Firefighters face punishing, blinding smoke, toxic fumes and temperatures hot enough to melt a fire helmet. Then add 70 pounds of protective gear.
"Like, anybody who's ever ran races and stuff like that, it's the same thing. You can feel your heart beating in your chest," said firefighter Richard Dodds.
Eighty-two on-duty firefighters died in the U.S. last year. Four percent of those deaths were of sudden cardiac arrest. Since 2004, it has accounted for 39 percent of all on-duty deaths.
"High heat levels, we know from other areas of research makes your blood coagulate faster. So if you have what otherwise might have been a small heart attack, it could be a large heart attack," said Dave Hostler, PhD of the University of Pittsburgh.
In a burning building, body temperatures routinely hit 104 degrees, so researchers at the University of Pittsburgh are testing two high-tech cooling techniques. Specially designed portable chairs have a pool of water in the arm rest.
"Because your arm is immersed in water from the elbow down, the blood in your veins, which is very close to the skin, exchanges its heat with the water, and returns cool blood to the body," said Hostler.
Firefighters are also testing cooling vests, like the ones used by NASCAR drivers. Tubes pump icy liquid through material near the body's core to cool it down. Experts are comparing the effectiveness of both methods.
The control group in that study was a group of firefighters cooling down the old-fashioned way: by simply taking a break.