Flame On!

At lvl 110 you just need to burn him down. ilvl 941 fury warrior.

Basicly the easiest way to do this is to make sure your ranged are spread out but only between the totems (also those who are not up). That way you will reduce the amount of damage done and have less deaths ;).
i just did this achievement with a small amount of ranged -which is also a pluspunt, since he will always go for ranged if there are - and i made sure they were carefull. its better that you die and he focuses another ranged than that he runs trough a firetotem.
always be aware there WILL be 2 totems up when the berserker rush starts, but around 50% of his cast a new totem will rise up... had to wipe a few times since he was on that specific totem when it rose up :/
anyway overall its a fair easy achievement - he had berserker rush 3 times and we were a team of all 645+ ppl. at the end we had only 2 ppl death out of 13 total so it is totally doable :)
good luck to ya'all and i hope this was helpfull.

Reference to the Marvel superhero, The Human Torch, who's commonly used catchphrase was "Flame on!"