Ive never found a use for a pblast in normal bgs, but I suppose if you arent in a pug you get a chance to blast a few. We'll see how it is after i get my Season 1 stuff.
Most groups wont take a fire spec in arena, its frost or nothing even with ice block.
pom is presence of mind
u can insta cast pyro, fire blast, then blast wave for a nice mass burst on your guys main target
basically wait for your team to blast off the initial damage to the target (priest bubble or prayer of mending or whatever), make him kinda get tripped, the pally wont necessarily heal yet when priest is at 90% because holy light heals for like 4k. then you do pom pyro, fireblat, then counterspell pally or whoever other healer is, blast wave, and then dead target, gg 5v4
if u have bloodlust u can chain fireball pretty well after that, errr after you frost nova, and back up, hehe