Scuba diver dies while exploring popular shipwreck, a third tragedy in the Florida Keys

[Eric802]

I took SDI Computer Nitrox earlier this year. The course materials still reference 1.6, and say 1.4 is for added safety.

 

[BoltSnap]

FWIW, I took my Recreational Nitrox course in 1993. We used Dick Rutkowski's "Enriched Air Nitrox" text. We were taught that PO2 = 1.6 ATA was the recreational limit, and that this should be dialed back for arduous diving (like diving in Lake Superior or diving in currents).

rx7diver

Yes, I took nitrox course with Dick circa 1990 and that was the limit, PO2 = 1.6ATA

 

[Dan G]

This is not something I learned in my PADI Enriched Air course, but I have been told that the issue is about prolonged exposure to higher ATA. Just like decompression sickness, people's bodies are different and therefore react differently to O2 exposure. In general, however, I have been told that it is best to stay at 1.4 ATA for less than 60 mins and 1.6 ATA for less than 30 minutes. I am sure there are additional factors that increase risk such as how hard you are working while at a particular ATA, as well. Thus, deco at 1.6 for quite some time is different than being at 1.6 during the working portion of the dive.

 

[BlueTrin]

Your a bad influence

Can I join, looks like fun?

 

[Jim Lapenta]

When I did my NAUI tech training there was an incident during it where a diver we knew and have dived Lake Erie with toxed in a cave where his max PO2 was 1.35. There were some other factors (high flow, previous dives the day before) but that stood out. According to all the literature that SHOULD have been safe.
O2 toxicity can be specific to the individual and their physiology. As well as other factors including workload, time of exposure, repeated exposures, etc.
To make a blanket statement that 1.4 or 1.6 is safe may be fatal to some who don't take those other factors into consideration.
Following this incident we were advised by the NAUI CD that trained my instructor to consider dropping max PO2 to 1.3 for the working portion of the dives we were doing in the Great Lakes.
We did that and I continued that practice for all my deco dives and carried it over to when I began teaching tech through TDI and no one complained.
And I felt the added safety was worth it.

 

[Manatee Diver]

This is not something I learned in my PADI Enriched Air course, but I have been told that the issue is about prolonged exposure to higher ATA. Just like decompression sickness, people's bodies are different and therefore react differently to O2 exposure.

This is third hand, but a friend that did some reporting with the NEDU said that the oxygen toxicity tolerance testing that the Navy used to do for diver training was ended because it was a crap shoot. Minor differences in fatigue or hydration could have drastically different results for the same person.

 

[boulderjohn]

This is third hand, but a friend that did some reporting with the NEDU said that the oxygen toxicity tolerance testing that the Navy used to do for diver training was ended because it was a crap shoot. Minor differences in fatigue or hydration could have drastically different results for the same person.

Are you talking about back when they did that testing in a dry chamber?

One of the key reasons that was stopped was the realization that dry chamber toxing pressures and water toxing chambers are vastly different. You can go much deeper in a chamber without toxing than in water.

 

[Bob DBF]

In 1978 NOAA formally established procedures for a standard mixture of 68% N2 / 32% O2. It is known as NOAA Nitrox I. A second standard mix that contains 36% O2 is known as NOAA Nitrox II. Since that time, a number of users, including the US Navy, commercial and academic diving operations have successfully used Nitrox in operations shallower than 130 feet.

The reason that 32% was chosen, and is now a standard recreational gas, was because 1.6ATA was considered safe for Scientific Divers at 130' at that time. When Nitrox initially moved into recreational diving, they followed the dive tables of NOAA and the US Navy. NOAA has since revised their acceptable PO2 to 1.4ATA

It's another risk v reward situation that is found in SCUBA. I would no longer plan a dive at 1.6, but I'm a much older now and don't trust my body as I once would.

 

[boulderjohn]

DAN used to have an article related to Toxicity and decongestants, but it is no longer up, I suppose because what they have now includes new information. The old one was very illuminating. At least half of the article was spent talking about how hard it was to draw conclusions due to a lack of data. As I recall, in the few cases cited by people as examples of people toxing on nitrox after using a decongestant, there was not a single one where you could definitively say the diver toxed. In a surprisingly large number of dive fatalities, the diver is found alone on the bottom with no clear cause of death. In these cases, the divers were diving on nitrox, and so people said, well, maybe they toxed. The toxing itself leaves no trace. It is possible that none of those deaths involved toxicity, even though toxicity was assumed for the purpose of the study.

 

[Capt Jim Wyatt]

This is third hand, but a friend that did some reporting with the NEDU said that the oxygen toxicity tolerance testing that the Navy used to do for diver training was ended because it was a crap shoot.

While serving as a U.S. Navy Diving Officer we had to undergo an oxygen tolerance test every 6 months. 60 feet deep, pure O2, 30 mins on a mask in a chamber. If we toxed we were grounded.