 Significant impairment due to narcosis is an increasing risk below depths of about 30 m ( 100 ft ) , corresponding to an ambient pressure of about 4 bar ( 400 kPa ) . Most sport scuba training organizations recommend depths of no more than 40 m ( 130 ft ) because of the risk of narcosis . When breathing air at depths of 90 m ( 300 ft ) – an ambient pressure of about 10 bar ( 1 @,@ 000 kPa ) – narcosis in most divers leads to hallucinations , loss of memory , and unconsciousness . A number of divers have died in attempts to set air depth records below 120 m ( 400 ft ) . Because of these incidents , Guinness World Records no longer reports on this figure . 
