It really depends on what state you are in. Some states have nothing set up for requirements and either their ER doctors or ER staff nurses are doing the SANE exams...this is very bad. Other states require SANE trained which is something like 40 hours of classroom stuff and a few exams under your belt. My state, Oregon, use to require SANE's to be certified through the state of oregon but has recently switched to just SANE trained...probably because the certification process is a bit difficult to get through. States can have their own certification like Oregon does (OR-SANE) or you can be nationally certified through IAFN.org. You need to good your state SANE or SART program. A lot of states are now requiring every county to have designated sart programs and SANEs. You just got to do the research for your area.
As for my state, there was a 2 year minimum ER experience level to get the SANE training. ER nurses do very well in SANE programs because they see a lot of violence in general in their jobs.
Hope that helps.