Hacker News Reader

Comment by blhack | Hacker News Reader

My dive-master friend has told me that the bends isn't an issue if you're holding your breath. The bends is a result of the air mixture that you're breathing with a SCUBA.

This is why freedivers can dive down to 100meters, and then come back up quickly without dieing.

View on HN

This is not true. DCS has been found in cases of free-divers who perform repeated deep dives. The primary gas that causes DCS is nitrogen, which exists in large quantities in the air you are breathing now. The reason you don't often see DCS in free divers is that it takes time for the high-pressure nitrogen to dissolve in the blood and enter tissue.

On the other hand, think about it. With a SCUBA tank, you are taking many breaths under high pressure. With a single free-dive, you only take one breath. With many free-dives, you take many breaths. Is it surprising that repeated deep free-dives cause DCS?

So, it's not a problem if you dive once and go home. But it is a problem if you dive again, and again, and again.

Makes sense.

Depends on how deep you dive and the time you spend down there. for instance, people that attempt world records in freediving might need some decompression time after the dive.

My dad was a doctor on a small island, for a year. The islanders dived for sponges and pearls. They couldn't afford a decompression chamber, so if someone got DCS (after freediving too long) they dropped them off the side of the jetty with an old diving helmet, and a friend to keep them company, and pumped air down to them as they gradually re-ascended. Apparently it worked OK.

I've also read when free-divers are down in such high pressure the plasma of their blood is squeezed out and fills their sinuses. In a way it helps protect them since the large open areas are now filled with fluid.

Reply on news.ycombinator.com