If a tank is going full to dead around 30ish, I'll assume it's the last boss in Haukke Manor. The void fire/thunder spells can be avoided by running behind the caster. If your tank is dropping when the adds come out, then they're somehow getting threat on all the adds when they pop rather than you (because you're healing) and then taking all of the hits to the face - three of them is some pretty nasty burst, just the two maidens casting can burst down a Conjurer that hasn't got their job crystal yet. Happened to me a few times at that level.

If they're going full to dead on pretty much any other boss before that, they more or less need to be unequipping gear + standing in the bad to drop that fast. On trash you can also sleep one at the start of the pull if you need to (lowers how much heals you need, thus less likely to pull off a tank with poor aoe threat).