Drowning and Safety

Measurement of entrapment hazards caused by drainage systems in swimming pools ir. Joost Avezaat, The Blue Cap Foundation, The Netherlands.

• 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

Contents

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

Flow in pipes is subjected to frictional effects

• Major pressure loss

∆𝑃 = 𝑓𝐿

𝐷

𝜌𝑉2

2

• Minor pressure loss

∆𝑃 = 𝐾𝜌𝑉2

2

Fluid dynamics

3

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.

Example:

Modeling suction entrapment risk

4

Example:

Modeling suction entrapment risk

𝑃𝑑𝑟𝑎𝑖𝑛 = 𝑃𝐴 = 𝑃𝐵 − ∆𝑃𝐵𝐴

𝑃𝐵 = 𝑃𝑎𝑡𝑚 + 𝜌𝑔𝑕 +1

2𝜌𝑉𝐵

2

∆𝑃𝐵𝐴 = 𝑓𝐿

𝐷

1

2𝜌

𝑄𝐵 + 𝑄𝐶

𝐴

2

𝐴 =𝜋

4𝐷2

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

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 m3/h)

10

Experimental research

Blocking 1 of 4 drainage intakes

Volume flow rate Q system (m3/h)

Min. gauge pressure 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

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)

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Conclusion

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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?

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

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