Pool Plant Courses - Blog

Swimming pool operators ought to be aware that it is possible to create highly toxic gaseous chemical substances if something goes wrong in the plant room. For example: mixing calcium hypochlorite (an alkaline substance that contains chlorine) with an acidic substance (like sodium bisulphate - which is commonly referred to as dry 'dry acid') will result in a reaction that will produce chlorine gas.

The above scenario may happen because an operator inadvertently introduces a chemical into the incorrect day tank. This has actually happened in numerous swimming pools in the UK. Procedures need to be in place to prevent this type of scenario. Staff training, selection, use and storage of chemicals, layout of the plant room and labelling of tanks and chemical feed lines are some examples of areas to scrutinise.

Another, perhaps less obvious thing to consider is the circulation system. Specifically - the hazards and risks that can be introduced when the circulation system stops (whether this be on purpose, or because of a system failure). When the circulation of the pool water stops, what should also happen is that the automatic dosing of all chemicals into the circulation pipework should also stop. This would usually be achieved by a electrical switch that is interlocked with the water flow sensor. If its working properly, this safety feature should work when need to stop the dosing of chemicals as soon as the main pool water circulation stops.

If the chemical doing does not stop, and chemicals continue to be injected into the circulation pipework while the water in that pipework is stagnant, there is the possibility that hazardous gases can be created as a product of chemical reactions. These gases could contain high levels of aggressive chloramines (chlorine + ammonia), or even worse, chlorine gas (as a result of the chlorine disinfectant coming into contact with the acidic pH correctant).

In order to minimise these risks, careful consideration should be given to the appropriate placement of chemical injection points (the further apart incompatible chemicals are injected, the better). There also needs to be a procedure in place to cover restarting the circulation system back up again after a stoppage. Pools should be clear of bathers (including the pool hall and changing rooms) when the circulation system is restarted. This is because if there were chemicals dosed into the system while circulation was halted (auto-shut-down systems can never be regarded as 100% reliable), and hazardous gases have been created in the pipework - the gasses will be introduced into the pool area when the circulation is started back up, potentially gassing anyone exposed.

Pool operators are urged to ensure that this issue is given due consideration by way of a suitable and sufficient risk assessment.