I know it is not easy to explain it, but what I mean is not stay away till you are sure not to get hurt...but don't throw yourself into a situation just because someone needs help. It is no use to the person in need if you jump into a situation where you start with a 0% chances of getting out of there alive
I'm not saying that intervention requires you jumping in. When a situation arises that requires your intervention there are three simple rules that you can apply over and over again.
Your may be able to intervene by throwing objects at the attacker giving the victim time to escape. Call others over and go in on mass. You must never think that intervention involves a physical alteration.
Intervention is a big call and you are the only one that can assess the situation. I have to intervene when working. The type intervention is dependant on who I'm working with and what tools I have at my disposal. When not working and faced with the same situation my type of intervention will of course be different.