Eric Hetzel, Butler Township parks and recreation director, uses a flare to burn the high grasses in the prairie at Preston Park in Butler Township.

BUTLER TWP — Part of Preston Park was purposely set on fire Thursday afternoon, but for good reason.

Firefighters and park volunteers participated in a controlled burn to maintain some of the fields in the park.

Dave Heltzell is the leader of the volunteers at Preston Park and a certified burnmaster.

“We do this once every year,” he said. “The purpose of doing this is to keep the impurities out of the prairie. It keeps invasives out and keeps it pure.”

Firefighters lit the fields with flares and stood by with rakes to ensure the field burns completely and doesn't get out of hand.

Once lit, each field took about 20 minutes to burn, and the whole event took about an hour and a half.

Heltzell said he keeps an eye on wind forecasts to know when to burn and how to start the blaze so that it's safe and under control.

“There's a lot of things to be careful of,” he said.

Heltzell said he's been working with the park since 2011. A local Scoutmaster, Heltzell helps his Scouts plan improvement projects at the park.