favorite MG blend

[greyface]

I'm in the process of taking the Nitrox cerification, and was wondering what is the most popular blend you Middle Ground dogs prefer, if there is such a thing. Also do y'all stay at or near 1.4 ata, or do you push it twords 1.6? Just curious, as to what to prepare myself for.:D

[johnhermes]

I personally use a 32-34% mix on a 1.6. I do make sure to take the safety stops. A hyperbaric doctor told me that the rate of ascent and the safety stops far outweigh, by a long shot, anything else you do. Don't ask me why I was talking to a hyperbaric doctor, no I was not bent!!

[fishhunta]

30-32. i use a 1.4-1.5 p02, not all the way to a 1.6 because you are probably doing many repetetive dives in the mg's and need to consider your total 02 absorbtion for the whole day.

[Reef Raider]

32% and 34% but I have gone with 36% too used it for short drops . Got a pony now with 40% for the stops and in case I slip in to deco or if some one else needs to bail out. You can never have too much gas in the MG. With the 34% I can go all week end with out slipping in to deco in the north grounds.So I would say 1.4 that inc. the 40% at the stops. Say John did the DOC tell you any thing about surface int. If not thats one other thing I would think a guy could not get enough of...

[Cock's Roost]

I'm also in the process of becoming nitrox certified, what is the maximum depth you guys dive? Do you follow the max depth on the tables or is there another way?:confused:

[Reef Raider]

The deepest MG dive I have done to date is 146fsw but you do not stay there very long so.Your going nitrox get a good nitrox computer and dive it by the numbers.If you want to do the MG get your D.A.N. too...

[junior]

Nitrox is the goods, for sure when doing repetitive dives over a few days period, unless you tag yourself into the red every dive. Then it's pretty much the same surface intervals because you have absorbed nitrogen to the same degree as someone diving air would have if they pushed it to the deco limit. I have yet to get out to the middle grounds, but have dove plenty of deep wrecks in the keys and deep reefs in the southest of fla. As the other guys mentioned, watch the p02 and use that as your guide. The only reason I hesitate to push it to 1.6 is that the symptoms of oxygen toxicity are so unpredictable and sudden with little chance for recovery, especially since it sounds like most of you guys dive like me, mostly alone when spearing. Definately gotta get the nitrox computer like Raider mentioned to reap the full benefits. Anybody remember what depth yields a P02 of 1.6 using compressed air??

[Reef Raider]

176+fsw or close to it I would think. I did 187ffw on air did not stay even 1 min what a BUZZ!!!!!!!!! Went back up to 170ffw and thats when I knew the fun was over for now as my computer was going in to deco.

[Steel Shootin']

I take a couple of different blends with me. I'm personally more conservative on the P02, so I take a couple of 29% with me. I like to plan my dive to stay right at 1.4, to get the full benefit of the nitrox (you're paying for that expensive fill, might as well get the full benefit). I also take a couple of 32s with me.

Good buoyancy control is important, because I will dive where the top of the ledge is 1.4, but the bottom would exceed 1.6. When that is the case, I'll hang near the top and shoot fish. I line shaft to avoid the possibility of having to retrieve a fish or shaft at the bottom. Watch your depth to make sure you haven't missed the ledge, heading towards the beach.

My Suunto is set at 1.5 for the alarm. It allows an alarm setting of 1.4, 1.5, or 1.6, so my setting is middle of the road.

Remember, an ox-tox hit is fatal. Why risk it?

[Cock's Roost]

I half to admit you guys know your shit !!! Once I get the certification and a little experience with it, I'll have to book a trip and head out to the MG with you guys.

[Cock's Roost]

One more question?:confused:
1) Name of good computers
2) When You say D.A.N. You are refering to the insurance -medical coverage. Correct.

[kitefisherman]

On air, you reach a partial pressure of 1.4 at 187 fsw and a partial pressure of 1.6 at 218 fsw.

Any buzzed sensation probably comes from being narced not the O2 partial pressure.

[Speargun]

One more question?
1) Name of good computers

If you want CONSERVATIVE, go with the Suunto Vyper or Cobra.
See my post here : http://spearboard.com/showthread.php?s=&threadid=831
I can't advise on other computers.

[kitefisherman]

Different computer manufacturers use different algorithms to calculate allowable dive time. Uwatec and Suunto are among the most conservative. Oceanic is among the most liberal.

I'm not saying that you should always dive the limits of your computer, but personally I'd rather have a computer that allows me to dive more conservatively (if I choose to) than a computer that insists that I do so under penalty of lockout. You should choose the computer that is right for you.

I don't know if you've already seen it, but various Nitrox computers were reviewed side by side in the Jan/Feb 2003 issue of Rodale's Scuba Diving. The article includes a "Freedom vs. Risk" chart that compares the conservatism of the various manufacturers. There is a similar chart that was done in 2000 at http://www.scubadiving.com/gear/2001gear/freedomrisk.shtml

[greyface]

Thanks for all the responces. Hey Scott, your suggestion about a 1.4 - 1.6 ledge height would also be useful over in the "how to work a ledge" thread! Good info! For now I'll be diving a Suunto Mosquito. I think setting the O2pp @ 1.5 is a good idea, as well.
Reef Raider, thanks for the D.A.N. suggestion. Will do.
Do you guys use the min. 1hr. S.I. rule? Looks like Spearboarders use every blend from 29% to 40%! I reckon that coversit!:p

[Steel Shootin']

Greyface, I remember that suggestion in the materials that they recommend that every dive have a one hour surface interval. However, they give absolutely no scientific reason for that. I am not telling you to ignore that suggestion, but I will respond to your question. The answer is "No," I have never dived with anyone who observes that minimum one hour rule. Most people view one of the benefits of Nitrox as being a shorter SI.

Furthermore, if this one hour thing is so important, why is it completely ignored in dive computer algorithms? However, that is just my personal observation, and I'm not suggesting to anyone that they ignore their text.

[johnhermes]

Reef -

The Hyperbaric DOC was only concerned about 1) rate of ascent, 2) safety stop. SI was not even a consideration to him. He said the people that get bent almost universally did one of those two items wrong.

[Divin' fool]

If you are looking for a good Nitrox computer....you can't beat the deal at Diver's Direct (most shops will match it). The Aeris Atmos Pro console for $299.00. Not the top of the line but a great little computer (just like the 300G...without the audibles).

[richhermes]

You can't hear the audibles on the 300G when you're at depth anyway!

[WreckDiver]

Suunto Vyper 275.00 WWW.leisurepro.com click on gauges.

[Steel Shootin']

Vyper a great computer, as is the Cobra, but I would just point out, if you're buying Suunto, and you think you may possibly want to get into advanced nitrox at some point, get the Vytec, which is the only one that permits multi-gas diving.

[Dive4Blood]

30%-34% percent is the mix depending on the depth which ranges from 85'-140' for the most part in the MG. If you get tech certified, doing your safety stop on an 80% stage bottle will improve your deco status and increase your the amount of dives you can safely do DRAMATICALLY. I 100% agree with John Hermes that ascent rate/SI are the main factors preventing/causing DCI. A 30'/minute ascent is highly recommended. We use a PO2 of 1.6, tests with Navy Divers have shown that the min. threshhold to take an O2 hit is around PO2 1.95. Remember that major conservatism is built into dive and O2 tables as part of the CYA factor for certifying agencies. Hope this helps.

[aue-mike]

Keep in mind that there is no hardset rule or threshold for O2 toxicity. There is a huge range of biological variablity, from person to person, and day to day. It is possible that you could take a PO2 of 2.0 for a limited duration with no problem one day and then tox at 1.2 another. That is reality. You can not build up a tolerance to O2. Keep in mind that USN divers crank up the PO2s because they can; they are diving surface supplied with hats -- if they tox it is no big deal as they won't drown and can be pulled to the surface. We don't have that luxury. A 1.4 maximum PO2 is the general working (i.e., swimming hard to catch a fish) guideline, with a 1.6 for resting stages (decompression). However, there are other O2 exposure considerations...

Another thing to consider is the repetitive nature of FMG diving. If you are pushing the PO2 over several dives, it can catch up to you. At high levels of O2 for extended durations, you can "fry" your lungs. When this starts to happen, even at levels before you feel physical pain, the efficiency of your lungs to offgas nitrogen is compromised, possibly increasing your chance at DCS. Though only temporary in of itself, the experience of pulmonary toxicity is not especially pleasant. Shortness of breath, tightness in the chest, etc. The point here is that this stuff is all interconnected and that increasing your O2 content does not necessarily reduce your chances of DCS across the board.

One other thing I did not see anyone mention is hydration levels -- I personally feel that rates just under ascent rate as a critical concern.

Cheers,
Mike

[greyface]

Inputimus Maximus! Keep it coming! I'm gonna start out concertively, but it's great, having you guys show me the ropes. Thanks!:)

[Steel Shootin']

Mike,

I hear what you're saying, and that's why I plan my dive for the recommended 1.4. However, I have never head of anyone taking a hit at 1.2, so I'm not sure where that came from. If my recollection is correct, there was something in the text about the lowest known hit being just over 1.6. I have never heard or read of a hit below 1.6.

Any specifics on that would be interesting reading, if you could provide it.

Thanks,

Scott

[dabulltrouble]

i like to keep mine at 1.4 also,because i,m a smoker and i dont believe my lungs offgas as well as a non smoker.i have been at 1.6 but not to often.i also use the aries pro computer and havent had any problems with it.its easy to figure out even if you,ve fried most of your brain cells back in the day like i did

[dlock]

I agree with D4B. 1.6 is used by several divers I know, a few of which are instructors. But when you get into multiple days then I believe you should keep to the conservative side. I mostly do shallower dives(30 to 40 fsw) but occasionally do wrecks at 80 to 90 fsw. I normally fill my tanks with 37% which gives me an MOD of about 107 fsw. So that way I'm covered. Nitrox is DEFINITELY the way to go. I use it on my shallower dives because you feel better and cramp less, it's worth the extra $. I haven't dove air since I was Nitrox certified. You're gonna love it!!!

[WreckDiver]

Recently Nitrox cer. myself, 1.4 norms ------- 1.6 pushes the safe limits, vyper is a great (conservitive TWO gas computer) scott is right about the Vytec for gas switching under water & O2 deco stops.

[Cock's Roost]

OK guys I have spent part of the night researching computers, and I think I want to go with the Uwatech smart Com air integrated. What do you guys think? Also is their a computer out there that analyzes your O2 or is that where the O2 analyzer itself comes into play.

[Steel Shootin']

Originally posted by Cock's Roost
OK guys I have spent part of the night researching computers, and I think I want to go with the Uwatech smart Com air integrated. What do you guys think? Also is their a computer out there that analyzes your O2 or is that where the O2 analyzer itself comes into play.
I can show you a way to make your computer an analyzer as well, but it will require caulk, a 1/8" vitek gasket, and a peanut shell.

I'm just busting your stones. I don't think any dive computer analyzes your mix.

[kitefisherman]

The Uwatech Smart Com is a very conservative computer that, unlike most computers (even the conservative Suuntos) totally locks you out for 24 hours after violation. It does not revert to guage mode. Not that I'm advocating that you violate you computer. I suppose that you could uninstall and reinstall your battery to reset it if you had to. Just something to consider.

[swimndive]

30/30 for the following reasons:
1) When you breathe high PO2's of oxygen you fully saturate your blood plasma and hemoglobin with O2. Up to 30% of your metabolic CO2 production is normally transported by unassociated hemoglobin. With this is now gone, you will lose 30% of your CO2 transport capabilities.
2) CO2 is 130 times more narcotic than nitrogen.
3) Gas density. WOB studies show a marked increase in CO2 buildup as gas density increases. Empirical studies show that breathing air at 4ATA decreases lung ventilation efficiency by 50%. At rest this is adequate to maintain low blood CO2 levels, but with exercise this efficiency has been shown to continue to drop resulting in a 20+% increase in blood CO2 levels.
4) An elevated CO2 levels is a key factor in the precipitation of an hyperoxic seizure.
5) Less wear and tear on the old bod (Say goodbye to those old post dive sleepies).

Scott computer's do penalize you for SI's<60min (some more than others). Sixty minutes is the amount of time the general population requires to be bubble free post dive according to numerous Doppler studies. The reason this is important is that you can self inflict a pfo like AGE if you do quick bounces. This is what killed Marc Sweazie during the St. Pete open two years ago. http://www.seahunters.com/spearfishing.htm

BTW the Navy revised that exceptional exposure table in 1993. The criteria defining exceptional exposure was quite specific. These exposures were designed for dives where a chamber was present, and in those cases, the at-risk divers are accompanied by tenders all the way through treatment. These exposures were not for working dives. A PPO2 of 1.4 is now the max allowed on any working dive. There are many factors which can lower individual O2 toxicity thresholds. Best not to fly too close to the flame. For certain cave dives PPO2<1.00 is not uncommon. ed

[Cock's Roost]

It just seems to me that a computer should be able to read the mix that way u take the chance of entering the wrong O2. Just a thought.

[Reef Raider]

uwatec makes one for rebreathers that will.

[MarkD]

Great thread here guys. I had the same questions as I am also going through Nitrox certification and wondered what you guys used in the Middle Grounds. I really appreciate all the info, it greatly reduces the learning curve for us newbies.

Sounds like I will use 1.4 as my plan. I have a Oceanic Data Plus computer that is on the liberal side of the spectrum. I will make sure to watch it closely.

Mark

[aue-mike]

Hi Scott-
I will try and dig up some references for you.
The point I was trying to make is that O2 toxicity is not a constant, and boosting your PO2 to the limit (whatever you define that as) is not always the best option, especially when considering repetitive diving.
Just because one happens to do fine with a PO2 of 3.0+ for a duration, does not mean that he/she has a "tolerance" for high O2 exposures. Anytime you breath O2 greater than 0.20 you have a chance for an O2 reaction. In any case, in regard to this thread, I would suspect that pulmonary toxicity is more of a concern than CNS, primarily due to the repetitive diving. All the more reason to knock the PO2 back a bit.
Cheers,
Mike

[Steel Shootin']

Originally posted by swimndive
Scott computer's do penalize you for SI's<60min (some more than others). I'm sure insufficient SI results in a penalty, so maybe I misworded what I was trying to say. I was trying to make the point that computer's allow you do dive without taking the one hour SI recommended in the PADI nitrox text, which most people use. For example, you come up from a 90 ft. dive, and you switch your computer to "plan" mode, and it shows you have 15 minutes of bottom time if you go back down to the same depth. It does not lock you out for an hour. Of course, the longer SI you take, the more bottom time you eventually get.

One of the ways that Suunto deals with this issue is by the "microbubble alert symbol." It's an exclamation mark. It does not prevent you from diving. When I started diving, I was a little concerned about the thing, so I wrote Suunto, and their reply was basically: Ignore it, you can dive through it.

Personally, regardless of what my computer says (even if I have a wealth of bottom time), I'll normally take at least a half hour. Does that make me more conservative than many? Yes. Am I worried about looking too conservative? No.

Interesting stuff on the C02 discussion. Correct me if I'm wrong, but isn't that why some people can get mini-anxiety attacks at depth? C02 build-up can cause anxiety and a sudden episode of shortness of breath, if my recollection is correct. Another good reason to avoid huge bursts of energy at depth. If you're prone to that kind of thing, you may want to avoid shooting Mr. Amberjack.

[Steel Shootin']

Originally posted by Cock's Roost
It just seems to me that a computer should be able to read the mix that way u take the chance of entering the wrong O2. Just a thought. I was just giving you a hard time. Yes, that would be cool as hell. One day, no doubt, all nitrox computers will probably have tiny 02 sensors that do that.

[deepfish]

It really depends on the time of year though I firmly beleive in starting the day with the right blend. Lately, while bracing myself against the somewhat coolish temps of water and air, I have equipped myself with a somewhat stronger blend. I have been going with a blend right off the shelf, Cafe Llave, purported blended by an expatriated Cuban, now living in PR, from Guatemalan beans grown from Cuban seed. I find using about 3 tablespoons in the bottom of a standard French Press followed by 2 tablesspoons of Turbinado and finally mixed with spring water heated to the point of atomization produces a superior dive warmup blend. Later in the year, as core temperatures increase, I might switch to a Tanzanian Peaberry or a simple Kenyan blend to get the day going.

Hope this helps.

Deeeeepfish

[kitefisherman]

Man, that Gag Reflex is one fancy boat! If that's coffee, I can't help but wonder what's for breakfast. :D

[johnhermes]

You have to book a trip to find out!! :D

[Cock's Roost]

Scott no need to worry about offending me to thick skined for that!!! I just want to be one of the guys. :D

[Cock's Roost]

As far as computers locking you out, what I don't understand is after reviewing Uwatec's web site. The maximum partial pressure of oxygen is controlled via a user programmable value, set with a PC and the Uwatec SmartTrak software. The maximum partial pressure of oxygen can be adjusted between 1.20 and 1.95 bar. Standard value is 1.4 bar and a PPO2 of more than 1.6 bar should not be set for safety reasons. So am I right in assuming that if you set it for say for 1.6 you should not get locked out if you follow what the computer tells you to (deco, etc.).

Keep it coming guys learning a lot don't hold back.

[greyface]

Semi dumb question: With this different approach to S.I.'s, is it common to anchor up on a spot, dump all shooters together on the first dive; then have shooters just come & go as they please, using their own idea of a S.I.? Bear with me, guys!:p

[Steel Shootin']

Greyface,

A good captain will never pressure someone to make a dive, so in a sense, yes, it is the diver's comfort zone that will dictate when he's ready to go in.

No, we don't send everyone in on the first drop. The way I personally like to see it done is to almost never drop more than three, and on some spots no more than two. Small wrecks, for example, should result in two divers, IMO.

When the first group is in the water, the guys topside are getting ready. Our second spot might only be 1/10 of a mile from the first spot, so the first group comes up, and the next is ready. Some guys take a much shorter SI than others, and may be ready to go on the second drop (especially if the first dive was short).

No one will (should) ever fault you for wanting to sit out a dive. People will get aggravated if you can't dive because:

1. You're disorganized, or
2. You don't know your gear (e.g., "I'm trying to figure out how to switch this damn thing to Nitrox mode").

Of course, if it's a charter trip, more tolerance is extended.

Originally posted by Cock's Roost
As far as computers locking you out, what I don't understand is after reviewing Uwatec's web site. The maximum partial pressure of oxygen is controlled via a user programmable value, set with a PC and the Uwatec SmartTrak software. The maximum partial pressure of oxygen can be adjusted between 1.20 and 1.95 bar. Standard value is 1.4 bar and a PPO2 of more than 1.6 bar should not be set for safety reasons. So am I right in assuming that if you set it for say for 1.6 you should not get locked out if you follow what the computer tells you to (deco, etc.).

Keep it coming guys learning a lot don't hold back.

Wow, I'm surprised that computer has a setting for 1.9. Is that the alarm setting??

I've never heard of a computer that will lock someone out for violating P02 parameters. The alarm is there to let you know that if you don't get your ass higher, you might die. You shouldn't need an alarm for that, as all of these considerations should have been a part of your dive plan (really, starting well before the trip, when you get your tanks filled).

On the other hand, although I've never seen it, I would imagine a computer might lock you out for violating total oxygen expsoure (if it doesn't, it should). Certainly, diving at a higher P02 will cause you to reach your total exposure limit faster.

[johnhermes]

Your total oxygen exposure is a concern on a dive for dive basis, it does not have near the accumulative effect that Nitrogen has. The Oxygen tissue loading is offgassed very quickly on SI's. I have come to the top with my O2 bar 3/4 of the way up, taken a half hour SI, and then have my O2 bar barely reading.

[Steel Shootin']

I still raise the point John because:

1. Some computers are going to be more conservative on total exposure, and

2. If you're using the tables to calculate total exposure, you can get to 100% much faster (no more than 100% exposure for any 24 hour period).

[swimndive]

Scott, the mini anxiety attacks you spoke of could have numerous origins and CO2 buildup will no doubt make things worse. Without knowing more of the specifics I wouldn't want to make a guess, but it could be something a Dr. should check out. If you ever get leg cramps, dizziness, vision distortions or a headache you could have a CO2 problem and you'll now know what the problem is and how to remedy it.

C.R.,The uwatec's wont go into SOS and lock you out for diving a high PPO2. They will beep and flash but they won't lock you out. Most people just set them at 1.95 so they don't have to deal with the beeping. Also this setting has no bearing on your actual O2 exposure. That is determined only by the %O2 you program in the thing and the depth you decide to take it. ed

[Cock's Roost]

So what we need to do is "Plan the dive, dive the plan." And let the computer take care of the technical stuff.