|
|
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
<< Lancair Builders' Mail List >>
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
>>
Methylene chloride is the most recent focus of attention from EPA and
OSHA, and as with most chemicals that are the days focus, some
misinformation gets mixed with the good information.
MC for years (until a couple of years ago) was the favorite carrier for
household items like hair spray. The 'glue' was dissolved in the MC,
the MC flashed off in the air between the spray tip and your wife's'
head, and the 'glue' continued on its trajectory. So for years it has
been discharged in your own house. Statistically, women outlive men.
MC is also used in some processes to remove the caffeine from coffee
beans. The caffeine dissolves in the MC and is carried away. The
reason why it can be used for consumable is because it leaves virtually
no residual material behind it. That's why it is good for cleaning
areas that you want to lay-up with glass. That's' also why I wouldn't
use the MC as purchased from places like Home Depot that has a lot of
other solvents added that do not have the same low 104 F boiling point
and completely evaporate quickly. The main reason for adding other
solvents is to lower the total rate of volatilization and make it easier
to meet the threshold level. For industrial use, the parts per million
(ppm) level is 25.
There have been comments about acetone being safer. It is and it isn't,
even apart from the flammability issue. Both acetone and MC readily
penetrate skin, and are great fat dissolvers, dissolving the layer of
fat under the skin. (don't recommend it for the spare tire about the
belt line) As far as I am concerned, the main hazard with both of these
solvents is the question of what they are carrying into my body as they
penetrate the skin. After all, we are using it to clean up epoxy, vinyl
ester or polyester resin. These non volatile products are dissolved in
the solvent, carried into sub skin levels, the solvent does evaporate
out, and leaves the rest behind. That's where the gloves serve their
purpose. There was a comment about butyl rubber gloves being used, but
as far as I know the only glove material suitable for MC barrier is made
from PVA. They generally are red in color, and rather clumsy to work
with. And they can be attacked and be penetrated by water!. Most
safety supply houses will have these available.
I have used MC and acetone for 20 years, with many of those years
without today's recommended protective gear. Through carelessness I
once had an acetone fire caused by the arcing of the brushes on an
electric drill too close to a split drum of cleanup acetone. Having
your shirt and hair catch on fire in an instant does generate a certain
level of terror, and creates an appreciation of MC. However, smokers
need to be careful when smoking around MC. When the vapors of MC are
drawn through the cigarette when taking a 'drag', the heat will modify
the methylene chloride vapor so that when this gas hits the moisture of
the lung, it forms an acid. I think its hydrochloric acid. I believe
this is the same as the mustard gas used in WW1, someone could probably
correct me if I'm wrong. I have had a both MC and acetone splashed in
my eyes several times. Your eyes will sting a lot, but the best thing
to do is to keep them as open as possible. The rapid evaporation rate
of both solvents means that they wont be around long enough to do long
term damage. Of course, flush your eyes asap with clean water as well
to help relieve the soreness.
A relatively new product that I find works well is actually a blend
called 'methyleze'. Part of the MC is replaced with another solvent
(about 20% I think) that has a very high ppm threshold level. The
boiling point is similar to MC. The combined product has an advertised
ppm threshold level of 200 ppm, compared with 25 for MC. The cost is
about twice that of straight MC. On a relative basis, we pay about
$0.42 per pound for MC (55 gal quantities) and the Methyleze is about
$0.90 per lb, drum quantities.
The company is called-
Chemisphere
2101 Clifton Ave
St Louis, MO 63139
tel 314 644 1300
fax 314 644 7194
The following sites provide additional information.
http://193.51.164.11/htdocs/monographs/Suppl7/Dichloromethane.html
http://www.epa.gov/ttnuatw1/hlthef/methylen.html
Regards,
Gary Rodgers
|
|