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Scuba Forum / General / November 2004Nitrox and that 2nd Dive on Vacation.
I am basically just starting out.(2yrs of vacation diving) I am going to be just a Vacation Diver, this is not something I will be doing locally. Most of my equipment purchasing days are still infront of me and will be comming out of my vacation budget. So, I am currently trying to find out why NOT Nitrox??? I thought I was closing in on an answer here at rec.scuba untill I looked down at read that most of the negative info was over 12 years old. Also it looked like alot of the problems involved everyday divers, extreme divers, and maybe some working divers. Why not just plan on making the rest of my Dives with Nitrox? I take about 2 vacations a year and am planning on turning them into dive vacations. Diving 3-5 days per week twice a day. Cost is not a problem as this will be out of my vacation budget. Why not just Sign up for a Nitrox cert. class and never look back. I found this in another thread: >>"this is direct from my NAUI ean dive tables. >>normal air 90fsw = 25 min. with no deco stop >>ean 32 90fsw = 40 min. with no deco stop >>ean 36 90fsw = 50 min. with no deco stop >> >>This is why those of us who dive nitrox do so. You get much better bottem >>time for only a few dollers more per tank. And for me I always seem to >>have more energy after each dive. More oxygen = more energy. >> >>Jim" Now, could someone complete a 2nd dive for me after you have had lunch? Thank you for any and all help. Brice >I am basically just starting out.(2yrs of vacation diving) I am going > to be just a Vacation Diver, this is not something I will be doing [quoted text clipped - 32 lines] > > Thank you for any and all help. Brice Your air consumption will remain the same on Nitrox as on air. You need to ask yourself if you can normally dive for 40/50 minutes on one tank using air. If not, the Nitrox will be of little benefit. > Your air consumption will remain the same on Nitrox as on air. > You need to ask yourself if you can normally dive for 40/50 minutes on one > tank using air. If not, the Nitrox will be of little benefit. It's not 40/50 minutes on one tank unless you're only planning one dive. If you are planning two or more, nitrox will either increase your total dive time or decrease your necessary surface interval times. Both translate to more time underwater. Lee <snip> Depends upon the type of diving that you are wanting to do... It will give you more time for shallow dives as long as you stay above the MOD for the mix you're diving due to higher PP02 for a given depth... Some people dive it with air tables (or air computer) and get an extra safety margin on their dives... On the other hand, you don't get narced as much and isn't that what we really started diving for anyway? <grin >I am basically just starting out.(2yrs of vacation diving) I am going > to be just a Vacation Diver, this is not something I will be doing > locally. Most of my equipment purchasing days are still infront of me > and will be comming out of my vacation budget. So, I am currently > trying to find out why NOT Nitrox??? A better question might be "Why not nitrox yet." Here's some things to think about: Anti 1. Nitrox is more expensive. If you don't have a reason to use it, it's a waste of money. 2. Nitrox increases one of your a risk factors, CNS Oxygen toxicity within the most common recreational diving limit, 130 fsw. To use nitrox safely, you have to ensure the gas you plan to use is safe at the maximum depth you plan to dive. There's a toxicity limit for air too, but it's well beyond the norm for recreational diving. It's not a big deal to do, but it's important to get it right. 3. If all that is available in your area is partial pressure blending, you're going to have to get your tanks cleaned to O2 service standards at each visual. This increased cost a bit. If you have a premix source, as I do, this is a moot point. 4. Most resort diving charters time their dives, depths and surface intervals to air on tables. If you're diving with somebody like this, there's little or no point in using nitrox. The operator won't let you take advantage of it anyway. Pro 1. When you begin to run out of dive time before you run out of gas, it's time to consider nitrox. It adds no deco time to your dive. A substantial portion of the people in this group have low enough consumption rates that they can reach deco status on a single dive, with a single 80 cubic foot tank, on the first dive. Most new divers can't. Some never do. Then again, some get bigger tanks to be able to stay with their lower consumption friends. 2. If you're going to be doing a lot of repetitive diving, you may find nitrox to be useful. While most people can't get into deco on a first dive with air, pretty much everybody can on a second one. With nitrox, you can spend more time underwater, with shorter surface intervals, without increased risk of DCS. It's nice to be able to get the most for all the money you paid to get to a dive site you like. 3. If you're diving with somebody that will let you do whatever your certification, abilities and/or equipment allows, you're really going to want nitrox. It's no fun sitting on a pitching boat while everybody else is still diving, dive after dive, after dive. 4. If you ever get into really intense diving, like the 6-7 dive a day trips I take each year, nitrox really comes into its own. Diving between 65 and 80 feet, I have a lot more flexibility on whether I'll be near the bottom, mid water or near the top. Sometimes that flexibility translates to food on the table . . . lobster, for example. I'm sold on nitrox. You may never care that much. The bottom line for me is, it's worth the money and slight bit more effort. YMMV. Lee The big "Pro" for me is that after a couple of dives on nitrox I actually feel like doing something other than crashing in a lounge chair by the pool...not that there's anything wrong with that ! My only "Anti" is the increased cost. I never approach O2 limits on recreational reef dives. > >I am basically just starting out.(2yrs of vacation diving) I am going > > to be just a Vacation Diver, this is not something I will be doing [quoted text clipped - 51 lines] > > Lee > I am basically just starting out.(2yrs of vacation diving) I am going > to be just a Vacation Diver, this is not something I will be doing > locally. Most of my equipment purchasing days are still infront of me > and will be comming out of my vacation budget. So, I am currently > trying to find out why NOT Nitrox??? Two reasons. First, if you plan to be a vacation diver, you will never develop the air consumption skills to make use of nitrox. If you run out of air before you run out of bottom time, nitrox has absolutely no benefit at all, just greater expense. Second, depending on where you vacation, you may find nitrox hard to find. >I am basically just starting out.(2yrs of vacation diving) I am going >to be just a Vacation Diver, this is not something I will be doing [quoted text clipped - 30 lines] >Now, could someone complete a 2nd dive for me after you have had >lunch? Benefits of Nitrox: Longer bottom time at same depths as air dive for same N2 exposure. Dive air table profiles and have lower N2 exposure for wider margin of safety against DCI. Feel better after a multi-dive day. Hazards of Nitrox: O2 exposure is higher and high PO2 deep dives increases risk of O2 toxicity. Diver must be aware of MOD and accumulated O2 time each dive. MOD is a HARD limit and should never be exceeded. Onset of O2 toxicity usually more abrupt than narcosis at shallower depths and diver must be aware of his situation at all times. Costs: Another certification is required. Per-unit refill costs are usually higher. O2 cleaning of equipment that is not already O2 clean. (This is very dependent on how your gas is mixed in your locale.) Safety is paramount so O2 cleaned regs and cylinders is highly desirable. Once O2 clean, this equipment should not be used with normally filtered EAN21 since contamination could occur. Some additional costs are associated with duplicate gear if the diver switches between EAN21 and other Nitrox mixes. ______ You don't say what the SIT was between the first dive and the second. Ok, I've had lunch... what was the question again? Oh, yes. Get Nitrox certified and you will be able to compute your own second dive plan easily. Using your examples above: EAN21: 90 fsw, 25 minutes, MDT is 25 minutes. EAN32: 90fsw, EAD is 80fsw, MOD @ 1.4 PO2 is 111fsw. At 40 minutes he's blown the NDT limits for an EAN21 diver and should probably do 5 minutes @ 15 feet even though he's on EAN32. EAN36: 90fsw, EAD is 70 fsw, MOD @ 1.4 PO2 is 95 fsw. A safe diver would do 5 min. at 15ft. safety stop no matter which profile/mix he was using. > MOD is a HARD limit and should never be exceeded. Onset of O2 toxicity > usually more abrupt than narcosis at shallower depths and diver must be > aware of his situation at all times. Under different conditions, I might say that the MOD for 32% is 111 fsw, 122 fsw and 131 fsw. Which one is the HARD limit you're referring to? > Safety is paramount so O2 cleaned regs and cylinders is highly desirable. O2 cleaned cylinders is important if your gas is partial pressure mixed, which is the case for much of the world. At recreational nitrox levels, an O2 cleaned regulator is a waste of money. > Once O2 clean, this equipment should not be used with normally filtered > EAN21 since contamination could occur. Care to explain why the air that is mixed with O2 to get nitrox, if added to your tank without O2, represents a contamination risk? > Some additional costs are associated with duplicate gear if the diver > switches between EAN21 and other Nitrox > mixes. My additional cost is . . . well, I have no additional cost. Somebody's been feeding you some bad information. I suspect it's the person selling you equipment and/or gas. Lee > Under different conditions, I might say that the MOD for 32% is 111 fsw, > 122 fsw and 131 fsw. Which one is the HARD limit you're referring to? But that depends which PPO2 you're happy with - if you aim for 1.4 you do have a safety margin built in, so it's not such a hard depth, if you don't mind eating into your safety margin.... If you use 1.6 or 1.8 it's less of a margin. > O2 cleaned cylinders is important if your gas is partial pressure mixed, > which is the case for much of the world. At recreational nitrox levels, > an O2 cleaned regulator is a waste of money. Yep, up to 40% you don't need an O2 clean reg, but if you use 50% you do... > Care to explain why the air that is mixed with O2 to get nitrox, if added > to your tank without O2, represents a contamination risk? If you get a fill from the wrong compressor, you can get oil contamination of you O2 clean tank, so when you add O2 before blending with air, it could go bang.... Double filtering should remove the hydrocarbon contamination. If someone is giving you a nitrox fill, they probably will be careful about contamination, if they don't supply it, they could be a bit less diligent. > My additional cost is . . . well, I have no additional cost. Somebody's > been feeding you some bad information. I suspect it's the person selling > you equipment and/or gas. Most filling stations will charge you more for nitrox than air, so you have an increased cost there. If you use a 50% deco mix in your pony, you may/will need a different mix to act as your bail-out at depth, so there could be some duplication of kit needed. Not all regs can be O2 cleaned, so again there may be costs there. > If you get a fill from the wrong compressor, you can get oil contamination > of you O2 clean tank, so when you add O2 before blending with air, it > could go bang.... Double filtering should remove the hydrocarbon > contamination. If someone is giving you a nitrox fill, they probably will > be careful about contamination, if they don't supply it, they could be a > bit less diligent. Any compressor could malfunction and people could be less diligent. My point, however, is that it's contamination that is to be avoided if you wish your tank to remain clean to O2 service standards, not filling with air. >> My additional cost is . . . well, I have no additional cost. Somebody's >> been feeding you some bad information. I suspect it's the person selling >> you equipment and/or gas. > Most filling stations will charge you more for nitrox than air, so you > have an increased cost there. If you use a 50% deco mix in your pony, you > may/will need a different mix to act as your bail-out at depth, so there > could be some duplication of kit needed. Not all regs can be O2 cleaned, > so again there may be costs there. If you use twins, stage tanks and deco tanks, you have a lot of additional cost, but it's not an additional equipment cost for the recreational diver. The original post specified the type of diving to be done. Lee >> MOD is a HARD limit and should never be exceeded. Onset of O2 toxicity >> usually more abrupt than narcosis at shallower depths and diver must be >> aware of his situation at all times. > >Under different conditions, I might say that the MOD for 32% is 111 fsw, 122 >fsw and 131 fsw. Which one is the HARD limit you're referring to? You must decide on a MOD and stick to it. For recreational use I haven't seen any recommendations above PO=1.4, and some recommend even going a little lower. >> Safety is paramount so O2 cleaned regs and cylinders is highly desirable. > >O2 cleaned cylinders is important if your gas is partial pressure mixed, >which is the case for much of the world. At recreational nitrox levels, an >O2 cleaned regulator is a waste of money. If you are exposed to "outhouse trimix"; (water, oil and air), yes, it will be contaminated at the first air fill. But it is still possible to make air fills that are O2 clean, so you can dive with pure air. >> Once O2 clean, this equipment should not be used with normally filtered >> EAN21 since contamination could occur. > >Care to explain why the air that is mixed with O2 to get nitrox, if added to >your tank without O2, represents a contamination risk? It is the not-particularly-well-filtered air, aka "outhouse trimix" that is referred to. >> Some additional costs are associated with duplicate gear if the diver >> switches between EAN21 and other Nitrox [quoted text clipped - 3 lines] >been feeding you some bad information. I suspect it's the person selling >you equipment and/or gas. Same for me. I pay for the O2, and do a "year's subscription" on the compressor. (i.e. free fills for a year for one person's diving. Cost here (=expensive place) is normally around $80 for a single tank, and $130 for all the tanks you own.) That air is O2 compatible; as a matter of fact, we are all religous in keeping it squeaky clean. You see, there is a second effect here, and that is a LOT less wear on tanks and regulators. My old 2x10's have now passed hydro for the 4th time, and nitrox vis for the 10th. Still mint condition, no qualms about using them for pure O2. The tester commented that this was the only set with that many stamps on that passed O2 cert without even a small tumble. That set now has around 400 dives on it. Likewise the regulators don't really need cleaning. They get a small, weak ultrasound and a light blue-gold wash just to be safe. Sinter filters are squeaky clean after hundreds of dives. Compare this to the normal statistics where the rejection rate on a visual inspection is around 40%, with around 2/3rds of that recoverable with tumbling, washing etc; but still a failure rate of around 12% on all tanks. Almost none fail hydro, but that is only because the bad ones never reach past the vis. I also see a large buildup of contamination in regs that have been travelling. This is really a comment that the prevailing air standards are somewhat too lax. Yes, and I do feel better after Nitrox dives. For a single ND dive there is not much difference; but it is noticable after the second and pretty strong after the third dive. On intensive dive vacations I am unable to do more than 4-2-3-2-3 dives on successive days; but on Nitrox 5-4-5-4-4 works pretty well. One interesting observation I made from technical dives with O2 decompression is that I feel a LOT better after those; so it does seem to be decompression related. And all the headaches from early diving is gone, even when diving air; so I suspect contaminants may enter into the picture more strongly than we suspect. But then, I am known locally as the resident O2 cleanlyness nazi. -- mrr > You must decide on a MOD and stick to it. For recreational use I haven't > seen any recommendations above PO=1.4, and some recommend even going a little > lower. It is true that 1.4 is the popular recommendation, but the recent reduction from 1.6 is not for the reason you think. For the recreational diver, anything below 1.8 is safe. 1.6 was selected for working divers as a limit controlling the cumulative effects of long-term exposure and, incidentally, increasing the allowable margin of MOD error. More recent research has indicated that the cumulative effects of exposure to hyperbaric Oxygen suggest a reduction to 1.4, which NOAA adopted. Recreational divers, who are unlikely to experience a cumulative lifetime exposure of more than a thousand hours are unaffected. But the recreational dive industry, for a number of reasons, accepts whatever number NOAA comes up with, and that is currently 1.4 It is not unlikely that further research by NOAA will lower the threshhold, perhaps as low as 0.8, for divers whose cumulative exposure might exceed several thousand hours. The recreational industry will certainly follow suit, but the increased safety to the recreational diver will be zero. >>Under different conditions, I might say that the MOD for 32% is 111 fsw, >>122 >>fsw and 131 fsw. Which one is the HARD limit you're referring to? > You must decide on a MOD and stick to it. There's no must to it. It's a personal risk decision, one that changes with circumstances. > For recreational use I haven't seen any recommendations above PO=1.4, and > some recommend even going a little > lower. You sight has been limited. Others have seen more. Lee >I am basically just starting out.(2yrs of vacation diving) I am going >to be just a Vacation Diver, this is not something I will be doing >locally. Most of my equipment purchasing days are still infront of me >and will be comming out of my vacation budget. So, I am currently >trying to find out why NOT Nitrox??? Good question. 1 - Cost. You've said that this is not an issue. 2 - Skills sufficient to plan the dive and stick to the plan, IE, do not violate the maximum depth of the gas... about 110ft for EAN32. Personally, I feel that if this is an issue, then you should not be diving with any gas. 3 - Availability. If this IS an issue, then you simply dive air. >Now, could someone complete a 2nd dive for me after you have had >lunch? There's more to it than increased available bottom time. Many feel less fatigued after a nitrox dive, simply because if you don't extend the bottom time, then as far as nitrogen uptake, it's the same as if you used air to a shallower depth, or for less time. To finish the above table, using a 1 hour SI, 90ft and 60ft, we get: Normal air 90fsw = 25 min. with no deco stop Dive #2 = 60ft, 38 minutes Ean 32 90fsw = 35 min. with no deco stop Dive #2 = 60ft, 62 minutes Ean 36 90fsw = 40 min. with no deco stop Dive #2 = 60ft, 83 minutes Notice that my numbers are different for the first dive... I used PADI's table. NAUI allows the following: Normal air 90fsw = 25 min. with no deco stop Dive #2 = 60ft, 36 minutes Ean 32 90fsw = 40 min. with no deco stop Dive #2 = 60ft, 56 minutes Ean 36 90fsw = 50 min. with no deco stop Dive #2 = 60ft, 66 minutes The NAUI tables are patterned more closely after Navy tables, and while more liberal on the initial dive, they are more restrictive on repetitive dives. In reality, what usually happens in places like Cozumel, you dive air on the first dive and EAN32 on the second. This allows you to run the wall down to 120 or 130, and they usually plan the second dive for around 80ft, but using EAN32 still allows the freedom to go as deep as 111 if you'd like to. Of course, you'll probably be using a dive computer anyways, so you'll be logging 110ft dives that last as long as 45 minutes or more, but the above gives you an idea of the advantages of nitrox. --- Rich http://richlockyer.tripod.com/ > 2 - Skills sufficient to plan the dive and stick to the plan, IE, do > not violate the maximum depth of the gas... about 110ft for EAN32. I did not expect this from you. 111 fsw is a PPO2 of 1.4 ata for EAN32. If you use 100% O2 for deco at 20 feet, you're at a PPO2 of 1.6 ata. If you're willing to accept a PPO2 of 1.6 ata, then you're MOD is considerably more than "about 110 feet . . . or do you not use 100% at 20 feet? > Personally, I feel that if this is an issue, then you should not be > diving with any gas. Agreed. Lee > > 2 - Skills sufficient to plan the dive and stick to the plan, IE, do > > not violate the maximum depth of the gas... about 110ft for EAN32. [quoted text clipped - 3 lines] > willing to accept a PPO2 of 1.6 ata, then you're MOD is considerably more > than "about 110 feet . . . or do you not use 100% at 20 feet? Working part of the dive vs. deco part of the dive. Brian Edmonton, Alberta www.mossmanscuba.com > Working part of the dive vs. deco part of the dive. You work when you dive? A PPO2 of 1.6 was the standard for a long time. Slowly but surely, the agencies became increasingly conservative. By the time I was trained, the standard was 1.4 for a dive that included significant exertion, 1.5 for one that did not and 1.6 for when you exert little or no energy, as in decompression. The point is, Mod is not an absolute. It's a personal choice that varies from diver to diver and from dive to dive. I happen to plan for a PPO2 of 1.4, but I also plan to descend to 1.5 without much provocation and will go to 1.6 for an assist without significant hesitation. Beyond that, I begin to wonder whether I'm more concerned about my own life than I am the life of somebody who forced me to make such a decision. Lee > > Working part of the dive vs. deco part of the dive. > > You work when you dive? Just a term to differentiate between the bottom part and the deco part. You want to use a different term go ahead. Brian Edmonton, Alberta www.mossmanscuba.com >> > Working part of the dive vs. deco part of the dive. >> >> You work when you dive? > > Just a term to differentiate between the bottom part and the deco part. > You want to use a different term go ahead. Don't get annoyed, but there is a point here. To the best of my knowledge, acceptable PPO2 is directly related to the amount of work you are actually doing. Recommendations during my course were that 1.5 was fine as long as you weren't working much, that 1.4 was better for dives where you are working such as moving about quickly or swimming against a current. While theory may have gotten more conservative since then, I think you can see why I take the word "working" to mean a bit more than simply the bottom part of a dive. In this context, to me, working means, well, working. Gotta go. I'm on my way to Pompano and, from there, up the state for some spring diving tomorrow. Lee Remember the guy I was working with on the recompression chamber? He used to run the chamber for the wash-out O2 tolerance tests for the US Navy. Jack 'em to 60 feet, and put them on O2 for a given time. If the Master Chief wanted to wash the guy out, he would smack the chamber with a big hammer; Instant tox hit. > Remember the guy I was working with on the recompression chamber? > [quoted text clipped - 6 lines] > > Instant tox hit. That would put everyone on deck into convulsions. > Remember the guy I was working with on the recompression chamber? > He used to run the chamber for the wash-out O2 tolerance tests for the US [quoted text clipped - 3 lines] > hammer; > Instant tox hit. I remember. >> 2 - Skills sufficient to plan the dive and stick to the plan, IE, do >> not violate the maximum depth of the gas... about 110ft for EAN32. [quoted text clipped - 3 lines] >willing to accept a PPO2 of 1.6 ata, then you're MOD is considerably more >than "about 110 feet . . . or do you not use 100% at 20 feet? He's a vacation diver, and 1.4 is the max acceptable for the "working" portion of the dive. Last time I checked, there weren't many vacation divers doing a 130ft stop on 32%. --- Rich http://richlockyer.tripod.com/ > He's a vacation diver, and 1.4 is the max acceptable for the "working" > portion of the dive. > > Last time I checked, there weren't many vacation divers doing a 130ft > stop on 32%. True enough. I guess I'm still hung up on whoever posted that the MOD is a HARD limit. Lee >> He's a vacation diver, and 1.4 is the max acceptable for the "working" >> portion of the dive. [quoted text clipped - 4 lines] >True enough. I guess I'm still hung up on whoever posted that the MOD is a >HARD limit. Well... there is another reason for planning with a limit of 1.4, especially for vacation divers, who will be diving with people who lack the needed skill indicated earlier. If I'm planning a max of 1.6 using "best mix" and I'm at 110, what do I do if my "assigned buddy" from the cattle boat gets into trouble at 120 or 130? In all likelyhood, I'll be fine violating 1.6, but above 1.6 is when the stuff can hit the fan very quickly... stress and exertion from a rescue attempt could be enough to push one over the edge. If I'm running "standard mix" and staying with EAN32, I can hit 130 without violating 1.6. --- Rich http://richlockyer.tripod.com/ > If I'm planning a max of 1.6 using "best mix" and I'm at 110, what do > I do if my "assigned buddy" from the cattle boat gets into trouble at > 120 or 130? Let him buddy up with Darwin for the rest of his dive. Depending on how much responsibility you want to accept, there's a good argument for having the same MOD as your buddy. This also bring up another advantage of using nitrox: "I really shouldn't be his buddy, since my MOD is a lot shallower than his."  SignatureSteve The above can be construed as personal opinion in the absence of a reasonable belief that it was intended as a statement of fact. If you want a reply to reach me, remove the SPAMTRAP from the address. > Well... there is another reason for planning with a limit of 1.4, > especially for vacation divers, who will be diving with people who [quoted text clipped - 9 lines] > If I'm running "standard mix" and staying with EAN32, I can hit 130 > without violating 1.6. I believe I posted something very similar in this same thread. Lee Rich Lockyer <rlockyer@linkline.DONTSPAMME.com> wrote in message PADI's table. > Normal air 90fsw = 25 min. with no deco stop > Dive #2 = 60ft, 36 minutes > Ean 32 90fsw = 40 min. with no deco stop > Dive #2 = 60ft, 56 minutes > Ean 36 90fsw = 50 min. with no deco stop > Dive #2 = 60ft, 66 minutes --- Rich > http://richlockyer.tripod.com/ Thanks rich that is what I thought I was reading between the lines. And it sounds like according to Lee Bell the time values continue to grow with each repetitive dive. I should of also indicated that if I dive with Nitrox, I will be planning on diving with a Nitrox computer. My personal diving experience always has me running out of air on my 1st dive and running out of lately I am beginning to run out of time on my second. >>4. Most resort diving charters time their dives, depths and surface >>intervals to air on tables. If you're diving with somebody like this, >>there's little or no point in using nitrox. The operator won't let you take >>advantage of it anyway. What exactly does this mean? Is it simply if 1 person in your party is diving with air then everyone might as well be diving on air? >In reality, what usually happens in places like Cozumel, you dive air >on the first dive and EAN32 on the second. This allows you to run the >wall down to 120 or 130, and they usually plan the second dive for >around 80ft, but using EAN32 still allows the freedom to go as deep as >111 if you'd like This sound like it would be illegal as hell. I figured you would have to stick to either air or nitrox for the entire day. I would think that you could not jump from one table to another. Maybe this is something you learn in class. One more question. Since I do no local diving and all my vacations come via Jet Airliner and I can't ever see myself hauling Air tanks. If I am renting filled air tanks for all my dives, will I need to change any of my personal equipment? From reading the materials here, it sounds like I could dive with nitrox on monday and air on tuesday without changing anything but my dive computer. Letting the dive shop do all the special maintance for the nitrox. I guess that would leave my only concern of finding a dive shop that rents Nitrox filled tanks, so worse case sceneraio is I get shut out and have to dive on air. The CO2 thing right now is beyond me and probably why there is a class set up. I am hoping that as long as I follow the rules I learn in class, it will be as safe as air??? Again, thanks for the input > Rich Lockyer <rlockyer@linkline.DONTSPAMME.com> wrote in message PADI's > table. [quoted text clipped - 58 lines] > > Again, thanks for the input Here is some reading for you.... http://www.americandivecenter.com/nitrox/n2o2_m00.htm#m43 R. >> Normal air 90fsw = 25 min. with no deco stop >> Dive #2 = 60ft, 36 minutes >> Ean 32 90fsw = 40 min. with no deco stop >> Dive #2 = 60ft, 56 minutes >> Ean 36 90fsw = 50 min. with no deco stop >> Dive #2 = 60ft, 66 minutes > Thanks rich that is what I thought I was reading between the lines. > And it sounds like according to Lee Bell the time values continue to > grow with each repetitive dive. I'd have to think this through and check as well before confirming this, and I've done neither. The advantage starts as soon as you're doing a dive during which you would run out of no deco time before you run out of gas. > I should of also indicated that if I dive with Nitrox, I will be > planning on diving with a Nitrox computer. My personal diving > experience always has me running out of air on my 1st dive and running > out of lately I am beginning to run out of time on my second. Assuming that the dive operator will allow you to dive longer on the second dive, you're at the point where the increased cost and slight increase in the things you have to watch out for begin to pay you back. It's a personal choice as to when the benefits equal or exceed the cost and added effort. > What exactly does this mean? Is it simply if 1 person in your party > is diving with air then everyone might as well be diving on air? While this is true when a DM turns the dive when the first person needs to, it's not quite what was meant. It means that many charters, particularly those that cater to holiday divers, set up their depths, dive times and schedules according to air tables. They're trying to control the risk that one of their customers will have a problem. If your operator gives you a maximum depth, or locates you over a hard bottom, and gives you a maximum time, particularly if it is less than an hour, there's a good chance he's using air tables to set things up. Sometime, when you're going out with somebody you know sets depth and time limits, work the dives on a table. I think you'll find that the dives and surface intervals are pretty much according to them. Those that allow real use of nitrox, or computers, will handle things differently. For example, they may ask if everybody is on nitrox and set different surface intervals and/or dive times for those that are not. They are also likely to say things like "tables divers, no more than 70 feet for 20 minutes, computer divers do what your computer tells you is safe." The latter are words us computer/nitrox divers love to hear, and seek out in an operator. >>In reality, what usually happens in places like Cozumel, you dive air >>on the first dive and EAN32 on the second. This allows you to run > > the wall down to 120 or 130, and they usually plan the second dive for >>around 80ft, but using EAN32 still allows the freedom to go as deep > > as 111 if you'd like > This sound like it would be illegal as hell. I figured you would have > to stick to either air or nitrox for the entire day. I would think > that you could not jump from one table to another. Maybe this is > something you learn in class. You need to take the class. All nitrox computers I know of allow you to change the gas you are using from one dive to another. Some, like mine, force it with outragiously conservative profiles if you forget. Keep in mind that air is, in fact, only nitrox with an oxygen percentage of 21%. You can, and in most courses, will learn to plan multiple dives on any combination of air or nitrox and why you might chose different mixes for different dives. Given information to do so, I usually chose my gas for the planned dives. The example of using air on the first dive and nitrox on subsequent ones is a good example, but only one of many options. Keep in mind that nitrox is not a deep water gas. It actually limits your depth to less than what you might do on air. The deeper you plan to go, the lower percentage of oxygen you will use and the less the no deco time benefit becomes. The oxygen replaces nitrogen in the mix. The same, by the way, is true of trimix, the difference being that both the oxygen and the helium (or other gas), replace nitrogen. Interestingly, very deep trimix has a lower percentage of oxygen than air. The math isn't hard, but you need to understand it before you'll understand the bigger picture. At any rate, assuming a maxium allowable PPO2, that's partial pressure of oxygen, of 1.4 and forgetting, for now, the risk or nitrogen narcoses, air will take you to 187 feet. Nitrox 32 will take you to 111 feet and Nitrox 36 will take you to 95 feet. The higher the O2 percentage, the shallower the depth and the greater the no deco time advantage. The "standard" blends of nitrox are 32% and 36%. These days, however, you can get pretty much anything you want, allowing you to customize you gas to the specific dive. A while back, I planned a 140 foot dive. That's below what I would do on Nitrox 32 or 36, but is almost spot on for a mix of 27%. On air, my computer allows me a maximum no deco time of 9 minutes. On 27%, the time increases to 12 minutes. Now I know that 3 minutes doesn't sound like a lot, but consider that it's a 1/3 increase in the amount of time I can spend at 140 feet without deco. Also keep in mind that the increased time is proportional. It also applies to a deco dive, which this one was. The no deco limit, in this case, is simply for illustration purposes. There are those that will tell you that the narcosis risk, a combination of the known narcotic effects of nitrogen and the widely believed narcotic effects of oxygen, make a 140 foot dive on air or nitrox, unwise and they may well be right. I'm not advocating the dive to others, only describing it. > One more question. Since I do no local diving and all my vacations > come via Jet Airliner and I can't ever see myself hauling Air tanks. [quoted text clipped - 3 lines] > without changing anything but my dive computer. Letting the dive shop > do all the special maintance for the nitrox. You're mostly right. You're not likely to take your tanks with you. Some people do, but they all have reasons beyond what you probably need. Up to about 40%, which is what we're almost always talking about when we're discussing diving on nitrox, you can use the same equipment for nitrox that you would use for air. The tank is the risk item. In many places, nitrox is made by putting a predetermined pressure of pure oxygen in the tank and topping it off with air. Safe handling of pure oxygen requires that equipment be free of flamable contamination. The tank needs to be clearn. By the time you hook a regulator to the tank, the air and oxygen are mixed. It's no longer a pure oxygen environment. Incidentally, you can use air and nitrox on the same day, with the same equipment, including your computer. As far as I know, all modern nitrox computers allow you to set your mix to air or 21% and to whole percentage increments from 22 to 40. Mine goes to 50%, higher than I'm ever likely to use it at. You can set it for air on the first dive and 32% on the second dive without a problem. On most computers, however, you can't set the computer back to air until you're both N2 and O2 stabilized at surface pressure (often a timer rather than a real calculation, but the idea is the same). Nitrox computers track both N2 and O2 issues when in nitrox mode and until both are clear, force you to select a mode that will allow them to continue to do so. If breathing air on a subsequent dive, you simply set the computer for 21% and keep on going. > I guess that would leave my only concern of finding a dive shop that > rents Nitrox filled tanks, so worse case sceneraio is I get shut out > and have to dive on air. Pretty much. > The CO2 thing right now is beyond me and probably why there is a class > set up. I am hoping that as long as I follow the rules I learn in > class, it will be as safe as air??? Yes, but understand the meaning of what you said. You are not absolutely safe on anything you breathe underwater. That's true for air, nitrox, trimix and everything else. Diving safety is a zone, not a point. Lee >I should of also indicated that if I dive with Nitrox, I will be >planning on diving with a Nitrox computer. My personal diving >experience always has me running out of air on my 1st dive and running >out of lately I am beginning to run out of time on my second. Keep in mind that nitrox is not a deep diving gas. It's greatest bottom time advantages are in the 50-80ft range. Deeper than that and your advantage turns into minutes instead of tens of minutes. >What exactly does this mean? Is it simply if 1 person in your party >is diving with air then everyone might as well be diving on air? It depends. In Cozumel, you're doing drift dives and the group tries to stay together. I've been on trips there where the "airhog" has been sent to the surface early and picked up by the boat while the rest of the group continues. In the Bahamas, the boat ties into a mooring and it's there for over an hour. If you are one of the first in the water, nitrox can help you be the last OUT of the water. Each buddy team is on their own, and until the captain sounds the recall, is free to dive as long as they like. >This sound like it would be illegal as hell. I figured you would have >to stick to either air or nitrox for the entire day. I would think >that you could not jump from one table to another. Maybe this is >something you learn in class. Ya... you'll learn it in class. You are completely free to change nitrox mixtures throughout the day. Personally, I only dive EAN32. Air if I can't get nitrox. Keep in mind that air basically is Nitrox-21. When using a computer, it will allow you to change the nitrox percentage between dives. Some computers revert back to 21% a few minutes after the dive... others, like Suunto wait a few hours. The idea there is if you forget to set your nitrox percentage, the computer is going to give you the most conservative profile. If diving tables, a "G" diver on the nitrox table can be carried through to the air table (you can't go from a PADI table to a NAUI table in the middle of any repetitive series, nitrox or air) You CAN use nitrox and use an air table, as long as you don't violate the MOD of the mix. This won't give you the advantage of an extended bottom time, but it will reduce your nitrogen uptake, reduce decompression stress, and reduce the likelyhood of an "undeserved" hit on long vacations. You can also use math to convert the nitrox percentage to an "equivalent depth" for an air table. This is the most versatile way to do it, since tables are only published for air, 32%, and 36%. Maybe you want to dive to 130ft... 32% is too hot, but you could use 28%. No table for 28%? No problem... convert it to an equivalent air depth. The NAUI course materials come with a wheel that'll do this for you :) >change any of my personal equipment? From reading the materials here, >it sounds like I could dive with nitrox on monday and air on tuesday >without changing anything but my dive computer. Letting the dive shop >do all the special maintance for the nitrox. For recreational nitrox mixes (40% and lower), you don't need to do anything special to your equipment. It would be wise to avoid purchasing a titanium regulator, but other than that, O2 cleaning only becomes important when dealing with deco gasses higher than 40% O2. >I guess that would leave my only concern of finding a dive shop that >rents Nitrox filled tanks, so worse case sceneraio is I get shut out >and have to dive on air. Bingo. Most shops that pump nitrox will rent tanks. I would recommend that you buy or build your own O2 analyzer. You can get a kit from Patrick at Oxycheq for about $100. Works like a champ... I'm going on 4 years on mine and the sensor is still fine, but I keep it capped with one of his "sensor savers" when not in use. The 9v battery lasted 3 years... I'd recommend replacing it every year though... don't ask :) >The CO2 thing right now is beyond me and probably why there is a class >set up. I am hoping that as long as I follow the rules I learn in >class, it will be as safe as air??? CO2 is not any more or less of an issue on nitrox than on air so long as you dive conservatively. CO2 buildup has been implicated as a promoter of tox, and tox is unlikely on air until you get well below 150ft, but in reality, I don't think there have been any recorded instances of recreational divers using recreational nitrox mixes within the depth limits of the gas. Every tox episode that I've heard of has been a matter of simply going too deep. Don't expect CO2 issues to be covered in your class :) --- Rich http://richlockyer.tripod.com/ > Some computers revert back to 21% a > few minutes after the dive... others, like Suunto wait a few hours. > The idea there is if you forget to set your nitrox percentage, the > computer is going to give you the most conservative profile. I've not heard of one that changes back to 21%/air, but there probably are some that do. My Oceanic and Genisis computers both revert to 78% nitrogen and 50% oxygen if you forget to reset it after a nitrox dive. Mine did that to me twice today. Most annoying. > You can also use math to convert the nitrox percentage to an > "equivalent depth" for an air table. This is the most versatile way > to do it . . . Next to using a computer. >I've not heard of one that changes back to 21%/air, but there probably are >some that do. My Oceanic and Genisis computers both revert to 78% nitrogen >and 50% oxygen if you forget to reset it after a nitrox dive. Mine did that >to me twice today. Most annoying. Ouch. Slam you with air tables and a 60ft MOD... lots of fun. Vyper reverts back to 21%, but it is quite a while, so forgetting to set it before a dive will most likely have you on the same mixture as the previous dive. --- Rich http://richlockyer.tripod.com/ >>I've not heard of one that changes back to 21%/air, but there probably are >>some that do. My Oceanic and Genisis computers both revert to 78% [quoted text clipped - 4 lines] > > Ouch. Slam you with air tables and a 60ft MOD... lots of fun. Tell me about it. We dove an Ocala area spring yesterday. My buddy and I were the first to be ready for the first dive. Just to check things out and take a look around, I slipped into the water, dropped to about 30 feet and, after a couple of minutes, surfaced to wait for the rest of our group. It didn't occur to me that my computer would consider that a dive and reset, but 10 minutes later, that's exactly what it did. I discovered it about 10 minutes into the dive, at almost 100 feet. According to the computer, I had a PPO2 of 1.9 something and a rapidly increasing N2 load. I headed for the surface, did my 10 minute wait, reset everything and headed back down. That wound up recording 3 dives. Lucky for me, I discovered the problem relatively early in the dive. It didn't add up to problems with the subsequent dive. After my third dive, and everybody else's first, I set up my second tank and took my first one up the slope to the setup area. I don't know how I managed to forget to set the computer this time, but I did. This time, I noticed the problem on the way down, immediately returned to the surface and waited for my 10 minutes to expire. I reset the computer and, once again, headed for the bottom. About an hour later, our dives were done. We loaded up and headed for dinner and home, about a 5 hour drive for my buddy and I. I've considered replacing my one buttom Oceanic and Genesis computers with a two button model specifically because it can be set to retain the nitrox mix you initially load. I only have problems like this when I'm doing several dives on the same gas. The act of planning for different gases always triggers a reset of the computer for what I'm doing. To be honest, this is usually not a problem except when there's been a period of non diving, as there has been lately, that allows my, otherwise good habits, to be temporarily overlooked. > Vyper reverts back to 21%, but it is quite a while, so forgetting to > set it before a dive will most likely have you on the same mixture as > the previous dive. I like that a lot better than my setup, even if I don't like the way Suunto products handle nitrox. Lee > after a couple of minutes, surfaced to wait for the rest of our group. It > didn't occur to me that my computer would consider that a dive and reset, > but 10 minutes later, that's exactly what it did. I discovered it about 10 > minutes into the dive, at almost 100 feet. According to the computer, I had > a PPO2 of 1.9 something and a rapidly increasing N2 load. I headed for the > surface, did my 10 minute wait, reset everything and headed back down. I just happen to be in the market for a nitrox computer and am considering Oceanic and Suunto. Since you've commented on both, maybe you'd be good enough to answer a couple of questions. Anyone else's opinions might also be useful. I'm assuming that the 10 minute wait is because your Oceanic won't allow you to reset your fO2 immediately upon surfacing, rather than a self-imposed SI? I didn't think I need a computer that offers gas switches during the dive but maybe I was wrong. > I don't like the way Suunto products handle nitrox. Just what is it you don't like? SignatureSteve The above can be construed as personal opinion in the absence of a reasonable belief that it was intended as a statement of fact. If you want a reply to reach me, remove the SPAMTRAP from the address. >> I don't like the way Suunto products handle nitrox. > >Just what is it you don't like? You mean other than the conservative profiles in general? Suunto basically adds 1% to the mix when calculating MOD. This results in an MOD of 107ft for EAN32. I don't see it as a big problem for a couple of reasons: 1 - That's what I was trained to do. If I get a tank of 32.3, I was trained to calc NDL based on 32%, but MOD based on 33%. Since my gas blender... as good as he is, never nails a mixture DEAD ON, it's not a proble. 2 - I set the computer's limit to 1.6 and use the computer between my ears to tell me when I'm too deep. I don't need the computer's alarm beeping if I happen to violate 107ft on a 32% mix. Which brings us to 3.... 3 - It totally freaks if you actually DO hit (what it considers to be) a 1.4... IE, 108ft on EAN32. Where NOAA allows 45 minutes at 1.6, Suunto goes to a max OLF in about 15 minutes at 1.4. This is irregardless of where you have the limit set... the limit is only where the alarm beep sounds. This still isn't a problem, because it does not affect the decompression profiles at all, so as long as you KNOW that you are diving within the limits as you were trained, you can simply ignore the OLF graph. You're not going to run into whole-body or CNS issues on typical rec dives anyways. I understand that the Vytec does not have this problem. I'm not sure how long you have to wait before changing mixtures. It does NOT revert to 21% very quickly... like I said, it's an hour or more. I haven't tried changing it immediately following a dive, but I would assume that it would have to wait a few minutes until it's going to log as a repetitive. As I understand that with the Vytec, while you can change between 3 different mixtures during the dive, they still need to be pre-programmed, and the intent is to use the feature for bottom/deco gasses. The feature is not a substitute for pre-dive diligence. --- Rich http://richlockyer.tripod.com/ > You mean other than the conservative profiles in general? > Suunto basically adds 1% to the mix when calculating MOD. > This results in an MOD of 107ft for EAN32. Those are two of the reasons. Looks like I got the second one wrong. It's the mod that's bumped down rather than the no deco time . . . or is it both? I didn't mention the one thing I like best about the Suunto line. They can be set to be nothing more than a guage + dive recorder. That's a nice feature for tech divers and for those that wear a wrist mounted unit that they don't want to remove when freediving. > I don't see it as a big problem for a couple of reasons: > > 1 - That's what I was trained to do. If I get a tank of 32.3, I was > trained to calc NDL based on 32%, but MOD based on 33%. > Since my gas blender... as good as he is, never nails a mixture DEAD > ON, it's not a proble. YOu need to meet the guys at fill express. They're remarkable in their ability to hit target mixes spot on. > 2 - I set the computer's limit to 1.6 and use the computer between my > ears to tell me when I'm too deep. I don't need the computer's alarm > beeping if I happen to violate 107ft on a 32% mix. My computer has not beepers. That's a big plus for me since I can't hear them anyway. Audible alarms don't do anything for me except annoy those I dive with. > Which brings us to 3.... > [quoted text clipped - 3 lines] > irregardless of where you have the limit set... the limit is only > where the alarm beep sounds. That's the problem that guarantees I won't use a Suunto. > This still isn't a problem, because it does not affect the > decompression profiles at all, so as long as you KNOW that you are > diving within the limits as you were trained, you can simply ignore > the OLF graph. You're not going to run into whole-body or CNS issues > on typical rec dives anyways. Personally, I find a computer that I know I'm going to ignore to be a less than desiarable purchase. > I understand that the Vytec does not have this problem. That's good news for Suunto, but will be a lot better when they do that same with their wrist mounted models. It is the compact size that attracted me to Suunto and their calculations that sent me elsewhere. > I'm not sure how long you have to wait before changing mixtures. It > does NOT revert to 21% very quickly... like I said, it's an hour or > more. I haven't tried changing it immediately following a dive, but I > would assume that it would have to wait a few minutes until it's going > to log as a repetitive. > As I understand that with the Vytec, while you can change between 3 > different mixtures during the dive, they still need to be > pre-programmed, and the intent is to use the feature for bottom/deco > gasses. The feature is not a substitute for pre-dive diligence. That's a feature I expect to find useful in the near future, but one I probably won't jump at the chance to purchase. Lee >Those are two of the reasons. Looks like I got the second one wrong. It's >the mod that's bumped down rather than the no deco time . . . or is it both? The MOD goes shallower... the NDL is just conservative, as the Suunto-modified RBGM is conservative... depending on how you view conservatism. >YOu need to meet the guys at fill express. They're remarkable in their >ability to hit target mixes spot on. Being in Kahlifohniah... if they'd ever get the bugs worked out of their freaking EtherFill, I'd be all over them. >My computer has not beepers. That's a big plus for me since I can't hear >them anyway. Audible alarms don't do anything for me except annoy those I >dive with. I can't hear them when I'm wearing a hood, but I can hear them without. Ya... they can get annoying. --- Rich http://richlockyer.tripod.com/ >>YOu need to meet the guys at fill express. They're remarkable in their >>ability to hit target mixes spot on. > > Being in Kahlifohniah... if they'd ever get the bugs worked out of > their freaking EtherFill, I'd be all over them. Sounds like a business opportunity to me. I wonder if they're interested in franchising their system. Next time I'm up there, I'll pay a bit more attention to what's going on. I know they bank some gas, have an oxygen booster that they're comfortable with and do not require O2 clean for anything up to 40%. They've expanded their dive shop inventory. If their claims are correct, they have more Dive-Rite stuff instock than Dive-Rite does. >>My computer has no beepers. That's a big plus for me since I can't hear >>them anyway. Audible alarms don't do anything for me except annoy those I >>dive with. > > I can't hear them when I'm wearing a hood, but I can hear them > without. Ya... they can get annoying. It's kind of interesting to watch sometimes. The Citizen HyperAqualand I normally wear has had the alarms disabled now, but it didn't always. It seems that just about every time I'd move, everyone around me would check their computers. It was not directly annoying to me, but knowing that I was annoying everybody else suggested I needed to do something different. I've got a second HA that will get the same treatment when it next goes in for a battery. Lee >>Those are two of the reasons. Looks like I got the second one wrong. It's >>the mod that's bumped down rather than the no deco time . . . or is it both? > > The MOD goes shallower... I'll guess that's what Lee meant by "bumped down". As far as the fO2 being bumped up, that makes sense. If the analyzer is only accurate to about +/- 1% a mix that tests at 32% may well be 33%. Of course it may well be 31%, so the safest assumption would be to base the NDL on 1% more N2. OTOH, that 1% difference is pretty unlikely to be a problem unless you really push the ppO2, and there isn't much NDL penalty. I gather that Suunto's (at least your model) don't allow you to choose the ppO2 at which it gets upset? I haven't looked closely at the Suunto's yet, but like the RGBM and don't mind a bit of conservatism. OTOH, I'd already gathered that they are probably much more conservative than necessary. I'm not sure just how she did it, but one of my friends managed to get her Suunto (not sure which model) to give her a 17 minute stop on one of our dives in Palau. She might have been a bit deeper for some of the dive, but I seriously doubt that her profile was substantially different than what most of us had. Thanks to both of you for the info. I've got some time before making decisions, but since my wife and I each need one I guess we're going to have an expensive Christmas. SignatureSteve The above can be construed as personal opinion in the absence of a reasonable belief that it was intended as a statement of fact. If you want a reply to reach me, remove the SPAMTRAP from the address. > Thanks to both of you for the info. I've got some time before making > decisions, but since my wife and I each need one I guess we're going to > have an expensive Christmas. You're welcome. You think you're going to have an expensive Christmas, you should see the total cost of the twinset package I'm looking at, and I've already got one of the tanks I'll eventually use. Lee >As far as the fO2 being bumped up, that makes sense. If the analyzer is only accurate >to about +/- 1% a mix that tests at 32% may well be 33%. Of course it may well be Don't get your "percent accuracy" confused with fraction scale. 1% of 32 is 0.32, not 1.0. The analox O2EII for instance, is: http://www.analox.net/site/content_datasheets/O2EII.pdf1 +/- 1% of *reading*, +/- 0.2% of O2 so, 31.65% <= 32% <= 32.32% safe diving, bullshark safe diving, bullshark > Don't get your "percent accuracy" confused with fraction scale. > 1% of 32 is 0.32, not 1.0. Depending on which analyzer, I've seen the accuracy represented as +/- 1% of full scale, "across" full scale and other phrasing. If I buy my own I'll hopefully know the claimed accuracy, (a lot of the info I've seen claims a resolution of 0.1% with no claim of accuracy), but in a shop or at a resort I may not have a clue about the specific model they're using. > The analox O2EII for instance, is: http://www.analox.net/site/content_datasheets/O2EII.pdf1 > +/- 1% of *reading*, > +/- 0.2% of O2 > > so, 31.65% <= 32% <= 32.32% What exactly does the "+/- 0.2% of O2" part mean? It sounds like they may be dealing with an accuracy in measurement as well as an accuracy in display. Depending on how I interpret the claim, 32% could have a range of 32% +/- 0.2 (31.8 to 32.2), the 31.68% to 32.32% you list, or 31.68% +/- 0.2 to 32.32 +/- 0.2 which would be 31.48% to 32.52%. The latter being a hair over .5% would suggest that the safest choice with a computer that accepts fO2 in 1% intervals should be bumped up to 33%. While there may be an occasional time when I'll wish I could go a few feet deeper, I don't think the difference between EANx and EANx+1 is going to be an unacceptable problem. For 32.32% the MOD at 1.6 is 130.4' and for 33% it's 127. I don't expect the 3.5 feet is likely to be so important that I'll be wishing I could take advantage of it very often, and if I'm going to be thoroughly anal about the MOD at 1.6 I'm going to have to find out how accurately the computer measures my depth, too. I may decide that the overall constraint of a Suunto is too conservative, but I wouldn't cross it off the list because of rounding up to the next 1%. SignatureSteve The above can be construed as personal opinion in the absence of a reasonable belief that it was intended as a statement of fact. If you want a reply to reach me, remove the SPAMTRAP from the address. > I just happen to be in the market for a nitrox computer and am considering > Oceanic and Suunto. Since you've commented on both, maybe you'd be good > enough to answer a couple of questions. Anyone else's opinions might also > be useful. > I'm assuming that the 10 minute wait is because your Oceanic won't allow > you to reset your fO2 immediately upon surfacing, rather than a > self-imposed SI? I didn't think I need a computer that offers gas switches > during the dive but maybe I was wrong. Your assumption is correct. My computer waits 10 minutes before concluding that the dive is done. If I reenter the water during that period, it treats it as a continuation of the first dive. >> I don't like the way Suunto products handle nitrox. > Just what is it you don't like? I no longer recall the exact details, so here's what I do recall. Verify the facts before you make a final decision. As I recall, the Suunto line treats each percentage of O2 in the gas like it is the next highest, at least I think it's percentage of O2. It might be PPO2. If I've got it right, that means that other computers allow you more time on 32% than the Suunto computers do. They also get a bit crazy when your PPO2 gets above 1.4 ata, again, I think. The net result is that they are very conservative and both more likely to require deco and/or to require more deco than other units. I've been told, by those that actually tested them against an Oceanic on the same dive, that the differences was significant. I have a hockey puck Oceanic and the same kind of Genesis. The Aeris line includes one or more just like them. Mine is a single button model. All three brands use the same formulas, differing only in appearance and layout of the screen. They all also make a two button model that can be set to retain the O2 percentage until it is reset or the O2 and N2 clocks run out. BTW, I assume it's a clock rather than an actual calculation. I've not verified this because it doesn't matter to me. I have my own ideas about when I will or won't fly and it's not based on what my computer says at the time. At any rate, if I were to purchase a computer now for the same reasons I bought the ones I have, it would be a two button model of the Oceanic, Aeris or Genesis line (I assume that all three are still made). One of the things I like best about this line is that Oceanic had, and I assume still does, a free simulator available on line. I can test my dive plans against the simulator, including multilevel, multidive days, on any of my four computers. I find that both fun and useful. Lee |
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