There are a lot of technologies out there capable of producing fog, mist, and haze.
Over time, many of these fog technologies have come under suspicion of causing health problems. Just because something can make fog doesn't necessarily mean it's good for making fog!
Please do additional research on any fog-making technology you decide to use. You'll be breathing that stuff, as will your actors and patrons.
We tend to use the terms "fog" and "mist" interchangeably, but there is a difference. Here's a particularly clear explanation from a mailing list posting (sorry, I don't have the full original posting):
> MISTS are droplets of liquid suspended in air. They are spherical in > shape with a size ranging from a few micrometers to over one hundred > micrometers in size. Mists are generated by the splashing, bubbling, or > spraying of liquids. The fine droplets comprising the mist remain the > same as the original liquid from which they were generated. So a toxic, > irritating, or infectious liquid will produce a mist with similar > characteristics when it is aerosolized. > > FOGS are similar to mists. They differ in the way they are formed. > Mists are formed when some type of vigorous actions cause droplets of > liquid to be suspended in the air. Fog is formed when vapors of a solid > or liquid condense in the air to form suspended droplets. The droplets > in fog are usually one to ten micrometers in diameter, which is slightly > smaller than the average mist droplet.
I would like to add "smoke" to this list, and would be tempted to define it as particles or vapor in the air as a byproduct of combustion.
In order to decide what is best for you, you must first think about your requirements in various areas:
Well, in truth, "maybe". But you don't want false alarms, so you should assume that your fog will cause false fire alarms,
and then look for ways to prevent it.
The first step in guarding against false fire alarms is to find out exactly what kind of alarm
system you are dealing with.
There are numerous kinds, and they are often used in combination.
Here are some of the things you might run into:
They are designed to sniff the air for the byproducts of combustion, and are unlikely to
react to modern fogging technologies. They will react to pyrotechnic smokes and incense.
Since this detector is triggered by the fact that smoke is visible and capable of casting a shadow,
it will trigger on all visible fogs, smokes, mists, etc.
This would include temperature-driven devices like thermostats. It also includes fusible-link
systems, like the sprinklers that are triggered by melting a piece of plastic or metal.
These detectors won't be triggered by most fogging technology, with the possible
exception of pyrotechnic mixtures.
But I'll bet that a black light sets them off!
These detectors might be triggered by pyrotechnic smoke or incense.
Trade-offs:
We have a page on dry ice fog.
Trade-offs:
Industrial mist systems are used to surpress dust and odors, neutralize static electricity, and cool people and things.
They are particularly handy in places like chicken farms, because it isn't economical to air-condition a barnyard.
Systems like this tend to be expensive, because they require:
We have a page on ultrasonic misters.
Trade-offs:
Unfortunately, steam has several drawbacks:
If you use "hard water" in such a device, prolonged use will produce a coating of white dust over everything in the room.
In general, humidifiers put less water into the air, and might not even produce a visible effect.
My grandmother liked to put a pan of water over the heating duct in the winter, to add humidity.
Now, let's think about this - Haunts have a reputation {deserved or not} as fire-traps.
Haunters often have strained relationships with the local Fire Marshal.
And you are thinking for even a minute that it's a good idea to add burning stuff to your haunt,
when other technologies exist?
Incense is available in sticks, cones, bricks - all of which are capable of continued smouldering
once you have lit them and gotten them going. You can also get powdered and resin forms of
incense that won't continue burning on their own, and must be placed on a burning piece of charcoal.
I don't really like the idea of any real fire in a haunt, even a smouldering stick of incense.
This type of fog machine was the industry standard a couple of decades ago.
Then they discovered that it isn't a good idea to breathe hot oil vapors.
Some folks turned to compressed-air oil cracker,
but that wasn't much better.
Nowadays, everybody has switched over to glycol foggers, including the toy train makers.
Trade-offs:
There are serious safety concerns about breathing any sort of oil vapors, and haunters should probably
avoid this technology.
But, just for technical completeness, we have information on oil crackers.
Trade-offs:
The technology evolved from
heating oil-based fluids
to
compressed-air oil cracker
to compressed-air vaporization of glycol/water mixes.
The current products are a cross between the mechanical technology of
compressed-air oil crackers
and the fog fluid technology of
water-based (glycol) foggers.
They use high-pressure air to break up glycol/water fluid into a mist of fine droplets.
Also, check out
buying a water hazer.
Trade-offs:
What should I look for?
There are numerous ways to produce fog.
The one that works best depends on exactly what you want for an effect and the situation in which
it will be used.
One man's perfect fog is another man's wasted steam.
Once you have answered these questions, it's time to take a look at the fog technologies
and consider which one(s) best address your needs.
Will it set off the smoke alarms?
Probably.
Dry Ice
Dry ice is usually the first thing that everybody thinks of when you say "fake fog".
And that's wrong.
Dry ice fog is still used occasionally for theatrical productions, but is becoming rather rare.
It is expensive and a hassle. It does have some desirable characteristics, but usually just isn't worth it.
Water-based (glycol) fogger
Honestly, glycol fog is the way to go - cheap, easy, safe, and lots of fog!
And we have a whole page of information to help you with it!
Also, check out
buying a glycol fogger.
Pressurized Water Mist
The idea here is very simple: take purified water and spray it out of a tiny pinhole, at high pressure.
The result is a mist that is about as safe as you can get, with no artificial ingredients.
Ultrasonic Mister
Ultrasonic units use high levels of inaudiable sound to break up water into mist droplets.
This produces a fog effect.
Steam
Steam is wonderfully simple to make. Just boil some water.
The bargain-haunter can certainly find some cheap humidifiers and vaporizers at the thrift store or garage sales.
Humidifiers and Vaporizers
Unfortunately, the words "humidifier" and "vaporizer" cover a lot of ground.
They can mean almost anything:
Pyrotechnic smoke
There are various pyrotechnic products that burn to produce smoke. You can even get it in colors.
Incense
If you just need a little smoke, perhaps with a particular scent, you might burn incense.
Oil Vaporizer
The original oil foggers worked by heating oil until it vaporized, and spewing out the vapors.
Tiny versions of this fogger were built into toy trains, making steam engines that really smoke.
Oil Cracker Hazer
The oil cracker uses high-pressure air to break up oil into a mist of fine droplets.
These were once sold as a safer alternative to foggers that
heated up oil-based fluids.
Because of their decreased output, they were usually marketed as "hazers" rather than "foggers".
Water-based hazer
A "hazer" differs from a "fogger" in that the goal is a much lighter and thinner effect.
Hazers are often used in dance clubs and theatre in order to produce a visible beam effect
from lights.