The most dependable way to insure that an OOA diver gets a working regulator is to donate the primary. You are verifying its operability right here - right now. No other method presents a greater degree of probability giving the desired result of providing the OOA diver with a working regulator.
Donating the primary does present the issue of having two divers without an air source in their mouth to breath from. OOA diver is out of gas anyways. But this interruption in continuos breathing access creates an increased risk to the donating diver with respect to breathing resumption which is now dependent on restoring the regulator to the mouth - over non interrupted breathing access, when octo is donated.
This increase in risk is not theoretical or impossible. It is within the realm of possibility for all. It is possible that you have removed and replaced the regulator from your mouth a millionth times without incident, but on the millionth and one time you start choking and gagging with no regulator in your mouth. Lets just attribute this to the nature of our imperfection and general unpredictability. Things can and will happen. Thus we are dealing with probabilities, in this case risk assessment, since this a negative consequence.
The increased risk this practice entails has to be measured as accurately as possible taking into consideration the peculiar and specific characteristics each individual diver possesses, as well as environmental conditions which have on impact on a divers ability to perform.
When this is done we will find that for some the increased risk is miniscule. This is possibly also true for the majority of divers after undergoing training and practice. However, we will also find that for some divers this maneuver will present a not so negligible risk increase. And for still a fewer number of divers this maneuver will
present a significant increased risk of complications. Since diving entails the possibility of accidental or willful removal of primary regulator from the mouth, these divers should seriously consider the risks they are taking when practicing this activity. Training and practice will help some - but donating the primary will not be the most practical, efficient, lowest risk option for some divers or their buddies. Quite the contrary, a diver uncomfortable or one prone to stressing to a degree that impairs his behavior when the regulator is out of his mouth should avoid using this method of donating gas.
Now lets assess the risk of having an octo malfunction. If it is operated, maintained and tested diligently the risk of malfunction will be miniscul. Proper maintenance, pre dive test, periodic testing throughout the dive, proper attachment in order to provide ease of access and minimal contamination, proper cleaning and storage after the dive.
We will likely find, if tested, that for the majority of divers who practice the above care with their octos only a minimal increase in probability of operability will be gained by donating their primary as opposed to their octo. However, we should also consider that there is a real risk, even if minute, of encountering a situation where the OOA diver will perish or panic in the time it takes to remedy a malfunctioning octo. Which can place the donor at risk as well.
This risk assessment must again, inescapably, be carried out taking into consideration the specific diver and specific circumstances. A diver that has a cheap octo, and/or does not
maintain it well, presents an increased risk that it will not function properly. Likewise if he drags it around. Some environmental conditions and dive requirements can also increase the risk of malfunction. Lots of solid matter in the water, squeezing through
spaces where contact is made with solid surfaces. Measures can always be taken to minimize negative exposure, but we are dealing with maximizing or minimizing probabilities, not eliminating them. For some of these divers and under some of these conditions it would be best to donate the primary regulator, assuming they are comfortable doing so.
The probability of some of the worst case scenarios developing, or of a having a scenario that compounds into a worst case event may be minute indeed in some cases. Nonetheless, it is in the interest of every diver to inform him/her self with objective facts, so that within reason, an accurate and objective understanding of the available options and risks encountered can be realized and assessed. When looking at the overall picture, these statistically minute chance of occurrence will occur and those not prepared for them will pay the ultimate price. It is true that we cant prepare for all foreseeable circumstances, much less unforeseeable ones, specially when we consider the cause and effect that is created when measures are implemented in order to minimize risk in one area. The risk is often shifted to another area, sometimes increasing it overall, something that often only becomes apparent when a thorough risk assessment is conducted.
All in all, under ideal conditions and with competent divers there probably is an insignificant difference in probability of operability comparing the donation of the primary or the octo. On the other hand, as I think Ive explained, when we consider the specific variables in any particular situation, the difference in risk can be significant from one method to the other.
