Swimming pools and fountains
In systems such as swimming pools or fountains where waste fluid is recirculated, the drain is the input to the Recirculating Pumping machine. These fixtures can be very dangerous because people do not expect to encounter more than the head pressure of water above the drain when contacting a drain. When there is a recirculating pump, the force of suction consists of the head of water, plus the suction of the pump (up to a maximum of 1 atmosphere).
Fatalities have occurred around drains as a result of suction entrapment (also known as pool suction-drain injury). In these situations, a portion of the body, hair, or clothing may become stuck against the drain and may become impossible to release, resulting in drowning. For example, in 1994, Cristin Fitzpatrick drowned in a Variety Village swimming pool when her hair became entangled in a water funnel.[2]
Properly designed drains in swimming pools and spas mitigate this hazard by either adding multiple drains, or increasing the surface area of the drain opening with the use of many holes or safety covers. Since drain suction increases rapidly when a portion of the drain flow is blocked, having two drains or a larger drain inlet allows alternative suction paths for the inflow. Also, swimming pool safety devices are available to automatically turn off an operating pump if a rapid increase in suction is detected, as could happen during a suction entrapment incident.
While fear of the drain may be counterproductive, children should be taught not to intentionally touch or attempt to block components of a swimming pool recirculation system.[according to whom?]
Since children often play in public fountains, the use of multiple drains is a mandatory safety feature, regardless of whether or not the architect or planner intends that the fountain be used as an aquatic play feature. This is to ensure minimal risk of plumbing entrapment, but vandals can sometimes break into drains in the night time and remove the covers (commonly known as "drain mugging"), leaving them in a hazardous condition.