We personally teach how to use a dive computer, but we also go through the tables and formula so that my students have an understanding of what is happening inside the computer and get a good understanding of the physics behind the theories. Any good instructor should be willing to go through the formula with you. Having done the classroom work, you do not actually have to dive on nitrox to complete the course as the only physical difference between diving with nitrox and diving with air is purely the planning (you can’t even taste the difference).
The amount of time needed will primarily depend on how much self-study you do beforehand. If your instructor teaches only the table method, you can expect to spend most of a day ensuring you can work both the tables and the formula. However, when using the computer method it shouldn’t last too long (approx. 1-2hours) if you have read through and understood the manual.
A lot of more experienced divers tell new divers “you’ve got to do nitrox!”. “Why?” I hear you ask. There is a misconception that you can dive deeper, but actually it is just the opposite, but you can dive for longer.
Another misconception is if you’re on a diving holiday using nitrox that it will make you feel less tired after doing many dives. Although there is no actual data to prove this, it is repeated by most divers. It could be just the ‘holiday’ effect where you’re more relaxed and there are no pressures.
So what is happening? Going back to your first lessons, you learnt that you have time and depth limits when diving. This is because as you dive your body absorbs the gas that you are breathing and, as you’re under pressure, you absorb more than you would at the surface. This becomes a problem as you ascend and the amount of pressure reduces which, if too fast, will allow those gases to bubble out. As you know oxygen is used in the body for various reasons, however nitrogen is not and therefore is more likely to form bubbles.
The idea behind enriched air, is that if you reduce the amount of nitrogen (by increasing the amount of oxygen) then the risk of bubbles is reduced (note: not eliminated). So extra oxygen = more energy and less nitrogen means your body doesn’t have to work so hard to get rid of the excess.
Sounds brilliant!! But is there a drawback? Why do you have to do a course in it? As mentioned above, as you dive deeper your body is subjected to more pressure. Chemicals, when under pressure and/or more molecules in each 100, react quicker, which for nitrogen isn’t a problem as it’s not used (no reactions) in the body and the number of nitrogen molecules is reduced. Oxygen on the other hand, is used and these speeded reactions can become a problem as more pressure is applied, and more oxygen is available in each breath. This in turn, if not properly limited, have serious consequences when under water.
Doing the PADI Enriched Air course eLearning/online, or any other course of a similar nature, will help you understand the relationship between pressures, gas absorption and why limits are important. If you’re looking to take your diving to a leadership role, e.g. Divemaster or above, then this understanding will help you explain to less experienced divers the why’s and wherefores of dive planning.