Could a rebreather Helmet revolutionize diving?
- Thread starter Zeagle Eagle
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"It’s important to note that the rebreather helmet, while exciting, is only in the conceptual phase, meaning that the idea is described and a model has been made, but no prototype exist, and no tests have been done."
This is because not only doesn't this thing exist, the design aspects make it impossible to exist outside of flights of diving fancy. A college student design project only.
This is because not only doesn't this thing exist, the design aspects make it impossible to exist outside of flights of diving fancy. A college student design project only.
It's an entertaining read.
1. It's being called the Orb - for Oxygen Re-Breather, which seems to telegraph a degree of ignorance about the limitations of oxygen rebreathers.
2. The designer also apparently fails to grasp the concept that having a pressure helmet on your head would not eliminate the need to clear your ears, unless you kept the pressure at 1 ATA.
If that’s his intention, the designer also seems to be unaware that if you did that, outside pressure acting on the rest of you would try to force the rest of you into the helmet. At a minimum, and in the early stages, it would force the air out of your lungs, force fluids into your head, etc. Get would get messy quickly.
3. If maintaining 1 ATA pressure isn’t the intent, it’s probable that he’s never tried to clear his ears in a full face mask or helmet. You’ll need to use a properly fitted block to allow you to restrict air through your nose to clear, unless you can clear very easily. That’s beyond most recreational divers’ ability.
4. This is where it starts to get interesting as the design would have to incorporate a counter lung in the helmet. A full helmet is already very buoyant and adding a counter lung inside will dramatically increase the buoyancy.
5. A helmet mounted counter lung would be very position sensitive. For example, if the counter lung is above the center of the lungs in the water column, the air will want to rush out of your lungs and into the counter lung, making exhalation very easy, but making inhalation very difficult.
That works fine if the diver is in a level swimming position, but the closer to the vertical they get, the harder it will be to inhale and if the diver were in a full head up vertical position it’s likely that inhaling would be very, very difficult. That’s likely to result in panic for a recreational diver, particularly when they panic as it’s getting hard to inhale and then go head up in the water to try to claw their way to the surface, aggravating and then continuing the problem that was causing the panic in the first place.
6. You also have to have room to fit the scrubber in the helmet, and you’ll need a fair amount of scrubber for a two tank boat dives – at least 3.5 to 4 pounds to cover a couple of one hour dives. That’s going to add more volume to the already enormous helmet. You’ll actually probably need more volume as the gas going through the scrubber has to have enough dwell time for the chemical reaction to occur. If the scrubber is too small, it won’t have enough dwell time to handle high work loads where the diver is breathing more.
It would also be very hard to pack a scrubber that conforms to the inside of a helmet – cylindrical shaped scrubbers are already challenging enough for some divers and the average recreational diver probably isn’t meticulous enough to do it. That would leave some form of replaceable cartridge, which would probably work fine, but it wouldn’t be cheap.
7. The unswept volume of a helmet would be very problematic for a helmet rebreather. You need to move the air in one direction through the scrubber and that requires at a minimum a well sealed oral/nasal cavity in the helmet, or a mouthpiece in the helmet to breath through when you are not actively using coms in the helmet. If you don’t have one or the other, the unswept areas of the mask will lead to elevated CO2 and issues with hypercapnia.
8. You’ll also need to breathable PO2 in the loop during the dive and in particular as the diver changes depth. If the PO2 is too low at depth and the diver makes a rapid ascent, the diver will become hypoxic, pass out and eventually die. Conversely, as the diver descends, the PO2 increases and if it becomes too high the diver will suffer oxygen toxicity and die. Plus of course, the diver will be metabolizing O2 at a rate of about 1 liter per minute at a slow swim speed and perhaps as high as 2.3 or 3 lpm at high work loads.
That O2 has to be replaced in the loop, so you need a source of O2. A 1 liter / 6 cu ft sized tank at 206 bar / 3000 psi will provide about 200 liters of O2, and 60-200 minutes of bottom time depending on workload.
You’ll also require a source of diluent to add volume to the loop as the depth increases, as well as to reduce the PO2 as the pressure increases to prevent hyperoxia. The diluent requirement is probably greater for the average recreational diver so you’d need a 2 liter / 13 cu ft tank to accommodate 2 hour long dives. They are not going to fit inside the helmet, so you’re going to have some off board tanks, regulators and connections involved.
9. Even if you go the manual CCR route and have a constant flow of O2 into the loop, you need O2 sensors. Three is about the minimum to accommodate redundancy, voting logic and an ability to cross check sensors if the readings differ. You’ll also need a dive computer that is wired to the helmet and can monitor those sensors. The Shearwater Nerd might be ideal for his and it and the sensors are the only piece of hardware that currently exists. You’ll also need manual add valves for the O2 and the diluent and those will probably have to go outside the helmet at well.
10. Finally there is the issue of what do you do when something goes wrong – a flooded scrubber producing caustic liquid in the breathing loop, a failed scrubber that is causing hypercapnia, high or low PO2 conditions, etc.
When you’re head is stuck inside the rebreather bailing out to open circuit is problematic. And of course you need to have an open circuit system to bail out to. The OC system and tank doesn’t have to be large, but your 13 cu ft dil tank probably isn’t enough, so you need to incorporate an OC regulator and another 13 to 30 cu ft tank for bailout for a recreational rebreather. Putting the bailout reg in the helmet may not be the perfect solution as a caustic event that floods the loop may also flood the mouthpiece of the bailout reg. And of course it’s hard to rinse caustic solution out of your mouth when you are stuck in a helmet.
11. In the end, you’ll have a enormous helmet that a Mk V hard hat diver would feel right at home in, along with about 70 pounds of weight to get it neutral, plus your O2 and dil systems, and an open circuit bailout system. That will all have to be meticulously maintained and the breathing loop sterilized at the end of every diving day. With luck you could get the consumables cost down to about $40 per diving day, and you might be able to keep the cost under $10,000.
It would truly revolutionize recreational diving, in terms of either killing divers right and left, or discouraging them from diving at all.
I’m not saying it’s impossible, I’m just saying the challenges are daunting, the benefits minimal and the technology needed to make it happen not yet in existence.
1. It's being called the Orb - for Oxygen Re-Breather, which seems to telegraph a degree of ignorance about the limitations of oxygen rebreathers.
2. The designer also apparently fails to grasp the concept that having a pressure helmet on your head would not eliminate the need to clear your ears, unless you kept the pressure at 1 ATA.
If that’s his intention, the designer also seems to be unaware that if you did that, outside pressure acting on the rest of you would try to force the rest of you into the helmet. At a minimum, and in the early stages, it would force the air out of your lungs, force fluids into your head, etc. Get would get messy quickly.
3. If maintaining 1 ATA pressure isn’t the intent, it’s probable that he’s never tried to clear his ears in a full face mask or helmet. You’ll need to use a properly fitted block to allow you to restrict air through your nose to clear, unless you can clear very easily. That’s beyond most recreational divers’ ability.
4. This is where it starts to get interesting as the design would have to incorporate a counter lung in the helmet. A full helmet is already very buoyant and adding a counter lung inside will dramatically increase the buoyancy.
5. A helmet mounted counter lung would be very position sensitive. For example, if the counter lung is above the center of the lungs in the water column, the air will want to rush out of your lungs and into the counter lung, making exhalation very easy, but making inhalation very difficult.
That works fine if the diver is in a level swimming position, but the closer to the vertical they get, the harder it will be to inhale and if the diver were in a full head up vertical position it’s likely that inhaling would be very, very difficult. That’s likely to result in panic for a recreational diver, particularly when they panic as it’s getting hard to inhale and then go head up in the water to try to claw their way to the surface, aggravating and then continuing the problem that was causing the panic in the first place.
6. You also have to have room to fit the scrubber in the helmet, and you’ll need a fair amount of scrubber for a two tank boat dives – at least 3.5 to 4 pounds to cover a couple of one hour dives. That’s going to add more volume to the already enormous helmet. You’ll actually probably need more volume as the gas going through the scrubber has to have enough dwell time for the chemical reaction to occur. If the scrubber is too small, it won’t have enough dwell time to handle high work loads where the diver is breathing more.
It would also be very hard to pack a scrubber that conforms to the inside of a helmet – cylindrical shaped scrubbers are already challenging enough for some divers and the average recreational diver probably isn’t meticulous enough to do it. That would leave some form of replaceable cartridge, which would probably work fine, but it wouldn’t be cheap.
7. The unswept volume of a helmet would be very problematic for a helmet rebreather. You need to move the air in one direction through the scrubber and that requires at a minimum a well sealed oral/nasal cavity in the helmet, or a mouthpiece in the helmet to breath through when you are not actively using coms in the helmet. If you don’t have one or the other, the unswept areas of the mask will lead to elevated CO2 and issues with hypercapnia.
8. You’ll also need to breathable PO2 in the loop during the dive and in particular as the diver changes depth. If the PO2 is too low at depth and the diver makes a rapid ascent, the diver will become hypoxic, pass out and eventually die. Conversely, as the diver descends, the PO2 increases and if it becomes too high the diver will suffer oxygen toxicity and die. Plus of course, the diver will be metabolizing O2 at a rate of about 1 liter per minute at a slow swim speed and perhaps as high as 2.3 or 3 lpm at high work loads.
That O2 has to be replaced in the loop, so you need a source of O2. A 1 liter / 6 cu ft sized tank at 206 bar / 3000 psi will provide about 200 liters of O2, and 60-200 minutes of bottom time depending on workload.
You’ll also require a source of diluent to add volume to the loop as the depth increases, as well as to reduce the PO2 as the pressure increases to prevent hyperoxia. The diluent requirement is probably greater for the average recreational diver so you’d need a 2 liter / 13 cu ft tank to accommodate 2 hour long dives. They are not going to fit inside the helmet, so you’re going to have some off board tanks, regulators and connections involved.
9. Even if you go the manual CCR route and have a constant flow of O2 into the loop, you need O2 sensors. Three is about the minimum to accommodate redundancy, voting logic and an ability to cross check sensors if the readings differ. You’ll also need a dive computer that is wired to the helmet and can monitor those sensors. The Shearwater Nerd might be ideal for his and it and the sensors are the only piece of hardware that currently exists. You’ll also need manual add valves for the O2 and the diluent and those will probably have to go outside the helmet at well.
10. Finally there is the issue of what do you do when something goes wrong – a flooded scrubber producing caustic liquid in the breathing loop, a failed scrubber that is causing hypercapnia, high or low PO2 conditions, etc.
When you’re head is stuck inside the rebreather bailing out to open circuit is problematic. And of course you need to have an open circuit system to bail out to. The OC system and tank doesn’t have to be large, but your 13 cu ft dil tank probably isn’t enough, so you need to incorporate an OC regulator and another 13 to 30 cu ft tank for bailout for a recreational rebreather. Putting the bailout reg in the helmet may not be the perfect solution as a caustic event that floods the loop may also flood the mouthpiece of the bailout reg. And of course it’s hard to rinse caustic solution out of your mouth when you are stuck in a helmet.
11. In the end, you’ll have a enormous helmet that a Mk V hard hat diver would feel right at home in, along with about 70 pounds of weight to get it neutral, plus your O2 and dil systems, and an open circuit bailout system. That will all have to be meticulously maintained and the breathing loop sterilized at the end of every diving day. With luck you could get the consumables cost down to about $40 per diving day, and you might be able to keep the cost under $10,000.
It would truly revolutionize recreational diving, in terms of either killing divers right and left, or discouraging them from diving at all.
I’m not saying it’s impossible, I’m just saying the challenges are daunting, the benefits minimal and the technology needed to make it happen not yet in existence.
OP
Zeagle Eagle
Contributor
Thanks for the insight DA. A guy can dream though.
CuzzA
Wetwork for Hire
12. I'm pretty certain Bluetooth doesn't work underwater.
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