Ozone and oxygen
Half-life
Half-life is the time it takes for half of a quantity of something to disappear. For ozone it is the time for half the gas present to revert to ordinary oxygen. Inside a hot steam sauna we estimate it at about 10 to 20 minutes, and heat, moisture and surfaces all shorten it.
Also called ozone half-life, decay time
The general idea
Half-life describes decay in a way that does not depend on how much you started with. If the half-life is ten minutes, half is gone after ten minutes, three quarters after twenty, and so on.
Why ozone has one
The third oxygen atom in O3 is loosely bound. It detaches, leaving stable O2. That short half-life is ozone’s practical advantage: it does its oxidising and then it is simply oxygen again, leaving no residual chemical behind.
The figure in our saunas
Inside a hot steam sauna, ozone’s half-life is estimated at roughly 10 to 20 minutes. It is a range rather than a single number because three things inside the sauna all consume it:
- Heat. Ozone begins to break down at around 40 °C and the process accelerates above that. A hotter session is therefore not automatically a stronger one.
- Moisture. Water vapour inside the sauna converts some of the ozone to hydrogen peroxide.
- Surfaces and organic matter. Anything oxidisable consumes ozone. In a used sauna that includes sweat and skin oils.
What follows in practice
- Ozone cannot be stored or shipped. It has to be made where it is used, which is why the cabinet contains a generator rather than a cylinder.
- Production stops five minutes before the session ends, so decay is already well under way by the time the doors open. That, with the half-life above and ordinary room ventilation, is why no ozone destructor is fitted.
- Nothing is left working afterwards. Whatever the ozone was going to do, it did during the session.
Why it matters here
It explains several things owners ask about: why the cabinet makes its own gas rather than storing it, why running hotter does not mean more ozone, and why the room clears with ordinary ventilation once the doors are open.