It's the levers you use to wind the springs or the wrench you use to tighten the 2-3 locking setscrews that cause the most common injuries. The spring is wound on its shaft by a capstan with radial holes and you wind it by putting two levers in the holes- one to hold it and one to advance it. if the capstan's light aluminum casting breaks or your lever slips, the next one comes around and takes out your head or impales you- the same thing can happen if a lever slips while you are locking the bolts and the wrench you are using takes your hand off or winds up inside you. All compounded by the fact that this typically happens to a DIY amateur standing on a ladder.

I've seen the springs unwind unexpectedly a few times but I've only seen two springs break and one of them just violently unwound on the shaft as you suggested but the other one threw a section of itself through 2 layers of drywall 60 feet away. I'll never touch another one.