As I said, I do it in my Vanagon all the time and, last I checked, I'm
not dead. Anyone who will travel, sleep, or play bingo in a sealed
container is just a contaminant in the gene pool.

Rick wrote:
Hey it sounds like we got a volunteer.

I personally know of 2 deaths due to folks breathing N2. Thats pure N2.

And what, pray tell, were these geniuses doing breathing pure N2? I
personally know of 4 individuals who died breathing N2O. They
were...uhm...what was that word? Stupid. Pressurized gas, sealed
environment, stupid. You'll note that in none of the scenarios
presented was anyone exposed to any prolonged exposure to "pure N2". Do
the math, it's not rocket science.

Please, feel free to demonstrate how any reasonable amount of CO2 or N2
can sublime or evaporate into an average size boat, **in the typical
amount of time required**, to result in a dangerous environment. Note
we are *not* talking about something like CO, which preferentially binds
with hemoglobin relative to O2, and thus presents a very real hazard.

Keith Hughes

Chris writes:

For water, the heat of fusion is about 80 times specific heat...

So -70 C ice would have almost twice the cooling effect
as the same amount of barely frozen ice, right?

No, because heat load is proportional to temperature differential.

Now if you put that supercooled ice into watery payload that freezes, then
the supercooling heat sink will convert to new ice in the payload, and a
different process is involved that is more "efficient". However, this is
no better than just freezing your food to start with.

Hardly anybody appreciates that temperature and heat are two different
things.

Keith Hughes writes:

When you do the math, it just isn't a problem when using any reasonable
amounts, and with only normal ventilation (which should *always* be
ensured under *any* use conditions).

Quite so.

A restaurant soda fountain typically has multiple 20 lb CO2 tanks sitting
around. If these were to leak out rapidly from a burst hose, which happens
frequently, there is no hazard to personnel.

A 20 lb CO2 fire extinguisher discharged indoors does not present an
asphyxiation hazard.

On Sun, 02 Jul 2006 08:31:58 -0400, Jeff wrote:

Chris wrote:
For water, the heat of fusion is about 80 times specific heat...
So -70 C ice would have almost twice the cooling effect
as the same amount of barely frozen ice, right?

Wrong. You should look up the Heat Capacity of cold ice. Its only
0.5 BTU/lb-degree at freezing, but it goes down so that by -50 F its
only 0.4.

Since the Heat of Fusion is 144 BTU/lb, sub-cooling even 100 degrees
only adds a small amount of cooling capacity.

Hardly 'hadly effective'.

No, its hardly effective.

This is in error: using old CGS units
heat for fusion of ice is 80 cal/gm specific heat cap near 0degC is
1 cal/gm

Supercool to -40 deg C and its worth roughly another 40% of cooling
power cf. ice at freezing.

Brian Whatcott Altus OK

On Sun, 02 Jul 2006 23:50:59 -0500, Richard J Kinch
wrote:

Chris writes:

For water, the heat of fusion is about 80 times specific heat...

So -70 C ice would have almost twice the cooling effect
as the same amount of barely frozen ice, right?

No, because heat load is proportional to temperature differential.

Now if you put that supercooled ice into watery payload that freezes, then
the supercooling heat sink will convert to new ice in the payload, and a
different process is involved that is more "efficient". However, this is
no better than just freezing your food to start with.

Hardly anybody appreciates that temperature and heat are two different
things.

This note looks suspect - especially the "what everybody doesn't know"
bit.

Brian Whatcott Altus OK

On Sun, 2 Jul 2006 12:12:44 -0500, "Rick"
wrote:

Lets look at the safety of both suggestions.

1) Nitrogen liquid will boil to gas. The gas is an asphyxiate. Many people
have died from nitrogen. Air contains 21.5% O2 mostly the rest is N2. If
you breath pure N2 the first breath you pass out and the second breath brain
damage and the third death. Think about passing out when reaching for
something in the ice chest. If you fall in your dead; if you fall out you
will probably be ok. The next day you will be ripping out your N2 system.
A closed boat can accumulate N2 which will displace air. Maybe get you in
your sleep or when you go down for a cold one.

2) CO2 is heaver then air and would accumulate in the low parts of the boat.
Same issue as with N2 but it would at least give you some warning signs.

Whats wrong with a little water from melting ice. You are on a boat
right???


Nitrogen displaces oxygen, so you pass out without warning. It is not
otherwise toxic. So figure being underwater for a few seconds. That's
as much time as you have with N2. With CO2 you pant.
Both gases diffuse of course.

Brian Whatcott Altus OK

Brian Whatcott wrote:
Nitrogen displaces oxygen, so you pass out without warning. It is not
otherwise toxic. So figure being underwater for a few seconds. That's
as much time as you have with N2. With CO2 you pant.
Both gases diffuse of course.

"Carbon dioxide is a colourless gas which, when inhaled at high
concentrations produces a sour taste in the mouth and a stinging
sensation in the nose and throat. These effects result from the gas
dissolving in the mucous membranes and saliva, forming a weak solution
of carbonic acid."

Material Safety Data Sheet
Gaseous Nitrogen:

SIMPLE ASPHYXIANT
Section 3 : HAZARD IDENTIFICATION
Emergency Overview:
Nitrogen gas is colorless, odorless and non-flammable.

It is non-toxic. The primary health hazard is asphyxiation by
displacement of oxygen.
Route of entry:
Inhalation, skin and eye contact.
Effects of acute exposure
Eye contact:
Vapor may cause a stinging sensation.
Skin contact:
No adverse effects from gas.
Inhalation:
May cause dizziness.
Asphyxiant.
Can cause vomiting.
May result in unconsciousness.
May cause excitation, excess salivation, rapid breathing.
May cause headaches and drowsiness.
May cause stinging of the nose and throat.
Ingestion:
Not a likely route of exposure.
Effects of chronic exposu
None known. Chronic exposure to abnormal concentrations unlikely
Reproductive effects:
Oxygen deficiency during pregnancy has produced developmental
abnormalities in humans and experimental animals.

Brian Whatcott wrote:


Nitrogen displaces oxygen, so you pass out without warning.

Nitrogen does not *displace* oxygen (O2 weighs more than N2). Excess
Nitrogen will reduce the partial pressure of oxygen. Respiration is
controlled not only on CO2 concentration, but on blood pH and O2
saturation as well. N2 does not bind with hemoglobin, and does not
significantly affect blood pH. As a result, an excess of N2 will cause
further depletion of oxyhemoglobin in the red blood cells (less than 25%
is typically transferred, leaving a reserve factor which prevents your
sudden passing out scenario). This results in a higher respiratory rate
due to low O2 saturation, as well as causing a higher partial pressure
of CO2 (bicarbonate in solution), further lowering the pH of the blood,
and triggering the same reactions as does CO2. CO2 does it somewhat
more quickly is all.

It is not
otherwise toxic. So figure being underwater for a few seconds. That's
as much time as you have with N2.

I'm afraid I don't understand what this is trying to say.

With CO2 you pant.

As you will with N2. Increased CO2 will initiate higher respiratory
rates more quickly than decreased O2 saturation rates will, since the
homeostatic control sensors are more sensitive to CO2.

Both gases diffuse of course.

Which is why, with any reasonable implementation, neither N2 (although
the handling hazards of liquid N2 make it fairly useless IMO) nor CO2
are an issue.

Keith Hughes

Brian Whatcott wrote:
Nitrogen displaces oxygen, so you pass out without warning.

Keith Hughes wrote:
Nitrogen does not *displace* oxygen (O2 weighs more than N2). Excess
Nitrogen will reduce the partial pressure of oxygen.
Snip

Once again, this is copied directly from the MSDS (Emphasis added):

Material Safety Data Sheet
Gaseous Nitrogen:

SIMPLE ASPHYXIANT
Section 3 : HAZARD IDENTIFICATION
Emergency Overview:
Nitrogen gas is colorless, odorless and non-flammable.
It is non-toxic. The primary health hazard is asphyxiation by
displacement of oxygen.

Snip

Brian Whatcott wrote:
Nitrogen displaces oxygen, so you pass out without warning.


Material Safety Data Sheet
Gaseous Nitrogen:

SIMPLE ASPHYXIANT
Section 3 : HAZARD IDENTIFICATION
Emergency Overview:

Inhalation:
May cause dizziness.
Asphyxiant.
Can cause vomiting.
May result in unconsciousness.
May cause excitation, excess salivation, rapid breathing.
May cause headaches and drowsiness.
May cause stinging of the nose and throat.


So maybe lots of warning before passing out. But like others have said,
it only happens at extreme concentrations.