Best Styles/Techniques to deal with people under the influence and much bigger hostile people without strikes

I was not sure how to word the subject,or if this is the right forum for it. Anywho I have started working at a wet homeless shelter, which means people can be messed up and still stay there. Also Maine now has an epidemic of bath salts which makes people very paranoid, also stronger and unpredictable. I used to take karate-do when younger, and am very interested in training again. I made a lot of bad choices in my life and got clean and went to school for substance abuse, and now Im working where I mentioned. we try deescalation and redirection on upset/hostile people, and we have the police backing us. These folks can be big, mean, and simply put crazy. Im looking to start training agian after many years. So the question, what are some good techniques and a overall style dealing with much bigger people, who could quite possibly not feel pain? These are a last resort for when the police cannot get there in time.