Safety Considerations for Pool Owners
The Blue Cap Foundation conducted scientific research in collaboration with the University of Twente to determine the causes of high suction forces of drains in swimming pools. High suction forces are the result of a negative gauge pressure (vacuum), which can built up if one or more suction inlets of a drainage system are being blocked. A swimmer which intentionally or unintentionally blocks a drain cover with bodyparts can be exposed to hundreds up to thousands of newtons of suction force. For comparison, 1000 newtons of force is approximately equal to 100 kilograms of weight. The magnitude of the suction force depends on the magnitude of the negative pressure, which builts up underneath a blocked drain cover, and the size of this drain cover.
Besides accidents in which the victim gets sucked onto a drain cover, a large number of accidents occurs in which the victim is trapped under water with long hair that is entangled on or behind a drain cover. The rate at which water is drawn in by a drain cover plays a crucial role in this type of accident. The probability that long hair is sucked into a drain cover, and becomes entangled behind it, is much larger at high water velocities.
How to recognize a potentially unsafe water drainage system and / or drain cover?
- There is no risk of entrapment by suction when water is only removed from the swimming pools by overflow gutters and skimmers. However, swimmers can become trapped when their long hair gets stuck inside a skimmer. If you doubt the safety of skimmers, you can perform a hair entrapment test according to European Standard EN 13451 part 3.
- Does your pool have multiple suction inlets with drain covers, which are located entirely below the water surface, then there is often a risk of entrapment by suction of body(parts) or long hair present. There is no risk of entrapment present when water is drained by inlets located at a place that is inaccessible to swimmers. E.g. suction inlets that are placed in a buffertank, behind a protective wall or underneath an adjustable poolfloor. Do the swimmers have access to the suction inlets in the swimming pool, then the number of inlets connected to a water circulation system determines the size of the risk of entrapment by suction and the risk of hair entrapment.
- A pool from which water is drained by a single suction inlet is in all cases very unsafe. A high negative gauge pressure (vacuum) will built up within a few seconds when such an inlet is partly or completely blocked by a swimmer. Pressure measurements conducted in scientific research have shown that the suction force in such cases can exceed 4000 newtons (400kg) easily. A swimmer will have no chance on surviving such an accident and apart from the risk of drowning severe injuries or organ failure can occur within seconds after blocking the inlet.
- When multiple suction inlets have been connected in one circulation system, it is of great importance that the dimensions of the pipes, the layout of the pipe system, the distance between the different suction inlets and the distance to the pump have been well calculated and implemented. In general, the risks of entrapment by suction decreases with each additionally added suction inlet to the pumps . However, not all risks can be completely eliminated. Multiple incidents have been reported in which multiple children became trapped by suction simultaneously, because they blocked multiple suction inlets with their bodies as a game.
- Although it is often not permitted by laws and regulations, it still occurs that water for playground equipment or water slides is taken from the accessible swimming pools. Then there is often a high risk of entrapment due to high suction forces on the inlets and drain covers.
- Research of the Blue Cap Foundation in collaboration with the University of Twente has shown that at a higher water velocity through an drain cover the risk of entanglement of long hair increases. Also research from Germany confirmed this assumption. The shape and the pattern of holes and appertures in a drain cover have only little influence on the risk of entrapment of long hair. Typically, the flow rate through a drain cover is often too high if the flow close to the surface of a drain cover is tangible by touch.
Certainty about entrapment risks
Do you want certainty about the presence of the risks of entrapment by suction of body(parts) and long hair on the inlets in your swimming pool? We recommend you to measure the risks. A major problem in the pool industry is that measuring equipment is hardly used during safety inspections. Safety assessments of inlets that are based on visual inspections are insufficient as entrapment risks cannot be determined with certainty this way. Certainty about the risks of entrapment can only be given when the negative gauge pressure behind a blocked inlet is measured and when hair tests are conducted on the drain covers. Read more about the measurement of risks, how you can build your own pressure measurement equipment, rent or purchase it, or how you can have the inlets and drain covers in your pool checked by our safety expert.
Laws and regulations
Article 22 of the Dutch law on hygiene and safety of bathing environments and swimming sites (WHVBZ) requires each inlet below the water surface to be applied in such way that swimmers can not become trapped. Read more about the current legislation. To achieve this goal, a number of guidelines are applied that can be found in European Standards:
- EN 15288 Swimming pools - Part 1 “Safety requirements for design”
- EN 1069 “Waterslides”
- EN 13451 Swimming pool equipment — Part 1: “General safety requirements and test methods”
- EN 13451 Swimming pool equipment — Part 3: “Additional specific safety requirements and test methods for inlets and outlets and water/air based water leisure features”
- EN 13451 Swimming pool equipment — Part 11: “Additional specific safety requirements and test methods for moveable pool floors and moveable bulkheads”
The current WHVBZ is outdated and in the course of 2015 additional safety guidelines will be added. The Blue Cap Foundation has given advise and submitted a concept for these guidelines to increase the technical safety in swimming pools and to minimalize the risks of entrapment of suction inlets and drain covers.