Ozone and oxygen
Ozone (O3)
Ozone is a gas whose molecules contain three oxygen atoms (O3); the oxygen in air has two (O2). The third atom is loosely bound, which makes ozone both a powerful oxidising agent and an unstable one that reverts to ordinary oxygen.
Also called O3, trioxygen
The molecule
Atmospheric oxygen is diatomic — two atoms, written O2. Ozone is triatomic, O3. It forms when enough energy is applied to split an O2 molecule into two free oxygen atoms, each of which then attaches to another intact O2 molecule.
What the extra atom does
The third atom is held loosely, and almost everything else about ozone follows from that:
- It oxidises. Ozone gives that atom up readily to whatever it meets, which is why it is used to disinfect water, strip odours from air and inactivate microorganisms.
- It does not last. Once it has reacted, or simply decayed, it is oxygen again. Ozone cannot be bottled or shipped and must be generated where it is used.
In our saunas
The cabinet contains an ozone generator fed with concentrated oxygen from a medical oxygen concentrator. Two figures describe it and they measure different things. 500 mg/h is what the generator produces, adjustable across ten levels. About 47 ppm is the ozone concentration reached in the whole air volume inside the sauna at our constant 2 litres per minute oxygen feed — a figure that fluctuates with the user’s size, body structure and weight. See Ozone concentration (ppm).
Never breathe it in
The same reactivity that makes ozone useful makes it damaging to lung tissue. Ozone must not be inhaled. That is why we keep the user’s head outside the cabinet with the neck opening covered, and why occupational limits for ozone in room air sit around 0.1 parts per million rather than 47. Those two numbers describe different things: one is the air a person breathes all day, the other is a gas applied to skin inside a closed sauna.
Why it matters here
Ozone is what separates an ozone sauna from an ordinary steam cabinet. Two things about it — that it oxidises strongly and that it disappears quickly — explain most of what you will read elsewhere about how these saunas are built, run and ventilated.