“It is possible to generate too much ozone for a given application, although due to economic reasons, it is more likely that ozone is misapplied. Generally speaking, if the ozone system allows residual ozone to enter the main body of water, be it a pool or a spa, exposure of the bathers to ozone gas is possible, “ he explained.
Following this line of reasoning, if ozone gas exposure is possible, it is also possible for a person to be exposed to a level that exceeds regulatory limits (OSHA 0.1ppmv TWA 8-hours; 0.3ppmv STEL).
Therefore, engineering controls are used to prevent ozone from entering the occupied space. First, ozone is applied in a manner which will cause it to be consumed prior to its being able to enter the main water body. In the case of a spa, this means injecting the ozone in the circulating filter line and allowing it to do its job before the water re-enters the spa. “The relatively low ozone levels applied, the high water temperatures, and the ozone demand all contribute to giving ozone a very short life,” Mouw noted.
Secondly, devices are available to destroy excess ozone, in either the dissolved phase or gas phase. In the case of swimming pools, in which relatively high ozone levels are applied to the filter flow and water temperatures are much lower, ozone is consumed during the time it is detained in a contact tank following the ozone injection point, with any residual ozone destroyed by passing through a GAC filter or UV unit prior to reentering the pool.