Your mention of Boyle's law got me thinking about the other gas properties like ideal gas law and Charle's law, and specifically the effect temperature would have on partial pressures and volume. I wonder what the benefits of heating breathing gasses to closer to body temperature (say 90F/32C) would be, and whether that could be a useful improvement in cold water/deep dives Both in reducing the PPO2 you're inhaling, and reducing the energy your body uses to heat up gasses. With how common suit heaters have gotten, I can't imagine it's much more effort to insulate and heat the regulator hose
14:35 interesting to learn that the Megalodon breathing loop is counter or anti-clockwise with the inhalation conning from the divers right side and exhaling out the left side. Opposite form what I see on most modern rebreathers. Good to see they remain consistent with O2 cylinder in the divers right side and DIL on the left at least for the configuration of the unit in this video.
I just love your videos and respect all you have achieved in cave diving. I was happy to hear that you loved the Nerd 2, because I was on the fence before your video.
Dr. Harris you are an amazing diver and anesthesiologist! Ps Ketamine is also used in the military in frontline injuries due to the pain killing and anesthesia effects it has without as many drawbacks present in morphine such as lowering of respiration/blood pressure/heart rate.
This is top quality content. Thanks for sharing. If CO2 scrubber is the limiting factor do you have a way to know during a dive how much of the absorbent is used up?
Excellent question, and one that rebreather manufacturers are working hard on solving. We use a time cut off as the first guide. There are other ways to monitor scrubber material and even the appearance of CO2 back in the breathing gas, but none of them are fool proof yet. Watch this space!
@@colmdoherty49 the rEVO system is a temperature based system that uses an algorithm to predict scrubber duration. A heat front moves through the scrubber material as the chemical reaction takes place, and this is detected by the thermistors. An algorithm that accounts for depth and temperature then predicts safe scrubber duration with an added degree of conservatism. So, like the APD temperature stick, it is using the physicochemical properties of the scrubber material to predict duration. These systems have been validated under various conditions and have certainly added to rebreather knowledge and safety if understood and used correctly. But, you do need to understand they are not giving us the best information which arguably be the diver's inhaled (should be zero) and end tidal CO2 (should be stable in the normal range). A scrubber using the temperature as a proxy can still be over breathed, and other non-scrubber based causes of high CO2 levels in the loop or the diver can still occur and go undetected.
Thanks for the videos harry. Are there any reason to use both o2 control systems i.e have a leaky valve and an electronic control system. Or would it not be worth the added complexity and points of failure?
Yes, it's called a hybrid CCR or hCCR. Use the rebreather in a primarily manual mode but have the solenoid activate if the PO2 is falling too far e.g. at 0.40 (a "parachute system". In some ways, the best of both worlds. rEVO does a nice version of this.
For the reason you mentioned about having a rebreather that is well supported in the area you are diving, and for ease of diving on boat, i'm leaning towards KISS Sidwinder in Mexico. Liberty Rebreather is what I would prefer.
I think KISS is ubiquitous throughout the southern U.S. and Mexico. Not a bad choice at all. I've seen a lot of ChOptima Rebreathers near me lately as well.
Brilliant! I've been teetering on the edge of closed circuit since reading a Pete Mesley article last year and you just took a lot of mystery out of the basic concept for me - Thank you Doc 🤿
What happens if that single solenoid on the eCCR fails, or sticks open/closed? Is there a redundancy/bypass to turn the system into a manual CCR if need be? Also, what happens in the event of a total power loss? Just got to bailout of the system?
Good questions. All of these possibilities are covered in rebreather training and there is a solution for all of them that may or may not enable the dive to be completed on the rebreather. Worst case scenario is bailing out onto the open circuit gas and completing the dive. But most scenarios like you describe can be resolved by either 'flying' the unit manually or in a semi-closed mode. The only times I have had to bailout and complete the whole dive on open circuit is following a catastrophic flood.
Awesome work mate but crap Harry... I'm that one guy diving a KISS Sidewinder in NZ :)! I love it though and luckily it's simple enough with a lot of info online and my local AP Inspo specialist diving shop has been awesome at supporting me.
Cheers Steve! Yes at least you have a popular unit. And you have spent some time diving with the occasional KISS expert too I believe! The Sidewinder is a good case in point though isn't it, as it takes a bit of trial and error to get sorted with your harness etc. Having other experts around can short cut that process.
Yep agree Harry. I am headed to Mexico in Nov to train and dive with Patrick and the Protec team... Skanda et al. Will be brilliant to see how they are set up and fully expect a heap of tweaking through that experience. Cheers again for the great overviews.
Come here from seeing you on dive talk. That deep dive cave project you talked about was amazing to see. I’m going to be starting my rebreather training in a week I’m really looking forward to it. Can I ask you what’s your view on miflex hoses on the oxygen side of the system? Everything I’ve seen about them say they are only suitable for upto 40% o2?
I hope the Miflex hoses are OK for oxygen use because I have used them extensively! Not sure if they are actually rated for this application or not. There are reports of braided hoses obstructing due to a problem with the interior lining turning into some weird crumbly crystalline substance. I have one friend who wont use them at all because of this. Our group has not experienced this issue, and I don't know whether it happens with genuine Miflex or only the others. The polyether based lining is alleged to not suffer the problem. Lots of articles on the web about this.
@@DrHarryH thanks for the reply. I had seen about older miflex hoses having that issue you say about the interior lining but nothing on the newer ones.
Hi Harry, what are your thoughts on Poseidon’s solid state oxygen sensors? From Poseidon’s brief description of their functionality, it seems that they sort of function the same way a pulse oximeter detects oxygen saturation in hemoglobin (I could be wrong). Do you have any experience with these?
Good question, they don't seem to have caught on. To quote Ashley Stewart from In depth "Galvanic sensors are essentially wet-cell batteries that generate a millivolt current proportional to the PO2 in the loop. Conversely, Poseidon’s solid state sensor uses luminescent quenching, wherein a red LED light excites the underside of a special polymer surface, which is covered with a hydrophobic membrane and exposed to the gas in the breathing loop. A digital color meter then measures the responding change in fluorescence, which is dependent on oxygen pressure, and an algorithm calculates the PO2." I don't think any other manufacturers have picked up the technology, and even Poseidon still uses the old fuel cell sensors in tandem. When we finally crack totally reliable long lasting oxygen sensors and CO2 detection (a whole other topic), rebreather safety will take a big step forward.
No. Like many technical divers I do all my filling for any mix in the shed. Two compressors, booster and bulk supplies of oxygen and helium at home. Heavily invested in this hobby!
Actually it it more common to see mCCRs with a "parachute" system or failsafe, with electronics kicking in if the PO2 falls too low, commonly around 0.4. The rEVO is/was commonly run tis way for example.
Could you incorporate pulse oximetry as an additional safety measure? I mean you're already completely encased in sensors, hoses, tanks, rubber bags, dry suit etc so a little pulse oximetry sensor would hardly be noticeable. This sensor would measure how well oxygenated your blood actually is, not just the pO2 in the breathing circuit. In this way you could adapt and optimize the pO2 in the breathing mix continously so as to always have as much O2 as is necessary and as little as possible for your blood to still remain optimally oxygenated.
Yes you could, but actually it wouldn't help. Your oxygen saturation will generally be in the normal range with any PO2 above ~0.18. Including dangerously high PO2s. Importantly, we aren't really interested in oxygen saturation, but rather PO2 (to avoid CNS toxicity) and the fractional concentration of the inert gases (to manage our decompresion). We infer the latter by knowing our PO2 and keeping it as high as safely possible.
Sir , are there any contraindications or precautions to be taken for someone who has Asthma and wants to join scuba diving training ? can you please suggest any books or articles related to this topic ?
Yes asthma may be a reason not to dive, but as usual, it "depends". Best thing to do is see a doctor trained in diving medicine to discuss your particular case and the possible risks. The DAN websites have some good information.
Yes you absolutely can use a full face mask (FFM) with a rebreather, however it introduces a number of potential hazards as well as the possible benefits. Benefits include a warmer face, protection from drowning in the event of a seizure, communications, less jaw fatigue and so on. However the hazards include potential for CO2 accumulation (so you need a mouthpiece still), difficulty equalising and most importantly, the issue of managing bailout. It introduces a level of complexity that should not be taken lightly. This would be a good topic for an episode actually.
@@DrHarryH so I was thinking for a bailout just do it like you have a malfunction with the mask . Face mask regulator and I'm on my way up I'm confused at how much more bottom time you get to where I would be in danger of getting the Benz because I run out of air because of deco times it makes me nervous lol
Good question. A new set of 3 cells every 12 months (about AUD140 each) and the rest is much like other scuba gear...hoses and o rings as required. A few batteries for computers etc. Soda lime for each dive can add up (AUD $10-15/kg). If you regularly dive using helium based gases, these costs are easily offset in helium savings. If no helium used, it is a more expensive way to dive for sure.
it's funny that we can't breathe water, but we can breathe a hydrogen oxygen mix. can someone completely replace helium and nitrogen with hydrogen for depths between surface level and say 60 or 80 meters?
expensive, requires specialized training and matinence, and they are very situational. And if something goes wrong, you have a very bad problem on your hands.
$10,000+ USD for entry, fairly complex, and expensive to maintain. If you are doing recreational diving and bumping up against no deco limits (not uncommon), a single open circuit cylinder lasts about as long as you can underwater.
![Noob To Max With DRAGON REWORK In Blox Fruits [FULL MOVIE]](http://i.ytimg.com/vi/LnBMOinoOvA/mqdefault.jpg)
Apologies for those who left a comment on the first version of this video. Unfortunately RUclips doesn't allow us to upload an improved version.
Here from the dive talk. I'm not a diver but am very interested in physics, biology and technical systems. Great content!
Thanks!
No worries, I watched PT 1 again to refresh before watching pt2.
Again, thanks for explaining simply and clearly, appreciated 👍🇬🇧
This is by far the best information about rebreathers I’ve seen so far. Well done!👌☀️🇸🇪
14:07 Kinda like the vibe when the canister turns around and the massive hazardous x reveals while he is having the chemicals in his hand 😂🥲
i`m not diver at all, but it is the case when you are watching video with interest and pleasure. thank you Sir!
you are a natural teacher....great job
We def want to see you dive more, of ANY kind of dives and comment more on other dives.
Awesomely informative video. Best general rebreather explanation I've found so far. Great job
Your mention of Boyle's law got me thinking about the other gas properties like ideal gas law and Charle's law, and specifically the effect temperature would have on partial pressures and volume. I wonder what the benefits of heating breathing gasses to closer to body temperature (say 90F/32C) would be, and whether that could be a useful improvement in cold water/deep dives
Both in reducing the PPO2 you're inhaling, and reducing the energy your body uses to heat up gasses. With how common suit heaters have gotten, I can't imagine it's much more effort to insulate and heat the regulator hose
14:35 interesting to learn that the Megalodon breathing loop is counter or anti-clockwise with the inhalation conning from the divers right side and exhaling out the left side. Opposite form what I see on most modern rebreathers. Good to see they remain consistent with O2 cylinder in the divers right side and DIL on the left at least for the configuration of the unit in this video.
I just love your videos and respect all you have achieved in cave diving. I was happy to hear that you loved the Nerd 2, because I was on the fence before your video.
Dr. Harris you are an amazing diver and anesthesiologist! Ps Ketamine is also used in the military in frontline injuries due to the pain killing and anesthesia effects it has without as many drawbacks present in morphine such as lowering of respiration/blood pressure/heart rate.
This is top quality content. Thanks for sharing.
If CO2 scrubber is the limiting factor do you have a way to know during a dive how much of the absorbent is used up?
Excellent question, and one that rebreather manufacturers are working hard on solving. We use a time cut off as the first guide. There are other ways to monitor scrubber material and even the appearance of CO2 back in the breathing gas, but none of them are fool proof yet. Watch this space!
Look up the rEvo RMS system this really work to calculate remaining scrubber time
@@colmdoherty49 the rEVO system is a temperature based system that uses an algorithm to predict scrubber duration. A heat front moves through the scrubber material as the chemical reaction takes place, and this is detected by the thermistors. An algorithm that accounts for depth and temperature then predicts safe scrubber duration with an added degree of conservatism. So, like the APD temperature stick, it is using the physicochemical properties of the scrubber material to predict duration. These systems have been validated under various conditions and have certainly added to rebreather knowledge and safety if understood and used correctly. But, you do need to understand they are not giving us the best information which arguably be the diver's inhaled (should be zero) and end tidal CO2 (should be stable in the normal range). A scrubber using the temperature as a proxy can still be over breathed, and other non-scrubber based causes of high CO2 levels in the loop or the diver can still occur and go undetected.
Great video. Simple, clear and very instructive
Would be very interested in seeing a video on helmets and other gear ideas for different kinds of dives, thanks Rich
Thanks for the videos harry. Are there any reason to use both o2 control systems i.e have a leaky valve and an electronic control system. Or would it not be worth the added complexity and points of failure?
Yes, it's called a hybrid CCR or hCCR. Use the rebreather in a primarily manual mode but have the solenoid activate if the PO2 is falling too far e.g. at 0.40 (a "parachute system". In some ways, the best of both worlds. rEVO does a nice version of this.
@@DrHarryH thanks for the info that’s interesting to hear that there are duel systems that can be used
Excellent presentation. 😃👌👌👌
This was fascinating. Thank you!
Thanks for the overview!
For the reason you mentioned about having a rebreather that is well supported in the area you are diving, and for ease of diving on boat, i'm leaning towards KISS Sidwinder in Mexico. Liberty Rebreather is what I would prefer.
Sounds like a good choice!
I think KISS is ubiquitous throughout the southern U.S. and Mexico. Not a bad choice at all. I've seen a lot of ChOptima Rebreathers near me lately as well.
Brilliant! I've been teetering on the edge of closed circuit since reading a Pete Mesley article last year and you just took a lot of mystery out of the basic concept for me - Thank you Doc 🤿
Pete is a great man!
What happens if that single solenoid on the eCCR fails, or sticks open/closed? Is there a redundancy/bypass to turn the system into a manual CCR if need be?
Also, what happens in the event of a total power loss? Just got to bailout of the system?
Good questions. All of these possibilities are covered in rebreather training and there is a solution for all of them that may or may not enable the dive to be completed on the rebreather. Worst case scenario is bailing out onto the open circuit gas and completing the dive. But most scenarios like you describe can be resolved by either 'flying' the unit manually or in a semi-closed mode. The only times I have had to bailout and complete the whole dive on open circuit is following a catastrophic flood.
@@DrHarryH Thank you for the reply, I really appreciate it!!
Awesome work mate but crap Harry... I'm that one guy diving a KISS Sidewinder in NZ :)! I love it though and luckily it's simple enough with a lot of info online and my local AP Inspo specialist diving shop has been awesome at supporting me.
Cheers Steve! Yes at least you have a popular unit. And you have spent some time diving with the occasional KISS expert too I believe! The Sidewinder is a good case in point though isn't it, as it takes a bit of trial and error to get sorted with your harness etc. Having other experts around can short cut that process.
Yep agree Harry. I am headed to Mexico in Nov to train and dive with Patrick and the Protec team... Skanda et al. Will be brilliant to see how they are set up and fully expect a heap of tweaking through that experience. Cheers again for the great overviews.
Thanks for being awesome 👍🏻 really great videos
First ccr dive was 2009 AP classic, saves considerably on gas costs, helium is expensive
Come here from seeing you on dive talk. That deep dive cave project you talked about was amazing to see. I’m going to be starting my rebreather training in a week I’m really looking forward to it.
Can I ask you what’s your view on miflex hoses on the oxygen side of the system? Everything I’ve seen about them say they are only suitable for upto 40% o2?
I hope the Miflex hoses are OK for oxygen use because I have used them extensively! Not sure if they are actually rated for this application or not. There are reports of braided hoses obstructing due to a problem with the interior lining turning into some weird crumbly crystalline substance. I have one friend who wont use them at all because of this. Our group has not experienced this issue, and I don't know whether it happens with genuine Miflex or only the others. The polyether based lining is alleged to not suffer the problem. Lots of articles on the web about this.
@@DrHarryH thanks for the reply. I had seen about older miflex hoses having that issue you say about the interior lining but nothing on the newer ones.
Thanks Richard, I found this really helpful
Hi Harry, what are your thoughts on Poseidon’s solid state oxygen sensors? From Poseidon’s brief description of their functionality, it seems that they sort of function the same way a pulse oximeter detects oxygen saturation in hemoglobin (I could be wrong). Do you have any experience with these?
Good question, they don't seem to have caught on. To quote Ashley Stewart from In depth "Galvanic sensors are essentially wet-cell batteries that generate a millivolt current proportional to the PO2 in the loop. Conversely, Poseidon’s solid state sensor uses luminescent quenching, wherein a red LED light excites the underside of a special polymer surface, which is covered with a hydrophobic membrane and exposed to the gas in the breathing loop. A digital color meter then measures the responding change in fluorescence, which is dependent on oxygen pressure, and an algorithm calculates the PO2."
I don't think any other manufacturers have picked up the technology, and even Poseidon still uses the old fuel cell sensors in tandem. When we finally crack totally reliable long lasting oxygen sensors and CO2 detection (a whole other topic), rebreather safety will take a big step forward.
I'm really curious Sir ,did you used rebreather on that thai cave rescue? Or just regular tanks?
Just regular tanks. The cave is very shallow and hard work; two factors which can make rebreather use risky.
Very well explained. Do you go to the dive shop to get your o2 tank topped up for your rebreather?
No. Like many technical divers I do all my filling for any mix in the shed. Two compressors, booster and bulk supplies of oxygen and helium at home. Heavily invested in this hobby!
Great explanation!
Are there any eccrs with a manual system installed as a backup? In cas ethe electronic fails.
Actually it it more common to see mCCRs with a "parachute" system or failsafe, with electronics kicking in if the PO2 falls too low, commonly around 0.4. The rEVO is/was commonly run tis way for example.
rEvo do a hybrid.
Could you incorporate pulse oximetry as an additional safety measure? I mean you're already completely encased in sensors, hoses, tanks, rubber bags, dry suit etc so a little pulse oximetry sensor would hardly be noticeable. This sensor would measure how well oxygenated your blood actually is, not just the pO2 in the breathing circuit. In this way you could adapt and optimize the pO2 in the breathing mix continously so as to always have as much O2 as is necessary and as little as possible for your blood to still remain optimally oxygenated.
Yes you could, but actually it wouldn't help. Your oxygen saturation will generally be in the normal range with any PO2 above ~0.18. Including dangerously high PO2s. Importantly, we aren't really interested in oxygen saturation, but rather PO2 (to avoid CNS toxicity) and the fractional concentration of the inert gases (to manage our decompresion). We infer the latter by knowing our PO2 and keeping it as high as safely possible.
No. Doesn’t matter.
Thanks so much, this is really helpful and nicely put
Sir , are there any contraindications or precautions to be taken for someone who has Asthma and wants to join scuba diving training ? can you please suggest any books or articles related to this topic ?
Yes asthma may be a reason not to dive, but as usual, it "depends". Best thing to do is see a doctor trained in diving medicine to discuss your particular case and the possible risks. The DAN websites have some good information.
Thank you Sir for your reply .. i will definitely check the DAN websites ..
@@ketanmhatre6709 If you do end up diving, get insured through DAN. Keep it up to date. They're great people.
“General overview” part 1. Christ. Here we go
HA HA! My friend…. Thanks for this.
Question can you use a ffm on a rebreather
Yes you absolutely can use a full face mask (FFM) with a rebreather, however it introduces a number of potential hazards as well as the possible benefits. Benefits include a warmer face, protection from drowning in the event of a seizure, communications, less jaw fatigue and so on. However the hazards include potential for CO2 accumulation (so you need a mouthpiece still), difficulty equalising and most importantly, the issue of managing bailout. It introduces a level of complexity that should not be taken lightly. This would be a good topic for an episode actually.
@@DrHarryH so I was thinking for a bailout just do it like you have a malfunction with the mask . Face mask regulator and I'm on my way up I'm confused at how much more bottom time you get to where I would be in danger of getting the Benz because I run out of air because of deco times it makes me nervous lol
So I just bought a ccr o2optima.chest mounted rebreather .any ideas on where I can take the class.im in va moving to nc
what is the "up keep" costs of a rebreathers?
Good question. A new set of 3 cells every 12 months (about AUD140 each) and the rest is much like other scuba gear...hoses and o rings as required. A few batteries for computers etc. Soda lime for each dive can add up (AUD $10-15/kg). If you regularly dive using helium based gases, these costs are easily offset in helium savings. If no helium used, it is a more expensive way to dive for sure.
Maybe better wording is “can you keep up with the increasing cost of wasted open circuit helium”? Bring on the rebreather!
At one point I had 7 cylinders. Keeping them O2 cleaned and in test is a big expense. 2 3ltr O2, 2 3ltr Dil, Suite inflation, 2 Ali 80's
it's funny that we can't breathe water, but we can breathe a hydrogen oxygen mix. can someone completely replace helium and nitrogen with hydrogen for depths between surface level and say 60 or 80 meters?
no. it is a volatile gas, and they normally use only a fraction of it. otherwise the smallest spark will send you to the moon.
As long as you keep the oxygen fraction
Why don’t people use the old navy cdba rebreathers ? Relatively cheap simple and reliable .
O2 only I believe, which limits their range.
Is air integration crucial for a drive computer that's used for CCR?
No, not at all. Analogue gauges are fine.
Why is it so complicated for humans to remain underwater? First person to invent human gills is going to be a billionaire! 😂
Hey .u should come to Greece and explore the vast cave system of Vouliagmeni.its a deep labyrinth, super clear waters and huge rooms
From the perspective of a non diver. Rebreathers seem far better than normal scuba. I wonder whats the catch, cost?
expensive, requires specialized training and matinence, and they are very situational. And if something goes wrong, you have a very bad problem on your hands.
Use bailout and all these dangers (sorta) go away
$10,000+ USD for entry, fairly complex, and expensive to maintain.
If you are doing recreational diving and bumping up against no deco limits (not uncommon), a single open circuit cylinder lasts about as long as you can underwater.
@@marcwanagas1234 are you referring to ocr?
I can go quite a long time on one cylinder open circuit. Usually do two cylinders per day.
Depending on the depth, that can last me 3+ hours.