Is ozone safe to breath?

Oxygen preferred. Two oxygen molecular (20% of air inhaled) oxygen is what we normally breath in. Triatomic molecule, trioxygen is ozone, which is blocked largely by protective ozone layer in atmosphere. Over time, there has been some loss of ozone layer, but still only makes up about 6 parts per million of the atmosphere. It is an oxidant and therefore damaging to respiratory system, prob above100 ppb.