I've had them break twice. Once was noticed immediately by me, and another was not noticed by either of us and apparently I'd been bare for the last little bit and actually finished inside her. Nothing came of it though, had a panel done even a year later. That is one reason that girls known for BBFS don't appeal to me, it obviously raises risks for everything, even accidental. But to each their own, obviously some people roll the dice their whole lives and never have any serious consequences, and I totally get the appeal. If it wasn't for STI's me and my girl would be going completely wild. Some of you met her a couple years ago
I'm so paranoid anytime it starts feeling too good, I check the wrapper!
Obviously nothing is guaranteed, but chance of any transmission is a factor of time. For a brief moment it's pretty low.