[John Woodgate]

I read in sci.electronics.design that Tim Wescott <[email protected]>

My point being that you can do some amazing things with a cheap cooler,
some nichrome wire and various frozen substances.

High-quality experimental physicists are the experts at this. Use stuff
that you'd find on a kids' TV model-making show to make an electron
microscope or something. Well, almost.

 

[John Woodgate]

I read in sci.electronics.design that martin griffith

I seem to remember a trick with dry ice and alcohol? What temp can you
get down to with it?

Not ethanol, but ether; see:

http://www.pc.chemie.uni-siegen.de/pci/versuche/english/v105-2.html

 

[Tim Wescott]

The real pain with going cold on the cheap is condensation. What I'd
really like is a LN2-cooled chamber, full of nice dry nitrogen. NOT
walk-in size, of course.

John

I would expect that sublimating dry ice would have the same effect as
boiling LN2: the gas generated would displace any water in the air (as
well as the air for that matter).

You want to be careful around LN2 it in a closed room because it'll
displace oxygen along with water and everything else. I don't _know_ if
the effects of CO2 would be worse but I suspect it would because your
body regulates breathing by measuring the CO2 in your blood rather than
oxygen; presumably lots of CO2 in a room would mess you up worse than an
equal amount of excess nitrogen.

 

[John Woodgate]

I read in sci.electronics.design that Tim Wescott <[email protected]>

I don't _know_ if the effects of CO2 would be worse but I suspect it
would because your body regulates breathing by measuring the CO2 in
your blood rather than oxygen; presumably lots of CO2 in a room would
mess you up worse than an equal amount of excess nitrogen.

I don't think it acts very quickly, but it can be nasty. See, for
example:

http://www.emedicinehealth.com/articles/26419-2.asp

Nitrogen is inert; of course you can't live in it, but it doesn't
disable you so you can't escape. CO2 can disable you, which is why there
are now strict rules on entering confined spaces that remain closed most
of the time.

 

[Keith Williams]

You want to be careful around LN2 it in a closed room because it'll
displace oxygen along with water and everything else. I don't _know_ if
the effects of CO2 would be worse but I suspect it would because your
body regulates breathing by measuring the CO2 in your blood rather than
oxygen; presumably lots of CO2 in a room would mess you up worse than an
equal amount of excess nitrogen.

IIRC CO2 is toxic because it raises the blood pH (carbonic acid).
SO in a forced low concentration (20% or so) CO2 might be worse.
OTOH, a room full of N2 would be worse than a room full of CO2. As
you point out, the body regulates oxygen intake by monitoring the
CO2 in the blood (pH). If N2 replaced the O2 the body wouldn't
react by demanding more oxygen, causing the brain to be starved of
oxygen. The subject would go into hypoxia and not even know it
(Payne Stewart). OTOH, if the CO2 concentration got too high one
naturally seeks more oxygen (lower blood pH). In this case panic
is better than bliss.

 

[John Woodgate]

I read in sci.electronics.design that Keith Williams <[email protected]>

If N2 replaced the O2

It can't. The lungs absorb O2 by chemically combining it with
haemoglobin. Nitrogen doesn't combine with it. Carbon monoxide is
especially dangerous because it does combine with haemoglobin.

the body wouldn't react by demanding more oxygen, causing the brain to
be starved of oxygen. The subject would go into hypoxia and not even
know it (Payne Stewart).

That's caused simply by low air pressure, like in the recent Greek plane
crash. If you don't notice the signs soon enough, you black out.

 

[Phil Hobbs]

I seem to remember a trick with dry ice and alcohol?
What temp can you get down to with it?

Dry ice and acetone gets you down to about -70 C.

Cheers,

Phil Hobbs

 

[Noone]

Dry ice and acetone gets you down to about -70 C.

Cheers,

Phil Hobbs

I worked back in college in a place we dubbed the "Good Time Photon
Shop", doing single photon fluoresence. The photomultipliers were
cooled by Dry Ice and
Acetone. The ice was stored in a big ice chest and you had to reach way
down to get the blocks. If you had to reach to the very bottom you
simply lost the ability to breathe. Very weird feeling..

Blakely

 

[Michael A. Terrell]

I read in sci.electronics.design that Tim Wescott <[email protected]>


I don't think it acts very quickly, but it can be nasty. See, for
example:

http://www.emedicinehealth.com/articles/26419-2.asp

Nitrogen is inert; of course you can't live in it, but it doesn't
disable you so you can't escape. CO2 can disable you, which is why there
are now strict rules on entering confined spaces that remain closed most
of the time.

A recent news story told of a truck driver who delivered liquid CO2
to restraunts. he died when there was a leak in the equipment. He was
in a room with no ventilation at the back of a restraunt. There is a
lawsuit in the works, of course.

 

[John Perry]

I read in sci.electronics.design that Tim Wescott <[email protected]>

The effects of N2 and CO2 are essentially the same. CO2 has a small
poisoning effect, but it's insignificant compared to the lack of O2.
Where the poisoning of CO2 is important is where the O2 level remains
high enough to support somewhat normal activity.

I don't think it acts very quickly, but it can be nasty. See, for example:

http://www.emedicinehealth.com/articles/26419-2.asp

Nitrogen is inert; of course you can't live in it, but it doesn't
disable you so you can't escape. CO2 can disable you, which is why there
are now strict rules on entering confined spaces that remain closed most
of the time.

No, the results are exactly the opposite. High levels of CO2 are
agonizing (the poisoning), so you're looking for a way out long before
you're in serious danger. N2 is dangerous only if it displaces oxygen
(the atmosphere is 79% N2, after all). But its effects are completely
imperceptible, and the typical result is that the victim suddenly,
without any warning at all, faints. And then dies quickly, if no help
arrives.

Enclosed places are most dangerous because of other gases either
displacing O2 or poisoning you without your feeling the poisoning
effects. Few people die of CO2 poisoning. Many die because of O2
dislaced by N2, or sewage, welding, etc. gas poisoning whose physical
effects they don't recognize.

_That's_ why there are strict regulations concerning entry into enclosed
spaces.

John Perry

 

[Pooh Bear]

We routinely blast our prototype circuits with freeze spray,
especially FPGAs and other fast logic that may have timing margin
issues. That gets them down to about -55C,

Common or garden freezer spray ?

I doubt that gets the device as low as -55C. It does go below 0C 'cos I've
seen ice form on the package.

The chip will be warmer than external temp due to dissipation too.

Graham

 

[przemek klosowski]

On the TV there was just a thing about fighting terrorists and
particularly nuclear devices.

One of the things in it was that a team had liquid nitrogen. They said
they didn't have info about what it was for, but sources said that it was
cold enough to freeze electronic devices.

So, is there any truth in that? I could see that batteries at that temp
might stop, but does really cold affect silicon circuits. Everything I
have heard makes me think silicon likes cold if it doesn't break wire
connections or such.

Liquid nitrogen (LN2) is used to lower the chemical activity of
conventional explosives to the point where they, well, don't explode.
Nuclear fission bombs use conventional explosives to squeeze nuclear
material together to achieve criticality and start the chain reaction
(see, e.g. http://www.fas.org/nuke/intro/nuke/design.htm)

Actually, the design is rather subtle: the conventional explosives are
usually very precisely timed to achieve uniform compression at the right
moment; if the nuclear material is not squeezed just right, the nuclear
explosion just peters out and scatters the material around, which isn't
even very radioactive. I have read that this is actually used as a
security measure: the timing of detonation of various segments of the
conventional explosive is the 'code' necessary to successfully explode
the weapon.

 

[John Woodgate]

No, the results are exactly the opposite. High levels of CO2 are
agonizing (the poisoning), so you're looking for a way out long before
you're in serious danger. N2 is dangerous only if it displaces oxygen
(the atmosphere is 79% N2, after all). But its effects are completely
imperceptible, and the typical result is that the victim suddenly,
without any warning at all, faints.

I don't intend to conduct any experiments, but there seem to be an
inconsistency. If anoxia is imperceptible, and results in sudden
fainting, then entering a pool of dense CO2 in the bottom of a closed
space will result in sudden fainting, and this is what I understand
happens. But nitrogen doesn't pool, so unless almost all the oxygen has
gone (absorbed by rusting metal?), you DO realise that breathing isn't
working and can retire quickly.

 

[Tony Williams]

I don't intend to conduct any experiments, but there seem to be
an inconsistency. If anoxia is imperceptible, and results in
sudden fainting, then entering a pool of dense CO2 in the bottom
of a closed space will result in sudden fainting, and this is
what I understand happens. But nitrogen doesn't pool, so unless
almost all the oxygen has gone (absorbed by rusting metal?), you
DO realise that breathing isn't working and can retire quickly.

Icy cold nitrogen in an enclosed space can pool.

Real event. Liquid Nitrogen (LN2) driving the refrigeration
side of an environmental chamber, running in a clean air room.
A solenoid valve stuck open (frozen), nitrogen evaporating
into the room (over the weekend). The security guard noticed
the huge stalactite of ice growing down the side of the chamber,
but fortunately did not enter the room to investigate.
The clean air room has since acquired oxygen depletion monitors.

 

[Robert Latest]

On Wed, 12 Oct 2005 20:53:41 +0100,

Nitrogen is inert; of course you can't live in it, but it doesn't
disable you so you can't escape. CO2 can disable you, which is why there
are now strict rules on entering confined spaces that remain closed most
of the time.

Problem with N2 is that you simply pass out before you notice anything.

robert

 

[Robert Latest]

On Thu, 13 Oct 2005 08:17:56 +0100,

But nitrogen doesn't pool, so unless almost all the oxygen has
gone (absorbed by rusting metal?), you DO realise that breathing isn't
working and can retire quickly.

The typical nitrogen accident happens during handling liquid N2, the
cold vapors of which indeed do pool.

Happened to an unfortunate physics student at a German university: He
went to refill a LN2 dewar at the main storage tank and never came back.
When he was found, he was dead on the floor with LN2 from the main tank
still spilling all over him because he hadn't had time to close the
valve.

robert

 

[Tony Williams]

One of the things in it was that a team had liquid nitrogen. They
said they didn't have info about what it was for, but sources
said that it was cold enough to freeze electronic devices.

During WW2, UK bomb disposal squads used liquid nitrogen
to freeze the mechanisms of booby traps on some German
bombs.

So, is there any truth in that? I could see that batteries at
that temp might stop, but does really cold affect silicon
circuits. Everything I have heard makes me think silicon likes
cold if it doesn't break wire connections or such.

Oscillators are the circuit elements that seem to give most
reliability problems at low temperatures, so attempting to
'stop the clock' of a device might be a useful thing to do.

 

[John Woodgate]

I read in sci.electronics.design that Tony Williams

Icy cold nitrogen in an enclosed space can pool.

Oh, well, if you are going to change the initial conditions....

On Pluto, you can't breathe the **oxygen**.

 

[martin griffith]

On Wed, 12 Oct 2005 20:53:41 +0100,


Problem with N2 is that you simply pass out before you notice anything.

robert

I always thought that this would be a way to clean sewers of rat
populations, rather than poisons. Just flood the sewers with N2.


martin

 

[Zak]

You want to be careful around LN2 it in a closed room because it'll
displace oxygen along with water and everything else. I don't _know_ if
the effects of CO2 would be worse but I suspect it would because your
body regulates breathing by measuring the CO2 in your blood rather than
oxygen; presumably lots of CO2 in a room would mess you up worse than an
equal amount of excess nitrogen.

ISTR that CO2 is 'safer' - the body notices teh excess CO2 and tells you
you suffocate - and run.

If you breathe N2, you produce no CO2 and everything seems fine. You
just fall.

But not everyone seems to react the same.


Thomas