June 16, 2019
In 2006, a six-year-old boy from Nebraska was hospitalized in an intensive care unit with respiratory distress after swimming in a public indoor pool on Christmas Day. An investigation by the local health department revealed 24 other people had become sick after swimming in the same pool. In 2007, more than 660 people suffered from respiratory and eye irritation after visiting or working at a new indoor waterpark in Ohio. Seventy-nine of those people became sick within the first month of the waterpark opening. A 2017 study published in the International Journal of Environmental Health Research found lifeguards who worked at indoor aquatic facilities more than 500 hours per year were much more likely to suffer from respiratory illnesses than lifeguards who worked fewer hours—clearly highlighting indoor pool environments can have adverse health effects on the respiratory system.
Why is this happening? As large indoor aquatic facilities with pools, waterparks, and other aquatic attractions continue to be built and frequented across North America, so do related reports of adverse health events. In fact, between 2000 and 2014, the Centers for Disease Control and Prevention (CDC) reported 22 outbreaks and more than 1000 cases of illness linked to pool chemistry at public aquatic facilities. The culprits are likely the chemical compounds known as volatile disinfection byproducts, like trichloramine.
Disinfection byproducts are formed when disinfectants used to kill germs, such as chlorine, react with other compounds in water; in pools, these are generally associated with body wastes swimmers bring into the water (e.g. sweat and urine). Researchers have identified more than 100 disinfection byproducts in pool water. Some of these are volatile and harmful to people’s health. When volatile compounds build up in the water, they can escape into the air over the pool. Volatile compounds can accumulate in the air above the water’s surface where swimmers, aquatic staff, and spectators can breathe them in. The extent to which this happens depends in part on the characteristics of the facility’s air handling system. Accumulation of volatile compounds can lead to outbreaks of illness impacting hundreds of people.
Researchers have identified at least 11 volatile disinfection byproducts common to chlorinated pools (see Table 1). These include inorganic chloramines, like trichloramine, along with several trihalomethanes, several halogenated nitriles, and at least one organic chloramine compound. The volatile compounds form when free chlorine reacts with certain precursor compounds in the water—mainly urea, uric acid, creatinine, and amino acids (mostly associated with sweat and urine).
|Inorganic Chloramines||NCl3, NHCl2, NH2Cl|
|Halonitriles||CNCl, CNBr, CNCHCl2|
|THMs||CHCl3, CHBrCl2, CHBr2Cl, CHBr3|
Volatile disinfection byproducts become most harmful to respiratory health when they transfer from liquid to gas form. There are multiple factors that increase the potential for this transfer to occur. One is the water quality, or the concentration of the volatile disinfection byproducts in the water. As the concentration builds up in the water, so does the potential for the transfer of the compounds from a liquid to a gas phase.
Mixing of water and air in an indoor aquatic facility also increases the transfer of volatile compounds to the air. The mixing processes are affected by several aspects of pool operations, including:
Swimmers and water or spray features are more effective than routine water circulation at transferring compounds from liquid to gas phase. This is one of the reasons why the concentration of volatile compounds in the air is often higher right after an increase in the number of swimmers.
Breathing in volatile compounds can lead to a variety of health issues—not only for swimmers, but also for spectators, or those working at the facility. These may include:
These health issues can be particularly harmful to children, people with existing respiratory illnesses, or others who are immunocompromised, with resulting visits to emergency rooms and intensive care units.
The design and operation of indoor pool water treatment and air handling systems should provide a healthy and safe environment for the swimmers, workers, and spectators. However, existing design and operational criteria are not keeping up with current use, activities, aquatic features, and building construction requirements to provide this healthy environment. More research is needed to determine how to best prevent these types of adverse health events from occurring at indoor aquatic facilities.
The Council for the Model Aquatic Health Code (CMAHC) has partnered with Purdue University and Michigan State University to conduct a study that will identify operating conditions for indoor pools that will help prevent the buildup of volatile compounds in the air and lead to air quality measurements known to be safe for swimmers and patrons. CMAHC’s indoor aquatic facility ventilation design and air quality ad hoc committee, comprised of leaders in the public health and the aquatic industry, saw a widening gap between existing ventilation standards in indoor aquatic facilities and growing aquatic needs. The committee is working with Ernest R. Blatchley III, Lee A. Rieth, professor in environmental engineering at Purdue University and principal investigator of the study, to collect data that will illustrate relationships between the operational features of indoor pool facilities and air quality.
Specifically, the study will focus on identifying design and operational characteristics that will allow indoor pools to stay at or below the safe concentrations of trichloramine in the air. The physical and chemical characteristics of trichloramine dictate it will behave similarly to other volatile compounds in indoor aquatic facilities. Therefore, it is likely the conditions that lead to effective control of trichloramine will also effectively control other volatile compounds.
The study is being conducted as a three-phase project. The first phase involves measuring water and air quality at indoor aquatic competition venues in Michigan and Indiana before and during competition events with a large number of swimmers. Researchers will compare the water and air quality measurements to determine the impact of heavy bather load.
This phase is already underway. So far, the data collected demonstrates how the number of swimmers in a pool (bather load) affects the concentration of trichloramine in the air. The measurements of trichloramine in the air with corresponding measurements of bather load in two pools that share a common air space is illustrated in Figure 1.
There is an obvious, strong correlation between air concentrations of trichloramine and the number of swimmers in the pool.
Phase two, expected to last an additional three months, will focus on continued monitoring and analysis of air and water quality from chlorinated, indoor pool facilities that are used for lap swimming and competitions. Phase three, expected to last 12 months, will include research at roughly 15 additional facilities selected for inclusion based on the results of a two-stage survey approach. The first stage of the survey will identify pool operators who are interested in offering their facility for participation. The second stage will involve a screening of the facilities to identify venues that span a wide range of use types and geographic locations. Factors that will be considered in the selection include pool type and bather load, the facility’s air handling system, the characteristics of water recirculation in the pool, and various water treatment processes.
Pool operators who are interested in offering their facility for inclusion in the study may complete the survey at www.cmahc.org/air-quality-survey.php. All facilities will remain anonymous. Phase two and three of the study is contingent based on available funding.
For each phase of the study, researchers will collect information about the facilities’ water and air quality, and pool operation. Data collection will occur at each pool for a period of one to two weeks. The following are brief descriptions of how researchers will measure and collect this data.
Researchers will collect water samples from each pool twice per day. The first samples will be collected early in the morning, before swimmers arrive, and the second will be collected later in the day, after a period of heavy bather loads. Researchers will analyze the water samples for:
Researchers will use a recently developed monitoring device called NEMo to collect real-time measurements of the indoor air quality at each facility, including relative humidity and concentrations of trichloramine, carbon dioxide, and volatile organic compounds (VOCs). While useful for this study, NEMo is costly to operate and might not be an option for some facilities to use in daily operations. Thus, researchers will also be collecting complementary measurements of each aspect of indoor air quality using less expensive instruments, including relative-humidity temperature meters, carbon dioxide sensors, and VOC sensors.
There are multiple characteristics of pool operation that influence the buildup of volatile compounds in the air within an indoor aquatic facility. Researchers will collect information about each of the following characteristics:
The research team will use the information collected during the study to develop a mathematical model that will describe the behaviour of trichloramine in indoor pool facilities. A schematic illustration of the mathematical model, which will include information about air and water quality, water treatment processes, the types of pools including presence of any water features and bather load, and the air handling system can be seen in Figure 2.
This model will help researchers develop updated guidance on the proper design and operation of indoor pools for acceptable air quality, which will be used to update the CDC’s MAHC.
The MAHC is CDC’s voluntary guidance document that brings together the latest knowledge based on science and best practices to help develop and update pool codes. The guidance is all-inclusive and covers design, construction, operation, and management of public aquatic facilities. If followed, the guidelines in the MAHC can help reduce risk for disease outbreaks, chemical injuries, and drownings.
As the only national all-inclusive model pool code, the MAHC is the ideal vehicle to use for promoting the indoor air quality standards for pools across the country. As of March 16, 2019, there have been five majority adoptions and seven partial adoptions of the MAHC by five states, three counties, and three U.S. government agencies. At least 22 states/counties are in the process of, or considering, adoption.
The current indoor aquatic facility air handling system design, and construction and installation requirements in the MAHC, including minimum outdoor air requirements, specify compliance with American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard 62.1, Ventilation for Acceptable Indoor Air Quality. However, reports of health issues linked to air quality at indoor pools are continuing to emerge, concerning members of the aquatic industry and public health alike. This led members of the CMAHC to form the indoor aquatic facility ventilation design and air quality ad hoc committee. The committee’s charge is to:
1. Identify and assess factors affecting air quality.
2. Review and evaluate current MAHC requirements to determine if identified factors are adequately addressed.
3. Develop revisions to the MAHC to better address ventilation/air quality design and operational criteria. The lack of needed supporting data regarding the various factors led to the request to conduct the indoor air quality study.
The committee will use the results of the study to propose changes to the indoor air quality guidelines in the MAHC and also share with ASHRAE for their consideration in revising its standards. Members of the CMAHC will vote on these changes at a subsequent triennial CMAHC conference. If the changes pass the vote, the CMAHC will submit them to CDC for approval and inclusion in the next edition of the MAHC. Members of the aquatic industry can join the CMAHC and vote on proposed changes to the MAHC by visiting the CMAHC website at www.cmahc.org.
Doug Sackett is the executive director of the Council for the Model Aquatic Health Code (CMAHC). He has held this position since October 2014. He worked in the pool and bathing beach programs in addition to numerous other environmental health regulatory programs throughout his 38 years with the New York State Department of Health before retiring in 2013. Beginning in 1987, he was involved in the management of the statewide pool and bathing beach regulatory program, including the co-ordination of investigations of illnesses associated with recreational water and drowning at regulated pools and beaches throughout the state and for the analysis of the data from these epidemiological investigations. Sackett was the director and steering committee member for the Centers for Disease Control and Prevention’s (CDC’s) project to develop the national Model Aquatic Health Code (MAHC) from its inception in 2007 until the first edition was launched in August 2014. He was instrumental in setting up the CMAHC as the vice-president and treasurer of the interim CMAHC board of directors. He can be reached via e-mail at email@example.com.
Ernest R. Blatchley III is the Lee A. Rieth professor in environmental engineering in the Lyles School of Civil Engineering and division of Environmental & Ecological Engineering at Purdue University. He received his bachelor of science from Purdue University, with masters and doctorate degrees from the University of California, Berkeley, all in civil (environmental) engineering. Professor Blatchley conducts research and teaches in the general area of physico/chemical processes of environmental engineering. Particular areas of focus include theory and applications of ultraviolet (UV) radiation, chlorine, or combinations of these agents in water treatment, either for disinfection of or transformation of chemical contaminants. As an application of these principles, Professor Blatchley and his group have been active in research that addresses pool chemistry, especially as related to volatile disinfection byproducts. He can be reached via e-mail at firstname.lastname@example.org.
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