Measurement of entrapment hazards caused by drainage … · Fluid dynamics 3 Pritchard, P. J., Fox,...
Transcript of Measurement of entrapment hazards caused by drainage … · Fluid dynamics 3 Pritchard, P. J., Fox,...
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.
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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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Flow in pipes is subjected to frictional effects
• Major pressure loss
∆𝑃 = 𝑓𝐿
𝐷
𝜌𝑉2
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• Minor pressure loss
∆𝑃 = 𝐾𝜌𝑉2
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Fluid dynamics
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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.
Example:
Modeling suction entrapment risk
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Example:
Modeling suction entrapment risk
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Example:
Modeling suction entrapment risk
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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
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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 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
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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
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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!
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Discussion
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