3 ms·

If the passages are narrow, why is an inflatable pod a preferred solution to a face mask? I'd imagine it would be at risk of puncture.

coatmatter 8y ago
There's less oxygen available with a face mask. It should also be noted that NASA has an inflatable module that's being tested against space, but I don't know if there's any similarity here.
- nradov 8y ago
  There is no less oxygen available with a face mask. The concern with full face masks is that they contain more dead space which can lead to dangerous CO2 accumulation. Divers who use full face masks or hard helmets often turn on at least a little free flow gas to supplement the demand valve regulator and keep their CO2 levels down.
  - richev 8y ago
    Full face diving masks are designed to have an air flow that helps minimize CO2 buildup[0]. The greater concern is that they might leak due to not fitting properly, and/or the user might panic and pull the mask off while underwater. [0] http://www.opstechnologies.com/products/scuba/full-face.html http://www.opstechnologies.com/products/scuba/full-face.html
sandworm101 8y ago
There are so many issues with either a pod or a solid tube. The biggest one is buoyancy. If it is full of air it will need to be weighted, and have air added/removed to adjust for pressure changes with depth. But imagine if the kid "turns turtle". Any brief head-down orientation will result in the fabric collapsing around the kid's head as the air rushes up to his feet. Correcting this requires forcefully turning the kid around to keep his head up. This is one (of many) reasons why commercial divers in dry suits use solid helmets. It isn't an issue for wetsuits. I'd rather slap a full helmet on the kid and tie him up into a bundle. It won't be pretty but does solve the buoyancy issues. I'm sure they are also considering drugging the kids to reduce the risk of panic attacks. Here is the nasa device, the personal rescue enclosure: http://www.astronautix.com/r/rescueball.html http://www.astronautix.com/r/rescueball.html (It wouldn't work. Wrong shape and no buoyancy control.)
- richev 8y ago
  Of the difficulties the pod solution poses, I don't think that neutral buoyancy us one of them, so long as the pod is rigid (e.g. steel) in construction. The best succinct definition for neutral buoyancy I could find was this one, from Wikipedia: > ...a condition in which a physical body's average density is equal to the density of the fluid in which it is immersed.[0] This means that once the pod has been weighted to be neutrally buoyant it will be so at any depth of water, since neither it or water are compressible[1] and thus their average densities are unchanged by depth. The challenges of maintaining neutral buoyancy arise when you submerge a compressible object, such as a scuba diver wearing an inflatable buoyancy control device (BCD). The water pressure (caused by the weight of the water above) will squeeze them and their equipment, compressing anything that is air filled. To sink from the surface, the diver has to deflate their BCD, and then put sufficient air in it to achieve neutral buoyancy at their desired depth. If they swim downwards, the higher water pressure will squeeze them some more, the air in their BCD will compress some more, and their average density will increase. They will now be negatively buoyant and will sink. The deeper they sink, the higher the water pressure will be, the more the air in their BCD will compress and the more negatively buoyant they will become. So they'll sink faster and faster. This happened to me once when I was first learning to scuba dive. It can be scary. The opposite applies to ascending. This is why good buoyancy control is such an important (and difficult) thing for scuba divers to learn.[2] From a buoyancy perspective, a metal pod is more like a camera in an underwater housing. These are rigid in construction (usually either plastic or metal) and their buoyancy characteristics don't change with depth. [0] https://en.wikipedia.org/wiki/Neutral_buoyancy https://en.wikipedia.org/wiki/Neutral_buoyancy [1] Not strictly true for water, but true enough for scuba diving depths [2] https://www.padi.com/courses/peak-performance-buoyancy https://www.padi.com/courses/peak-performance-buoyancy
  - nradov 8y ago
    None of this is relevant because the cave contains a restriction so tight that a rigid pod wouldn't fit through. The last thing they want is a solid object wedged into the restriction. The SpaceX design is apparently flexible to fit through the cave, so some buoyancy adjustments would be necessary.
jdietrich 8y ago
1) Maintaining trim requires a significant degree of skill. A badly trimmed diver can't purposefully swim and is very difficult to tow. It's potentially safer and easier to bundle someone up as a package and manage their trim externally. https://en.wikipedia.org/wiki/Diver_trim https://en.wikipedia.org/wiki/Diver_trim 2) Scuba gear presents a considerable entanglement hazard in a confined space. There are a lot of hoses and protrusions that could get snagged on a rock feature, a guide line or another diver's gear. There's nothing stopping you from using a face mask and some kind of protective vessel to make the kids easier to drag through a cave. That vessel doesn't need to be pressurised to be useful. 3) A panicked diver can be absolutely terrifying. They do wild, irrational and often violent things. Many divers have died or killed a dive partner because of panic, even in quite benign open water conditions. A totally inexperienced diver in a difficult cave system poses a tremendous risk. Brutal as it might seem, a panicked diver doesn't pose a hazard if they're immobilised. https://www.youtube.com/watch?v=dnWKS5DzKRU https://www.youtube.com/watch?v=dnWKS5DzKRU https://www.youtube.com/watch?v=SF3dQDgynT4 https://www.youtube.com/watch?v=SF3dQDgynT4

coatmatter 8y ago

There's less oxygen available with a face mask. It should also be noted that NASA has an inflatable module that's being tested against space, but I don't know if there's any similarity here.

nradov 8y ago
There is no less oxygen available with a face mask. The concern with full face masks is that they contain more dead space which can lead to dangerous CO2 accumulation. Divers who use full face masks or hard helmets often turn on at least a little free flow gas to supplement the demand valve regulator and keep their CO2 levels down.
- richev 8y ago
  Full face diving masks are designed to have an air flow that helps minimize CO2 buildup[0]. The greater concern is that they might leak due to not fitting properly, and/or the user might panic and pull the mask off while underwater. [0] http://www.opstechnologies.com/products/scuba/full-face.html http://www.opstechnologies.com/products/scuba/full-face.html

sandworm101 8y ago

There are so many issues with either a pod or a solid tube. The biggest one is buoyancy. If it is full of air it will need to be weighted, and have air added/removed to adjust for pressure changes with depth. But imagine if the kid "turns turtle". Any brief head-down orientation will result in the fabric collapsing around the kid's head as the air rushes up to his feet. Correcting this requires forcefully turning the kid around to keep his head up. This is one (of many) reasons why commercial divers in dry suits use solid helmets. It isn't an issue for wetsuits. I'd rather slap a full helmet on the kid and tie him up into a bundle. It won't be pretty but does solve the buoyancy issues. I'm sure they are also considering drugging the kids to reduce the risk of panic attacks. Here is the nasa device, the personal rescue enclosure: http://www.astronautix.com/r/rescueball.html http://www.astronautix.com/r/rescueball.html (It wouldn't work. Wrong shape and no buoyancy control.)

richev 8y ago
Of the difficulties the pod solution poses, I don't think that neutral buoyancy us one of them, so long as the pod is rigid (e.g. steel) in construction. The best succinct definition for neutral buoyancy I could find was this one, from Wikipedia: > ...a condition in which a physical body's average density is equal to the density of the fluid in which it is immersed.[0] This means that once the pod has been weighted to be neutrally buoyant it will be so at any depth of water, since neither it or water are compressible[1] and thus their average densities are unchanged by depth. The challenges of maintaining neutral buoyancy arise when you submerge a compressible object, such as a scuba diver wearing an inflatable buoyancy control device (BCD). The water pressure (caused by the weight of the water above) will squeeze them and their equipment, compressing anything that is air filled. To sink from the surface, the diver has to deflate their BCD, and then put sufficient air in it to achieve neutral buoyancy at their desired depth. If they swim downwards, the higher water pressure will squeeze them some more, the air in their BCD will compress some more, and their average density will increase. They will now be negatively buoyant and will sink. The deeper they sink, the higher the water pressure will be, the more the air in their BCD will compress and the more negatively buoyant they will become. So they'll sink faster and faster. This happened to me once when I was first learning to scuba dive. It can be scary. The opposite applies to ascending. This is why good buoyancy control is such an important (and difficult) thing for scuba divers to learn.[2] From a buoyancy perspective, a metal pod is more like a camera in an underwater housing. These are rigid in construction (usually either plastic or metal) and their buoyancy characteristics don't change with depth. [0] https://en.wikipedia.org/wiki/Neutral_buoyancy https://en.wikipedia.org/wiki/Neutral_buoyancy [1] Not strictly true for water, but true enough for scuba diving depths [2] https://www.padi.com/courses/peak-performance-buoyancy https://www.padi.com/courses/peak-performance-buoyancy
- nradov 8y ago
  None of this is relevant because the cave contains a restriction so tight that a rigid pod wouldn't fit through. The last thing they want is a solid object wedged into the restriction. The SpaceX design is apparently flexible to fit through the cave, so some buoyancy adjustments would be necessary.

jdietrich 8y ago

1) Maintaining trim requires a significant degree of skill. A badly trimmed diver can't purposefully swim and is very difficult to tow. It's potentially safer and easier to bundle someone up as a package and manage their trim externally. https://en.wikipedia.org/wiki/Diver_trim https://en.wikipedia.org/wiki/Diver_trim 2) Scuba gear presents a considerable entanglement hazard in a confined space. There are a lot of hoses and protrusions that could get snagged on a rock feature, a guide line or another diver's gear. There's nothing stopping you from using a face mask and some kind of protective vessel to make the kids easier to drag through a cave. That vessel doesn't need to be pressurised to be useful. 3) A panicked diver can be absolutely terrifying. They do wild, irrational and often violent things. Many divers have died or killed a dive partner because of panic, even in quite benign open water conditions. A totally inexperienced diver in a difficult cave system poses a tremendous risk. Brutal as it might seem, a panicked diver doesn't pose a hazard if they're immobilised. https://www.youtube.com/watch?v=dnWKS5DzKRU https://www.youtube.com/watch?v=dnWKS5DzKRU https://www.youtube.com/watch?v=SF3dQDgynT4 https://www.youtube.com/watch?v=SF3dQDgynT4