Water hammer plays a critical role on suction entrapment accidents. When water is suddenly stopped, the energy of motion is released and it can instantly vaporize water as is seen here. Once that occurs, waves move along the length of the pipe and can cause this repeated trapping force. SVRS and other vacuum release technology has 3-4 seconds to react. As can be seen in this video, in those 3-4 seconds an arm, or intestines, can be completely engulfed by the pipe. It takes only .25 seconds, the time to blink and eye, for your arm to be in the pipe up to your elbow or to have eviscerated (disemboweled) a small child. With limb entrapment, one often needs to have the pipe surgically removed - if they survive.