Nitrox - enriching your bottom time
Posted By Christopher Chin on 26 September 2005
You and your buddy drift along what might be the most amazing dive site you've ever seen. The visibility is endless and the sealife is flourishing. Your ear to ear grins wane a bit as a dutiful glance towards your computer indicates that it's time to head back to the ascent line. You signal "up" to your buddy as you approach your maximum allowable bottom time, and you begin your ascent together.
While you perform your safety stop, you and your buddy reflect upon the dive. Just as you begin to wish that you had had more time, you look down and notice two other divers still enjoying the scenery, and you wonder how it's possible that they could safely stay so much longer than you....
Welcome to the wonderful world of Nitrox!
Primarily used to extend No Decompression Limits (NDL), Enriched Air Nitrox is known by many names: Enriched Air, EANx, or simply "Nitrox".
There are a few other benefits of Nitrox as well, and we will examine each of these in turn. Of course, because the universe is balanced, there are also disadvantages to its use, and these must be taken into consideration when deciding if it's safe or appropriate.
To better understand what Nitrox is and how it works, we should first examine the air that we breathe.
As we all learned in our entry level scuba class, inert nitrogen is absorbed by our tissues under pressure, and this plays a role in determining our no decompression depth and time limits.
Air, and the compressed variety found in our scuba cylinders, contains approximately 21% oxygen. The bulk of the remaining gas is nitrogen, so for simplicity's sake we'll call that 79%.
If we replace some of that Nitrogen with oxygen, we shift those percentages, and can adjust our NDL.
For example, the NDL for 80ft/24m is 30 minutes according to the PADI tables. If we're using EANx36 (pronounced "Enriched Air Nitrox 36", or simply "36%") there is only 64% nitrogen. The reduced nitrogen content is equivalent to air at a shallower depth, so when we are using EANx36 at 80ft, we're absorbing the inert gas *as if* we were only diving to 59ft/18m, where the NDL is a significantly longer 55 minutes!
You'll learn how to use Equivalent Air Depths and Tables in your basic Nitrox course, but many modern dive computers are "nitrox capable" and can calculate these adjusted limits for you when properly programmed.
Of course, 80ft is a significant depth, and while your NDL may be extended, you'll still want to keep a watchful eye on your Submersible Pressure Gauge. You might find that your air consumption is now the limiting factor on certain dives.
- Bookmark with :
- what are these?
