From: bernstei@romeo.cs.colorado.edu (Michael Bernstein)
Subject: Re: Smoke/fog machines...
Organization: University of Colorado at Boulder
Date: Tue, 13 Oct 1992 22:27:41 GMT

In article <DRAKE.92Oct12143722@dragon.cpe.ulowell.edu> drake@dragon.cpe.ulowell.edu (Frank Drake) writes:
>[I could not find a FAQ and don't know where else on the net to ask this,
> so here goes...]
>
>I've gotten myself involved in creating a haunted house for halloween (to
>benefit a charity). We would like to have a fog or smoke effect in
>several of the areas. Those involved have little or no experience with
>this. More importantly, the haunted house is being created in a 160 year-
>old inn and we do not want to use anything that will leave any kind of
>residue.
>
>We have several applications, some of which will require more control of
>the fog, but others would be as simple as leaving a pail of dry ice in
>the corner.
>
>I am looking for information about:
>	1. Potential problems using dry ice;
>	2. Other methods of creating fog or smoke.
>
>It could very will be that the answer is "You can't safely do this - you
>run the risk of damaging the house". That's OK. I just want to know
>what our options are.

Here's my little packaged discourse on foggers:

FOGGERS

DRY ICE

Dry ice foggers work by immersing dry ice (frozen carbon dioxide) in hot
water.  The CO2 sublimates rapidly, carrying with it tiny droplets of water
(water vapor) -- that's the visible part.  The hotter the water, and the
smaller the flakes of dry ice, the faster it goes (with correspondingly
greater volume of vapor.)  The vapor you see falling off dry ice is of
the same sort, condensed from the surrounding air, but without the big
thermal mass of water to heat it, or provide water for vapor, you don't
get as much volume.

Here's the typical design I have seen for theatrical use:  Take a 55-gallon
drum (still waterproof on at least one end).  Build a heater coil into the
bottom.  Most people use water-heater elements.  It's more convenient and
safer if the heater(s) are switchable.  Modify the top so it can be clamped
down; a good fogger will generate a lot of pressure as the dry ice rapidly
sublimates.  Build a bail into the middle of the drum so that you can lower
and raise the cakes of dry ice in and out of the hot water as needed -- this 
will allow some control over the volume of fog, albeit a very sloppy sort.
Finally, build a port or nozzle into the top of the drum (generally, where
a household clothes drier hose may be attached, so you can direct the fog 
elsewhere).  I've seen some foggers with fans built in the top, to move the
mist faster when necessary.

You can also just fill a pan with hot water and throw cakes, chunks, or
shards of dry ice in it.  The effect is not as impressive, but will 
suffice in limited circumstances.

DRY ICE, ADVANTAGES:

You can generally build the fogger for about $50-$150.  Dry ice is cheap.
It tends to lie along the floor.  The only residue it will leave is water.

DRY ICE, DISADVANTAGES:

** It's dangerous ** : NEVER USE DRY ICE FOGGERS IN UNVENTILATED, ENCLOSED
SPACES..especially if you have actors "hiding" in a pit or other low spot.  
The vapor will fall to the ground, and the CO2 will (being heavier) push the
air (and thus, the oxygen) out, and your actors will suffocate.  

It generally takes two or more hours to heat 20-30 gallons of water to a 
good working temperature.  You have to find a place to put a 55 gallon
drum, and a means to fill it and mop up any spills.  Your floor has to
be strong enough to support the water's weight.

You have to buy the dry ice regularly, and store it in a freezer or cooler.
It doesn't last that long.  It's hard to handle (don't touch it with your
bare hands, you can lose skin!).

CHEMICAL FOG 

I've seen two sorts: "stove top" and the sort generated by an actual fogger.
The stove top fog is just that -- you put a pan on a heating element, and
in the pan goes a chemical that turns into fog when heated.  I've seen
rock and roll companies do this; the fog was to make the light beams
visible and was rather thin.  I don't know any more about that.

Of the other sort, I've only used Rosco's.  Rosco's list for $469 for the
model 1000, their bottom-of-the-line version; American DJ's best sells for
$349 list, but I know them only on dealer recommendation.  (All price quotes
are for October 1992.)

Rosco's fogger works by piping a thin stream of non-toxic viscous "fog juice"
past a heating element.  The juice vaporizes, producing a white fog that
tends to rise.  You can cool the fog to make it hug the ground by running it
through a hose (drier hose, as mentioned above) that passes through an
ice-packed cooler.  The mist, according to Rosco, is completely safe to
breathe, although professional singers will doubtless be very suspicious of
it.  It comes in a variety of scents, including strawberry and coconut.

CHEMICAL FOG, ADVANTAGES:

It's absolutely safe, except for the very tip of the fogger, which can burn
anyone who runs into it in the dark.  You can generate fog very precisely,
on demand.  Preheat time is only about 10 minutes, and the foggers themselves
are pretty compact (c. 40cm x 15cm x 15cm) and don't require that much power.

CHEMICAL FOG, DISADVANTAGES:

The foggers themselves are expensive (see above).  I haven't priced fog 
juice, but I imagine that the cost per volume of dense mist is comparable 
for the same amount of dry ice.  If you use a lot of fog, an oily residue 
will build up on the surfaces with which it most often comes in contact 
(I've poured puddles of the stuff out of a hose we used to direct the fog).  
It doesn't seem to be much trouble to clean up from non-porous surfaces, but 
I imagine you'd have to shampoo a carpet after a heavy fogging.  Some actors 
and singers believe their voices are affected by the fog (not so, according to
Rosco. Dancers seem to have no problem with the stuff).

Michael Bernstein

bernstei@cs.colorado.edu / Student, SysAdmin, Actor, Stagehand, Designer
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