I've had to do this on several occasions, where customers have run
low on air. It can be highly task loading.
The
first time I ever had to do a DSMB deployment, whilst sharing air, I had never practiced those skills combined. I had done literally hundreds of DSMB deployments and literally hundreds of practice AAS ascents. Doing them together was a lot more taxing. The 'real life factor' added a lot of stress too. Environmental factors, like current, added even more stress. Other considerations: like planning for surface conditions, danger from boats etc added
even more stress. In addition, other divers in the group added, rather than reduced, stress through their behaviour.
At the time, I was a newly qualified instructor, just leading "experienced" fun divers on a deep dive in relatively strong current site. There were several dive boats on the surface and it would be dangerous to ascend without DSMB.
The diver concerned was a CMAS 2-star diver...and he was signalling 'ok' on air right up until he told me he was on 300psi. We were still at 28m. I opted to share air immediately, so that he could preserve his 300psi for emergencies and for BCD inflation at the surface. The current was strong and I was also having to virtually drag the low on air diver along with me...as he was going a bit 'passive' once on my air. Add to that the fact that I had to keep the rest of the group together in strong current. It was frustrating because several members of the group of 6 divers were completely unaware. I had called the dive, had a diver on my octopus, and I struggled to get their attention because they were photographing etc. What was worse - even when I
did get their attention and had begun to ascend (up the side of a pinnacle), they kept
stopping to take more photos!! I had a trainee divemaster in the group who was oblivious and in 'fun diver mode' - too busy finding critters for customers to take photos of. Luckily, they eventually 'switched on', noticed the problem and started helping me marshal the group on the ascent.
I opted to postpone the deployment of DSMB until we were shallower. My priority was to get the group up from depth. As the group got to 12m, I decided deploy the DSMB. I was glad it was an small capacity oral inflate...and I used finger reel. First, I had to make sure that the 'victim' had a good grip on my harness, so that we wouldn't separate when my hands were busy. I remember literally squeezing his hand around my harness to make sure he got the message. First, I made sure our (his) buoyancy was good. The big danger is that the person you are assisting can drag you up or down. Then I moved my SPG from my hip onto my chest d-ring...so that I could see it at a glance. Once I was happy with the situation, it only took a few seconds to deploy the DSMB. I was quite slick at this, because I did it on nearly every dive, every day.
The few seconds it took to organize myself was rewarded in the following ascent.
Once the DSMB was up, we continued to ascend until the safety stop. I can reel-in a finger reel single handed, which gave me a free arm to vent air on ascent, keep control of the diver and signal my group when necessary. When we reached the safety stop, I decided to let the diver go back onto his own air. The 300psi he had remaining was enough to last him 3min at 6m and still inflate his BCD. I had around 600psi remaining at that point, as the air consumption had been high, sharing air in strong current for the ascent. All the group were on their safety stop, most oblivious to anything and contentedly showing each other photos on their cameras.
At that point, there was a further complication. The trainee divemaster approached me and showed me the display on their dive computer... showing me the universal sign for 'confused'
At a glance... their computer had entered deco mode. They had never seen that before and thought it was "a computer display glitch or something". In the end, the entire group did an extended safety stop of 8 minutes, whilst the DMT decompressed. Because I had a diver still low on air, the DMT concerned got to practice air-sharing with them... I didn't want to send the group up without me, as there were numerous boats on the surface (they probably wouldn't recognize our boat), surface current, boat movement, swell....
and I already believed the group was not 'switched on' and aware of risks. I wanted to keep control for their safety.
On the boat, the low on air diver said he just 'lost track' of his air and couldn't explain how it had gone from 'ok' to low so suddenly. I suspect he was giving
false 'ok' signals, as he was too
proud to be the one who cut the dive short (a relatively common problem amongst moderately experienced male divers).
The divemaster trainee had done several dives that morning that she hadn't told me about when we planned that dive. She hadn't thought about the impact of those dives on her NDLs, as she had "just gotten used to a routine of diving 4x as day" without thinking about the dives. She also didn't understand her dive computer and was mystified when the computer entered deco mode. She believed the computer had malfunctioned and was
about to abort her safety stop to check out her computer on the boat!!!
Lessons Learned
1) Task loading can lead to exponential stress increase with each additional input.
2) Experienced divers can allow pride to skew their judgement and safe dive practices.
3) Dive leaders should
physically check divers SPGs, wherever possible.
4) Divers can easily 'switch off' if they percieve that a dive guide is looking after them.
5) Divers can easily abdicate all responsibility for group and/or personal safety to the dive leader.
6) Dive leaders should not anticipate or rely upon assistance or awareness from other divers.
7) Divers need to be familiar with Emergency Deco procedures with their dive computers.
8) DSMB deployment needs to be second-nature and take seconds.
9) Finger reels can be used 1 handed.
10) (
Trainee) Divemasters can sometimes be more hinderance than help.
11) Divers may prioritise personal dive enjoyment over someone else's emergency needs.
12) Dive pros must maintain emergency awareness, regardless of the 'tour duties' of a dive guide.
Specific DSMB Lessons1) If you only train to inflate DSMB using your AAS, then you will have no familiar options when your AAS is unavailable.
2) Finger reels offer simplicity, that decreases task loading on ascent.
3) Small capacity oral-inflate DSMBs are quick and easy to deploy, even from shallow.
4) Practice to manage an ascent with only one available hand.
5) A diver must be able to deploy and ascend a DSMB without assistance.
Specific AAS Lessons
1) The typical 'roman handshake' grip permanently occupies a rescuer's hand. This adds task loading and reduces flexibility. Where possible, get the OOA diver to grip directly onto your harness/BCD so that you have a free hand.
2) On several occasions, I've attached a diver directly to me using a double-ended boltsnap between chest d-rings. This has pros and cons, but gives certain control whilst preserving both hands free.
3) Longer AAS hoses provide a lot more flexibility. Less 'tugging' on the AAS means less stress for the 'victim'.
4) Don't lose overall group and situational awareness, when engaged in AAS assistance... if one is low/out of air, then others easily could be also.
5) Monitor your own air carefully when sharing air. Both divers are likely to have an elevated air consumption rate and that will drain your cylinder at a surprisingly fast rate. Have, or move, the SPG to a location where you can see it at a glance.
6) Buoyancy control is critical for both divers. The donor should be prepared (and able) to manage this if necessary. At worst, with a panicked diver, this can be almost identical to a controlled buoyant lift of an unresponsive casualty.