Some info about dry ice

Used outdoors in a cauldron, dry ice attracts mosquitoes from at least ten thousand miles away. When they find there is no gigantic, CO2 exhaling whale present, as they were lead to believe, they feed on whatever else may be handy.
Keep it in a styrofoam chest, not the freezer. It’s cold enough that the freezer doesn’t really help as much as you might think, and it’s drafty in there as the cold air blows around. The dry ice evaporates much faster than in a decent cheap cooler.

I’ll elaborate. You have a piece of dry ice. The only way to keep it in it’s solid form is to apply a heck of a lot of pressure to it, or maintain it really cold. Otherwise sublimation occurs, i.e., the solid CO2 becomes gaseous CO2, a very expanded, energy-filled form of the same CO2. So, we drop this into cold water, which rapidly forms around the block of CO2. The CO2, though, isn’t being maintained at any pressure, nor at or below the freezing point of CO2, so it still sublimates, right? So I guess my question is, what happens to the ice? Presumably CO2 is still sublimating and it has to go somewhere, right? Otherwise, hey, I can keep dry ice around forever and ever if I drop it into a tub of cold water!

Yes, the ice is not strong enough to contain the gaseous CO[sub]2[/sub] so it leaks out though cracks in the ice. It’s a minor visual effect compared to the copious amounts of fog usually desired, though.

Okay, I may be paranoid - scratch that, I AM paranoid - but my healthy dose of paranoia has managed to keep me off the permanently dead list. Here’s my paranoid thought regarding dry ice:

As a long-time theatre designer, I’ve had more than my share of experience with dry ice fog - with no serious injuries. The fog itself is pretty harmless. But it is a very high concentration of CO2, which is very good at displacing oxygen. CO2 is heavier than air, which is (in part) why the fog creeps along the ground. And as it collects in low-lying areas, oxygen is displaced from that area. History has shown that people have suffocated from CO2 that has collected in the cargo holds of ships, and that escaped from lakes in Africa. Here comes the paranoia…

I doubt that any responsible adults would be in danger from the use of dry ice fog at a party. But suppose the CO2 were to crawl down the stairs and collect in the basement. Were the family pet to happen along, it is possible that Fido could pass out within seconds, and then suffocate to death while unconscious. The same goes for any small animal - dog, cat or human.

By all means, still use the dry ice - it is fun stuff! But just keep this in mind and exercise a little common sense. Keep the pets and kids upstairs.

Whaddaya think, my fellow armchiar experts? Am I being too cautious?

For the record, I don’t think that CO2 sublimation (from solid to gas) is a major problem in most household setting, but the expansion of volume is substantial, so I thought I’d throw out a few numbers on he magnitude of the effect, for all my fellow sci-heads.

I used to use dry ice extensively in a lab, when I was a teenager. I won’t recount some of my more foolish stunts, but it was fun to play with.

One mole of CO2 weighs 44 grams (1 1/2 oz) and occupies 22.4 liters (0.8 cu. ft) at standard temperature (32 F, the temperature of freezing water) and pressure (760 torr, or midrange barometric pressure at sea level), Therefore 10 lbs of dry ice is 82.5 cubic feet of pure CO2 at 32F (industry standards say 83 cu ft). This is the equivalent of 10.5 sq ft of floor space (floor to ceiling) in a house with standard 8ft ceilings.

At room temperature, or in your warm lungs, CO2 occupies 10-15% more volume than at 32F. 44g of crystalline dry ice can occupy just over 1 cubic inch, but expands more than 1500x as it becomes gas at room temperature. The loose crushed ice you’ll be buying won’t expand quite as much, but it’s still substantial.

Blood Ph/Bicarb

However, CO2 can exert its effects at far less than 100% concentration. Carbon dioxide dissolves in water to form carbonic acid (a weak acid) which further dissociates to bicarbonate. This is an important bichemical buffering reaction; it is the primary buffering reaction that controls your blood/tissue pH from minute to minute.

The level of CO2 and H+, which are buffered by bicarb in your blood, are among the most potent controllers of your automatic breathing rate. If you replace all the oxygen in in the air with an inert gas, you’ll be 80% suffocated before your brainstem notices much. If you add 1% CO2 to the air, people will begin to hyperventilate. This is because high blood CO2 happens all the time (e.g. when you exert yourself) but, evolutionarily, there are few cases where cavement (or animals) found their oxygen displaced, and could do anything about it.

Normal room air contains about 0.035% CO2. Exhaled air contains up to 5%. Breathing into a paper bag doesn’t much affect most healthy people until the O2 starts to drop (10-20 breaths at 5% extraction of the remaining O2 per breath) though it does have physiological effects - which is why we do it. Some people, however, can be very affected. In hyperventillation, the rapid breathing usually causes a loss of CO2, which causes the brain to restore a more normal breathing rate, but if you’re breathing in high CO2, your brainstem may not notice you are hyperventilating, with effects from dizziness to acid blood pH (which can have many physiological consequences) to exhaustion of the accessory muscles of breathing (particularly dangerous to people with asthma, emphysema or other lung conditions)

Relatively low concentrations of inhaled CO2 (well under 1%) will be noticed by the brainstem, and may provoke panic attacks and other effects in some people. Some people feel “they need air” under conditions when the Oxygen and CO2 are barely affected.


In a small kitchen, it could easily displace enough ‘normal air’ to reduce the oxygen in the room by 25% or more, when on accounts for sequestered volumes (you don’t usually breath the air in the cabinets, oven, etc.)

The problem is exaggerated nearer the floor because CO2 is considerably heavier than air (1.8 g/liter vs .64 g/liter at STP) and the freshly evaporated CO2 will be much colder then room temperature, and therefore much denser. This means that you might be breathing happily in he relatively oxygen rich air at head-height, but might grow dizzy or pass out if you are hunched down,- checking the oven, getting stuff out of a cabinet, or maybe even bobbing for apples in a high-walled tub bubbling near-pure CO2 - you could experience a very substantial decrease in available oXygen.

I am not aware of any CO2-related fatalities among healthy sober young people, but every year, we see a few minor bobbing-related injuries, and since the cause is transient, we never know what role dizziness may play. I’d bet it was a minor factor.

another fun thing to do is put dry ice into soapy water.

also, it’s not that bad to pick up, your fingers won’t freeze and fall off immediately, that would only happen if you held it for a minute :wink:
We have a huge chest (50 lbs) or more at work we use for research purposes, and occasionally do some “recreational” studies of the properties of dry ice. One thing, don’t put it directly into your sink, unless your goal is to crack it, or the pipes!

For making fog, the “pellet form” of dry ice is best. It looks like white cheet-os. No need for a hammer and screwdriver. The dry ice suppliers found in the yellow pages ususally have both cake and pellet.

As for suffocation, CO2 is somewhat safer than other gases (nitrogen, etc.), since a buildup of CO2 in your body feels stuffy and makes you breath fast. You’ll want to escape into the clear outdoors. Other gases just displace oxygen, and you can faint without any warning. It’s a bad idea to faint while in a room with no oxygen. :slight_smile: PS, whenever you hold your breath, the urge to breathe grows large because there is dissolved CO2 building up in your blood. Breathing too high a concentration of CO2 can feel as bad as holding your breath.