Then we are both correct. You were talking about PSIA (absolute) and I
was talking PSIG (Gage or relative to atmospheric).

In the context of this thread however, I made the more correct
application of the terminology.

Paul wrote:

My point had nothing to do with differential pressure. I don't care if
someone can breathe with the difference in pressure at 40" depth. I honestly
don't.

I was simply pointing out that this statement:


One atmosphere of pressure (14.7 psi) is 33 feet of seawater


was incorrect.

That's all. Nothing more. Really.


"Glenn Ashmore" wrote in message
news:j4Dpb.880$62.544@lakeread04...

You guys don't seem to concieve the problem. We are NOT talking
absolute pressure here. Nitrogen absorption is not an issue. The
DIFFERENTIAL pressure is what we need to look at. The other end of the
hose is at one atmosphere not a vacuum and the lungs are at some higher
pressure. The lungs have to overcome the difference in pressure and
they will not be able to do so below about 40" of depth.

Debbie Griggs wrote:

I'm sorry but that's not correct. At least according to when I was

taught

dive physics. One atmosphere of pressure is every 33 feet of sea water.

At

sea level, above the surface of the water you are at one atmosphere of
pressure. Zero atmospheres of pressure would be a vacum. As you descend

in

salt water (it's slightly different in fresh water but not by much) to a
depth of 33 feet you're at two atmospheres of pressure, 66 feet equals 3
atmospheres, 99 feet 4 atmospheres etc.... 1.5 atmospheres of pressure

is

16.5 feet of sea water.


Jerry




"Glenn Ashmore" wrote in message
news:F5Cpb.875$62.52@lakeread04...


One atmosphere of pressure (14.7 psi) is 33 feet of seawater. THe .445
is correct but your math is wrong. 1.5 atmospheres would be about 50
feet. Regardless, the normal pressure differential that our lungs
produce is about 12 millibar or .17 psi. A person in very good health
can inhale at a maximum pressure differential of about 100 milibars or
1.45 psi. That is about 39 inches of seawater.

Just to verify the figures I went out to the boat shed, cranked up the
vacuum system and tried to breathe from the vacuum tube. I couldn't get
any air after 1.3 psi but I have probably inhaled more than my share of
Cabosil.



Rick wrote:



Jim Richardson wrote:




2) The pressure at say, 7 feet depth, is about 1.5 atmospheres,


The pressure at say, 7 feet depth, (in seawater) is about 3 psig. It
would take another 9 feet to reach 1.5 ats.

Seawater pressure increases at around .445 psig per foot.

Rick


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com





--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com