A refrigeration system was being installed in a new wing of an ice cream plant in 1984. A leak test was being performed by employee #1 on a “low-pressure tank” which was filled with a mixture of ammonia and air under a pressure of 150 psi. As he squirted a soap bubble solution onto a butterfly valve, the valve suddenly popped completely open. The force of the outrushing NH3/Air gases slammed employee #1 against the back of the elevated basket in which he was working. He consequently fell approximately 15 feet onto a concrete floor, suffering a broken arm, broken leg, and other injuries. The other 6 hospitalized employees suffered burning sensations in the respiratory tract due to inhalation of ammonia. The workers were performing electrical work & other duties in the same section of the building.