Chloramines in a swim hall come from chlorine reacting with what bathers bring into the water, and the volatile one, trichloramine, leaves the surface and sits in the air at breathing height. Indoor air quality in a swim hall is therefore mostly decided by how much of that contamination reaches the water, how well the treatment loop removes it, and how the ventilation handles what escapes. Treatment and ventilation are one system, not two budgets.
What Are Chloramines and Why Do They End Up in the Air?
Free chlorine disinfects by reacting with contamination: sweat, urine, skin cells, cosmetics, sunscreen. When chlorine meets nitrogen-containing compounds from bathers, it forms chloramines, also called combined chlorine. Monochloramine and dichloramine mostly stay in the water. Trichloramine is different: it is volatile, so it leaves the surface, especially where the water is disturbed by waves, splash features, slides and swimmers kicking at the edge.
That is why a hall can smell sharp even when the water test looks fine. The smell is not chlorine. It is a by-product of chlorine doing its job against a heavy load. If you want the water-side explanation, we cover it in the article on why a pool smells of chlorine (see the NanoSWIM blog): a strong smell usually means too little free chlorine relative to load, not too much.
Who Is Exposed in a Swim Hall?
The occupational picture matters more than the consumer one. A casual swimmer spends a short time in the hall. Instructors, lifeguards, cleaners and technical staff spend whole shifts at the water's edge, in the layer of air where trichloramine is highest. Staff in this position commonly report irritated eyes, nose and throat. We make no medical claims here; the point for a driftsansvarlig is that the people who notice the air first are the ones who work in it, and their complaints are early information about the plant.
If staff are raising concerns, treat that as a reason to involve your occupational health service and to measure, not to guess.
What Controls the Chloramine Level in a Hall?
| Lever | What it does | Limit |
|---|---|---|
| Pre-swim shower and hygiene | Fewer contaminants reach the water, so fewer chloramines form | Depends on bather behaviour and on facilities that make it easy |
| Filtration and circulation | Removes particles and organic load before they react | A poor filter undermines everything downstream |
| Water treatment in the loop | Oxidises organic load and chloramine precursors; can lower the chlorine demand | Acts on water passing through the system, not on air already in the hall |
| Water temperature and surface disturbance | Warmer, more agitated water releases more trichloramine to the air | Features and comfort temperature are often fixed by the use of the pool |
| Ventilation and air distribution | Dilutes and removes what reaches the air; supply and extract must sit where the pollutant is | Costs energy; poorly placed extract does little at the water surface |
Can Water Treatment Improve Air Quality in a Swim Hall?
It can reduce the source. NanoSWIM nanobubble treatment is installed inline in the existing circulation loop, after filtration, with no separate contact tank. Nanobubbles are gas-filled bubbles under roughly 200 nanometres in diameter. When ozone is the gas, their collapse releases concentrated oxidative energy, advanced oxidation, which breaks down organic load. Less organic load in the water means less for chlorine to react with, and so less chloramine formed. Ozone reverts to oxygen and leaves no residue.
Our published figure for oxidative disinfection in the treatment loop is 99.9% pathogen reduction, and up to 90% reduction in chemical use against a conventional chlorine dosing regime on comparable pools. A documented example is the resort pool case, a pool complex of 2,500 m² in southern Europe, with 85% less chlorine consumption. That case study reports chlorine consumption and water-treatment operating cost; it does not report air measurements, and we will not suggest it does.
What Does Treatment Not Do for Air Quality?
This is the part a buyer should hear plainly.
- It does not replace ventilation. Air in the hall still has to be extracted and replaced, and the ventilation design stays your responsibility.
- It acts on water passing through the loop, like UV and ozone injection. It does not clean air that is already above the pool.
- It leaves no persistent residual in the basin on its own. A Norwegian public pool must generally maintain a measurable disinfectant residual, so the realistic outcome there is strongly reduced chlorine, not zero.
- It does not replace correct filtration, sensible pH control or competent operation.
- Capital cost is higher than dosing pumps and drums.
If your hall has poor air distribution, an undersized air handling unit or heavy surface features, treatment will help at the margin and the ventilation is still where the problem sits. Other loop-side options such as UV and ozone have their own place; compare them against your plant, not against a brochure.
Why Does Air Quality Matter to the Building as Well as the People?
Chloramines in humid air are corrosive. Stainless steel fixings, ventilation ducts, ceiling elements and suspended equipment suffer in halls where combined chlorine runs high. In our experience buyers ask about the chemical bill first, but the argument that tends to land is ventilation load and building corrosion, because those costs show up in the maintenance budget years later. A hall that needs less air exchange to stay comfortable also asks less of the air handling plant.
What Should a Facility Manager Check Before Changing Anything?
- Measure combined chlorine in the water at a routine point and log it with bather load.
- Ask staff where in the hall the air feels worst, and when.
- Check whether supply and extract air actually reach the water surface zone.
- Review filtration condition and backwash records.
- Confirm the pre-swim shower is used and usable.
- Ask your ventilation supplier what the design assumed about bather load.
- Involve occupational health if staff report symptoms.
- Only then ask any treatment supplier, including NanoSWIM, what it would change in the loop.
For Norwegian public pools, the requirements sit in forskrift om badeanlegg, bassengbad og badstu, enforced by the municipal health authority, and Folkehelseinstituttet (FHI) publishes guidance on pool operation. NanoSWIM does not claim any certificate or approval; ask every supplier what documentation they can provide. See our standards page and our approach for public facilities. For the wider chlorine-reduction picture, read about the chlorine-free pool option. A system such as the NanoSWIM Pool System handles up to 500 m³/h; whether it fits depends on your flow rate and plant-room space.
In my own experience, the people who feel a change first are never the managers, it is the instructors and lifeguards who stand at the water's edge all day. On a job I worked on myself, nobody had mentioned air at all in the brief; then one of the instructors told me, almost in passing, that she could finally leave her office door by the pool hall open without the corridor smelling. That told me more than any report. I always ask staff first now, before I look at a single pipe.
If you run a swim hall and want to know whether treatment in the loop would help, contact NanoSWIM in Bergen with your pool volume, flow rate and a short description of the air problem. We will say plainly if the answer is in your ventilation instead.