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Fog FAQs

Theatre Effects is one of the largest suppliers of theatrical fog machines in the United States, so it's not surprising that we answer lots of questions about working with fog. This week, I'd like to take a look at some of the most common questions we answer about our fog machines and fluids, as well as general questions about using fog effects. So without further ado,
let's get foggy!

Q - How does a fog machine work?
A - This is the most FA'd fog-related FAQ I can think of and I've answered it already in other articles but since the answers to many other questions require some knowledge of how a fogger does its job, let's go through it again, briefly. A fog machine has three main components, a fluid tank, a fluid pump and a heat exchanger. Once the heat exchanger has reached a temperature of around 400ºF, the fluid pump pulls fluid from the tank and
squirts it into the heat exchanger. The water in the fog fluid "flashes" into steam and rapidly expands, filling the heat exchanger and escaping from a small nozzle on the front of the unit. When the vapor hits the relatively cooler air outside of the fogger, it forms a thick, opaque cloud of "fog."

Q - Will adding food coloring or dye to the fog fluid make colored fog?
A - No. In fact, adding anything to fog fluid will damage the fog machine and invalidate the warranty; it may also produce harmful smoke or fumes. The only safe way to do a colored fog effect is to light the cloud of fog with a colored spotlight.

Q - Are scented fog fluids still available?
A - No. At one time, fog machines used oil-based fluids that produced fog that smelled bad and was hard to breathe. Even some of the earlier water-based fluids created foul-smelling fog. Because of this, many manufacturers offered perfumed oils that could be added to fog fluid to cover up the smell of the fog. Modern fog machines, however, use fluids that are much less irritating; in fact, many people feel that using a fog scent in a modern fog fluid only makes the fog smell worse!

Q - Will my fog effect trigger the smoke alarms in my
A - Possibly. Because many venues use smoke detectors that measure the density of particles in the air, fog effects (especially dense fog effects) can "fool" the detectors and trigger a fire alarm. If you are unsure of what type of smoke detector your venue has, consult with the head of maintenance or, as a last resort, notify the fire department and do a test shot.

Q - My fog effect triggers the fire alarms! Does this mean I can't do fog?
A - Not necessarily. It's a little-known fact that, according to NFPA regulations, smoke detectors do not have to be turned on during a performance; all that is required is some way of notifying you and the fire department in the event of a fire. While this is almost always the electronic smoke detectors, it could also be a human being. For example, you may be allowed to hire off-duty firemen to act as your "smoke detectors" during the show. Consult with your local fire marshal for more details.

Q - Is there a fluid I can use to create a low-hanging fog effect from my machine?
A - No. Go back to the top of this article and note the description of how a fog machine works. Do you notice that it says the fog is basically a cloud of steam? Because steam is warmer than room temperature, it will naturally rise. The only way to create a low-lying fog with a standard, water-based fog machine is to cool the fog as it comes out of the machine. Descriptions and plans for fog-chillers are available many places online, but there is no fluid that creates a low-hanging fog effect right out of the machine.

Q - You didn't answer my question! Where can I get more information about fog effects?
A - Right here! Check the Fun Facts archives for many more articles about fog as well as many other special effects. Take advantage of the Search tool at the top of the right navigation bar of this page. If you still can't find an answer to your question, feel free to call or email us. We're always happy to answer your questions! 


Theatre Effects Customer Service Department
Theatre Effects, 1810 Airport Exchange Blvd. #400, Erlanger, KY 41018
Phone: 1-800-791-7646 or 513-772-7646 Fax: 513-772-3579


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