Fun Facts & Helpful Tips: Foggy (Fluid) Notions

By Paul Shillinger, Jr.
Posted Friday, July 25, 2003

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We get lots of questions about fog effects, and many of those questions have to do with the fluid that our foggers use. The fluid that you use in your fog machine is probably the single most important factor in keeping it in good working order. I'd like to take some time to talk about how fog fluids work, and offer some tips on keeping your fogger in good working order.

Customers often ask us if a brand name fluid is the only fluid that will work in our fog machines. To be perfectly honest, you could use just about any fog fluid in one of our machines and it would probably still produce fog; however, you could also be damaging the fog machine at the same time, and you may be creating fog that's not healthy to breathe. To understand why this is so, we'll need to take a quick refresher course on how a fog machine works.

In its simplest state, a fogger is just a tank filled with fluid, a fluid pump and a heated chamber. First, the heated chamber (often called the heat exchanger or heater block) is heated to around 400ºF. Then, the pump moves some fluid from the tank into the heat exchanger. When the fluid hits the chamber, it flashes over instantly into a vapor and expands rapidly. This expansion drives the vapor out through a small nozzle at the front of the heat exchanger. When the vapor reaches the cooler air outside the machine, it forms the opaque white cloud that we know and love.

Since all foggers use the same basic technology, and the same type of fluid, it seems reasonable to assume that any fog fluid should work in any fog machine. However, there are differences in fog machines and fluids that you should be aware of if you're thinking of attempting a substitution.
All fog machines operate at different temperatures. This is mainly due to differences in the design of the heater block, and the materials used in building the machine. Manufacturers create their fog fluids to be work at the temperature of their fog machines. When you substitute a fluid from another manufacturer, two problems can arise. First, if your fog machine is not hot enough to properly vaporize the fluid, the result will be a "wet" fog that leaves a slippery residue, or a fog machine that spits hot fluid from its front nozzle. Alternatively, if the fogger is too hot the fluid could burn inside the heat exchanger and produce a foul-smelling smoke that could contain harmful byproducts.

In addition to differences in operating temperatures, there are also other differences in fog fluids. Think of your fog fluid like beer—I'm writing this on a Friday, so a beer analogy makes sense right now. Beer can be made from the highest quality ingredients—just think microbrew—or from the cheapest ingredients available—just think of whatever beer you can get for $3 a case. Both products are technically beer, but there's a definite difference between the two! Just as using cheap ingredients can result in funny-tasting beer, using cheap ingredients in fog fluid can produce foul-smelling fog or clogged fluid lines in your machine. This is why some manufacturers recommend purging their machines with water after every use. Foggers using Theatre Effects fog fluid, on the other hand, may be stored with the fog fluid in the lines.

A final thought about fog fluid: one of the more common questions about fog that I hear is, "what can I add to my fog fluid to create colored fog?" This is an especially popular request around Saint Patrick's Day. The fact is that there is currently nothing you can add to fog fluid that will produce a colored fog. Adding dye or food coloring to your fog fluid will do nothing at best; at worst, it can damage the heater and result in expensive repairs to your machine. The best way to make a cloud of colored fog is to shoot a colored spotlight through the fog. If the resulting color isn't bright enough, you should consider using a colored smoke powder, but that's another article!

For more information contact Paul the Theatre Effects Customer Service Wizard at www.theatrefx.com