If both people are clean there is 0% risk which is hard to tell when the not all punters are tested regularly, the risk of catching anything life threating through BBFS for female-to-male transmission is 0.04% per act, latex condoms reduce this by about 85%... Take into account most WL's are required to be tested its a very very low risk, safe sex punting is obviously the safest but you can see the risks are actually low...