Escaping Down Drafts

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Especially along the walls of Peleliu (Palau) --when you see your Dive Guide gesturing to ascend up and away from the wall, do so without delay and stay together with the Guide. There can be a strong down current on the Peleliu Express drift dive near the end, where the wall starts to quickly descend beyond 18m/60' to well over 39m/130' & deeper (i.e. Past Nitrox32 MOD, and getting low on tank pressure). And do not forget to bring an SMB and know how to deploy it from depth.

Too many divers (usually novices) start the Peleliu Express dive using the wall as reference, and before they know it, they inadvertently follow it as it slopes away, finding themselves at 30m/100' deep AND caught in a stiff downcurrent, drifting right to left past the south point plateau descending into blue water abyss (see map link).

Deploy your SMB at least at your safety stop if you get separated from the group; if you're not low on gas or fightng a downcurrent, deploy earlier at depth depending on how much spool/reel length you've got. You gotta get that SMB up so the dive skiff driver can see you early, before passing the wall drop-off & into blue water open ocean with potential surface swells (makes seeing a small SMB harder to see). For this dive site, I always carry extra length spools, a Halcyon inflatable Life Raft, and a surface deployed Personal Locator Beacon (PLB -Mcmurdo Fastfind Plus in a dive canister; some of the Liveaboards are utilizing similar units).

Last time I was there was an early AM special advanced dive charter to see the Black Snapper schooling/spawning, during a full moon (i.e. very strong currents); got caught and swept over the south point plateau in a 3 knot current and decided to ride it out as it it pulled me down to 36m --on Eanx32-- and hence the worst case Nitrox Diver's Dilemma & Nightmare: You just inflate your BCD/Wing and do the best you can to slow or maintain depth; try not at all to physically over exert yourself which induces Hypercapnia which increases the chances of Oxygen Toxicity; hope the downcurrent slacks off in time to ascend back above MOD; and deploy your SMB from depth quickly so the boat crew sees you early for eventual pick-up (or else next pick-up point is 1000km to the west in Mindanao Philippines). . .

So perhaps the simple rule is "dive sites are named "express" for a reason".
 
Okay, I have no experience in ocean down currents. From what I can determine here, these are localized currents near a reef. It seems that these currents are limited in width and height (cross-sectional height). If so, they are very similar to classic "rip currents," except they go down, not at the surface. To escape a classic rip current, we teach to swim at 90 degrees to the current. Would this work for a down current? If so, it lends credence to not using the BC inflation to escape it, as this is directly opposing the current. If swimming to get out of the current, move your arms over your head and lock your hand together to get as streamlined as possible, then use several hard, powerful dolphin kicks to initiate the swimming escape, possibly at a 90 degree angle to the current rather than directly opposing it, to gain the edge of the down current.

SeaRat

Here are some of my take-aways:

Things can go to hell from out of nowhere, and that's okay. Down currents are entirely survivable.

Exercise your safety gear - if you are crappy at deploying an SMB in calm, non-emergency conditions you're probably going to be worse when things go pear shaped.

Intention is as critical as execution - doing something on purpose is better than doing nothing. I think one of the reasons I wound up in the (perhaps arguably) best situation is because I pig-headedly stuck to a plan. Get to the wall, stabilize, get to the top of the wall, stabilize, wait for stragglers for a fixed amount of time, safety stop, surface. I think we were the only group to do a safety stop.

There's more than one right way out - I talked to one of the divers who went deep right off the drop and she went from 20 feet to 90 feet in a few seconds. She filled her BC and swam horizontally away from the wall until she started going up again. She wound up over half a mile down from me but her dive time was only 6 minutes.

You are in charge of your dive no matter what happens. Aspire to be able to provide help, not need it.

Split fins may be instant death in caves but they will get you out of a down current.

A slate is handy for more than just gabbing and fish ID.
 
Downcurrents can be the worst dilemma any diver can face especially if you've got Nitrox MOD limits to consider as well being pulled down: the more you exert against the downdraft; the harder you breath & use up gas; CO2 retention-Narcosis/Hypercapnia sets in and increases the chances of Ox-tox hit as you approach & go beyond PO2 MOD limits if you cannot arrest the descent. Last resort if in blue water with no reef wall topography to climb back up is to inflate BCD and make your way up without overexertion as best you can. . .

Although I have never encountered a down current I have a personal rule that I won't dive any Nitrox mix on a dive where the hard bottom exceeds the MOD unless I have two independent buoyancy systems. Don't flame me, it is a personal decision, but on wetsuit dives along a wall where a loss of lift can potentially send me below the MOD of my back gas and ruin my day I dive air only. If I am dealing with a loss of buoyancy or a down current I don't need to add an O2 tox to my growing list of concerns.

I wouldn't have worried about this until after my Coz down welling. Now that it's happened, it's definitely at least going to become part of my pre-dive briefing discussion.
Note that if you go past recommended ppO2/MOD, there is no certainty that you will "instantaneously" suffer an Ox-Tox seizure event --then again there is no guarantee that you won't.

Again, I believe the remedy (and the last hope?) is not to over exert yourself into physical exhaustion, and the vicious cycle of hyperventilation & Hypercapnic CO2 Retention/Narcosis which is thought to be a trigger to Cerebral/CNS/O2 Toxicity Seizures; And if that means not to fight the downcurrent -trading depth for time in order to recover nominal breathing & desist further physical exertion to break the CO2 cycle- then so be it. If you cannot fight it, or flee from it (and you've got plenty of breathing gas remaining); just go flow with it for a few minutes until it slackens or ebbs . . .and then make a forceful effort to escape.

The only paradigm I know of to suggest and support this idea is an anecdotal "field study":
End tidal CO2 in recreational rebreather divers on surfacing after decompression dives. - PubMed - NCBI
. . .Deep dives using rebreather devices result in oxygen exposures that carry a risk of cerebral oxygen toxicity. Elevation of arterial CO2 levels increases this risk. CO2 retention may occur during the deep working phases of dives, but it has not been investigated in 'real world' dives at the end of resting decompression when oxygen exposures are peaking, often to levels higher than recommended maxima . . .We found no general tendency to CO2 retention during decompression. It is plausible that breaching oxygen exposure limits during resting decompression is less hazardous than equivalent breaches when exercising at deep depths. . .

Here are some extreme examples of incidents, in which the victim tragically & unknowingly was breathing a high ppO2 deco mix past MOD, and did not tox into seizures until after some minutes:
An infamous tragic accident, as told by Dan Volker:
Then, there was the Jane Orenstein death... In it, tech instructor Derrick McNulty, had his buddy and student with him on ascent from a 280 foot dive. He did not watch her switch gas from bottom mix to travel gas at 100 feet, and missed that she went to her O2 bottle. Jane breathed the O2 from 100 feet, through the 50 foot, 40 foot, and 30 foot stops....at the 30 foot stop, she signalled she was low on gas, and McNulty waved her up to the 20 foot stop direction--she ascended by herself, and then McNulty watched her stop ascending, and begin a plunge downward.....He just watched as she began falling, and the 2 tech students below saw her dropping at their 50 foot stop, and one tried to chase after her, but could not equlalize, and had to stop....The instructor later said that he could not follow her, because he did not have enough gas to go after her and to rescue her.


http://www.scubaboard.com/forums/accidents-and-incidents/385666-fatality-wkp-8.html
I'm very sorry to report to you that our friend and fellow explorer Jim Miller died today during a dive in the WKP.

It's too early for us to report on the dive in great detail, but what I can tell you is that he seized and drowned in the cave after breathing a 70ft deco bottle [Eanx50] for an extended period of time on his way into the cave. The bottle was marked and analyzed correctly. The depth was approximately 200ft and the incident occurred soon after the team turned and began their exit. He was brought back to the basin by his buddies following an unsuccessful attempt to revive him at depth, and then to the surface by other team members.

Interesting too, that the victim OxTox-seizured not immediately, but after nearly an hour on a RB80 Rebreather inadvertently gas switched to a 21m/70' MOD tank (~50% Oxygen) at approx 7 ATA. . .
 
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Things can go to hell from out of nowhere, and that's okay. Down currents are entirely survivable.
bold added

They usually are, but one of the factors is probably at what point the downcurrent occurs. If it happens at the end of the dive, what if you were to run out of gas trying to deal with it?

My friends were lucky that it happened to them at the beginning of a dive with nearly full tanks and let go of them fairly quickly. After three people went missing on a dive in Mexico the following year or so, and it was surmised that they disappeared in a downcurrent never to be seen again, we wondered if they had enough gas at the point they encountered the downcurrent to deal with it effectively.

It's yet another reason to carry enough gas and leave more of a reserve than we might think (at least minimum gas).
 
bold added

They usually are, but one of the factors is probably at what point the downcurrent occurs. If it happens at the end of the dive, what if you were to run out of gas trying to deal with it?

My friends were lucky that it happened to them at the beginning of a dive with nearly full tanks and let go of them fairly quickly. After three people went missing on a dive in Mexico the following year or so, and it was surmised that they disappeared in a downcurrent never to be seen again, we wondered if they had enough gas at the point they encountered the downcurrent to deal with it effectively.

It's yet another reason to carry enough gas and leave more of a reserve than we might think (at least minimum gas).
. . .And listen to the dive site briefing & following your Dive Guide as well.

This is another view of Peleliu Wall, and shows how it deceptively slopes away left-to-right at the southern end of the plateau -and where I got caught in the downcurrent by not paying attention to the topography (was looking up instead at the schooling/spawning Black Snappers around me). . .
 
Somebody mentioned "blasting" air into their BC. yes, you are going to do this. But boy do you need to be ready to dump, because not only might the downcurrent stop - it can very well turn into an UPcurrent, at which point you will be going up nearly as fast as you were going down.

This is from another diver who was on the same downcurrent dive I did last year. Cindy told me during our debrief that they were in a full on upwelling, not just neutral water.

We did Palancar (?) yesterday, and had a bunch of random current issues. I was adding/subtracting air from my BCD all throughout the dive. At one point, I was on the wall and noticed my bubbles in front of me and heading down. Got the heart rate going a bit, but it never did turn into a full downcurrent. Reading these posts sure helps to think about the correct course of action before you are in an actual downcurrent. I think it should be part of the dive briefing, since not many know what to do.
 
Somebody mentioned "blasting" air into their BC. yes, you are going to do this. But boy do you need to be ready to dump, because not only might the downcurrent stop - it can very well turn into an UPcurrent, at which point you will be going up nearly as fast as you were going down.

This is from another diver who was on the same downcurrent dive I did last year. Cindy told me during our debrief that they were in a full on upwelling, not just neutral water.

I think a pull dump on your inflator hose would be a good idea if you knew you were diving in an area that is prone to wild currents.
 
I think a pull dump on your inflator hose would be a good idea if you knew you were diving in an area that is prone to wild currents.

A pull dump can be your worst enemy in those circumstances as well ... I've watched (twice) someone literally pull the hose off of their BCD using one of those. And in an emotional moment such as you're likely to experience if you are caught in a down current and a subsequent imminent cork event, it's unlikely that you're going to be in a mood to be subtle with your corrections. You can exhaust your gas equally quickly by simply raising your inflator hose and pushing the dump button on the valve. An added plus if you're wearing a drysuit, as putting your arm in that position will automatically vent the drysuit as well (assuming the standard placement, shoulder or wrist, of the valve on the left arm) ...

... Bob (Grateful Diver)
 
A pull dump can be your worst enemy in those circumstances as well ... I've watched (twice) someone literally pull the hose off of their BCD using one of those. And in an emotional moment such as you're likely to experience if you are caught in a down current and a subsequent imminent cork event, it's unlikely that you're going to be in a mood to be subtle with your corrections. You can exhaust your gas equally quickly by simply raising your inflator hose and pushing the dump button on the valve. An added plus if you're wearing a drysuit, as putting your arm in that position will automatically vent the drysuit as well (assuming the standard placement, shoulder or wrist, of the valve on the left arm) ...

... Bob (Grateful Diver)

I use my pull dump pretty frequently. I find I can stay compact and better manage movement and trim without having to lift my arm over my head. When I get air bubbles I just wiggle a little bit or I use another dump valve.

I've torn it down to check on it more than once and at least in mine it's pretty robust. In my BC there's a steel cable that runs from the fitting at the BC through the hose down to the valve and it's connected at both ends via the steel pins. It would take a lot of force to break those.

I'm not familiar with the insides of other BCs - do they not use robust internals designed for pulling?
 
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