ST. JOHNSBURY — Firefighters say a hot chain saw on a dry field started a five-acre brush fire in St. Johnsbury.

The four-alarm fire broke out in a field behind a home Wednesday afternoon as the homeowner was cutting down a tree and set the chain saw down in the field for just a moment. Firefighters said the blaze was driven by wind up a steep hill to the northbound lane of Interstate 91.

Firefighters from 10 communities responded. St. Johnsbury Fire Chief Troy Ruggles said one firefighter suffered from heat exhaustion and another suffered a back injury.