21 bars. .
The two types of oxygen toxicity are Central Nervous System (CNS) oxygen toxicity and pulmonary oxygen toxicity. Exposure to partial pressures above 1.4-1.6 bar results in an unacceptable risk for this type of toxicity to occur. It results in trembling, nausea, lip twitching, convulsions and unconsciousness. Breathing air, a diver is exposed to a partial pressure of 1.4 bars at a depth of 57 meters. So in recreational diving, this type of toxicity is not common. However, in pulmonary oxygen toxicity a diver is exposed to partial pressures of 0.5-1.4 bar for a longer period of time. At a depth of 15 meters the partial pressure is 0.5 bars. Toxicity problems are to be expected after exposures of more than 90 hours. At a depth of 40 meters the partial pressure is 1 bar. Problems are to be expected after a 12 hour exposure. Using oxygen enriched air (Nitrox) makes this toxicity possible, though still not very likely. Symptoms are burning sensations in the chest and an irritating cough. When continuing the exposure, effects get worse.
When the symptoms are observed, immediately bring the diver to the surface (shore or boat if possible). You have to continuously monitor the airway, breathing and pulse, and be prepared to resuscitate if necessary. (Clendenen and Orr 22) Emplacing simple safety measures can reduce the chances of oxygen toxicity. The main one is staying above the maximum recommended depth. Always ensure the air you breathe is clean by getting your tanks filled at a reputable store.
Nitrogen narcosis "getting narked- is a fairly harmless phenomenon, if the diver is aware of its existence. The narcosis develops with an increasing nitrogen partial pressure. Typically, it occurs at depths greater than 30 meters, causing an anesthetic like effect making the diver feel sleepy, drowsy and a little intoxicated. "The effects vary from individual to individual, depending on their physical state and environmental factors- (Newman 70).