The firefighters received electric shocks when a ladder came close to main a power line. Officials said at a news conference that electrical energy apparently "arced over and ladder didn't actually hit lines."
"If you get within certain radius that can happen," Cambellsville President Michael Carter said.
The firefighters were on hand to spray freezing water on the university's marching band, Carter said. The challenge was being held on a university athletic field.
Two of the firefighters were airlifted to the burn unit at the University of Louisville Hospital, where Simon Grider was reported to be in critical condition. Another, Tony Quinn, was in fair condition.
The others were treated at Taylorsville Regional Hospital.
The challenge to raise money for amyotrophic lateral sclerosis or Lou Gehrig's disease became a viral phenomenon this summer, attracting celebrities including President George W. Bush, Ben Affleck and Mark Zuckerberg. .