Forty firefighters from Pennsylvania and Mississippi were on their way to Alabama to help battle a wildfire that had burned more than 400 acres of wilderness Thursday as temperatures soared into triple digits yet again in a month of record heat.

The blaze was still growing in the Talladega National Forest between Lineville and Talladega, but officials hoped to contain it before it could spread further through east Alabama.

Jorge Hersel, a spokesman for the U.S. Forestry Service, said about 100 firefighters would be working on the fire by Friday after the arrival of the out-of-state crews.

Hersel said firefighters “made significant progress” Thursday and had the fire “80 percent well-contained” by the end of the day. Firefighters had to stop work around 5 p.m. because of lightning in the area.

“We are cautiously optimistic, but this fire is by no means through or finished,” Hersel said.

He said six miles of fire line have been dug around the edge of the fire to contain it. He said firefighters on Friday would check to make sure the fire hadn’t jumped the line and finish putting it out.

Aside from fighting the fire, crews were having to bring in loads of water to keep workers hydrated, said Hersel.

“It’s very hot and dry out there,” he said. “We’ve had a couple of people who got a little weak and we had to pull them off the fire line, but we haven’t had any major problems.”

Hersel said Thursday evening that two people overheated on Wednesday and one on Thursday. He said all three were mild cases, and the firefighters recovered after they were pulled off the line.

Firefighters have been working since Monday to extinguish the wildfire, which has left a smoky haze in Clay County. Hersel said authorities believe it was sparked by lightning over the weekend. He said that by the time the fire is extinguished it will have burned more than 400 acres and possibly as many as 500.

The National Weather Service said temperatures climbed to 105 in Birmingham and 103 in Anniston Thursday afternoon, extending a heat spell that has been blamed for 12 deaths statewide and set records for triple-digit temperatures in cities including Birmingham and Montgomery.

State climatologist John Christy said the smothering heat and drought could break soon as fall approaches, but there are no guarantees. The state’s hottest all-time temperature — 112 degrees — was recorded on Sept. 5, 1925, in Centreville, he said.

“And that followed what was the driest August on record,” said Christy.

Christy, of the University of Alabama in Huntsville, helps compile the U.S. Drought Monitor, which classifies the entire state as being in a drought. Nearly 75 percent of Alabama is experiencing an exceptional drought, the worst rating, with rainfall deficits of more than two feet for the year in Tuscaloosa and Anniston.

Only six counties in southwest Alabama around Mobile are outside the area of exceptional drought, and Christy said they may eventually be included.

“Anything can happen,” said Christy. “It could get larger if the southwest part of the state doesn’t get rain.”

The Alabama Department of Public Health has warned people to stay inside in air conditioning as much as possible. Officials said the heat has contibuted to 12 deaths since Aug. 1, with 78 people admitted to hospitals for heat-related problems and another 274 seen in emergency rooms.

Heat-related deaths have occurred in Autauga, Chilton, Coffee, Elmore, Greene, Henry, Montgomery and Morgan counties.