There's an acronym in BDSM, SSC. It stands for safe, sane, consensual.
There are safe words, so that at any given moment, a person can withdraw consent. Anyone that participates as an ethical member of said community, knows, that as soon as someone passes out, you stop.
They can no longer use a safe word, or maintain consent.
The SCC didn't just pull this out of their collective asses.
Understand that I am not condemning the activity. I am questioning the premise that consenting to participate an activity that runs a high risk of losing consciousness can be retracted after the fact when that risk has been realized.
The safe words you outlined require a conscious state of mind to employ the mechanism. If the participants are aware of the consciousness risk in advance, the knowledgeable consent (and trust) must be in place to begin with.