“Regardless of where the ‘parachute’ is set, nobody has yet explained why this is anything other than a daft idea.”
The above quote was taken from a recent discussion on an internet dive forum about gradient factors. As per the norm, it eventually morphed into a sub-discussion about about the benefits (or lack thereof) of diving an ECCR (Electronic Closed Circuit Rebreather) manually. I considered joining the fray but then thought better of it. Having wasted time discussing topics with people who don’t want to hear what you have to say, I decided it would be more productive to write an article expressing my views.
For me … the concept of using the solenoid as a failsafe or parachute is for the express purpose of developing both muscle memory and an internal clock in your head. This will eventually enable you to intuitively know when the solenoid is supposed to fire. Contrary to the opinions of some, it is NOT because anyone believes the electronics are unreliable.
When I dive I often like to use a controller set point of 1.0 and maintain a 1.2 or 1.3 manually. When I hear the solenoid fire I view it as the machine telling me “Hey, dummy! Pay attention!” To make it interesting I try to make a game out of it. I like to see how long I can go without the solenoid firing. In the spirit of “every dive is a training dive” I use this as a learning / teaching tool. If the machine fails I will (hopefully) easily catch it because I have trained myself to be acutely aware of what is going on with my ppO2, all by making it a game rather than a “chore”. Of course, when I have a “busy” dive, I use the solenoid and fully appreciate the convenience it brings to the table. Interestingly, I also find that subconsciously I know about when I should hear it fire and have found myself reaching for the manual add O2 button at the same time the solenoid is doing its job. This kind of validates the main purpose of the exercise.
For a seriously deep dive I favor not using the solenoid at depth. My preference is to dial it back to a safe level that is well below the desired set point. The idea is that it is far less likely to stick in the open position if it is not opening and closing. Also, remembering that it is not necessary to add O2 on descent, if you use the correct diluent, you should be close to your desired set point once you reach target depth. My rationale is that a stuck open solenoid at say 5 – 600 feet is quite serious and its risk should be minimized. I mitigate that risk by using the proper diluent gas for the dive; one that gives me an acceptable ppO2 at depth, manually tweaking it when necessary. I use the solenoid on ascent where a stuck open failure is not quite so serious and much easier to manage.
To those whose opinions differ and believe utilizing the electronics is the preferred way to dive I say fine. I agree that the human hand on a button is no match for the precision with which todays modern controllers hold set point. I just prefer to retain as much control over the unit as is reasonably possible. If I were to buy a Ferrari or a Lamborghini I would want a manual transmission even if an automatic was available because I want to DRIVE the car, not the other way around. In that same spirit, I want to DIVE my rebreather.