In an open environment, the ozone isn't a hazard, is the theory behind its use. And chlorine is horribly toxic, so perhaps it is something that is determined by degree of hazard.

You know the smell the air gets right when it starts raining? I've always understood that to be the ozone in the air. It's that smell that you get in hot tubs that use this kind of system to keep the bio-hazards in the water away.

SRS