When an explosion happens in an enclosed space, water hammer can cause the walls of the container to deform. However, it can also impart momentum to the enclosure if it is free to move. An underwater explosion in the SL-1 reactor vessel caused the water to accelerate upwards through 2.5 feet (0.76 m) of air before it struck the vessel head at 160 feet per second (49 m/s) with a pressure of 10,000 pounds per square inch (69,000 kPa). This pressure wave caused the 26,000 pounds (12,000 kg) steel vessel to jump 9 feet 1 inch (2.77 m) into the air before it dropped into its prior location.