I didn't finish the whole vid - but, at about 3 min or so, the hose appeared to have broken off and the stream was comming from the valve . . . .
The white cloud is mostly vapor not ammonimum liquid.  Rain or fire dept water would help keep the cloud contained somewhat . . .
What is surpriseding is someone with proper safety equipment and holding their breath, didn't walk in there and shut the valve ? Especially after the hose broke off and liquid was shooting streight out the front.
Proper safety equipment would be googles, face sheild, long sleaaved shirt/jacket and rubber gloves that covered past the cuffs. As long as all skin is covered, keeping any liquid off the skin, would have allowed the person safety.
Now, I haven't worked with NH3 for 25yrs or more . . . I wouldn't attempt to shut it off with that hose wrangleing about like it was . . . .
As a CAUTION - If you are not comfortable or experenced working around NH3 - do as the guy recording - stand back and watch / record.
As posted above, water does help lock down the vapor and liquid.
A tank tipped over in my FIL lawn - broke open the valve . . . Firedept wouldn't touch it. Co-op guy put on safety gear, held his breath and walked in and shut the valve off. Problem solved.