Possible causes of problem I witnessed

[SCUBA_Phil]

Dave,
Many people are color blind red/green (me included). I can tell the difference but it is not huge. I'm sure some people can't tell the difference.

Rick,
The Meg has a flash code. Basicly, green is above 1.0 and red is below 1.0, amber is 1.0. So 1.3 looks like blink, blink, blink, pause, blink, blink, blink, pause, blink, blink, blink, long pause (all blinks are green), then repeats. It is looking at each O2 sensor. If your color blind, it looks the same. 0.7 is 3/10ths below 1.0. Being color blind requires extra attention. So when I dive the system, I start at 0.7 at the surface. If my diluent is 10/50 (50% he +an air top off), I pay attention if adding diluent above 20', below, no issues. I watch the HUD on the way down. When hitting the bottom (150 to 200), the system is near 1.0. Here, I change the set point and look at my pressure gauges to ensure (one more time) that the gasses are on. The sytem will now inject O2. On the Meg, it is a 2 second on followed by 8 seconds off, repeated until O2 is above set point. So here I listen for the next minute and when it stops the firing cycle, I look at the hand set (1.3) to ensure all sensors are healthy. At this point, I look at the HUD every 45 to 60 seconds for just a single blink, blink, blink. Every 5 min., I look at the hand sets for real numbers. On the ascent, I pay very close attention, this is when most problems happen due to reduced pressure. I'm not stating that my way is best, just that I have a system and won't be complacent on a RB. This is another reason I chose the Meg, it is not automatic - you have to fly it!

Phil

 

[caveseeker7]

Ahem, cough, cough ... the No.1 mantra for RB divers is "ALWAYS KNOW YOUR PO2!" ...
which of course doesn't mean they all do all the time.

As mentioned, at the surface the pO2 can reach only 1.0 ata, hence a lower setpoint is chosen/maintained. Otherwise O2 would inject continuously. Some electronics switch to a chosen higher setpoint automatically, some manually, some offer a choice of either.

Usually the pO2 is checked throughout the dive in regular intervals, and some units offer HUDs to either signal the actual pO2 value or high/low warnings. If the unit wasn't equipped with a HUD, and setpoint didn't switch automatically the additional deco seems reasonable.

Even if you watch your pO2 during descent it can be hard to know the chosen setpoint until it's displayed, as ambient pressure rises. Quite a few divers let their pO2 "spike" on descent (to say 1.4 or 1.5 ata) and breathe it down to whatever their chosen setpoint is (say 1.2 ata) ... knowing they're above they may not notice until it's dropped back to 0.7 ata that they forgot to switch.

 

[netmage]

I'm not a RB diver, so my question comes from a "curious but ignorant" perspective.

Yesterday on a charter, a 2 man team of RB divers stayed an additional 30 mins of deco beyond their plan. We were all on the boat looking down at them. When they were on their shallow stop, a crew member dived down and checked on them. They signaled back that they were OK but that one of them needed to complete additional deco.

I never heard what the issue was, but both were OK.

The dive was planned to 200', and that was the bottom, so they couldn't have gone beyond their max depth. They began their deco pretty much with the rest of us (after 20 mins), so I seriously doubt they exceeded their bottom time. In fact, I think their bottom time was cut short. I'm not 100% sure, but I think they were on Megs. They never left the loop.

What could cause the additional obligation? PPo2 setting errors? Some kind of PPO2 error, I would think...

Just wondering...

Meg's in Pompano... Hmmm, Oliver, George, Mempilot, Padipro, Tom Mount... There's a few guys over in Naples area, and the AUE dudes; but I couldn't see them running into this unless something was wrong, their more on the experienced side. Wasn't me.., and doubt Monkey woulda been up for the Lowrance. Curtis and his buddy, Stephen I think, or Matt R. Mike is in S. Afria, and it wasn't Lesley. Off the top of my head, thats the local megs. There's more than a few...

I'm think I know who they are, only because one dives a VR3, the other dives a Shearwater, and the scenerio you describe has played out before on charters down in Miami...

Well, one issue, pO2 mismatch aside, as others have already mentioned... Howabout just a bad plan...? Or more to the point, a misaligned computer plan...

Say they used V-planner and cut tables to plan the dive, then 'dove' the VR3... Often the VR3 will not quite keep up, even if you use vplanner set to +4 (which I sometimes use to approximate) or if you lag behind on the deeper stops and don't stick to the ascent rate, it'll kill you racking up deco. It really wants you at the stop, or even a smidge higher to really give credit.

Say deepstops and I do the hydro on OC.., I fly more conservatively, plan to +4 (Brian - that ***** plans to nominal, but he still sticks with me). We give our plan to Capt Oliver and splash..., generally we're 5-10 mins long at the last two stops, just cause I wait for the vr3 to clear and do a slow ascent from last stop.

-Tim

 

[Rick Inman]

Meg's in Pompano... Hmmm, Oliver, George, Mempilot, Padipro, Tom Mount... There's a few guys over in Naples area, and the AUE dudes; but I couldn't see them running into this unless something was wrong, their more on the experienced side. Wasn't me.., and doubt Monkey woulda been up for the Lowrance. Curtis and his buddy, Stephen I think, or Matt R. Mike is in S. Afria, and it wasn't Lesley. Off the top of my head, thats the local megs. There's more than a few...

I'm think I know who they are, only because one dives a VR3, the other dives a Shearwater, and the scenerio you describe has played out before on charters down in Miami...
-Tim

I think they were with the group from TX.

BTW, Tom was scedualed to go out with Capt. Oliver Mon and Tue this week and Andrew Driver Wed, Thurs, but I heard the the boat is down.

 

[PacketSniffer]

I think they were with the group from TX.

It wasn't me.


...but I might know who it was. Hehe...