Top 10 Seawater Swimming Pools in Europe

September 5, 2016
The natural volcano swimming pool at Porto Moniz, Madeira.

We usually focus on indoor swimming pools on this blog, but a recent article by the Guardian provides an opportunity to take a look at some of the best seawater pools in Europe. No chlorine, pH correction, dilution, circulation, filtration, coagulation or heating required.

Bather Loads, Pollution, Turnover...It's All Relative.

August 26, 2016
Swimming Pool Pollutionl

Relative Pollution
A pool that is 25 metres long, 12 metres wide, with an average depth of 1.5 metres will hold 450 cubic metres of water. If there are, say, 30 people in the pool, each of them will have 15 cubic metres of water each.
Contrast this situation with a spa pool. A spa will only hold about 3 - 10 cubic metres of water, depending on the type. Let's say we have a spa pool that holds 5 cubic metres and has 10 people in it. Each person now has only half of one cubic metre of water each.

Even though there are more people in the swimming pool (and therefore more total pollution), the relative pollution is higher in the spa due to the fact that as a percentage of volume, the pollution levels are higher. The spa is said to have higher relative pollution levels. Spa pools are not the only types of pool that suffer from high relative pollution. Any pool that has an unfavourable pollution to water ratio will also have high relative pollution. Examples are:

•    paddling pools
•    splash zones
•    teaching pools
•    hydrotherapy pools  

Bather Load and Turnover Period
The more bathers in a body water (bather load), the more pollution will be introduced (all other factors being equal) and the more important it will be to get rid of the dirty water and introduce fresh water quickly. This is achieved via circulation of the water and the time it takes to move water around the system is an important factor in maintaining good water quality. The quality of the pool water will deteriorate the longer it takes to circulate the water around the system. 

Bather Load
It is important that pool operators do not over load a pool with bathers. It makes it difficult for lifeguards to spot people in trouble and it also has a negative impact in the quality of the pool water. 
Pool operators need to establish two different types of bather load:

1.    Instantaneous bather load
2.    Total daily bather load

In order to calculate the instantaneous bather load, the following formulae should be used:
•    For water that is under 1.0m deep, each swimmer should have 2.2m2 of surface area each
•    For water that is 1.0 – 1.5m deep, each swimmer should have 2.7m2 of surface area each
•    For water that is over 1.5m deep, each swimmer should have 4m2 of surface area each

As an example, for a swimming pool that is:

•    20m long;
•    12m wide;
•    with a deep end that is 2.0m deep and ;
•    a shallow end that is 1.0m deep…

…the bather load would be calculated as follows:

•    Shallow End: 10m x 12m / 2.2m = 55 bathers
•    Deep End: 10m x 12m / 4.0m = 30 bathers

The total instantaneous bather load for the whole pool would therefore be 85 bathers at any one time.

In order to calculate the total daily bather load the following formula should be used:

•    Instantaneous bather load x 25 – 50% x 12 

As an example for the same swimming pool as above:

•    85 x 25 – 50% x 12 = 255 - 510 bathers per day.

Pool operators should only go to the upper end of this range if they are confident that the pool plant system can handle it and maintain good water quality. If in doubt, the advice would be to stay in the bottom half of the range.

Turnover Period
In order to achieve the correct turnover period, the circulation pumps need to be pumping water around the system quickly enough. The rate at which the water is moving around the system is called the flow rate. A rough guide when designing and sizing swimming pool circulation systems is to multiply the instantaneous bathing load (referred to earlier) by 1.7 to give a target flow rate to aim for. Therefore, using the example from earlier, the target flow rate can be calculated as follows:

•    85 x 1.7 = 144.5 m3/hr

Pool operators should ensure that the pool water is being circulated quickly enough by establishing and documenting the turnover period, that is; the amount of time it takes to for a volume of water equal to the pool volume, to pass through the system. This is done by dividing the pool volume by the flow rate. The flow rate is simply the rate of flow of pool water through the system, usually expressed as cubic metres per hour (m3/hr). See the worked example below:

•    Pool Volume -    300m3
•    Flow Rate -    144.5 m3/hr
•    Turnover Period -    2 hours

Run a Swimming Pool? You Need a PSOP!

August 26, 2016
Pool Safety Operating Procedures

The swimming pool and associated plant and facilities (such as the changing rooms, showers, pumps, filters etc.) should be operated and managed according to a robust set of procedures that have been devised following a comprehensive and rigorous assessment of the hazards and risks that are present.  These procedure are referred to as the Pool Safety Operating Procedures (PSOP) and are comprised of two sections, the Normal Operating Procedures (NOP) and the Emergency Action Plans (EAP). These are discussed in more detail below.

Normal Operating Procedures
These procedures set out how the pool should operate under normal day-to-day conditions. The following types of information should be included:

•    Pool dimensions
•    Features and equipment (such as flumes etc.)
•    Rescue equipment
•    Location of pool alarms
•    Floor plan of pool and pool hall
•    Potential hazards
•    Access and restrictions
•    Bathing loads
•    Diving policy
•    Vulnerable swimmers
•    Lifeguarding procedures
•    Pool rules
•    Cleaning procedures
•    Hiring procedures
•    Accident reporting 

Emergency Action Plans
These set out the actions to be taken for the range of reasonably foreseeable emergency scenarios. Examples of those that should be included are included here and some are discussed in more detail below:

•    Fire
•    Gas escape
•    Chemical spill
•    Structural failure
•    Bomb threat
•    Power failure
•    Pool rescue 
•    Evacuation of disabled users
•    Overcrowding
•    Contamination of pool water
•    Disorderly behaviour
•    Sexual assault
•    Flooding

Fires and Explosions
The risk of fire and explosion in pool plant rooms is particularly high due to the chemical properties of the chemicals involved. A thorough and robust fire and explosion risk assessment must be carried out. Good prevention management strategies, including training of staff, correct storage of chemicals etc. will go a long way to reducing the risk. Emergency situations should be thought about in advance, and procedure for dealing with them should be practiced regularly. The fire service will need to be made aware of the chemicals that are stored on the premises, so it would be a good idea to prepare a file in advance to hand over to the fire service in the event of an emergency.

Chemical Incidents
The main ways chemicals can harm the body are via:

•    Contact with skin, eyes etc.
•    Ingestion
•    Inhalation

For contact with skin, it’s important to flush the affected area with water. Drench showers should be provided close to chemical storage areas for this purpose. If much of the body is affected, it may be better to carefully lower the casualty into the swimming pool and remove any contaminated clothing.
For contact with eyes, the chemical will need to be flushed out (whilst taking care to avoid the nose and risk inhalation). This should continue for at least 10 minutes. Eye wash stations should be provided close to chemical storage areas for this purpose.
For ingestion of chemicals, the casualty should sip water or milk to help dilute the chemicals. Vomiting should not be encouraged. If the casualty becomes unconscious, they should be placed into the recovery position and monitored, if they stop breathing, then artificial respiration should commence.
For inhalation of chemicals, the casualty should be evacuated to a safe environment with fresh air to purge the lungs. If the casualty becomes unconscious, they should be placed into the recovery position and monitored, if they stop breathing, then artificial respiration should commence. Equipment should be used, such as a resuscitation face mask, to prevent the person administering the breaths from inhaling the gas themselves.
In the above scenarios, kit’s likely that the casualty will need to go to hospital for further treatment. The medical staff will need to know more about the particular chemical that the casualty has been in contact with, so the relevant Material Safety Data Sheet (MSDS) must accompany the casualty to the hospital. 

For spillages of chemicals, the Pool Water Treatment Advisory Group (PWTAG) provide the following procedure:
In any emergency a quick but calm reaction is necessary. Personnel and the public must be protected. Only personnel that know the product and have been trained to handle spills should be allowed in the area. Appropriate protective equipment should be worn when dealing with a spill.
Whatever the cause, the approach to any spill is to:

•    follow the emergency action plan
•    protect the public
•    protect staff
•    contain the spill
•    stop the leak
•    clean up the spill
•    protect the environment

Large spillages
If the spillage is over 45 litres (10 gallons) immediately evacuate the area; remove sources of ignition; provide maximum ventilation. If the risk to people or environment is considerable, call the emergency services. Only personnel with proper respiratory and eye/skin protection should be permitted in the area.
Dam and absorb spillages with dry sand, soil or other inert material. Do not use combustible adsorbents such as sawdust. Then collect the absorbed material in containers, seal securely (with a vent) and deliver for disposal according to local regulations. Containers with collected absorbed material must be properly labelled with correct contents and hazard symbol.
Wash spillage site well with water and detergent; be aware of the potential for surfaces to become slippery. Continue to ventilate the site of the spillage.
Spillages or uncontrolled discharges into watercourse, drains or sewers must be notified immediately to the National Rivers Authority or other appropriate regulatory body.

Small spillages
If the spillage is under 45 litres, it can be diluted with large quantities of water and then if local regulations allow, run to drain with copious amounts of water. Otherwise, absorb and dispose of as above.
Leaks in the piping or discharge hose
Close the primary valve at the base of the storage tank. In leaks in piping or hoses, closing a valve between the leak and the source of the material (tank) will minimise the loss.
Leak in the bulk storage tank, or its primary valve
Empty the tank as quickly as possible into other suitable containers – which might be intermediate bulk containers (­IBCs). Call the supplier of the tank. Lowering the level of the product in the tank stops or reduces the amount leaking. Drum the material and return it to the supplier for recycling. Uncontaminated spillages may be able to be used in the pool.

Chemical or Microbiological Contamination Outbreaks
A chemical or microbiological outbreak has occurred if more than two people have symptoms from the same source at roughly the same time. Written procedure are needed for dealing with an outbreak and included as part of the EAP (Emergency Action Plan) section of the PSOP (Pool Safety Operating Procedures). Inadequacies in the management approach taken with regard to swimming pools and spas has been identified as a major causal factor in a number of outbreaks in the UK. Typical problems that have led to outbreaks are listed below:

•    Inadequate water disinfection
•    Sewage contamination
•    Inadequate filtration
•    Incorrect backwash procedures
•    Inadequate disinfection of pool surround and changing room floors
•    Sharing of towels
•    Hot and cold water system design faults
•    Inadequate cleaning of showerheads
•    Release of faecal matter and/or vomit into pool and/or surrounding area
•    Lack of pre-swim showering
•    Inadequate cleaning of pool inflatables

An outbreak might be detected by pool staff, or may be picked up by local or national surveillance and reporting systems, such as those managed by Environmental Health Departments or the Health Protection Agency (HPA).
An Outbreak Control Team (OCT) is typically established by the HPA in the event of an outbreak, which is headed up by a Consultant in Communicable Disease Control (CCDC). The OCT will seek to establish the source of the outbreak and identify direct and root causes. This might well involve site visits by members of the OCT and the collection of samples of water for testing, inspection of the pool plant system, close scrutiny of documentation, and the interviewing of key staff.

Faecal Contamination
This is a difficult area, both for pool operators and for those attempting definitive guidelines. And there is potentially a lot at stake, as diarrhoea may contain the chlorine-resistant pathogen Cryptosporidium – a significant cause of gastroenteritis, particularly in pools.
If faecal contamination has only been reported, and there is some doubt about the accuracy of the report, its presence should be confirmed by pool staff. If it cannot be confirmed, pool operators should assess the risk and may decide that the risk of harmful contamination is low and allow bathing to resume. This assumes that pH and disinfection are within normal limits.

Solid faeces: the stools should immediately be removed from the pool using a scoop or fine mesh net and flushed down the toilet (not put in any pool drains). If there is any doubt that all the faeces have been captured and disposed of, and there is possible widespread distribution of the faeces in the pool, then the pool should be closed and the advice below for runny faeces followed.

Depending on the extent of the contamination, how public it has been, and how quickly it can be dealt with, operators should consider clearing the pool of bathers for, say, 30 minutes while the cleaning operation described above is taking place. Bathing should not resume until all the faeces have been removed.

All equipment that has been used in this process should be disinfected using a 1% solution of hypochlorite (1:10 dilution of commercially available sodium hypochlorite).

If the pool is operating properly with appropriate disinfectant residuals and pH values, no further action is necessary.
Runny faeces: watery, runny or soft stool (diarrhoea) is more likely to carry enteric pathogens, and be spread through the pool water. It will be impossible to remove like solid stool.

Operators are unlikely to know if Cryptosporidium is involved, so the safest option is to assume it is, close the pool and follow the procedures below.

There are in principle three procedures that will in time remove Crypto – coagulation/filtration, UV and super-chlorination. The procedures to be followed primarily depend on the efficiency of the pool’s filtration.

Pools with medium-rate filtration (up to 25 metres per hour)
This should include most public pools. Here, the main emphasis is on filtration, which if effective should remove some 99% of the Cryptosporidium oocysts in each pass of pool water through the filter.
Coagulation is critical in this: it should be continuous, and the residence time (that between the injection of coagulant and treated water reaching the filter) must be long enough for flocculation to happen – at least 10 seconds at a flow velocity no more than 1.5m/sec. 
Secondary disinfection (UV or ozone) and superchlorination are also relevant – see below.
How long it takes for all the pool water to pass through the filter will depend on two factors. First is the pool hydraulics – crucially, how well mixed the pool water is. Dead spots will delay the passage of all the pool water through the filters. The second factor is the turnover period – the length of time it takes for a volume of water equivalent to the pool water volume to go from pool to plant room and round to the pool again. It might take as long as 24 hours for all the pool water to pass through the filters – based on the 3 to 4-hour turnover period common to many pools.

1.    Close the pool – and any other pools whose water treatment is linked to the fouled pool. If people transfer to another pool, perhaps from a teaching pool to a main or leisure pool, they should shower first using soap and water.
2.    Hold the disinfectant residual at the top of its set range for the particular pool (eg 2.0mg/l free chlorine if the range is 1.0 to 2.0mg/l) and the pH value at the bottom of its range (eg pH 7.2-7.4). This will maintain the normal level of microbiological protection.
3.    Ensure that the coagulant dose is correct – for continually dosed PAC, 0.1ml/m3 of the total flow rate.
4.    Filter for six turnover cycles (which may mean closing the pool for a day). This assumes good hydraulics and well maintained filters with a bed depth of 800mm and 16/30 sand. This applies also to pools with secondary disinfection. 
5.    Monitor disinfection residuals throughout this period.
6.    Vacuum and sweep the pool. Cleaning equipment, including automatic cleaners, should be disinfected after use. This will at least move faecal contamination off surfaces and into the main pool water circulation, for eventual removal.
7.    Make sure the pool treatment plant is operating as it should (filters, circulation, and disinfection).
8.    After six turnovers, backwash the filters.
9.    Allow the filter media to settle by running water to drain for a few minutes before reconnecting the filter to the pool.
10.    Circulate the water for 8 hours. This will remove any remaining oocyst contamination of the pool and allow the filters to ripen. It is optional, depending on the pool operator’s confidence in backwashing procedures.
11.    Check disinfection levels and pH. If they are satisfactory re-open the pool.
12.    Any moveable floors and booms should be moved around from time to time during the whole process.

Pools with high-rate filtration (over 25 and up to 50 metres per hour)
High-rate filters do not filter Cryptosporidium oocysts, or anything else, as well as medium-rate filters. But because many pools have them, it is important to know how to deal with faecal contamination.
The main emphasis is on superchlorination. High-rate filters without coagulation remove as little as 10% of Cryptosporidium oocysts in each pass. Even with coagulation, and perhaps 50% removal, it could take two days to be safe. 

1.    Close the pool – and any other pools whose water treatment is linked to the fouled pool. If people transfer to another pool, they should shower first using soap and water.
2.    If coagulation is not the norm, a supply of polyelectrolyte coagulant should be available so it can be hand-dosed in these circumstances, following manufacturers’ instructions.
3.    Superchlorinate to 20mg/l adjusting the pH to 7.2-7.4 and leave for 13 hours (or 50mg/l for 5 hours). Procedures and supplies must be in place for this.
4.    Vacuum and sweep the pool.
5.    Make sure the pool treatment plant is operating as it should.
6.    Backwash the filters.
7.    Allow the filter media to settle by running to drain for a few minutes (rinse cycle) before reconnecting the filter to the pool.
8.    Reduce the free chlorine residual to normal by dilution with fresh water or using an approved chemical. This may mean using the chemical gradually; procedures and supplies must be in place for this. 
9.    When the disinfectant residual and pH are at normal levels for the pool, re-open.
10.    Superchlorination should remove any current contamination but will not guarantee future water quality. So it is important to review procedures for the control and removal of contamination by Cryptosporidia.

For further information on cryptosporidia outbreaks, refer to the Public Health Wales Publication: ‘Guidance for the investigation of Cryptosporidium linked to swimming pools’.

Blood Contamination
Pool disinfectants should kill any pathogenic microorganisms in blood or vomit, provided disinfectant residuals and pH values are within recommended ranges. But there are some precautions to take.

Small amounts of blood, from a nose bleed say, will be quickly dispersed and any pathogens present killed by the disinfectant in the water. If significant amounts of blood are spilled into the pool, it should be temporarily cleared of people, to allow the pollution to disperse and any infective particles to be neutralised by the residual disinfectant. Operators should confirm that disinfectant residuals and pH values are within the recommended ranges; bathing can then resume.

Any blood spillage on the poolside should not be washed into the pool or poolside drains and channels. Instead, like blood spillage anywhere in the building, it should be dealt with using strong disinfectant – of a concentration equivalent to 10,000mg/l of available chlorine. A 10:1 dilution of the sodium hypochlorite in use may be convenient. Using disposable gloves, the blood should be covered with paper towels, gently flooded with the disinfectant and left for at least two minutes before it is cleared away. On the poolside, the affected area can then be washed with pool water (and the washings disposed of – not in the pool). Elsewhere, the disinfected area should be washed with water and detergent and, if possible, left to dry. The bagged paper towels and gloves are classed as offensive/hygiene waste, which in only small quantities may be disposed of with the general waste.

Vomit Contamination
It is not unusual for swimmers to vomit slightly. It often results from swallowing too much water, or over-exertion, and so is very unlikely to present a threat through infection. But if the contents of the stomach are vomited into a pool, the bather may be suffering from a gastrointestinal infection. And if that is cryptosporidiosis, infective, chlorine-resistant Cryptosporidium oocysts will be present. This is a rather theoretical, unevaluated risk.
PWTAG recommends that vomit in the pool should be treated as if it were blood (ditto vomit on the poolside). 
Pool Plant Operations/Swimming Pool Technical Operations
These refer to the procedures required for the safe and effective management and operation of the technical aspects of a swimming pool facility, such as:

•    Circulation system (pumps, valves etc);
•    Filtration System (filters);
•    Chemical Storage and Dosing System (chemical pumps, lines, tanks, injection points etc);
•    Heating & Ventilation Systems (boilers, calorifiers, thermostats, motorised valves etc);
•    Water Quality Monitoring Systems (sensors, probes, sample lines, test kits etc).

The Pool Water Treatment Advisory Group (PWTAG) have produced a code of practice, which can be used to ensure minimum standards are met. This can be downloaded from their website:

O&M Manuals & Health and Safety Files
An O&M (operation and maintenance) manual is provided to the management of a building(s) by either the organisation that designed it, or the organisation that constructed it. It will contain details such as manufacturers’ instructions and health and safety guidance, and as-built drawings and schematics of the building.

The O&M manual may form part of the Health and Safety File that a Principal Designer, or Principal Contractor is required to hand over to the Client at the end of a construction project under the Construction (Design and Management) Regulations 2015.

The O&M Manual and Health and Safety File should be used as resources to help inform risk assessments, which in turn inform risk control systems, safe systems of work and the Pool Safety Operating Procedures (PSOP).

If the O&M Manuals contain schematic drawings of the pool and associated plant, these should be referred to when any work is carried out on the system (eg. addition of chemical dosing units, UV disinfection systems etc.).
They can also be used to help in training staff on the layout and operation of the pool plant system.

Could Your Pool Turn Green, Like The Olympic Pool In Rio?

August 25, 2016

Apparently, an operator added hydrogen peroxide to the Rio Olympic Pool. The rationale behind the decision to add this chemical is not clear. It could have been intentional, as hydrogen peroxide is used in some swimming pools as an oxidiser. The problem is that the chemical is also used as a chlorine neutraliser. So when the hydrogen peroxide was added, it went to work and promptly neutralised all of the chlorine thus allowing organic plant life to thrive, since it now had water, sunlight, nutrition and the absence of a biocide (chlorine).

Could it happen in your pool?
Yes, possibly, but probably not because of the addition of hydrogen peroxide. The pool water is more likely to turn green in outdoor pools because of exposure to sunlight, which contains ultra violet light (UV light neutralises chlorine). Some outdoor pools end up looking more like ponds due to water that is green because of algal growth.

The pool plant operator needs a way of 'stabilising' the chlorine. Cyanuric acid is used for this purpose. Cyanuric acid binds with the hypochlorous acid (the disinfectant element of chlorine) and makes it more resistant to degradation by UV. The drawback is that it also makes the hypochlorous acid less effective as a disinfectant and for that reason, higher free chlorine residuals must be maintained when using cyanuric acid (2.5 - 5.0 mg/l).

Dosing the correct amount of cyanuric acid can be tricky. Too little and you won't stabilise the chlorine enough, too much and you will over-stabilise and the hypochlorous acid will not be available to act as a disinfectant. The pool plant operator must ensure that the cyanuric acid levels are kept below 200 mg/l, with the ideal range being 50 - 100mg/l. The most effective way of keeping cyanuric acid levels in check is through dilution with fresh water.


Overchlorination - How to deal with it and get the pool open for business again!

July 22, 2016

It may be necessary to decrease the levels of chlorine on occasion and certainly following superchlorination. If you are going to be dumping a significant quality of swimming pool water for any reason, there would usually be a requirement to let the local water authority know and they would almost certainly require you to eliminate all traces of chlorine from the water before they granted permission to discharge (chlorine is harmful to aquatic organisms).

In normal operations, it would usually be better to bring the chlorine levels down by simply diluting the swimming pool with fresh water. This is safer and would contribute to less chemical pollution as well.

If you do need to decrease the chlorine quickly though, the chemical to use is sodium thiosulphate. The principle to bear in mind is that it takes 5g of sodium thiosulphate to neutralise 1g of chlorine. So if, for example, you had 10.00mg/l of chlorine in a 300m3 pool, that equates to 3000g of chlorine in the pool, since each m3 would have 10g of chlorine in it, and 300m3 X 10g = 3000g. The simplest thing to do would be to calculate how much sodium thiosulphate you would need in order to decrease the free chlorine level by 1.00mg/l. See he worked example below:

300g chlorine X 5g sodium thiosulphate = 1500g

So, in this particular example of a 300m3 pool, it would take 1500g of sodium thiosulphate to reduce the free chlorine level by 1.00mg/l/

From here, the same steps can be taken as given above in order to create a jug for the purposes of hand-dosing sodium thiosulphate (different jug – NEVER mix chemicals). Then, just add the required number of jugs in the same way as for adding calcium hypochlorite. So, in the example given, we would be adding 8 jugs of sodium thiosulphate in order to get the free chlorine down from 10.00mg/l to 2.00mg/l.


Superchlorination - The Correct Way

July 21, 2016

Image result for superchlorination

Following on from our previous post regarding hand-dosing of chlorine, here is some guidance on superchlorination.

Superchlorination is not recommended as a routine or even occasional method of shock dosing to compensate for inadequacies in pool treatment. It is generally bad practice, and can generate unwelcome by-products. But if something has gone wrong – poor results from microbiological testing perhaps, or a catastrophic breakdown in treatment – it may be necessary to superchlorinate. It can also be a way to deal with contamination by diarrhoea, as some intestinal pathogens (eg Cryptosporidium) are resistant to normal levels of chlorine residual. In this case it may be needed where filtration is inadequate (high-rate for example, or regular coagulation not practised). Superchlorination can also deal with other organisms should the need arise.

Two pool parameters are needed as a starting point:

·         the capacity of the pool in litres. Note: 1m3 = 1,000 litres, 1 gallon = 4.54 litres

·         the pool turnover period (the number of hours for a volume of water equivalent to the entire water volume of the pool to pass once through the water treatment plant).

The following chemicals and equipment will be required to undertake the procedure (which of course must include subsequent dechlorination):

·         a suitable chlorine donor – sodium or calcium hypochlorite (not any cyanurate-based disinfectants as they are not effective enough)

·         a dechlorinator – normally sodium thiosulphate pentahydrate

·         a pool water test kit together with a dilution pot

·         one or more clean 10-litre plastic buckets

·         a cold water supply.

Operators must be confident that the pool plant (valves, seals etc) will withstand superchlorination.

Step 1. Close the pool to swimmers. If more than one pool uses the same filtration system, all pools will have to be closed to swimmers and superchlorinated. Do not allow anyone to enter the pool(s) until superchlorination and subsequent dechlorination is completed. Isolate automatic dosing controllers to avoid damage to the sensors.

Step 2. Raise the free chlorine concentration as required to deal with the problem, based on the chart below.

Reason for superchlorination

Concentration required mg/l

Contact time

Diarrhoea (possible contamination with Cryptosporidium


13 h

Algal growth


24 h

Legionella (spas)


16 h

Raised colony counts, coliforms, E. coli


1 h

Raised P aeruginosa


12 h


Step 3. Add the total amount of calcium hypochlorite to tap water in the bucket(s) until fully dissolved/mixed. Then spread evenly around the pool surrounds and mix well by agitation. Failure to dilute and spread evenly can result in the precipitation of hardness scale. Superchlorination will raise pH, so acid will be needed to reduce the pH value to 7.5 or less. In the case of contamination by diarrhoea ensure the water temperature is 25°C or higher.

Step 4. Ensure that the filtration system is operating while the water reaches and is maintained at the chlorine level required for superchlorination (see Table). With spas, all aerators, sprays etc. should be operating throughout.

Step 5. Test the free chlorine concentration 15 minutes after the initial addition to ensure that the correct concentration has been achieved (see Table). This may necessitate dilution of the sample with chlorine-free water to give an accurate measurement.

Step 6. Leave for the desired contact time (see Table). Check every two hours to ensure the concentration is being maintained. If necessary re-dose to reinstate the required free chlorine residual, again checking pH.

Step 7. Backwash the filter thoroughly after the given contact time and top up pool to the required water level. Be sure the backwash effluent is discharged directly to waste (and not to a septic tank or water course). As usual, rinse the filter before resuming filtration.


How to Hand-Dose Chlorine...The Right Way!

July 14, 2016

Sometimes there will arise a need to introduce chemicals into the pool manually (hand-dosing). This is a potential hazardous activity and should not be performed by people who have not received the appropriate level of training.

General Procedures

Always wear the appropriate PPE.

Always add the chemical to the water, NEVER add water to the chemical.

NEVER mix a chemical with another chemical. Only ever mix with water.

Never hand-dose chemicals into the swimming pool when occupied.

Always allow time for thorough mixing and distribution of the chemical into all areas of the swimming pool water.

Increasing Chlorine

The following method will outline how to add a hypochlorite disinfectant to the swimming pool. If you’re using a chlorinated isocyanurate disinfectant, follow the manufacturers’ instructions as the method will be different.

We recommend using calcium hypochlorite granules for the purpose of hand-dosing. It’s safer to store and handle than sodium hypochlorite.

Step 1. The first thing you need to do is calculate how many cubic metres of water you have in your swimming pool. Do this by multiplying the length by the width by the average depth. See the worked example below:

Length (20m) X Width (10m) X Average Depth (1.5m) = 300m3

Step 2. The next thing to do is calculate how much calcium hypochlorite granules you need to add in order to increase the free chlorine reading by 1mg/l. Do this by dividing the pool volume figure (from step 1.) by 0.65. The reason you need to divide by 0.65 is because calcium hypochlorite is typically only 65% chlorine. Some products are 70% chlorine, in which case you would divide by 0.70. See the worked example below:

300m3 / 0.65 = 462

The figure obtained provides you with the amount of grams of calcium hypochlorite granules you need to add to the swimming pool in order to increase the free chlorine reading by 1.00mg/l.

Step 3. Use a set of kitchen scales to measure out 462g of calcium hypochlorite granules into a clear plastic jug.

Mark a clear line on the jug to indicate the level of calcium hypochlorite granules at 462g.

Step 4. Decide how much you need to increase the free chlorine reading by. For example, if you have zero free chlorine in the pool and you would normally operate at 2.00mg/l, then you need to increase by 2.00mg/l. This equates to the number of jugs of calcium hypochlorite granules you need to add to the swimming pool, i.e. 2 jugs.

Step 5. Now you need to add the granules to the swimming pool water. This can be done by carefully depositing the granules into either the overflow channel (in a deck-level pool) or the skimmer baskets (in a skimmer-basket pool). From here, the granules will be drawn into the balance tank (if there is one), or directly into the suction-side pipework of the circulation system. 

Step 6. Allow some time for the granules to dissolve and make their way around the system and into all areas of the swimming pool. How long this will take will be dependent on a number of factors, such as the efficiency of the system hydraulics.

Step 7. Carry out a set of pool tests, taking the sample from a point in the swimming pool as far as possible from the inlets. This is to help you determine whether the chlorine you have introduced has been distributed to all areas of the swimming pool. If necessary, carry out further tests in order to be sure that all areas of the swimming pool have a sufficient level of disinfectant. Once you are satisfied of this, you can open the pool again to bathers.


Pool Managers - Do You Know How Your Filters Actually Work?

June 23, 2016

Filtration is an important element of effective pool water treatment. The basic principle is that the untreated water is passed through a filtering medium (such as a bed of sand). The water is able to pass through the gaps between the grains of sand (called ‘pores’), but anything larger than the pore size is trapped within the filtering medium.

Pool Water Clarity
A reduction in the clarity of the pool water is a risk to pool users. It is essential that bathers are able to assess the depth of the water and for lifeguards to see a casualty below the surface of the water. If the water clarity falls below a stated level (defined in the EAP), the EAP should identify the procedures for suspending admissions and clearing the pool until the clarity reaches an acceptable level (as a minimum, the ability to see the body of a small child if it were located on the floor of the pool in the deepest water). The clarity of the pool water should be constantly monitored.

The pool water treatment system should be capable of providing clarity of no more than 0.5 nephelometric turbidity units (NTU). Clarity is reduced by turbidity – colloidal or particulate matter in suspension in the water. It is important to know the source of excess turbidity – whether pollution from bathers, external contamination, inadequate circulation/turnover or disinfection, or incorrect use of water treatment chemicals – in case this can be dealt with directly. The likeliest remedy, however, is adequate filtration and backwashing, coupled with coagulation.

Filter Design and Construction
Swimming pool filters are usually designed to a vertical orientation and are made out of various types of material:
  • Mild steel
  • Stainless steel
  • Plastic
  • Concrete
The most commonly used is mild steel. The inside surface is lined with either rubber or epoxy paint in order to protect the vessel from corrosion.

Inspection and Maintenance
Filters that have been appropriately selected and installed should last at least 25 years with proper arrangements in place for inspection and maintenance. On an annual basis, the filters should be opened and inspected by a competent person. For most facilities, this will mean using an external contractor. They should be looking for signs of physical wear or damage to the filter vessel and lining and the condition of the media bed. Issues such as an uneven or shallow bed, mud-balling, crack, fissures etc. should be identified and rectified.

The filter media bed may need to be replaced every 5-10 years, depending on its condition during the routine annual inspections. This provides an opportunity to inspect the underdrains for damage and repair or replace as needed. Deposits of sand on the pool bottom can be a sigh of damage to the underdrain system 

The basic sand filtration process work as follows:
Water moves in a downward direction through the filter and gets passed through the pores between the sand grains. T

Pollution within the water becomes entrained within the sand bed layer via processes of sedimentation, adsorption and mechanical straining. 

In swimming pool filters, the size of the sand grains is usually 0.5 - 1.0mm. This results in a pore size of approx. 50 – 70 microns (1mm = 1000 microns). Anything too big to pass through the pores will become entrapped, anything smaller may pass through unless they settle on the upper-facing surface of a sand grain, or they stick to the surface of a sand grain via adsorption. 

Sedimentation is where fine particulate matter settles on the upward-facing surfaces of the sand grains. The process of sedimentation can remove finer particles of pollution than straining. As the amount of sediment increases, the amount of space in between sand grains (pores) decreases. This will cause the velocity of water through the filter to increase. Further sedimentation can then no longer occur and, due to the higher velocity, some sediment could get pushed further down into the filter bed.  

Adsorption is where particles of pollution adhere to the sand grains. It is not to be confused with absorption. The process is promoted by electrostatic charges within the particles (similar to a balloon 'sticking' to a wall). Once particles begin to adhere to the sand grains, a sticky coating builds up, which promotes further adherence of particles onto the filter media. 

Filtration Rates
The filtration rate is the rate (in metres per hour) at which the pool water moves down through the filter during normal operation. It is not to be confused with the flow rate, which is the rate (in cubic metres per hour) at which water is moving through the circulation system.

The filtration rate is calculated by dividing the flow rate by the surface area of the filter. For example:

Circulation Rate: 100 cubic metres per hour 
Filter Surface Area: 5.72 metres squared
Filtration Rate: 100m3 / 5.72m2 = 17.48m3/m2/hr

You may already have a flow rate meter fitted onto the circulation pipework in your plant room to tell you what the flow rate is. If you do not have one fitted, it is highly recommended that you get one fitted as soon as possible as it will be difficult to calculate the turnover time and filtration rate without having the key piece of data that a flow rate meter provides.

If you are trying to calculate your filtration rate, but don’t know the surface area of the filter, you can easily calculate what the filter surface area is by using the formula: r2 x pi. This formula means the radius squared multiplied by pi. See below for an example using a filter that is 2.7 metres wide: 

Width of filter: 2.7 metres (this is also the diameter) 
Radius: 2.7m     /     2         =    1.35m 
Radius Squared: 1.35m  x    1.35m =    1.82 m2 
Surface Area: 1.82m   x    3.14 (pi)   =    5.72 m 2

There are three categories of filtration rate and they are set out below:

Low Rate: up to 10 m3/m2/hr very good filtration, but requires a very large surface area
Medium Rate: 10 - 25 m3/m2/hr recommended for public pools
High Rate: 25 - 50 m3/m2/hr recommended for small domestic pools only because this rate is too fast to deal with pollution in public pools


Swimming Pool Outlets Can Kill!

June 17, 2016

This week, the Royal Life Saving Society published a news article concerning the risk of drowning via suction entrapment in hot tubs.

The outlets of a swimming/spa pool are connected to a powerful circulation pumping system. If the outlets are blocked, whatever is causing the blockage will be exposed to the suction force of the circulation pumping system. The circulation pumps will be sucking on whatever is causing the blockage, causing a vacuum. At this point, it will be very difficult to remove the blockage without turning off the circulation pump(s).

If the blockage is a person, then tragic consequences can occur, including drowning, disembowelment and transanal evisceration, which is where internal organs are forcefully drawn out through the anus.

There are various ways that suction entrapment can be avoided:

  • Emergency cut-off devices that automatically turn off the suction pumps when an increase in suction force is detected
  • Multiple outlets being fitted so that even if one of the outlets gets covered, the remaining outlets take the increased water flow and prevent a vacuum being created at the blocked outlet. The distance between outlets should be a minimum of 2m.
  • Outlets being designed so that it is impossible to cover them and form a seal. This can be achieved via having the grill surface area of sufficient size (the outlet should have a surface area greater than 1m2).
  • It can also be achieved by the use of outlets that are designed to prevent a seal being formed around them when they are covered. These are called anti-vortex drain covers. Some examples below.
  • Installing a break tank between the pool tank and the circulation system. The break tank is gravity fed, so there is no risk of being exposed to the suction of the circulation pump(s).
  • Ensuring that the water velocity through each outlet is 0.5m/s or less.
  • All outlets should be fitted to a sump where the outlet pipe is located a distance 1.5 x the pipe diameter from the grid.
  • To prevent finger and toe entrapment the gap in the grille covering the outlet shall be a maximum of 8mm.
  • Ensuring that all outlet fittings and fixtures comply with BS EN 13451–1 and 3.

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

Entanglement Hazards
Entanglement hazards are slightly different to entrapment hazards. They involve hair being drawn into the outlet and then entwining on the other side of the outlet due to the circular motion of the water is it goes through the outlet. It may be impossible to free the hair from the outlet, even if the circulation pumps are turned off. People using spa pools are at an increased risk of suction entanglement due to the fact that they will be in close proximity 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 sufficiently so that they are aware of the hazards associated with outlets.


Is the commercial swimming pool sector regulated? YES (but not very well)!

May 25, 2016

Whilst there is no specific legislation covering the management of commercial swimming pool water, there is plenty of general legislation that is applicable. Read on for a quick primer.

Management Responsibility
The Health and Safety at Work etc. Act 1974 (HSWA) , the Management of Health and Safety at Work Regulations1999 (MHSWR) and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) impose certain statutory duties on all managers of non-domestic swimming pools. Duties under the HSWA extend to risks from infectious agents arising from work activities, ie risks to non-employees. The MHSWR provide a broad framework for controlling health and safety at work. COSHH provides a framework aimed at controlling the risks from hazardous substances including infectious agents.

Duties under the Health and Safety at Work Act 1974
It shall be the duty of every employer to ensure, so far as is reasonably practicable, the health, safety and welfare at work of all his employees.

It shall be the duty of every employer to conduct his undertaking in such a way as to ensure, so far as is reasonably practicable, that persons not in his employment who may be affected thereby are not thereby exposed to risks to their health or safety.

It shall be the duty of each person who has, to any extent, control of premises or of the means of access or egress or of any plant or substance in such premises to take such measures as it is reasonable for a person in his position to take to ensure, so far as is reasonably practicable, that the premises, all means of access or egress available for use by persons using the premises, and any plant or substance in the premises or, provided for use there, is safe and without risks to health.

If people working under the control and direction of others are treated as self-employed for tax and national insurance purposes, they are nevertheless treated as employees for health and safety purposes. It may, therefore, be necessary to take appropriate action to protect them. If any doubt exists about who is responsible for the health and safety of a worker, this could be clarified and included in the terms of a contract. However, a legal duty under Section 3 of HSWA cannot be passed on by means of a contract and there will still be duties towards others under Section 3 of HSWA. If such workers are employed on the basis that they are responsible for their own health and safety, legal advice should be sought before doing so.

Management of Health and Safety at Work Regulations 1999
Under these Regulations the manager of a pool is required to
  • assess the risks in their workplace
  • use competent help to apply health and safety legislation
  • establish procedures to use if an employee is presented with serious and imminent danger
  • co-operate and co-ordinate health and safety if there is more than one employer in a workplace

Approved Codes of Practice
Approved Codes of Practice (ACoP) offer practical examples of good practice and how to comply with the law. If, for example, regulations use words like ‘suitable and sufficient’ or ‘reasonably practicable’, an ACoP can illustrate what this requires in particular circumstances. 

Approved Codes of Practice have a special legal status which can be expressed positively or negatively.
The Approved Code of Practice for the Management of Health and Safety at Work Regulations 1999 (L21) (now withdrawn) states: 

If you follow the advice you will be doing enough to comply with the law in respect of those specific matters on which the Code gives advice. You may use alternative methods to those set out in the Code in order to comply with the law.

The ACoP for the Workplace (Health, Safety and Welfare) Regulations 1992 (L24) states: 

This Code has been approved by the Health and Safety Commission and gives advice on how to comply with the law. This Code has a special legal status. If you are prosecuted for breach of health and safety law, and it is proved that you have not followed the relevant provisions of the Code, a court will find you at fault, unless you can show that you have complied with the law in some other way.

However, a failure on the part of any person to observe the provisions contained in an ACoP does not, of itself, render that person liable to any criminal or civil proceedings. 

In criminal proceedings the provisions of a relevant ACoP are admissible in evidence, and a failure to observe them constitutes proof of the breach of duty or contravention of the legal duty in question, unless the accused satisfies the court that he complied with the requirement of the law in some other equally effective manner. 

In civil proceedings it is likely that a failure to observe the provisions of an ACoP could constitute prima facie evidence of negligence, which would have to be rebutted by evidence to the contrary.

Guidance Notes
Guidance notes may be specific to the health and safety problems of an industry or of a particular process used in a number of industries. 

The main purposes of guidance notes are to: 
  • help people to understand what the law says including, for example, how requirements based on EC Directives fit with those under the Health and Safety at Work Act 
  • help people comply with the law 
  • give technical advice

The HSE may issue a guidance note together with an Approved Code of Practice (ACoP), or independently. Guidance notes contain practical advice and sound suggestions, and are frequently more informative than the related ACoP. The HSE aims to keep guidance up to date, because as technologies advance, workplace risks and appropriate control measures change too. 

Following guidance is not compulsory and employers are free to take other action but if they do follow guidance they will normally be doing enough to comply with the law. 

Although guidance notes have no legal standing they can be used as evidence of the state of knowledge at the time of issue.

An example of guidance, published by the HSE and relevant to the management of swimming pools is ‘HSG179 Managing Health and Safety in Swimming Pools’. This document can be downloaded, free of charge from the HSE website.

A further example of guidance, published by the Pool Water Advisory Group (PWTAG) is ‘Swimming Pool Water: Treatment and Quality Standards for Pools and Spas, which has more detailed information regarding pool water treatment than the HSG170 guidance.

Enforcement of health and safety legislation falls to two bodies, the Health and Safety Executive and Local Authorities (LAs). The HSE are responsible for enforcement with respect to designers, manufacturers and installers and for pools in premises where HSE is the enforcing authority eg. government buildings, factories. LAs are responsible for enforcement in hotels, retail outlets, and private sports and fitness clubs. 

The majority of commercial pools will be under the enforcement of Local Authorities. Both HSE and LA inspectors will expect employers to meet their legal responsibilities as explained in the COSHH ACoP and L8. Each LA will make their own arrangements for inspections and water quality monitoring. 

The enforcing authorities have the power to close a pool (Prohibition Notice) if there is an imminent risk to health. They can also require improvements (Improvement Notice) where the management of a pool is falling below legal standards.

Can you smell chlorine? Then it's probably a badly managed swimming pool.

May 23, 2016
combined chlorine

When the disinfectant gets into the pool water, the free chlorine contained within in immediately gets to work and starts combining with pollution. Once chlorine combines it hangs around in the pool water and is no longer effective as a disinfectant and is now actually more of a pollutant itself. It needs to be removed from the pool by a combination of dilution and filtration.

Combined chlorine is measured by calculating the difference between the total chlorine and the free chlorine.
Free Chlorine (DPD1) + Combined Chlorine (total minus free) = Total Chlorine (DPD3)

Much of the chemical pollution in swimming pools is in the firm of ammonia, which is a decomposition by-product of urea (which comes from sweat and urine etc. from bathers). This ammonia reacts with chlorine to form what are known as ‘chloramines’. These are measured as combined chlorine by subtracting the free chlorine reading from the total chlorine reading.

Combined chlorine levels should be kept as low as possible, and certainly no more than 50% of the free chlorine level.

There are four main categories of chloramines to be aware of:

•    Monochloramine 
•    Dichloramine
•    Trichloramines
•    Organic Chloramines  

Monochloramine is one of the chloramines which contribute to the level of combined chlorine in the water. It is produced when chlorine reacts with ammonia. In simple terms, the reaction is:

Chlorine + Ammonia > Monochloramine

Monochloramine isn't really that much of a problem, in fact, it acts as a disinfectant itself, although it is nowhere near as effective as free chlorine. Things don't stop there though and further chemical reactions will take place to produce dichloramine and trichloramine (these are the chloramines that are the cause of problems and a pool plant operator needs to know how to get rid of them and minimise their production in the first place).

Dichloramine is one of the chloramines that contribute to combined chlorine levels in the pool water. It is the second stage of the chemical reaction that takes place between chlorine and ammonia. It is produced when chlorine (or, to be more specific; hypochlorous acid) reacts with monochloramine (which are produced during the first stage of the reaction):

Hypochlorous Acid + Monochloramine > Dichloramine

You don't want high levels of dichloramine in your pool as it can go on to form further chemical reaction by-products such as trichloramine. It's an unstable chemical though and as long as your pH is at the correct level it will break down fairly easily. At this point, your combined chlorine readings will reduce because there are no chloramines left to react with. This is known as 'breakpoint chlorination'.

Typically, in practice, you won’t know how much monochloramine and dichloramine you have in your pool as normal testing procedures don't distinguish between the two. As long as you keep combined chlorine levels under control (i.e., less than half of the free chlorine), you won’t really need to know, but if you start having difficulties keeping combined chlorine levels low enough, you may need to carry out a DPD2 test in order to find out which of the chloramines is contributing most to the combined chlorine levels.

Breakpoint Chlorination
In basic terms, as far as pool plant operators are concerned, breakpoint chlorination describes the point at which there is twice the amount of free chlorine than combined chlorine.

Imagine a swimming pool that has high levels of pollution. If you were to introduce some much-needed chlorine into the pool, it would quickly end up as combined chlorine as it literally combines with bacteria etc. kills it and then becomes virtually useless as a disinfectant. In fact, combined chlorine could now be classed as pollution and it is combined chlorine that makes people’s eyes sting and causes irritation to nasal passages etc. Combined chlorine is something we want as little of as possible, as close to zero as we can possibly get it and certainly no more than 1.00mg/l.

As all the chlorine we have introduced has now become combined chlorine, we need to add some more. We always need to have some chlorine available (or, free) in order to quickly neutralize microbiological contamination. This is referred to as 'free chlorine'. We need the free chlorine levels to be at least double the combined chlorine levels. Free Chlorine is measured with the DPD 1 test, Total Chlorine is measured with the DPD 3 test, and Combined Chlorine is the difference between the two.

As you continue to add free chlorine into the pool, and as that free chlorine continues to convert into combined chlorine, the combined chlorine reading (the difference between the free and the total chlorine readings) will increase. Eventually though, if everything is operating properly, the chemical reactions that were discussed earlier will continue and progress even further:

Monochloramine + Dichloramine > Hydrochloric Acid + Nitrogen

The above reaction is dichloramine decomposing, and as long as this reaction continues, there will come a point where there is no more dichloramine left for the monochloramine to react with. At this point, the combined readings will start to fall, rather than continue to rise. This is referred to as breakpoint chlorination, which can be more easily achieved by adopting the following good practices:

  • Get people into the habit of taking a shower before swimming so that there is less pollution available for the chlorine to combine with;
  • Dilute the swimming pool water with enough fresh water (30 litres per bather, per day);
  • Ensure enough chlorine is being dosed into the swimming pool (an automated system is always recommended for any type of commercial facility);
  • Make sure that the pool turnover time is fast enough for your type of pool;
  • Make sure you’re not overloading your pool.
  • Keep the pH within the recommended parameters.

If you follow these steps, you should have no problem achieving breakpoint chlorination. However, if these good practices are not followed, things can start to go wrong. Instead of the dichloramine decomposing away, it starts to react with the hypochlorous acid in the pool and forms hydrochloric acid and trichloramine. The reaction looks like this:

Dichloramine + Hypochlorous Acid > Hydrochloric Acid + Trichloramine (Nitrogen Trichloride)

Trichloramine (and to a lesser extent dichloramine) are the chemicals that can cause the strong chlorine smell in badly-run swimming pools. It can also cause irritation to the mucous membranes by forming hydrochloric acid on them when they react with water. They can also trigger asthma attacks in people already suffering from asthma, but are not thought to actually cause the condition.

Organic chloramines are formed by the reaction between chlorine and organic nitrogen compounds. These are introduced into the pool at the same time as ammonia from bather urine/sweat etc. The key difference for the pool operator with organic chloramines is that they are stable and will not break down by the addition of more chlorine. In fact, the opposite is true; the levels will increase with the addition of more chlorine. Therefore, the levels must be kept under control by a process of dilution at the appropriate rate.

Not bothering with water balance tests? You're asking for trouble!

May 19, 2016
swimming pool water balance testing

Balanced water testing is something that swimming pools should be doing weekly in order to determine whether pool water is 'balanced'. This refers to whether the water is corrosive or scale-forming, or neither (balanced).

Corrosive water is contains little calcium (soft water) and is therefore ‘hungry’ for that substance. It will eat away at anything that contains the calcium it needs. Tile grout is usually high in calcium and is therefore very vulnerable to attack from corrosive water. 

Scale-forming water does the opposite of corrosive water and instead of eating away at things it will deposit a scale on them (you're likely to have seen the effect of this on the heating element of your kettle if you live in a hard water area). It does this because it contains high amounts of calcium (hard water) and will readily give up this excess calcium onto the various surfaces it comes into contact with. This scale-forming can be a problem if it is allowed to build up on the inside of pool circulation pipework etc. where it will affect pipe diameters and flow rates. It also looks unsightly, especially on darker surfaces.

The aim of good water balance management is to have water that is neither corrosive, nor scale-forming (i.e., balanced). The main factor that drives the need for good water balance is planned preventative maintenance (PPM). This is different to the tests for chlorine and pH levels, where the main factor is bather safety and reducing the risk of cross-contamination. Therefore, the water balance test results are lower priority than the chlorine and pH test results. This does not mean that the water balance tests should be neglected though because if they are, the result could be many thousands of pounds worth of remedial maintenance repairs and replacement parts further down the line.

Step 1. 
Carry out tests and note results for:
  • Calcium hardness
  • Total alkalinity
  • Pool water temperature  
  • Total dissolved solids

Step 2.
Convert the results from the above tests to factors as indicated in the tables below (figures in bold provide a worked example).

Step 3. 
Add the factors for temperature, calcium, alkalinity to the pH (there is no factor for pH).

Step 4. 
Minus the factor for TDS from the figure obtained in step 3.

The ideal result is somewhere between 0.1 - 0.4. The pH level is the value that has the most impact on water balance test results. A high pH would contribute to scale-forming water, a low pH would contribute to corrosive water. However, it is not advisable to start adjusting pH levels just to try and get good water balance results, as pH is a critical factor in the efficiency of your disinfection and coagulation, both of which are more important than water balance results. Better ways to either increase or decrease the water balance result are listed below:

To increase: 
Increase the levels of calcium hardness by adding calcium chloride 
Increase the levels of total alkalinity, by adding sodium bicarbonate 
Reduce the TDS levels (if they are particularly high) by diluting with fresh water.

To decrease: 
Take a look at your pH result. If it's high, you need to decrease it anyway as your chlorine is not going to be as effective at higher pH levels
Reduce the levels of calcium hardness by diluting with fresh water
Reduce the levels of total alkalinity by diluting with fresh water.

Got a Spa, Hot Tub etc.? You need to know about legionella.

May 13, 2016
legionella in hot tubs

Legionella is a type of bacteria that is of particular concern to the pool operator, or indeed, any operator of a facility that has a hot and cold water system. The legionella bacteria causes legionairres disease, which is an infection of the lungs. The mortality rate is currently 12%, which means that if 100 people were to contract the disease during an outbreak, approximately 12 of them would die.

Legionella bacteria multiply in water and the disease is caught by inhalation. This means that wherever it is possible to inhale water, there is a risk of contracting legionairres disease. Anywhere where the water can form an aerosol (tiny droplets of water suspended in the air) is at risk. For the pool plant operator the danger areas are:

1. Spa pools - the turbulence of the water at the surface, caused by the air jets.
2. Showers - when someone takes a shower, they will inevitably inhale some of the mist.
3. Taps - when the tap water hits the basin, there is a risk of creating the aerosol, which is then breathed in.

What are the control measures?
Like with many things, it's better to prevent legionella from multiplying in the first place. This can be done by not providing the legionella bacteria with an environment in which they can thrive. Legionella bacteria do very well in an environment that is warm (between 20 - 50 degrees Celsius) and has a source of nutrition (such as bio-films). Keeping water outside of the 20 - 50 degrees Celsius range is one of the key control measures. The other main control measure is biocides. Chlorine is very efficient at killing legionella bacteria and levels should be closely monitored to make sure they are in the correct range (which for a spa pool is 3-5 ppm). Another control measure is the physical removal of legionella and bio-films via filtration (spa pool filters should be backwashed daily) and cleaning/de-scaling/scrubbing any and all areas where legionella could multiply (spa pool pipework, shower heads, balance tanks etc.)

Recent Outbreak
A DIY chain has paid over £200,000 in damages to the relatives of three men who were killed after being struck down with Legionnaires' disease caused by a filthy hot tub on display. Delivery driver Richard Griffin, 64, and customers William Hammersley, 79, and Harry Cadman, 71, died after contracting the disease in the summer of 2012. 
A report by the Health Protection Agency (HPA) said the 'probable source' came from a hot tub on display at the JTF Warehouse in Fenton, Stoke-on-Trent, Staffordshire. 

The report found that had not been filtered or cleaned for weeks, causing the water to stagnate and leading to the 
formation of bacteria and build up of Legionnaires' disease droplets. When the hot tub was then turned on it is believed the particles became airborne and spread around the garden centre. 

Father-of-two Mr Griffin, from Clayton, Staffordshire, was the first victim of the outbreak. It is believed he 
contracted the disease while delivering meat to the store's cafe and started getting headaches, fever and 
hallucinations. He later lost consciousness at his home and died at the University Hospital of North Staffordshire from multiple organ failure on August 2, 2012, after spending a week in hospital. 

Grandfather-of-two Mr Hammersley, from Chesterton, Staffordshire, passed away on August 4 while Mr Cadman, from Stoke-on-Trent, died from the disease days later. 

Following their deaths the grieving relatives of the three men took legal action against the DIY firm who admitted civil liability earlier this year. 

Lawyers working for the families revealed they had been paid a substantial payout by the company for their 'pain and suffering, lost earnings and care'. 

Mr Griffin's daughter, Rachel Griffin, 46, who now lives in Cumbria, said: 'We're relieved that the legal case has now concluded without the need for a court battle. 

'But we do hope that there is progress with the criminal prosecution case and the inquest over the coming 
months so that we can begin to move on with our lives. 

'The whole family misses my dad so much. He had a great sense of humour and always cheered us all up. 

'Losing him was horrific and to know that he died through no fault of his own is devastating. 

'He was due to retire later that year and was in good health. We just never expected anything like this. 

'Nothing can ever bring our dad back, but we just wanted to make sure that justice was done and that there was some accountability for his death. 

'I truly hope no one ever has to go through what we have.'  

A further 18 people needed hospital treatment following the outbreak that summer. 

In total 14 survivors and the families of the three men who died, all sought compensation for the horror caused by the disease. 

While 13 cases were settled out-of-court, the families of those who lost relatives and one survivor who contracted a serious lung infection pursued their cases through the courts. 

Personal injury lawyers Irwin Mitchell issued formal court proceedings against JTF Wholesale Limited, which has 13 branches across the UK. 

Amandeep Dhillon, a lawyer from Irwin Mitchell, said: 'Nothing can turn back the clock but we are pleased to have finally concluded these cases, allowing those families affected to begin to move on with their lives. 

'There are strict controls in place which are designed to reduce the risk of Legionella contamination in public 
spaces, but sadly all of those who contracted this dreadful condition were badly let down by JTF Wholesale on this occasion. 

'It's important that lessons are learned from this incident to ensure that the risk of any similar outbreak in the 
future is reduced.' 

Chlorine Gas Leaks - Pool Operators Beware

April 26, 2016
danger of chlorine gas in swimming pools

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.

What is pH and Why is it so Important?

April 25, 2016
pH in swimming pools

pH stands for the 'power of hydrogen' and is a critical factor in the treatment of pool water. The recommended range for the pH level to be maintained at is 7.2 - 7.4. The reason that the pH level needs to be kept between these values is that the disinfection efficiency of the chlorine  falls off significantly at higher pH levels and the coagulant will also not be as effective. At lower pH values, the pool water will be too corrosive.

The effect of the pH level on the disinfection process is an area that many pool plant operators fail to fully understand. Therefore, they don't take the correct actions and end up with low quality swimming pool water and an excessive yearly spend on chlorine. Let's take a look at what's going on with pH and chlorine:

The blue line is the percentage of active disinfectant in the chlorine and as you can see, the percentage of active disinfectant is dependant on the pH level. When you add chlorine to the swimming pool water, chemical reactions start to occur. The chlorine reacts with the water and ends up producing hypochlorous acid and hypochlorite. The key disinfectant in chlorine is hypochlorous acid, which is about x100 stronger than the hypochlorite, so that's what we want more of. The higher the pH level, the higher the proportion of hypochlorite, the lower the pH level, the higher the proportion of hypochlorous acid. At a pH level of 7.4, you've got about 60% of the chlorine as hypochlorous acid, so if your free chlorine reading was 1.0 mg/l when tested, in real terms the amount of active disinfectant would only be around 0.6 mg/l. If the pH level was allowed to get to 7.8, then only 30% of the chlorine would be hypochlorous acid, so if the test reading came out at 1.0 mg/l again, the actual amount of active disinfectant would only be 0.3 mg/l, which would be too low for adequate disinfection.

You need to bear in mind that the free chlorine reading includes both the hypochlorous acid and the hypochlorite, but it does not tell you the proportion of each. This is why it's so important for pool plant operators to understand how and why the pH levels have such a dramatic effect on the disinfection process.

Emptying Swimming Pools

April 25, 2016
the risks involved when emptying swimming pools

The first thing to consider before going ahead with this task is whether it is really necessary to empty the pool at all. Many repairs to the pool lining and/or tiles etc. can be carried out by trained divers, without the need to empty the swimming pool at all. However, there are occasions where the pool water will need to be emptied. An example would be if any broken glass somehow found its way into the pool water. Because glass is completely invisible when submerged in water, the entire pool contents would need to be emptied and a thorough clean-up operation carried out to ensure that all traces of glass have been removed.

If you have assessed the requirement to empty and have decide to go ahead, here's what you should do:

1. Carry out a suitable and sufficient risk assessment for this job before going ahead with anything. This risk assessment will need to be carried out by a person who is competent and understands all of the hazards and risks involved.

2. Contact the local water supplier and the Environment Agency and inform them of what you intend to do. You may need their explicit permission before going ahead. Also, they may require you to remove all of the chlorine from the water prior to discharging it and also discharging the water at a slower rate than you were originally intending.

3. Before releasing any water, turn off the air and water heating system and let the temperature come down to as close to the ambient temperature as possible.

4. Neutralise all of the chlorine in the water using sodium thiosulphate. Every 1 gram of free chlorine will need 5 grams of sodium thiosuphate to neutralise it. For example, if your pool volume is 450 cubic metres and your free chlorine reading is 2.0 mg/l, then there is 900 grams of free chlorine. Times this by 5 (4500g) and you have the amount of sodium thiosulphate you will need to add.

5. Start discharging the water. This needs to be done slowly, at a rate of no more than 750mm per 24 hour period. So for a pool that's 2 metres deep, it's going to take the best part of 3 days to empty it.
6. Before refilling, try to get the pool tiles to as close as possible to the incoming water temperature. This will obviously be more difficult to achieve in the winter months, so have a think about when would be the best time to schedule this work. Heat the water slowly at a rate of no more than 0.25 degrees Celsius per hour. So if the water is, say, 5 degrees Celcius, you may be looking at a four-day period in order to get it up to bathing temperature. 

Gross Microbiological Contamination

April 25, 2016
microbiological contamination in swimming pools

All commercial swimming pools should be getting the pool water tested at a UKAS-accredited laboratory for microbiological contamination. In most pools this should be done on a monthly frequency, but certain pools, such as hydrotherapy pools, should be done on a weekly basis. The four standard tests and the acceptable levels for each are:

  • Aerobic Colony Count  > 10cfu/ml
  • Total Coliforms  >10cfu/100ml 
  • E. Coli  >1cfu/100ml
  • Pseudomonas Aeruginosa  >50cfu/100ml 

If you get the lab results back and any of them are outside of these ranges, you need to get the water tested again as the samples may have been taken just after someone 'released' something into the water and the system has not had time to deal with it yet. If the repeat tests are still not within the acceptable ranges, the pool operator should take this as an indication that the pool water treatment and/or management system is not functioning as it should. The system and arrangements for managing the pool water quality will need to be looked at with a view to pinpointing exactly what is wrong and then putting it right. 
What if the results are way outside the acceptable ranges though? At what point does the pool operator need to close the pool down due to gross microbiological contamination? The official guidance is that the pool should be closed down if any of the routine monthly microbiological test results indicate either of the following scenarios:

  • Greater than 10 E.coli per 100ml in combination with an unsatisfactory aerobic colony count (>10 per 100ml) and/or an unsatisfactory P.aeruginosa count (>10 per 100ml) 
  • greater than 50 P.aeruginosa per 100ml in combination with a high aerobic colony count (>100 per ml) 
You may find it easier to interpret the above conditions by using the flow chart:
microbiological contamination in swimming pools flow chart

"Do I Need To Send My Staff On A Pool Plant Course?"

December 28, 2015
First, let's take a look at what the law says (only the parts directly relevant to training have been included)...

The Health and Safety at Work etc. Act 1974 places the following duties on employers:

Section 2. General duties of employers to their employees.
...the provision of such information, instruction, training and supervision as is necessary to ensure, so far as is reasonably practicable, the health and safety at work of his employees.

The Management of Health and Safety at Work Regulations 1999 places the following duties on employers:

Regulation 13 Capabilities and training 
...every employer shall ensure that his employees are provided with adequate health and safety training.

The Control of Substances Hazardous to Health Regulations 2002 places the following duties on employers:
Regulation 12 Information, instruction and training for persons who may be exposed to substances hazardous to health
...every employer who undertakes work which is liable to expose an employee to a substance hazardous to health shall provide that employee with suitable and sufficient information, instruction and training(2)  Without prejudice to the generality of paragraph, the information, instruction and training provided under that paragraph shall include details of the substances hazardous to health to which the employee is liable to be exposed including i. the names of those substances and the risk which they present to health, ii. any relevant workplace exposure limit or similar occupational 
exposure limit, iii. access to any relevant safety data sheet, and iv. other legislative provisions which concern the hazardous properties of those substances.
In addition to the legal requirements set out above, the Health and Safety Executive have produced guidance to assist pool operators to manage their pools safety. The guidance document is called HSG 179 Managing Health and Safety in Swimming Pools. The following is what this guidance says about training for staff:

...relevant training will be required to provide pool operators with the necessary knowledge to effectively operate spa pools. Appendix 7 lists national bodies that can give advice on relevant training.

...the COSHH Regulations require that staff involved in the handling and use of chemicals should receive appropriate training and instruction. Even the most thorough arrangements to comply with the COSHH Regulations will fail unless 
all employees are aware of the risks associated with their work and how these risks can be avoided. (See Appendix 7 for training providers).

...the training for the safe operation and use of equipment and chemicals will need to be related specifically to the operation and maintenance of the particular plant, hazards associated with it, and substances used. Employees’ 
attention should be drawn to any manufacturers’ instructions, and copies made conveniently available (eg secured to the plant itself); be given to enough employees to ensure that plant need never be operated by untrained staff; include pool managers, to ensure they understand the functioning of the pool water system,including the plant and associated hazards, sufficiently to supervise safe operation; include the use, care and maintenance of personal protective equipment; require those who have been trained, to demonstrate that they can operate and maintain the plant safely.

...pool operators will need to check that staff understand and follow all procedures and responsibilities. Monitoring and review of the effectiveness of arrangements should then follow. Details of actual training sessions will need to be recorded and reviewed. Information, instruction, and training are the essential requirements for all staff involved in the storage, handling, and use of swimming pool chemicals.

...there are many ways to disinfect a pool, and the choice can seem complicated. The key considerations are: the efficacy of disinfection; compatibility with the source water supply (for fill and make-up); type and size of pool; bathing load, etc; operation of the pool; training and competency of staff.

...any system, whether manual or automatic, needs to be maintained. The operation, maintenance and modification of such systems need to be carried out by competent staff with appropriate training and experience. Systems to ensure this need to be devised and managed.

In conclusion, we think that all operators of commercial wet-side facilities should be sending their staff onto industry recognised pool plant courses, rather than trying to deliver this training themselves.

Use a bucket to discover if your pool has a leak

January 24, 2013
swimming pool leaks

If you suspect your pool has a leak, but need to know for sure, you can find out very easily by using the 'bucket-test'. Put some pool water in a bucket and then put the bucket in the pool on the top step. Get it so the level of the pool water is exactly level with the water in the bucket. Leave it for a couple of days and then compare the water levels. If there is a leek, the level of the pool water will be lower than the water level in the bucket.


June 12, 2012
cryptosporidia in swimming pools

Cryptosporidia is a parasite that is of particular concern for pool plant operators because it is not killed by chlorine. The parasites live inside a protective shell called an oocyst which protect them from the chlorine in the swimming pool or spa water. If these oocysts are ingested by swallowing contaminated water, the cryptosporidia with hatch out of the shells and reproduce, causing a gastro-intestinal illness. When the newly-created oocysts are expelled from the body via the faeces, the whole cycle starts again.

As chlorine is an ineffective defence, the pool plant operator must use other methods. The key operational defence is keeping cryptosporidium out of the swimming pool in the first place. Anyone who has been ill with diarrhoea must not go swimming until they are symptom-free for at least 14 days. We recommend putting up some signage about this at reception as well as in the changing rooms etc. You also need to ensure the effective coagulation and filtration of the oocysts. The thing to bear in mind is the fact that without the addition of a coagulant (such as poly-aluminium chloride) to the circulation system at the correct dosing rate, the oocysts will pass straight through the sand in a commercial swimming pool filter. This is because the oocysts are about 5 microns in diameter, whereas the gaps between the sand grains are about 10 microns in width in a ripened sand filter. The addition of a coagulant will cause the minute particles of pollution (including the cryptosporidium oocysts) to clump together to form what are know as 'flocs'. These flocs are large enough so as not to pass through the sand filter and end up in the swimming pool.

Ultra violet radiation and ozone disinfection have been found to eliminate cryptosporidia, but even when using these types of disinfection processes, the use of a coagulant is still recommended.

It is vital that pool plant operators keep their sand filters clean and well-maintained. This means that for swimming pools, the sand filters should be backwashed at least weekly, or according to the filter manufacturers instructions. Spa pool filters should be backwashed every day.

If you end up with loose, runny stool in the swimming pool, you will need to assume that cryptosporidia is present and clear the pool and keep it closed for 6 turnover cycles. While your closed down, backwash the filters, get the chlorine up at the high end of the acceptable range and get the pH at the low end of the acceptable range. Also, scrub, sweep, brush, squeegy, net, hoover the whole area before re-opening.


Possible Electrical Hazard?

May 16, 2012

the dangers of electricity in swimming pools can make chlorine from salt?

February 27, 2012
Sodium Hypochlorite is the chlorine disinfectant most commonly used in UK swimming pools. It's supplied in liquid form and is similar in appearance to household bleach, which itself contains approximately 5% Sodium Hypochlorite. It is possible to produce Sodium Hypochlorite on-site by passing an electrical charge through a solution of Sodium Chloride (salt water).

 sodium hypochlorite generation from salt

The benefits of this type of system are that there is no direct handling of hypochlorite chemicals and there will be reduced amounts of chloramines (combined chlorine). Some disadvantage of the system are that it produces hydrogen gas, which is explosive and the equipment required can be expensive.



The Most Effective Pool Water Treatment Method Ever!

February 22, 2012
In many areas of management (and life in general), there are a limited number of issues and concerns that have the most impact on whatever it is your trying to manage. Effective swimming pool water treatment and pool plant operation is no different. During one of our pool plant courses, you will learn all sorts of things in order to understand what's happening with the swimming pool water and be able to diagnose and rectify problems quickly. 

All sorts of things can go wrong with swimming pool water for any number of different reasons. Things can get out of hand very quickly if you don't know what you're doing. However, there is one key variable that can have a dramatic influence on the quality of your pool water. Get this issue right, and you will experience far fewer problems with regard to pool water quality, you'll spend far less money on expensive chemicals and you and your duty managers will spend far less time trying to resolve issues. What's more, to implement and control this issue is very easy and simple to do and will hardly cost you anything in time, money or effort. So, what is this issue that can have such a dramatic effect? Pre-swim showering! 

I're probably feeling a little bit disappointed because after the build-up, you were expecting this article to discuss some fantastic product, new on the market, that would be the answer to your pool water treatment problems. Sorry about that. But really, you should look at your pre-swim showering policy and consider the following facts:

#1. the pollution on bather bodies is what makes up most of the pollution into the pool
#2. the remainder of the pollution only exists in the first place because of the chemical reactions resulting  from the chemicals your are having to add to deal with #1.
#3. pre-swim showering removes most of the pollution on bathers

#4. less bather pollution = less chemicals = less chemical by-products = better pool water = happy bathers

How difficult would it be to ensure that every bather, without fail, showers before entering your pool? It is, after all, your pool and your responsibility to keep it clean and safe. 


Relative Pollution

February 21, 2012
A pool that is 25 metres long, 12 metres wide, with an average depth of 1.5 metres will hold 450 cubic metres of water. If there are, say, 30 people in the pool, each of them will have 15 cubic metres of water each.

Contrast this situation with a spa pool. A spa will only hold about 3 - 10 cubic metres of water, depending on the type. Let's say we have a spa pool that holds 5 cubic metres and has 10 people in it. Each person now has only half of one cubic metre of water each.

Even though there are more people in the swimming pool (and therefore more total pollution), the relative pollution is higher in the spa due to the fact that as a percentage of volume, the pollution levels are higher. The spa is said to have higher relative pollution levels. Spa pools are not the only types of pool that suffer from high relative pollution. Any pool, that has an unfavourable pollution to water ratio will also have high relative pollution. Examples are:

  • paddling pools
  • splash zones
  • teaching pools
  • hydrotherapy pools  
It is also possible to have high relative pollution in fairly large pools too, as this video clearly demonstrates:


Breakpoint Chlorination

February 13, 2012
A few people struggle to fully understand the concept of what is known as 'breakpoint chlorination' during the pool plant operators course. In basic terms, as far as pool plant operators are concerned, breakpoint chlorination describes the point at which there is twice the amount of free chlorine than combined chlorine.

Imagine a swimming pool that has high levels of pollution. If you were to introduce some much-needed chlorine into the pool, it would quickly end up as combined chlorine as it literally combines with bacteria etc. and becomes useless as a disinfectant as soon as it does so. In fact, combined chlorine as now classed as pollution and it's combined chlorine that makes peoples eyes sting. So, in a nutshell; combined chlorine is something we want as little of as possible, as close to zero as we can possibly get it and certainly no more than 1mg/l.

As all the chlorine we have introduced has become combined chlorine, we need to add some more. We always need to have some chlorine available in order to quickly neutralize contamination. This is referred to as 'free chlorine'. This is the good stuff and we want it in our swimming pool. To be precise, we need the free chlorine levels to be at least double the combined chlorine levels. Free Chlorine is measured with the DPD 1 test, Total Chlorine is measured with the DPD 3 test, and Combined Chlorine is the difference between the two.

But, if the chlorine we introduce turns into combined chlorine, how are we, as pool plant operators, supposed to maintain twice the amount of free chlorine than combined chlorine? Well, that's simple:

  • Get people into the habit of taking a shower before swimming so that there is less bacteria available for the chlorine to combine with;
  • Dilute the swimming pool water with enough fresh water (30 litres per bather, per day);
  • Ensure enough chlorine is being dosed into the swimming pool (an automated system is always recommended for any type of commercial facility);
  • Make sure that the pool turnover time is fast enough for your type of pool;
  • Male sure your not overloading your pool.
Not of the above is particularly difficult, and if you follow these steps, you should have no problem achieving breakpoint chlorination.

Latent Heat Transfer

January 23, 2012
Energy is used when increasing the temperature of something. Heat is transferred from something hot to something cool.This heat is called 'sensible heat'. Energy is also used when a change takes place in the state of something. For example, when liquid water turns into water vapour. 

Both of these forms of heat are used to achieve energy efficiencies in some air handling systems for swimming pool halls. In order to provide a healthy and comfortable environment for bathers, spectators and staff, it is necessary to introduce fresh air into the building. Continually recirculating the air would lead to poor environmental conditions. In order to make way for the incoming fresh air, some of the air already in the pool hall will need to be expelled. The fresh air will need heating and it is possible to obtain some of the energy necessary for this from the outgoing air, which is hot and contains much more moisture than the incoming air (at least in the UK anyway). 

What you may find surprising is that both the sensible heat (the difference in temperature) AND the latent heat (the difference in state, ie, liquid to water vapour) can be transferred. The video below provides a good explanation and demonstration as to how this happens. It demonstrates how energy is released when water turns to ice, but the priciples are the same when water vapour (in the outgoing air) is turned into water (as it condenses onto the condensing coil in the air handling system).


The Chemistry of Water

January 23, 2012

Personal Protective Equipment (PPE) Assessments

January 23, 2012
This article aims to provide a worked example of a PPE assessment for the routine task of filling up the chlorine day tank with calcium hypochlorite granules. Please note that the assessment does not cover issues relating to chlorine gas and therefore, a separate assessment would need to be carried out for this.

  • Download (free) HSG53 - Respiratory Protective Equipment at Work.
  • Get the MSDS sheet for the substance in question (go here for calcium hypochlorite MSDS).
  • Work through the steps. There are several worked examples in the guidance, but for a worked example for the task described above go here.  
What I should also point out is that the PPE assessment is not the risk assessment. The PPE assessment only needs to be used if your risk assessment has established that a residual risk remains after the consideration of other factors (PPE is always the last resort). The other control measures that should be considered prior to the use of PPE are:

Can the risk be completely eliminated, if not;
Can the risk be reduced (using a less hazardous substance);
Can the person be isolated from the task (mechanising the process);
Control (engineering or management controls to reduce the risk);
Can safe systems of work (SSW) make the task safer;

This process is known as the hierarchy of control and can easily be remembered by using the acronym ERIC:

  • Eliminate
  • Reduce
  • Isolate
  • Control  
If some risk remains after consideration of the above, then go ahead and issue PPE, but make sure it's the right type (that's where the PPE assessment comes in).

When Should I Backwash?

January 19, 2012
If you have the filter manufacturers instructions, refer to those as they will inform you of how often a backwash needs to take place. Quite often though, these instructions have been lost long ago, so this article will outline some recommendations. What happens to a filter over time is that as it does its job and collects within it all the pollution and contaminants that you don't want getting in your pool, it becomes blocked up. This process is actually helpful towards the beginning of the cycle as it causes narrower gaps between sand grains (known as pores). This means that the filter will be capable of trapping smaller particles. This process is known as 'filter ripening'. As this process is happening, the resistance to flow encountered by the pool water as it enters the top of the filter will increase. At the same time, the force at which the water comes out of the filter at the bottom decreases. It's a bit like when you get a kink in a hosepipe; you'll only get a trickle out of the end of the hose, and the pressure will build up behind the kink. There are usually pressure gauges located on the inlet and outlet of a filter and their job is to tell the pool plant operator what the pressure differential (or head loss) is. As the pressure increases at the inlet, the needle on the gauge will move up and as the pressure at the outlet decreases, the needle will move down. By reading the values at the gauges and comparing them, you can work out the pressure differential across the filter bed. As a rough guide, when this pressure differential reaches 0.4bar, it's time to do a backwash. What usually works better from an operational point of view is to do a backwash every week. Keep an eye on the pressure differential and review the policy if needs be.


January 18, 2012
Backwashing is the process of cleaning the filters. Consider that the job of the filters is to trap as much of the various types of pollution as possible and you will appreciate that over time, more and more of this pollution will build up within the filter media. At regular intervals, this accumulated pollution needs to be gotten rid of. The method is to reverse the flow of water through the filter, so instead of water going in at the top and coming out at the bottom, the water goes in at the bottom and out at the top. As it does this, the pressure of the water moving up through the sand in the filter causes the sand to break up and eventually 'fluidise'. When this happens, the pollution is forced out of the sand and through the top of the filter,and from there it is directed to the drains (NOT back into the swimming pool!).

It is a fairly simple and straight-forward process, and there should be a step-by-step guide contained within your normals operating procedures or systems of work etc. to guide you through it. For the pool plant operator, it is recommended that they get to know their pool plant system well enough that, eventually, they will not need to refer to a guidance document in order to properly perform a backwash. A very simplified, generic backwash description is given below:

1. Switch off circulation and chemical dosing.
2. Adjust valves so that the pool water goes into the filter at bottom and out at top, and from there to drains.
3. Switch circulation back on and leave running until pool water is visibly clear.
4. Switch circulation off.
5. Adjust valves so that the pool water goes in at the top and out at the bottom, but still runs to drains.
6. Switch circulation back on and leave running for a couple of minutes (this is called the 'rinse'.
7. Switch circulation off.
8. Adjust valves so that the pool water goes in at the top and out at the bottom, but this time returns to the pool.
9. Switch the circulation back on.
10. Open the air release valve to purge the system of trapped air.

As previously mentioned, this is a very watered-down (excuse the pun) description of the process. Other factors need to be considered such as air scouring, backwash velocity and filter pressure differential.

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