I understand the fear of leaving someone who is prone to raging. The advice I got was to plan carefully and have an escape package somewhere safe - with a trusted friend or at work. Any battered women's shelter can give you advice on what that emergency it should contain.
Just be aware that the shift in your behavior when you start planning may set him off even more, even if you don't think you're changing. That's what I saw happening - I had to leave much earlier than planned and with much less preparation.