Dry Ice in Drinks
Dry ice is compressed carbon dioxide gas. The same gas all animals exhale during breathing. The smoke is not harmfull. Although possible getting too much gas could deprice someone of oxygen and cause light headedness. Don't be overly concerned about kids or adults breathing the smoke unless they continue for a long time.
More to the fun stuff. When putting Dry ice in any drink or pot it will bubble UNTIL the drink freezes around the dry ice chunk. The ice is so cold the drink freezes and the smoke stops. To solve this use smaller pieces of dry ice, warm the drink so it does not get too cold. When using dry ice start with warm pop and water. The initial effect will quickly cool the drink and have a big show.
Do not add the dry ice ahead of time. Wait until the crowd shows since the effect of the dry ice is short. Keep the unused dry ice wrapped as much as possible and buy right before the party. In your freezer dry ice will evaporate and just disappear from it's packaging. So don't store it expecting it to keep. You may unexpectedly find it gone.
When using dry ice in punches or drinks there are some cautions to keep in mind. Accidentally drinking a large piece of dry ice could cause some serious harm. Dry ice when handled directly can seriously burn you. It's like a freezer burn or frostbite.
IMPORTANT NOTE: Purchase your dry ice right before your party/event. many stores at Halloween let you reserve the amount you need. Dry ice will dissapate quickly. Storing dry ice (Even in the freezer) will not keep for more than 8 hours. Therefore plan on purchasing only what is needed and using it right away.