Drowning and Safety Measurement of entrapment hazards caused by drainage systems in swimming pools ir. Joost Avezaat, The Blue Cap Foundation, The Netherlands.
Contents • The Blue Cap Foundation • Hazard potential of drainage intakes • Modeling suction entrapment risk • Measurement of entrapment risk • Experimental research • Suction force as a guideline parameter • Conclusion and discussion
The Blue Cap Foundation • Founded in 2010 by the grandfather of a suction entrapment victim that died in an Italian hotel pool. • Non-profit knowledge and research institute. 1
Hazard potential of drainage intakes Risk of drowning • Entrapment by suction and entanglement of hair on the grille covering submerged drainage intakes. Risk of severe injuries (vacuum) • Effusion of blood (hemorrhage) • Disembowelment • Failure of vital organs 2
Fluid dynamics Flow in pipes is subjected to frictional effects • Major pressure loss 𝜍𝑊 2 𝑀 ∆𝑄 = 𝑔 2 𝐸 • Minor pressure loss 𝜍𝑊 2 ∆𝑄 = 𝐿 2 Pritchard, P. J., Fox, R. W., McDonald, A. T. (2011). Fox and McDonald's introduction to fluid mechanics. Çengel, Y. A., Cimbala, J. M. (2010). Fluid mechanics: fundamentals and applications. 3
Modeling suction entrapment risk Example: 4
Modeling suction entrapment risk Example: 4
Modeling suction entrapment risk Example: 4
Modeling suction entrapment risk Example: 2 ∆𝑄 𝐶𝐵 = 𝑔 𝑀 2 𝜍 𝑅 𝐶 + 𝑅 𝐷 1 𝑄 𝑒𝑠𝑏𝑗𝑜 = 𝑄 𝐵 = 𝑄 𝐶 − ∆𝑄 𝐶𝐵 𝐸 𝐵 𝑄 𝐶 = 𝑄 𝑏𝑢𝑛 + 𝜍𝑖 + 1 𝐵 = 𝜌 2 4 𝐸 2 2 𝜍𝑊 𝐶 5
Modeling suction entrapment risk A swimmer that blocks an intake can be exposed to a large negative gauge pressure (vacuum). • Negative gauge pressure can be predicted with analytical and computational models. • Magnitude largely depends on the length - diameter ratio of pipes used and the flow velocity through these pipes. • High risks of suction entrapment can be reduced with the design of the piping system. • The use of multiple drainage intakes in a drainage system does not exclude that suction entrapment can occur. • Though, it is often assumed that the use of multiple drainage intakes provides sufficient protection against suction entrapment. EN 13451-3+A1 (2013). 6
Modeling suction entrapment risk • Problems arise when modeling risk in existing pools. • The water circulation system is often encased in concrete, making it difficult to model and predict the negative gauge pressure. 7
Measurement of suction entrapment risk • A solution was found in the measurement of entrapment risk. • Measurement of the negative gauge pressure during suction entrapment simulation. 8
Measurement of suction entrapment risk • A solution was found in the measurement of entrapment risk. • Measurement of the negative gauge pressure during suction entrapment simulation. 8
Experimental research • Testpool built for master thesis at University of Twente. • Research the influence of system properties on entrapment risk. • To test various safety measures and technical solutions. 9
Experimental research • Testpool built for master thesis at University of Twente. • Research the influence of system properties on entrapment risk. • To test various safety measures and technical solutions. 9
Experimental research • Blocking 1 of 1 drainage intakes (at initial Q = 35.6 m 3 /h) 10
Experimental research Blocking 1 of 4 drainage intakes Volume flow rate Min. gauge pressure Max. gauge pressure Q system (m 3 /h) P G (kPa) P G (kPa) 28.3 (1 pump) 0.51 1.01 43.0 (1 pump) -0.34 -2.35 86.4 (1 pump) -19.95 -23.86 108.4 (2 pumps) -24.89 -29.68 11
Suction force as a guideline parameter • Measurement of gauge pressure P G (Pa) • Calculation of hydrostatic pressure P H (Pa) Increases with 9.8 kPa for each metre in depth • Surface area of the grille covering a drain (m 2 ) • F SUCTION = (P H – P G )∙A • Example: Square grille (25 cm x 25 cm) Depth of 1 metre P G = -20 kPa. F SUCTION = 1.86 kN ≈ 190 kg of weight 12
Conclusion • Current safety assessments rely on visual inspections. • Protection against entrapment risks can only be guaranteed with on-site measurements. 1. Negative gauge pressure and suction force. 2. Hair entrapment test (conform EN 13451-3). 3. Flow velocity through grille covering an intake. ( ≈ 0.3 m/s, at least < 0.5 m/s) 13
Conclusion Obstruction test for floor outlets suction grilles (EN 13451-3). • Dimensions are based on a 8-year-old child. • Is protection against entrapment age related? 14
Conclusion Responsibility of pool owners, operators, travel agencies: • Plan: Assessment of entrapment risks. • Do: Measure risks. • Check: Evaluate the results of your assessment. • Act: If necessary, implement safety measures. Unblockable grilles. Pressure-activated shut-off. Aeration and ventilation of negative gauge pressures. Reduce flow velocities. Add intakes or place them in inaccessible areas (behind barrier, buffer tank). • Start over to make sure that the implemented safety measures have effect, i.e. risks are minimized to an acceptable level! 15
Discussion 16
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