 The ratio of gases in a particular mix is chosen to give a safe maximum operating depth and comfortable equivalent narcotic depth for the planned dive.Safe limits for mix of gases in trimix are generally accepted to be a maximum partial pressure of oxygen (PO2—see Dalton's law) of 1.0 to 1.6 bar and maximum equivalent narcotic depth of .At , "12/52" has a PO2 of 1.3 bar and an equivalent narcotic depth of .