I’m sure as long as you had a fire extinguisher nearby you’d be fine man.I hold admiration and disbelief in equal measure for the person who filmed that.
Yes, it’s flowing slowly and at a constant rate, but if it were to break, they’d be caught out.
Imagine the difference between cold oil and hot oil in a pan tilted to a gradient.
That flow Is slow as it’s cooling. Very easy for a hotter more viscous flow to break the head wall.