Abstract: Seven employees were conducting developmental tests on a compressor (at 290 psig) to ensure that it would operate under specific conditions. The compressor's two lines fed into a calorimeter which measured the capacity of the compressor. When the compressor was shut down, the pressure atmosphere of about 290 psi remained within. Approximately two minutes after shutdown, six 3/16 in. diameter bolts broke. The face plate of the motor housing broke away from the motor housing, resulting in the pump separating from the motor. The pump, while still connected to the hose attached to the calorimeter, became a projectile. While airborne, the pump struck Employee #1 in the head; he sustained a massive contusion to the head. The pump continued to flop around and struck the calorimeter five times while pressure escaped from it. While the pump was airborne, the rotor inside the pump ejected with a number of its laminated discs. The laminated discs were projected through the air and struck the walls and ceiling duct in a number of places. No other employees were injured. The employer had not developed a general policy or specific work procedures for conducting developmental tests on apparatus such as the compressor. The test was being conducted in an engineering test lab without a test chamber or containment system to separate the employees from the apparatus being tested.