My guess is all the contestants had to sign some sort of contract indicating the radio station would not beheld liable in case of accident/injury.
That would be a general liability waiver. I have some working familiarity with these. For a few years I ran a glider tow operation from my airstrip. One of the biggest reasons I shut down was because of liability exposure and the threat of being sued by an insurance company of one of the participants for events that were completely beyond my control, other than they occured on my property.
Waivers don't always hold up. You cannot sign away your right to bring suit. That precedent has already been set in Federal court. You can, however, agree to waive any judgement you might receive from legal action you bring against me and you can also agree to pay my attorney fees......that has been proven to stop this crap in it's tracks.....usually before it ever makes it to the first hearing.