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Mixed Gases
Frog	Overheard some divers talking about mixed gases, namely 'trimix'. What is it, and what's it used for? Deep diving I take it? I heard 'heliox' mentioned to. If they're both for deep diving, why the different mixes? If they're not for deep diving, what are they used for? No complicated answers please, just wanting my curiosity satisfied! Thanks in anticipation
Davey_Willo	Hi Frog Hope this helps WHAT IS HELIOX? Heliox is a mixture of helium and oxygen used for very deep diving, usually to greater than 200 feet. Helium's great advantage is that it does not lead to nitrogen narcosis. Helium diving requires as much or more decompression time as nitrogen, so there is no saving there. Beyond 300 feet heliox may cause the 'high pressure nervous syndrome', a shaking sensation that can be incapacitating. Another disadvantage of helium is that it conducts heat about six times faster than nitrogen, so divers get colder than with air diving. A third problem is caused by the fact that helium is much less dense than nitrogen or air; as a result, the vocal cords vibrate much faster and divers sound like Donald Duck. Professional divers can use voice unscramblers to make their speech intelligible. Overall, helium offers no advantage for recreational divers. Diving with heliox is strictly for technical and professional divers. WHAT IS TRIMIX? Trimix is a mixture of oxygen, helium and nitrogen. Nitrogen, usually in a small percentage (e.g., 15%), is added back to heliox to create trimix, in order to lessen the risk of the high pressure nervous syndrome seen with helium breathing. Nitrogen slows down nerve conduction. Trimix is used for the deepest scuba dives, usually greater than 400 feet. Like Heliox, Trimix is strictly for non-recreational use: military, scientific, commercial, and advanced technical diving. Heres some more info I've found What are Trimix & Heliair, and what are the differences? Do we need special labelling to identify each. Trimix is a term used for a gas which usually contains oxygen, helium & nitrogen. 'Tri' meaning three and 'mix' from mixture. The proportions of the three gases is determined by the depth of the dive and what levels of oxygen (to limit toxicity) and nitrogen (to limit narcosis) partial pressures are desired. The greater the amount of helium in your mix means that decompression will generally be required to start at a deeper depth during the dive. It will also mean that the cost of the mix will be greater as Helium is the most expensive component of the mix. Trimix is usually made by adding oxygen, helium & nitrogen (or Oxygen, helium & nitrox) in separate procedures. Heliair is also Trimix, but made up of Helium and then adding Air, air being 21% oxygen and 79% nitrogen. As a guide, use recommended limits on oxygen at 1.5 bar (to limit toxicity) and nitrogen at 4.5 bar (to limit narcosis) during the dive. This means that a 80m dive could use 16% oxygen and 50% nitrogen with a remainder of 34% Helium. The common technical diving term for this mix would be a 16/34 mix (oxygen then helium). This mix though contains a ratio of oxygen to nitrogen of 16:50. This means that different proportions of oxygen and nitrogen would need to be added to make the desired mix. We could do that by pumping these gases from two separate cylinders or by adding oxygen and then helium & then topping with air having calculated the required amounts. If using Heliair, the ratio of oxygen to nitrogen would always be constant at 21:79 or about 1:3.8. Therefore a 16% oxygen mix would require you to use 60% nitrogen (and so 24% helium). To stay within the limits used for the 80m dive above (a maximum 16% oxygen and 50% nitrogen) the closest Heliair mix that could be blended would be 14% oxygen, 53% nitrogen and 33% helium. This mix could be easily made by filling a cylinder a third full with the required amount of helium & then topping with air to the desired pressure. Heliair is easier to make than desired Trimix, but will generally mean that your selection of mixes is limited, resulting usually in longer decompression times or a higher narcosis factor. In addition, as you are using more Helium to make the Heliair mix the cost is also greater. There are no differences in the labelling. Cylinders need to clearly state that Custom or Mixed Gas is inside and a cylinder contents label must be affixed showing actual contents and maximum safe breathing depth. What is Heliox and how does it differ from Trimix? Heliox is simply a mixture of Helium & Oxygen, with no Nitrogen, and is used primarily in the commercial diving industry and in most mixed gas rebreathers. As there is no nitrogen in the mix, there is therefore minimal narcosis. Heliox mixtures can be used at depths over 100msw / 330fsw, though beyond this depth we begin to run the risk of High Pressure Nervous Syndrome, or HPNS. HPNS is believed to be a result of a lack of nutrition to the brain, resulting from a constriction in the surface tension in membranes caused by the biological effect of absorbed Helium. As nitrogen causes the opposite, a rise in constriction in surface tension in membranes, nitrogen is often used as a "buffer" for deep mixed gas dives. Thus the use of Trimix. The symptoms of HPNS include tremors of the hands, whole body tremors, personality changes and convulsions. In addition to the physiological factors associated with Heliox, as we are using high partial pressures of Helium we therefore have a far greater rate of absorption and elimination of Helium into and out of the tissues. In comparing Trimix for dives less than 100msw we actually can have significantly reduced decompression times whilst for dives over 100msw we can have an increased decompression liability. Of course the amount of Helium we are using will also directly increase the cost. Now when we meet up in Abbs for a dive some time we can talk mixed gases like two old pro's eh
PeterT	Now thats what I call an answer not like the couple of lines I usually post. ~~ PeterT ~~ Those who do not learn from history are doomed to repeat its mistakes. [UNKNOWN]
AndyC	I don't think I can add to much to that answer. However, something you should know is that depending on the particular blend of trimix etc you are going to use you can't necessarily breath it at the surface. As you reduce the oxygen % so that you will not encounter oxygen toxicity at depth, you reach a point at which there isn't enough oxygen partial pressure to support life at the surface. A lot of Trimix divers will therefore use a 'travel mix' to get them to a depth at which the partial pressure of the oxygen in the trimix can support life. Then as they ascend they will obviously switch back to travel/deco mixes to avoid the problem again.
Davey_Willo	Aaaaaah Nice one Andy I'd wondered what travel mix was when I'd heard it refered to, now I know thanks.... Hows Oz mate? its lashing it down here, typical UK crap.... I'm looking out of my office at the grey clouds full of it and thinking of you... Hey not in THAT way Dave
Frog	Thank you for taking the time and patience to answer folks. I'm going to print off the answers and read them more thoroughly at home, as I'm supposed (ha!) to be working. Reminds me - I have to go and see what goodies cook has on the menu today. Home made soup is on for a start off, I think followed by home made steak pie and home made trifle for desserts. Fat frog!!
AndyC	Dave All going well down under thanks mate - You can tell it's winter here by the general temperature (not UK levels obviously) but there are still plenty of sunny days. The ski-season is in full swing further south (about 5hrs) - yes it gets cold enough for snow and they actually have a few hills big enough to be called the 'Australian Alps' although I haven't been to see for myself yet. The water is now around 13-14oC but the semi-dry is still keeping me warm underwater although I freeze my nuts off once I get out and have to change. I have ordered a new O3 dry-suit which should be here soon - I can't wait. Glad to see that England hasn't lost any of it's Summer appeal in terms of the weather. I've been watching a bit of the Tennis and have to laugh when matches that are only 1 hr long are taking all day to play as they dodge the rain.
Frog	Andy C - how cold is cold in Australia? 14 degrees - a nice warm bath then! See ya, keep blowing bubbles!
Davey_Willo	Hey Dom/AndyC My plans are to take my 'TDI Advanced Nitrox' in November, followed soon thereafter by doing a 'TDI Decompression Procedures' course.... then I'll hammer out a load of both simulated and real decompression stop dives for a few months taking a stage bottle with me, then hopefully, sometime in the middle of next year, when I feel confidant enough, I'm gonna take a 'TDI Entry Level Trimix' as I really fancy using Normoxic Trimix and getting into some deeper stuff, but be able to do so safely and with a nice clear head.... I'm not interested in having to carry multiple gases really, thats all too much and I don't want to go THAT deep, so a nice Normoxic mix and a deco gas to to finish off with will be the sort of thing I'm after. What do you know about it, can you give any advice, have you or any of your mates gone down this route? Anything I should be aware of? Best regards Dave.
Kevin	Many thanks for the info. Kevin
Davey_Willo	LOL!! They ignore theoretical tissue compartments and M values?? I thought that they were the basis for the Buhlmann algorithms.. BSAC use Buhlmann don't they? or do they? I dunno.... Anyway, yes I'm very much looking forward to moving into my next level of training. If you'd asked me last year if I wanted to go techie I'd have laughed in your face but I can feel myself being inexorably drawn into it, and after diving with Andy Hayhurst and getting to use a 30/30 mix at depth, I'm convinced of the uses of mixed gases, and then when I read articles such as this... well I'm sold. [url]http://www.divernet.com/travel/0502trimix.htm [/url]
Davey_Willo	Hmmm.... good reading, the guys sounds very knowledgeable and is very articulate in his explanations, although I'm not convinced that simple means better, even if the Buhlmman tables are harder to understand for calculating residual nitrogen on repetitive dives, I personally feel a lot safer rising at a 10m/min and doing stops while still under the water, of course this is probably down to the fact that, what one learns first, is usually what one is most comfortable with. I wonder... as BSAC divers are mainly wrapped up in a nice cuddly drysuit these days isn't the fact that the 88 tables were designed for divers who had to get out of the water quickly because of the dangers of hypothermia making them a bit out of step now?
AndyC	Hi Dave Doing the Advanced Deco & Deco courses are definately worth while and very imformative (depending on your instructor I guess!!). Depending which agencies you do it through you will probably find that they will let you do it as just one course (you don't really learn anything new in the advanced nitrox course over the theory you learn in the regular Nitrox course). I did mine with SSI as that was what the local tech dive shop recommended for that level - the shop is affiliated to & teaches most agencies so didn't have any particular profit benefit from the advice. The main reason I did the course was to get into wreck diving. You definately want to have a reason for diving deep and I wouldn't recommend it just for the sake of 'Going Deeper'. You will (should) learn a lot about decompression theory and the various models used in deco tables and computers etc. Having done the deco courses moving onto Trimix would be the next logical step and will elliminate most of that warm fuzzy narcotic feeling you will enjoy during your deep deco dives. Trimix is obviously a lot more expensive in terms of gas than just using air so make sure you are happy with the ongoing costs. Practice is definately the key - being able to handle an emergency at depth both mentally and in terms of equipment is what may well save your life one day. Definately try to get as much experience at each level as possible before you think about moving onto the next one. After 20mins at 55m you can't just bolt to the surface if something goes wrong. It is great fun, definately worth doing and will open a whole new world up to you.
Davey_Willo	Hi Andy Yup I've picked my instructor, a guy called Andy Hayhurst, he's one of our Tech moderators over on 'Yorkshire Divers' forum, he's not only a good bloke and friend but a kick *rse instructor too, so I'm in good hands. His website (which isn't quite finished yet i.e. a few dead links) is... [url]http://www.dalesdivers.co.uk/[/url] Heres a reason for me to go techy mate, although some of these wrecks will still be out of my reach with only a Normoxic ticket, at least you'll get the idea of whats giving me a buzz... [url]http://www.divernet.com/travel/0502trimix.htm[/url]
Kevin	Hi Guys. I'd like to resurrect this one of sorts. I am curious about decompression modelling software. My diving is not yet that complex that I need this sort of thing, but I would like to see the software in use. I would be interested to hear of any freeware or sites containing a full or working demo version. Cheers
Dominic Humphries	There are several freebies. Zplanner, DDplan, and a quite interesting Excel thingy which is worth taking a look at. Links: http://www.coastnet.com~powercheck/zplanner.html http://www.drogon.net/ddplan/ ftp://ftp.cisatlantic.com/outgoing/gve_table.xls If you've got a Palm, try Decoweenie, http://www.decoweenie.com/ Be warned, different people have different ideas about Helium and deco: Some say it saturates the tissues faster, and so leads to MORE deco. Others say it off-gasses faster, so means LESS deco, and still others say that the faster offgassing is cancelled out by the faster saturation, and therefore means no difference. I don't know how standardised they are with numbers of tissue compartments and M values and the like, I'm afraid.. There are 10 kinds of people in the world. Those who understand binary and Those who don't
Dominic Humphries	Well, I'm qualified for Advanced Nitrox with BSAC. I confess, I learnt more about Nitrox from my own reading than I did from the BSAC course, but it only cost £70 so I can't complain :) I find it's very handy to be able to do deco. Again, I was trained to do it with BSAC, but learnt a lot more about it elsewhere. Tissue compartments, M values and deep stops are ignored by the BSAC syllabus, and by their tables as well, come to think of it. Anyway, it's definitely very worthwhile doing the courses. Nitrox and decompression both make planning your dive a much higher priority, which is always a good thing. You'll also either improve your buoyancy control or gain much more faith in it. eg, when I did my Nitrox training, I had to swim from the Stanegarth to the wall at Stoney without going below 18m or separating from my buddy. My buddy, of course sat just below 18m, so I couldn't play it safe by going up to 15 and leaving a nice margin for error. So I had to do the whole swim at 17.9m, with no visual references - the vis was so crap I couldn't see the floor. I managed it (Despite a leg cramp), but I hadn't honestly expected to. I was surprised I was that good at buoyancy control. Same goes for ascending and holding a deco stop with no references. It's not easy or fun, but it's a big confidence boost when you know you can do it. I think that getting fully Nitrox qualified before doing any major deco stuff is a very good idea. Because decompression is very boring. Using Nitrox to avoid as much as possible, and then a rich mix to accelerate what you still have to do, is a very good idea. Trimix is something I may eventually get into - I get noticeble narcosis at 35 meters on air, so would hesitate to go any deeper without Nitrox or Trimix, and Nitrox doesn't go that far down. I hope you're prepared for the expense :) There are 10 kinds of people in the world. Those who understand binary and Those who don't
Dominic Humphries	Okay, I confess I exaggerated slightly.. The BSAC tables are in no way, shape or form, Buhlmann. And they work by considering the entire body as a single compartment - there are no fast tissues or slow tissues, just one single 'slab'. They also regard the surface interval as an integral part of the deco schedule, ie Where a Buhlmann deco might tell you to spend five minutes at 3m, BSAC will send you straight to the surface, but the first five minutes of surfacing are considered a "zero meters deco stop". [url="http://groups.google.com/groups?q=%22unfair+to+Mr+Hennessey%22+group:uk.rec.scuba+group:uk.rec.scuba&hl=en&lr=lang_en&ie=UTF-8&safe=off&selm=562e300c.0107030244.86d2d7%40posting.google.com&rnum=1"]THIS[/url] is an interesting post on UKRS about the 88s There are 10 kinds of people in the world. Those who understand binary and Those who don't
Dominic Humphries	I think the tables are certainly out of date, just the fact that they haven't been updated in over a decade makes me unhappy to follow them. Considering how many advances have been made since then, I think it's high time BSAC reviewed their tables. But to be fair, very few people get bent using them. Like you, I prefer to skip the recommended 15m/min in favour of a slower ascent. I'm not quite in the "One meter a minute from 6m to the surface" camp, but I certainly don't rocket to the surface as fast as some people I know.. :) There are 10 kinds of people in the world. Those who understand binary and Those who don't
AndyC	That's certainly a good incentive to be able to get a bit deeper!!!! Maybe I should get my arse in gear and do the trimix course too - but I'll miss that warm fuzzy feeling at 55m!!!
Davey_Willo	That warm fuzzy feeling is exactly what I don't want at 55m mate Lol!! you can keep that Andy... I want a sharp mind whilst pootling about in the cold dark waters off the UK (Well as sharp is its ever gonna be after so many years of abuse) Anyway.... Didn't anybody tell you.... air is old fashioned these days...
AndyC	Do you have any idea what the average trimix fill costs in the UK? I realise it depends on the He content but just curious on a ballpark figure. Out here it starts getting a pretty expenisve way to go diving at the w/e (unless you buy a rebreather I guess)
cthomase	looking back at DIVER, where they reviewed the new PSA trimix course, the equipment is likely to cost a few £`s, around 3000 i think!! that course was taken at Dorothea, twin 12`s, 2 7ltr stage cylinders, and as you can imagine, a huge wing to support it all. the gas used was around 15% oxgen, 50% nitrogen, therefore 35% helium, in the stage was nitrox80 and nitrox40. the cost, for 2 dives......£66 (this figures are from memory, im at college now so i havent got this with me, but it gives a rough idea) training from just a nitrox qualification is expensive too. Go TDI and do it somewhere warm, like the red sea (red sea diving college (sharm) was reviewed last november, for the PADI Tec Rec Course, and host Leigh Cunningham who is attempting a world record), but, if you wanna do it in the uk, check this site www.scapaflowtechnical.com happy diving!
Davey_Willo	A difficult one to answer Andy, as you say there are quite a few variables, depending on the percentage of the mix, where you buy it from and how much your charged by the litre etc etc. But being the tight arsed Yorkshireman that I am, I also intend to take my Gas Blending courses so that i can mix my own gases relatively cheaply. Talking to a guy in the know I'm informed that a 'J' of He can be bought for about £45 and that this should give 4-5 good dives with a fairly substantial set of twins, so not too expensive, but of course the initial outlay for training and the equipment will be rather expensive, so it's swings and roundabouts in that respect.
AndyC	Blimey that's a lot cheaper than doing it out here. 4-5 dives for Gbp45 + top up gases sounds great value. I've obviously got the rest of the gear, it was just the potential cost of the gas that has always been in the back of my mind. If its only going to cost me that sort of money back home then I will definitely have to get the course done before I leave Aus.
driftwood	I'd just like to point out the disadvantages of doing the nitrox / trimix in the shiney briney - namely that the conditions may be so much better you may not be fully prepared to cope with 'trox or tri in the UK. I've been warm water diving and have been far more relaxed and less narked than in the UK. Remember the old PADI one - diving in conditions equal to or better than those you have experience in...... Davey, so when we gonna persuade Jay to set up a YD helium account at Linde? Yes, it's me again....
Geffy	cthomase, the Red Sea Diving College is great there in Sharm. I had loads of fun, despite the fact that I was doing a DM course which was hard, but still fun. If you do the Trimix or Nitrox, I think you checkout on an old WWII wreck called the Thistlegorm, not sure on that but if you dont checkout on it, try to do it. I wasnt able to do it as I was on my course for the three weeks, but my dad who also went said it was great. Also if you do the Nitrox course you get Free Nitrox refills for the rest of the week. http://www.redseacollege.com You can also stay at the college, the rooms are quite nice. Good night life as well for the last day, or if you are takin a day off. Also recommend, Straits of Tiran and Ras Mohammed, great dives. Loved it.
cthomase	i appriciate what you say driftwood, diving in the Red Sea is much easier, and can lead to difficulties when using that training in the UK due to conditions. thanks for the info geffy, i did the thistlegorm with Anthias divers (near the beach in the Sonesta Beach Resort) and would recommend them to anyone! Frank (guide on thistlegorm, and shark bay) and Hubert (guide on shark reef and owner) were amazing and Maurizio (who taught me my advanced and nitrox) was great! they are a close bunch, go to the pub most nights (dont dive drunk...tut tut) and we even went go-karting. i would like to do my Instructor course with the red sea diving college because of thier good reputation, and i would like to learn tech from Leigh. do you know if they do the course ( divemaster and instructor ) as a year internship?? thanks
cthomase	just thought i would make some of the less adventurous web viewers aware of a mixed gas info page on this site, somehting to do with 'fizzology'
uri	hay thats so cool! went diving in Shalm with frank last summer. anyone have his email address? would appreciate it!! cheers uri