iainwilliams
Contributor
Hi - I have a question regarding partial pressure of oxygen, EAN mixes and repetitive diving.
We know that the NOAA CNS % exposure table recommends a maximum PO2 of 1.6 atmospheres. We also know that EAN mixes have been calculated on the basis of equivalent air depth (EAD), and NOT the PO2 100% which at 1.6 atmospheres is 6m / 20 feet.
QUESTION: If I use an EAN mix above (less than) 1.6 atmospheres on a dive (say to 30 meters/100 feet) then at the safety stop (6-4 m) decide to breath 100% O2 for say 5-10 minutes; will I be risking a lowering of CNS tolerance and possible convulsion? I know what CNS% level I am from the mix, depth and bottom time (from the table or computer) but will the extra 100% oxygen increase my CNS too much?
I know that I can do this dive on normal air, swim to the safety stop and outgas on 100% oxygen (I do this regularly to offset against DCS).
Furthermore, will this add to my CNS debt at the surface during my surface interval, if I decide to do a repetitive dive? Im pretty sure it will. If I am using nitrox tables, say EAN32, and off-gas at 4 m on 100% oxygen for 5 minutes thereabouts, how should I calculate my surface time interval? How much do I add? Or is the added CNS debt acquired from my 100% oxygen spell hardly worth the worry?
I hope this makes sense. Thank you. Iain
We know that the NOAA CNS % exposure table recommends a maximum PO2 of 1.6 atmospheres. We also know that EAN mixes have been calculated on the basis of equivalent air depth (EAD), and NOT the PO2 100% which at 1.6 atmospheres is 6m / 20 feet.
QUESTION: If I use an EAN mix above (less than) 1.6 atmospheres on a dive (say to 30 meters/100 feet) then at the safety stop (6-4 m) decide to breath 100% O2 for say 5-10 minutes; will I be risking a lowering of CNS tolerance and possible convulsion? I know what CNS% level I am from the mix, depth and bottom time (from the table or computer) but will the extra 100% oxygen increase my CNS too much?
I know that I can do this dive on normal air, swim to the safety stop and outgas on 100% oxygen (I do this regularly to offset against DCS).
Furthermore, will this add to my CNS debt at the surface during my surface interval, if I decide to do a repetitive dive? Im pretty sure it will. If I am using nitrox tables, say EAN32, and off-gas at 4 m on 100% oxygen for 5 minutes thereabouts, how should I calculate my surface time interval? How much do I add? Or is the added CNS debt acquired from my 100% oxygen spell hardly worth the worry?
I hope this makes sense. Thank you. Iain