How Deep Can Humans Go?

Original Article ↗ Hacker News Discussion ↗

Human depth limits are explored through freediving and scuba examples, focusing on how pressure, gas mixtures, and physiology constrain how far and how long people can safely go underwater. Commenters explain decompression sickness, nitrogen narcosis, shallow-water blackout, and why practices like hyperventilation or mixing freediving with recent scuba dives are dangerous, while also touching on experimental ideas such as hydrogen-based breathing gases and liquid ventilation. Alongside technical details, they note that marine mammals have evolved only partial protection from these effects and that extreme dives push close to the boundaries of what the human body can tolerate.

Theoretical human limits & performance enhancement

  • Thread connects freediving limits with other “human limit” analyses (e.g., sprinting), noting that elite performance is now very close to biomechanical models.
  • Some wonder if knowing theoretical limits will make records feel routine, or if future records will surpass current models, exposing them as crude.
  • Discussion of “Enhanced Games” (drug-permitted events): expectation of better results than clean sports, but still bounded by biomechanics.
  • Mention of surgical tendon reattachment and gene doping (e.g., myostatin) as more radical, but still not breaking hard physical constraints.

Freediving vs. SCUBA & decompression sickness

  • Clarification: freedivers generally avoid breathing compressed gas at depth, which is why DCS (“the bends”) is mostly a SCUBA problem.
  • However, extreme single dives or repeated freedives can cause DCS due to nitrogen dissolved from the single breath at high pressure; one famous deep dive is cited as an example.
  • Serious warnings about:
    • Freediving/snorkeling soon after SCUBA.
    • Flying shortly after diving due to cabin pressure being below 1 atm.
  • Explanations reference partial pressures, tissue saturation, and standard dive tables/computers.

Gas mixes, extreme depths & liquid breathing

  • Deep SCUBA uses mixes with reduced oxygen and nitrogen, adding helium; each gas has its own toxicity or neurological limits (oxygen toxicity, narcosis, HPNS).
  • Hydrogen-based mixes are experimentally used but seen as operationally risky.
  • Liquid breathing with perfluorocarbons has been tested medically and in animals; for diving or high‑G spaceflight it is seen as impractical or highly constrained.

Shallow-water blackout & pool safety

  • Shallow-water blackout is highlighted as a real risk from breath-hold swimming, especially when preceded by hyperventilation.
  • Some pools now ban prolonged underwater breath-holding; lifeguard and liability concerns are emphasized.
  • There is debate over whether such rules are overcautious vs. reasonable given documented deaths and difficulty distinguishing blackout from normal underwater behavior.

Freediving practice & sensations

  • Experienced freedivers stress that intentional hyperventilation is unsafe and not standard practice; training focuses on tolerating high CO₂ and using its discomfort as a timing cue.
  • Subjective reports:
    • Down to ~20–30 m feels relatively normal if you start fully inhaled.
    • Deeper dives feel like a progressive chest “squeeze.”
    • Nitrogen narcosis and shallow-water blackout can feel pleasant or disinhibiting, which increases danger.

Miscellaneous

  • Questions about how marine mammals handle nitrogen; linked material suggests they have adaptations but may still experience some DCS.
  • Multiple recommendations for books, long‑form articles, and films about freediving for further context and storytelling.