A diver I know asked a senior member of their club to help them set their computer the appropriate mix of nitrox that they diving. The senior diver told them that they should leave it set to air as it would give them a safer dive.
My views on this are:
1. Surely this negates the benefits of nitrox.
2. The CNS exposure is not being calculated.
3. The computer wouldn't warn if the diver went below MOD.
4. Possibly the senior diver didn't know how to set his computer and was saving face.
What are you views? I've had a search on this topic and didn't really come up with much.
1. It negates one benefit of nitrox (the extended bottom time) but gives you a different benefit of lower nitrogen loading for a given dive and thus safer than what the computer thinks.
2. Correct, the CNS is not being calculated bot for recreational dives this is likely a non-issue. This sounds like a recreational diver.
3. Correct, the computer wouldn't automatically warn when going below the MOD but you can manually set depth warnings a different way. Don't blindly rely on your computer for warnings though, think for yourself. What if one day you forget to change your computer from air to nitrox the computer wouldn't warn you then.
4. Yes, perhaps he didn't know but there are other reasons this info could have been given. Maybe he was a bit old school, this was a common way of diving nitrox. Maybe the person asking was using nitrox to increase safety, diving up to the no deco limit on nitrox is as risky as diving up to the no deco limit on air so no safety improvement, diving nitrox whilst following an air computer gives an increased margin of error.
Why didn't you ask the senior diver there and then? Maybe they would have been happy to explain and then everyone would have been happy.
Thanks for comments, it makes sense. I did ask at the time and was told it makes the dive safer. I made sure my computer was set right and change the other divers for her. I think your right though it was an old school guy.