Thursday, March 29, 2012
Fighting Fire With Fire -- And Science.
An out-of-control wildfire in Colorado that’s already killed two people and destroyed more than 20 buildings has renewed the debate over the use of intentionally set fires.
Colorado Governor John Hickenlooper issued a temporary statewide ban on all prescribed burns until officials investigate how this fire was allowed to spread outside the planned acreage southwest of Denver.
Prescribed burns, while used routinely in recent years, continue to be a source of controversy when accidents or poorly conducted exercises result in property damage or loss of life.
The tragedy came during the height of controlled burn season in Nebraska, a time of year when columns of smoke on the horizon are a common sight across the state. The practice has been aggressively promoted by agriculture and conservation advocates as an effective way to cleanse the land of old grasses, plants and trees that can take over valuable acreage from crops or livestock.
Over the past two decades, plans for controlled burns have been developed using a blend of new science and knowledge handed down by farmers and Native Americans, who have used the practice for more than a century.
Last week, a dozen ecologists and firefighters from all over the country had the chance to put the art and science of fire into practice during a two-week long clinic in Nebraska hosted by The Nature Conservancy. The Conservancy, a non-profit group emphasizing the preservation of environmentally-important land and bodies of water, promotes the use of fire when appropriate to help eco-systems.
“The science (involved in fire behavior) is weather and fuel loading and topography,” said Jeremy Bailey, the lead trainer for the exercise. “A lot of our firefighters train for years to get the point where they can supervise a burn like this.”
They gathered on a ranch south of Gothenburg. Most in the group had some classroom training on ecology and/or land management. Others are full- or part-time firefighters. Their training will emphasize how to plan for and implement a burn that will be safe while accomplishing specific goals in an ecosystem.
Bailey hoped to get the burn started earlier in the day, but steady winds meant the crews spent their time getting a refresher course in priming the pumps on a fire truck and making another survey of the landscape.
Finally, at about 4:30 in the afternoon, the weather began to calm. Bailey called the group together. Conditions appeared favorable, but the short timeframe meant a change in plans.
“We’ve been planning and planning for the past 48 hours, and now we’re going to do something different,” he told the eager firefighters, who would soon become fire starters.
The decision to proceed would be based on a number of variables, including data collected by the weather specialist in the group. Lou Schnapp, a graduate student completing her ecology studies in Texas, climbed to the top of a hill overlooking the pasture where the fire team assembled around a small armada of fire-fighting equipment.
Rummaging through her backpack, she pulled out an instrument called a “sling” psychrometer -- all day, the group made reference to “slinging weather,” and this device is the origin of the term. The psychrometer was two pieces of metal attached by a chain with two thermometers attached. One was wrapped in cotton that Schnapp moistened with distilled water.
“This one is our dry bulb, and this is our wet bulb,” Schnapp said as she prepared the device.
She stood and twirled the chain in tight circles, looking like she was armed with a pair of high-tech nunchucks.
As the two thermometers spun around, water on the wet bulb evaporated from the wick, cooling the thermometer to the lowest temperature possible in minutes. The drier the air, the more the thermometer cools, so it provides a measurement of moisture in the atmosphere, or the relative humidity.
Schnapp called in her readings on a crackling two-way radio. “Dry bulb 47, wet bulb 46, which puts at an RH of 43. Lou out.” RH would be the relative humidity. An RH below 20 is considered too dry to burn.
The burn boss, Bob Bale, also assessed the wind speed (it was a steady 6 miles per hour with some gusts up to 13 mph), short-term forecasts from the National Weather Service and other observations made at the site to determine whether conditions would meet the objectives of this specific burn.
More and more, field operations for controlled burns are dictated by knowledge gleaned from scientific research. It’s long been known that fire behavior is influenced by weather, the amount and type of available fuel and the lay of the land.
Since so much knowledge has been passed from one generation to the next, there’s an unusual tension between new science and the traditional, often effective, methods of harnessing the benefits of fire.
“I think that prescribed burning is more of an art than a science, but you do have to understand fire behavior and use that,” said Doug Wisenhunt of the USDA’s Natural Resource Conservation Service. He admitted to mixed feelings about crews in the field relying too much on computer models and mathematical formulas.
“You can calculate some of that, but in general, it’s just kind of knowing how the fire is going to react when you are burning at that time.”
Wisenhunt’s conducted dozens of burns in Nebraska and has helped form and train coalitions of ranchers and land owners to conduct prescribed burns in their regions. His advice, which he shared with the Nature Conservancy clinic, frequently mixes the intuition that comes from experience with the latest research.
One study he cites as especially useful for fire safety originated at Oklahoma State University. Data showed when the humidity drops below 20 percent on the Great Plains “you increase your chance of spot fires, of stuff carrying across the fire line and starting another fire on the downwind side,” said Wisenhunt. It’s had a major influence on when to safely conduct burns.
Whisenhunt said an ideal burn day has temperatures below 80 degrees, winds less than 20 miles per hour and humidity above that crucial 20 percent mark. Some of the most influential research focuses on the influence of temperature and humidity.
In 1998, the Forest Service began providing fire safety forecasts based on theories developed by meteorologist Donald Haines from the University of Wisconsin. The Haines Index is a mathematical formula calculating the potential for large wildfires to experience extreme fire behavior. It does not predict the possibility for a fire, like a tornado warning, but it can, according to the 2012 Iowa Fire Weather Operating Plan, “identify weather conditions that may allow an existing fire to spread rapidly or exhibit extreme fire behavior.”
It’s a tool that became tremendously useful for those planning fires they wish to keep under control, as well.
Research by academic institutions and the U.S. Forest Service has focused on very specific areas, hoping to improve both the effectiveness and safety of prescribed burns. Recent studies have concentrated on how smoke is dispersed from fires and whether it has negative effects on the environment.
On the day of the burn near Gothenburg, the Nature Conservancy’s Bailey decided the weather data met the parameters set out in the burn plan they had fine-tuned the day before.
As the teams prepared to ignite the first test plot, some of the shifts in wind direction prompted him to caution, “be heads up on the slope in these winds. The fire may not be running uphill, it may be running downhill.”
With that, the test burn got underway. There were more than two thousand acres on this ranch scheduled for burning during the exercise. They knew they would only get a fraction of that done on the first day.
In a prescribed burn, it’s important to recognize that not all fires are created equal. Different prescriptions, and different types of fire, solve different problems.
“The objective (of this burn) is to decrease the amount of eastern red cedar in the area, so we want to make sure we get a decent kill on all the cedar five-foot or below,” said Michael Henn of the Wyoming State Land Office. He was one of the students, but also has worked on the fire lines at many controlled burns and wildfires on his home turf.
Had the goal been to target the largest trees for destruction, a day with lower humidity levels might dried them more completely and turned them into volatile fuel.
“(In) other cases you might not want to burn certain trees,” Henn said. “If you are in a different fuel type and you are in a timber stand, than the objective is to not burn the mature trees but take out the stuff underneath.”
That would have required an entirely different burn plan.
Henn watched as Bailey moved across a ridge carrying a large, bright red canister resembling an oilcan. This was his torch, dripping flaming kerosene into the dry grass. It ignited immediately.
Astride an all-terrain four-wheeler was Capt. John Pawlik, a firefighter from the suburbs north of Denver, Colo. He watched as the crews carried out the first step of the burn plan: creating a buffer strip of burnt grass along a cattle trail. It’s a common practice designed to contain a larger fire that Pawlik said would “let the fire run with the wind, so the embers will fall on that black part” when they torched the larger pasture the following day.
Crews with torches left a trail of fire behind them along the cattle trail and a county road a couple of miles to the east. The next day, the crew planned to burn off any remaining grass in the valleys in-between. By sunset, about 400 acres were blackened. This was a training burn, and the organizers with the Nature Conservancy said in that regard, it was successful. The second goal, killing off the cedars, fell short of expectations.
The relative humidity continued to creep up as the sun went down.
“We’re not having the flame lengths that we ordinarily would have if the sun was out and everything was a little bit drier,” Pawlik said. “The fire is having to do all the work by drying out the fuel.”
Jeremy Bailey, covered in soot and exhausted, pulled off his helmet.
“Right now, we’re at a threshold where our fire is no longer carrying. We’re no longer creating black, so there is no more work to be done this evening other than patrol, get the firefighters back in bed and well-rested so they can come out in the morning and start all over.”
For those brought in for the training, it was a good example of how small changes in a single factor, like the humidity, can help or hinder the goals set out for a prescribed burn.
at 4:42 PM