Accident on Southern Cal Oil Rigs Dive

[vladodessit]

Isn't 4 rather deep dives in a day a bit pushing the limits? No speculation, just a question

It is normally 3 tank day trip.

 

[MaxBottomtime]

The rigs can be a really beautiful dive. Many of the local boats make the same schedule, first dive at the Olympic II wreck in 98 feet and then two dives at the rigs. If I was on one of those boats I would skip the first dive so I could enjoy what the rigs offer at greater depths. It's amazing when you can actually witness the change in the type of marine life as you change depth. After passing through the baitfish, garibaldis and mussels of the shallows you find cabezons and plumose anemones below. The deeper you go, the larger the anemones and the variety of rockfish appear. Two of my deepest dives were on the rigs, so I can see what draws divers to venture too deep there. You definitely need to plan your dives and stick to your plans.

 

[boulderjohn]

There is a picture on the Sheriffs twitter account showing the discovery but blurred. The diver was carrying a tank with a Nitrox sticker so it is likely that O2 toxicity may have played a role

Ken has done a nice job explaining why we should not be speculating on the likelihood of anything with the scant information we have now.

As for the likelihood of oxygen toxicity, the safety margin for recreational nitrox is huge. It would be extremely unusual for anyone using a recreational nitrox at recreational depths to have a problem with oxygen toxicity. Even if you were to violate the limits to the greatest degree possible--EANx 40 to 130 feet---you would probably have to stay at that depth for a while to make that happen, probably longer than your gas supply would allow.

Oxygen toxicity is a serious hazard for technical divers, and a number of memorable deaths have occurred because of it. In just about every case I know, though, the problem was caused by a very serious mistake in using the wrong gas at the wrong depth. For example, a diver who thought he had air in his double tanks but actually had EANx 36 was diving at about 160 feet for about 20 minutes when he toxed. Oxygen toxicity is so rare in recreational diving that I don't recall ever hearing of a case.

 

[Buoy_A]

The rigs can be a really beautiful dive.

For me, it's probably the best single dive in Southern California. Here's my favorite video from the Rigs, created by "Rainer" here on Scubaboard:


One aspect of the Rigs that I haven't heard discussed is how there is often a "layer" on top of the water column. Typically from 0 to 60 ft there can be a "haze" that can dramatically reduce visibility. Then below this layer it can open up to 100+ feet of viz. I've seen instances where a layer at the top reduces viz to 20 feet, but at 100 ft you can see clear across the structure. For me, I immediately drop deep on these dives to get the best viz. It's a shorter dive, but worth it.

 

[MaxBottomtime]

The opposite can be true as well. I've experienced blue water at the surface only to find a brown layer midwater and night dive conditions below. Without lights we couldn't see anything on the Redondo Artificial Reef one day in spite of some of the best surface water I've ever seen in SoCal.

 

[Dizzi Lizzi]

For me, it's probably the best single dive in Southern California. Here's my favorite video from the Rigs, created by "Rainer" here on Scubaboard:


That is truly spectacular.

 

[Ken Kurtis]

Isn't 4 rather deep dives in a day a bit pushing the limits? No speculation, just a question

Love the white flag . . .

Given your location of Brussels, I assume you're unfamiliar with SoCal diving. This was most likely the third dive of the day. 3-4/day is a pretty typical SoCal pattern and 3 rig dives is sort of the norm. It also seems from what others have said that Dive #1 was the wreck of the Olympic, which is 60-100' deep, and then #2 and #3 were at the rigs. Just because the rescue attempt was at 100+' doesn't mean the dive was that deep. You could, in theory, dive the rigs at 20' (surge notwithstanding). Many times people do the first dive around 100', the second dive at 60', and the third dive at 60' or above.

That all being said, yes, there should be concern about multiple deep dives and whether they push the No-D limits but also remember that there are numerous variables to factor in that would mitigate the nitrogen load. They include what N2% gas was being used, what was the actual depth of the dive, and - if a multi-level dive - what time at what depths. So it's certainly possible to do these dives without even going into a computer caution zone, let alone pushing No-D limits.

And to apply your question specifically to this tragedy, exceeding a No-D limit (and I'm not suggesting he did that) will not cause you to pass out underwater. And it seems that that is what the initial problem was.

 

[Kevrumbo]

Rule Out Hypercapnia in Scuba in 55 year-old Male as likely primary precipitating event.

• Physical activity/exertion at depth resulting in metabolic Carbon Dioxide retention. Inefficient ventilatory response to eliminate excess CO2 because of increased pressure differential, gas density and work-of-breathing at deep depth. Inability to recover normal respiratory rate during heavy exercise of the dive and following strict instructions to actively remain inside the boundary of the oil rig platform in a strong current environment, culminating in a vicious cycle of quickly spiraling hyperventilation (Tachypnea), difficulty in breathing (Dyspnea), further CO2 poisoning with possible developing cardiac arrhythmia, and further narcosis, stupor & incapacitation finally leading into unconsciousness.
• Rule Out Oxygen Toxicity Seizure as related secondary medical event.

For example, look at this simple graphic demonstration of immersion work-of-breathing, exercise, and ambient pressure differential just by trying to talk and tread water at the surface at the same time:

Imagine the gross effects at depth heavily exercising and breathing Air/Nitrox through a regulator at five times or more the pressure of the surface:
Note the impact of the current on the tech divers above in the video (tell-tale of the exhaust bubbles) and how little headway they make, or the effort in stationary keeping with frog and flutter kicks.

. . .Rising blood CO2 (‘hypercapnia’) is a problem in diving for several reasons. First it can cause unpleasant symptoms such as headache, anxiety and shortness of breath. These can precipitate panic. If the levels get high enough CO2 can cause incapacitation and unconsciousness. . . To give you some sense of the small changes in arterial blood levels required for these phenomena, PCO2 around 5kPa is the average normal level, 6.2kPa is the upper limit of the normal range, and over 8.5kPa sudden incapacitation is likely. Experiments show that levels between 6.5 and 7.5 are not uncommon in divers working underwater. The point is that small changes in PCO2 of 1kPa or less can have very important implications for the safety of the diver.

. . .The second reason high levels of CO2 are a problem in diving is that CO2 can precipitate other diving related problems. In particular, CO2 is a narcotic gas and high CO2 levels will substantially worsen nitrogen narcosis. Similarly, high levels of CO2 are known to substantially increase the risk of cerebral oxygen toxicity which can manifest as a seizure. The mechanism for this is probably that CO2 causes a substantial increase in blood flow to the brain, thus increasing the brain’s exposure to oxygen when a diver is inspiring a high pressure of oxygen. It goes without saying that the loss of consciousness associated with a seizure would often be fatal under water. . .

Again, good additional explanation here of the hazards of CO2 build-up & retention:
Advanced Knowledge Series: Basic Carbon Dioxide Physiology
Advanced Knowledge Series: Carbon Dioxide Retention
Advanced Knowledge Series: The Gas Density Conundrum

See also DAN articles:
Alert Diver | Your Lungs and Diving
Alert Diver | Understanding Oxygen Toxicity
Alert Diver | Matters of the Heart

. . .All divers are likely to have increased CO2 levels (to some degree) during a dive. The manifestations are usually minor — such as a throbbing headache — and if the diver realizes this and immediately resumes normal breathing, the headache may subside. If not, it is wise to shorten the dive but also to make sure that adequate ventilation is maintained during ascent. Relaxed, deep breathing at the safety stop also helps in many cases.

 

[vladodessit]

It really looks like any "blamestorming" has been exhausted and we need to wait for exam and investigation.

 

[Ken Kurtis]

It really looks like any "blamestorming" has been exhausted and we need to wait for exam and investigation.

Vlad, stop being another voice of reason . . .