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Drowning and Safety
Measurement of entrapment hazards caused by
drainage systems in swimming pools
ir. Joost Avezaat, The Blue Cap Foundation, The Netherlands.
Contents
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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.
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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
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Fluid dynamics
Flow in pipes is subjected to frictional effects
• Major pressure loss
∆𝑃 =
𝐿 𝜌𝑉 2
𝑓
𝐷 2
• Minor pressure loss
∆𝑃 =
𝜌𝑉 2
𝐾
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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.
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Modeling suction entrapment risk
Example:
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Modeling suction entrapment risk
Example:
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Modeling suction entrapment risk
Example:
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Modeling suction entrapment risk
Example:
𝐿 1 𝑄𝐵 + 𝑄𝐶
=𝑓
𝜌
𝐷2
𝐴
𝑃𝑑𝑟𝑎𝑖𝑛 = 𝑃𝐴 = 𝑃𝐵 − ∆𝑃𝐵𝐴
∆𝑃𝐵𝐴
1
𝑃𝐵 = 𝑃𝑎𝑡𝑚 + 𝜌𝑔𝑕 + 𝜌𝑉𝐵 2
2
𝜋 2
𝐴= 𝐷
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2
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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).
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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.
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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.
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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.
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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.
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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.
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Experimental research
• Blocking 1 of 1 drainage intakes (at initial Q = 35.6 m3/h)
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Experimental research
Blocking 1 of 4 drainage intakes
Volume flow rate Min. gauge pressure
Q system (m3/h) PG (kPa)
Max. gauge pressure
PG (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
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Suction force as a guideline parameter
• Measurement of gauge pressure PG (Pa)
• Calculation of hydrostatic pressure PH (Pa)
 Increases with 9.8 kPa for each metre in depth
• Surface area of the grille covering a drain (m2)
• FSUCTION = (PH – PG)∙A
• Example:
Square grille (25 cm x 25 cm)
Depth of 1 metre
PG = -20 kPa.
FSUCTION = 1.86 kN
≈ 190 kg of weight
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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)
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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?
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Conclusion
Responsibility of pool owners, operators, travel agencies:
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Plan: Assessment of entrapment risks.
Do: Measure risks.
Check: Evaluate the results of your assessment.
Act: If necessary, implement safety measures.
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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!
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Discussion
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