Dude, I hate to be somewhat anal but you don't die instantly when the partial pressure of O2 gets to 1.6 bar.

The body is designed to take a partial pressure of about 0.21 bar. Subjecting it to higher partial pressures causes complex physiological changes to the way the body works. These changes and effects of the exposure is know as oxygen toxicity.

What Happens When the Partial Pressure of O2 Gets Too High

There are two types of adverse reaction one, the first is caused by the brain basically going into epileptic fit when exposed to high partial pressures over 1.6 bar (the classic O2 hit ). The fit itself is not dangerous but as the victim is under water trying to hold a regulator between their teeth, the danger of losing consiousness and dropping the regulator and drowning is somewhat high.

The second is caused by caissons disease above 0.21 bar (Pulmonary oxygen toxicity). The effect of this is the lungs start to ache and then burn and respiration becomes somewhat difficult, eventually the lining of the lung itself starts to decompose.

Both of these toxic reactions will cure themselves if the body is returned to the atmospheric pressure it is designed for ( i.e. you get out of the water). The only problem is both the hits and the O2 pulmonary toxicity are not easy to predict and each individual is totally random in how resistant they are to the effects. Being fit young and healthy is no real indicator either, as it is also dependent on the individual's physiological makeup and frame of mind.

The Influence of Nitrox

When the first nitrox tables were created by Haldane for the mine clearance divers on the D-Day landing beaches he recommended the partial pressure of O2 to be no higher than 2.0 bar. Subsequent table designs have reduced this over the years.


The modern recommendation from the RSTA is 1.4 bar and a absolute maximum of 1.6 bar (this is working on the assumption that some fool will just try and break the rules if they are written down so they recommend as low as possible). A working pressure of 1.2 bar is recommended as best practise best benefits of O2 for metabolism and the least danger of getting a 'hit'.

If you want to learn more about this do a Nitrox course !

All from the recesses of the back of my mind, all info. originated from RSTA, PADI, BSAC or IANTD official training manuals / courses.
All Formatting Done by : OneDragons