The rate at which oxygen toxicity develops is directly related to
the partial pressure of inspired oxygen. Oxygen toxicity does not
usually occur when the concentration of oxygen is less than 50%
(an oxygen fraction of 50% at normal atmospheric pressure
corresponds to exposure to oxygen at 50kpa) [14]. This data,
however, is obtained from young, healthy subjects. It should also
be noted that hyperventilation of air at atmospheric pressures does
not cause oxygen toxicity, because sea-level air has a partial
pressure of oxygen of 21kpa and the lower limit for toxicity is more
than 30kpa