I can’t tell you how many times non-divers ask: Are your tanks filled with Oxygen? Usually, I’ll jokingly reply; Are you kidding that stuff can KILL ya! Scuba cylinders are simply filled with compressed air. That’s all, just air.
Interestingly enough, the scuba regulator is designed to deliver air at the same pressure as the surrounding water pressure. So the deeper you dive the regulator compensates for increased ambient water pressure and delivers air at higher pressure. This make it easy for divers to breath.
Air is comprised of several gasses. The two major components are approximately 20% Oxygen (O2)and 80% Nitrogen (N2). Now I know you’re going to say, but Tom, you mentioned several gasses and the O2 and N2 percentages add up to 100%, What gives? The other gases in our atmosphere are so negligible, for the purpose of scuba, we simply ignore them.
Tom, why are you spending so much time on this topic – you ask? Well interestingly enough, over time the science behind diving has learned that if we decrease the amount of N2 is our air mixture by increasing the amount of O2, divers can stay down longer. That means more bottom time and that’s what all divers are looking for. All divers want to stay in the water for as long as possible.
Divers use dive tables or dive computers to determine how long they stay down for a given maximum depth. So let’s look at what the dive table tells us. The PADI Recreational Dive Planner indicates a diver can dive to a 60 foot limit and must start their ascent after 55 minutes at that depth. The other limiting factor is a diver should arrive back on the boat with at least 500 psi left in the cylinder.
So a diver is limited by the maximum bottom time of 55 minutes or be on the boat with 500 psi in the cylinder. If after 55 minutes at 60 foot my tank pressure reads 1500 psi, I could stay down longer based solely on tank pressure. But the dive tables limits me to 55 minutes. Darn, still plenty of air to stay down longer.
Remember earlier I mentioned decreasing the amount of N2 in the breathing gas by increasing the amount of O2 gives divers more bottom time? Now here’s a good reason to adjust the O2 level of my breathing gas. By doing so a diver can take advantage of the extra pressure in the tank mentioned in the earlier example. By changing the blend of a diver’s breathing gas to 32% O2, the maximum bottom time at 60 feet increases to 90 minutes. Ninety minutes – That’s an increase of over 80% in bottom time. Most divers would love that! Again remember that divers should still be back on the boat with 500 psi of gas in the tank. So you still have to watch the tank air pressure very closely. These altered gas mixtures are often referred to as “Enriched Air Nitrox” or “Nitrox” for short.
Maybe you’ve heard the old adage: You don’t get something for nothing! That’s true in this case. At deeper depths, the higher pressure O2 can become toxic. So that means a diver has to watch just how much O2 exposure accumulates when diving. The major toxic concern in the body is Central Nervous System Toxicity. That can make a diver prone to convulsions. Sixty feet below the surface of the water is not the place to go into convulsion.
To prevent this from happening, the dive planning tools used for Nitrox have allowable exposure rates for different O2 blends. This helps divers stay well within safe limits. DivingNitrox is very safe as proven over time. It simply means that divers need to exercise care in the dive planning process and follow their plan.
So, can just any certified diver use Nitrox? No. Divers need to be trained to use it. In order to get Nitrox fills, you have to show that you are certified to dive Nitrox blends. The certification is a rather simple process. It involves some reading, answering questions, taking an exam and some practical work with your instructor. The instructor completes some paper work and sends it to the certifying agency and you’re certified. Then you’re ready to dive Nitrox and enjoy more bottom time with your dive buddy and the marine creatures below. Check with your local dive center or your instructor for more information. Oh yes, you can also contact me!
