More than 500 acres burned Friday in the Mark Twain National Forest in Iron County. The smoke from that fire created hazards leading to the closure of Highway 32.  The fire is burning on both sides of the highway and started shortly after 10 am on Thursday morning east of Bixby.  Trees have reportedly fallen into the roadway and minimal visibility has caused the road to shut down between Highway 1 and Highway 49.  US Forest Services Spokeswoman Jody Eberly the heat and humidity have created new challenges. As of 2 O’clock Friday the fire was 40 percent contained.  Firefighters have used three fire engines, a bull dozer, and a helicopter to fight the blaze.