Re: dancers and fog

Richard Grevers (
Wed, 3 Dec 1997 23:12:12 +1300

Here are the thoughts on a non-dancing technician on fog:

Firstly, there are an increasingly bewildering number of fog ("smoke")
preparations on the market. The notable trend is away from mineral oils
towards mixes that are
close to pure water.

All these mixes need different temperatures and pressures to work properly, so
It is VERY important to only use the recommended mixture for any brand of

I prefer to use the term "fog" for dry ice fog, the white stuff which rolls
close to the floor. Depending on the quality of the machine dispensing it,
this can be cold and clammy, or even warm and clammy if too much steam is
escaping, and can wet the floor. It is basically CO2, which is dangerous in
concentrations above 3%, the biggest danger being in low-lying areas where
the gas can collect, such as orchestra pits. Your supplier of dry ice should
be able to loan out a portable CO2 detector, which will sound an audible
alarm above 1.5%. We did a show where a fog plume was dropped into the
centre aisle amid the audience. Even mid-plume readings were safe, and only
one audience member showed any discomfort at the experience (a critic,
alas). CO2 fog is generally difficult to control as to volume and dissipates

The smoke you have most probably experienced is from the original "Academy
Award Winning" Rosco smoke juice, which was about the only choice until
10-12 years ago. In my opinion, it was irritating to some people, and it
smelt fairly strongly (hence the introduction of "apple", "rose" etc (even
worse!). It dissipates fast when used in small quantities, but tends to form
nice strongly-layered wisps of smoke when used in quantity. Being
mineral-oil based, an oily residue can settle on things after an extensive

Companies such as Jem introduced variations such as fast dissipating smoke
and long-persistance smoke (so nightclubs couls save money).

Many effects now come under the term "haze" - which I would define as a
persistent, even, degraded atmosphere in which light beams will show clearly
- typical of a rock concert. Sometimes on a frosty winter's night in
Christchurch, nature provides this free by way of smog!
A haze effect which should definitely be avoided for dance is an "oil
cracker" which works constantly and imperceptably to create a fine haze -
but leaves oil residue everywhere.

One machine which I have had excellent results with was a Le Maitre G300,
using a fluid of a type known as "c-beam" (mostly water, I think). The smoke
was odourless and totally non-choking, and the machine's output could vary
from maintaining a fine, sourceless mist to a major blast of smoke.

You can run into real fun trying to control smoke effects, and learn a lot
about fluid dynamics and thermodynamics. Air conditioning can be your bane
or your saviour (so long as its quiet). Unfortunately, the biggest variable
in the behaviour of air in a building is that large heat-source known as the
audience. I once had a situation where a smoke blast hung around beautifully
in a column of light on stage during dress rehearsal, but on opening night
swept around the light and engulfed the audience!

So, be prepared to shop around and experiment. hopefully most suppliers will
be happy to demonstrate their products for you.


Richard Grevers

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