caveseeker7
Contributor
This is very sad news indeed. I talked with local law enforcement/water rescue at the Scuba Show in Long Beach just before I returned to Germany and at that time they were unaware of any rebreather diving fatalities in SoCal. My condolences to the family and friends of the victim.
The small number on the top left is the setpoint, 0.7 ata. That means that the unit is set to keep the partial pressure of oxygen at that level. CCRs mix pure O2 with a diluent, for recreational depth limits usually air. I doubt that this was the number remebered, small as it is, and as mentioned, it can't be set to 2+ ata in the first place.
Partial pressure of air at the surface is about 0.21 (about 21% O2 at 1 ata). Pure O2 hence has a pp of 1.0 (100% at 1 ata). Hence the loop content at the surface could not have been 2.43 ata unless the loop was overpressured to 2.43 ata, as padiscubapro explained. Aside from the overpressure valve, if the loop had been overpressured the diver would not have drowned. The counterlungs are located over the shoulders abd down the chest and would have provided plenty of bouyancy.
In the picture (taken at a dive show) the three large numbers across the center are the actual readings from the three O2 sensors, 0.94 and 0.95 ata. Those numbers change with depth (ambient pressure) and O2 content in the bag.
By mixing the O2 with the diluent during the dive, the ppO stays at a preset level, the setpoint. Close to the surface it's 0.7 ata as in the picture, during the dive it can be set by the diver to a higher value, 1.0 - 1.3 ata are common. O2 is added as needed to keep the setpoint, diluent is added to maintain the volume of gas in the loop (like you would to your BCD on descent).
So does O2, as Jason pointed out. Elevated partial pressure of nitrogen narks people.
Which makes me agree with MHK, a buddy could have most likely done some good keeping a panicked or injured diver at the surface. Assist dropping weights, inflating BCD and/or loop, doff the unit, keep him afloat till help arrives. Unless it was an uncontrolled ascent and he would have stayed behind, making a controlled one. Even then, from 70' he would have probably reached the surface in time.
The display on the Vision equiped Inspiration shows a bunch of data, I enclosed a picture of them below.Divmstr223:
The small number on the top left is the setpoint, 0.7 ata. That means that the unit is set to keep the partial pressure of oxygen at that level. CCRs mix pure O2 with a diluent, for recreational depth limits usually air. I doubt that this was the number remebered, small as it is, and as mentioned, it can't be set to 2+ ata in the first place.
Partial pressure of air at the surface is about 0.21 (about 21% O2 at 1 ata). Pure O2 hence has a pp of 1.0 (100% at 1 ata). Hence the loop content at the surface could not have been 2.43 ata unless the loop was overpressured to 2.43 ata, as padiscubapro explained. Aside from the overpressure valve, if the loop had been overpressured the diver would not have drowned. The counterlungs are located over the shoulders abd down the chest and would have provided plenty of bouyancy.
In the picture (taken at a dive show) the three large numbers across the center are the actual readings from the three O2 sensors, 0.94 and 0.95 ata. Those numbers change with depth (ambient pressure) and O2 content in the bag.
It's the partial pressure of oxygen in the loop, the product of ambient pressure multiplied by the % of oxygen of the gas. For example, air has 21% O2, so at the surface the ppO2 would be 0.21 ata. When you dive to 10m, the ambient pressure increases by 1ata, so ppO2 would be 0.42 ata. For Nitrox32 those two numbers would be 0.32 ata and 0.64 ata, for pure O2 they would be 1.0 ata and 2.0 ata, respectively.
By mixing the O2 with the diluent during the dive, the ppO stays at a preset level, the setpoint. Close to the surface it's 0.7 ata as in the picture, during the dive it can be set by the diver to a higher value, 1.0 - 1.3 ata are common. O2 is added as needed to keep the setpoint, diluent is added to maintain the volume of gas in the loop (like you would to your BCD on descent).
If the unit was indeed equiped with Vision electronics the data is recorded and downloadable, much like deco computers, with additional info like the loop's ppO2.
It chemically binds the CO2 that is generated when O2 is metabolized, thus removing it from the loop. CO2 becomes highly toxic at higher partial pressure.
So does O2, as Jason pointed out. Elevated partial pressure of nitrogen narks people.
That's a lot of failures. The loop can be drained to quite some extend, both uw and at the surface. In an OOG situation both can be inflated manually. Due to the large gas volume most RB divers need to carry more lead than OC divers. Dumping that would be easier and quicker than dumping the entire rig.Seuss:
Which makes me agree with MHK, a buddy could have most likely done some good keeping a panicked or injured diver at the surface. Assist dropping weights, inflating BCD and/or loop, doff the unit, keep him afloat till help arrives. Unless it was an uncontrolled ascent and he would have stayed behind, making a controlled one. Even then, from 70' he would have probably reached the surface in time.
No, that I'm certainly not. 
