Mixing free diving with tank diving - The Hull Truth

bigtuna · 08-16-2007, 09:07 PM

Whats the general consensus on this?? We usually do 3 tanks on a dive trip. 140ft, 110ft, and 70 ft on three different dives. Do you guys think it is safe to do some freediving in between dives? Better to do it before or after the tank dives?? Any insite would be appreciated!

First Light · 08-16-2007, 09:50 PM

There is generally no problem with freediving before, between, or after tank dives as when free diving you are breathing ambient air, not compressed air.

WATERDOG91 · 08-16-2007, 11:23 PM

This is a big no no! As the body offgases nitrogen after a tank dive, there can occur small nitrogen bubbles on the venous side. The lungs do a great job of filtering out these bubbles (you can actually hear these bubbles with a doppler...I have heard them before testing divers after a dive). If you freedive after a tank dive, you could potentially compress these bubbles back into solution, have them pass the lungs and into the arterial flow, and when you ascend on the freedive have the bubbles come back out of solution, but be in the arteries this time headed to the brain and getting lodged in the blood vessels. Classic Type II hit. Also, you do load additional nitrogen as you freedive and with the nitrogen already in your bloodstream, coupled with the ascent it may make the nitrogen bubble out of solution. These type of hits are usually Type II DCS - Neurological Hits...nasty stuff. I would recommend doing any freediving first, and avoid it after any compressed gas diving. Too risky for me. Will you take a hit every time? Maybe not.... Do some people get away with this? Probably. Still a bad idea...Think about what you are risking. It is always better to err on the side of safety. You can always dive another day.

bigtuna · 08-17-2007, 11:33 AM

That is exactly the answer I was looking for waterdog! Thanks! Do you think it is ok to freedive before tank diving to say 30-40ft?? I could freedive a few hours then tank dive towards the end of the day???

catfoiler · 08-17-2007, 06:24 PM

Always consider time under compression. All of the dive tables are based upon the gradual build up of nitrogen. If you freedive deep for a couple of hours then it could be a problem tank diving at 40 feet for a hour. Again the risks vary with your age, water temperature, if you were drinking a lot the night before, if it is an easy dive or hard dive.
It is generally best to play safe with this. Excellent freedivers have gotten the bends. I am not that good

WATERDOG91 · 08-19-2007, 11:47 AM

Breath hold diving does hold a decompression risk and in-gassing from the breath holds can not be accurately tracked at this time. Any gas you take on during the "pre-dive" exposures would need to be taken into account on the subsequent dives. So as you can see there is no easy answer to your question. As catfoiler said, it could be a problem, but for a variety of reasons. If we could pin it down, then we could account for it on later dives. Personally, I just snorkel on the surface, and avoid any freediving. It just too unknown for my peace of mind.

Here is a sample search for breath hold diving and decompression. Some interesting articles.

http://archive.rubicon-foundation.or...sion&submit=Go

As a disclaimer, I am involved with the Rubicon Foundation, but we are a Non-Profit. No commercial interests.