List the most important risks associated with breath play. ('most important' meaning either higher-likelihood, or higher-severity combined with lower-likelihood)
To get you started, I found someone from outside the BDSM community suggest the risks are -- irregular heart rate, cardiac arrest, brain damage from lack of oxygen, and death.
Then, see if there's any data on the probability of each. Don't spend more than a couple minutes on each however, since I bet there's some real rabbit holes here.