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Subject: Fire extinguishers

Fire extinguishers

From: Michael Trinkley <chicora1>
Date: Wednesday, May 27, 1998
Recently there have been a few posts regarding extinguisher
clean-up. Perhaps I missed some replies, but I didn't notice any
detailed information regarding clean-up. There are, as Donia Conn,
mentions two generic "types" of dry chemical extinguishers. One is a
multipurpose, suitable for Class A, B, and C fires. The other may be
called "ordinary dry chemical" and is suitable for Class B, and C
fires.

An example of an "ordinary dry chemical" is Ansul's Plus-Fifty C,
which is a mixture of talc (less than 5%), magnesium silicate (less
than 4%), sodium bicarbonate (around 90%), methyl hydrogen
polysiloxane and a blue pigment (hostaperm blue) which together
account for less than 1%. As you might imagine, it is mildly
alkaline and can be corrosive to surfaces that are affected by
alkaline residue. The average size of the particles is about 20
microns.

An example of a multipurpose chemical is Ansul's Foray product,
which is a mixture of magnesium aluminum silicate (5 to 7%), calcium
carbonate (less than 2%), monoammonium phosphate (65 to 82%),
ammonium sulfate (12 to 22%), methyl hydrogen polysiloxane (less
than 1%) and yellow pigment (less than 0.5%). This product is
slightly acidic in the presence of moisture. In addition, when
heated, it becomes slightly gummy, adhering to heated materials.
Again, the average particle size is about 20 microns.

While it is certainly good to be concerned about clean-up issues, it
is important to realize that the clean-up will depend on the
circumstances of the release. There are any number of factors
involved, not the least of which being what was on fire and the
experience of the individual using the extinguisher. There is good
evidence that an experienced user can fight larger fires more
successfully with an extinguisher than can an inexperienced user.
There are lots of reasons for this, but one is that inexperienced
users tend to aim high--at the flames, not at the base of the fire.
>From personal experience, aiming high will dramatically spread the
extinguishing agent, causing more wide-spread contamination and more
problems in clean-up.

In addition, clean-up will be affected by whether the power stays
dry (making cleaning easier) or whether it is mixed with water
(increasing the potential for corrosion). To some degree the
presence of water will be affected by the success of the initial
attack by a portable extinguisher (if the effort was successful it
is less likely that either sprinkler heads will go off or that the
fire department will use hand lines).

Clean-up is also affected by exactly what was contaminated--an
office, a trash can next to a desk with a computer, or a box of
papers next to a fully loaded book truck. On the other hand, since
many institutions (at least in my little part of the world) don't
have sprinklers,  the choice may at times come down to cleaning up a
small amount of chemical or cleaning up massive amounts of water.
True, we know how to deal with water recovery, but chances are that
it will affect a far larger proportion of the collections than one,
or two, extinguishers.

At any rate, most manufactures, such as Ansul, do have technical
bulletins describing clean-up operations. Granted, they aren't
designed for museums, libraries, or archives, but they do offer a
starting point. For example, Ansul recommends the use of a HEPA vac
to collect dry power. Afterwards residual amounts, which I wouldn't
think would be large, can be wiped up with a damp cloth. Probably a
more appropriate choice for special collections might be something
like a dry Dust Bunny. The Ansul literature also notes that the
silicone in the power, a mixture of isopropanol and water can be
used, although I wonder if this is more likely to be necessary if
there has been heat? They also offer methods for neutralizing the
acid or base, then recommend washing, and blow drying. Of course
this isn't necessarily appropriate for collections, but again--it
does provide a jumping off place since all clean-ups are going to be
different.

In terms of carbon dioxide extinguishers I think it is important to
note that they are *not* rated for Class A (ordinary combustibles)
fires. Even the typically largest used in most institutions (the
so-called 20 pound extinguisher) is rated only 10B:C. This means
that these extinguishers will not "meet code" requirements for the
placement of extinguishers for Class A fires--the type that most
institutions are likely to experience.

A typical extinguisher of this type, fully charged, will weigh about
55 pounds. In contrast, a multipurpose extinguisher, with a rating
of 2A:10B:C will weigh less than 9 pounds fully charged. From a
simple ease of use perspective (especially with so few institutions
taking the responsibility to train staff), dry chemical
extinguishers are perhaps preferable.

There is also the issue of thermal shock, if the carbon dioxide is
sprayed (as a gas or snow cloud) directly on the collection. In
addition, the carbon dioxide is stored under high pressure--upwards
of 800 psi--and that force upon release can cause dramatic movement
of collections.

The point here is that while there is a place for carbon dioxide
extinguishers, that place really ought to be evaluated on a
case-by-case basis and we should resist sweeping generalizations
concerning their appropriateness or inappropriateness.

Michael Trinkley, Ph.D.
Director
Chicora Foundation, Inc.
PO Box 8664
Columbia, SC  29202
803-787-6910

                                  ***
                  Conservation DistList Instance 11:96
                   Distributed: Friday, May 29, 1998
                       Message Id: cdl-11-96-011
                                  ***
Received on Wednesday, 27 May, 1998

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