Recent content by boulderjohn

  1. boulderjohn

    Diving with gradient factors for a new recreational diver

    PFOs are congenital. Everyone has one in utero, and they are supposed to heal after birth. They occur in about 25% of the population, and no one knows they have one until tested for it. The test is expensive and often not covered by insurance, so even divers who suspect they might have one often...
  2. boulderjohn

    Diving with gradient factors for a new recreational diver

    It depends upon which of the many studies done over more than a century you are talking about. Haldane used goats. I am not aware of the prevalence of PFOs in goats. I am sure the early navy studies used fit sailors, but I don't know the composition of the studies done by Buhlmann, DSAT, DCIEM...
  3. boulderjohn

    CONCEPTION AFTERMATH - COAST GUARD ISSUES NEW RULES/REGULATIONS

    No, it would not have helped in that specific situation, but it would have helped in a different situation. As it was designed, the exit hatch over the top of the third bunk would not have been a viable escape under any situation. It would have taken too long for any person to get out while...
  4. boulderjohn

    Diving with gradient factors for a new recreational diver

    I agree with Dr. Mike above. The algorithms were created based on observations of divers doing dives. They did not filter out people with PFOs, so we have to assume that the percentage of test divers with PFOs was the same as the general population.
  5. boulderjohn

    CONCEPTION AFTERMATH - COAST GUARD ISSUES NEW RULES/REGULATIONS

    Let's look at the cost factor related to the Conception. The boat had a good sized load of passengers, but it was not nearly 100% full. How often was it 100% full? I suspect not often. If the bunks blocking the escape hatch had been removed, it would have cost them a couple of paying customers...
  6. boulderjohn

    Diving with gradient factors for a new recreational diver

    Yes, I believe standard training makes people too much afraid of violating NDLs, to the point that people who suddenly realize they are near NDL will risk an arterial gas embolism by sprinting to the surface to avoid violating NDLs. (Yes, I have seen it.)
  7. boulderjohn

    Diving with gradient factors for a new recreational diver

    Would it shock you to learn that the overwhelming majority of people who die in Germany are German citizens? That must mean it is for some reason not safe to be a German citizen, right? Should Germans renounce their citizenship in the hope of living longer? Almost everyone who does recreational...
  8. boulderjohn

    Tom Mount

    A true legend in the world of diving, one of the true pioneers in scuba, has passed. https://en.wikipedia.org/wiki/Tom_Mount
  9. boulderjohn

    Diving with gradient factors for a new recreational diver

    You are probably right. It's a good example of a phenomenon that occurs in almost all activities--a practice that made sense originally carries on even though changing circumstances mean it no longer makes sense.
  10. boulderjohn

    Diving with gradient factors for a new recreational diver

    Correct. Years ago someone got the idea of diving nitrox on an air setting, and the idea has taken on a life of its own. It's as if you only have two choices--air or nitrox. Why not dive nitrox 32 but use a nitrox 24 setting? O any other combination? Don't lie to your computer. If you are...
  11. boulderjohn

    Question Why own an aluminum tank?

    As Tom said above, the buoyancy swing during a dive is 100% determined by the loss of the weight of the gas you consumed. The composition of the tank is not a factor. This is a very common misunderstanding in scuba. The evidence people cite is the fact that an aluminum tank goes from negatively...
  12. boulderjohn

    Diving with gradient factors for a new recreational diver

    Your fastest tissues will be off-gassing, but slower tissues will be on-gassing. Your slowest tissues will continue to on-gas throughout the dive, even during a safety stop. At that point, though, they can only on-gas to the pressure at that depth, and it has been shown that those levels are...
  13. boulderjohn

    Diving with gradient factors for a new recreational diver

    I researched and published an article on deep stops for decompression dives. I had a lot of help from renowned decompression expert Dr. Simon MItchell. When I was done, I wanted to write an article on deep stops for recreational dives, but Dr. Mitchell would not help me with it. He said there is...
  14. boulderjohn

    Question What's your safety stop depth?

    Of course. When the safety stop is over, the ascent to the surface should be nice and slow. As I said earlier, that last 10 feet has a significant drop in ambient pressure.
  15. boulderjohn

    Question What's your safety stop depth?

    The real issue is on what dives should you do a safety stop, and on what dives can you skip it. The practice nowadays is to do a safety stop on all dives, but newer computer technology may play a role in that. When I do an NDL dive with my Shearwater computers, I leave them in tech mode, and I...
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