measurement of entrapment hazards caused by drainage ......• protection against entrapment risks...
TRANSCRIPT
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
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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.
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.
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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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