PDA

View Full Version : Can You Exhale Dry Ice at -111 Degrees Fahrenheit?

Mr. Milton Banana
2005-Jul-27, 03:44 PM
At Vostok, Antarctica, it's currently -111 degrees Fahrenheit. I just thought of something...

Dry ice's temperature is -109 F. If you were standing at Vostok now and exhaled, is it possible that some of your breath would turn into carbon dioxide snow? Also, could there some be some dry ice snow mixed in with water ice at Vostok?

:-k

Laser Jock
2005-Jul-27, 04:55 PM
Wow, that's cold!! I wouldn't think that you would see any dry ice snow from you breath; you don't see water snow from your breath when it's 30 F. However, I would not be surprised that a little of the CO2 has not frozen out of the air and is sitting on the ground. A pail of air (http://www.baen.com/chapters/W200501/0743498747___6.htm) anyone? :wink:

pghnative
2005-Jul-27, 09:04 PM
At Vostok, Antarctica, it's currently -111 degrees Fahrenheit. I just thought of something...

Dry ice's temperature is -109 F. If you were standing at Vostok now and exhaled, is it possible that some of your breath would turn into carbon dioxide snow? Also, could there some be some dry ice snow mixed in with water ice at Vostok?

:-k
No chance of either.

To understand this, you need to understand that there is an equilibrium between solid CO2 (dry ice) and the concentration of CO2 vapor in the air. At -111 F, the equilibrium is such that you need approximately 66% of the vapor to be CO2 in order for CO2 snow to form. The percentage of CO2 in your breath is nowhere near that high. (I think it is about a percent or two -- maybe even less).

edited to add that it may be more like 95%, not 66% -- the chart I looked at was hard to read. EIther way, you get the point.

Taks
2005-Jul-27, 09:19 PM
soooo... is this a normal temp at this time of year? i didn't realize things got that cold down (er, standard globe view) there.
taks

Mr. Milton Banana
2005-Jul-27, 09:47 PM
soooo... is this a normal temp at this time of year? i didn't realize things got that cold down (er, standard globe view) there.
taks

Vostok, Antarctica Current Conditions/Forecast (Weather Underground) (http://www.weatherunderground.com/global/stations/89606.html)

As of this writing, it's still -111 F. To give you some perspective, at Luke Air Force Base in Arizona, it's 108 F.

That's a 219-degree difference! :o

Meteora
2005-Jul-28, 04:40 PM
soooo... is this a normal temp at this time of year? i didn't realize things got that cold down (er, standard globe view) there.
taks

No too unusual. I think the average temperature in that part of the world is about -80 F (roughly -60 C), and the all-time record low, last time I checked, was almost -130 F (-90 C).

Taks
2005-Jul-28, 04:50 PM
unbelievable. there are places that have been hitting nearly 120 lately, which is a 230 degree delta. the earth is an amazing place.

taks

Meteora
2005-Jul-28, 04:56 PM
The last time I looked (a few years ago), the accepted world records were 136 F/58 C (in Libya) and -130 F/-90 C (rounded - at Vostok).

Mr. Milton Banana
2005-Jul-28, 10:58 PM
The last time I looked (a few years ago), the accepted world records were 136 F/58 C (in Libya) and -130 F/-90 C (rounded - at Vostok).

Lowest temperature on Earth was -128.6 F in 1983. There is an unconfirmed report of a -130 F reading in 1997.

8)

Meteora
2005-Jul-30, 04:31 PM
The last time I looked (a few years ago), the accepted world records were 136 F/58 C (in Libya) and -130 F/-90 C (rounded - at Vostok).

Lowest temperature on Earth was -128.6 F in 1983. There is an unconfirmed report of a -130 F reading in 1997.

8)

That's what I get for relying on my memory. :roll: I was thinking it was -129.something. Oops. #-o

I hadn't heard about the -130 F report. Why is it unconfirmed?

Mr. Milton Banana
2005-Jul-31, 12:49 AM
^

I've been trying to find out, Meteora-and I still don't have an answer to that. I have read some online diaries from folks who've worked at Vostok, and one person mentioned the wind chill going down as low as -155 F. :o :o :o

Here's another question: suppose you knew you'd have a week of -100 F readings at night, with a few nights of -110 F readings. Would it be possible as an experiment to set up a small box pumped with pure carbon dioxide gas, using the -110 F air to create some carbon dioxide snow? I'm trying to keep in mind pghnative's statement of needing at least 66% CO2 vapor in the box. Hmmm-but then, how many hours would be needed to create CO2 snow?

I'm not talking about a large amount of CO2 snow-I'm talking small amounts.

:-k

Eoanthropus Dawsoni
2005-Jul-31, 02:11 AM
^

I've been trying to find out, Meteora-and I still don't have an answer to that. I have read some online diaries from folks who've worked at Vostok, and one person mentioned the wind chill going down as low as -155 F. :o :o :o

I think at those temperatures wind chill probably becomes rather meaningless. Since wind chill is based on heat loss to exposed skin, I suspect that at -100 exposed skin is going to freeze pretty damn fast with or without the wind.

Meteora
2005-Jul-31, 08:43 AM
^

I've been trying to find out, Meteora-and I still don't have an answer to that. I have read some online diaries from folks who've worked at Vostok, and one person mentioned the wind chill going down as low as -155 F. :o :o :o

I think at those temperatures wind chill probably becomes rather meaningless. Since wind chill is based on heat loss to exposed skin, I suspect that at -100 exposed skin is going to freeze pretty damn fast with or without the wind.

At -100 F (for example), it's not at all difficult to get to -155 F wind chill, even by the more-conservative new scale. [Does some quick calculations.] Ah - 22 mph does it.

Yes, I think -75 F is considered essentially "instant freeze," so anything lower is not really significant. (I am again relying on my memory here, so I expect to see someone correct me....) :)

Eoanthropus Dawsoni
2005-Jul-31, 02:43 PM
The whole wind chill thing has become one of my pet peeves. Too many times I have heard TV or radio people reporting the wind chill as if it is the actual air temperature, to the point that now it seems that most people no longer know the difference. Typically I'll hear someone say something like "It's sixty below, I can't believe my car started." I'll respond with "No, it is twenty below zero and windy." I then try to explain that since their car is a non-living object, wind chill is irrelevant in whether or not it will start. Very few understand.

Meteora
2005-Aug-01, 08:02 AM
The whole wind chill thing has become one of my pet peeves. Too many times I have heard TV or radio people reporting the wind chill as if it is the actual air temperature, to the point that now it seems that most people no longer know the difference. Typically I'll hear someone say something like "It's sixty below, I can't believe my car started." I'll respond with "No, it is twenty below zero and windy." I then try to explain that since their car is a non-living object, wind chill is irrelevant in whether or not it will start. Very few understand.

I agree.

Many years ago, one of my then-coworkers told me that our mutual supervisor was asked if rain could freeze if the wind chill was below freezing (implying an above-freezing air temperature). His answer was that it might. :o #-o :roll:

Then there's the heat index....

pghnative
2005-Aug-02, 06:19 PM
Here's another question: suppose you knew you'd have a week of -100 F readings at night, with a few nights of -110 F readings. Would it be possible as an experiment to set up a small box pumped with pure carbon dioxide gas, using the -110 F air to create some carbon dioxide snow? I'm trying to keep in mind pghnative's statement of needing at least 66% CO2 vapor in the box. Hmmm-but then, how many hours would be needed to create CO2 snow?

That would definitely work --- impossible to calculate the "number of hours", --- depends on how quickly the box cooled. (here, the "wind chill effect" would matter. The final temp doesn't change, but the rate at which it gets there does).

And of course, you could always increase the pressure of CO2 in the box -- that'll raise it's "freezing" point.

Finally, if all you want is CO2 snow, then just grab a fire extinguisher (http://www.wfrfire.com/website/front/index.htm?/website/interior/exting/carbon.htm&amp;front) and blast away. The pressurized CO2 cools down so much when it comes out, that some of it precipitates. (Some of the white stuff is water ice, I'm sure, but you'd get a mix.) Won't last very long, though...

Charlie in Dayton
2005-Aug-03, 12:02 AM
As of this writing, it's still -111 F. To give you some perspective, at Luke Air Force Base in Arizona, it's 108 F.
That's a 219-degree difference!

...there are places that have been hitting nearly 120 lately, which is a 230 degree delta. the earth is an amazing place...

...Yes, I think -75 F is considered essentially "instant freeze,"...

I personally have witnessed a (perceived) 180-degree delta...that night when they had us shovelin' the runway lights away back when in Uncle Sugar's Flyin' Circus, the wind chill was -75. Since that night, I have been uncomfortable, I have been chilled, but I have not been truly cold...

And a summer or so later, I was crankin' down the road on the old Bim-Dub when the thermometer at the Credit Union read 105...

Giving the instruments and personnel the benefit of the doubt, that makes it a long way from freezin' yer somethingorothers off to fryin' eggs on the pavement...

Mr. Milton Banana
2005-Aug-03, 02:46 AM
Here's another question: suppose you knew you'd have a week of -100 F readings at night, with a few nights of -110 F readings. Would it be possible as an experiment to set up a small box pumped with pure carbon dioxide gas, using the -110 F air to create some carbon dioxide snow? I'm trying to keep in mind pghnative's statement of needing at least 66% CO2 vapor in the box. Hmmm-but then, how many hours would be needed to create CO2 snow?

That would definitely work --- impossible to calculate the "number of hours", --- depends on how quickly the box cooled. (here, the "wind chill effect" would matter. The final temp doesn't change, but the rate at which it gets there does).

And of course, you could always increase the pressure of CO2 in the box -- that'll raise it's "freezing" point.

Finally, if all you want is CO2 snow, then just grab a fire extinguisher (http://www.wfrfire.com/website/front/index.htm?/website/interior/exting/carbon.htm&amp;front) and blast away. The pressurized CO2 cools down so much when it comes out, that some of it precipitates. (Some of the white stuff is water ice, I'm sure, but you'd get a mix.) Won't last very long, though...

Thanks for the response. 8)

I've experienced +100 F-but not the -100 F stuff-and I must say that I'm very fascinated by it. Again-the idea is to create a small amount of CO2 snow. I'm just fascinated that the temperature at Vostok can be colder than the temperature of dry ice-and that's pretty darn cold!! :o

Right now, it's -106 F at Vostok. At Death Valley, California, it's 100 F . That makes for a 206 degree difference. Again-it's VERY fascinating that humans can live at either extreme.

8)

Eoanthropus Dawsoni
2005-Aug-03, 03:03 AM
In 1983 Williston, ND had a high temperature of 107F on July 14 and August 6, and a low of -50F on December 23, for a 158 degree temperature spread within the same year at one location.

The 107F is not unusual, in many years it gets warmer. But the -50 was quite unusual. As I recall the wind was also very bad that night, probably blowing in the 35-45 mph range. Visibility was almost zero due to blowing snow. I have no idea what the wind chill may have been. It was a cold night.

Bender
2005-Aug-03, 03:13 AM
If you want to see big temp extremes you need to join the 300 Club.

The entry requirements are rather unusual...

At the Amundson/Scott base at the South Pole, on the first day of winter when the temp is -100F or colder you fire up the sauna to +200F, and clad only in "appropriate footwear" dash the 100 or so yards from the base entrance to the Pole and back.

Drink is usually taken.... :o

Eoanthropus Dawsoni
2005-Aug-03, 03:29 AM
I do have a wood burning sauna in the back yard that I like to use in the winter, but certainly do not experience temperature extremes like that. The dash from sauna to house is not bad because the skin seems to take a while to cool off, but the trip out to the sauna can be a bit nippy.

Meteora
2005-Aug-03, 11:32 AM
In 1983 Williston, ND had a high temperature of 107F on July 14 and August 6, and a low of -50F on December 23, for a 158 degree temperature spread within the same year at one location.

The 107F is not unusual, in many years it gets warmer. But the -50 was quite unusual. As I recall the wind was also very bad that night, probably blowing in the 35-45 mph range. Visibility was almost zero due to blowing snow. I have no idea what the wind chill may have been. It was a cold night.

I think I remember that day (noticed the -50 at Williston in the weather observations that morning). I was in Omaha, Nebraska, and it was blinking cold there, too.[/quote]

(Edited to add note in parentheses)

pghnative
2005-Aug-03, 01:12 PM
In 1983 Williston, ND had a high temperature of 107F on July 14 and August 6, and a low of -50F on December 23, for a 158 degree temperature spread within the same year at one location.

The 107F is not unusual, in many years it gets warmer. But the -50 was quite unusual. As I recall the wind was also very bad that night, probably blowing in the 35-45 mph range. Visibility was almost zero due to blowing snow. I have no idea what the wind chill may have been. It was a cold night.

I think I remember that day (noticed the -50 at Williston in the weather observations that morning). I was in Omaha, Nebraska, and it was blinking cold there, too.
I remember that cold snap too, though it may have hit Pittsburgh a day later. (Was a relatively balmy -30F, but with high winds). I remember having to get up to deliver the Sunday papers.

Again-it's VERY fascinating that humans can live at either extreme.
One of my favorite sayings (supposedly Norwegian in origin) is "There is no such thing as bad weather --- only bad clothing"

Eoanthropus Dawsoni
2005-Aug-03, 01:34 PM
I think the entire continent was frozen that week.

February 1996 was another cold one. The little town of Tower MN hit -60 on Ground Hog Day. That could not have been fun.

Mr. Milton Banana
2005-Aug-03, 01:39 PM
If you want to see big temp extremes you need to join the 300 Club.

The entry requirements are rather unusual...

At the Amundson/Scott base at the South Pole, on the first day of winter when the temp is -100F or colder you fire up the sauna to +200F, and clad only in "appropriate footwear" dash the 100 or so yards from the base entrance to the Pole and back.

Drink is usually taken.... :o

Yes, I'm aware of the 300 Club. :D

Those folks bring lunacy to a whole new level. :P :P :P :P

Eoanthropus Dawsoni
2005-Aug-03, 01:48 PM
These two are interesting:

January 20, 1943 -

famous temperature antics occurred in the Black Hills of South Dakota. The temperature was 52 degrees above zero at Lead and 16 degrees below zero degrees at Deadwood simultaneously. The places are only 1.5 miles apart, but there is an elevation difference of 600 feet.

January 22, 1943 -

Chinook winds caused wild temperatures fluctuations at Spearfish, SD. The temperature rose 49 degrees between 7:30 and 7:32 am (4 below to 45 above zero). Around 9 am the temperature plunged 58 degrees in 27 minutes (54 above to 4 below zero). Plate glass windows cracked as a result of the quick thermal expansion and contraction.

http://www.intellicast.com/Almanac/NorthernPlains/January/

Mr. Milton Banana
2005-Aug-03, 09:44 PM
^

Cool. 8)

Vostok IIRC is 11,000 feet above sea level.

There's some interesting info at this link as well. (http://64.233.161.104/search?q=cache:dD0EcROQ3rgJ:www.gsfc.nasa.gov/scienceques2001/20020118.htm+Vostok+12,000+feet&amp;hl=en)

:)

sts60
2005-Aug-05, 05:40 PM
The last time I looked (a few years ago), the accepted world records were 136 F/58 C (in Libya) and -130 F/-90 C (rounded - at Vostok).I'm pretty sure they've measured hotter temperatures at Boulder Dam. I am sure I remember a Scientific American article (I think it's this one (http://www.sciamdigital.com/browse.cfm?sequencenameCHAR=item2&amp;methodnameCHAR=r esource_getitembrowse&amp;interfacenameCHAR=browse.cfm &amp;ISSUEID_CHAR=95C97E8D-4E3A-4EE5-A478-944FC3A850A&amp;ARTICLEID_CHAR=C1344241-B796-4712-BEF1-279D123CF91&amp;sc=I100322)) that describes an expedition to look for an old meteorite site in Saudi Arabia.

Now this site was in an area known to the nomads as the "Empty Quarter". That tells you something straight off. The expedition got out there, and the temperature was sixty-two degress Celsius.

Doesn't that look like a misprint? 62 C. That's over 140 degrees F.

I grew up in southern Arizona. But that is some kinda toasty.

Meteora
2005-Aug-06, 06:45 AM
The last time I looked (a few years ago), the accepted world records were 136 F/58 C (in Libya) and -130 F/-90 C (rounded - at Vostok).I'm pretty sure they've measured hotter temperatures at Boulder Dam. I am sure I remember a Scientific American article (I think it's this one (http://www.sciamdigital.com/browse.cfm?sequencenameCHAR=item2&amp;methodnameCHAR=r esource_getitembrowse&amp;interfacenameCHAR=browse.cfm &amp;ISSUEID_CHAR=95C97E8D-4E3A-4EE5-A478-944FC3A850A&amp;ARTICLEID_CHAR=C1344241-B796-4712-BEF1-279D123CF91&amp;sc=I100322)) that describes an expedition to look for an old meteorite site in Saudi Arabia.

Now this site was in an area known to the nomads as the "Empty Quarter". That tells you something straight off. The expedition got out there, and the temperature was sixty-two degress Celsius.

Doesn't that look like a misprint? 62 C. That's over 140 degrees F.

I grew up in southern Arizona. But that is some kinda toasty.

According to this article (http://www.micmacmedia.com/Weather/Nevada_Climate_History/hotcold/hotcold.html), the highest unofficial temperature at Boulder Dam was 131 F. But, I'm not sure how current, or accurate, that article is, either. Looks like it's either from 1990 or 2005.

The summary of the Scientific American article doesn't mention 62 C, and I'm not a subscriber, so I can't see what's in the article itself. There are specific requirements on what can be called an "official" temperature, though, and I have no idea if they measured the temperature that way or not. 62 C is extremely hot for a shade temperature at 4 feet above ground level (above a vegetated surface, if one is available). The highest outdoor shade temperature I've personally experienced was approximately 120 F (49 C) at Death Valley, California. :o

Maksutov
2005-Aug-06, 06:59 AM
The coldest temperature I've ever heard of was mentioned in an episode of Futurama called "The Birdbot Of Ice-Catraz", all about an endangered penguin refuge on Pluto. It's kind of like March of the Penguins on acid.

Leela: Hey, why weren't you Kong donkeys outside cleaning up?

Zoidberg: They sent us inside for doing an unsatisfactory job. [Yolk drips from his mouth.] (sadly) And eating penguin eggs.

Fry: You ate most of them. So, where's Captain Bender? Off catastrophising some other planet?

[He chuckles. Zoidberg slaps him.]

Zoidberg: Dammit Fry! He may have done wrong, but he's still your captain.

Leela: I'm worried about him. He didn't come back with the group.

Fry: He didn't?

Leela: No. And with windchill it's 20 degrees below absolute zero. I'd better go find him.

[She pulls her hood over her head and starts to leave. Fry grabs her shoulder.]

Fry: Wait. Let me. Bender and I have our disagreements, but we're still friends and I'm gonna show him what that means. [He puts on Leela's jacket and Bender's hat.] To the ship.

Leela: Why don't you just walk? He was only about 20 yards from here.

Fry: Madam, I am in command now.

[He walks out and Zoidberg follows him.]

Zoidberg: Such a man. I'd follow him to hell and back I would.

Meteora
2005-Aug-07, 08:19 AM
Leela: No. And with windchill it's 20 degrees below absolute zero. I'd better go find him.

[Does some quick calculations.]

Hmm... guessing that 50 K isn't too unreasonable a temperature for Pluto, it looks like you can hit -20 K with a little less than 8 m/s winds. Of course, that assumes near-surface Earth winds. My... fun with equations outside their useful range. :P :D

I was at a restaurant once and overheard one of the customers talking to the cashier. IIRC, he was referring to the cold fusion experiments of about 10 years ago (that's when I heard this). His comments went like this:

Him: They cool it to 20 below Kelvin.
Him: That's really cold.

:o

Eoanthropus Dawsoni
2005-Aug-07, 01:34 PM
Leela: No. And with windchill it's 20 degrees below absolute zero. I'd better go find him.

[Does some quick calculations.]

Hmm... guessing that 50 K isn't too unreasonable a temperature for Pluto, it looks like you can hit -20 K with a little less than 8 m/s winds. Of course, that assumes near-surface Earth winds. My... fun with equations outside their useful range. :P :D

I was at a restaurant once and overheard one of the customers talking to the cashier. IIRC, he was referring to the cold fusion experiments of about 10 years ago (that's when I heard this). His comments went like this:

Him: They cool it to 20 below Kelvin.
Him: That's really cold.

:o

And wouldn't wind-chill on Pluto imply that someone was wandering around on the planet with bare skin??

Meteora
2005-Aug-08, 07:13 AM
Leela: No. And with windchill it's 20 degrees below absolute zero. I'd better go find him.

[Does some quick calculations.]

Hmm... guessing that 50 K isn't too unreasonable a temperature for Pluto, it looks like you can hit -20 K with a little less than 8 m/s winds. Of course, that assumes near-surface Earth winds. My... fun with equations outside their useful range. :P :D
[edited]

And wouldn't wind-chill on Pluto imply that someone was wandering around on the planet with bare skin??

Why yes! Yes it would!

...And I'm sure someone will eventually do this in a movie (if they haven't already). :)

Avatar28
2005-Sep-27, 10:59 PM
Speaking of rapid temperature drops, I had gone out to the movies with my ex-girlfriend (she was already ex at the time). I'm not sure exactly what month it was, but when we came out of the theater, the weather was comfortable (I had on short sleeves with no jacket or maybe just a very light one), I'd guess probably upper 60's maybe low 70's (i'm cold natured so it couldn't have been very cool). You could tell that it would be raining soon and that a front was about to move through from the feel to the air. Anywho, after the movie we drove over to a nearby Mickey D's to grab a bite to eat. While we were in the restaruant eating, it starting raining (hard). About 15-20 minutes after that started and we were about done eating, I had to dash outside and it was COLD! I didn't have a thermometer to give you an exact temperature, of course. But we left a few minutes later when it had stopped raining and I do recall that I looked at the temp displayed on a sign and it was in the 30's so there was probably a good 30-35 degree drop in a matter of minutes. And that was in Nashville.

hhEb09'1
2005-Sep-28, 06:46 AM
Finally, if all you want is CO2 snow, then just grab a fire extinguisher (http://www.wfrfire.com/website/front/index.htm?/website/interior/exting/carbon.htm&amp;front) and blast away. The pressurized CO2 cools down so much when it comes out, that some of it precipitates. (Some of the white stuff is water ice, I'm sure, but you'd get a mix.) Won't last very long, though...I'm pretty sure it's almost all water ice. If there were significant amounts of dry ice, it'd be pretty dangerous. If I want dry ice snow, I just go scrape it off the chunks down at Food Lion. :)

I'll have to go back and look at the records, but I experienced a significant temperature increase (drop) in a matter of seconds--over thirty years ago, driving from our farm to town, the temperature at the farm was way below freezing. The town was experiencing a chinook. As I climbed a hill, going sixty miles an hour, my windshield instantly and completely frosted over. That was a big surprise.

Taks
2005-Sep-28, 06:54 AM
i've been party to about a 50-60 degree (F) difference in one day in st. louis. i think it was a record. near 80 in the morning and some sort of storm moved in dropping the temps to below 20 that evening. amazing. it was in november i think. pretty nasty around that time of year.

taks

Charlie in Dayton
2005-Sep-28, 07:28 AM
Away back when, up in Michigan's UP, on duty with Uncle Sugar's Flyin' Service, I sat there one December Saturday when we had this very unseasonable heat wave and rainstorm...and watched a puddle on the sidewalk outside the window freeze over. The ice was visibly crawling across the surface...

Avatar28
2005-Sep-28, 10:52 PM
Away back when, up in Michigan's UP, on duty with Uncle Sugar's Flyin' Service, I sat there one December Saturday when we had this very unseasonable heat wave and rainstorm...and watched a puddle on the sidewalk outside the window freeze over. The ice was visibly crawling across the surface...

Wow, sounds like a scene out of The Day After Tomorrow. Now there's a piece of horrible science for you.

pghnative
2005-Sep-29, 02:38 AM
Finally, if all you want is CO2 snow, then just grab a fire extinguisher (http://www.wfrfire.com/website/front/index.htm?/website/interior/exting/carbon.htm&amp;front) and blast away. The pressurized CO2 cools down so much when it comes out, that some of it precipitates. (Some of the white stuff is water ice, I'm sure, but you'd get a mix.) Won't last very long, though...I'm pretty sure it's almost all water ice. If there were significant amounts of dry ice, it'd be pretty dangerous.
Nope, it's dry ice. (http://chemmovies.unl.edu/chemistry/smallscale/SS009.html)

Lab Hints-
Obtain dry ice from an ice house, a packing house, a grocery store, or a hospital (among possible sources). Dry ice can be manufactured from a CO2 fire extinguisher by discharging the gas through a piece of cheese cloth. Recharging fire extinguishers is expensive, so this should be done as a last resort and only when other fire extinguishers remain available to deal with emergencies.
Besides, while solid CO2 can be dangerous (it's ~ -80C, after all) one can actually be pretty casual around it with little concern. I've gotten fine CO2 powder all over my arm, and it's easy to shake off before any ill effect occurs.