Volume 6, Number 2, May 1984, pp.5-6
The San Diego Historical Society recently tested its newly installed Halon fire extinguishing system and I thought the results of that test might be of interest to WAAC members. Halon gas has many advantages over water or carbon dioxide systems. It is odorless, tasteless, colorless, leaves no residue, is electrically nonconductive, is non-toxic and completely harmless to humans. It is, however, quite expensive, and an accidental "dump" could cost thousands of dollars depending on the volume of space protected.
The space covered by our system includes the historical photograph, library and manuscript, and the curatorial departments. We were able to divide this space into four separate halon zones, each with its own gas tanks and independent alarm system. In this way, should there be an accidental dump in one zone, the entire supply of gas would not be expelled.
Before approving the system, the Fire Department requires that a test be made. In order for the gas to maintain an effective level after its expulsion, all doors must have been fitted with gasket seals to avoid seepage outside the area and, for the same reason, air handling systems should be equipped with automatic shut-off valves. Freon, which is relatively inexpensive, was used as a test gas. The test zone remained sealed while the gas level was monitored for ten minutes before approval was given. Since Freon is not safe for humans, staff members watched the test through viewing lab windows and closed circuit television.
The major problem with Halon is that, to be effective, all of the gas must be expelled in ten seconds. If any lightweight objects, papers, etc. are placed on shelves or tables near the nozzles, they will be blown off by the extremely high velocities created by the gas shooting from the tanks. To minimize this potential hazard, we installed pegboard sheets at the ends of shelving units near the nozzles in order to allow penetration, but deflect the blast. Ceiling panels must be secured or they will be blown out. The initial blast will also discharge anything remaining in the pipes from manufacture or installation. Be prepared for a dirty, oily mess! Fortunately, once the system has been tested, the pipes should remain clean.
Because the gas comes out in a fog and causes a temperature drop of 10°. or more, moisture condensed on the pipes and nozzles causing them to drip. In areas where there are ceiling tiles this is not a concern, but a problem did arise in the open storage rooms where rain from exposed pipes made it necessary to move some items. In one area it actually started snowing.
Considering the disastrous effects of water on collections and carbon dioxide on humans, Halon is an excellent alternative. When compared with loss or damage to collections (and staff), the cost is justified. Keeping the velocity and condensation problems in mind, potential tragedies can be avoided.Bruce Kamerling
Timestamp: Thursday, 11-Dec-2008 13:02:26 PST
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