Tanteh, I started using a spareair last summer for freediving when I got my scooter. With a scooter it is very easy to cover much more distance without effort. However, if you find yourself in a situation where you "NEED" that scooter to finish the dive safely, and something goes wrong with it, then the spareair bails you out. The important thing to realize is "WHEN" you will need the spareair, before you are actually in danger. I guess what I mean is, that kicking to the surface in an out of air situation will not give you time to realize you need the air. It will hit you too suddenly. Like when you suspect there is a good chance your car will not make it to the next gas station. But you really think you will make it there. When your car starts to sputter, you had no idea when to predict exactly when, where and IF it was going to happen. But the instant sputtering begins, is when you black out with no time to pull your spareair out of its holster to breathe from. IT IS TOO LATE! Game over. The important thing is to know your limits and to recognize when a dive will not finish smoothly with a margin of safety. This awareness should not happen on the way up, but a little voice in your head tips you off before you head for the surface. Maybe you know you stayed a little too long, or you were a little too deep. Or perhaps you tangled a fin on some fishing line and it took precious moments to free yourself before heading to the surface. These few moments of panic will burn even more O2 than the time you weren't calm. So don't be fooled into rationalizing that "I was only tangled for 10 seconds". Maybe you burned 30 or more seconds of O2 from the adrenalin. Whenever you have the notion that the finish of the dive will be marginal, THAT is the time to admit to yourself you screwed up and to use the bottle. Then you must ascend slower than when freediving, and make a safety stop if possible. This is why it's also important to practice with your bottle. I have made it a point at the end of the day to "drill" and become familiar and comfortable with it. The time to LEARN it, is not when you need it. For example, the first time I practiced with it I simulated an emergency at 95'. There was absolutely not enough air in the lungs to purge the water out of the mouthpiece. I was monemtarily startled but not surprised, as there is often not even enough air to equalize. You must do the math also, and be familiar with it too. The 3.0 cu. ft. size bottle holds 57 breaths at the surface (assuming 1.6 L breaths). It helps to know how your individual body uses air in contrast to the rated specs. If you know you get 57 breaths at the surface, then you know at 99', or 3 atmospheres, you will expect 57/4 (14 breaths). But you will be ascending and getting increasingly more breaths as you surface. In one drill I started ascending at 100' and finished my safety stop with a total time on the spare air of over 5 minutes. It is imperative that you be familiar and confident with what to expect. If during an emergency you expect less performance than what you will actually get, you might be more prone to uneccesary panic. One way to look at it is, I dove down on 5L or so not expecting to use the bottle, but expecting a couple of minutes bottom time. If I were forced to use the bottle in an emergency, I take comfort in the fact that it holds 85L of air. That is the total oxygen content of 17 full inhales. Everyday I perform 25 minutes of "single-inhale" statics on just 14 total breaths. If I were tangled and prevented from surfacing for minutes, the confidence in these numbers can make the difference of a calm enough head to correct the situation, or a panic and wasting of precious Liters. I would encourage your buddy to familiarize himself with the bottle also. You never know if you will have to hand it to him while he frees himself and you surface. He needs to be just as confident in the equipment BEFORE the need arrises. There is never a second chance to be prepared for the unexpected once it happens.
I think the spare-air is a great insurance policy, but don't grow to rely on it in place of common sense safety. And remember, once you use it, you will have elevated nitrogen levels in your blood. So figure on ceasing freediving for an hour to be sure you're more than thoroughly purged of nitrogen. I hope this answered your question, and gave you some insight to the benefits.
Safe diving,
Jim
