I can so relate. difficult child 2 would blow up with or without provocation in a split second. And believe me, he was dangerous, even at 12 years old. It took us forever to get it under control. In actuality, it wasn't until he was much older and we made drastic life changes that things started to calm down.
I can tell you the first step was supervision. Heck, there were days I couldn't even leave difficult child 2 alone long enough to shower or go pee. But what I didn't learn until much later was that supervision wasn't enough. medications weren't enough. The real key was observation - noting everything about situations where he started to spiral into a meltdown or had some display of violent behavior. I made notes about everything, including what he ate. (I'm talking I kept copious notes, looking for any kind of a clue.) Eventually, patterns did start to emerge. Sometimes it had nothing to do with what was going on at that moment. Sometimes it started that morning with him just having a grumpy mood day. I learned over time to find ways to counteract or at least spot some triggers. Not all, but some. It helped us minimize his meltdowns.
Granted, I was lucky in that I started homeschooling the kids and working from home, so I was around him 24/7. It gave me a unique opportunity to really get to know him, his moods, his behaviors, little signals and cues. As he got older and was better able to communicate what was going on in his head, it got a lot easier. I know that doesn't help you right now, but I promise, there is light at the end of the tunnel - even for the most hopeless of cases (which we thought difficult child 2 would be.) You would have never been able to make me believe that a few years ago. Especially not on days when all I could do was lock myself in the bathroom at night and ball my eyes out.