Small Tank Scuba Diving

In the late nineties of the last century we started diving in the Adriatic Sea. For various reasons, mostly financial, our equipment was limited to bare minimum. We were using 7L tanks which we could occasionally buy cheaply as the fire department surplus. We were breathing via the old Czechoslovak regulators Tajfun updated to accommodate the pressure gauges from Chirana Stara Tura. We used an Italian mechanical depth meter. Unfortunately we could not afford a dive watch or timer.
To overcome that problem of not having a timer I developed a method that allowed us to dive without watching our dive time. I compared the no decompression limits for various depths with the corresponding figures for various small tanks (7-10L) and realised there was no risk in using the smallest one (7L) at any depth. It was enough to watch the depth meter and the pressure gauge. Within the whole reasonable range of depths it was not possible to get into decompression obligations before all the available gas was consumed. It was quite similar with the 8L tank too. I was considering that tank because occasionally I could borrow one. A 10L tank introduced a bit more complexity, it was at least theoretically possible one would be able to earn some decompression obligations. To avoid that risk we stuck to our 7L tanks and enjoyed “careless” diving.
The chart shows details for various depths. All the numbers are based on quite a high air consumption of 20L per minute and a 3MPa reserve. Anybody who wants to use a similar method must consider that experienced divers can have a lot lower gas consumption which means longer bottom times and a higher risk of decompression obligations. To overcome this risk we added a rule: A half of the available air volume serves for the descent and the time in depth, another one for the slow ascent plus the safety stop.

The method described above was developed out of necessity. It tries do explain it is possible to scuba dive if one does not have or cannot have a time measuring device. I do not recommend diving without a timer or a computer. Quite the opposite. I dive with a computer more-or-less all the time. Except when I forget it at home 🙂

* No decompression limit, based on NAUI tables