I have some left over medical experience from the Army and I’ll say this about it. If you find your self in that position of “no one else is around and they aren’t breathing”, take off the helmet and perfrom CPR! If they’re not breathing THEY…WILL….DIE period. If they’re neck is broken and you remove the helmet they may die or suffer a worse injury to the spinal cord but still be alive. If you don’t remove the helmet it does seem possible to perform CPR through some helmets especially modulars. If that’s not possible, I say screw it and take it off. Just remember law states now that if you perform CPR that you must continue to perform CPR until properly relieved by a EMT or you just can’t continue. If you fail to do either of these after you begin CPR you can be prosecuted for various negligence type charges. On the other hand if you think your playing it safe and don’t give mouth to mouth and they die from it it’s their blood on your hands for your failure to act. As a little bonus the family of whom ever you failed to help could feasibly bring charges against you since you were CPR qualified and failed to do anything. I’m sure you could say it was for relegious reasons or you were scared but, either way your just going to cheapen your own soul. As you can see it’s a double edged sword. If it were me you better rip my helmet off and give my heart a thrashing like someones life depends on it because in that case mine would. Just do the right thing.