I started teaching SDI’s Recreational Solo Diver course in 2003.
Many divers who did not meet the prerequisites to enter the solo diver course or didn’t actually wish to dive solo still wanted the convenience of an independent air source.
So in 2009 I started training open water divers with Submersible Systems' Spare Air unit.
Next to come along were advanced divers who wanted to dive to a depth greater than the open water divers but not past 100 feet or 30 meters.
For these dives I started training the divers with small pony cylinders.
In 2012 I created the SDI Independent Air Source course using both a Spare Air and a small pony cylinder.
So, given this experience I get a lot of questions about the subject. Here's my FAQ:
FAQ on Independent Air Sources for Scuba Diving
What size cylinder is best for me?
This is a question I get asked whenever the subject of solo diving or pony cylinders comes up.
I answer with this question. How much air will you need?
Now in my old age I have become a warm shallow water specialist, so I do not need a lot of extra air should I need to use my independent air source, so I am okay with a Spare Air or 6 cf cylinder on very shallow dives.
If I am going deeper then a 13 or 19 cf will suit. Really deep... well we are not going there in this discussion.
I made dozens of out-of-air ascents using these small units when creating this course.
Can a diver make an out-of-air ascent from 100 ft or 30 meters with only a 3 cf cylinder of air?
Yes they can. Would they want to? Well I would rather have a small amount of air in my independent air source than no air at all.
So the simple answer is to carry enough air to ascend from the greatest depth that you will be diving to.
What do I learn in the the Independent Air Source Course?
The actual course is almost the same as the Solo Diver course.
It involves two training dives where the student learns how to deploy their independent air source in an out-of-air emergency and make their way to their buddy or to make a direct ascent to the surface.
Consideration is given to sizes of cylinders and mounting of the cylinders.
How does the independent air source work in a buddy pair?
I dive with an independent air source on just about every dive, even if diving with a buddy or in a group.
Having it there is just insurance in the worst possible situation: out of air at depth.
If I am asked to share air with an out-of-air diver I simply offer my independent air source.
I believe that two well trained divers equipped with an independent air source are a much safer team than two divers not so trained or equipped.