Exercise-induced asthma and indoor swimming pools.

A recent front page headline in USA Today exposed the tip of the iceberg for aquatic facility managers, particularly those working at indoor localities. The article that caused the stir, "Asthma on Rise; Indoor Air a Culprit?," revealed statistics compiled by the Centers for Disease Control and Prevention (CDC) indicating that asthma has been rapidly on the rise in this country since 1982. Apparently, the effects of indoor air pollution, including secondhand smoke, are even more severe in the air-tight homes and offices built during the 1970s in response to the energy crisis.

This concerns those of us in parks and recreation because indoor aquatic facilities likewise have been constructed to save energy and money with the installation of sophisticated heat reclamation systems. In addition to having to heat large volumes of water, indoor aquatic facilities also must heat large expanses of air to temperatures much greater than room temperature (82[degrees]-86[degrees]F). While saving significant sums of money by recirculating previously heated air, some of these systems have created uncomfortable and perhaps even unhealthy environments by also recirculating chemically tainted air. This situation is most likely to occur in heavily used pools which are energy-efficient but laden with chloramine (combined chlorine) fumes.

Indoor swimming facilities today must be engineered so that, while they are recycling valuable heat, they are not recycling chloramine. The greatest challenge for pool designers is to place "bad air" with outside "fresh air" without being wasteful. Unfortunately, there is a direct relationship between the amount of fresh air brought into a facility and the amount of money required to heat this new air.

Ironically, older aquatic facilities constructed before the 1970s -- those with mechanical ventilators including ducts fans, and dampers that simply brought in plenty of fresh air to replace the bad, chloramine laden air -- did not present many of the "bad air" problems that some energy efficient pools produce. Although energy-inefficient and terribly wasteful, these older natatoriums remain a joy to work and swim in. Conversely, swimmers frequenting many of our newer, more energy-efficient aquatic facilities are developing exercise-induced asthma because of poor ventilation.

Good Ventilation and Other Factors

Good ventilation would not be as crucial to comfort if chloramine levels were not allowed to become excessively high. In most instances, when the combined available chlorine count in the pool water exceeds .5 ppm, the odors produced become irritating to the nose, skin, eyes, and lungs. Chlorine compounds naturally combine with the nitrogenous wastes of swimmers, particularly sweat and urine, to produce chloramines in the aquatic environment. The more swimmers there are in the water, the more chloramines are produced and released into the air. If the chloramines are not "shocked" out of the water with either additional high levels of free chlorine or non-chlorine shocking agents and removed from the facility with proper ventilation, health problems will result.

Outdoor pools usually do not present these problems because as chloramines are produced they are quickly carried away rather than becoming trapped in an enclosed structure.

The distribution of chloramines is dependent on the pH of the water, temperature, time of exposure, and the hypochloride/ammonia ratio. An improper distribution of chloramines can result in excessive gas formation in the form of nitrogen trichloride, which escapes as a volatile gas into the atmosphere and causes noxious irritating chlorine odors. The degree of dissociation is influenced by temperature and dissolved solids as well as pH.

The medical evidence supporting the claim that poor air quality at indoor pools may be hazardous is becoming clear. A recent study published in the British Medical Journal studied 20 swimmers who were asked to swim vigorously for 20 minutes and then allowed to rest at poolside. The standard temperature was 27.8[degrees]C in the water and 28.9[degrees]C in the air.

This study clearly demonstrated that many of those swimmers with asthma, plus those with no history of wheezing, suffered attacks of bronchospasm or asthma when heat reclamation systems were in operation. It is well known that the chlorine smells in the swimming pools were caused not by chlorine gas but by nitrogen trichloride (an intense irritant) and -- to a lesser extent -- monochloramine and chloroform, which are produced when free chlorine reacts with organic contaminants introduced to the pool by bathers. These contaminants are urea and creatinine, which comes from urine and sweat. The mechanisms of the bronchospasm or wheezing is probably similar to the effects of well known irritants like chlorinated compounds on hyperreactive bronchial tubes.

Many competitive swimmers suffer more in the winter because modern pools have automatically controlled heat reclamation systems which recirculate a high portion of air in the winter to conserve heat and expel a high proportion of warm air in the summer because of solar heat gain. Therefore, nitrogen trichloride was more concentrated in the winter. Ironically, older pools that do not have such systems but rely on simple air extraction via ventilation have less problems with hyperreactive airways.

What Causes Asthma?

It has been well studied and thought that the primary stimulus for exercise-induced asthma may be heat loss and/or water loss from the airways during strenuous exercise. It additionally is suggested that the bronchoconstriction or asthma induced by water loss from the airways during exercise may be due to a change in the chemistry of the respiratory tract fluid. Exact mechanisms by which chlorine irritants -- when inhaled -- cause this effect is not known. However, respiratory injury from chlorine gas inhalation has been well described in the past. And severe exposure to chlorine gas can cause profound irritation and lead to severe tracheobronchitis, pulmonary edema, (fluid in the lungs), hypoxemia (severe drop in oxygen level).

In a study published in Thorax in 1979, 24 children were trained intensively for two-hour sessions in a similar pool environment; all developed cough and sore throat. The pool in question was treated with chlorine dioxide, generated by the addition of hydrochloric acid and sodium hypochloride in the mixing chamber. Chlorine dioxide is a gas at room temperature and, although correctly treated water was described by the equipment manufacturer as odorless, a strong smell was reported by the children in the study.

Recreational swimmers also may experience a milder degree of bronchial irritation from a lower concentration of chlorine gas coming from the water. The victims, following long periods of vigorous swimming when inevitably large volumes of air including gaseous chlorine liberated at the water surface are inhaled, have the most severe symptoms and appear to represent the effects of excessive quantities of chlorine or a derivative. Those children more prone to allergies may develop a greater level of bronchial hyperreactivity with less exposure. Therefore, these stressful breathing situations may occur in recreational, non-competitive environments.

Outdoors Vs. Indoors

It has been well documented in the past that swimming at least outdoors creates less exercise-induced asthma than other forms of exercise. Why this is true is not quite clear. It has been postulated that humid air breathed during swimming is protective. And some authors suggest that the protective effect of swimming might result from hypoventilation (insufficient breathing) and hypercapnia (subsequent C[O.sub.2] retention) due to constrained breathing patterns during swimming. This, in turn, may provide further bronchodilatation (or dilating of the bronchial tubes) that is preventive and protective. The prevailing theory, however, is that the improved ventilation provided by being outdoors simply carries away noxious odors rather than trapping them just above the water's surface as with indoor facilities.

A high anaerobic tolerance has been regarded as important for competitive swimmers and many common training programs incorporate control frequency breathing where swimmers restrict breathing frequencies in a pattern that lead to decreased overall minute ventilation, or simply stated, the training effect is enhanced. However, the harmful effect of swimming while suffering from asthma is two-fold. One is the exacerbated parasympathetic tone due to the "diving reflex" that has been shown to trigger bronchoconstriction or wheezing. The other is airway irritation because of chlorinated compounds.

One study of 14 competitive swimmers and 14 matched controls suggested that mainly competitive swimmers complained about the air quality of swimming pools and about bronchial and pulmonary symptoms occurring especially after training. These trained swimmers did so for 30-35 hours per week in the respective pools. The major toxic effects on the cells caused by the inhaled chlorinated gas were believed to result from chemical reactions. It has been well documented that the pathophysiologic consequences include edema, or swelling, of the respiratory mucous membrane, which lead to alteration, degeneration, and death of the bronchial tree, inflammatory reaction, and bronchial hyperresponsiveness. It was alarming that the author found an average concentration of chloroform in the blood of competitive swimmers after two hours of training to be extremely high, reflecting a high uptake of disinfecting agents by the airways. Sensitization to allergy-causing substances such as molds and ragweed may be encouraged by damage to the bronchial defense barrier as well as by direct alteration of the cellular immune system due to chlorine uptake.

In addition these same swimmers were shown to be sensitized to a large number of various allergens identified by skin tests. An impaired cellular immune system was found in half of the competitive swimmers, possibly reflecting a noxious effect of chlorine exposure. The development of more frequent and stronger bronchial hyperresponsiveness might lead to asthma and possibly represent a major key in the development and onset of respiratory disorders such as "asthma".

Exposure to Chlorine Makes a Difference

There is compelling evidence that frequent exposure to chlorine, chlorine gas, and their components may lead to severe bronchial hyperresponsiveness and subsequent asthma. The environment in many indoor pools may be creating the milieu necessary for these physiologic reactions.

Survey of other swimmers and facilities show that there may be some relief with the use of ozone as an alternative to chlorine as a sanitizer. Problems with the chlorine smells are virtually non-existent when the organic contaminants are removed by the powerful oxidizing action of ozone. And in the process, swimming pool water is treated with ozone during filtration; but it can only be used as a point contact disinfectant here in the United States. Another sanitizer such as bromine or chlorine must be added to the pool, but only a small residual needs to be maintained. The ozone must be removed by a carbon filter before the water is returned to the pool. Proper sizing of the ozonator is a key factor in producing an effective ozone system. Unfortunately, this process is relatively new in American aquatic facilities and expensive to install in existing pools.

More research and attention are needed to ensure adequate pool ventilation for indoor aquatic facilities along with increased vigilance of chloramine production and elimination by aquatic facility operators. As managers and operators try to reduce energy costs in their facilities, they must balance these efforts with adequate ventilation and proper water chemistry. If left unaddressed, this problem will lead to poor air quality which not only may take much of the enjoyment from swimming; but it also may result in more serious medical/legal consequences. Well designed and maintained facilities simply should not experience these problems. To prevent malodorous indoor aquatic facilities that can become uncomfortable as well as unhealthy, the following suggestions are recommended:

* Carefully monitor combined available chlorine levels. Make every attempt to keep chloramines below.3 ppm.

* Shock regularly, but particularly whenever the chloramine levels approach 5.ppm. Free chlorine must be added to the pool quickly in this case to a level that is 10 times greater than the combined chlorine count.

* Whenever shocking, doors and windows must be opened to allow the chloramines to "off-gas" and escape the facility. A non-chlorine shocking agent should be used when the facility must be used shortly after shocking.

* When designing ventilation systems, follow ASHRACE standards (American Society of Heating Refrigeration and Air Conditioning Engineers). At a minimum, indoor aquatic facilities must bring in .5 cubic feet of fresh air per minute for every square foot of pool and deck surface area when empty and an additional 15 - 25 cubic feet per minute of exchanged air for each person in the water and on the deck or in the spectator area.

References

Smith, Rich. "Putting on Airs," Pool and Spa News, January 12, 1994, pp. 70-78.

Manning, Anita. "Asthma on Rise; Indoor

Air a Culprit," USA Today, January 6, 1995, p. 1.

Jackson, Eden, Ed. "Controlling Indoor Environments For Comfort, Structure Protection", Aquatics International, November, December, 1991, pp. 19-27.

British Medical Journal Volume 287. August 1993.

Chlorine inhalation toxicity from vapors generated by swimming pool Chlorinator tablets. Pediatrics, Volume 79, Number 3, March 1987.

Coughing water, bronchial hyper-reactivity induced by swimming in a chlorinated pool. Thorax, 1979. Volume 34, pp. 682-683.

Exercise induced asthma: the protective role of C[O.sub.2] during swimming, Lancet, Volume 337, January 1991.

Swimming and asthma benefits and deleterious affects, Sports Medicine, 1992.