Life-threatening suction entrapment events have been recorded in swimming pools and spas since before World War II, although formal documentation and investigation did not occur until the Consumer Product Safety Commission began maintaining National Electronic Incident Surveillance System data. Of 147 incidents documented between 1985 and 2002, 36 incidents, 1 in 4, were fatal. Suction entrapment occurs in wading pools, spas, or swimming pools when a person’s body blocks the flow of water from a pool or spa to the circulation pump. When the source of suction to the pump is blocked, the pump continues to operate creating a strong suction on whatever is blocking the water flow. The dual-main-drain-suction-entrapment tests were developed to determine the effectiveness of dual main drains as a means of avoiding suction-entrapment accidents.