You can create a cool fog effect using dry ice and warm water or dry ice and a drink. This is perfect for halloween, parties or even to create fog for stage productions.
But how long should you expect the dry ice fog to last?
Dry ice fog usually lasts between 10-15 minutes, shorter in small drinks and longer in large containers. It stops when the dry ice makes the liquid too cold to create the fog. You can make fog last longer by adding fresh warm water or by using more warm water to begin with.
Knowing how long dry ice fog lasts is important because if you prepare things too early you might not have fog by the time you need it.
What Is Dry Ice Fog?
Dry ice is frozen carbon dioxide. It's super cold at -109ºF (-78ºC) and sublimates (turns directly from a solid into a gas) as it warms up.
To make dry ice you need a combination of warm or room temperature water and some dry ice. This can even be done in drinks like cocktails.
Dry ice fog is actually condensed water vapor. As you put dry ice in warm water it sublimates (or turns to gas). As the bubbles escape the water it cools down the water in the air (steam from the water) and condenses it into fog (like how clouds are formed).
The cold fog then falls to the ground because it's colder than the air around it.
You can't actually see the “dry ice” or carbon dioxide gas. What you are seeing is condenses water vapor from the air above your container of warm water (or above your drink).
This is a pretty cool effect. As the fog begins to warm up it'll start to disappear again as the condensed water vapor expands back to normal.
How Long Does Dry Ice Fog Last?
Dry ice fog usually lasts between 10-15 minutes but the length of time it lasts depends on the temperature of the water as well as the amount of dry ice and the amount of water used.
When you place your dry ice in your warm water or drink the dry ice makes fog, but it also begins to cool down the water that it's in.
The reason fog is made so well in warm water is because there is lots of steam and moisture directly above the water which the dry ice can quickly cool and turn into fog.
However, the colder the water gets the less steam and moisture it releases. Eventually your water will get so cold that there is not enough moisture and no fog will be created.
This is why small drinks might only make fog for a few minutes while large containers can sometimes make dry ice fog for up to 30 minutes.
The small drinks cool quickly because there isn't much liquid to cool. The larger container of water, on the other hand, takes much longer to cool down and so the fog lasts longer.
Dry ice fog will usually run out and stop when the water/drink becomes too cold, but it can also stop if the block of dry ice is completely used up or has become so small it doesn't release enough gas.
Once the dry ice block completely sublimates (or completely turns to gas) there is nothing left to cool and condense the air thus creating the fog.
How To Make Dry Ice Fog Last Longer
If you want to extend the length of your dry ice fog there are a few different things you can do so it lasts longer.
Start With Hotter Water
The main reason your dry ice fog will stop is that your water becomes too cold.
Starting with warmer water means it'll take longer for water too cool down to the point where the fog stops.
This is a double edged sword though because the hotter the water is the faster your dry ice bricks are going to disappear so I don't usually advise boiling or super hot water for this reason and usually it's better to just add water as you go.
Add Warm Water (or Replace Old Water)
If your dry ice fog is slowing down or stopping then adding some warm water to your mix can keep your fog going for longer.
Another good solution is to simply tip out the cold water (make sure you don't tip out your dry ice brick with it) and completely replace it with a fresh new warm water.
If you continue to do this then your dry ice fog will last as long as the dry ice does.
Use A Larger Quantity of Water
The more water or liquid you use the longer your dry ice fog is going to last. This is because it will take longer for the dry ice to cool down a large quantity of water versus a small quantity.
Just think of how long it takes the sun to warm up a small cup of water versus trying to warm up your backyard pool.
Dry ice fog in drinks will only last around 2-5 minutes whereas large containers filled with water can last up to 30 minutes.
Better Dry Ice/Water Ratio
The ratio of dry ice to water takes a bit of testing and tweaking to get right.
But you don't want to use too much dry ice. Using too much dry ice compared to water means it will cool down the water much faster and your fog will stop earlier.
Using two little dry ice on the other hand won't give you enough sublimation and that your fog will be lack luster.
Replace Lost Dry Ice
If your dry ice has completely disappeared then your fog is going to stop completely no matter what temperature the water is.
If your fog has stopped check whether or not you still have dry ice left and replace where necessary.