Flames moved across the prairie feeding on dry grass and leaving behind a carpet of black, scorched land. In a few days, bright green shoots of new vegetation emerged to provide food and habitat to numerous mammals, birds and insects.The land management ritual of burning the prairie dates back to when Native Americans lived and hunted this land. "Native Americans knew that after a fire, the fresh green grass would attract the bison and the elk," said Steve Wahle, the wildland fire management coordinator for Fort Riley. "Prescribed burning is the greatest tool we have for managing our prairie ecosystem … and Fort Riley's natural resources." The burn season, which starts in late summer is coming to an end."We usually do not do burns after May 1 because things green up and it's harder to burn, and then too because of (ground) nesting birds," Wahle said.The goal each season is to burn about 30,000 to 35,000 acres, which is about one-third of the installation's acreage. However, there are several factors that play into whether that is accomplished or not, such as manpower and weather.The 2018/2019 plan called for burning 37,440 acres. As of April 30, they were 47 percent complete with 17,515 acres burned.If the burns did not happen, the prairie would revert to woodland. It also helps reduce the incidents of wildfires starting from military training by removing a potential fuel source for the fire.Where and when to burnEvery morning the National Weather Service issues a weather graph that predicts several factors such as relative humidity, temperatures, wind direction and wind speed.Wahle studies those graphs and looks at the Haines Index, which measures the potential for dry, unstable air giving him an idea of how the fires will behave. During a recent fire at Training Area 10 Alpha, several dirt devils formed alongside the burning prairie."Those are a sign of an unstable atmosphere," he said. "The fire is lowering the (relative humidity) it's kind of making its own fire weather where the fire is changing how the wind blows, or how much warm air sucked up and cold air brought down."When deciding where to burn -- there are just as many factors to consider. Even though prescribed burns are carefully monitored, they can get out of control. To help mitigate a fire from spreading off post, Wahle will make sure the burn plan includes scorching an area as a fire break to ensure fuel is gone and fire cannot pass it.He includes the training areas in the burn plan because of the risk for wildfires igniting. In the first three quarters of fiscal year 2018, they had 57 wildfires."Wildfires happen a lot," he said. "The fire department will respond to all wildland fires on Fort Riley. There are some times, like if the fire is in the impact area, that we can't drive the trucks in there. So basically, they do a burnout operation to kind of burn off the fields on the edges. That way, if the wind shifts, it wouldn't jump out of the impact area."Wildland Urban InterfaceThe Wildland Urban Interface is where the populated areas and the prairie come into contact. There are several areas on Fort Riley where this occurs.Wahle said they use care when doing prescribed burning in those areas, taking into consideration housing, schools and roads."We have to look at wind direction and not just the wind direction for that day," he said. "After you burn an area, sometimes logs and stuff still smoke. So, you want to look at a several-day period."They try to let residents know when they will be in the area burning, but it's not always possible because of the uncertainty of weather and manning."We try to send out notifications a day or two before we burn," he said. "But sometimes as forecast changes and we have to either cancel the burn or sometimes the forecast shows the wind will be too high then all of a sudden, it's a perfect day."Health concernsFor most people, the thick, acrid smoke is an inconvenience. But there are some people who can experience difficulties.Eric Coates, chief of industrial hygiene for the Department of Public Health, said normally, healthy people won't have issues with the smoke beyond the inconvenience."We get more concerned about the young and the elderly," he said. "People with respiratory illnesses such as asthma, it can really affect them. People that have something like COPD -- Chronic Obstructive Pulmonary Disease, it can affect them. It affects some people's allergies. We have a lot of people that move here that never have allergies before they get to Kansas."The concern rests on the particular matter of 10 microns and smaller, which is inhalable."(The Environmental Protection Agency) also looks at PM 2.5," he said. "PM 2.5 is 2.5 microns in size and smaller and that's what gets deep into the lungs. That's where people that start to have more of the issues is when the PM 2.5 is higher."The problem is nobody can know what that level is by being around it, he said. It can be smelled and the smoke can be seen, but there's no real way to know the level.People who do find themselves susceptible to breathing problems when the smoke gets heavy should stay indoors with the windows closed, he said.When in a car, he recommends using the air recirculation option to prevent air coming in from the outside."The other thing (even for healthy people) that we caution on is (to) limit the amount of outdoor exercise to where you really exert yourself and your lungs are really working hard," he said. "Limit that outside exercise during that time when the smoke is the heaviest. We recommend if it's super smoky outside, maybe that's a good day to hit the gym, rather than going for an outside run."Parents of small children should be alert if breathing becomes labored. They should call the pediatrician if that happens. Overall, Coates said there is not a big reason for concern."We did a study several years ago," he said. "We tried to go back and look during burns, did we see an uptick at the emergency room of people coming in with respiratory illnesses? We couldn't find any sort of pattern that said, 'hey, we're doing heavy burns this day. And we had (an) increase in the number of people.' It really is a small, small amount of people that will ever have issues."