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From the Centers for Disease Control and Prevention
June 24, 2009

Pool Chemical–Associated Health Events in Public and Residential Settings—United States, 1983-2007

JAMA. 2009;301(24):2543-2545. doi:

MMWR. 2009;58:489-493

1 figure, 1 table omitted

Swimming is the second most popular exercise in the United States, with approximately 339 million swimming visits to recreational water venues, including disinfected ones (e.g., pools, water parks, and interactive fountains), each year.1 Pool chemicals* are added to the water in these venues to prevent transmission of infectious pathogens. These chemicals can cause injury when handled inappropriately or when operators fail to use appropriate personal protective equipment. This report summarizes 36 pool chemical–associated health events reported to the New York State Department of Health (NYSDOH) for public aquatic venues during 1983-2006 and includes analyses of 1998-2007 data from the National Electronic Injury Surveillance System (NEISS) and 2007 data from the National Poison Data System (NPDS). NYSDOH reported primarily summertime health events resulting in acute respiratory illness. NEISS and NPDS data revealed that pool chemical–associated injuries or exposures led to thousands of estimated annual emergency department (ED) visits or actual poison center consultations, respectively. These pool chemical–associated health events can be prevented through (1) improved design and engineering and (2) education and training that stresses safe pool-chemical handling and storage practices and safe and preventive maintenance of equipment.

New York State Surveillance

Since 1948, NYSDOH has mandated the reporting of injury or illness occurring at public aquatic facilities. Since 1986, events resulting in (1) death, (2) referral to hospitals or other facilities for medical attention, or (3) illness associated with water quality, specifically must be reported. NYSDOH conducted a retrospective review of reports on pool chemical–associated injuries for the period 1983-2006. Subsequently, NYSDOH reported 36 pool chemical–associated health events (range: 0-4 events/year) to CDC's Waterborne Disease and Outbreak Surveillance System (WBDOSS).2 These health events were characterized by acute respiratory illness (34 [94%]) and affected a median of five persons (range: 1-91 persons), with no deaths reported. The reported health events occurred in schools or colleges (13 [36%]), membership clubs (10 [28%]), housing complexes or hotels (six [17%]), community aquatic facilities (five [14%]), and institutions (two [6%]). The majority of events (31 [86%]) occurred in settings where pools might be viewed as an amenity (i.e., not in a community aquatic facility). Twenty-one (58%) occurred during the summer swim season, from Memorial Day through Labor Day. Five events (14%) involved direct exposure to chlorine bleach or acid. The other 31 health events (86%) resulted from exposure to toxic chlorine gas. Of these 31 events, 27 (87%) were caused by exposure to chlorine gas generated by mixing incompatible pool chemicals, most frequently chlorine bleach and acid (24 [89%]). The primary contributing factors to the 36 events were poor chemical handling or storage practices (25 events [69%]), poor equipment maintenance practices (six [17%]), poor facility design and engineering (four [11%]), and unknown (one [3%]). Two New York state health events that illustrate the contributing factors follow.

Poor Facility Design and Engineering

In 1988, the main recirculation pump of an outdoor community pool shut down after a momentary power outage. However, the chlorine bleach and acid† delivery pumps continued running, allowing chlorine bleach and acid to mix within the piping without dilution. When the recirculation pump was restarted, the chlorine gas generated in the static water return lines vented in the shallow end of the pool. Consequently, according to the police report, 21 children were taken to the hospital for difficulty breathing; of these, three were admitted to the pediatric intensive-care unit and seven to the general pediatric unit. Emergency response required seven ambulances, two paramedic units, and 11 police officers. This and similar events supported New York state pool code revisions requiring installation of a device that automatically deactivates chlorine bleach and acid delivery pumps when no water is flowing in the recirculation system.3

Poor Chemical Handling or Storage Practices

In 1995, a custodian maintaining the indoor school pool ordered 5-gallon containers of chlorine bleach but instead received 5-gallon containers that looked the same but contained acid. Two custodians reported failing to read the product labels and mistakenly pouring acid into the chlorine bleach tank, thus generating chlorine gas. The school was evacuated; at least 81 students, likely exposed to gas spread through the ventilation system, and the two custodians were taken to the hospital with acute respiratory symptoms. Emergency response involved multiple fire departments and government agencies (e.g., the county disaster office). NYSDOH consequently developed a health education campaign focused on safe chemical handling and storage practices.

National Surveillance Systems

The U.S. Consumer Product Safety Commission's NEISS captures data on ED visits for injuries associated with consumer products, such as pool chemicals. NEISS records include NEISS product codes (pool chemical code: 938); primary diagnosis; primary injured body part; disposition; incident location; age, sex, and race/ethnicity of the patient; and brief narratives describing activities leading to injury. The program collects these data from a nationally representative probability sample of approximately 100 hospitals in the United States.4 Each case was weighted based on the inverse probability of the hospital being selected, and the weights were summed to produce national estimates. Rates per 100,000 population were calculated using these estimates and U.S. Census Bureau population estimates; 95% confidence intervals were calculated using statistical software that accounted for the sample weights and complex sampling design. During 1998-2007, the estimated median number of annual ED visits for pool chemical–associated injuries was 4,120 (range: 3,315-5,216). In 2007, an estimated 4,635 persons (1.5 per 100,000 population [95% confidence interval = 1.0-2.1]) visited the ED for pool chemical–associated injuries. More than half (58% [2,698 (range: 1,992-3,404)]) of the estimated injuries occurred during the summer swim season. Some patients inhaled chemical fumes (38 [33%] of the 115 actual NEISS ED visits) when opening pool chemical containers, attempting to predissolve pool chemicals, or handling chemicals; eye injuries resulting from pool chemicals splashing also occurred (22 [19%] of 115). No deaths were documented.


The American Association of Poison Control Centers maintains the NPDS, which collects real-time exposure data from the majority (60 of 61) of poison centers. During 2007, the poison centers received calls regarding 9,573 human exposures to a single pool or aquarium chemical.5‡ Of these exposures, 39% (3,775) involved persons aged <6 years, 97% (9,287) were unintentional, and 19% (1,781) resulted in injuries for which patients sought health-care treatment. No deaths were documented.

Reported by:

DC Sackett, EJ Wiegert, JS Egan, MPH, DC Nicholas, MPH, Bur of Community Environmental Health and Food Protection, New York State Dept of Health. MC Hlavsa, MPH, MJ Beach, PhD, Div of Parasitic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases; J Gilchrist, MD, Div of Unintentional Injury Prevention, National Center for Injury Prevention and Control, CDC.

CDC Editorial Note:

Operation of public aquatic venues requires balancing different risk reduction plans to protect the health of staff members and patrons. Since the 1920s, chemical disinfection and filtration have served as the primary barriers to waterborne pathogen transmission at aquatic venues. However, the need for chemical disinfection to control waterborne disease outbreaks must be balanced with reducing the number of injuries associated with use of these same chemicals. With the increasing number of reports of recreational water–associated outbreaks, public pool operators and residential pool owners need to remain vigilant in maintaining good water quality and disinfection to protect swimmer health.2

Reporting of pool chemical–associated health events in the United States is not universally mandated, and no single surveillance system exists to characterize completely the number of exposures or associated injuries. The national NEISS and NPDS data presented in this report indicate that pool chemical exposures and associated injuries are common. Although no one data source alone elucidates completely the epidemiology of pool chemical–associated injuries, together they reveal multiple commonalities that suggest these injuries are preventable. Poor chemical handling and storage practices at public aquatic venues, particularly those leading to mixing of incompatible chemicals, were the primary contributing factors to New York state health events. Data from NEISS show that inhalation of chemical fumes and splashing pool chemicals into the eyes were the primary pool chemical–associated injuries for which patients sought ED treatment. Finally, NPDS data reveal that nearly all single pool chemical exposures likely were unintentional.

New CDC recommendations for preventing injuries associated with pool chemicals were based on a review of the health events and data in this report and other government regulatory guidance.6 These recommendations focus on improving (1) facility design and engineering and (2) education and training (see Box) that stresses safe chemical handling and storage practices and safe and preventive maintenance of equipment.

BOX. CDC recommendations for preventing pool chemical–associated injuries for public pool operators and residential pool owners*

  • Learn about pool chemical safety

    Always read entire product label or material safety data sheet (MSDS).

    Always complete appropriate training or education.

  • Store pool chemicals safely

    Always secure chemicals away from children and animals.

    Always store chemicals as recommended by the manufacturer.

    Always protect stored chemicals from mixing or getting wet.

    Always respond to pool chemical spills immediately.

  • Use pool chemicals safely

    Always read product label and manufacturer's directions before each use.

    Always use chemicals in manufacturer's original, labeled container.

    Always use appropriate protective gear, such as safety glasses and gloves.

    Never predissolve solid chemicals or add water to liquid chemicals.

    Never mix chlorine products with each other, with acid, or with any other substance.

*Additional information available at http://www.cdc.gov/healthyswimming/pdf/pool_chem_assoc_inj.pdf.

The NYSDOH reports illustrate that these health events at public aquatic venues can injure a large number of persons and likely are preventable through appropriate education and training (e.g., instructing persons to never mix chlorine products with acid). Previous studies underscore that requiring pool operator training can reduce the number of water-quality violations.7,8 Future prevention efforts should require training for all public pool operators. The disproportionate (86%) number of pool chemical–associated health events occurring in settings where pools were not the primary focus (e.g., schools or hotels) specifically calls for emphasizing training efforts in these settings. Additionally, because at least 43% of ED-treated, pool chemical–associated injuries occurred at a residence, messages about safe chemical handling and storage, particularly the use of personal protective equipment (e.g., safety glasses and appropriate masks), also should target residential pool owners.

Health departments conducting or considering surveillance of pool chemical–associated injuries might consider formalizing mechanisms to capture data from emergency response agencies. This could increase the representativeness of the data by increasing detection of events that otherwise might not be reported. Data completeness and validity also might improve because emergency responders often are on scene soon after these health events occur.

Pool codes governing aquatic venue design, construction, operation, and maintenance are written and approved by state and/or local officials. No single federal agency is responsible for regulating treated aquatic venues. To raise national awareness and minimize the occurrence of preventable health events, CDC supports the development of a nonregulatory, model aquatic health code (MAHC).9 The MAHC effort, currently led by NYSDOH, will produce a code for voluntary adoption by health jurisdictions as individual modules are finalized. The MAHC is designed to be a data-driven, knowledge-based, national model pool code that balances the control measures needed for both waterborne disease transmission and safe chemical use.


The findings in this report are based, in part, on contributions by staff members in local health departments and first responder units in New York State; and JS Yoder and V Roberts, Div of Parasitic Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, and J Carpenter, Div of Healthcare Quality Promotion, National Center for Preparedness, Detection, and Control of Infectious Disease, CDC.

*The term “pool chemicals” includes but is not limited to chlorine bleach (calcium hypochlorite or sodium hypochlorite used to make a hypochlorous acid solution), stabilized chlorine (dichlor-s-triazinetrione or trichloro-s-triazinetrione), bromine (hypobromous acid), hydrogen peroxide, and hydrochloric (muriatic) acid.

†Typically, hydrochloric acid or another acid is added to swimming pools to maintain pH at 7.2-7.8 to improve the disinfection efficacy of chlorine bleach.

‡Report cited in reference aggregates statistics for exposures to pool and aquarium chemicals.

US Census Bureau.  2009 statistical abstract of the United States. Recreation and leisure activities: participation in selected sports activities 2006. Available at http://www.census.gov/compendia/statab/tables/09s1209.pdf
CDC.  Surveillance for waterborne disease and outbreaks associated with recreational water use and other aquatic facility-associated health events—United States, 2005-2006.  MMWR. 2008;57(SS-9):
New York State Department of Health.  Official compilation of codes, rules, and regulations of the state of New York (NYCRR), Title 10 (health), state sanitary code, subpart 6-1, section 6-1.29, item 11.7.  Available at http://www.health.state.ny.us/nysdoh/phforum/nycrr10.htm
National Electronic Injury Surveillance System.  Estimates query builder [Internet]. Bethesda, MD: US Consumer Product Safety Commission; 2009. Available at https://www.cpsc.gov/cgibin/neissquery/home.aspx
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CDC.  Recommendations for preventing pool chemical–associated injuries. Available at http://www.cdc.gov/healthyswimming/pdf/pool_chem_assoc_inj.pdf
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Johnston K, Kinziger M. Certified operators: does certification provide significant results in real-world pool and spa chemistry?  Int J Aquatic Res Educ. 2007;1:18-33
CDC.  Model aquatic health code. Available at http://www.cdc.gov/healthyswimming/mahc/model_code.htm