Blast Furnace is a Pack-a-Punched upgrade module in Call of Duty: Black Ops III. It gives the weapon a chance to shoot out a bullet that will burst into flames and kill any zombies in the immediate area. If a zombie comes into contact with the flame they will eventually burn to death. It is a very powerful upgrade, as it is capable of killing zombies even past round 100, and the upgrade only needs a bullet to kill an entire horde of zombies. This upgrade can be used infinitely many times as long as ammo is present and it has a recharge of 15 seconds per use. While it is arguably the best upgrade to take out zombies it must be used wisely and carefully as zombies under the effect of burning still go after a player two to three seconds after being shot, making it a risky upgrade of camping and a more ideal perk for training zombies. As of an update, it has a smaller effect radius.