On Tue, 26 May 1998 14:34:12 -0400, Paltz, Art wrote:

>		With all this talk about body recoveries and emergency
>ascents to save people I think it brings up some good questions about
>what to do.  I feel I've been lucky in that with the exception of
>entanglement I've never been in situation where by buddy was in trouble.
>My question has to do with the situation where you're in the middle of
>your dive and have already accumulated a deco obligation and must make
>an ascent to save your buddy.
>
>		1). Realistically, how much time can you spend on the
>surface?  I know this is probably subjective and based upon time/depth
>but I've heard that about 5 minutes is a good "rule of thumb".

	This (interrupted deco) is an issue of much contention (and
unrationalized fear) among many divers, but is something that may be 
practiced safely.  Commercial operations often bring their guys up and 
slam them in a chamber to decompress, from extreme or even saturated 
profiles without the use of a bell or transfer capsule. (extreme time, 
not depth). Typically, these companies allow a window of five to eight 
minutes for the transfer, but if they blow it it's not as big a deal 
because they can treat the diver(s) on a table 6 on site.  Technical
divers generally do not have that option, but can still employ this 
practice safely by minimizing the time spent at the surface.  Trying 
to define a safe maximum time limit for a deco interruption is a bit 
of a moot point.  Common sense dictates that if you have to do it, as 
in an emergency, then you do it but you do it as quickly as is 
practicable.  IMPORTANT:  Statistically, rapid ascent from a deco 
interruption causes (or more appropriately, significantly increases 
the likelihood of) a type II hit, much more so than the effect of a 
little extra time spent at the surface during an interruption.  Upon 
making the decision to interrupt deco for the purpose of dealing with a
medical emergency, communicating with surface support, equipment transfer 
or other emergency task, the risk/benefit ratio of speed of ascent 
versus importance of task must be considered.  If you are able to 
perform a slow ascent from the depth of interruption - do it.  Just be 
aware of the extra time spent on ascent, and don't waste time 
lolligagging about on the surface.  Obviously, divers who are out of gas 
do not have this option.  Bends you can live through - drowning you do 
not.


>		2). After you've surfaced with the diver and
>communicated all the information necessary to the surface support people
>where do you resume you deco?  Example would be, say your dive profile
>called for a bottom time of 40 minutes @ 130 and you were doing the dive
>on air, trying to keep things simple here.  According to Decom you're
>decompression schedule would be 5 min @ 40, 8 min @ 30, 17 min @ 20 and
>27 min @ 10.  How would you modify the schedule to handle the "pop to
>the surface"?

	It is important here to make the distinction between interrupted 
deco and ommitted deco.  I have only had to blow deco once, so I can't 
speak statistically on this (perhaps someone with more experience can 
step up to the plate on this one) but it seems reasonable to me that, 
provided the diver exhibits no signs or symptoms of DCS (either type), no 
other injuries or afflictions and has not been at the surface for an 
excessive amount of time, there should be no problem with returning to 
the dive profile at the exact point of interruption and continuing the 
deco schedule as originally planned, or with extension of the stop 
durations for conservatism.  For those of that attended the Undersea & 
Hyperbaric Medical Society workshop and symposium on in-water 
recompression last Sunday, my thoughts differ from Rich Pyle's at this
point, in that without exhibiting any clinical signs or symptoms of DCS 
or other injuries, if the time at surface is excessive (and this is IMO 
completely arbitrary and not derivable by algorithm pending further 
research into the subject.  Divers and researchers with more experience
and insight into this subject may wish to comment) and the diver is 
worried about potential problems to the point where modifications to the 
profile including depth spikes, gas changes or deco stop depth changes 
are warranted, this ceases IMO to be an interrupted deco and becomes an
ommitted deco scenario, possibly warranting IWR despite the absence of 
clinical indications.

>		Using the above example, what if you had been down for
>only 30 minutes, what about the full 40 minutes??

	My thoughts are addressed above, and summarized below:

	INTERRUPTED DECO
	Return to deco schedule as originally planned or with just
	extension of stop durations.

	- No signs or symptoms of DCS (either type)
	- No signs or symptoms of any other injury or affliction
	- Time at surface (including slow ascent from interruption
	  depth) not excessive, dependent upon dive profile, diver 
	  comfort level, and 5-8 minute window of commercial operators.
	- sufficient gas remaining
	- surface support MUST be aware of your intentions

	OMMITTED DECO
	Treatment scenario, however diver is not necessarily injured
	(preventative).
	Options may include new deco schedule, IWR or chamber treatment.

	- Any sign or symptom of any injury, including DCS, AGE, etc.
	- Any history of traumatic experience 
	  (uncontrolled ascent, etc.)
	- Excessive time at surface	
	- Inability to resume a deco interruption (no modification) for
	  any reason


	This is just a point of semantics, but ommitted deco does not
necessarily mean that the diver is a casualty and needs a chamber ride.  
My thinking is (and you should credit my thinking as much as you would 
grafitti on a dumpster until you get some additional input) that any 
circumstance which requires a modification of the original deco schedule 
(with the exception of slightly lengthened stop times) is a deco omission, 
and hence a treatment scenario.  For preventative treatment this may be 
as simple as following an emergency bailout table or extending deco on O2.  
Reactive treatment measures for serious decompression omissions may 
include various in-water recompression regimes, chamber rides or surface 
oxygen.


>		I'm trying to make the question as generic as possible
>so others, including myself can apply it should we be caught in a bad
>situation.  Please no flames like I should be using mix, Nitrox 28% or
>pure O2 for deco.  I think the question is simple and straight forward
>that we can keep the ego's in check on this one.  Also, a reply that
>"I'd calculate it on the fly from experience" isn't really going to help
>anyone in this situation so keep the comment to yourself!  Maybe some
>good can IMMEDIATLY come out of the diving emergencies we've had
>lately...


	This comment is not intended to be a flame, but this is a
perfect example of why proper gas selection is critical in this type 
of diving.  Ideally, a diver should be able to interrupt deco, complete 
his surface task and resume his schedule regardless of dive profile, 
gas choice, etc.  The effect that gas selection has on this is the 
amount of time that may be spent at the surface before resuming deco, 
as a diver who has been decompressing on O2 for a while has a much 
better chance at avoiding a type II hit during an interruption or 
ommision than the same diver on a Nitrox mixture, especially when you 
consider the chance of circumstances arising which may delay or prevent 
altogether the resuming of an interruption.  I refer you to the previous 
(and infamous) "Baker's Dozen" post on deco gas selection on this forum.


>		Thanks,
>		Art.

	You're welcome.  I hope I have contributed something useful.

-Sean







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