You'll need to know what your RMV is, to start. Let's assume it's .5 CFM. At 130, you are at 5ATA, so your consumption at that depth is 2.5CFM, assuming you are as relaxed at depth as you were when you determined your SCR to be .5. If something renders your primary gas supply unusable, there is a high likelihood that this will excite you to the point that your rate of consumption will double. Figure you'll burn 5CFM at that point. How's that 3CF looking, now?
True, but that 5cfm consumption rate changes dynamically because I am going up at a steady 40 ft/min or more at that depth, so its not like I am going to sit at the bottom and suck down my pony at 4-5cfm (and I know my consumption rate does not double in an emergency from experience, so it is more likely around 3-4cfm). So my first breath or two might be at 4cfm, but by then I am up 10 feet or so.
And who is talking about 3cfm for a pony? I bought a 6cf pony, which I thought would give me about 4 minutes to ascend ... though I am now considering upping that based on the previous posts. Read my post please before attacking. And yes, I meant boyle's law. It has been a while but I can still do the math, its just that the equations involved, when you are moving and partial pressures and relative gas volumes (and ascent rate) are changing constantly, get a little complex and involve some differential equations that I would really prefer to just find rather than create.