Is this true for dive computers?

[Akimbo]

Are you really going to obsess over semantics based on a trivial 1.3% difference that is mostly outweighed by the daily fluctuations of barometric pressure (i.e. weather)???

It can be more than semantics. I don't think any divers care about atmospheric fluctuations in pressure, it is the cumulative pressure exerted by water that counts. A 1.3% variation is not that big a deal at 5 ATA, but starts to count long before you get to 50 ATA, which the Navy Diving Manual supports. The safe margins between hypoxic and a target bottom mix for saturation divers (typical PPO2 around 0.3) is already pretty close after factoring in analyzer tolerances and response times.

Deep (100-150M) technical divers should also be concerned about "rounding errors" and analyzer tolerances when operating at the high end of the PPO2 (1.4-1.6 PPO2) range.

 

[Kevrumbo]

It can be more than semantics. I don't think any divers care about atmospheric fluctuations in pressure, it is the cumulative pressure exerted by water that counts. A 1.3% variation is not that big a deal at 5 ATA, but starts to count long before you get to 50 ATA, which the Navy Diving Manual supports. The safe margins between hypoxic and a target bottom mix for saturation divers (typical PPO2 around 0.3) is already pretty close after factoring in analyzer tolerances and response times.

So if you're saying a 1.3% variation makes a big difference at 50 ATA (!), then wouldn't the use of an ADS be better indicated instead?

Deep (100-150M) technical divers should also be concerned about "rounding errors" and analyzer tolerances when operating at the high end of the PPO2 (1.4-1.6 PPO2) range.

For sport recreation technical divers, pathophysiologic work-of-breathing at deep depth is now becoming a more critical parameter causing or compounding the potential problems of high end ppO2 and END:

• Choose a bottom mix gas with low density, and make this a priority over other considerations for very deep dives where significant exercise is anticipated.

Advanced Knowledge Series: The Gas Density Conundrum | Dive Magazine
DAN Technical Diving Conference Proceedings 2008, pp12-33

 

[Akimbo]

o if you're saying for a typical ppO2 around 0.3 bar at 50 ATA (FiO2 of 0.6% ???), a 1.3% variation makes a big difference, then wouldn't the use of an ADS be better indicated instead?

Yes, bottom mix at 500M is 0.59% O2, just under 1% at 1,000'/300M. The hypoxic limit is 0.31% (0.16 PPO2). You can see why we don't run at 0.21 (air equivalent) since the hypoxic margin gets really close.

ADSs aren't used that much since ROVs can do as much or more than an ADS at a lower cost, zero human risk, and virtually unlimited endurance. ADSs are a lot worse than working in a Mark V hat. ROVs often have force-feedback manipulators, interchangeable "hands", and more motion than a human hand; let alone a claw on an ADS. Good ROV operators can pick up an egg, set it down, and then pick up a 300 Lb tool. The technology was developed for handling radioactive materials. It's not the same as the sensation of touch but a long way from the old hydraulic claws.