The relationship between pool water quality and ventilation.
In late 1992, the Park Ridge Park District in Illinois, completed construction of a new aquatic center that included an 80,000-gallon lap pool, a 20,000-gallon leisure pool and a 1,300-gallon spa. During the first routine inspection of this facility in January 1993, extremely high levels of chloramines, ranging from two to five parts per million (ppm), were found in both swimming pools. Chloramines, also known as combined chlorine, result from the combination of chlorine and ammonia. They may be organic or inorganic. Under normal conditions, superchlorination, at 10 times the concentration of the chloramine level, is sufficient to bring the pool water to the chlorine breakpoint, releasing the ammonia from the pool water and leaving only free chlorine (1-3). This process is known as "shocking." The State of Illinois Swimming Pool Regulations stipulate that whenever chloramines are present at a concentration greater than 0.2 ppm, the pool must be shocked to remove them (4). Despite numerous attempts, however, no shock treatment succeeded in eliminating the chloramines from the park district pools. In fact, chloramine levels remained relatively unchanged.
Failure to reach breakpoint chlorination is a recent phenomenon that seems to be restricted to new pools with energy-efficient air-handling systems (3,5-9). In 1992, county and state inspectors were consulted, but no one had ever encountered this situation. It was suggested that the pool be shocked at 20 times the chloramine level. Even after this extreme oxidation treatment, which resulted in a chlorine concentration at 100 ppm in one of the pools, chloramine levels remained the same. No one with whom the author spoke at that time could explain this phenomenon. The park district's chemical supply company suggested installing an ozonator. According to the supplier, an ozonator seemed to have corrected this problem at some other indoor pools.
At the February 1994 Mid-America Spa/Pool Show, sponsored by the National Swimming Pool Institute (NSPI), the author attended a swimming pool water seminar and presented this problem to the speaker. Although the speaker could not provide a solution, a member of the audience made some comments about adding more air to the pool area. These comments seemed to support statements made by the park district pool operators, who set up fans and opened doors to the outside to ventilate the natatorium whenever they shocked the pool. They claimed that ventilation aided the shocking procedure. Current literature confirms that fresh air should be forced over the surface of the pool to eliminate chloramines and other chlorination byproducts such as trihalomethanes (3,6-9).
The comments of the pool operators at the pool district and the comments made at the Mid-America Spa/Pool Show suggested the hypothesis that the air quality in the pool area must have a direct influence on the water quality in the swimming pools. Investigation of the problem led to an examination of the building department plans for the park district natatorium ventilation system.
Air Changes per Hour-Calculations and Experiments
Reviewing ventilation system plans requires an understanding of terms such as "air exchange rate." Air exchange rate is the rate at which indoor air is exchanged with outdoor air. It includes infiltration, exfiltration, natural ventilation, and mechanical ventilation. To calculate air exchange rate, the quantity of outdoor air that enters a structure is divided by the volume of the structure. The formula is as follows:
Outdoor air entering structure (in cubic feet per hour [[ft.sup.3]/hr]) + Volume of the structure (in [ft.sup.3]) = Air changes per hour (ACH) (10).
Both the air exchange rate and ventilation air rate use air changes per hour as their units of measure. The air exchange rate must not be confused with the ventilation air rate. The ventilation air rate refers to the total amount of air being supplied through the heating, ventilation, and air conditioning (HVAC) system. It incorporates the recirculation air, which in this facility was being forced through a dehumidifier. To calculate the ventilation air rate, the total amount of air supplied to the structure is divided by the volume of the structure. The volume of the park district natatorium is 153,000 [ft.sup.3]. According to the architect, the ventilation air rate in the natatorium at the time of this investigation was
(23,000 [ft.sup.3]/min x 60 min/hr) + 153,000 [ft.sup.3] = 9 ACH
Although nine air changes per hour might seem more than adequate, the total amount of outside air being supplied to the natatorium was only 2,000 cubic feet per minute (cfm). Of these 1,000 cfm was added to the HVAC system, and 1,000 cfm was supplied from a make-up air unit on the roof. To balance the system, a 2,000 cfm exhaust fan was also located on the roof. Therefore, the total amount of outdoor air entering the structure was 2,000 cfm x 60 min/hr = 120,000 [ft.sup.3]/hour. If all other sources of fresh air are assumed to have been negligible, the air exchange rate for the natatorium was as follows:
120,00 [ft.sup.3]/hr + 153,000 [ft.sup.3] = 0.78 ACH
The architect justified this low air exchange rate by claiming that the ventilation design conformed to the 1984 National Mechanical Code of the Building Officials and Code Administrators International, Inc. (BOCA) (11). Unfortunately, all the BOCA national mechanical codes from 1984 until 1993 permitted recirculation of up to 67 percent of the required ventilation air specified in the code. The engineers at BOCA explained that the 1993 code eliminated the provision that permitted recirculation of the required ventilation air and now stipulates a minimum amount of outside air to be provided (12).
Although the standards applied to the natatorium ventilation system by the architect did comply with the 1984 National Mechanical Code, the City of Park Ridge was following the 1981 BOCA National Mechanical Code at the time the natatorium was constructed. If the ventilation system had been constructed to the standards contained in the 1981 BOCA National Mechanical Code, the air quality in the natatorium would have been better. The 1981 code set the following standards:
* Section M1001.1: Required ventilation air for a swimming pool is 15 cfm per occupant.
* Section M1009.1: Recirculation of required ventilation air is prohibited in swimming pool areas (13).
The number of occupants as calculated from the bather load permitted by the Illinois Department of Public Health swimming pool regulations is 253 (14). The required ventilation air according to the 1981 BOCA standards is as follows:
253 occupants x 15 cfm per occupant = 3,795 cfm
Therefore, the air exchange rate would be
3795 [ft.sup.3]/min x 60 min/hr = 227,700 [ft.sup.3]/hr 227,700 [ft.sup.3]/hr + 153,000 [ft.sup.3] = 1.49 ACH
This rate is about twice the air exchange rate currently being provided.
It is interesting to note that the 1993 BOCA National Mechanical Code requires that 0.5 cfm of outside air be supplied per square foot of pool and deck areas. Applying this standard would produce the following air exchange rate (ACH) for a natatorium area of 9,000 square feet ([ft.sup.2]):
0.5 cfm/[ft.sup.2] x 9000 [ft.sup.2] = 4,500 cfm of outside air 4,500 [ft.sup.3]/min x 60 min/hr = 270,000 [ft.sup.3]/hr 270,000 [ft.sup.3]/hr [divided by] 153,000 [ft.sup.3] = 1.76 ACH
The low air exchange rate may be exacerbated because the 2,000 cfm exhaust fan located on the roof, which is needed to balance the 2,000 cfm supply of outside air, may be short-circuiting the 1,000 cfm supply of fresh air coming from the rooftop make-up air unit. Because the outside air is introduced in the same area where the exhaust fan is located, the outside air may not adequately mix with the air in the natatorium. To make matters even worse, all of the supplied air is directed up along the exterior windows of the facility to eliminate condensation on the glass. No air is directed over the pools.
In 1995, the mechanical engineers for the architect of the natatorium increased the amount of outside air supply from 2,000 cfm to 3,500 cfm and simultaneously increased the capacity of the exhaust fan on the roof to 3,500 cfm to compensate for the additional outside air. Inspections made five to six weeks following the ventilation changes found that the chloramine concentration in the pools had decreased only slightly. The manner of introducing the fresh air and the manner of distributing the ventilation air had not been altered.
To determine whether ammonia in the air may become entrained in pool water to form chloramines, a simple experiment was performed in the office. A bowl of ammonia was floated in a covered bucket of chlorinated water that did not contain any chloramines. After 3.5 hours, over half of the free chlorine had been converted to combined chlorine. With this same concept in mind, the author conducted an experiment in 1997 to determine whether nitrogenous (ammonia) compounds were becoming trapped in the air of the natatorium and re-entering the pool. Two buckets of chlorinated water were placed on the pool deck of the park district pool, and two buckets were placed on the deck of one of the indoor pools at the high school. At each location, one bucket was covered and the other left open. A 0.5 ppm residual of free chlorine and a pH of 7.2 to 7.6 were maintained for all the buckets. After two weeks, no chloramines were found in any of the buckets at either location, even though they had been on the deck during shocking of the pools.
One reason chloramines did not develop in the buckets of water may have been that the vapor density of some of the chloramine compounds is significantly heavier than air. Vapor density is the weight of a volume of pure vapor or gas relative to the weight of an equal volume of dry air at the same temperature and pressure. Vapor densities greater than 1 indicate that the vapor or gas is heavier than air (15). Compounds with heavy vapor densities are likely to stay near the surface of the pool water if they are not moved by the ventilation air, and in this experiment, the buckets had to be placed in an out-of-the-way location in the corner of the deck.
An article in the newsletter of the Professional Pool Operators of America seems to support the theory that chloramines and other by-products of chlorination stay near the pool water surface. This article explains how the U.S. Olympic Committee responded to air quality complaints by athletes and coaches at the Olympic Aquatic Center built in 1993 in Colorado Springs, Colorado. Swimmers using the facility for training were experiencing symptoms that result from exposure to chloramines and possibly other by-products of chlorination. Smoke tests revealed dead air zones over the pool. After the ventilation system was improved with fresh air over the pool water, the complaints ceased. A subsequent smoke test confirmed that ventilation over the pool was improved. The movement of air over the pool water appears to have reduced the concentration of chloramines or other chlorinated by-products that were the source of the complaints (7).
Ratner and Griffiths have presented evidence that because of poor ventilation, the air in newer pool facilities has chloramine vapors that may contribute to adverse health conditions - particularly asthma - in swimmers. That study also observed that older pools and outdoor pools do not have chloramine problems because they have adequate ventilation (9). In 18 years of inspecting pools, the author of the present study has never found a chloramine problem in an outdoor pool or in an older indoor pool. One of the recommendations made by Ratner and Griffiths is to open doors and windows during shocking to allow chloramines to gas-off and escape the facility (9).
Two other studies found chloroform, a trihalomethane, in the blood, urine, and alveolar air of swimmers and attendants at indoor swimming pools (16,17). Trihalomethanes are produced by the reaction of free chlorine and certain organic compounds in water (18). Aggazzotti et al. collected air samples at a height of 150 centimeters (cm) above the water surface and found that chloroform concentrations at the water surface and at a height of 150 cm varied as a result of water turbulence caused by swimmers, the number of swimmers present, and other factors (17). If chloroform, which has a vapor density of 4.1, is found near the pool water surface unless moved by air turbulence, then it can be expected that organochloramines with high vapor densities behave in a similar fashion. Air movement across the water surface should be provided to move compounds that are heavier than air away from the pool water where the compounds are being generated and released.
The literature and the chloramine phenomenon described in this paper both indicate that swimmers and attendants are being exposed to chloramines and other chlorination byproducts in pools that have poor ventilation. Effective ventilation systems are needed both to reduce user exposure to potentially harmful and noxious chlorinated compounds and to maintain chloramine concentrations that conform with state and national swimming pool water quality regulations and standards. It would be prudent for any health department review of indoor swimming pool plans to include a review of the pool area ventilation system. Further research is needed to determine what kind of ventilation system design is best for indoor swimming pool facilities. How much fresh air is supplied and how that air is introduced influences not only air quality in an indoor aquatic facility, but also the water quality.
1. Environmental Health Ready Reference (1983), Lansing, Michigan: Michigan Environmental Health Association, p. 189.
2. Pool-Spa Operator's Handbook (1990), San Antonio, Texas: National Swimming Pool Foundation, pp. 30-31.
3. Williams, K. (1995/1996), "The Basics of Breakpoint Chlorination," The PPOA Pumproom Press [Professional Pool Operators of America], 9(Winter):2-4.
4. Illinois Swimming Pool and Bathing Beach Code (1990), Springfield, Illinois: Illinois Department of Public Health, p. 40.
5. Williams, K. (1995/1996), "Beyond Superchlorination," PPOA Pumproom Press [Professional Pool Operators of America], 9(Winter):6-8.
6. Williams, K. (1996), "Superchlorination Follow-Up," The PPOA Pumproom Press [Professional Pool Operators of America], 10(Spring):3.
7. Williams, K. (1996), "Providing Air Quality for Competitive Swimmers," The PPOA Pumproom Press [Professional Pool Operators of America], 12(Fall):2.
8. Bard, M. (1996), "I'll Be O.K., I Just Need Some Fresh Air," The PPOA Pumproom Press [Professional Pool Operators of America], 11(Summer):6.
9. Rattner, J., and T. Griffiths (1995), "Exercise-Induced Asthma and Indoor Swimming Pools," Parks and Recreation, 30(7):46-52.
10. U.S. Public Health Service and National Environmental Association (1991), Introduction to Indoor Air Quality: A Self-Paced Learning Module, U.S. EPA/400/3-91/002, Washington D.C.: U.S. Environmental Protection Agency, pp. 9-12.
11. The BOCA National Mechanical Code/84 (1984), Country Club Hills, Illinois: Building Officials and Code Administrators International, Inc., pp.131-141.
12. The BOCA National Mechanical Code/93 (1993), Country Club Hills, Illinois: Building Officials and Code Administrators International, Inc., pp. 83-85.
13. The BOCA National Mechanical Code/81 (1981), Country Club Hills, Illinois: Building Officials and Code Administrators International, Inc., pp. 212-224.
14. Illinois Swimming Pool and Bathing Beach Code (1990), Springfield, Illinois: Illinois Department of Public Health, pp. 10-12.
15. NFPA 325M Fire Hazard Properties of Flammable Liquids, Gases and Volatile Solids (1984), Quincy, Mass.: National Fire Protection Association, p. 4.
16. Camman, K., and K. Hubner (1995), "Trihalomethane Concentrations in Swimmers' and Bath Attendants' Blood and Urine After Swimming or Working in Indoor Swimming Pools," Archives of Environmental Health, 50(1):61-65.
17. Aggazzotti, G., T. Cassinadri, G. Fantuzzi, G. Predieri, E. Righi, and P. Tartoni (1993), "Chloroform in Alveolar Air of Individuals Attending Indoor Swimming Pools," Archives of Environmental Health, 48(4):250-255.
18. Salvato, J.E. (1982), Environmental Engineering and Sanitation, New York: John Wiley and Sons, pp. 313-315.
Corresponding Author: Brian P Emanuel, R.S., M.P.H., City of Park Ridge Health Department, 505 Butler Place, Park Ridge, IL 60068.