4 ms·

The bends are caused by accumulated nitrogen dissolving in tissue\blood. No breathing, means no added nitrogen, so no build up. Also it is a somewhat slow pro

The bends are caused by accumulated nitrogen dissolving in tissue\blood. No breathing, means no added nitrogen, so no build up. Also it is a somewhat slow process, no breathing means they aren't under long enough for it to develop even if they had extra nitrogen. It is a problem caused by Scuba, and the fact that Scuba does what it is supposed to, extend the time you can spend underwater, is what causes the bends.

itishappy 2y ago
> It is a problem caused by Scuba, and the fact that Scuba does what it is supposed to, extend the time you can spend underwater, is what causes the bends. To expand on this a bit (pun intended), freediving after SCUBA is extremely dangerous, and this even includes shallow stuff like snorkeling. SCUBA adds dissolved gas to your blood, but once it's there decompression from any source puts you at risk for the bends. Repeated dives will have additional safety limits imposed due to the residual gas, which is managed by a complicated series of dive tables or a modern dive computer. https://www.naui.org/resources/dive-tables-review/ https://www.naui.org/resources/dive-tables-review/
- Ostrogoth 2y ago
  To further expound on why snorkeling and freediving after scuba can be dangerous, it is helpful to understand that the greatest gas compression occurs in the first 10 meters underwater (Boyle’s law). Scuba divers are trained to ascend slowly (~10m/minute) in order to off-gas expanding nitrogen (and other gasses) and prevent bubbles from forming in tissue (which causes decompression illness). After scuba diving the human body still has a much higher residual nitrogen saturation, so even fairly shallow (less than 10m) rapid descents/ascents in the water column can cause bubbles to form.
- knodi123 2y ago
  I was told that I shouldn't go scuba diving the day before an early-morning flight, because if the plane decompresses, I could get the bends while everyone else just gets a little hypoxic and uses their handy drop-down O2 supply.
  - Ostrogoth 2y ago
    There is also an increased risk of decompression illness simply because passenger aircraft typically maintain a lower atmospheric cabin pressure (US federal limits pressure equivalent to 8,000 ft elevation). Going from a high pressure environment (underwater) to a low pressure environment (8,000 ft equivalent elevation in aircraft cabin) too quickly can also cause the bends. Dive computers use algorithms to calculate when it is safe to fly post-dive.
    - Dylan16807 2y ago
      I'm really surprised by that. Looking at some charts, depending on the dive you're probably spending 30 minutes or less going from 2atm to 1atm, but now you need several hours or even a day before it's safe to go to .75atm.
      - itishappy 2y ago
        We'd spend more time, but it's difficult to loiter 10m underwater. The residual gas from a dive takes about a day to release, and this impacts both follow-up dives and flights. Treatment options are different as well: an airlift (or just diving again and surfacing slower) vs diverting a whole flight.
      - Ostrogoth 2y ago
        There are wide safety margins in diving. Most dive trips involve multiple dives per day (starting with deepest dive first, with subsequent dives shallower). The times I’ve gone deeper or same depth on subsequent dives my computer usually puts me into deco fairly quickly. At some point subsequent dives aren’t feasible (typically no more than 4-5/day, less is prudent). I think it is with this in mind that the recommendation against flying is made, along with an abundance of caution due to limited experimental evidence (Navy dive tables were developed based on human subjects, so the effects are better understood). It looks like there are some civilian studies done, but more is needed on flying. https://dan.org/health-medicine/health-resources/diseases-conditions/flying-after-diving/ https://dan.org/health-medicine/health-resources/diseases-co...
  - 2y ago
- dexen 2y ago
  To further expand upon this, quickly ascending to high altitude (flying airplane or balloon) after diving is also dangerous, for the very same reason. Pilots are trained to wait out at least 24 hours after a dive, or at least 12 hours if the dive didn't require decompression steps.
throwway_278314 2y ago
Not quite. They do have the nitrogen in the air they brought down with them in their lungs. Repeated freediving can cause the bends. https://www.tdisdi.com/pfi-diver-news/freediving-and-dcs/ https://www.tdisdi.com/pfi-diver-news/freediving-and-dcs/ has some tables for freediving surface intervals
scirpaceus 2y ago
In the case of Herbert Nitsch's accident, he went so deep that even the short bottom time was sufficient to cause DCS on the ascent with just the standard air he was carrying. N2 diffusion is a function of both time spent at depth and the partial pressure of N2 from depth itself, and in his case, time was short but depth was extraordinary. In hindsight, his attempt would have qualified for a deco stop, had he had the lung capacity to do one on the way up.
- ethbr1 2y ago
  Indeed, if you're doing extreme free diving, it would make more sense to breathe a more depth-compatible (nitrogen-replaced) mix at the surface before diving, no? Then your lungs (and blood) would be full of a safer gas mix at depth. I'm not sure if any of the deeper gas mixes are safe to breathe at surface level though? I think so?
  - nradov 2y ago
    Yes, some "technical" freedivers do pre-breathe nitrox or pure oxygen at the surface before descending. https://www.deeperblue.com/technical-freediving-are-breathhold-divers-ready-to-mix-it-up/ https://www.deeperblue.com/technical-freediving-are-breathho...

itishappy 2y ago

> It is a problem caused by Scuba, and the fact that Scuba does what it is supposed to, extend the time you can spend underwater, is what causes the bends. To expand on this a bit (pun intended), freediving after SCUBA is extremely dangerous, and this even includes shallow stuff like snorkeling. SCUBA adds dissolved gas to your blood, but once it's there decompression from any source puts you at risk for the bends. Repeated dives will have additional safety limits imposed due to the residual gas, which is managed by a complicated series of dive tables or a modern dive computer. https://www.naui.org/resources/dive-tables-review/ https://www.naui.org/resources/dive-tables-review/

Ostrogoth 2y ago
To further expound on why snorkeling and freediving after scuba can be dangerous, it is helpful to understand that the greatest gas compression occurs in the first 10 meters underwater (Boyle’s law). Scuba divers are trained to ascend slowly (~10m/minute) in order to off-gas expanding nitrogen (and other gasses) and prevent bubbles from forming in tissue (which causes decompression illness). After scuba diving the human body still has a much higher residual nitrogen saturation, so even fairly shallow (less than 10m) rapid descents/ascents in the water column can cause bubbles to form.
knodi123 2y ago
I was told that I shouldn't go scuba diving the day before an early-morning flight, because if the plane decompresses, I could get the bends while everyone else just gets a little hypoxic and uses their handy drop-down O2 supply.
- Ostrogoth 2y ago
  There is also an increased risk of decompression illness simply because passenger aircraft typically maintain a lower atmospheric cabin pressure (US federal limits pressure equivalent to 8,000 ft elevation). Going from a high pressure environment (underwater) to a low pressure environment (8,000 ft equivalent elevation in aircraft cabin) too quickly can also cause the bends. Dive computers use algorithms to calculate when it is safe to fly post-dive.
  - Dylan16807 2y ago
    I'm really surprised by that. Looking at some charts, depending on the dive you're probably spending 30 minutes or less going from 2atm to 1atm, but now you need several hours or even a day before it's safe to go to .75atm.
    - itishappy 2y ago
      We'd spend more time, but it's difficult to loiter 10m underwater. The residual gas from a dive takes about a day to release, and this impacts both follow-up dives and flights. Treatment options are different as well: an airlift (or just diving again and surfacing slower) vs diverting a whole flight.
    - Ostrogoth 2y ago
      There are wide safety margins in diving. Most dive trips involve multiple dives per day (starting with deepest dive first, with subsequent dives shallower). The times I’ve gone deeper or same depth on subsequent dives my computer usually puts me into deco fairly quickly. At some point subsequent dives aren’t feasible (typically no more than 4-5/day, less is prudent). I think it is with this in mind that the recommendation against flying is made, along with an abundance of caution due to limited experimental evidence (Navy dive tables were developed based on human subjects, so the effects are better understood). It looks like there are some civilian studies done, but more is needed on flying. https://dan.org/health-medicine/health-resources/diseases-conditions/flying-after-diving/ https://dan.org/health-medicine/health-resources/diseases-co...
- 2y ago
dexen 2y ago
To further expand upon this, quickly ascending to high altitude (flying airplane or balloon) after diving is also dangerous, for the very same reason. Pilots are trained to wait out at least 24 hours after a dive, or at least 12 hours if the dive didn't require decompression steps.

throwway_278314 2y ago

Not quite. They do have the nitrogen in the air they brought down with them in their lungs. Repeated freediving can cause the bends. https://www.tdisdi.com/pfi-diver-news/freediving-and-dcs/ https://www.tdisdi.com/pfi-diver-news/freediving-and-dcs/ has some tables for freediving surface intervals

scirpaceus 2y ago

In the case of Herbert Nitsch's accident, he went so deep that even the short bottom time was sufficient to cause DCS on the ascent with just the standard air he was carrying. N2 diffusion is a function of both time spent at depth and the partial pressure of N2 from depth itself, and in his case, time was short but depth was extraordinary. In hindsight, his attempt would have qualified for a deco stop, had he had the lung capacity to do one on the way up.

ethbr1 2y ago
Indeed, if you're doing extreme free diving, it would make more sense to breathe a more depth-compatible (nitrogen-replaced) mix at the surface before diving, no? Then your lungs (and blood) would be full of a safer gas mix at depth. I'm not sure if any of the deeper gas mixes are safe to breathe at surface level though? I think so?
- nradov 2y ago
  Yes, some "technical" freedivers do pre-breathe nitrox or pure oxygen at the surface before descending. https://www.deeperblue.com/technical-freediving-are-breathhold-divers-ready-to-mix-it-up/ https://www.deeperblue.com/technical-freediving-are-breathho...