brutus_scuba
Guest
As many folks have said yes they can be. I like Crowley's comments. It doesn't hurt to use your Nitrox on the first dive of the day if it's deeper.
In an open water diving class they teach you to do you deepest dive of the day first and to get shallower with each dive. Well in terms of Nitrogen loading you need to remeber Henry's Law which states:
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
So you want make sure that the highest partial pressure of Nitrogen occurs on your first dive. In order to determine this you can simply calculate PN2 or more simply comparing the EADs. So if you were going to do your first dive to 85 feet and your second to 70 feet and you had one bottle with a 32% blend and one with a 21% blend then by the fundamentals taught in your OW class you should dive the 32% blend on the second dive. If you were to breath the 32% blend on the first dive your EAD would be 68 feet which means you would have a higher partial pressure of Nitrogen on the second dive, which you want to avoid.
However, here's the other side of the coin. If you decide that you're going to dive the Nitrox first and the Air on the second dive giving yourself a slightly higher PPN2 (1% higher than your first dive) on the second dive and you do both dives for 20 minutes with a 2 hr surace interval on the YMCA dive tables you would come up as a G diver vs. an H diver which means you're actually doing less Nitrogen loading.
At the end of the day here's my two cents on the issue: YES you can mix air and Nitrox on the same day. If you have a good understanding of how the gases work, you understand some basic dive principles, you're going to be okay. If you're doing dives aggressive enough that you're pushing these limits to the edge than you're actually going to need a few class above Nitrox and AOW. (i.e. Adv Nitrox and Deco Procedures)
In an open water diving class they teach you to do you deepest dive of the day first and to get shallower with each dive. Well in terms of Nitrogen loading you need to remeber Henry's Law which states:
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
So you want make sure that the highest partial pressure of Nitrogen occurs on your first dive. In order to determine this you can simply calculate PN2 or more simply comparing the EADs. So if you were going to do your first dive to 85 feet and your second to 70 feet and you had one bottle with a 32% blend and one with a 21% blend then by the fundamentals taught in your OW class you should dive the 32% blend on the second dive. If you were to breath the 32% blend on the first dive your EAD would be 68 feet which means you would have a higher partial pressure of Nitrogen on the second dive, which you want to avoid.
However, here's the other side of the coin. If you decide that you're going to dive the Nitrox first and the Air on the second dive giving yourself a slightly higher PPN2 (1% higher than your first dive) on the second dive and you do both dives for 20 minutes with a 2 hr surace interval on the YMCA dive tables you would come up as a G diver vs. an H diver which means you're actually doing less Nitrogen loading.
At the end of the day here's my two cents on the issue: YES you can mix air and Nitrox on the same day. If you have a good understanding of how the gases work, you understand some basic dive principles, you're going to be okay. If you're doing dives aggressive enough that you're pushing these limits to the edge than you're actually going to need a few class above Nitrox and AOW. (i.e. Adv Nitrox and Deco Procedures)
