Pool Safety - Entrapment
Understand the risks of entrapment. Entrapment is the risk of being pulled/sucked onto the suction fittings of a pool pump. These fittings include, but are not limited to skimmers, main drains, wall suction lines and Spa suction drains. The result of entrapment can lead to drowning and/or evisceration (disembowelment).
The risk here is when the suction velocity is high, it will draw hair, loose bathing suits and body parts towards them and "entrap" the swimmer onto them with suction power. The key to making a pool safe is to keep velocity down. Velocity at any particular pool suction fitting is dependent upon how many other suction fittings are hooked up in that plumbing system and how powerful the pump is. In the past we generally did not hear about this as much because pools were simpler.
Traditionally, a pool had one or two skimmers and a main drain. This gave the pump (which was older and not as powerful) 2 or 3 separate places to pull water from. By having several suction fittings, the overall velocity at any one of them is not excessive. In a situation where a swimmer came close to a fitting, they most likely would not be drawn to it. In addition if they did get pulled onto the fitting they would most likely be able to pull away easily because the pump will be able to draw water from the other suction fitting(s).
Today, most pools still have a single main drain and one or two skimmers. However, current pumps are much stronger than the pumps of thirty years ago and older pools have been updated to modern, more powerful pumps. These powerful pumps are great for circulation but increase velocity at all suction fittings. Most of the time these pool systems will operate safely, however on a day with leaves and debris falling into the pool, the skimmer(s) may become clogged. When this happens, the pump will draw the majority of its water from the main drain, creating high velocity near the main drain. In a system with only one main drain, this will create a dangerously high velocity at that main drain. For this reason, dual main drains are a very good idea, and required on new pools.
In 2007, we replaced approximately 140 main drain covers with Ansi certified covers. We tested these single drains with a doll (hair approximately 14" long) and found the hair was drawn very moderately if at all towards the main drain. In all cases the doll could be pulled off the main drain. This test was conducted with clean skimmers and fully opened valves (normal operation). If however the skimmer valves were closed, the doll is sucked and held onto the main drain and required force to be pulled away.
Today, many pools have spas, waterfalls and high-powered pump(s). All of these water features require a large amount of water to be pulled from somewhere. These are generally our greatest risk areas. By current Code, all pumps need at least two places to draw water a minimum of 3 feet apart, and be covered by an approved drain cover. This code was only adopted in New York State in December of 2007 and most of the rest of the country in December 2006. As a result MOST pools and spas do not have this type of suction. Many spas have only 1 suction fitting with the risk being potentially magnified by having 2 or more pumps drawing from it during spa operation.
Ecopool feels that all spas that do not meet current code should be upgraded to do so or minimally install a Stingl switch or Vac Alert to sense and stop entrapment once it has happened. Ecopool also recommends that any pool undergoing a renovation, re-plastering or new liner installation have drains installed to meet current codes and keep people safe.
Kiddie pools are another area where entrapment is an issue due to the shallow nature and the necessity to turn water over rapidly (high volume circulation requirements). Floor drains can be pulling strongly and are within reach/touch of children. They should all be updated well beyond code. Ecopool recommends that a minimum of four drains be plumbed together by oversized plumbing. It is a good idea to know where the emergency shut off button is at commercial pools, and it is required by law to have one.
