So far as I know, this is a true story. My friend tells very good stories, and has had enough odd things happen in his life that I believe this one. A labratory tub full of bromine, in itself, would release toxic amounts of bromine gas. Maybe it was done under a fume hood. However a fume hood would have been no use when the explosion blew all that bromine into the room.
Elemental bromine combines with water to form hydrobromic acid.
The gas would combine with the water in eyes, nose, mouth, and lungs to cause an extremly painful death for everyone present. I as a poison. Potasium liquifies just a little above body temprature and, on a humid day, will generate enough heat to become totaly liquid. The exploding potasium would have spread droplets of liquid potasium over a fairly large area. Potasium is so reactive that it is normally stored in oil to prevent reaction with humidity and oxygen.