Fire Shield relevant text:
While this power is in effect, any character in range and line of sight that successfully strikes the psyker with an attack immediately suffers Energy damage equal to the psyker’s psy rating. The degrees of success on this attack are equal to those from the Focus Power test, and the inflicted damage is not reduced by Armour or Toughness bonus.
There doesn't seem to be any way to avoid taking this damage, which is odd considering how little health most acolytes will have, and suffering guaranteed damage (which could be as much as half of your health) whenever you attack someone sustaining this power (which is a Free Action) seems overly powerful/limiting.
- The armour modification Ceramite Plating from Enemies Within that gives enhanced armour against flame attacks is bypassed by the last sentence
- For the same reason, cover seems to be irrelevant
- The armour modification Hexagrammatic Wards from Enemies Within which grants bonuses to checks to resist psychic powers and which makes it so warp-weapons don't ignore your armour doesn't come into play against an auto-hit psychic power
- It doesn't seem like you can make a Dodge reaction against the attack, as the psychic power says 'the target immediately suffers Energy damage'
The only two ways (aside from attacking from outside the power's range) I can think of are a force-field, which should block the damage if it rolls successfully to come into effect, and to force the psyker to drop the power (possibly by knocking him out or throwing some anti-psyker grenade, etc) and cut it off at the source. Once the damage is triggered, can it be avoided?