nolatom
Contributor
hudson_hawk:im a new diver
i also seen the show last night
when i heard 250 foot dive on reg air i thought wow there luck all 3 didnt die
i was taught that the max deepth for air was 140 ft
im new so if im wrong /im wrong
im going to re read my manule tonite
If you look at your manual, you'll probably find the conservative maximum depth for compressed air is 1.4 atmospheres of oxygen. With 21% oxygen in air, that works out to 6.6 atmospheres (1.4 divided by .21 equals 6.66). At 10 meters salt water per atmosphere, that's 66 meters, or 218 feet. Below that depth (i.e. above 1.4 ata) the risk of oxygen toxicity rises to where trimix is a much better choice.
Most divers don't make a practice of going that deep on air anyway, as nitrogen narcosis makes such dives more difficult compared to trimix. So wherever you got the idea that 140 is plenty of depth for air, it's probably a good idea just from a narcosis standpoint.
I'm a rec diver so don't make a practice of going that deep anyway, I'm repeating what I've read and heard. You'll study these calculations when and if you take a basic nitrox course, since increased oxygen in the nitrox mix means oxygen toxicity occurs at shallower depths than with regular air, and you have to guard against it.