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As an EH director at a local health authority, helping to review provincial guidelines on swimming pools, you want to know if scientific evidence supports pool closure orders when free available chlorine (FAC) is found to be at or above 10 ppm. Should the level be different and are there other factors to be considered for closure, instead of or in addition to FAC?
What is Free Available Chlorine (FAC)?
Chlorine and chlorine compounds have a high reactivity and oxidative capacity which is crucial in the degradation of organic compounds and microorganisms. There are a number of factors which impact the disinfecting efficiency of chlorine in swimming pools: type of chlorine, pH of the pool water, contaminants in pool water, water temperature and duration of contact. Disinfection by products (DBP), such as trihalomethanes can also be produced with the addition of chlorine, depending on the organic material; generally, the production of chloramines is a more important issue in maintaining pool water quality.
When chlorine is added to water, hypochlorous acid (HOCl), and the hypochlorite ion (OCl-) are formed. Hypochlorous acid is the most effective antibacterial species formed by chlorine.
Cl2 + H2O ↔ HOCl + H+ + Cl-
HOCl ↔ H+ + OCl-
A measure of chlorine in these two chemicals is known as Free Available Chlorine (FAC). These compounds are available to oxidize contaminants in pool water. Hypochlorous acid can react with contaminants containing ammonia (NH3), often found in pool water due mainly to perspiration and urine, to form chloramines. Chloramines are the cause of chlorine smell or pool odour and can be a source of irritation to eyes, lungs and skin of swimmers. The strong odour caused by chloramines usually means there is too little free chlorine (hypochlorous acid), rather than too much.
Chloramine formation occurs when hypochlorous acid combines with ammonia to form monochloramine (NH2Cl). Monochloramine can combine further with hypochlorous acid to form dichloramine (NHCl2), and again to form trichloramine (NCl3) as shown below.
HOCl + NH3 ↔ NH2Cl + H20 monochloramine
HOCl + NH2Cl ↔ NHCl2 + H20 dichloramine
HOCl + NHCl2 ↔ NCl3 + H20 trichloramine
Monochloramine is a weaker disinfectant than hypochlorous acid, but more stable; therefore, often used as a disinfectant in the distribution lines of water treatment systems.1 Monochloramine is also the most abundant chloramine when the water is a pH of 7 or higher. Combined Available Chlorine (CAC) refers to chloramines or compounds formed when free chlorine reacts with organic nitrogen-containing compounds produced by bathers. While both FAC and CAC have disinfecting properties, CAC (as monochloramine) has less disinfecting power than FAC.2,3 Total chlorine simply refers to all the FAC and CAC combined in a swimming pool. To be effective, total chlorine should be maintained between 1-3 ppm with the bulk of this as FAC.1
Shock, superchlorination or breakpoint chlorination, is a technique used to control an excess of chloramines by adjusting the pH to 7.5 or lower and by adding sufficient chlorine to achieve a FAC concentration ten times (10-20 ppm) the CAC concentration.4,5 Oxidation of the chloramines occurs which converts to gaseous nitrogen.1 Adding 10 times the level of combined chlorine or chloramines in the water achieves so-called breakpoint chlorination when there is enough extra chlorine to consume the nuisance chloramines which cause odours.
The concentration of hypochlorous acid and hypochlorite ions in chlorinated water will also depend on the water's pH. A higher pH (above 7.5) facilitates the formation of more hypochlorite ions and results in less hypochlorous acid (which is a more effective disinfectant) in the water.1 Therefore disinfection is more efficient at a lower pH (with large quantities of hypochlorous acid in the water). Most recommendations specify a pH range of 7.2 to 7.8 to maintain efficient disinfection but also to prevent eye and skin irritation.6
What are the regulations and guidelines around chlorine levels in swimming pools?
Swimming pool chlorination guidelines and regulations vary across provinces and territories in Canada. Some jurisdictions require minimum free chlorine concentrations, but not maximums; others specify a free available chlorine (FAC) range. The FAC ranges stipulated by these jurisdictions range from 0.8 ppm to 5.0 ppm (see Table 1).
Table 1. Swimming pool and whirlpool FAC and CAC requirements in Canada
||Free Available Chlorine (ppm)
||Combined Available Chlorine (ppm)
||min 0.5 if ≤ 30°C
min 1.5 if > 30°C
||British Columbia 20107
min 1.0 if cyanuric acid is used
min 5 for spas
||min 2.0 for swimming pools
min 3.0 for whirlpools
||min 0.5 if ≤ 30°C
min 1.0 if > 30°C
|< 1.0 in swimming pools
<1.5 in whirlpools
|Yukon Territory 198911
||Show a residual as close to 1.2 as possible, should fall between 1.0 and 1.5 inclusive
|Free chlorine level should reach 10 ppm at least once per day; Nunavut 199012
||Show a residual as close to 1.2 as possible, should fall between 1.0 and 1.5 inclusive
|Free chlorine level should reach 10 ppm at least once per day; Northwest Territories 199013
|Newfoundland and Labrador
1.5 for indoor pools (min 0.5)
3.0 for outdoor pools (min 1.0)
2-3 for whirlpools, spas
Should not be greater than 5 when bathers present
|Legislation only stipulates “…safe and satisfactory bacteriological and chemical quality”; Newfoundland and Labrador 200414
||min 1.0 if ≤ 30°C
min 2.0 if > 30°C
|Prince Edward Island
||1.0-3.0 for swimming pools
min 3.0 for whirlpools
||Prince Edward Island 200516
||0.8-2.0 for indoor pools
0.8-3 for outdoor pools
|< 0.5 for indoor pools
< 1.0 for outdoor pools
||1.0-5.0 for pools and whirlpools
||No guideline or legislation accessed
||Nova Scotia 199819
Looking beyond Canada, a Department of Health swimming pool regulation in San Diego, CA mentions that the FAC level be no more than 10 ppm.20
Also, the U.S. Centres for Disease Control (US CDC) is currently developing Model Aquatic Health Code (MAHC) which may address this issue. However, in email correspondence with the US CDC concerning maximum FAC levels, it was mentioned that although it is common practice to close at 10 ppm, the correspondent was not aware of any “definitive information” to support this level.21
The Department of Health in Sydney, Australia published a swimming pool guideline that recommends all pools, including swimming pools and spa pools, should have a maximum total available chlorine concentration of 10 ppm.22
The WHO indicates that during shock chlorination the pool should be closed to patrons but swimming can resume after the chlorine level has been reduced to < 5.0 ppm; most likely tied to drinking water standards.23
What are the health effects of chlorine and chlorination by-products?
Although chlorine has been used for pool disinfection since the 1920s (due largely to its inexpensive cost and excellent disinfecting properties), there has been an ongoing debate over its safety and its adverse health effects on humans.
A number of dose-response studies, involving animals, discuss the irritating effects of chlorine on eye conjunctiva, skin, and nasopharyngeal mucosa. A study by Mood et al (1951)24 showed that irritant effects on eye conjunctiva began at a concentration of about 8 ppm of FAC, whereas another study25 showed no reaction at 0-8 ppm FAC, uncertain reaction at 16 ppm FAC, and a clear reaction at 20 ppm FAC. With chloramines, on the other hand, the irritant effects began at a lower concentration of 2 ppm24 and 3 ppm25 with severe reaction occurring at 5 ppm.25 Severe lysis, or breakdown of membrane cells occurred at a concentration of 9.8 ppm free chlorine, and 6.3 ppm of combined chlorine.26
Exposure to chlorine and chlorination by-products can occur through ingestion of pool water; some drinking water guidelines provide maximum acceptable concentrations (MAC) for chemicals in water.27 However, risk assessment methods used to set these levels are based on long-term exposure to a standard volume of water (usually 2 litres/day in a healthy adult). Pool patrons do not normally ingest 2L of pool water while at the pool on a given day. The average bather may ingest approximately 10 millilitres (mL) of pool water while swimming and 3.7 mL while wading/splashing.28 Therefore exposure through the ingestion of swimming pool water is likely to be much lower.
Health Canada does not specify a MAC guideline for chlorine in water, due to insufficient evidence for health effects associated with ingestion of chlorine in drinking water.29 On the other hand, the WHO established a guideline value of 5 ppm in drinking water.27 Therefore, at recommended swimming pool FAC levels (ranging from 0.8-5.0 ppm according to swimming pool guidelines and regulations across Canada), ingestion of pool water does not have adverse health effects on bathers. In fact, past incidents have shown that short-term consumption of water with chlorine concentration as high as 50 ppm posed no ill effects, and consumption of water with greater than 90 ppm of chlorine resulted in momentary constriction of the throat and irritation of the mouth and throat.29
Inhalation and dermal exposure
A number of outbreaks involving the inhalation of aerosolized chlorine by-products at improperly chlorinated pool facilities or accidental release of chlorine gas have been documented.30-33 In addition, there are also reports of occupational asthma in pool workers as a result of aerosolized chlorine by-products, notably nitrogen trichloride (trichloramine). Common symptoms of chlorine inhalation include cough, throat irritation, wheezing, difficulty breathing, sneezing, headache, rash, nausea, and vomiting. Occupational asthma can also result from prolonged exposure to chloramines in indoor swimming pool air. Two such case studies were documented where exposure to airborne nitrogen trichloride resulted in occupational asthma, which improved when the employees were away from the swimming pool atmosphere.30,34
Chlorine by-products, including trihalomethanes (THM) and nitrogen trichlorides (trichloramines), have been mentioned as culprits for health effects in bathers. THMs are volatile, and their air concentration depends on several factors: concentration in the pool, temperature, amount of splashing and surface disturbance, ventilation, size of facility, and air circulation.23 Nitrogen trichlorides (trichloramines) are also volatile, therefore, more likely to be found in the atmosphere of swimming pools than monochloramines and dichloramines, which are more likely to be aerosolized through splashing and surface disturbances.34
A study conducted by Hery et al. (1995)31 monitored the atmosphere in 13 swimming pools, and interviewed lifeguards and other pool workers regarding irritation symptoms, in order to establish a recommended maximum allowable airborne concentration of nitrogen trichlorides. They found that the first irritation complaints registered at around 0.5 ppm of nitrogen trichlorides in the air, and at 0.7 ppm, all individuals reported irritation symptoms.31 No information is available on the concentrations of FAC or CAC in water that may relate to these air concentrations.
Kaydos-Daniels (2007)32 and Safranek (2006)33 describe two incidences involving exposure to chloramines. The first incident occurred in West Virginia in 2002. Guests at a hotel attended a birthday party at an indoor swimming pool and reported symptoms consistent with chloramine exposure. Further investigation revealed that while FAC levels were within the acceptable range of 1.0-5.0 ppm, both combined chlorine and pH were beyond the acceptable range prescribed by the city; CAC was found to be ≥ 0.7 ppm, and pH of the water was found to be ≥ 8.5.32 The symptoms were strongly attributed to exposure to pool water and atmosphere in the pool room. The second incidence occurred in Nebraska in 2006.33 Guests reported symptoms including burning eyes, sore throat, watery eyes, coughing, sneezing, burning inside the nose, chest tightness, and shortness of breath. Inspection of the pool found the FAC to be 0.8 ppm; the CAC was 4.2 ppm, and the pH was 3.95.33 All of these levels were in violation of the Nebraska health code.
So where did the common practice of closing pools at 10 ppm FAC come from?
No literature was found to provide concrete evidence for the closure of pools at a free chlorine level of 10 ppm; however, based on Eichelsdörfer’s animal study (1975)25 on eye irritation, 8 ppm appears to be the NOAEL (no observable adverse effect level) for FAC on eye conjunctiva. Additionally, Erdinger et al. (1998)26 showed that severe lysis of membrane cells occurred at 9.8 ppm of FAC. Therefore, these two studies could potentially provide a plausible reason for the 10 ppm FAC limit.
The literature does provide some information concerning disinfection and health effects at different levels of free available chlorine (FAC) and combined chlorine CAC or chloramine levels. Most provincial regulations in Canada specify a minimum level or range of FAC and a maximum level of combined chlorine CAC or chloramines but do not specify a maximum level of FAC at which a pool should be closed. Manitoba, for instance, has a FAC range from 1 to 5 ppm which was the highest specified range of the provinces and territories reviewed. San Diego Department of Health guidelines recommend that there be no more than 10 ppm FAC.20 While the US CDC recognises this limit is used elsewhere in practice, they were not aware of any definitive evidence as to why. The city of Sydney, Australia is the only known jurisdiction that actually specifies 10 ppm as the upper limit for chlorine.
If CAC rises beyond acceptable levels, generally above 0.2 ppm, the pool can be superchlorinated by adding excess chlorine up to 10 times the CAC level to reduce chloramines (references sometimes specify 10 ppm).22 This level may be where the 10 ppm limit originated.
Health effects of free chlorine and chloramines indicate that irritation can occur at levels below 10 ppm but are generally for combined chlorine levels or chloramines. The World Health Organization (WHO) does report that swimming can resume once the FAC reaches 5 ppm but this may be based on ingestion (WHO drinking water guidelines specify that FAC levels should be below 5 ppm).23 Since exposure via ingestion during swimming is significantly lower, this does not provide necessary evidence for setting a limit.
In conclusion, while there is no specific evidence to support the 10 ppm level used as an upper limit for pool closures based on health effects through ingestion, inhalation, and dermal exposure, animal studies on eye irritation do provide some evidence for the 10 ppm FAC limit. Important factors to consider are the combined chlorine levels (chloramines), to which most of the health impacts are attributed during swimming, and maintaining appropriate pH levels, which affect chloramine production and effectiveness of disinfection.
We would like to thank the following individuals for their valuable input and review of this document: Tina Chen and Sylvia Struck for content; Nelson Fok, Tom Kosatsky, and Ralph Stanley for input and review.
- Salter C, Langhus DL. The chemistry of swimming pool maintenance. J Chem Educ. 2007;84(7):1124.
- Fok N (Alberta Health Services). Disinfection power of monochloramine versus free available chlorine. Email communication. Shum M, Stanley R, Chen T, Struck S. (National Collaborating Centre for Environmental Health, Vancouver, BC); 2011, March 15.
- Stachecki J, De Haan W. Swimming pool pest management: A training guide for commercial pesticide applicators & swimming pool operators. East Lansing, MI: Michigan State University; 1997.
- American Chemistry Council. Chloramines: Understanding "pool smell" Washington, DC: AMC; 2006 [cited 2011 February 28].
- New South Wales Government. Controlling chloramines in indoor swimming pools (factsheet) North Sydney, NSW, Australia: NSW Government; 2010 [cited 2010 February 28].
- Centers for Disease Control and Prevention. Healthy swimming/recreational water Atlanta, GA: U.S. Department of Health and Human Services; 2010 [cited 2011 February 24].
- Pool regulation, B.C. Reg. 296/2010. Public Health Act. Government of British Columbia.(2010).
- Public pools, R.R.O. 1990, Reg. 565. Health Protection and Promotion Act. Government of Ontario.(2007).
- Public spas, O. Reg. 428/05. Health Protection and Promotion Act. Government of Ontario.(2005).
- Swimming pool regulations, 1999, R.R.S. c. P-37.1 Reg. 7. Government of Saskatchewan.(2006).
- Public pool regulations, Y.O.I.C. 1989/130. Public Health Act. Government of Yukon Territories.(1989).
- Public Pool Regulations, R.R.N.W.T. (Nu.) 1990 c. P-21. Public Health Act. Government of Nunavut.(1990).
- Public pool regulations, R.R.N.W.T. 1990, c. P-21. Public Health Act. Government of the Northwest Territories.(1990).
- Newfoundland and Labrador. Public pools water quality & record keeping standards. St John's, NL: Government of Newfoundland and Labrador, Department of Health and Community Services; 2004 Mar.
- Swimming pool, wading pool and water spray park regulation, Alberta Regulation. 293/2006. Public Health Act. Government of Alberta.(2006).
- Swimming pool and waterslide regulations, P.E.I. Reg. EC93/01. Public Health Act. Government of Prince Edward Island.(2005).
- Regulation respecting water quality in swimming pools and other artificial pools, 2006 G.O.Q. 2, 3930. Environmental Quality Act. Government of Quebec.(2006).
- Swimming pools and other water recreational facilities regulation, Manitoba Regulation. 132/97. Public Health Act. Government of Manitoba.(1997).
- Nova Scotia. Safety supervision guidelines for public swimming pools In Nova Scotia. Halifax, NS: Government of Nova Scotia; 1998.
- San Diego Department of Environmental Health. Pool and spa terms and maintenance information. San Diego, CA: County of San Diego, Food and Housing Division; 2007. Report No.: DEH:FH-374
- Lee Tate (U.S. Centers for Disease Control and Prevention). Pool upper limit for FAC. Email communication. Struck S. (National Collaborating Centre for Environmental Health, Vancouver, BC); 2011, March 8.
- Department of Health NSW. Public swimming pool and spa pool guidelines. North Sydney, NSW, Australia: NSW Government; 1996 June.
- World Health Organization. Guidelines for safe recreational waters. Geneva, Switzerland: WHO; 2008a.
- Mood E, Clarke C, Gelperin A. The effect of available residual chlorine and hydrogen-ion concentration upon the eyes of swimmers. Amer J Hygiene. 1951;54:144-9.
- Eichelsdörfer D, Slovak J, Dirnagl K, Schmid K. Irritant effect (conjunctivitis) of chlorine and chloramines in swimming pool water. Vom Wasser. 1975;45:17-28.
- Erdinger L, Kirsch F, Sonntag H-G. Irritant effect of disinfection byproducts in swimming pool water. Zentralblatt fuer Hygiene und Umweltmedizin. 1998;200:491-503.
- World Health Organization. Guidelines for drinking-water quality. Geneva, Switzerland: WHO; 2008b.
- Dorevitch S, Panthi S, Huang Y, Li H, Michalek AM, Pratap P, et al. Water ingestion during water recreation. Water Res. 2011;45:2020-8.
- Health Canada. Guidelines for Canadian drinking water quality - Chlorine guideline technical document. Ottawa, ON: Health Canada; 2009 June.
- Dang B, Chen L, Mueller C, Dunn K, D A, J R, et al. Ocular and respiratory symptoms among lifeguards at a hotel indoor waterpark resort. J Occup Environ Med. 2010;52(2):7.
- Hery M, Hecht G, Gerber JM, Gendre JC, Hubert G, Rebuffaud J. Exposure to chloramines in the atmosphere of indoor wwimming pools. Ann Occup Hyg. 1995;39(4):427-39.
- Kaydos-Daniels SC, Beach MJ, Shwe T, Magri J, Bixler D. Health effects associated with indoor swimming pools: A suspected toxic chloramine exposure. J Royal Inst Public Health. 2007(122):195-200.
- Safranek T, Semerena S, Huffman T, Theis M, Magri J, Török T, et al. Ocular and respiratory illness associated with an indoor swimming pool - Nebraska, 2006. MMWR Morb Mortal Wkly Rep. 2006;56(36):929-32.
- Thickett K, McCoach J, Gerber J, Sadhra S, Burge P. Occupational asthma caused by chloramines in indoor swimming-pool air. Eur Respir J. 2002 May;19(5):827-32.