If the diver exceeds the relevant gas mix's maximum diving depth (MOD) there is a risk of oxygen toxicity. The same applies if the diver has an incorrectly high oxygen content in the Nitrox mixture in relation to the depth of the dive.

When acute oxygen toxicity occurs this is partly due to how sensitive the person is to elevated oxygen partial pressure, and partly on how long he was exposed, as well as the diver's intensity of work.

In excess of 1.6 bar oxygen partial pressure, the risk of oxygen toxicity increases, the risk increases further the harder a diver works and the longer he is exposed. It is therefore important that the diver does not exceed the applicable depth limits, and he ensures that the correct gas mixture is used at the right depth.

Symptoms of acute oxygen toxicity:Acute oxygen toxicity suddenly occurs and starts with a general anxiety, hand tremors and nausea that need not be constant. Within a few minutes, twitching of facial muscles occurs, the eyes blacken and epileptic seizures set in, usually followed by unconsciousness.

Action:Reduce the oxygen partial pressure immediately by going to the surface. The symptoms will then disappear immediately without any further inconvenience.