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\technote{$\ihat$}{Dan Ports}{2004/05/16}{drkp@mit.edu}
\tntitle{Safety Issues for Glycol/Glycerol Water-Based Atmospheric Effects}


\section{Overview}
\label{sec:overview}

Atmospheric effects --- fog, haze, and smoke --- are commonly used in
the theater. Various different mechanisms are currently used to
achieve them. Among the most common and least expensive are those that
create fog using a water-based fluid containing glycols or glycerol.
Much has been said about their safety, and there are still no shortage
of controversies. This note provides a brief overview of some of the
issues related to safely using atmospheric effects. Overwhelmingly,
they are quite safe. There are, however, a few issues related to
irritation caused by the fog.


This report discusses glycol/glycerol water-based foggers: foggers
that create a smoke-like effect by heating and vaporizing a
water-based fog fluid containing glycols or glycerols, producing an
opaque aerosol when mixed with the surrounding air. These are some of
the most common --- and most studied --- foggers in use today. The
resulting effect is generally a rising smoke, though they can be used
to create low-lying fogs by using chiller units to chill the output.

\nocite{rosco-fog-tn}


\section{Ingestion and Inhalation Toxicity}
\label{sec:toxicity}


The chemicals used in the fog fluids are not toxic. Despite some
claims to the contrary, they are not carcinogenic and they do not
cause asthma. Indeed, they can be safely ingested in fairly large
quantities: drinking 30 milliliters of glycerol three times a day for
fifty days has been proven harmless to healthy individuals, and
drinking 1 to 1.5 grams of propylene glycol per kilogram of body
weight is a safe dose for medical uses (it is sometimes used to reduce
interocular pressure) \cite{ruling-stagecraft}. This is far more than
is ingested in normal use, and since most of us are not in the habit
of drinking bottles of fog fluid\footnote{And dare I say that if you
  are, you have more problems than this tech note is going to be able
  to solve?}, there is little danger of toxicity from ingestion.


There are similarly few problems with inhalation. The Actors' Equity
Association, which if anything has a conservative bias towards
allowable limits, sets forth a recommended level limiting an actor's
exposure to 40 milligrams per cubic
meter. \cite{equity-guidelines}. This is a heavy level; Ruling notes
that glycol levels on Broadway stages have consistently been measured
at less than 10 $\nicefrac{\textrm{mg}}{\textrm{m}^3}$
\cite{ruling-stagecraft}. The Equity report provides a summary of how
long it takes for the glycol levels from various fog machines to drop
below the recommended level; at three feet from the largest fog
machines, the time is less than 230 seconds, and considerably less at
greater distances \cite{equity-guidelines}. It does not provide
an analogous guideline for glycerol levels, but a similar limit would
still allow for extensive use of smoke --- indeed, the confusion from
the dense cloud of smoke might become a danger before toxicity from
the smoke itself would.


\section{Irritation Effects}
\label{sec:irritation}

One valid concern, however, is that both glycols and glycerols have a
throat-drying effect. The Cohen Group report to ESTA notes that ``the
chemical nature of glycols is such that prolonged or repeated contact
with a glycol mist is likely to dry out moist tissues (i.e., the
mucous membranes of the upper respiratory track and, possibly, the
eye)'' \cite{cohen-group}. The extent to which this takes place is
where controversy lies. In particular, it is a concern for singers,
especially opera singers, for whom a dry throat can be especially
problematic. It has unquestionably been reported that performers have
complained about throat irritation due to fog \cite{ubc-report}. This
effect may also have a psychological component in addition to a
physiological one. 

There are some ways to, if not eliminate, at least minimize these
effects. Here are some suggestions:

\begin{itemize}
\item The obvious first suggestion is to minimize the amount of
  atmospheric effects used in the production. This calls for asking
  ``is fog really necessary here?'' Of course, it does no good to
  simply suggest eliminating fog in all cases, but it may be helpful
  to limit the amount of fog used at certain times.
\item The Equity report sets for time-and-distance guidelines as to
  how long the fog should be allowed to dissipate before an actor is
  required to come within a certain distance of the fogger. These
  should be followed.
\item It may be possible to use a less-concentrated fog fluid,
  containing less glycol or glycerol. This can be accomplished by
  watering down the fluid, though this typically violates the
  manufacturer's recommendations (the glycols also serve as a
  lubricant for the pump). Sometimes, however, ``light haze'' fluids
  are available. They tend to dissipate faster --- this may even be a
  more desirable effect.
\item Since the effects may be partially psychological, it may help to
  inform the performers that fog is being used, how it is being used,
  the reason it is called for, and the safety information for
  it. (This is not a bad thing to do even if they aren't
  complaining!)
\end{itemize}


\section{Other concerns}
\label{sec:other-concerns}

Water-based foggers do generally contain a heating element. This
should not be a hazard, however, since it is enclosed within the
fogger.

Though it is not directly a safety issue and we do not address it in
detail, we must at least mention that glycol foggers, like all other
atmospheric effects, can trigger certain types of smoke
detectors. Those that detect particulate matter in the air can be
affected; rate-of-heat-rise detectors are unaffected. If atmospheric
effects are being used in a space that has particulate detectors,
these detectors may need to be disabled for the duration of the show
in order to avoid triggering the alarms. This needs to be authorized
by and coordinated with the Authority Having Jurisdiction.


\nocite{hse-report}
\nocite{stagecraft}
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