cold enough

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

Cheers,

Phil Hobbs

I read in sci.electronics.design that Tim Wescott wrote (in ) about 'cold enough', on Wed, 12 Oct 2005:

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.

I read in sci.electronics.design that martin griffith wrote (in ) about 'cold enough', on Wed, 12 Oct 2005:

Not ethanol, but ether; see:

I read in sci.electronics.design that Tim Wescott wrote (in ) about 'cold enough', on Wed, 12 Oct 2005:

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

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.

snip

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

martin

I read in sci.electronics.design that Keith Williams wrote (in ) about 'cold enough', on Wed, 12 Oct 2005:

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.

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.

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.

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

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

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.

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.

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.

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

I read in sci.electronics.design that John Perry wrote (in ) about 'cold enough', on Wed, 12 Oct

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.

If you enter an area of highish CO2 concentration, you feel stifled; just hold your breath for 30 seconds to simulate the sensation. At

John

On Wed, 12 Oct 2005 20:53:41 +0100, John Woodgate wrote in Msg.

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

robert

On Thu, 13 Oct 2005 08:17:56 +0100, John Woodgate wrote in Msg.

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

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.

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

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.

I didn't mean N2 blood concentration, rather pure N2 in the room. Halon fire extinguishers have the same problem.

Not low pressure. Low oxygen. A pure oxygen environment at .25ATM is safe (oxygen masks don't increase pressure).

I read in sci.electronics.design that Tony Williams wrote (in ) about 'cold enough', on Thu, 13 Oct 2005:

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

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