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"The biggest problem with a day like today is the heat," said Irmo Fire Marshal Jeff Allen.

"You just get dizzy, you get weak -- really thirsty," said Nick Powell, an Irmo firefighter.

On days when temperatures reach into the hundreds, adding humidity, 50 pounds of equipment, and direct sunlight can mean 130 degree temperatures for a firefighter. That can lead to heat cramps, heat exhaustion, and sometimes even heat stroke.

"They need to consume at least one quart of water per hour, and obviously with this type of heat and humidity, that would go up," said Allen.

Allen said in addition to liquids and electrolytes, he considers exercise the most important factor for preventing heat-related illness.

"The first thing is being proactive," said Allen. "We need to make sure that the firefighters that are out there are physically fit. The largest killer of firefighters in this country is cardiac events. Why? Because they're not physically fit."

So Irmo Fire District makes sure its firefighters have a gym membership.

"We're required to go to the gym on shift every third day," said Powell. "We've also got a physical adgility test."

As firefighters encounter extreme heat on the job, Allen says the best way to fight heat-related illness is to take frequent water breaks and keep a close watch on blood pressure and body temperature.