Risk factors When breathing air, serious impairment due to narcosis starts at depths of about 30 metres (100 feet) or a nitrogen partial pressure of 3.2 bar. At depths of 90 metres (300 feet) or nitrogen partial pressure of 8 bar nitrogen narcosis leads to hallucinations and unconsciousness. Although narcosis is most commonly reported below 30 meters, it may be that the divers` cognition is affected before that, but that they are unaware of the changes. Even so there is no reliable method to predict the severity of the effect on an individual diver, and as noted the effect may vary from dive to dive (even on the same day). Nitrogen narcosis has been compared with altitude sickness insofar as its variability (though not its symptoms); its effects depend on many factors, with variations between individuals. Excellent cardiovascular health is no protection and poor health is not necessarily a predictor. Thermal cold, stress, heavy work, fatigue, and carbon dioxide retention all increase the risk and severity of nitrogen narcosis. Nitrogen narcosis is known to be additive to even minimal alcohol intoxication, and also to the effects of other drugs such as marijuana (which is more likely than alcohol to have effects which last into a day of abstinence from use). Other sedative and analgesic drugs, such as opiate narcotics and benzodiazepines, add to nitrogen narcosis.