fisherdvm
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I would like anyone who post here strictly abide by the subject. There has been enough debate about the worthlessness of spare air, and about the value of pony tanks. Please keep comments and reply directed toward the safe use of spare air in the emergency situation.
My feelings about spare air is that it should not be used until one is above 50 ft. My logics is as followed:
An 80 cu ft scuba tank at 3200 psi holds 80 cu ft of air. At the surface, when emptied, it will hold 0.39 cu ft of air (80 cf / 204 ATM(3200 psi)). At 33 ft, it will hold 0.78 cf (you are now at 2atm). At 66 ft, it will hold 1.18 cf (3atm). At 100 ft, it will hold 1.569 cf (4 atm).
A 3 cf spare air is supposed to give about 40 breaths at surface. This would be 20 at 33, 13 at 66, and only 10 at 100 ft.
If one were to have an incident at 33 ft. My simple minded understanding would be simply to keep my airway open, suck on the regulator, and kick my way slowly up to the top without the spare air. Of course, if I have been at deeper depths at prolonged time, I should stop at 15 ft and suck the spare air dry. But I likely would be safe (maybe achy from the bends, but no spinal paralysis or brain emboli) even without the 15 ft safety stop. If my calculations were correct, at 15 ft, I would have 0.585 cf of air if the tank was emptied. But I rose up from 33 ft, so my "emtied tank" should give me 0.195 cf of air, and my spare air should give me only 2 cf (3 cf divided by 1.5 ATM).
If one were to have an incident at 66 ft, I would hold my breath, but keep my airway open. If I kicked up to 33 ft, I would have an extra 0.4 cf from the empty tank. If I kicked up to 15 ft, I would have 0.595 extra cf from the empty tank, plus 2 cf from the spare air.
If one were to have no air at 100 ft, I would hold my breath, and kick up to 33 ft, and start breathing from my regulator at 33 ft. At this stage, I should have 0.789 cf from the tank. But if I wait till 15 ft, I should have almost 1 full cf of extra air from my empty tank and regulator, plus 2 cf from a full spare air.
My question is, to the experienced divers and researchers in air embolism and the bends:
1. What is the best way to ascend without having air embolism: a. hold your breath completly while you still have the regulator in your mouth (which I assume would mean that your airway is still open as your lips are not clamped shut). b. take only tiny breaths until you reach 33 or 15 ft. c. suck every last bit of air from the tank as you ascend. d. breath from your spare air from the bottom till the top.
2. When and where is the best place to start using your spare air: a. Starting at the bottom. b. Only after your emptied tank is really emptied (it technically will really be not emptied until you reached the surface). c. at 33 ft, after you have used up your main tank. d. at 15 ft, after you have used up your main tank.
3. Where is the best place to do a decompression stop with the limitation of your spare air (2 cf at 15 ft, 1.5 cf at 33 ft, 1 cf at 66 ft): a. at 15 ft or b. at 1/2 of your maximum depth.
Based on my calculations above, and based on my understanding of air ways, you are safe to hold your breath as long as your lips are pursed around a regulator and thus air embolism should not occur. As your lung expands, the air should escape from the regulator. Based on the above understanding, I would hold my breath until 15 ft. I would ascend at a rate which I would feel comfortable without overshooting the 15 ft mark. Then I would breath from the tank, then I would switch to spare air, then I would surface.
Would the physics of diffusion favor decompression at 1/2 of the maximum depth, or the traditional 15 ft (1.5 atm) spot?? Especially when your time is limitted by the tiny amount of air you have here?
My feelings about spare air is that it should not be used until one is above 50 ft. My logics is as followed:
An 80 cu ft scuba tank at 3200 psi holds 80 cu ft of air. At the surface, when emptied, it will hold 0.39 cu ft of air (80 cf / 204 ATM(3200 psi)). At 33 ft, it will hold 0.78 cf (you are now at 2atm). At 66 ft, it will hold 1.18 cf (3atm). At 100 ft, it will hold 1.569 cf (4 atm).
A 3 cf spare air is supposed to give about 40 breaths at surface. This would be 20 at 33, 13 at 66, and only 10 at 100 ft.
If one were to have an incident at 33 ft. My simple minded understanding would be simply to keep my airway open, suck on the regulator, and kick my way slowly up to the top without the spare air. Of course, if I have been at deeper depths at prolonged time, I should stop at 15 ft and suck the spare air dry. But I likely would be safe (maybe achy from the bends, but no spinal paralysis or brain emboli) even without the 15 ft safety stop. If my calculations were correct, at 15 ft, I would have 0.585 cf of air if the tank was emptied. But I rose up from 33 ft, so my "emtied tank" should give me 0.195 cf of air, and my spare air should give me only 2 cf (3 cf divided by 1.5 ATM).
If one were to have an incident at 66 ft, I would hold my breath, but keep my airway open. If I kicked up to 33 ft, I would have an extra 0.4 cf from the empty tank. If I kicked up to 15 ft, I would have 0.595 extra cf from the empty tank, plus 2 cf from the spare air.
If one were to have no air at 100 ft, I would hold my breath, and kick up to 33 ft, and start breathing from my regulator at 33 ft. At this stage, I should have 0.789 cf from the tank. But if I wait till 15 ft, I should have almost 1 full cf of extra air from my empty tank and regulator, plus 2 cf from a full spare air.
My question is, to the experienced divers and researchers in air embolism and the bends:
1. What is the best way to ascend without having air embolism: a. hold your breath completly while you still have the regulator in your mouth (which I assume would mean that your airway is still open as your lips are not clamped shut). b. take only tiny breaths until you reach 33 or 15 ft. c. suck every last bit of air from the tank as you ascend. d. breath from your spare air from the bottom till the top.
2. When and where is the best place to start using your spare air: a. Starting at the bottom. b. Only after your emptied tank is really emptied (it technically will really be not emptied until you reached the surface). c. at 33 ft, after you have used up your main tank. d. at 15 ft, after you have used up your main tank.
3. Where is the best place to do a decompression stop with the limitation of your spare air (2 cf at 15 ft, 1.5 cf at 33 ft, 1 cf at 66 ft): a. at 15 ft or b. at 1/2 of your maximum depth.
Based on my calculations above, and based on my understanding of air ways, you are safe to hold your breath as long as your lips are pursed around a regulator and thus air embolism should not occur. As your lung expands, the air should escape from the regulator. Based on the above understanding, I would hold my breath until 15 ft. I would ascend at a rate which I would feel comfortable without overshooting the 15 ft mark. Then I would breath from the tank, then I would switch to spare air, then I would surface.
Would the physics of diffusion favor decompression at 1/2 of the maximum depth, or the traditional 15 ft (1.5 atm) spot?? Especially when your time is limitted by the tiny amount of air you have here?