What helps you in a meltdown/shutdown?

I hope its alright to ask this question but what helps you when you are having a meltdown or a shutdown? We, as a school, are trying to improve and are really trying to help our students, who are all autistic. We deal with meltdowns and shutdowns on a daily basis and we would like to know ways we can help our students even more when they are struggling or overwhelmed. How long does a meltdown/shutdown last for you? How long does it take to recover? I hope its ok to ask this, if not please let me know. 

For us, students meltdowns are all completely different, some will last 5 minutes, some maybe hours. It all depends on what's troubling them. To recover, sometimes it takes 5/10 minutes and sometimes some students need the rest of the day. What works for you?