[SML] Dry Ice

[jdunfee12 at yahoo.com]

 It is important to consider that the amount of time it will last is very important. Also, how much it is going to be disturbed.  
The big advantage of dry ice fog over chilled glycol based fog or a hazer, is that the dry ice fog tends to rapidly evaporate once it is mixing with regular air.  It is probably also affected by the humidity at the time, though I don't know to what extent.  This, plus the heavier nature of the CO2 fog, helps to keep the line of demarcation between the heavy fog and the ambient air. Chilled fog can be used with a rapidly dissipating fog juice, but it is still a bit different, in that the line of demarcation is less crisp.  Sometimes this is an advantage. For example in an outdoor natural fog look, the crisp line of separation is not desirable.
I have also personally experimented with a CO2 cylinder and mixing that with the output from a fogger.  It definitely works, and I am surprised there is not a commercial unit out there that has the provision to have a CO2 tank attached, and automatically activated.  Though there may be safety issues, since if you let the CO2 out of the tank too fast, you end up making CO2 snow.
Since the original poster only wants a 4" depth, then I don't think they they have a choice.  They have to use dry ice.

Buy a few pounds and experiment with a smaller area, perhaps half, or even 1/4.  Then just multiply to figure what you need for the whole area, plus a generous amount extra, since running short will ruin your day.
-joe  
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