I’ve been in the garage when one of those springs broke. It’s really violent and if you’re in the way, I’m sure you’d be injured. I believe there may be a standard now to run a cable through the middle of the spring so when it does fail, it doesn’t fly around uncontrolled as what I saw. (And replacing the spring wasn’t difficult, as long as we had the door propped open so the spring was not in tension.)
I used to own a house in which the garage door was fitted with linear/tension springs, and I could well imagine that if one of them broke the pieces could certainly go places; I don’t recall any anti-scatter cable threaded along their interiors. I think most modern garage doors use torsional springs that are coiled around the shaft that they are connected to (the one that drives the pulley that reels in the cable that raises the door). When those torsional springs break, they usually don’t go anywhere, since they’re coiled around the shaft. A nice safety feature.
Having said that, I can confirm from direct experience that it’s loud as hell when one of those torsional springs breaks, like a shotgun going off. It tends not to break until the door is nearly closed, when it’s at its highest energy state and highest stress. Definitely gets your attention!