Karl´s Rebreather Page

 Staying too long under high oxygen pressure can cause hyperoxie problems,
so there are depth limits (better O2-partialpressure-limits) and partialpressure-time limits.

Getting a spasm similar to epilepsy is under water, breathing through a mouthpeace, much more dangerous than in the save environment of a decompression chamber, thats why the limits are so wide spread. CO2, that means workload, increases the risk of getting CNS problems when breathing gas with high ppO2. The risk to get an oxygen-spasm increases with ppO2, exposition-time, workload, stress, fear and indisposition.

Diving with Oxygen partial pressures above 0,5bar means that you have two clocks running that limitate your dive by toxic effects.

At Oxygen partial pressures above 1,7bar it comes within relatively short time to spasm similar to epilepsy. That is extremely dangerous when loosing your mouthpeace means inhaling water ! With higher partial pressure the time, until the risk of spasms becomes unacceptable, decreases rapidly.

The attacks mostly start with jerks around the mouth and the eyelids, before that nausea, dizzy feeling and tube-vision might be the first signals. Difficultys in breathing in the manner of quick shallow breathing attached with anxiety and suffocation feeling are leading very quickly to a tonic cramp of the entire body and unconsciousness.

Between two Dives should be a surface time (ppO2=0,21bar) of at least 45 minutes.

Symptoms may appear in any chronological order: cough without cough up, raising breathing resistance, complete inhaling becomes difficult, lower vital capacity, pain in the chest- and breatbone area, clumsiness and coordination problems.

In the early 60´s a unit was defined to measure the lung toxic effects:
UPTD (unit pulmonary toxic dose) = OTU (oxygen tolerance unit) = CPTD (cumulative pulmonary toxic dose)