Hyperbaric chamber treatment

I'm reading the ending of The Last Dive by Bernie Chowdhury, and it involves a diver being placed in a hyperbaric chamber at the equivalent of 60ft, then later 165ft. The diver had come up abruptly from 230ft. My question is, why wouldn't you start out by placing the diver in 230ft (or the lowest the chamber can go - in this case, the 165ft mentioned) instead of starting out at 60ft? Wouldn't you want the nitrogen bubbles in the blood stream to shrink as quickly as possible? Or is there some other physiological issue I'm not considering that makes this a bad plan? (Or maybe, is a hyperbaric chamber different at all from diving at that depth/pressure?)

My question is, why wouldn't you start out by placing the diver in 230ft (or the lowest the chamber can go - in this case, the 165ft mentioned) instead of starting out at 60ft?

It's a case of shrinking the bubbles to a size where they are not symptomatic/causing damage. You don't need to go to an extreme pressure to do that.

I can't answer with more detail, but would suggest you request move of this topic to either Diving Medicine or Dr Deco forums for a more in-depth answer if required.

Wouldn't you want the nitrogen bubbles in the blood stream to shrink as quickly as possible?

I don't believe that there would be a strong correlation between the absolute pressure reached and the speed of bubble shrinkage?

Getting to a chamber quickly, having an accurate, quick diagnosis and then prompt treatment is the main factor effecting this.

Or is there some other physiological issue I'm not considering that makes this a bad plan?


1. Provision of 100% O2 to the casualty.
2. Repetitive exposure to pressure by chamber medic.
3. Possible issues with the effects of other critical medication administered to the casualty.

..probably a bunch of other factors...

The most common treatment tables are for 165' (Arterial Gas Embolism) or 60' (DCS).

You do want to make the bubble smaller but you don't want to cause problems for the tender either. (including narcosis)

You also have to have the breathing (treatment) gasses available for the depths you will be treating at, Normally 100% O2 at 60' & 30' and 50% O2 at 165'.

Going past 165' for treatments becomes much more expensive in terms of the length of the treatment, the chamber hardware, compressors needed to get to the depth and the exposure to your tender with only a small return in the reduction of the bubble size.

The advantage of the 60' treatment tables are you can put them on pure oxygen sessions that removes diluent gas from the system very rapidly. Since you have compressed the gas in the body to a about a third you are sometimes better off being able to administer pure O2 at 2.8 ATA. There is a fairly involved decision tree based primarily on symptoms to determine which treatment table to start with.

If the doc or treatment supervisor judges that greater treatment depth is appropriate they will drop to 165'. Most hyperbaric treatment facilities are not equipped with treatment gases other than pure oxygen so they can’t give high PPO2 mixes nor are standard treatment tables available. The most common tables are 5 & 6. Tables 5A and 6A drop to 165', but there are several others including table 8 that drops to 225'.

Large sophisticated treatment or saturation facilities have the ability to blend any mix they want and run a full saturation decompression schedule supplemented with high PPO2 mixes, but here aren’t many around or the people to run them.