[isotope]

Recently i happened to hold dry ice with bare hand. First, i felt very cold but within second i had feeling of burning on my hand. can somebody explain the reason for it?

[lemonoman]

"The areas of the body affected by frostbite feel cold and firm. Burning, tingling, stinging, or numbing sensations may be present" - from MedicineNet

"A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C)." - from HowStuffWorks

THIS chart gives various times for frostbite at different temperatures and wind speeds.  In your case, wind speed = 0 because it's being held in your hand.  Now, the table doesn't go as low as liquid carbon dioxide temperature.  So I made a very rough plot.  It should really be a hyperbolic function (so it doesn't cross certain intercepts), but this was the best fit Excel would give me.

Anyways, according to this VERY rough plot, a temperature of -109°F could give you frostbite in 0.214 minutes ~12 seconds.

I was bored, and did that out of curiosity.  Long story short, don't do it again.

[xiankai]

... and try to do it in celsius instead

[Will]

Your thermal nociceptors were responding to the extremely cold CO_2(s).

[IChO2007]

Haha I did that too by accident. Actually I held it for about 3 seconds because one of my DNA samples was underneath a slab of ice. It didnt feel weird until the third second. Then I let it go, and ran some cold water over my fingertips. The pain went away within 5 minutes. It's a good thing I was wearing latex gloves, since they were "scorched" orange from the cold temperature.

[xiankai]

http://www.chemicalforums.com/index.php?topic=4566.0

seems like there is something about the '3 seconds'

[Salter]

I put a cube in my mouth and rolled it around really fast. Cool effects, smoke was pouring out of my mouth. Yeah a dumb thing to do i know but fun none the less.