Smoke and fog was: Conductive Dirt

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

To keep it TC related, since we are coming to Halloween season and folks
will be operating their coils near fog and smoke generators...

Here's a rundown on fog and smoke generating techniques you're likely to
encounter

First off, to make good looking smoke or fog, you want particles that are
around 1-10 microns in diameter.  Bigger and they settle out too fast,
smaller and they don't scatter enough light.


Dry Ice/LN2  - water fog, cold, sits next to the ground, evaporates
eventually, gotta keep pumping it in because the little droplets evaporate.
 Watch out for suffocation hazard in low lying areas, esp with Dry Ice
(several reported fatalities in theaters from this, where a stagehand was
in a trap under the stage, for instance).  If you keep the coil warm, then
this won't present much of a problem, because the droplets settle out, and
if they do, they evaporate off.

Glycol foggers - inexpensive fog/smoke machines that take a "fog juice".
They basically boil the fog juice and spray it at high pressure out into
the air, where it condenses and forms "steam".  The fog juice is a blend of
water and one or more glycols, propylene and tri-ethylene are popular
(glycerine/glycerol is used sometimes, but it's expensive, and the others
work better anyway).  The mixture (an azeotrope, normally) has a boiling
point somewhat higher than water (depending on the mix).  Very nice dense
fog, and if you run it through a chiller, it will sit on the ground like
CO2 or LN2 fog.  The spray into the air approach generates droplets with
non-uniform size, so the big heavy ones settle out rapidly, and the little
tiny ones evaporate into vapor almost instantly, leaving a fair number of
the ones in the right size range.  As the particles evaporate, they
disappear (visually), so you keep needing to squirt more fog/smoke to keep
the desired haze level.  However, the !
 glycol is
still there, in the room air, as a gas.  In a room with limited ventilation
(usually the case, because adding ventilation means that you need more fog,
and fog is expensive) the glycol vapor level can get pretty high by the end
of the evening.  Also, cold surfaces can cause the glycol to condense out,
likewise with wet surfaces.

The problem is that glycols have a distinct taste (sort of sweetish) and
they gas form also rapidly absorbs into water (one big commercial
application for glycols is as a drying agent).  Since your mouth and tongue
are wet, when you breathe, the glycol absorbs into your saliva, and you
taste the glycol.  A bit of experience and you can walk into a facility
that is fogged in and you can actually identify which glycol (if any) they
are using.

Mineral Oil foggers - these work by creating a very fine (1-10 micron) mist
of mineral oil particles.  The oil doesn't evaporate, but eventually, it
does settle out on the walls floors and furniture. (It looks like dust, but
if you look with a microscope, you'll see little spherical particles of
oil). There are 3 basic ways to make the fine mist.  The oldest way is with
heat.  You run oil onto a hot surface and some of it dissociates, and the
rest boils and then recondenses.  That smoking car in front of you with the
oil leak is a good example. This is the best way if you want to make huge
amounts of smoke (they have nifty devices that are a scaled down pulse jet
as a heater/blower that blow out copious amounts... insecticide foggers
work on this principle.. you mix some insecticide in the oil, and the
fogger blasts it out as a fine particulate smoke)  Really, really
unhealthy, though... that boiling/dissociating process is guaranteed to
create all sorts of evil substances.

Another approach is called (generically) a cracker barrel, where you have
an air jet in a tank of oil, and the frothing and spraying makes lots of
oil particles of various sizes.  The biggest ones fall back in, and the
rest billow out.  The problem here is that it's somewhat inefficient and
you get a lot of bigger particles which creates a real oily mess.

Finally, the professional mineral oil gear uses a specially designed
atomizing nozzle to generate a mist of fairly uniform particles and then
runs it through a filter to remove the larger ones (recirculating the oil
trapped by the filter).  A typical fogger uses about 5-15 ml of oil per
hour, and will fog a 50x50x50 foot room to 10 mg/m^3 (enough to be visibly
hazy and a beam of light easily visible).  The halflife of the fog is about
4 hours, depending on how many surfaces there are for particles to settle
out on. The 50x50x50 room has about 15000 square feet of surface, but
typically, there's about twice that surface area, given that there's
something in the room.  This is what the big rock and roll shows use to
make the light beams visible.

You can create a dense fog that you can't see through, but it takes a while
to get that density, and the oil content will be fairly high (i.e. surfaces
will get oily).  Some laser tag places use oil foggers.  The real problem
is getting rid of the oil fog, because conventional air filters don't stop
the particles, and your HVAC system will spread the fog everywhere.

(There are fog in a spray can forms of this, but they are very expensive...
they rely on a suitable solvent/propellant (isobutane, isopropane, etc.)
that can be used to spray big particles with solvent that rapidly
evaporates to make small particles (like spray paint).

And last, but not least, there is straight water mist fog.  The best
example is the very high pressure nozzles and equipment made by MEE, Inc.
They pressurize the water to 1000-3000 psi, then shoot it out very tiny
carbide nozzles to impinge on a sharpened wire point, where the water
"shatters" into tiny (1-10 micron) particles, forming a very realistic
mist.(realistic, nothing, it IS mist).  The fog in the Disney "Pirates of
the Caribbean" ride, where you go through the pirate ships, is an example
of MEE fog.   There are also ultrasonic foggers that do the same, and for
less performance, the "Arizona Mist" type water spray coolers.  Basic rule:
higher pressure, finer mist, better "look".  Even the cheap mister nozzles
do a lot better when run at 200 psi than at the nominal 30-50 psi from the
garden tap.  (Better use something other than cheap vinyl tubing though!)

To recap the health effects from worst to best:

Heat based oil smokers (Igeba, Navy fogger, etc.) - horrid - carcinogens, etc.

Glycol based - If in good repair, glycol itself isn't particularly toxic,
but it's dehydrating effect will dry your skin and air passages (singers
hate glycol foggers..).  If the fogger gets too hot, toxic breakdown
products (good foggers have overtemp cutouts).

Atomized oil - virtually no health effects (providing the oil is clean...
if it's ratty old cutting oil with all sorts of stuff in it, you're in
trouble.. most commercial foggers using oil use USP white mineral oil (for
what it's worth, in ton lots it runs about $2-3/gallon)

Water mist - the safest (bear in mind asphyxiation hazard if you use LN2 or
Dry Ice).. in long duration installations water mist systems have a problem
with Legionnaire's disease, by the way.




Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<PsychoticMinds1-at-aol-dot-com>
> 
> The residue that is left is glierol or glyserin (spelling?)  its used as a
> laxative and was talked about on the list as a possible dielectric but scince
> its organic has a very low dielectric strenght the "Fog juice" used in fog
> machines is part water and part glyserin the heated fog is then passed
threw a
> cooler which causes it to fall to the ground.  So i can see how it
casuied your
> coil to short.  Just my 2 cents
> 
> 
>      Frank guido