Limits for decompression

[ddevane]

Hi there

I am working on a project and need serious advice on questions that I can't seem to find the answer to anywhere:

1. Breathing air at 5mtrs, is there a time limit? The dive tables and computer algorithms I have seen bottom out after about 300mins whereas I have heard that at this depth the safe time limit before decompression required is unlimited i.e. one could, assuming adequate hypothermia protection etc, stay at this depth safely for days/weeks.

2. What difference would breathing air at 10 mtrs nake to the above?

3. If doing a prolonged dive at shallow depth (5 mtrs or so) is there a benefit of using nitrox?

4. Would people recomend going to 100% O2 for last hour or so after a prolonged dive at 5mtrs?

Thanks a lot for your help

Declan

 

[Gene_Hobbs]

You might find these helpful!

Van Liew, HD; Flynn, ET. Direct ascent from air and N2-O2 saturation dives in humans: DCS risk and evidence of a threshold. Undersea Hyperb Med. 2005 Nov-Dec;32(6):409-19. RRR ID: 4058

Hamilton Jr, RW; Thalmann, ED; Temple, DJ. 2002. Multi-Day Air Saturation at 20 and 22 FSW With Direct Ascent: Data Report on Project 92-09. Naval Medical Research Center Technical Report NMRC-02-01. RRR ID: 4585

Eckenhoff, RG; Osborne, SF; Parker, JW; Bondi, KR. Direct ascent from shallow air saturation exposures. Undersea Biomed Res. 1986 Sep;13(3):305-16. RRR ID: 3049

As for the O2 breathing, the intro to this paper gives a nice overview of the work that has been done:

Blogg, SL; Gennser, M; Loveman, GAM; Seddon, FM; Thacker, JC; White, MG. The effect of breathing hyperoxic gas during simulated submarine escape on venous gas emboli and decompression illness. Undersea Hyperb Med. 2003 Fall; 30(3):163-74. RRR ID: 3969

These should get you started, let us know if you need more... Good luck!

 

[Dr Deco]

Hello:

1. Breathing air at 5mtrs, is there a time limit? The dive tables and computer algorithms I have seen bottom out after about 300mins whereas I have heard that at this depth the safe time limit before decompression required is unlimited i.e. one could, assuming adequate hypothermia protection etc, stay at this depth safely for days/weeks.

Yes, you could basically stay there with little DCS worry. Some divers would probably form some Doppler-detectable bubbles.


2. What difference would breathing air at 10 mtrs make to the above?

Ten meters definitely would have limits and could be a problem for some people after more than a day at pressure.


3. If doing a prolonged dive at shallow depth (5 mtrs or so) is there a benefit of using nitrox?

There is not really a benefit that could be demonstrated with respect to DCS.


4. Would people recommend going to 100% O2 for last hour or so after a prolonged dive at 5 mtrs?

Oxygen is not necessary unless you are near the limit - and you are not. :cool2:

 

[ddevane]

Hi Gene-Hobbs and Dr Deco

Thanks Gene for the cittaions and for the PDF links.

Thaks Dr. Deco for th eexplicit advice.

I feel much more informed now and this is thnak to you both.

Declan