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Subject: Flammable film Dehumidification

Flammable film Dehumidification

From: Doug Nishimura <dwnpph>
Date: Sunday, March 22, 1992
Walter:  As usual I'm behind in my readings (by months) but here are
some reverent and irreverent (possibly too irreverent) comments about
the burning of Plus-X and the reduction in humidity from air filters.

In my experience and talking with people such as Michael Hager, it seems
that sometimes the film burn test is not entirely reliable.  It may,
however, just be a matter of our expectations being wrong.

Although the test described in ANSI PH1.25-1984 is a little more
elaborate, it roughly says to cut a piece of film 35mm wide and 40 mm
long.  Mark two points, each 5mm from an end of the film.  Hang the film
vertically and light it.  If elapsed time from the moment the flame
reaches the first mark to the time it reaches the second mark is less
than 45 seconds for films 0.08mm thick or more or less than 30 seconds
for films less than 0.08 mm thick, then it fails the test.  A smaller
burn test is described as a field test using a piece of film 35mm long
and 16mm wide.  The film is folded into a "V" along its length such that
it will stand freely (35mm high).  It is then ignited from a top corner.
"If the film sample ignites with difficulty and burns only partially, or
if it burns completely in a time not under 15 seconds, compliance with
this standard and classification as safety film may be considered
probable." (Safety film must also take more than 10 minutes to ignite
when put in an oven at 300 C (572 F).)  (NOTE THAT ANSI PH1.25-1884 IS

It is therefore possible that safety film may burn downwards and
completely consume the film and still be considered safety film.  I
prefer to use the diphenylamine test, although it also has a number of
problems (including a positive response to the subbing layer in safety
film.)  The trick to using the DPA test is knowing how known samples of
safety and nitrate film behave. Film also must be reasonably clean since
even some dusts and dirt will produce a very strong positive test.

As for the mysterious drop in humidity with an air purifier, Ellen
McCrady is entirely correct, a filter won't remove water from the air
unless it is finer than about 3.2 angstroms (roughly 3/10,000 of a
micron) in diameter.  There are only seven possible ways that the
humidity in the air may drop:

1) The dry bulb temperature in the room increases.

2) Water is physically removed from the room as a gas, liquid or solid.

3) Water is absorbed or adsorbed onto or into something (silica gel,
molecular sieves, sulfuric acid, etc.)

4) Water is chemically converted (such as in a hydrolysis reaction.)

5) Water is converted by nuclear transmutation  (does your collection
have high neutron, alpha or beta emissions?) :-)

6) Statistical localization of water particles in the room.  (All water
moves away from your detector following a statistical version of Fick's
law et al.) :^)

7) Most of water in the room is made from virtual particles.  (Quantum
laws allow certain particles to appear out of nothing and to exist as
long as the rest of the universe doesn't know that they're there.) :^)

Since the last three possibilities are not very likely, then one of the
remaining five possibilities must be true.   Given time, if the water is
chemically converted, absorbed or adsorbed, then eventually this air
purifier must lose its ability to lower the humidity.

Radioactive tagging of all the water in the room would be the fastest
and easiest way to solve the mystery (although not necessarily the
safest way. :-) )


                  Conservation DistList Instance 5:46
                  Distributed: Tuesday, March 31, 1992
                        Message Id: cdl-5-46-002
Received on Sunday, 22 March, 1992

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