Dang, Bich MD; Chen, Lilia MS; Mueller, Charles MS; Dunn, Kevin H. MS; Almaguer, Daniel MS; Roberts, Jennifer L. BS; Otto, Charles S. MPS
The hotel indoor waterpark resort industry is rapidly growing. The first hotel indoor waterpark resort opened in 1994, and by 2007, there were an estimated 184 facilities nationwide.1 Many indoor waterparks have extensive splash features that aerosolize water contaminants and may introduce more risk for recreational water illness than typical indoor pools.
Trichloramine exposure has been suspected as the cause of eye and respiratory irritation at indoor pool facilities.2–4 Chloramines are disinfection by-products formed when chlorine combines with nitrogen-containing compounds like sweat and urine. Chloramines include monochloramine, dichloramine, and trichloramine. Trichloramine is the most volatile and is the main chloramine compound detected above chlorinated water surfaces.5 It is a strong mucous membrane irritant6 and has been associated with eye and respiratory irritation and asthma in swimmers and pool attendants.7,8
Trichloramine can rapidly accumulate in indoor pools with inadequate ventilation and poor water chemistry control. Increased bather load (number of occupants in the pool) has also been associated with increased levels,9 likely because of increased concentrations of nitrogen compounds from bathers. Other factors affecting airborne trichloramine concentration include aerosolization of water contaminants from splashing and spraying, and air recirculation.7,10,11
During January 2007 to March 2007, eye and respiratory irritation symptoms were reported by patrons and lifeguards of a large hotel indoor waterpark resort. The waterpark opened in December 2006, and within 1 month, the local health department received 79 complaints from patrons and employees. Reported symptoms included cough, wheezing, shortness of breath, chest tightness, sore throat, eye and nose irritation, and skin rashes. The waterpark management responded by inspecting the ventilation and water systems and hiring a consultant to collect chlorine air samples. Water chemistry tests complied with state codes and chlorine air sample concentrations were below the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit of 0.5 part per million (ppm) and the Occupational Safety and Health Administration permissible exposure limit of 1 ppm. Management added supply diffusers to the ventilation system, increased the frequency of water chemistry checks, and added more fresh water to all systems. Despite these changes, the local health department continued to receive complaints from patrons and lifeguards. By March 2007, the local health department had received an additional 586 symptom reports. Exposure to airborne trichloramine was suspected as the cause of symptoms, and the health department's concern over the number of reports prompted a technical assistance request to NIOSH. Because NIOSH's mission is to assure safe and healthy working conditions, NIOSH investigators focused their investigation on the waterpark employees.
To determine the scope of symptoms, NIOSH investigators preliminarily interviewed 10 lifeguards. All reported coughing at work, seven reported eye irritation, and three reported nose irritation. One employee reported episodes of flu-like symptoms with cough, fever, and body aches, and one reported intermittent blurry and halo vision, which started after the beginning of the shift and typically resolved within a couple of hours after leaving work. These lifeguards reported that all symptoms were worse when the number of patrons using the waterpark was high and that their symptoms improved on days away from work. NIOSH investigators suspected that trichloramine exposure was the cause of the irritation symptoms. The episodes of cough, fever, and body aches also raised the possibility of either hypersensitivity pneumonitis or Pontiac fever; endotoxin, non-tuberculous Mycobacteria, and Legionella were considered as possible etiologic agents.
The resort includes hotel rooms, an indoor waterpark, a conference center, a fitness center, restaurants, shops, and an arcade. The waterpark measures ∼80,000 sq ft and has 11 waterslides, two activity pools, two hot tubs, a wave pool, a leisure river, a four-story interactive play system, and a variety of features that splash, spray, and aerate large amounts of water. The maximum occupancy for the waterpark is 3,746.
The facility has seven major water systems with a total water volume of 400,000 gallons. Each water system is self-contained with individual monitoring and regulating components that circulate, disinfect, and filter water 24 hours a day. Water flows by gravity from the pools through the main drains and gutter systems into designated surge tanks. Water for the spray features is drawn directly from the surge tanks. Nevertheless, most of the water is pumped out of the surge tanks into the filtration system and processed through diatomaceous filters. The filtered water then passes through a medium pressure ultraviolet lamp unit that breaks down combined chlorine and provides secondary disinfection. Next, water passes through an automated chemical controller system that monitors and maintains pH and free chlorine. The controller injects sulfuric acid solution (to adjust the pH) and sodium hypochlorite solution (to disinfect) into the recirculation pipe. The water is then heated to maintain pool temperature and sent back to the pool through floor diffusers.
Eight air handling units provide heating, dehumidification, and ventilation for the waterpark. The air handling units deliver 100% outdoor air when the outdoor air temperature is above 40°F. Below 40°F, the units recirculate a portion of the air up to 33% with a minimum of 67% outdoor air brought in at all times. Air supply and return registers are located 30 to 80 ft above the deck level.
MATERIALS AND METHODS
Between March 20 and April 24, 2007, exposed individuals (lifeguards working inside the pool area) and unexposed individuals (hotel employees working outside the pool area) completed a questionnaire concerning demographics, workplace information, smoking status, medical history, episodes of pneumonia or chest flu with fever and cough since working at the waterpark, and work-related symptoms within the previous month.
Health outcomes of interest included work-related respiratory symptoms (cough, wheezing, shortness of breath, and chest tightness), mucous membrane irritation (cough, sore throat, and eye and nose irritation), and systemic symptoms (fever and body aches). Participants were asked not to report symptoms associated with a cold or respiratory infection. Symptoms were considered work-related if they occurred on days or evenings the employee worked and improved on days off work. Questions about recurrent episodes of pneumonia or chest flu with fever and cough were used to identify potential cases of hypersensitivity pneumonitis.
On days that chloramine air sampling was conducted, lifeguards completed a daily questionnaire on work-related symptoms. Work-related symptoms were symptoms experienced at work, starting at the beginning, middle, or end of their shift. To assess the effect of bather load on work-related symptoms, we administered daily questionnaires on two high (>1,000) hotel occupancy days and one low (<100) hotel occupancy day. Because a direct counting of bathers was not possible and only hotel guests could access the waterpark, the number of people booked at the hotel (ie, hotel occupancy) was used as a proxy for bather load. March 20 and April 14 were high occupancy days with >1,000 patrons booked, and April 24 was a low occupancy day with less than 100 patrons booked.
Area air samples for chloramines were taken at eight locations ∼3 to 4 ft above the deck level of the indoor waterpark, and a control sample was taken in an administrative office outside the pool area. Personal breathing zone air samples were not taken because of concern that sampling equipment attached to lifeguards could interfere with rescue duties or get wet and malfunction. In addition, air samples placed on lifeguard chairs could not be used to estimate personal exposure because lifeguards rotate through different sections of the waterpark every 30 minutes.
To assess the effect of bather load on air chloramine concentrations, we collected area air samples for chloramines on two high occupancy days and one low occupancy day. Unless specified, the term, chloramines, refers to both trichloramine and soluble chlorine compounds.
On high occupancy day 1, trichloramine concentrations were measured over one 8-hour shift in 4-hour intervals, and the soluble chlorine concentrations were measured in 2- and 4-hour intervals. The soluble chlorine concentrations were measured over varying time periods to assess whether the humidity in the pool area would saturate the sampling media. On high occupancy day 2 and the low occupancy day, both trichloramine and soluble chlorine samples were taken over two consecutive 8-hour shifts in 4-hour intervals, and over a 2-hour interval before the pool opened and after it closed.
Air samples were collected using AircheckTM 2000 sampling pumps (SKC, Eighty Four, PA) calibrated at 1.0 L/min. Sampling pumps pulled air through a sorbent tube that traps soluble chlorine compounds (monochloramine, dichloramine, hypochlorous acid, and hypochlorite) onto silica gel coated with sulfamic acid. The air passes from the sorbent tube through a 37-mm polystyrene cassette loaded with two sodium carbonate and diarsenic trioxide-coated quartz fiber filters to capture trichloramine. Samples were refrigerated in the dark and analyzed within 6 days of collection.
Sample collection and analysis were performed according to the NIOSH draft method, which was adapted from the Institut National de Recherche et de Securite method.12 Samples from the impregnated silica gel tubes were desorbed in 10 mL of a 1.0 g/L sulfamic acid solution, periodically agitated for 30 minutes, decanted, and refrigerated until analysis. Filters were removed from the cassettes, desorbed in 10 mL of deionized water, periodically agitated for 30 minutes, refrigerated, and filtered before analysis. Samples were analyzed for chlorine by inductively coupled plasma-atomic emission spectroscopy.
Air Temperature and Relative Humidity
Temperature and relative humidity were monitored at each chloramine sampling location. Data were recorded every minute using a Hobo® H8 Pro Series data-logger (Onset Computer Corporation, Pocasset, MA).
Bulk water samples for endotoxin were taken poolside at elbow depth from each water filtration system and two of seven surge tanks. Control samples were taken from restroom tap water. Area air samples for endotoxin were collected throughout the waterpark, and a control sample was taken in an office.
Air samples were collected on endotoxin-free three-piece 37-mm closed-face cassettes, preloaded with 0.45 μm pore-size polyvinyl chloride filters connected to AirCheck 2000 personal air sampling pumps calibrated at 2 L/min. Water samples were collected with sterile screw-cap containers free of detectable endotoxin. Endotoxin analysis was performed by Aerotech P&K (Cherry Hill, NJ; Phoenix, AZ) using the Limulus amoebocyte lysate assay.13
Bulk water samples for Legionella, Mycobacteria, and fecal coliform bacteria were taken at elbow depth from nine locations, with at least one sample collected poolside from each water filtration system and two of seven surge tanks.
Bulk water samples of 100 mL were poured into sterile bottles coated with sodium thiosulfate. Samples were kept cold and in the dark until analysis. Analysis for Legionella, Mycobacteria, and fecal coliform bacteria was performed by Microbiology Specialists Inc. (Houston, TX). Total coliforms and Escherichia coli were analyzed by the Colilert® test (Idexx, Westbrook, ME). For Mycobacteria analysis, the samples were concentrated with a centrifuge, placed in a BACTECTM system (BD Diagnostics, Sparks, MD) and monitored weekly for 6 weeks. Simultaneously, the samples were plated on 7H10 agar and cultured. Legionella samples were centrifuged, plated on buffered charcoal yeast extract agar, and cultured for 7 to 10 days.
Pool water was tested for pH, free and total chlorine, and alkalinity. Multiple measurements in each system were taken to identify potential areas of inadequate water circulation. Free and total chlorine levels were measured using a standard color-matching DPD test kit (Taylor Technologies Inc., Sparks, MD), and combined chlorine was calculated by subtracting free chlorine from the total chlorine.14 We also toured the facility and reviewed the construction plans to assess water system design, including water recirculation, filtration, and disinfection processes.
The maintenance manager and the ventilation design contractor were interviewed to obtain information on the ventilation system. The ventilation system serving the pool area, including the air handling units and the supply and return diffusers, was examined. The design drawings were reviewed to assess system layout and to document parameters such as pool and deck area and overall air supply flow rate. Nominal design air supply flow rates specified on the drawings were compared to those measured by a test and balance technician. The total square footage and volume of the indoor waterpark area were calculated and used to compute outside ventilation rates per pool and deck area for comparison with building code and consensus standards.
Statistical analysis was performed with SAS version 9.1.3 software (SAS Institute, Cary, NC). One-way analysis of variance was used to compare the humidity and temperature arithmetic means for various locations in the pool area. A P-value ≤0.05 was considered statistically significant. Mean chloramine concentrations were calculated across location using time-weighted means. To calculate time-weighted means, sampling results that were below the limit of detection (LOD) were assigned a value by dividing the LOD by the square root of two.15 Values between the LOD and limit of quantitation (LOQ) were calculated from the laboratory's best estimate.
Prevalence ratios with 95% CIs were calculated to compare work-related symptoms in the previous month for the exposed and unexposed employees. A prevalence ratio was considered statistically significant if the 95% CI excluded the number 1. Generalized linear models were used to compare respiratory symptoms for the exposure groups while controlling for smoking status (current smoker or not) and asthma status. An employee was defined as having asthma if he or she had it currently, it was diagnosed by a health professional, and it began before starting work at the indoor waterpark.
Prevalence ratios were calculated to compare work-related symptoms for lifeguards on days of high and low hotel occupancy. Generalized estimating equations were used to account for possible correlations between responses when a lifeguard completed questionnaires on more than 1 day. The analyses involving respiratory symptoms were adjusted for smoking status and excluded employees with asthma.
The initial questionnaires were administered to exposed lifeguards and unexposed employees working outside the pool area between March 20 and April 24, 2007. Data analysis was restricted to questionnaires received March 20, 2007, to April 2, 2007, because these days were colder and more representative of the environmental conditions when symptoms were initially reported. Between March 20, 2007, to April 2, 2007, 70 of 103 (68%) exposed lifeguards and 74 of 99 (75%) employees working outside the pool area completed the initial questionnaire. This date restriction excluded data from 12 exposed individuals.
Demographic characteristics are summarized in Table 1. On average, exposed individuals were younger and more likely to be male than unexposed individuals. They were similar in average work hours per week, personal history of asthma diagnosed by a doctor or other health professional before employment at the waterpark, smoking status, and personal history of hay fever or other allergy not due to medications.
Exposed individuals were significantly more likely than unexposed individuals to report work-related respiratory symptoms, fever, body aches, sore throat, and eye and nose irritation during the month before survey completion (Table 2). Exposed employees were also 5.8 times more likely to report an episode of chest flu (defined as fever and cough or pneumonia) since employment at the waterpark. Among exposed employees who reported at least one episode, the average number of episodes was 2.3.
All individuals who reported a history of asthma diagnosed by a doctor or health professional had asthma before working at the waterpark. Six of the 10 exposed individuals who still had asthma reported that their asthma seemed worse at work compared with none of the seven unexposed individuals with asthma.
Daily Symptom Questionnaire
Fourteen of 17 exposed lifeguards (82%) completed the daily symptom questionnaire during the day shift on high occupancy day 1, 29 of 43 (67%) during the day and evening shifts on high occupancy day 2, and 27 of 33 (82%) during the day and evening shifts on the low occupancy day. Most participating lifeguards who worked on the high occupancy days reported work-related cough and eye irritation (Table 3). None reported blurry, foggy, or halo vision on the low occupancy day. In contrast, on high occupancy day 2, 9 of 29 (31%) reported blurry, foggy, or halo vision.
Data from high occupancy days 1 and 2 were combined to compare symptom prevalences on high hotel occupancy days versus the low hotel occupancy day. Working on high hotel occupancy days was associated with a significantly increased likelihood of work-related cough and eye irritation (Table 4). No significant association existed for blue-gray vision, and prevalence ratios could not be defined for blurry, foggy, or halo vision because no one reported those symptoms on the low occupancy day.
Two hundred five area air samples were taken inside the pool area. Summaries of measurements collected on high occupancy days 1 and 2 and the low occupancy day are shown in Tables 5 and 6, which indicate the percentage of samples that fell below the LOD (non-detectable), between the LOD and LOQ (trace), and above the LOQ (quantifiable). The LOD and LOQ values varied greatly between days.
On high occupancy day 1, 16 trichloramine and 22 soluble chlorine samples were taken. Of the trichloramine samples, 94% were quantifiable, and the mean concentration was 0.44 mg/m3. The highest mean trichloramine concentration by location (0.57 mg/m3) and the overall highest trichloramine concentration found on high occupancy day 1 (0.66 mg/m3) were at the leisure river attraction, which contains water slides, spray features, and splash pools. Ninety-four percent of soluble chlorine concentrations fell below the LOD, and therefore, we did not calculate a mean.
On high occupancy day 2, 45 trichloramine and 45 soluble chlorine samples were taken. Of the trichloramine samples, 82% had detectable concentrations; however, only 20% of all samples were quantifiable. Although these results included many nonquantifiable concentrations, they included the highest trichloramine concentration found (1.06 mg/m3) of all quantifiable samples collected. This result was obtained at the leisure river, which also had the highest mean concentration by location (0.80 mg/m3). Eighty percent of soluble chlorine concentrations were quantifiable, with a maximum concentration of 0.25 mg/m3, and a mean of 0.17 mg/m3. No major differences were observed across locations for soluble chlorine.
On the low occupancy day, 38 trichloramine and 39 soluble chlorine samples were collected. All soluble chlorine samples were non-detectable. One trichloramine sample contained a detectable concentration, which was reported at a trace level. Therefore, averages were not calculated.
Air Temperature and Relative Humidity
Daily air temperature averages taken across locations throughout the waterpark ranged between 82°F and 89°F. Daily relative humidity averages throughout the waterpark ranged from 41% to 69%. Temperature and relative humidity taken at deck level differed significantly across locations (P < 0.01). The average relative humidity varied by about 37% across locations at deck level on high occupancy day 1, and it differed by more than 30% across locations at deck level on high occupancy day 2 and the low occupancy day.
Air endotoxin concentrations in the pool area ranged from 18 to 84 endotoxin units (EU)/m3 with a mean concentration of 45 EU/m3. These concentrations were about 10 to 40 times higher than concentrations measured in an office outside the pool area. Locations with the highest air concentrations were the wave pool (84 EU/m3) and leisure river (67 EU/m3). The highest water endotoxin concentrations were also found in the wave pool (61 EU/mL) and leisure river (77 EU/mL). Endotoxin concentrations were similar in the water systems where samples were taken from both the surge tanks and surface water. Endotoxin concentrations in water samples taken from the hot tubs were very low, and in some cases, measured lower than concentrations found in tap water, which we sampled for comparison.
No culturable Legionella, fecal coliform bacteria, or Mycobacteria were found in any water samples.
With the exception of two low pH readings (7.0 and 7.1), disinfection parameters were within acceptable ranges. The water chemistry tests met state and local standards.16
Most water systems had consistent chemistry measurements; however, differences were noted in some. At the children's pool, water collected at the geyser spray feature had a pH of 7.8 whereas water collected on the west pool edge had a pH of 7.0. The geyser source water is drawn from the feature's surge tank which bypasses the treatment system.
Based on air supply volumetric flow rates taken from the test and balance report, the calculated maximum air exchange rate (without recirculation) is ∼2.0 air changes per hour (ACH), and the minimum air exchange rate is ∼1.3 ACH (with 33% of air recirculated). The minimum outdoor airflow introduction rate is ∼88,000 cubic feet per minute (cfm) during the maximum recirculation condition of 33%.
Chloramines and Associated Symptoms
The trichloramine concentrations found at this waterpark were similar to levels found in other indoor swimming pool studies and some were at levels reported to cause mucous membrane irritation. Symptoms reported by the lifeguards are consistent with those associated with trichloramine exposure.4,7–10 Twenty-five percent of the trichloramine samples taken on high occupancy day 1 and 20% taken on high occupancy day 2 exceeded a concentration of 0.5 mg/m3, the concentration at which irritation symptoms have been documented.10 In a study of 334 lifeguards at 63 indoor pools, the prevalence of mucous membrane irritation among lifeguards exposed to trichloramine concentrations above 0.5 mg/m3 was 86% for eye irritation, 61% for nose irritation, 29% for throat irritation, and 42% for dry cough.7 Jacobs et al measured trichloramine concentrations at six indoor swimming facilities and found an elevated prevalence of respiratory symptoms in workers. The mean trichloramine concentration was 0.56 mg/m3, with a maximum of 1.34 mg/m3.9 Based on concentration-response data in mice, Gagnaire et al17 recommended a short-term exposure limit of 1.5 mg/m3 and a time-weighted average of 0.5 mg/m3 for trichloramine. A time-weighted average exposure refers to the average airborne concentration of a substance during a normal 8- to 10-hour workday. Although proposed standards and past studies indicate that trichloramine concentrations in indoor pools should be kept below 0.5 mg/m3, there have been some concerns that this concentration may not be low enough to prevent symptoms.7 A study comparing the prevalence of respiratory complaints between young competitive swimmers and soccer players showed a significant increase in upper respiratory symptoms and eye irritation among swimmers exposed to air chloramine levels ≥0.37 mg/m3.18 The World Health Organization recommends a provisional value of 0.5 mg/m3 for trichloramine in air, although it states that more research is needed to investigate health effects in people who use the pool for extended periods of time and the role of trichloramine in possibly causing or exacerbating asthma.19
Proper air movement and distribution play a key role in reducing chloramine concentrations and preventing health effects. In 1983, an occupational medicine physician reported a swimmer who developed coughing and wheezing only when visiting a pool equipped with an automatically controlled heat reclamation system.20 Symptoms were worse in the winter months when the heat reclamation system recirculated a higher amount of air to conserve energy. The patient had no respiratory symptoms when he visited an older pool with a simple air extractor.
Recent studies have raised questions about whether inhalation of disinfection by-products may cause or exacerbate existing asthma. A study of two lifeguards and a swimming instructor showed that asthma can occur in workers exposed to chloramines. The researchers generated trichloramine at 0.5 mg/m3 in a challenge chamber and exposed the participants to a series of 10-minute exposures followed by spirometry. Results showed a decrease in pulmonary function.8
Water attractions that create surface water disturbances can increase aeration of water contaminants. In our investigation, higher trichloramine concentrations were found in areas around the leisure river. This attraction contains a high water-to-air surface area in constant motion and many splash features that can aerosolize water contaminants. A study conducted at a large indoor municipal recreation center demonstrated that the operation of a water slide increased the number of respirable particles by 2.3-fold and increased by 5.2-fold with full water feature use.11 In another study, mean trichloramine concentrations were 0.24 mg/m3 at still water pools and 0.67 mg/m3 at leisure pools (pools containing water-disturbing features like slides).7 Hery et al10 also reported that air chloramine concentrations were higher in leisure pools and when water was disturbed by fountains, slides, and other features.
Indoor pool environments have been associated with hypersensitivity pneumonitis, a rare inflammatory lung condition causing cough, fever, and body aches. In pool environments, this condition can be caused by inhalation of bioaerosols such as endotoxin. Endotoxin is the cell wall remnants of gram-negative bacteria that are released with bacterial death. Inhaling high concentrations of endotoxin can cause airway and alveolar inflammation. The airborne endotoxin concentrations measured in this waterpark were ∼10 to 40 times higher than background levels, and exceeded the proposed American Conference of Governmental Industrial Hygienists' relative limit values for endotoxin exposure.21 These values are comparable to a relative value of 25 times higher than outside air measured during an outbreak of hypersensitivity pneumonitis at a municipal indoor swimming pool with extensive water spray features.11
Although no cases of hypersensitivity pneumonitis were diagnosed among lifeguards at this waterpark, elevated airborne endotoxin levels and symptoms of cough, fever, and body aches raise the possibility of undetected disease. Lifeguards may have been misdiagnosed as having pneumonia or chest flu or did not seek care because their symptoms resolved.
Several lifeguards reported blurry or foggy, blue-gray, and/or halo vision while at work. Although blurry vision is not an uncommon symptom and could reflect eye irritation, halo vision is more unusual. A variety of amine compounds have been reported to cause similar visual symptoms.22 We offered to have an ophthalmologist examine lifeguards with blurry or halo vision, however, none of the lifeguards presented to the opthalmologist. Because the opthalmologist's office was located off-site, and he was only available in the evenings, it is possible that his times of availability and office location were not convenient for the lifeguards, or that they did not seek care because their symptoms resolved. In addition, the environmental conditions during the study period were much different from when visual symptoms reportedly peaked, and we may not have captured visual symptoms during a time of peak trichloramine exposure.
About 80% (14 of 17) of the pool surface water samples and none of the hot tub surface water samples, exceeded the National Swimming Pool Foundation's recommended maximum combined chlorine concentration of 0.2 ppm for pools and 0.5 ppm for spas and hot tubs.23 The highest combined chlorine concentration measured was 0.4 ppm. This is not exceptionally high when compared with several state code regulations on maximum combined chlorine, which range from 0.2 to 1.0 ppm.
Although combined chlorine concentrations in water contribute to airborne chloramine concentrations, airborne chloramine concentrations depend on a variety of additional factors including ventilation system design, air recirculation, and aerosolization of water contaminants from splashing and spraying. An indoor pool with normal combined chlorine concentrations can have high air trichloramine concentrations if there is insufficient supply of outdoor air.24 Conversely, an indoor pool with relatively high combined chlorine concentrations can have lower air trichloramine concentrations if the ventilation system is highly efficient. Therefore, interpretation of combined chlorine concentrations in water samples needs to take into account all factors affecting airborne chloramine concentration.
Investigation into the differences in pH from the pool water and spray features of the same water system showed that all the spray features drew water directly from the surge tanks. Because surge tank water is the starting point of the water filtration cycle, it could contain more contaminants than water taken at the end of the filtration cycle. Even though the spray features contribute a minute amount of water to the pool, any water contaminants present could be aerosolized.
Current ventilation guidelines and standards were developed to provide adequate ventilation for more traditional still water-type pools, similar to what one might encounter at a hotel or other small recreational facility. This waterpark's design and active aquatic features differ greatly from standard pools, therefore, the ventilation guidelines currently in place for pool facilities may not be suitable for this waterpark environment.
The facility provided an outdoor air supply rate of 88,000 cfm during maximum recirculation, which exceeded the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) specification of 40,000 cfm for pools.25 However, the overall air exchange rate for the waterpark was much less than that recommended by ASHRAE Heating, Ventilating, and Air-conditioning guidelines—the ASHRAE guidelines recommend 4 to 8 ACH whereas the facility provided ∼1.3 to 2 ACH.26
The design of the air distribution system, however, may be more important than the air exchange rate. Adequate airflow is necessary to move contaminants from the deck level to the return ducts for removal from the building. The air distribution system design at this waterpark may have created short circuiting of airflow because of the placement of supply and return air registers in close proximity of each other in the high bay area. The height of the supply diffusers at 30 to 80 ft also hinders the ability of the ventilation system to provide adequate air movement at deck level. In addition, the placement of four large air returns ∼60 to 80 ft above the deck makes them poorly positioned to capture and remove contaminants, such as chloramines, which concentrate at deck level.
Pockets of higher levels of relative humidity were consistently seen throughout each sampling period. The variations were significant (P < 0.01) and may represent poor air movement at the deck level and potential build-up of contaminants. Pockets of high contaminant concentrations can occur at locations where flow is insufficient to move air to the exhaust ducts, where aerosolization from spray features occurs, or where structures may obstruct air movement.
Because we did not measure personal exposures to chloramines and endotoxin, our ability to evaluate any possible associations between chloramine and endotoxin concentrations and reported symptoms are limited. Also, the NIOSH chloramine sampling and analytical methods used in this study have not been fully evaluated by NIOSH, and because of the wide differences in LODs and LOQs for each day of sampling, data could not be compared across all sampling days. It is also possible that an unmeasured compound present in the indoor pool environment may have been responsible for or exacerbated reported symptoms.
Outdoor environmental conditions significantly differed between the period of peak health complaints (January and February 2007) and the days of our study. Outdoor temperatures averaged 35°F in January 2007, and 20°F in February 2007. When outdoor temperatures were below 40°F, the air handling system recirculated up to 33% indoor air. In contrast, the outdoor temperature remained above 40°F during our sampling periods in March 2007 (average 49°F) and April 2007 (average 52°F). Because indoor air was not recirculated during our study, the chloramine concentrations found may have been lower than when the initial outbreak of symptoms was reported. Also, because lifeguards reported that their symptoms had improved significantly with the warmer weather, the symptom data captured during this investigation may not represent what the lifeguards might have experienced during the colder months when indoor air was recirculated.
A limitation of the ventilation assessment was the difficulty in using standard ventilation system evaluation methods. Standard airflow evaluation techniques such as the use of smoke visualization and tracer gas testing were not performed because of the large size of the waterpark. Instead, a visual inspection of the ventilation system serving the pool area was conducted, ventilation system designs were reviewed, and ACH were calculated based on available airflow data to identify potential design concerns and explore ways to increase air movement at deck level.
Environmental and procedural changes made from January to March 2007, in response to patron health concerns could have also contributed to reducing air contaminant concentrations on the days we sampled compared with when the symptoms were first reported. Also, the number of bathers may have varied from when reported symptoms peaked (January/February) and the time of our evaluation.
During our evaluation, the media reported on eye and respiratory symptoms at the waterpark. Because of the heightened awareness, recall bias may have been introduced into the initial questionnaire (lifeguards may have been more inclined to recall symptoms than employees working outside the waterpark area). Also, asthmatics may be more likely to take up swimming instead of other sports because swimming is considered a sport that is less likely to cause exercise-induced asthma. Therefore, swimmers may be more likely to have asthma than people who participate in other sports.
Because only 68% of lifeguards filled out the initial questionnaire, participation bias may have occurred. In addition, because several lifeguards were reported to have quit before the evaluation period due to work-related symptoms, our results may underestimate the prevalence of symptoms.
Indoor waterpark environments are complex, and a holistic approach is necessary to reduce potential symptoms caused by the aerosolization of water contaminants. Source control methods include increasing fresh water dilution, reducing activation time of splash features, and keeping combined chlorine concentrations as low as possible. In addition, ventilation design should provide adequate air movement and contaminant capture at deck level. Clinicians, public health officials, managers, and employees need to understand the importance of source control and proper ventilation at indoor waterparks in reducing chloramine-associated irritation symptoms. In addition, efforts to reduce combined chlorine levels in water must be balanced by efforts to maintain adequate disinfectant levels of chlorine to prevent infectious diseases.
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