Ammonia is nasty stuff. Last job I was at, cool storage of seafood we had regular training and trial evacuations for ammonia leaks.
Doesn't take much to kill you and even less to fak you up for a long time.
It forms a cloud when it leaks from refrigeration plant and sits near the ground... So it the opposite to a fire emergency. You don't drop to the ground. You get the hell out, raise alarm and get up wind (If there is any).
It's amazing how much it expands on contact with air. Dangerous stuff.