STA POOL PLANT – ENTRAPMENT AND ENTANGLEMENT
Suction Entrapment And Hair
ommercial swimming pools, hydrotherapy pools, wading/paddling pools, interactive water features, whirl pools and spas all have one thing in common – a circulation system. This means that water must leave the pool and then re-enter at another point following filtering and disinfection. This in turn means water being pulled under suction from the pool. As we’ve seen in the news again recently, this can have serious repercussions on users if not properly risk assessed. We discuss the two main dangers here.
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SUCTION ENTRAPMENT Bottom drains in swimming pools should be at least 2 metres apart and also have all openings 8mm in width or diameter (larger slots / holes make it easier for finger entrapment). There should be sufficient open water area. If one drain becomes blocked then the other can still divert a proportion of flow to prevent a vacuum being formed. Ideally these bottom drains should have raised large centres or other purpose designed grilles to prevent a bather sealing the entire drain with their body, Circulation pumps can also have a pressure sensor enabling it to shut off before a vacuum is formed.
The bottom drain suction risk can be seriously increased if water levels drop below the skimmer / scum trough overflow system as both are considered suction lines – this is with a single bottom drain (a single suction line is a high risk system). If this occurs, and the surface draw off line is isolated to prevent air getting into the system, for example, then all suction water from the pool will be
Entanglement
Robbie Phillips and Richard Lamburn, STA’s Technical Pool Plant Team look at the dangers of suction entrapment and hair entanglement posed by some pool and spa drains
through the single bottom drain, increasing its suction and velocity. No pool should ever be run on bottom drain alone due to the danger of suction entrapment and / or possible hair entanglement on the bottom or side of the pool or spa tank. Flow meter testing to enable you to risk assess this danger comprehensively in your pool can be accomplished using specific technical equipment. There are also simple methods to see if a vacuum forms on any suction outlet line.
outlets where a vortex is formed, their hair may become entangled in the grilles / outlets. In a spa this danger is increased by the narrow suction pipe work often increasing velocity and also the design of the outlets which often moves in a circular motion (vortex) aiding entanglement. If a bather becomes trapped often the only way to free them is to cut the hair, what is surprising to note is that scissors do not work efficiently underwater, and often a knife is the only implement that will suffice. It has also been noted that any fitting with these design defects at a specific outlet fitting will potentially cause this entanglement – e.g. main circulating and / or booster pumps.
EXAMPLES OF POTENTIAL SOURCES OF SUCTION ENTRAPMENT • Incorrect operation • Incorrect fittings • Poor design of drain outlets and covers • Insufficient number of drains • Creation of one line suction to main or ancillary circulation pumps
Suction entrapment occurs when a swimmer, usually a small child, is trapped by the suction forces created by the water rushing out of the drain at the bottom of the pool (human flesh is unfortunately able to form a perfect seal!). In some cases swimmers have been trapped underwater until they drowned and in other cases they have suffered serious injuries to various parts of their bodies including the bowel.
HAIR ENTANGLEMENT In spas mainly, and, also pools, the danger of hair entanglement is very real. When bathers swim too close to bottom drains or suction outlets of incorrect design, or place their heads underwater in a spa too close to water
Flow meter testing to enable you to risk assess this danger comprehensively in your
pool can be accomplished using specific technical equipment. There are also simple methods to see if a vacuum forms on any suction outlet line”
www.swimmingpoolnews.co.uk
• All fittings made secure so they cannot be removed
• All one line suctions eliminated or valves locked to prevent the creation of one line suctions
• Velocities from outlets not adhering to recommended rates
• Broken grids – a potentially lethal problem.
It is therefore imperative that all involved in the design, manufacture and construction should work to produce a safe facility. It is essential that knowledgeable pool contractors and consultants are employed. The operator should also be fully trained and aware of the potential dangers, and continuously risk assess the operation of critical valves, line velocities and fittings etc.
STA 01922 645097
www.sta.co.uk
SPN December 2015 39
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