Many plumbers, firefighters, and steamfitters are aware of this phenomenon, which is called "water hammer". A several-ounce "slug" of water passing through a steam line at high velocity and striking a 90-degree elbow can instantly fracture a fitting that is otherwise capable of handling several times the normal static pressure. It can then be understood that a few hundred, or even a few thousand pounds of water "moving at the same velocity" inside a boiler shell can easily blow out a tube sheet, collapse a firebox, even toss the entire boiler a surprising distance through reaction as the water exits the boiler, like the recoil of a heavy cannon firing a ball.