A few things to watch with dry ice.
You need some ventilation, but nothing extreme. CO2 is slightly acidic, so you will start to feel like your lungs are burning well before the concentration gets high enough to be dangerous. Other than sticking your head in a large box full of dry ice vapor, you would be hard pressed to get it in a high enough concentration to cause you to black out.
A real danger however is in storing it. Do not ever put it in an airtight container. It WILL explode. Glass bottles are very dangerous in this respect.
Another danger is instant frostbite. Don't touch it. Use heavy gloves, tongs if you have them.
There is no way to keep dry ice in storage without using specal equipment that can hit 80 below. Don't put it in your freezer, as the intense cold could hurt it. Best is in a plastic cooler. Don't buy some and plan to use it 3 days later. It will be gone.
Lots of small peices will sublimate faster than one large peice. The bigger it is, the longer it will last. Get twice as much and it will last 3 times as long in storage.
And don't forget to drop a peice in some soapy water. That is very cool. Try the screaming spoon and knife trick too.
And although dry ice is nontoxic and you CAN put it in your drink safely... you have no idea where it's been stored or how it was made. Contaminants may be inside it, so avoid this particular gimic.
