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--- Forwarded mail from Zwaneveld Eddy <E.HA.ZWANEVELD at NFB-ONF.CA>
Our CF3000 MkVI has been online and in daily use for 6 months. Other than
that it has to run at the lowest speed, about 50% of the speed we used to
run at with CF-2 (tricholoethane) and which is very costly and hardly
available anymore, we are satisfied with it. We are also recovering our Perc
and that works well.
It is therefore quite academical as to whether one prefers trichloroethane.
However, it is preferable from the health and safety perspective.
Trichloroethane, also known as Methyl Chloroform has a Permissible Exposure
Level (PEL) for an 8-hour Time Weighted Average (TWA) of 350 parts per
million (ppm). Overexposure by inhalation could irritate the eyes, skin
contact can also be irritating and drying. It can have an effect on the
central nervous system (CNS) and cardiovascular system (CVS) and respiratory
tract, but it is considered one of the least toxic of the liquid chlorinated
hydrocarbons. It is not listed as a carcinogen. It contributes to the
depletion of the ozone layer, hence manufacturers and users are committed to
replace it with another cleaning agent, hence increased taxes and limited
availability. It has a boiling point of 165 degrees F ( 75 degrees C).
Perchloroethylene, also referred to as Perc, or tetrachloroethylene, which
is used by dry cleaners and textile processors, has been used for years in
wetgate immersion printing, because its refractive index of 1.50534 at 68
degrees F (20 degrees C) for light, matches that of the film, it
temporarily eliminates the reproducibility of filmbase scratches (while the
film remains wet and the scratch filled with the liquid). It has a boiling
point of 250 degrees F (121.2 degrees C), which explains it much slower
Its Permissible exposure Level (PEL) for an 8-hour Time Weighted Average
(TWA) of only 25 ppm, is much lower than of Trichloroethane. The US
National Institute for Occupational Health and Safety considers it a
Carcinogen, which is based on animal tests, human data is not yet available
in sufficient quantity, however the animal evidence make it justifyable to
assume it to be carcinogenic to humans as well. Percholoethylene is stored
in the fatty tissue and slowly metabolized with the loss of chlorine. It has
its greatest impact on the central nervous system (CNS), and its symptoms
range from lightheadedness and slight inebriation to unconsciousness. Liver
damage is possible after severe acute or minor long-term exposure.
This means that doors to the cleaning equipment must be kept closed until
air saturated with perchloethylene (or trichloroethane) has been evacuated.
This depends on the efficiency of the local exhaust. It can be measured with
a Draeger Air Sampling pump, using a glass indicator test tube for perc or
tricholoethane. Exhaust systems have been known to fail, overexposing
employees, so ongoing vigilance is required.
For these reasons, perchloroethylene as a film or (dry)cleaning agent is
transitional and temporary, until a suitable agent is found which meets all
the film cleaning and human interface criteria, without causing the users to
lose their shirts.
Ed H. Zwaneveld
National Film Board of Canada
e-mail: e.ha.zwaneveld at nfb-onf.ca
--- End of forwarded message from Zwaneveld Eddy <E.HA.ZWANEVELD at NFB-ONF.CA>
Rob Lingelbach | 2660 Hollyridge Dr., Los Angeles, CA 90068
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