Unless I've been playing wrong, fanatics only deal 1 damage. They then roll a die. A roll of 5 or 6 deals 3 damage on top of the previous 1 damage.
A fanatic can blow up and then blow up another fanatic. If you're in there then you're in trouble!
Make sure someone plays as the Psychic and move them out of the way.
We've played two games with the Preacher and co and it's been a lot of fun!
Dean is correct, this is the way you play Fanatics. They deal 1 damage, then you roll a die and if the result is 5 or 6 they detonate and deal 3 damage to everyone in the zone, including Redeemers.