By Jeff Boynton
An increasing number of natatoriums have problems with indoor air quality. When the air in an indoor aquatic facility smells like chlorine, this is the first indicator that something is wrong. The odour is often worse at water level, but can be extremely irritating at deck level or in the viewing area as well. In many cases, the trademark ‘chlorine’ odour is not the only problem, eye irritation and difficulty breathing may also be experienced. The second indicator is rusting on metal fittings in and around the pool.
Heating, ventilating, and air conditioning (HVAC) systems are designed to control air temperature by regulating humidity and air flow with fresh air when necessary. However, as USASwimming.org points out, HVAC systems are not air scrubbers; therefore, air quality is directly affected by the pool’s water quality. Poor water quality, in fact, leads to bad air quality.
In the past few years, ‘bad air’ has been proven to come from chloramines (NH2Cl) in pool water. They are a chlorine (Cl) compound that easily burn off in the water and are released into the air during evaporation as well as when bathers agitate the water (e.g. swimming, splashing, etc.). Chloramines smell like chlorine (and sometimes ammonia) and can cause serious respiratory problems for swimmers, pool staff, and spectators.
This has become a widespread problem in indoor pools, resulting in many spectators feeling ill or uncomfortable. It is not uncommon to overhear conversations about how awful the air smells and how they prefer to leave for fresh air.
That said, the problem is not chlorine, rather what it turns into when combined with organics (e.g. sweat, dander, urine, etc.) that are introduced to the pool via bathers. When chlorine reacts with these organics, nitrogen trichloride (NCl3), aldehydes (R-CHO), halogenated hydrocarbons, chloroform (CHCl3), trihalomethanes (THMs), and chloramines are produced.
One method of combating this problem is using ultraviolet (UV) light to sanitize pool water, as it can help to improve indoor air quality as well. Essentially, UV sanitizers effectively eradicate waterborne pathogens while also reducing chemical reliance (i.e. using fewer chemicals results in less chemical byproducts).
This article will explain the corollary benefit of UV water treatment with respect to improving indoor air quality.
What is UV?
UV germicidal light is situated in the electro-magnetic spectrum between X-rays and visible light. The area between 240 and 280 nanometres (nm) is UV-C, commonly known as germicidal light. This is the UV light used to treat and/or sanitize pool water.
Pool water must be continuously treated with chemicals to deactivate pathogenic micro-organisms and to prevent the spread of recreational waterborne illnesses (RWIs). Ensuring proper water chemistry is the key to maintaining a safe pool environment. This means not only maintaining the proper level of oxidizers, but also correctly monitoring pH, water hardness, alkalinity, etc. However, there are only a few options available to pool operators looking to reduce chloramines in the pool environment.
The five available techniques are: hyper-chlorinating, non-chlorine shock, ozone (O3), adding fresh water, or installing a UV-sanitizing system.
In terms of the latter, pool water will pass through the UV system according to the local health requirements for filtration cycles. When the water is treated with UV-C germicidal light, the pathogenic micro-organisms are eradicated. At the same time, mono-chloramines are stopped from forming, thus preventing the ‘chlorine’ odour. Di-chloramines can only form with a building block of mono-chloramines that are present, and the tri-chloramines form only after the presence of di-. This means once the mono-chloramines do not form, it is much more difficult for the di- and tri- to form. However, in competition pools or those with high bather loads, medium pressure UV-C treatment is better suited since it works on mono-, di-, and tri-chloramines at the same time.