Water circulation, entrapments in pools

There are five different types of entrapment:
– Hair entrapment is the most common and most deadly. It occurs when long hair passes through a suction outlet cover and then entangles beyond the cover, locking the head to the cover. High water velocity and long hair length increase the possibility that entanglement and entrapment might occur.
– Limp entrapment occurs when the cover is missing or broken and a limb (leg, arm, knuckle, finger or toe) is held within the plumbing due to the suction. Limp entrapment can also occur when a limb becomes physically stuck.
– Body entrapment occurs when the body is held against a suction outlet and forms a seal.
– Evisceration/disembowelment occurs when buttocks seal a suction outlet causing the rectum to burst and viscera to be withdrawn from the body.
– Mechanical entrapment occurs when something attached to the bather (necklace, bathing suit, etc) tangles with a structure below the water.
A system can be designed and operated to reduce or eliminate the possibility that direct suction can entrap and injure a person.
The first line of defense involves ensuring that a drain cover is in place over any suction outlet to prevent entrapment or hair entanglement. Manufacturers often sell screws that are different colours to make them more obvious when the pool or spa is being inspected.
Next, anti-entrapment drain covers can be used. These covers should be installed so that the maximum flow rating is not exceeded. The anti-entrapment is designed to keep the torso and arms from blocking the cover.
In addition, they prevent hair from entangling around the cover. Dual main drains which are covered with an anti-entrapment when plumbed and spaced at a sufficient distance apart to ensure that an individual can not block both drains.
Some systems remove direct suction outlets from the pool or spa by using a gutter system or a surge tank. In these systems, water leaves the pool by atmospheric pressure and flows to a collection pit or balance tank.
The water in the collection or balance tank is then drawn up by the pump’s suction. The pump creates pressure, forcing water through the piping, the other system components and back to the pool.
Main Drains
Main drains are located at the deepest part of the pool. A controlled amount of water is drawn through the main drain to allow development of water circulation patterns in the pool.
Water flow patterns are determined by the return outlet placements and control. These patterns eliminate the presence of “dead spots” or areas of poor circulation. Dead spots can support algae growth and collect dirt and debris.
Main drains are sized during the pool design phase by the engineer or architect. There should be no changes made to size, design, location or operation of the main drain in later years. Dangerous conditions could result with the possibility of serious trauma or even death to a bather.
The openings in the main drain covers are part of the original design and are controlled by standards. The main drain should be visually observed on a daily basis as part of the vacuuming process and any crack or broken element is cause for pool closure until the cover is replaced. A bather’s finger could become entrapped in the defect.
There should be a method of controlling the amount of water exiting the pool from the main drain. It is important to maximise the flow from the surface, which has the greatest concentration of pollutants and floating debris.
It is important to minimise the flow through the main drain for entrapment considerations.
The flow velocity through the main drain must not exceed the maximum flow for the main drain cover.
ENJOY YOUR POOL THIS SUMMER!!!!