When you are arrested for a DUI in San Francisco, the officer will take your driver's license away from you and give you a temporary license.  When you are offered a blood or breath test, you submit to the test, and your BAC is 0.08 or more, your license will be suspended for four months.  If you have a previous DUI in the last ten years, your license will be suspended for one year. 

If you are under 21 years of age, and a preliminary alcohol screening test or other test shows a BAC of 0.01 or more, your driving privileges will be suspended for one year.

Refusing to take a chemical test of any kind when asked will result in a suspension of your driving privileges for one year.

A qualified San Francisco DUI attorney can explain the various driving suspension times, as well as avenues to prevent the suspension through a hearing with the Department of Motor Vehicles.  You must request a DMV hearing within ten days of your arrest.