Mailing List Archive

Mailing List: techdiver

Message Display

On Thu, 28 Jul 1994, David Story wrote:

> Actually, this is a little more complicated.  The rate of N2
> absorption is determined by the *ratio* of inspired PPN2 to dissolved
> PPN2.  That means that ongassing slows down as your dissolved PPN2
> level approaches that of the inspired gas, forming the traditional
> "exponential" curves.

Didn't I mention N2 concentration GRADIENT somewhere in that post?  If
not, it was only an oversight in the heat of a passionate flurry of
message composition....:-)  By "only depends on the PPN2", I meant that it
didn't directly depend on the ambient pressure, not that inspired PPN2 was
the ONLY factor affecting rates of Nitrogen uptake.  Bad wording on my
part. (I know, I know, I'm just bickering now...)

> >Decompression "Ceiling" DEPTHS are determined by the AMBIENT PRESSURE
required
> > to prevent excess nitrogen in the blood & tissues from coming out in the
> > form of bubbles, and thus are not affected by what the diver is breathing
> > - only by the amount of excess dissolved nitrogen. 
> 
> A simpler way to state this is to state it as a ratio: the model
> limits for Haldanean models (which includes Buehlmann models) are
> simply the supersaturation ratios for various compartments.  That
> means that you have a ratio, say 5:1, below which you will not form
> bubbles.
> 
> Put another way, if your dissolved nitrogen PPN2 is less than 5 ATM
> absolute (ATA), you can safely return to 1 ATA (the surface.)  If it
> is more than 5:1, you cannot safely surface: you can only ascend to a
> depth at which the ratio is 5:1 or less.
> 
> For example, if your dissolved PPN2 is 10 ATA, you can ascend to 2 ATA
> (10:2 == 5:1) without forming bubbles -- in theory, at least.
> 
> By doing some examples, you can see that your ceiling may vary.  If
> you then add one more complication -- multiple compartments, each with
> a different supersaturation ratio -- then you are pretty close to
> understanding the basics of Haldanean theory.

Was that really a SIMPLER explanation?  More accurate, yes. More
insightful, yes. More educational, yes.  But SIMPLER?  I kinda thought my
explanation was simpler (probably TOO simple) :-)

Many thanks for the additional input!

Aloha,

Rich

deepreef@bi*.bi*.ha*.or*

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]