Choose Your Poison - Part 3 - TRIMIX
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- เผยแพร่เมื่อ 18 เม.ย. 2022
- The third episode describing the different gases we breath in technical diving, this time focussing on the use of helium based mixtures in deep diving. With a shout out to Scubapro, a company which I proudly support as an ambassador! www.scubapro.com/global-dive-...
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The example dives to different depths were very useful to bring all of the theory together into a practice.
Very cool videos, Richard.
I am just a recreational diver, but I am very fascinated by the science and technicality that goes into techdiving.
Sounds like tech diving is in your future. Enjoy it!
@@DrHarryH I hope to dip my toes into it some day. Considering the prices on training and equipment, it will probably be after I am done being a ramen-packet-sustenanced student. Until then, I'll binge watch your videos on the topic!
Thank you Richard for doing this videos.
You've managed to explain, and make sense, of concepts that some instructors have a hard time on doing so. Also, a huge value to the community, for those willing to learn.
Wish you safe divings.
Cheers!
I'm impressed how you can explain such a rather complex topic so clearly. Well done!
Thanks, glad it is helpful.
18 tanks… is about right. I helped carry tanks for Ron Allum’s deep dive in Slug Lake at Jenolan. That was open circuit, three different grades of gas, staged tanks for deco and fifty odd cave packs of gear to get into and out of the cave. Carrying that lot into and out of the cave took every dry caver on the trip the best part of a day, each way.
So you need to price in the cost of beer for the coolies, as well as the helium…
As a relatively new technical diver I find your videos amazing, I am eager to learn as much as possible in theory about things that I know I will end up doing in the future. For me, Trimix is the next course in line. There is very little technical content on YT, most of the stuff is just entertainment. Thank you so much for the education.
Just wanted to say thank you for taking the time to make these educational videos. To be able to learn from someone with your experience and passion for diving is a real treat! . Its videos like these that make the internet so amazing! I'm looking forward to getting my open water certification this summer. Videos like this and your others are such a great source of information to serve as both a primer for formal education/training, and an exciting glimpse into the possibilities of diving. Thank you!
Glad it is of interest!
Great video again mate! Looking forward to your next segment. Can I put in a request? As a non tech, non rebreather diver we'd love to see more about rebreathers. The stuff you probably think is boring. ie. setting it up pre dive and tearing it down post dive, what each component in the rebreather does, what happens if your mouthpiece gets knocked out under water, can you adjust your H2 levels on the fly like you do with O2 or do you need to carry different diluent bottles, do they have a CO2 sensor in the loop etc etc. Thanks again. Awesome content!
Good thoughts, I will do my best!
I look forward to part 4 on hydrogen.
Great explanation from a real pro 👏🏻. Have you considered doing a more saturation style dive in the Pearse Resurgance with a more permanent habitat?
Thanks Harry, great series. I watch the techies gearing up at the dive shop and do get a bit envious of their ability to get to where we can't go, then I just look at my camera still in a million pieces and move for our dives. Please keep the videos coming...
This is amazing video for who are curious about the Trimix concept. Thank you for sharing
Brilliant stuff again, even knowing the subject matter I couldn't help but watch all the way through. Sums up the concepts concisely and clearly.
I'm looking forward to your gas density video. An interesting subject especially when rebreathers/scrubbers are thrown into the mix.
Thanks for the entertainment!
👍
Would you be able to speak about Co2 hits.
(recovery times, best way to recover, I believe it can take along time, to recover underwater?)
Cheers again for a great vid 🍻
Awesome video once again. Heaps of knowledge and well explained, appreciate it.
Thanks. This is my first comment to any TH-camr. You have a fantastic way of explaining quite 'geeky' topics in a simple and understandable way. Being educated in thermo- and fluiddynamics, I appreciate the link you make towards human biology as this is, in my opinion, the non-linear behaviour which is hard to understand for me. Thanks again for your efford in presenting and sharing your knowledge. It is very much appreciate. Thanks again.
Great video sir
Brilliant as always! Thanks again, On your first point, do agree Scubapro definitely make some good gear and I haven't had any issues with the gear they make, as I've torture tested plenty of their gear (only to 40m but none the less) wish I could say the same with Oceanic and Hollis which have failed me time and again.
I just bought my first ccr, a Meg Tiburon, and am super excited to start learning and diving it. I'm happy that you put together these great videos considering your medical expertise. I've been diving since I was 16, now 42, and have become much more acutely aware of subtle cues of narcosis around 30m. I've now more interested in trimix to dive safer and not push it.
Also, congrats on your recent hydrogen dive!
This has been a fabulously informative video. You manage to pack a lot of information into a small space. That ability is a rare talent. Thank you for posting. There was just one detail that seemed to possibly be a bit off, but didn’t already have a written correction. At about 15:30 you state that 5/90 leaves you with 10% N. Should that not be 5% N?
Quite right! Maths never my strong suite!
Watched this again with a CCR mindset as I continue to train and work up to trimix… really great video and explanations. I got a lot out of this the second time around as well.
These are really enformativ Richard, when can we expect your next upload from the pearse resurgence? have you considered making a video on diets for long dives? this id imagine would be a what works best for the individual sinario though
Awesome work, thank you for sharing! 😊
Just started my rebreather class on P2 hollis. very excited to get it in the pool and start diving it. Thanks for the videos.
Awesome...enjoy it!
Extremely clear explanations, thank you for this!
As always a great and educational video. Keep them coming!!
Excellent video once again. Looking forward to watching more!
Keep them coming mate, excellent videos.
Thanks Harry for a great video.
Great video. Thanks for sharing your knowledge 👍
great presentation Harry, very well, and clearly, explained.
Great vid!
Very very well explained Rich! Sign. Mike
Very interesting indeed! 👍
Thank you this is a really great video
I was a recreational sport diver Naui certified although I did a couple of years of scuba diving before I got certified
I had been a free diver before that and tended to hold my breath (skip breathing ) on scuba way too long before I was certified trying to save air (pretty Stupid) I think the main thing that saved me was I didn’t dive below 40’
Still very dangerous so glad I got the training to become a safer diver
Back to your video your research and presentation are both excellent
You answered questions I’d had for years and years and you made it easy to understand even for a novice like myself
This video is 5 out of 5 stars
⭐️⭐️⭐️⭐️⭐️
I will share with my family and friends and they will do the same
Best wishes always from Las Vegas Craig
✅👍
Bravo 👏🏻
Thanks mate, glad you found it useful!
Thanks for the video! This is a nice primer to get aquatinted with the terminology.
A very basic intro, but hopefully helpful for newcomers.
After watching this video...I am using a snorkel.
You can my anesthetist anytime !
Sorry be my Anaethetist anytime ! Great videos
Amazing Video yet again. Thank you so mich. Super interesting. I will never have the need for heliumin my diving I guess. But I love the theory behind it.
Still trying to wrap my head around the fact that the body is ok with 7% O2 at depth - compared to at the surface. Seems it only really cares about the partial pressure being high enough. What is a safe lower level? Just curious.
Looking forward to your next video.
Greetings from Munich
Stephan
Hi Stephan, the body tissues (like the brain) only care about having enough molecules of oxygen to keep the home fires burning. In other words, if a cell needs 1000 molecules of O2 per minute to function, it will need that whether it is at the surface or at 100m depth. It doesn't know or care if that comes from 2% oxygen, or 20% oxygen mixtures. The same number of molecules will be present in 20% on the surface, as in 2% at ten times the pressure (90m depth). The (partial) pressure of the oxygen (and therefore the number of molecules) will be the same in both examples.
@@DrHarryH thanks Richard for taking the time to explain.
Btw. Totally random - i loved your attempt to pronounce Prüfpumpe.
Great videos! Any chance you’ll be doing one on gas density or gradient factors?
Will do something on density. But can't go past this talk by Simon Mitchell on GFs and decompression controversies. th-cam.com/video/UY61E49lyos/w-d-xo.html
With depths in the 6% O2 and lower range when will tech diving start using hydrogen? Lower density, less? Narcotic effect, faster tissue transfer? Not to mention far cheaper. I'm familiar with some of the earlier research with it but question why no one has attempted to pick it back up
Hi Eric, very good question. I am actually part of an international working party having a look at hydrogen diving from the recreation-technical perspective. The low gas density offers a definite advantage, however there are some equally daunting challenges - explosion risk, the thermal and hence respiratory issues, unknown decompression and gas switching strategies in bounce diving and the slightly weird narcotic properties. Watch this space!
@@DrHarryH wow that's super exciting to hear! I'll be following closely and hopefully breathing it soon
Found my new poison, your videos. Makes me addicted! Thank you very much for your effort to put together the information and present it, even for cert.tec.divers like myself, in a very interesting way. Looking forward to more videos on your channel.
I was just pondering today, instead of hydrogen, what about using a heavier inert gas at a lower concentration to achieve the same narcotic potential to alleviate HPNS? Xenon, while having a staggering density of 5.894g/L, 4.7x denser than nitrogen (1.2506g/L), allegedly has a narcotic potential 25.6 times that of nitrogen. Gram for gram, at least at STP, that gives it a 5.43x advantage to nitrogen. Of course, there is the "at STP" clause there, as I haven't dug into compressibility factors, and decompression is a huge unknown although the partial pressure may possibly be low enough to make it negligible. What are your thoughts?
Would love it if you could talk about the risks of cumulative oxygen exposure as the long decos at high PPO2 required for extreme dives far exceed NOAA oxygen exposure limits that commonly used.
Hi Arnaud, good thought. In short, our deepest dive to 245m with a total dive time of 16hrs accumulated a CNS score of 1070%, and UPTDs around 1400. We definitely suffer from pulmonary oxygen toxicity after these dives, but have yet to have suffered CNS toxicity. Draw your own conclusions, but I thing that short exposures to PO2s above 1.6 are more dangerous than very long ones at 1.2 - 1.4. High levels of CO2 however may make even moderate elevations in PO2 very much more hazardous.
@@DrHarryH Very interesting, what symptoms of pulmonary toxicity do you experience and how long do they take to subside?
The NOAA CNS limits get drilled Into you by the training agencies and incorporated in most dive computers (although their scientific basis is dubious, e.g. www.plongeesout.ch/PDF-dateien/SPUMS/SPUMS_V27N1_10.pdf ). Your dives blow way past those CNS limits, how did you become comfortable with this, do you take specific steps to mitigate the increased risk?
@@arnaudkoetsier5557 Always wise not to be the first! I watched with interest other divers doing similar exposures around the world and we built up slowly over many years. The same way we have gradually refined our GFs to hopefully safe, but moderately aggressive levels. I feel our conservatism is padded by the time we spend in dry habitats, and obviously that helps with the risk mitigation of a seizure should it happen. The pulmonary toxicity presents as the classically described retrosternal discomfort and breathlessness, dry cough. It lasts a few days in me. Spirometry has confirmed a temporary drop in vital capacity. Of course what seems to be working for me might not be safe for you or vice versa, so I would never say do what I do!
Sir .. have you released the talk on Gas density and Respiratory physiology ? i was not able to find it in the channels playlist ..
Great education video! I've been binging on dive physiology videos on DAN south africa YT channel featuring you and Dr Simon Mitchell before I fell into this rabbit hole of learning about deep tech diving. I just wanted to ask why wasn't the narcotic effects of oxygen factored into the calculation for trimix as it is as narcotic, if not more so compared to nitrogen? Despite the fact that oxygen would be metabolized, wouldn't it be more conservative to factor it into calculation with nitrogen?
I decided to leave oxygen out of the narcosis discussion for simplicity, but I wondered how long before someone would bring it up! It remains controversial in my opinion whether it has a practical narcotic effect. I tend to ignore it in my calculations but I accept it is more conservative to assume it is narcotic. As the thrust of theories around inert gas narcosis now centre on receptor actions rather than membrane effects (as correlated with lipid solubility), the arguments for O2 narcosis seem even less convincing. But I am happy to admit it is not my area of expertise. I might get a real expert to come on and discuss narcosis.
@@DrHarryH Thank you for your response!
Very interesting. Thanks for the explanations. Back in about 1989 I dived to below 50m (in Truk) on open circuit air. After what you say here it sounds like that was not wise :-)
Also you mentioned that about 250m is some sort of limit for trimix. Is it possible at all to go beyond 250m?
Hi, many of us did deep air dives back in the day (50-70m), and the generation before me did extremely deep dives (70-100m). The incident rate was pretty high. Trimix dives have certainly been done beyond 250m, but the margin of safety rapidly decreases. This means that if anything goes wrong, the chance of recovering from a problem becomes smaller and smaller.
Another good video, question for you... the cave bottom is 55M but along the way you need to descend to 65M before you go back up to 55M. Going there and returning you would hit 65M twice. Plan the trimix for 65M? In theory, would you be slightly hypoxic at 55M?
Yes you'll need to plan for the deepest depth and accept a slight decompression penalty for the time at 55m. But better still, use a CCR which will optimise PO2 for both depths.
@@DrHarryH You know that’s something I didn’t comment on, but I think this video is the best argument I’ve heard for a CCR if you want to go deeper and have it be enjoyable / manageable. I had narcosis at 65M and it’s something I won’t forget… nor do again. Since then I just avoid the deeper stuff.
Dr. Harris,
Can you elaborate on Heliox gas at great depth. I saw somewhere that Nitrogen must be a part of the mix below 150m because of the increased risk of High Pressure Nervous Syndrome. Is this true? Why does nitrogen help?
It seems to make sense as Heliox would have the lowest work of breathing, but people still use trimix for very deep diving.
Thanks for the content.
Hi Jonathan, great question. HPNS is caused by a pressure effect on the nerve cells in the central nervous system. It is almost certainly not a specific "toxic" effect of helium at depth. We know that nitrogen has a narcotic or anaesthetic effect at depth which can oppose this excitatory pressure effect. HPNS also is more prevalent with rapid compression, hence it is much more an issue with the rapid descents that recreational bounce diving involves. Saturation divers can be compressed to depth very slowly and so the HPNS can be more easily managed, hence heliox may still be used (they also heat their gases and reclaim/recycle the helium to keep costs down). In recreational diving, a small amount of nitrogen can prevent the disabling symptoms of HPNS. But, as you point out, nitrogen is much more dense and can introduce issues with respiratory work at depth. Everything is a careful balance and by the time you reach 250m, you have pretty much run out of options in recreational diving!
How is decompression calculated? Is that proportional to partial pressure of nitrogen, or based on ambient pressure (excluding time)?
I hear a "Choose Your Poison - Part 4 - Hydreliox" is in order? :P
Yes, time to do it I guess!
Hi Richard Tony here from Brisbane, what's the chancers of talking about the full face mask like the Drager FFM..looking at buying one but like to know but more on using with my Meg..pros and cons please:)
Hi Tony, that's a great idea, and it's a very controversial and interesting topic. I'll add it to my list! I have a good collection of FFMs I can chat about.
@@DrHarryH awesome Richard I'm planning on using with my Meg rebreather, wanting to know pros and cons.
Would really love to know about the gas mixes and parameters specifically around ultra deep diving, namely 300+ meters. How similar is such depths to saturation diving if any.?? 😊
Hi, good thought. I'm going to do a talk about just this... coming soon.
@@DrHarryH awesome, can’t wait for that one 😁🙂 have a great day sir
Hi. I had readed that helium its an gas who is comming directly fro the uranium accumulations. If so, better think twice before using it.
I believe that's correct, but helium is not radioactive. Anyway a little background radiation is supposed to be good for us!
Oh what about the hydrogen you mentioned in part 1. Or is hydrogen not really used. I dunno. But I'm curious.
It has been tested extensively in the commercial sector, but not yet in recreational diving. Lots of unknowns and hazards!
@@DrHarryH I remember from school that hydrogen goes “pop” when you light it. I imagine that might be problematic for a diving gas.
@@clivepat yes I'd call that one of the 'known' hazards!
Is it possible to dive with Helitrox to a certain depth (e.g. 90m) without decompression since there is no nitrogen in the gas mix? If yes, why is it not done?
No, sadly helium is an inert gas like nitrogen and therefore can generate decompression sickness just like nitrogen. No escaping the penalty of time at depth!
I'm curious how you even know if you got a CO2 hit, or if you're absorbing too much CO2. Is it just guesswork and hyperbaric chamber experiments? Is there a way to measure the CO2 in you blood, the way you can measure O2 saturation? Ideally non-invasively and with something you could use underwater, or at least in a dry habitat.
Hi Marcel that is a massive topic and worthy of its own episode. Watch this space!
When part 4 on Hydrox coming out?
Will do it at some stage.
@@DrHarryHAwsome. I was mostly joking, but that would be really cool to see.
So on your 245m dive you mentioned another diver who had a CO2 episode at death in that cave. I was wondering why that happened. but after watching this am I correct in assuming it's related to the gas density rather than a simple issue of over breathing the rebreather?
Hi Mathew, as you may know there are several causes of CO2 toxicity whilst rebreather diving. The case I referred to was primarily caused by excessive exertion at ~195m. The diver started to sink in a vertical shaft and rather than just allowing himself to sink, he started to fin vigorously whilst reaching for his wing inflator (which unfortunately didn't come straight to hand). He rapidly felt overwhelmed with CO2 and was fortunately able to stop, relax and bring his breathing back under control before exiting the cave. So probably a combination of exercise and gas density which either led to the scrubber being over breathed, and/or some effort independent respiratory failure in the diver (a large component in the Dave Shaw fatality). CO2 is a fickle bugger!
@@DrHarryH while this is unrelated to that specific incident, as a doctor diver do you have any experience regarding IPO? I watched this video receny and it was very eye opening. th-cam.com/video/El9Sy4_MjEQ/w-d-xo.html . It seems to indicate that different body attitudes in the water could increase or decrease the risk, depending on the gear setup you have; open circuit, ccr, front or rear counterlungs...
The video mentioned flash ipo as something anesthesiologists may encounter when dealing with the removal of breathing tubes. This obviously made me think of you.
@@matthewwyjad Yes I have seen both minor and fatal cases of IPO, and also flash pulmonary oedema in the setting of anaesthesia. Peter Wilmshurst's talk is an excellent overview. If you ever feel breathless on a dive you should get back to the surface as soon as safely possible and keep your buddy close in case you are in trouble on the surface. I would definitely recommend giving up diving thereafter as there are well documented cases of the subsequent episode being the fatal one.
@@DrHarryH thank you for the info. The whole topic has been a fascinating rabbit hole, and I'm blow away that i have not heard more about it previously.
Peter mentioned two things that i had questions about.
1st, that when your legs are below you in the water the fluids are pushed back up, increasing fluid volumes in your core and organs. Another article simply says that immersion immediately redistributes blood from the extremities to the chest. How does body attitude in the water impact the redistribution of fluids? If your legs are shallow and your core is deeper (as trimmed in cave diving) does the opposite happen? Or is it simply a response to increased pressure in general, similar to the response to cold?
2nd, he mentioned that increased pp02 is a risk factor, but he did not elaborate, and i have not found any articles yet shedding light on the matter other than if you are dealing with ipo at depth, then the drop in pp02 in your blood as you ascend exacerbates the onset of hypoxia. But does pp02 level play a role in the actual onset of ipo?
I'm trying to get a sense for the aspects that are general to immersion and the aspects that are more specific to diving.
I know this is a lot.... and i have more...as i said, this is a fascinating rabbit hole, but i think a very important one.
@@matthewwyjad It is a fascinating topic and one that is still not fully understood. I wouldn't worry too much about the body's position in the water, rather focus on the effect of immersion itself (you see the same issues in zero gravity in space). You will be familiar with the concept of immersion diuresis i.e. as soon as you start diving or swimming you produce more urine. This is a problem for divers who don't want to pee in their suits and so stop drinking before diving which may exacerbate any decompression sickness that occurs. This diuresis occurs due to the "centralisation of blood volume" from the peripheries to the central circulation. When sensors in the heart detect more blood volume, they assume there is too much fluid and so they tell the kidneys to get rid of it. Of course we are not carrying excessive fluid at that moment, it's just moved from the skin and muscles to the central circulation (heart, lungs, kidneys, brain, big blood vessels). The same occurs in cold temperatures (water or air) due to vasoconstriction i.e. skin blood vessels clamp down to stop peripheral heat loss, pushing blood centrally. The final effect Peter talks about is the effect of high PO2 on blood vessels. We know definitely that high PO2 constricts cerebral blood vessels (CO2 has the opposite effect) but I actually wasn't really aware that the same effect occurs peripherally (I would assume Peter knows his facts!). So he is saying is has an effect a bit like cold water.
In the end, all these forces push blood centrally and increase the pressure in the capillaries around the alveoli until if high enough, fluid starts to leak into the airspaces and you start to "drown" from the inside. If the distance oxygen has to travel across from airspace to blood is longer or blocked by fluid, then the oxygen levels in the blood starts to fall. CO2 is not affected initially because it passes more readily and also we increase our breathing to try and compensate for the falling oxygen levels, thus blowing off more CO2. In fact CO2 levels may fall as a result.
Now if you are breathing air at 30m (4ATA) and the PO2 in your blood has fallen from say 150mmHg to 80mmHg due to the IPO, ascending to the surface might cause the shallow water blackout we see in freedivers who have allowed their PO2 to fall too far. The result is unconsciousness on the surface and high risk of death. Hence it is important to ascend at the first sign of respiratory distress.
What I have described is highly simplistic. There are complex neuro-humoral factors at work with immersion and its effects. And probably a genetic disposition to getting this problem in the first place, otherwise we'd all be copping a dose at some point. Here's a nice overview from DAN alertdiver.eu/en_US/articles/the-p-phenomenon
Will you cover hydrogen containing mixtures, have you ever considered such a mixture?
H2 is very experimental obviously and has never been used in recreational divers. Look up HYDRA experiments on the web to see lots of info about commercial testing. Here's a great summary from John Clarke johnclarkeonline.com/2021/03/07/hydrogen-in-diving-the-good-the-bad-the-ugly/
It seems like the trimix limit is around 300 m.... Is that right? What if the Pearce goes further below 300m?
At 245m with a PO2 of 1.2, the gas density of our trimix is 7.89g/L which is already pushing the limits should the diver need to engage in significant work. Divers have used rebreathers to 300m on trimix but the safety margins are rapidly diminishing.
@@DrHarryH this makes it even more impressive! So this really means the scooter is an essential tool! I can't wait to see how you guys overcome the gas density challenges. Could you use external pumps to help your lungs cope with the depth? Or are you eventually going to have to come up with something more dramatic?
Absolutely love seeing the work you guys are doing, I'm very easily narked so living vicariously through you lot is the next best thing to being able to go deeper 😄
A big mistake, you can not use 30 meters as haft of 60 meters and use it for percentage of gaz because the percentage of gaz as the partial pressure of gaz is not a linear equation . Big big mistake
Thanks Michael, you are right. I should have been clear this is a guide only. I assume you are referring to the example of halving the amount to nitrogen in a 30m mix, to get the same narcosis at 60m. The PN2 of AIR (~80%N2) at 30m is roughly 3.2bar, the PN2 of trimix 20/40/40 at 60m is roughly 2.8bar. It is not linear but serves as a guide for gas planning. And if the narcotic effect of oxygen is ignored (which I personally do), the calculations are more and more conservative the deeper you go i.e. safer. So in my opinion, not a "big big mistake", but a mistake nonetheless. Appreciate the feeedback.
Do cave divers who use re breathers carry back up oxygen tanks in case the re breather malfunctions? I’m talking about cave diving..
Also I’m am not a diver just a fan of the channel wanting to learn. Cheers
All divers using rebreathers should carry sufficient bailout gas to allow a safe return to the surface in the event of a complete rebreather failure.
Hi Harry, hope your fit n well. Just stumbled on your Chanel. I know I'm a bit behind still very interesting.
Great gas & Lighting talks really informative. Well done for the Pearse dives unbelievable exploration, the twin Meg, what great idea.
Rick's dive to 177m still remains a bold dive using his homemade kit, truly outstanding exploration from the team. I believe your now using Hydrogen, seriously advanced diving.
Safe diving good luck with the project.
All the best
Dave.
@@davidmorris-zz1iu Rick's dive was amazing and really opened my eyes to the possibilities of deep exploration. He is a legend.
This is fascinating, and presented in such an accessible way that it feels far more retainable. Did you perchance create the video(s) discussing the gas density issues and distinctions been nitrogen and helium decompression?
Not yet! Need more hours in the day 🙂