Martin County firefighters have spent more than a dozen hours battling a mulch fire that sparked west of Hobe Sound last night.

The fire has been contained to an area of about 1 1/2 acres off Bridge Road and Powerline Avenue, Martin County Fire Rescue spokesman Jon Belding said this morning.

Now crews are working with the Martin County engineering and solid waste departments to haul in heavy equipment to separate unburned tree branches from burning material, Belding said.

Firefighters were called at about 8:30 p.m., Belding said. What sparked the blaze is unknown.

The blaze is located on a roughly 40-acre parcel recently acquired by the county, Belding said.