As well as leaving the pool via the surface water draw-off system, water is also leaving via the sumps (drains). In a traditional swimming pool, these outlets are usually located on the floor of the deep end and are covered with a grill.
If pool drains are blocked, whatever is causing the blockage will be exposed to the suction force of the circulation pumping system.
Therefore, removing the blockage without turning off the circulation pump(s) will be impossible.
Suppose the blockage is in the form of a person. In that case, tragic consequences can occur, including drowning and/or disembowelment.
There are various ways that suction entrapment rik can be reduced:
Once the above design-based precautions have been considered, other precautions can be implemented such as providing training for all relevant staff regarding the dangers of suction entrapment.
See below for some examples of what would have to be considered highly dangerous outlets:
Entanglement hazards are slightly different from entrapment hazards. They involve hair being drawn into the outlet and then entwining on the other side due to the circular motion of the water as it goes through the outlet.
Freeing the hair from the outlet may be impossible, even if the circulation pumps are turned off.
People using spa pools are at an increased risk of suction entanglement because they will be close to an outlet no matter where they are situated within the spa pool.
For this reason, people using spa pools should be advised to tie long hair back and refrain from submerging their head under the water.
Staff responsible for supervising the spa pool should be trained to be aware of the hazards associated with outlets.
Now would be a good time to make notes about any risk factors you may be aware of with the pool outlets at your own facility.
Things to consider…
The PWTAG Code of Practice has a procedure for conducting a test to ensure that there is minimal risk of hair becoming entangled in a swimming pools outlet drain. It can be downloaded here. The procedure is at Annex D, towards the end of the document.