Dangerous Allure of the Single Tank Deep Air Bounce Dive
A 60 meter bounce dive on a single AL80/11litre per bar cylinder, you will need well over half a tank (130bar out of a full tank of 200bar) just to get both you & a buddy to the surface in an emergency air sharing contingency --and that's assuming an "under control" max recommended ascent rate of 18m/min, a "non-stressed & nominal" breathing rate of 2 bar/min per ATA for both divers, and also most likely performing a deco/"safety" stop of several minutes with whatever air remains (a very narrow & non-robust set of assumption parameters to meet for recovery from this contingency, given the single tank).
So after reserving 130bar for the contingency above, that leaves you 70bar of gas usable for the dive. Assume you use 20bar of this usable gas on the fast descent to level off at 60m (initial exertion entering the water, inflating the BCD for neutral buoyancy at depth etc) --so you actually have 50bar usable at 60m.
At 60m (7ATA), your gas consumption rate will increase sevenfold from 2bar/min to 14bar/minute, so with only 50bar usable from above, you've got a maximum of three minutes at this depth. In short conclusion, this bounce dive is "do-able" on a single AL80, provided you can handle the extreme narcosis. . .
BUT YOU ABSOLUTELY HAVE ZERO ERROR MARGIN FOR ADDITIONAL PROBLEM SOLVING & RECOVERY TIME WITHIN THE ABOVE NARROW PARAMETERS, FOR EITHER YOURSELF OR YOUR DIVE BUDDY.
Now to relate my own Deep Air/Dark Narc encounter to 80m on Oil Rig Eureka here in offshore Southern California a year ago, in 12deg C water temp depth at the time: I used double AL 11L manifolded cylinders, an AL 11L deco tank of Oxygen, a drysuit for exposure & redundant buoyancy, and a DPV Scooter.
Planned dive was a quick powered scooter descent to 90m for a few minutes, and then multi-level profile up with most of the time spent at 18m, with O2 deco at 6m as needed. Total Dive Time was 50min, with deco obligation cleared before 12m (per Petrel Computer on 30/85 GF).
With the scooter off and stowed, all it took was three frog kicks into the current at 80m depth, and I was instantly overcome with a narcotic CO2 hit: Hyperventilation & difficulty breathing the regulator, high density & flow viscosity of the Air mix & resulting Hypercapnia came on immediately. In the dim ambient light, the only thing I was able to perceive was my Petrel Computer flashing an expected extreme PPO2 Warning prompt of 1.9, and it took a few minutes focused concentration not to panic, just to hang onto a rig structure support beam and try to regain a nominal breathing rate & clear head before starting the ascent using the scooter. (Note: Elevated CO2 levels increase the likelihood of hyperoxic seizures as well). Not at all pleasant and I don't want to do that again. . .
The point is that a Deep Air bounce dive can be treacherous enough even if reasonably planned and prepared as a solo twinset technical dive with the aid of a scooter above . . .On single tank however, any emergent contingency at depth will most likely result in tragedy. . .