He actually starts out with no damage shield. When your group's DPS rise aboves a certain threshold, he will emote and self-buff with a small, manageable damageshield. If you slow down your DPS within two ticks, this damageshield will fade and he will emote accordingly. If your DPS continues to remain above the threshold after two ticks, his damageshield powers up a level to a damage shield that can kill you if you are not very fast to react. If your DPS still remains above the threshold after two more ticks, it powers up to a third level that is effectively a death touch to anyone who nukes or attacks him.
Even the second level of the damageshield is nearly enough to one-round a hasted tier-4 raid geared melee character. By the time you see the message that it is powering up, any melee DPS (including your tank) will be nearly dead. The goal is to not even let it get to that point. You need to DPS at a snail's pace here. Whenever the first (small) damage shield appears, you need to back off all DPS until it powers back down and it fades. To be safe, you may also wish to tank him with attack off and without any weapon, just in-case the DPS powers up his damageshield, so you don't lose your tank.
