Fog maker and fog chiller

Ran across this tutorial for making your own fog maker to scare little children during Halloween. My current qualm about it was this one paragraph:

I’ve been told that overheating fog fluid can cause it to oxidize and produce toxic chemicals such as formaldehyde. I don’t see how my fog machine design can overheat fog fluid because the fluid evaporates as soon as it reaches its boiling point. I would think the fluid would have to be pressurized in order to overheat it. Nevertheless, if you build a fog machine and the fog smells unpleasant or burns your nose, you shouldn’t use it in such a way that anyone will breathe the fog. The fog should only have a somewhat sweet odor.

Otherwise, a very fun project it sounds like. Especially for an underbudget haunted house type fun.
One key note: This fog maker produces hot fog. To make the fog hang over the ground, the fog must be chilled. Two different tutorials for for different types of fog chillers can be found here and here.
You buy a perfectly good fogger if you shop around for around $30 according to Allen. But why buy when you can make something that would be quieter, more powerful and cover more area? Oh yeah… maybe that one paragraph….
Via AllensHalloweenPage