What does

[Look Out Below]

Everyone have there PO2 set at? Being new to the Nitrox thing(six months), after 17 years of straight air. I am just curious...

[Hogwild]

My Suunuto Viper is on the conservative side, so I set mine to 1.5.

[inletsurf]

LOB

For our stuff usually @ 80'-95' I use a 1.5 ATA max, which translates into about 36%. So that's the mix I usually get.

http://www.abovenbelow.com/nitroxcalc.htm

[fernandezh]

I keep mine set at 1.6 Nobody on record has ever taken an oxygen toxicity hit at 1.6

The little that I do remember from Navy Dive School (11 years ago) is that the Navy allows its divers to a PO2 level of 2.0 under working conditons for a maxiumum of 25 minutes at a time. But that is taking into consideration that the diver is in the top of the human food chain physical condition too. I highly recommend against anybody taking the chance of going further than 1.6 The recreational dive agencies (PADI, SSI etc.) set the industry standard arbitrarialy to 1.6 because they know that nobody will ever take a PO2 hit (regardless of the physical condition) at that level and they don't want to worry about a lawsuit. While some dive agencies even took it a step forward by saying that the max safe level is 1.4

I know all of you guys do this but I can't emphasize enough the importance of checking your mixes before you take your tanks out of the dive shop after a fill. Last month I was picking up 6 tanks from a Pinellas dive shop and every one of them had bad fills with as much as 16% more oxygen in them than I had requested. On one tank it was labeled as having a 32% mix when it actually had 48%. At such a mix at the 130 ft. depth that I was diving it would have taken to me a PO2 level of 2.37 and most likely would have killed me. Sharpshooter will tell you, I was not a happy camper that day as I take dying pretty seriously.

Hector

[BobK]

I always use 1.4, because I think the few extra minutes isn't worth the extra O2 loading. I'm sure up to 1.6 is fine, though.

I ALWAYS analyze my mixes, either with the shops' analyzer, my analyzer, or sometimes both. If you take anyone's word for what is in the tank you are breathing, you are literally putting your life in their hands.

[Charlestondivin]

1.5

Hector same thing happened to me. I think everyone that dives nitrox should have their own 02 analyzer.

I built mine for about $100 http://www.oxycheq.com/el_cheapo_II.html

The real scary thing is that the dive shop that gave me the high mixes only had one analyzer and had filled everyones tanks that way.

[greyface]

:eek: That's some scarry shit! The tank bitch at my LDS verifies the mix. Then you personally verify again before you're allowed to leave with the tank. Luckily, the guy is a REAL perfectionist, the mix is always within 2 10ths of a %, if not spot on. 1.4 or 1.5 max for me.

[Look Out Below]

Thanks dudes!

Hector,

Me thinks the Navy has turned a normal, recreational diver into a Peta hate'in, spear chuck'in O2 suck'in MO FO....:D

[Rob Holman]

If you’re going to dive Nitrox, spring for the 200 bucks and buy an analyzer! Money well spent. It is too easy to make a mistake. It is a good idea to verify your mix the day of the dive anyway. I have seen a 2% change after letting the tank sit for a day or two. Would that push you over the edge? Probably not, but if you are diving a 1.6 PO2 then it does make a significant difference on MOD. Who knows? Who is to say that the dive shop's analyzer is accurate? Checking with two different analyzers does not hurt. Some of the dive boats in our area continually blend Nitrox on board. Having an analyzer you trust is a nice idea for that situation as well.

PO2’s and Ox Tox is an art, not a science. Too many variables from person to person and day to day. Why push the edge? We push so many anyways! A percent or two probably would not kill you, but for only 200 bucks, why take the chance?

[fernandezh]

Originally posted by Look Out Below
Thanks dudes!
Hector,
Me thinks the Navy has turned a normal, recreational diver into a Peta hate'in, spear chuck'in O2 suck'in MO FO....:D

I just want to clarify the fact that I have more self respect than to be in the Navy. :D


Hector Fernandez
Captain, U.S. Army Airborne Infantry
Rangers Lead The Way!

[blue gun]

I use a 3 point reference. My LDS uses partial pressure fills so the o2 psi added is the first and then the LDS o2 analyzer is the second and I like to check them with my own o2 analyzer (cheapest one I could find). Charlestondivin is right you can make one cheap. If you want to save money don't hesitate building your own (IMHO) and use it as A reference but not the only reference. I wouldn't use even the best analyzer as a "stand alone" reference.

Hector you should double check everything you do because murphy has your number.:D

BTW: any good crazy bitch stories this week? All us married guys like crazy bitch stories.:D

[dlock]

1.6 here too. I get my tanks filled at Scuba Quest which also requires that you analyze your own tanks before leaving the shop with them. Most LDS' use the partial pressure method and sometimes they may get distracted while filling tanks and not top off your tanks with air and assume that they are done when in fact they have pure oxygen in them. ALWAYS CHECK YOUR OWN TANKS!!!

[swimndive]

Guys, you are confusing PO2 w/ FO2. You control your PO2 by using your depth gauge to keep you above your MOD which is what you calculate using your FO2.

In Hector's example he wants to dive a PO2 of 1.6 (which I disagree with strongly but that's another issue).
If he's diving 32% his MOD is [((1.6/.32)*33)-33] or 132'FSW. At any depth < 132' his PO2 < 1.6 as long as he is breathing gas with an FO2 of 32%.

When you set your computer, you can only set the FO2 of the gas you are breathing, not it's pressure, which will vary according to your depth. Carry on. ed

[bgbill]

Originally posted by swimndive
Guys, you are confusing PO2 w/ FO2. You control your PO2 by using your depth gauge to keep you above your MOD which is what you calculate using your FO2.

In Hector's example he wants to dive a PO2 of 1.6 (which I disagree with strongly but that's another issue).
If he's diving 32% his MOD is [((1.6/.32)*33)-33] or 132'FSW. At any depth < 132' his PO2 < 1.6 as long as he is breathing gas with an FO2 of 32%.

When you set your computer, you can only set the FO2 of the gas you are breathing, not it's pressure, which will vary according to your depth. Carry on. ed

There are several dive computers that you can set your maximum PO2, I assume that is why he was asking what the maximum PO2 people use is.

[swimndive]

True. On many computers you can set the PO2, but this has no bearing on your NDL's which is what most people are trying to maximize by using a nitrox computer in the first place. If you set it at 1.0 or 1.95 you will still wind up with the same NDL. The only possible difference it would make depends on how the computer is designed to handle PO2's above the set point. Say for exampple it goes into lockout mode. If that's the logic, then it would be wise to set it as high as possible and just mind your MOD, which was my original point. ed

[blue gun]

swimdive your right about the nomenclator but I thought the question was about o2 toxic levels and how high will people feel comfortable. Every comp I have had didn't have a setting for po2 and am not sure what it would do for the diver. does it scroll through your MODs at that fo2 you have programed. That would be pretty cool I guess. I never really run into deco or o2 problems spearfishing but cave diving we would weigh the long deco (hours) vs. a high o2 exposure and come up with some very interesting solutions. Anyway, this is starting to sound like scubaboard so I will step down by saying if your blowing high trox please be careful. :)

[Speargun]

The only thing that setting the PO2 on my computer does, is change the displayed MOD & adjusts the depth alarm.
I always dive with it set to 1.6 (the max it will allow) because the Suunto Vyper is so conservative. Even at 1.6, my MOD is 6 feet shallower than the tables.


Here's a good article on OXTOX I found on DAN's website.

OXTOX: If You Dive Nitrox You Should Know About OXTOX (http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35)

[fernandezh]

I just made a phone call down to the Army Dive school located at Key West concerning this subject and spoke to the Senior TAC NCO. 2 years ago the U.S. Navy changed it's procedures concerning PO2 levels in NITROX diving.

While diving at at a 1.6 PO2 level for 30 minutes a Navy Diver took an OXTOX hit and an Article 15-6 investigation was conducted to find out the cause of the incident. This particular diver had been diving at 1.6 for 4 dives a day consecutively for several days doing underwater welding operations. The investigation later concluded that the physical exertion from several days of working/diving at 1.6 and the fact that he had been drinking alcohol heavily the night before played a significant role in the incident. This incident as well as another study contributed to the military change its standard for acceptable PO2 levels. Currently, all dives PO2 1.4 and under can be conducted. All dives between 1.4 to 1.6 require a commander's approval as an exception to policy.

The school Senior TAC NCO told me that typically this exception to policy to PO2 to 1.6 is granted 99% of the time after a risk assessment analysis was conducted. Typically, the only reason why an exception to policy to 1.6 is not granted is if alcohol is not involved, the physical condition of the diver is in question, or that it has been deemed that the diver has been doing a series of consecutive dives at high PO2 levels for several days or more.

Furthermore, PO2 levels to 2.0 are granted only in life-saving situations (i.e. retrieving sailors trapped in a submarine in trouble).

Granted,
1.4 and below is totally safe and there is no doubt about that but undoubtedly diving to 1.6 is a bit riskier and everybody needs to do a risk assessment themselves prior to making such a dive. But the chances of taking a OXTOX hit at that level are still very low. My last .02 cents on this subject.

[blue gun]

that some cool research Hector. I like to hear real world sh!t.:cool:

[Look Out Below]

Thanks a million guys! I've got mine set for 1.5 and after drinking the night before thought I was pushing it...:D

Hector,

You have too much time on your hands.;)

[Spearchucker]

I have mine set to 1.6, but my drinking commences on the ride in!! I guess I am good!

[rusty]

I try to keep it below 1.4, but I mark all my tanks with a 1.4 and 1.6 depth, as well as the mix. My computer uses 1.6.

[sharpshooter]

When I get within about 3' of the mod with a setting of 1.6 ;mine will do a audible alarm to let me know. that's it folks.

[Divin' fool]

1.6 is safe and some say even conservative

[swimndive]

Without getting into the biochemistry and hemodynamics of oxtox, there is quite a bit of research that has identified several risk factors known to increase this likelihood in divers doing wet exposures.

1) exertion
2) elevated CO2 levels (breathing any eanx below 120' decreases CO2 ventilation by at least 30%)
3) cold
4) dehydration
5) lack of sleep
6) use of decongestants
7) repetitive dives
8) time (multi day trips)

How much is difficult to say, but as a general rule, for each risk factor encountered subtract .1.
So, if you start with the assumption that under ideal circumstances a ppo2 of 1.6 is safe, and you know that you are going to be fighting a fish at 120+ feet, you would have two additional risk factors to account for. You would subtract .2 form 1.6 and use 1.4 as your ppo2 at your MOD. On the following day you might have to account for a few additional factors. Rather than change your mix's FO2, you can adjust your MOD, if re mixing is not an option

The risk/reward ratio does not favor pushing the oxygen bet to save a little bit of time on deco. If your fear of deco is such that you want to avoid it at all costs just remember that all dives are deco dives. Some just have longer stops and need to planed a little more carefully. ed

[blue gun]

Originally posted by swimndive
If your fear of deco is such that you want to avoid it at all costs just remember that all dives are deco dives. Some just have longer stops and need to planed a little more carefully. ed
Ok swimdive, are you a PADI instructor?:D
Nice avatar also.:D