On the fire line

Published:  15 August, 2017

New research using thermal imaging cameras is improving our understanding of how wildfires behave and has the potential to aid firefighters in containment and mop up, reports Michael Davies

Forests are fire-dependent ecosystems. Those that have ground fires every few years have a vibrant ecosystem with healthy trees and a variety of plant species. Forests that have not burned for many years, however, tend to be overgrown. Trees must compete for nutrients and are often stunted, and the understory is more homogenous and does not provide opportunities for plant diversity.

Lightning strikes start fires regularly. These fires serve to clean up litter and overgrowth on the forest floor. If these fires are allowed to burn frequently, the fuel load remains low and the fires burn at a lower intensity, clearing the forest floor of debris and thinning young trees, but not killing mature ones.

On the other hand, if a forest has not burned for many years, the amount of dead plant material, twigs, branches, and fallen trees will build up. When a fire does occur, this heavy fuel load will burn so intensely that the fire destroys everything in its path, leaving nothing but degraded soil and blackened trunks in its wake.

In May 2017, I was deployed to West Mims, a 152,500-acre wildfire that had been triggered by a lightning strike on the Okefenokee National Wildlife Refuge. While I was there I met research ecologist Dr Joseph O’Brien and his colleague wildland fire scientist Kevin Hiers, who have been working together for a number of years to understand the variation of fire intensity in forests that experience frequent fires.

As well as being a research ecologist, Dr O’Brien is fire science team leader at the US Forest Service's Center for Forest Disturbance Science and has spent the last 30 years studying forest ecology and the role that wildfire plays in a healthy ecosystem. He has studied forest ecosystems from Costa Rica to Alaska. His current area of research is the ecology of frequently-burned fire-dependent ecosystems.

Kevin Hiers works at Florida's Tall Timbers Research Station. As part of his work, he studies the interface of fire research and prescribed fire, connecting combustion science to its ecological effects. Hiers is also a firefighter and has served at West Mims as situation unit leader for the southern area incident management red team. He was able to arrange access to the West Mims fire for Dr O’Brien as it was the perfect laboratory for their research on fire intensity.

Dr O'Brien explained that if you walk through a forest after a low-intensity wildfire, you will see that almost all available ground fuel has been consumed. This might lead you to assume that the fire burned with uniform intensity through the entire area, but that's not how wildfires work.

Differences in fuel loading, moisture content, and topography result in fires burning less intensely in some areas and more so in others. In some sections, plants have been burned on the surface but their root systems remain intact and can regenerate, or viable seeds may remain buried in the soil. In other areas, the heat of the fire is so great that all plant life is destroyed. These barren areas may now be populated by different plant species. The result, when vegetation returns, is a healthy mixture of grasses, brush, and young trees.

In the past, there was no effective way to measure the intensity of fire over a large area. Scientists placed buckets of water in multiple locations in front of an advancing wildfire and then returned to measure the amount of water that had been lost to map the fire's intensity. Another approach was to apply wax to steel plates and then measure the amount of wax that had melted. Now, by using today's infrared technology, Dr O'Brien can achieve far more accurate studies of fire behaviour.

Dr O’Brien came to West Mims with a cache of thermal imaging cameras and taught a group of field observers (FOBs) to use these TICs to detect hidden heat sources, commonly referred to as hot spots. Finding hot spots is critical to ensuring that containment lines are secure and that the fire will not escape. Armed with this knowledge and portable infrared cameras, these FOBs will be sent to new fires where they will share what they have learned with others.

When I caught up with Dr O'Brien, he had just returned from hiking the fire line with his trainees. They had taken their thermal imaging equipment to a section of the fire where hotshot crews were working to secure control lines. The FOBs were using Flir One TICs that plug into a charging port on a smartphone. They weigh less than two ounces and cost under US$400. While they may not be as powerful as more expensive cameras, in the hands of an experienced firefighter they can be very effective for locating hot spots.

The team began walking a tractor plough line. In the southern region, the tractor plough is one of the primary firefighting tools. It is a bulldozer that pulls a specially designed trailer-mounted plough. The bulldozer blade scrapes away ground vegetation and small trees and pushes them away from the advancing fire. As the bulldozer moves forward, the trailer plough cuts a deep trench into the soil. Two angled plough blades then guide the excavated soil to either side of the trailer, creating a wide channel with berms of freshly turned soil on either side.

This is a highly effective method for constructing containment lines, but when the tractor plough is used in direct attack – carving the trench directly on the line between the advancing fire and the unburned forest – soil on the hot side of the berm is piled over burning material. Some of these fuels may continue to smoulder, buried under a foot or more of soil. These concealed hot spots have the potential to burn to the surface and reignite. Under the right conditions, this could allow the fire to cross the containment line and make its way into unburned fuels, resulting in an escape.

The group walked a few miles of tractor plough line, scanning the berms with thermal imaging cameras. With the TIC and a smartphone, one experienced firefighter can scan a large area, marking the location of hot spots. This work would otherwise require a crew of firefighters walking in a grid formation to cover the same amount of ground. And, although fire crews had checked the line, Dr O'Brien found four concealed hot spots.

There are also other ways that thermal imaging technology could benefit wildland fire suppression. To ensure that a wildfire cannot advance, a perimeter must be established that holds no available fuel or ignition sources. This perimeter is called a containment line. It commonly extends 20 to 40 metres in from the edge of the fire. This cold zone between burned and unburned fuels denies the fire a pathway to escape and prevents it from spreading. Once a continuous perimeter is established, the fire is considered contained. Mop up is this process of ensuring that no available fuel or ignition sources exist in the containment line.

During mop up, hand crews (typically 20 to 22 firefighters per crew) fan out into the fire area and inspect every square foot of the perimeter. This is called cold training. Firefighters use hand tools to rake through the ash to find concealed hot spots. To determine if the ash is ‘cold’, firefighters remove a glove and use the back of their hand to feel for heat.

Mop up is a difficult and dirty job. There were more than 94 miles of containment line on the West Mims fire. Mop up operations required hundreds of firefighters and accounted for thousands of hours of labour.

Dr O'Brien demonstrated that the TICs made mop up more efficient. The test wasn't a complete success, however. During the heat of the day, ash covering the soil absorbed heat and raised ground temperatures to as high as 60°C. This made it difficult to pick out hot spots beneath the surface. The IR cameras were most effective when used at night and during the early morning hours.

Even with these limitations, portable thermal imaging cameras could potentially save thousands of dollars by reducing the number of firefighters required for mop up. They could also reduce the number of undetected hot spots. One single blow-out on the West Mims fire, reportedly a consequence of a missed hot spot, resulted in the loss of over US$21 million in commercial forestry.

Large wildfires cost millions of dollars to control, and the cost of fighting these fires increases each year. In 2016, US wildland firefighting costs exceeded US$1,975,000,000. Twenty years ago firefighting accounted for only 16% of the US Forest Service's budget. Today that figure is nearing 50%.

‘Given the astronomical costs, why shouldn't every hotshot crew be equipped with this technology?’ asked Dr O’Brien.

Certainly, we need to work smarter and take advantage of technologies that allow us to complete our missions safely, at lower cost and without compromising the quality of our work. Dr O’Brien and Kevin Hiers have shown us a way to significantly reduce the costs of mop up and possibly improve the quality of our containment lines. I hope the US Forest Service and other stakeholders embrace this time-saving technology and give our hotshot crews a valuable tool.

  • Operation Florian

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