Nothing is ever 100%, but DATY is not as dangereous obviously as other thinks.

If you do some research on here and The Erotic Highway Board, you'll find links to articles and data bases such as the CDC which have statistics that you can use to make an informed decision on what activites you want to participate in up to your risk tolerance level.

For what it is worth, I have seen well over 200 gals on about a weekly basis for the last 30 years or so and to date have not encountered any STDs from any professional gal.  

On the other hand, I did get a couple of STDs from civies a long time ago, but a few shots cleared them up.

Safe: Go home, screw your dish towel, go to bed.

Not Safe: Having fun with women.

Sorry to be blunt, but common man!  Safe!  Really?  How do you know that she won't stick a gun in your back the instant you bend over to drop your pants?  What the hell is safe!  Do I think she will?  No.  But I also don't think you'll catch anything from DATY with a professional either.