Disaster narrowly avoided on deep drift dive

[Snoweman]

If we look at your example... You leave the bottom with around 700 and get on the boat with 300, so it took 400 lbs (give or take) to get you up. What if your buddy who is on your octopus is also requiring 400 (or maybe even more) to make the ascent? Now 700 psi remaining for TWO divers to ascend is NOT extremely "conservative". It might be adequate, especially if you move things along and skip a safety stop.

You missed a some nuances in my post. First, I have said that I have gone up with less than 700 PSI. I also said that after I have gotten into the boat with 300 PSI, it was after a swim and fully inflating my BCD. I don't think I use more than 100 PSI to get up and get through my safety stop. I will check my online dive logs, though. Personally, I don't understand using more air on the way up, unless it is in full panic mode.

EDIT: Checked my dive logs. I was good on my last dives in Coz, signaling at 700 and going up to my safety stop after inflating my safety sausage (at around 50'). From there, I was at about 610 PSI for the start of my 5 minute (the dive company required five minutes) safety stop and got on the boat with about with a little under 500 PSI. From the start of the safety stop to getting on the boat was about seven minutes.

 

[johndiver999]

Sounds like you are really good on air. That is somewhat of a blessing and a curse. You're cursed with a perspective on air consumption that is biased toward your own low rate.

Have you ever been mugged underwater by a panicked or near panicked diver seeking your air? If not, you might be surprised just how fast they can suck a tank down. Which is emphasized quite well in the OP's video.

To be honest, 700 psi in an 80 tank should be able to get two divers up from 100 feet, but if one person is freaking out, the ascent needs to go smoothly and the safety stop might be less safe than it should be. In any regard, 700 psi is not a huge buffer when/if things go south. It is more of an issue with the unpredictability of the buddy than your own air use.

 

[Snoweman]

Sounds like you are really good on air. That is somewhat of a blessing and a curse. You're cursed with a perspective on air consumption that is biased toward your own low rate.

Have you ever been mugged underwater by a panicked or near panicked diver seeking your air? If not, you might be surprised just how fast they can suck a tank down. Which is emphasized quite well in the OP's video.

To be honest, 700 psi in an 80 tank should be able to get two divers up from 100 feet, but if one person is freaking out, the ascent needs to go smoothly and the safety stop might be less safe than it should be. In any regard, 700 psi is not a huge buffer when/if things go south. It is more of an issue with the unpredictability of the buddy than your own air use.

No. I have never been mugged by an OOA diver. I am a vacation diver. My SAC rate sux (is that a pun?). My dive buddies and I are checking each other's tank pressure about every five to ten minutes during the dive. It's what we learned to do (from different instructors), and we stick with it. I have seen another diver with a SAC rate much worse than mine, the dm sent him up with a marker buoy (retracted by the DM when the diver reached the surface).

As I said, my SAC rate sux. If someone is latching on to me with an OOA emergency, I am probably higher than 700 psi. BTW, the person is probably going to be a little upset that my rig is primary donate, and I will breathe off of the reg on my inflator hose. If the depth is about 90' max, I may elect to forgo the safety stop, but reserve the right to make the decision at that time. Some of that will depend on ascension rate, and some will depend on remaining air. The DM that decided to share air was asking for trouble when staying low. I know this can be a common practice at some dive shops, but it's the DM's responsibility to assess the situation and make changes to the dive plan - maybe a little faster that what happened in the original scenarios.

 

[wnissen]

Another good video.

During the regional training I run on Scotland’s West coast, we had a student burn through a 12Lt 232bar tank in 9 minutes at 6m. It was an eye opener for my instructors. I’ve not signed off the final qualifying dive for Ocean Diver on many occasions because the student didn’t turn the dive at the planned time or pressure point. During Sports Diver lessons I come across poor gas management in students who’ve done a lot of operator lead (normally warm water locations) diving; I won’t sign off lessons because they didn’t manage their gas, even when all the new skills are successfully completed. Gas management is an integral part of all open water lessons.

Narcosis, when I was survey diving in Belize back in the 1990s one of the scientists established the effects of N start at 15m.

The OP and this post are really eye-opening. It would never, ever occur to me to check a buddy's air that early. I have consistent trouble equalizing, and can blow through 10 bar in a 12L (150 psi in a HP 100) in a few minutes because my breathing is janky while I'm twisting around, making minor ascents and descents. But obviously it is possible to use much, much more air than that. Scary. That's one reason I do like the air-integrated computer, because there's at least a chance that I would hear my buddy's low air alarm, or vice versa.

 

[johndiver999]

The OP and this post are really eye-opening. It would never, ever occur to me to check a buddy's air that early. I have consistent trouble equalizing, and can blow through 10 bar in a 12L (150 psi in a HP 100) in a few minutes because my breathing is janky while I'm twisting around, making minor ascents and descents. But obviously it is possible to use much, much more air than that. Scary. That's one reason I do like the air-integrated computer, because there's at least a chance that I would hear my buddy's low air alarm, or vice versa.

If you think about it, the BEST time to check the buddy's air is early in the dive. You want to know early in the dive how they are doing, so this can at least give you a shot at salvaging the dive. If you know after 5 minutes into the dive that it is going to be cut short due to excessive air consumption by the buddy, then you can plan accordingly.

Also, if you have developed some situational awareness and you are maintaining a tight buddy team, then it should not be too hard to pay attention to the frequency and volume of the air your buddy is blowing off. Even in low vis, you should be especially close so you can hear their breathing cycle. Once you get used to doing this, it makes it less likely that you will get an unpleasant surprise when you look at their spg.

 

[ChuckP]

If it is a drift dive, why go up at half a tank? I have gone up at 30 meters with less than 700 psi (don't tell the DM), and not had any problems at all. I think the lowest my tank has been boarding the boat is 300 psi, after a swim and fully inflating my BCD.

I am extremely safety conscious. I have a smb, radio, whistle and mirror. I think that coming up at 700 psi is a safety factor of two.

I'm telling!!

This dive site sounds like Barracuda on steriods and sounds like a must go to place, where is it and can I get there on the way to Indonesia area LOL!

 

[hroark2112]

“Near death” seems a bit dramatic. Sounds like the DM did a great job though!!

 

[hammet]

17min?
anyone got the cliffs notes version?

 

[Scraps]

If you think about it, the BEST time to check the buddy's air is early in the dive. You want to know early in the dive how they are doing, so this can at least give you a shot at salvaging the dive. If you know after 5 minutes into the dive that it is going to be cut short due to excessive air consumption by the buddy, then you can plan accordingly.

Agree 100%. When I'm guiding nervous/inexperienced divers, I want an early read on their air consumption to get an idea of when I need to ask again.

The other day I guided a diver on his first boat dive/first offshore dive/first salt water dive. He was a bit intimidated by the surface chop (maybe 1 ft.) and a bit winded by the swim from the stern to the mooring buoy in the current (definitely < 0.5 kts.). When we got to depth, he had already used 700 PSI, which is a third of the gas he had available to breathe prior to his ascent, which I had told him to begin at 1,000 PSI.

He settled down once neutral-ish at the bottom and managed to eke out 31 minutes of total dive time with a max depth of 45 feet, starting the ascent at 1000 PSI, and reaching the boat with 500 PSI. I believe that perhaps 30% of the air he consumed during the dive was burned at the surface between the mooring buoy and the ladder. That was the part he was nervous about: that was the part where he breathed the hardest.

To his credit, he knew he was new, acknowledged that he was nervous, listened to instructions, stayed close to me, and followed instructions conscientiously.

He did better on the second dive, making it 44 minutes to the same depth in the same surface conditions.

 

[Esprise Me]

17min?
anyone got the cliffs notes version?

Pinnacle dive off the coast of Japan requiring negative entry due to swift currents. Diver Z didn't descend far enough and burned most of his air finning into the current. He ended up with 30 bar at 26m and had to share air with the DM, who also ended up at 30 bar by the time they got to the surface. Meanwhile OP's buddy was panicking and he had to ascend with her. OP subsequently buddied with Diver Z to try to help him, and told Diver Z to tell him when he reached turn pressure. Diver Z couldn't do that and kept running low on deep dives.