I dunno, the headline makes it sound like he pulled some real bullet-time shit and heroically jumped out of the way at the last moment. But instead he sauntered into a shop, presumably unaware that it was even coming, and then many seconds later the saw appeared.
That's like saying I have a miraculous near-miss every time I cross the road.
Yeah but we're all seconds from being killed every single day. He had enough time between being in that spot and the blade arriving that he was able to saunter quite casually into the shop and probably make it several meters inside. In the grand scheme of things that's an eternity.
Put another way, considering all of the other places in the world he could've been stood at the moment of impact (and indeed was), he'd have been extremely unlucky to have been hit by it. It's like saying I almost won the lottery jackpot because I matched 3 numbers.
Sorry, I'm not attacking you. It's an interesting video, and I'm not saying you shouldn't have posted it. I'm just annoyed by the BBC's clickbaity, hyperbolic headline.
Now I'd like to know how a saw blade could actually run away like that?
I can imagine a lose saw blade rolling down a hill, but it probably won't gain that much speed. And within a saw, it is mounted on an axis and surrounded by a lot of other stuff, so even if the nut comes lose on the axis, it won't be going anywhere much, at least not while taking that much rotational energy.
The blade got spun up, then came off the saw, likely because the retaining nut came off. The blades aren't on some long mandrel, they're on a short bump of a shaft that the nut screws down to. Take a look at how discs connect to angle grinders and you'll have a good idea of how concrete saws do it
It is perplexing, because those usually have a guard over them aswell. Maybe the shaft stud snapped right at the blade, and machine had the blade without guard rotated down over it?
To be fair, it would have been a cool way to die. Painful af, but cool. Of course we live in the worst timeline so he'd probably have lived with life-ruining injuries if he'd been hit. Regardless, good thing he wasn't 5 seconds slower.