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When air quality is bad in a natatorium, swimmers, coaches, lifeguards and spectators all suffer. Exposure to airborne DBPs like trichloramine can cause swimmers to cough. Often for many hours–or even days–after swimming.

This article will focus on three points:

Why does swimming indoors often make people cough?

The best way to describe breathing in chloramine vapor is a dry burn. The throat gets dry, itchy and sore. Sinuses flare up, and lungs burn. Your nose quickly becomes irritated and runny like you just ate a really hot chicken wing that you have to sign a waiver to eat. It's miserable.

Airborne chloramines are usually the cause of swimmers coughing.

When we say chloramines, as mentioned in previous articles, we are generally referring to all airborne disinfection byproducts (DBPs) in the air in a natatorium, including trihalomethanes (THMs) like chloroform. We don't know the exact percentages of what is in the air, but we know when the air gets bad enough, we could not care less about exact percentages. We just want fresh air to breathe.

Since chloramines and other DBPs are heavier than oxygen, they stay low in the natatorium, right above the surface of the water and the wet deck. The worst air builds in the bottom of the room–thanks, gravity–which happens to be the swimmers' breathing zone. And swimmers who are training do not simply breathe normally. They are exercising and holding their breath underwater, so swimmers gasp when they inhale. Which leads us into our next topic...

The health consequences of chloramines

girl with inhaler, chloramine air, indoor pool air quality, natatorium IAQ, airborne chloramines, coughing after swimmingThere is abundant research available online that shows how inhaling chloramine-related pollution is harmful. We have aggregated many of the sources for you on our research page. Swimming indoors is directly correlated with cases of sport-induced asthma, bronchitis, and other respiratory distress. For those with prolonged exposure, there is even a condition nicknamed "lifeguard lung", which is basically scarring of lung tissue. The medical name is endemic granulomatous pneumonitis, and it is a problem worldwide.

Most people who spend a lot of time in natatoriums merely notice the discomfort, irritation and 'mugginess' of a hot, humid room. The fortunate ones are able to recover pretty quickly after they leave, but many of us are not so lucky. We can remember coughing fits for hours after leaving the pool. Many swimmers we know developed chronic bronchitis they just could not seem to get rid of. No matter the severity of someone's symptoms, the research is clear: breathing in airborne DBPs is not healthy.

And yet, DBPs are inevitable in a chlorinated (or brominated) swimming pool.

Related: How to Reduce Combined Chlorine

How to improve the air

This is the million dollar question, and the core reason Chloramine Consulting exists. In short, improving the air requires a combination of proper airflow/ventilation and water quality. We cover water quality in several of our other articles, like our comparison of secondary systems, so let's focus on air quality. 

Related: Indoor Pool Air Quality Resources

Dilution and circulation

Most natatoriums attempt to address air quality problems by way of additional outside air (dilution), or increased circulation. The logic is reasonable, except that chloramines are heavier than air, and do not behave like normal air pollution. Additional outdoor air can help dilute chloramines, but does nothing for getting them out of the natatorium. Increased turnover rates means the pool dehumidification system will see more air per hour, but that does not necessarily mean more chloramine removal...though it should help. In fact, increased circulation means more air velocity, which can actually stir up chloramines in some natatoriums. It just depends on the HVAC duct design.

stratification vs recirculation

From a mechanical engineer's perspective, there are basically two types of chloramine problems. stratification and recirculation. Stratification means heavy chloramines do not get stirred up much, and build up until they finally get high enough to be pulled into the return.  During normal operation, air could be pretty bad, because there is nowhere for the chloramines to go.  The other issue, recirculation, is when there is either a low return, or air is stirred up. In either case, the pool dehumidifier recirculates chloramines more than in a natatorium with a stratification problem. This means air quality would be better during low-use hours, but when the swim team gets in, air quality can go from decent to bad to horrible in a short amount of time. The problem compounds itself.

corroded coils, dehumidifier coils, rusty dehumidifier, rusty HVAC, HVAC rust, pool HVAC rust

It's like the pool dehumidifier is chain smoking chloramines. And the metal corrosion inside these expensive dehumidifiers is eye opening. Dehumidifier coils and other components are not cheap, and unless they are coated for corrosion resistance, chloramines will corrode them from the inside out.

Mistakes to avoid

We have another article about the most common mistakes in natatorium design, and on that list is ceiling exhausts. Why exhaust the least-polluted air in the room? From a dehumidification standpoint it would make sense, but only if the room did not have heavy air pollution like natatoriums do. Instead, the optimal location for dedicated exhaust is low in the room, utilizing source-capture.

Another mistake made by operators and swim coaches is opening outside doors. While this introduces fresh outside air, it is not conditioned air. Opening doors in the summer can throw off the balance of a natatorium, but it's not as bad as opening doors in the winter. When it's cold air flooding into the natatorium, evaporation rates change, and the PDU gets stressed in a number of ways. In short, opening doors makes natatorium air quality worse.

Goals to strive for

If you have an existing indoor pool that has air quality challenges, the first thing we strongly recommend you do is have your facility evaluated.  We offer this consultation service to help facility owners (and their mechanical engineer of choice) diagnose what is actually going on. Sometimes, air quality problems can be corrected rather easily, but it takes a trained eye to identify what needs to be modified in the natatorium. And that's where we come in.

Request an Evaluation

Once you know the fundamental reasons for the air quality problem, develop a plan to address them. Trying to solve everything at once can be a costly mistake. It makes more sense to go in a sequence that is not self-defeating. For instance, we recommend doing things that will be compatible with future changes if they are necessary.  If you are going to install a Paddock Evacuator® system, for example, it would behoove you to design it for compatibility with the future pool dehumidifier, because the current system has a lifespan. We would help you design it for the life of the building, not for short term convenience.

Finally, set realistic expectations. Retrofit projects to help existing natatoriums will get the air as good as it can be, and that may still fall short of perfection. We have to keep in mind the physical limitations of a building, as well as budgetary constraints. Set realistic expectations with your members that use the pool, and have a clear idea of what "success" means to you. Our objective is to get the air quality as pristine as possible, given the circumstances. Yours should be too.


Swimmers cough because of swimming pool disinfection byproducts (DBPs) that go airborne. These airborne DBPs are commonly referred to generally as chloramines, but include other things like trihalomethane and cyanogen chloride. Either way, there is an abundance of research showing that inhaling these airborne pollutants is unhealthy.  To prevent coughing and general discomfort of patrons, lifeguards and anyone else that uses the natatorium, we strongly suggest having your facility professionally evaluated for air quality issues, and develop a plan for addressing them.

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