Mailing List Archive Mailing List Archive
uunet!joyce.cs.su.OZ.AU!gregr (Greg Ryan) writes:
>
>There was some discussion in this list about O2 decompression in-water.
>I recently got a copy of the DCIEM Diving Manual which included an in-water
>O2 decompression table (Table 2).
>
>I was surprised to find that their O2 deco procedures were based on using O2
>at 9m (30ft) only. The table gives air stop up to 9m, at which stage you go
>on to O2 and remain there for the full O2 deco schedule. Five minute air
>breaks (not counted as deco) can be taken each 30 minutes.
>
>Admittedly the DCIEM procedures only recommend this if the diver is
>accompanied (two people on O2 is acceptable) and a chamber is within an hour's
>travelling time. The manual claims that this depth (9m) is conservative but
>"the possibility of O2 toxicity problems still exist".
>
>The table reduces deco time by 35 to 40% of the times given in their
>standard air table (Table 1).
>
>As I said, I was surprised at this use of O2 at a PPO2 of 2 ATA, especially
>an agency like IAND has backed away to a very conservative maximum PPO2 of
>1.4 ATA for nitrox dives, and only advise O2 stops at 6 and 3m.
>
>Does anyone out there use the DCIEM In-Water O2 table, or is this an area
>where DCIEM just hasn't caught up with the conservative trends in some
>other areas of the "technical" (I hate that term!) diving community?
>
> Greg Ryan gregr@cs*.su*.oz*.au*
DCIEM has updated their manual since this came out. As I understand it,
they decided to just advise taking the air stop at 30 feet (9m) without
calculating the decompression credit, and then do the full time for the
30 foot inwater 02 stop at 20 feet (6m), rather than recalculate the model
and give credit for the 30 foot air stop.
This pretty much allows you to use table 2, though table 2S is now rather
harder to use.
The rationale was that this procedure could still be considered validated
by the existing, large database of test dives. For table 2 dives the extra
couple of minutes is negligible. However, for table 2S dives I would like
to see a new schedule devised, something like the table 1S. This might
be something like:
Up to 60 feet: No Stop
5 mins 02 at 20 feet
10 mins 02 at 20 feet
15 mins 02 at 20 feet
20 mins 02 at 20 feet
Over 60 feet: No Stop
5 mins 02 at 20 feet
10 mins 02 at 20 feet
5 mins air at 30 feet + 15 mins 02 at 20 feet
5 mins air at 30 feet + 20 mins 02 at 20 feet
I have not yet received my updates - apparently there is some problem (still!)
with the update package, although if you buy a new copy you get the revisions.
I use DCIEM air tables, for now just 1S. Over the course of this years diving
I plan on exploring most of the deeper edges of 1S, then move up to diving
doubles and on to table 1. When I dive 1S in groups planned on other tables
as no-stop dives, I tend to wind up with a 5 minute stop. So in reality
DCIEM tables in this area come out about the same as USN or PADI as used in
practice - the divemaster calls it a "no decompression" with a five minute
"safety stop", I and DCIEM call a stop a stop. The DCIEM manual explicitly
says that the tables are designed to be used as printed, not with extra little
rules of thumb (add a safety stop, add a group, etc.)
Safe diving.
Wrolf
Wrolf Courtney First Boston Corporation My employer thinks
(212) 322-7017 Park Avenue Plaza I'm crazy.
uunet!csfb1!wrolf New York, NY 10055
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]