Quote: (Originally Posted by
Faceless)
Here are first bugs:
PPO2 setpoing was set to 1.3
The PPO2 profile seems to be correct.
The reason it drops to 0.4 is because the initial descent caused the PPO2 to spike above 1.6. This means the diver's CNS clock was burnt up in the descent. The CNS clock lasts just seconds with PPO2 above 1.6.
So, with no CNS margin available anymore, the system reduces the PPO2 reduced automatically to 0.4 to avoid the diver having a convulsion.
The 1.6 limit is reduced if you are running the "Safe CNS" by a 0.2/0.3 margin. There is a thread on this,
HERE.
The reason PPO2 rises at the end of the dive, is that if the diver is ascending and within 10m of the surface, it increases O2 to the same fraction of air, in case the diver decides to rocket to the surface. Unless this is done, the diver will die if he runs out of O2, or turned his O2 off near the surface: he would not have time to respond. This is one of the failure modes listed in the "How Rebreathers Kill People" list, and the solution is just what the simulation shows happens.
The spike of PPO2 at 25m is due to running into the CNS clock again: it has not wound down enough for the system to increase PPO2. You can see it trying to increase PPO2 again at 34 minutes, only to hit the same limit. Then at 42 minutes you are going for the surface, and are too close to the surface to allow the PPO2 to be lower than the fraction in air with a margin for your O2 consumption. It therefore raises PPO2 to avoid any risk of a hypoxic loop.
The final diagonal is the PPO2 reducing as you are on the surface.
So quite a useful profile, in demonstrating two of the hazards of rebreather diving: PPO2 spiking on descent burning up the CNS clock, giving rise to an O2 tox hazard if it is not dealt with, and the hazard of low PPO2 near the surface.
I missed one of your earlier questions, sorry, it was:
Quote: (Originally Posted by
Faceless)
1. Does setting failure modes has any impact on predive checks ?
No, though the predive checks picks up many of them, the failures can occur during the dive. The purpose of the simulation is to check what the effect is of the failure on the ability of the system to keep the diver alive.
Our job is to find all routes by which you can kill the diver and prevent them, if at all possible. Some things like a breath hold from 50m are outside the scope, but anything attached to the Rebreather should be within scope.
Have some green for a good post!
Cheers,
Alex