Air quality and its known health effects have garnered the attention of the World Health Organization (WHO) and US Centers for Disease Control (CDC). All of the information contained in this article is accessible online through credible resources, and we encourage all of you to research these topics on your own so that we can, together, keep our sport as safe and healthy as possible.
In our last article, we discussed how pool water chemistry and swimmers contribute to indoor air quality problems. Quickly, to recap: chlorine cleans the pool by oxidizing organics, and the result is disinfectant byproducts (DBPs)—the primary type being chloramines. Chloramines off-gas into the air and when they do, they stay low, right above the surface of the water in the “breathing zone.”
Chloramines are in the air, now what? At this point in the process, chloramines need to be dealt with as an air issue. To be clear, water chemistry still affects the production rate…but once airborne, trichloramines are not affected by the water chemistry anymore. So, for this article, our focus is on the natatorium and its air—not the pool and its water.
There are several different ways in which natatorium air is conditioned, or in some cases, not conditioned. Depending on geographic location, natatorium air is addressed in these different manners:
- Open Air – open the windows, open the doors, turn on the fans – this can work well in a climate that does not have extreme climate swings and if the building is designed for it. Temperature and humidity levels cannot be controlled.
- Outside Air Make-up Systems – Introduces 100% outside air with heat if needed. Not capable of dehumidifying or cooling. No recirculation.
- HVAC Systems – This is most common for indoor pools. Designed to manage air conditions, controlling temperature and humidity levels. These systems recirculate air, condition it, and put it back in the natatorium.
So here’s what we know: every natatorium is unique, and so is each air system. As you can imagine, there is a wide variation in air quality, which explains why some pools struggle, and others are seemingly fine. No matter what type of air system is used, here’s a short list of factors that make a big impact:
- Turnover rate – air recirculation takes time, and it happens several times per hour. If it’s too slow, you get short circuiting (‘dead zones’), and if its too fast you get excessive mixing. Both are problems.
- Location of air duct and return vents – this drives most aspects of air flow in the room; if there’s a problem with the duct layout, it may require a total redesign to fix the problem. This is very common.
- Size and capability of the air system – often times these systems are improperly sized, which puts operators at a disadvantage from day one. Just imagine trying to use a drinking straw for a snorkel…many air systems are that undersized.
- Temperature and agitation of water – Ideally, the pool is two degrees cooler than the air. Therefore, the warmer the water, the warmer the air, and the faster chloramines are off-gassed. Same goes with agitation, such as swimmers kicking and splashing, spray features, spas and slides. These factors accelerate the production of bad air.
- The problem is this: Until just recently, natatoriums have not been designed to handle chloramines or other DBPs. Air quality has only recently been understood enough to address. The design of duct and return vents determines airflow in the natatorium, which in turn affects air quality. The two most common problems with natatorium air designs are 1) short circuiting, and 2) excessive mixing.
1) Short circuiting is when air is supplied into the natatorium and fails to reach much of the room because it shortcuts back into the return vent beforehand. This can be caused by a poor duct layout (i.e. high supply and high return), or by an under-designed HVAC system. This effect creates voids in air flow, or “dead zones.” What do you think is the most common dead zone in a natatorium? You guessed it: the surface of the pool itself…the breathing zone.
2) Excessive mixing is the opposite of short circuiting, when air flows too fast and mixes everything up, especially airborne contaminants like chloramines. This is usually caused by too high of a turnover rate, which forces air to move too fast in the space. This is usually the cause of a breeze or draft on a pool deck, where swimmers get really cold. This effect spreads bad air all over the place, and is intensified by the use of large fans. Look for rust around your pool… if you see any on metal components in your roof (support beams, lights, etc), chances are, there is mixing going on.
In either case, if your pool has a recirculating air system, chloramines will recirculate and the problem builds upon itself; with each cycle, the air quality gets worse and worse. HVAC systems typically exhaust 10-25% of their recirculating air, and replace it with outside air. That means about 75-90% of the indoor pool’s air goes right back into the pool. HVAC systems are not designed to eliminate airborne contaminants like chloramines—that is, unless they incorporate a source-capture system.
If there is rust inside your pool’s HVAC system, that proves chloramines are being recirculated. It’s only a matter of time before a component (or the entire system) needs to be replaced. Think about that for a second. Chloramines corrode and destroy metal—what does it do to us?
To recap, airborne chloramines off-gas from the pool and get trapped inside the natatorium, recirculate and spread around, and have no place to go. This is why swim meets tend to get worse as the meet progresses. Even overnight, those airborne chloramines are still trapped in the natatorium. Combine that with the increased production rate of a heavy bather load, and it’s a recipe for problems.
Perhaps, as pool users, we should focus less on the problem, and more on the solution. When we accept that chloramines are always being produced, the question becomes “now what?” instead of “who’s fault is this?”. If you think the issue can be ignored, just wait until you learn the costs of having bad air…it is an unbelievable burden placed on the owners and operators of swimming pools. The numbers are staggering.
We know how miserable an indoor pool can be during swim practice or a meet, because we’ve lived it. It is personal to us, and we have devoted our careers to not only educating the swimming community about air quality, but actually solving the problem. Our mission is to make the indoor pool a healthy, desirable place to be—not just a tolerated amenity. More at www.paddockevacuator.com.
Courtesy of Paddock Evacuator, a SwimSwam partner.