Psyk-Out grenades

I'm looking again at Psyk-Out grenades. How do they work exactly? I understand the whole 'reduced to initiative 1' part. But when do they get thrown? Since one model per unit can throw 1 grenade in the shooting phase, do they go off here? This would make the most logical sense. The blast goes off, impacts the enemy, but not the Knights because their out of range. (Oh...8" range I'd assume?) Or are they used in melee since no range is given? If so, when do they go off? At the highest grey knight initiative? (If they are used in melee then please no one tell GW! ...because shouldn't the Knights be caught in the blast; as well?) Do they just auto-launch themselves with their holy powers and simple work because the unit is equipped with them? Or do you need to designate a model as tossing a psyk-out grenade (and if so in what phase?)? Thanks for the help! The answer is probably easy, but I'm too lost in multiple books on multiple pages to see it!

You're confusing our special grenades with the new rules in the BRB that can be thrown. Ours don't have to be thrown, nor do they use any blast markers so they won't hit your own guys. They go off automatically as soon as you move into b2b so the targets will be reduced to I1 before anyone does anything.

Got it. I thought I was too close to the trees to see the forest! Thanks!