Jay Wiseman, the emergency medical technician and kink educator who's studied and written about this the most, comes down firmly against it in his well-known article, "The Medical Realities of Breath Control Play." The other authority on such subjects, the much-published Charles Moser, MD, is somewhat more equivocal: when I talked to him about it, he basically said, "It can kill you. I won't tell you not to do it, though. Oh, but it can absolutely kill you, and you'd never see it coming. People have a right to do it, though...." He might have kept on like this "Kill you! Right to! Kill You! Right to!" until I slapped him, Chinatown-style, but we don't have that sort of relationship. If you and the b-friend are negotiating this stuff, and you'd better be or I'm coming over there and kicking your ass myself, I suggest you agree to oh, I dunno, carve "I LUV BRITNEY" on his chest and flog him through the streets with a flaming medieval flail, but you should refuse, categorically, to choke or black him out. Just say no.
As for playing without a safeword: fine, whatever. You know and he knows that if he were really in trouble he'd manage to communicate this to you, and you would stop what you were doing. No big deal. There's one more thing we haven't covered about consensuality though, and it's a big one for you, the presumptive top: Do you even want to do this? You get to say no too, you know. Call out your own "safeword" if you have to.
Andrea is home with the kids and going stir-crazy. Write her a letter! Ask her a question! Send her your tedious e-mail forwards! On second thought, don't do that. Just ask her a question.