Nah, the scariest is that aluminum, like other alkali metals, literally explodes when it comes into contact with water. This is extremely rare with aluminum since aluminum quickly forms a layer of oxide, and even when casting it's unlikely to happen, at least in hobbyist foundries. You can even find videos of idiots pouring molten aluminum into a swimming pool to show that it's "safe" and nothing bad happens. But the possibility is very real, and while it's pretty dang unlikely there's no good reason to intentionally pour your molten aluminum anywhere near water.
Edit: found a Hackaday article that covers this in more detail
Must watch video for anybody thinking of doing metal casting.
I came this close to setting my garage on fire, some old rags were stored in a box quite a ways off where I was welding something and a tiny bead of molten metal somehow made it in there and set the whole thing off. What still gets me is how fast it happened, and that I wasn't initially aware of what was happening because the fire wasn't emitting enough light to make it through my protective goggles (auto darkening...).
Lots of lessons learned that day, all is well that ends well but I'd rather not repeat that.
They really softballed the chastising in this video. Dirty bench full of other objects, including a beaker of... something? If the aluminum had landed somewhere else we could have had a bunch of other stuff going on here.
Also if you're going to bother to have a partner in such a situation, they should be touching safety equipment while you're pouring. I bet these guys don't even know where the fire extinguisher is.
Yes, there is more wrong than right what that whole setup.
Casting on a bench top to begin with isn't the brightest idea, you place your mold in the center of a concrete floor and you cast with something long enough to keep you safe, and you wear heat resistant aprons instead of lab coats. They got off very light, fortunately. I hope that they also realize they're out of their depth in the education department, because by showing this stuff to others when it does work they are passing on a ton of bad practices.
The same goes for a lot of videos and articles about home made batteries. I think I spent more time and effort on safety while doing my battery build than I did on the actual building and I'm pretty sure that if I had not that I would have had a real problem.
But casting metal and welding are still far safer than working on large Lithium-Ion packs in my opinion.
Edit: found a Hackaday article that covers this in more detail
https://hackaday.com/2020/12/30/water-and-molten-aluminium-i...