity and gain as they investigate anomalies. They view it from multiple angles and are able to decipher false positives without having to send in ground crews to investigate.”

Several burgeoning applications are drawing heavily from the military's use of thermal imaging. Thermal imaging sensors can be mounted on remotely piloted drone aircrafts that can fly behind the fire line to monitor the progress of the fire or map hot spots. The data gathered by the ir sensors can help create detailed 3-d maps of the area.

In addition, P&R Technologies of Portland, Ore., is creating a robot equipped with a thermal imaging camera and a trench-digger mechanism that will be able to see fire spots and create new fire lines to prevent the spread of fires. “The Forest Service is interested in the robot because it may prove to be a quicker and cheaper way to fight a fire, because they can go into more hazardous conditions and aren't susceptible to fatigue like humans,” explains P&R Technologies President George Osgood.

After the fire

Mop up is a critical period after the fire; unless the fire is completely out, there's a chance that the fire could escape and cause additional damage to unburned timber “islands” within the fire area or encroach on homes, private property or timber lands outside of the fire perimeter. Firefighters must scan potentially suspect areas from more than one perspective and investigate even small anomalies to detect thermal differences. “A tree may look normal from the outside, but be burning on the inside,” explains Hogan. “The only way you might detect it is through a hot spot, like a bird hole, where the heat is venting.”

The mop-up period can range from days to weeks, depending on the size and scope of the fire. Thermal imaging scanning for larger fires is done primarily from the air in one-to two-hour helicopter flights. Pilots fly along the perimeter line at 20 to 25 knots and circle around suspect spots as identified by the thermal imager operator.

“Once I identify hotspots, I use a hand-held gps unit to get the specific coordinates,” Mark Gamroth says. “When I get on the ground, I download the image and the coordinates into a proprietary computer system that produces detailed contour maps, so the ground crews can easily find the specific location of the fire.”

Thermal imaging systems are especially helpful in monitoring burned out areas in the spring after the fire, because fires can smolder in crevices and roots three to four feet underground for up to three years through snowfalls and rains before they show smoke. Low humidity and high temperatures increase the possibility of “sleeper” fires igniting to flame.

“Land and fire managers typically schedule thermal imaging operators to fly in helicopters over the burned out areas, particularly near highways, wildlife refuges, homes, and national and state parks, to scan for hot spots and smoldering hold-over fires that could rekindle into large fires,” says Jerry Gamroth, director of operations of Infrared Inc., a thermal imaging camera distributor, and Wildland Services, a professional firefighting services company.

While most wildfires are started by lightning strikes or by accident, some fires are started intentionally in the process of forest health management. This controlled burning takes two forms: broadcast burning of clear cut areas on private timber lands and burning of underbrush, mainly on public lands to thin out fuel sources to reduce fire danger hazards. Each fire has a prescribed burn and safety plan, and thermal imaging plays a large role in the monitoring phase because all fires must be 100% mopped up. “We typically come back several times over a couple of days to scan the area on foot and by car to make sure that it's completely out,” Jerry Gamroth says.

Because arcing from utility transmission lines has such a high potential to cause wildland fires, thermal imaging systems can be used to detect lines that are over capacity and are especially vulnerable to arcing, blowing up, and creating sparks and fires. In addition, railroad companies hire thermal imaging operators to scan the rights-of-way along the tracks for sparks and potential fires following the grinding and routine maintenance of the rails.

“Thermal imaging is becoming an indispensable tool in wildland firefighting because it gives firefighters an extra edge — the ability to not only find invisible sources of fires, but the way to locate small fires or sparks amidst thousands of acres of woods. It lets firefighters find that needle in the haystack,” Jerry Gamroth says. “It gives firefighters a precious commodity — time — to get to and knock out a fire before it gets out of control and threatens people, animals and the environment.”

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David Fisher brings more than 12 years of experience in infrared technology to his role as oem account manager with Raytheon Commercial Infrared. He holds a Bachelor of Science degree from the U.S. Naval Academy, and has completed continuing education courses on basic infrared design and infrared technology and applications at Georgia Tech in Dallas. Currently, he's attending basic firefighter training through the Fire Science Academy of Colin County (Texas) Community College. Fisher has lectured on the use of thermal imaging in firefighting at Industrial Fire World 2000 and has contributed technical information to several articles on the use of thermal imaging in public safety.

Thermal imaging, then and now

Early thermal imaging cameras were heavy, weighing 10.5 pounds, required both hands to operate, and couldn't be used during the day, when there's more solar interference and less of a temperature difference between smoldering fires, hot spots and the surrounding areas. In addition, there was no way to save the video images, so operators couldn't give exact coordinates of hot spots and, when scanning from the air, had to fly in grid patterns to define the location of a fire.

New models of thermal imaging cameras weigh only four pounds, can be operated with one hand, and provide the operator with high resolution images that are clearer and have more topographic detail including roads and landmarks. The cameras can now record the video images, which can be transferred to a videotape, printed or downloaded, and matched against GPS data.

Infrared in wildland

Thermal imaging has five primary roles in wildland firefighting:

• Aerial reconnaissance to detect fires after lightning storms;
• Maintaining the fire perimeter, projecting the path of the fire, and locating escaped sparks to prevent them from becoming involved fires;
• Finding resources (personnel, trucks, equipment, water) in dense smoke and in active fire areas;
• Confirming a “fire out,” and scanning to make sure there are no smoldering fires in roots, trees, logs, etc.; and
• Monitoring during the mop-up phase after the fire is out to detect if any new fires have emerged, such as in the picture above.