Underwater Wakulla- November 17, 2011 You Never Know… By TRAVIS KERSTING Thursday, November 17, 2011 at 5:00 am (Updated: February 3, 11:14 am)

I would argue that most people driving a car do so with a spare tire, perhaps a few tools, and even a flashlight. These people may go their entire driving career without ever having a flat or some other road side emergency, but they still don’t go without these safety precautions. You also don’t see many sky divers jumping from air planes without a redundant parachute. Those parachutes even require maintenance up to four times a year. In SCUBA such a means having an additional source of sufficient gas available. To handle emergency situations under water, the community, including cave divers, wreck divers, and those folks doing very “deep” dives, have adopted the . This rule means that they use 1/3rd of their for descent and exploring e.g. a wreck. They have 1/3rd of their gas supply for their ascent to the surface. This leaves a 1/3rd, which is for emergency situations, unplanned obligations, or any other issue which might prevent return to terra firma. These “technical” divers usually have a minimum of two large cylinders and frequently upwards of 4 or 5. Each cylinder goes 1/3rd unused if the dive goes as planned. Commercial divers and divers have adopted what they call “bailout” cylinders for use as a redundant supply of open circuit breathing gas. Most of the time this means carrying at least one cylinder, the size of a standard aluminum diving tank, which they have no plan on actually using. In contrast, most recreational open water divers don’t carry much for redundant equipment. Recreational divers frequently come in asking me about something divers call a “”. When I started diving, about 10 years ago, the pony bottles I saw were small. Divers in my local area carried the small “Spare Air” branded device which contains a mere 3 cubic feet of air. Some carried a 6 cubic foot tank and fewer carried a 13 or 19 cuft tank. These cylinders are not very large, and the is negligible compared to the standard 80cuft SCUBA tank. In the water these redundant air sources will go almost unnoticed to a skilled diver, depending on how they are carried. They all require the same care and maintenance of your standard scuba kit even if they are never used. That being said, I rarely advise a diver to carry a pony tank. In my diving past I did carry one at some point, and still own a variety of them, but I have not carried one in 3 or 4 years. Why? Because most divers look for a pony bottle because they are diving deeper and they want it to get them back to the surface in case of emergency. That makes sense until you start looking at the math: Your average diver uses about .5 to .7 cubic feet of breathing gas on the surface. As we descend we use DOUBLE that amount of gas at 33ft. An aluminum 19cuft that lasts for 27 minutes on the surface now only lasts 13 minutes. At 66ft your cylinder lasts 9 minutes. Now most of the people I have talked to, who want a pony bottle, say they only want it for dives between 130, which is the recreational limit, and 150 feet. These divers may get 5 minutes worth of gas from that cylinder assuming their breathing rate has not increased due to or work load. I took a “Spare Air” to 146ft and calmly took 1 full breath while kneeling on the bottom, with 3 friends watching. I took one more small breath and was out of gas. I switched back to my primary gas supply to finish the dive. That experiment proved to me that I could easily drain that cylinder just getting to the surface, much less try and solve a problem, complete any necessary decompression, search for a buddy, etc. As a result, I tend to urge people to carry a redundant supply of gas that is proportional to the they plan to do. In most cases that means a tank of considerable size. Some of you will argue that you have a buddy with additional air, and you might be right. I can almost guarantee that at some point you will be separated from them for whatever reason. That would be a bad time to need them and their breathing gas just to get YOU home. Just because you have a buddy doesn’t mean they have the ability to get you both out of trouble. If you are both low on gas and nearing the end of your dive when a problem arises then the buddy will be of little help. If you are frequently pushing recreational depth limits, or approach decompression diving, or have a higher SAC rate, then you are probably a candidate for larger bailout supplies or even double cylinders. The good news is: these larger tanks, and the training about how to handle them, are available today, unlike 15 years ago. Each diver needs to evaluate their needs. You can never go wrong with visiting your local dive store, physically trying a dive with a redundant gas supply and asking lots of questions. It’s not that you might need it, but more a matter of when.