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Submicron particulates are much more dangerous to sensitive computer hardware,
because they remain airborne for a much longer period of time, and they are more
apt to bypass filters.
Operator Activity
Human movement within the computer space is probably the single greatest source
of contamination in an otherwise clean computer room. Normal movement can
dislodge tissue fragments, such as dander or hair, or fabric fibers from clothing. The
opening and closing of drawers or hardware panels or any metal-on-metal activity
can produce metal filings. Simply walking across the floor can agitate settled
contamination making it airborne and potentially dangerous.
Hardware Movement
Hardware installation or reconfiguration involves a great deal of subfloor activity,
and settled contaminants can very easily be disturbed, forcing them to become
airborne in the supply air stream to the room's hardware. This is particularly
dangerous if the subfloor deck is unsealed. Unsealed concrete sheds fine dust
particles into the airstream, and is susceptible to efflorescence -- mineral salts brought
to the surface of the deck through evaporation or hydrostatic pressure.
Outside Air
Inadequately filtered air from outside the controlled environment can introduce
innumerable contaminants. Post-filtration contamination in duct work can be
dislodged by air flow, and introduced into the hardware environment. This is
particularly important in a downward-flow air conditioning system in which the sub-
floor void is used as a supply air duct. If the structural deck is contaminated, or if the
concrete slab is not sealed, fine particulate matter (such as concrete dust or
efflorescence) can be carried directly to the room's hardware.
Stored Items
Storage and handling of unused hardware or supplies can also be a source of
contamination. Corrugated cardboard boxes or wooden skids shed fibers when
moved or handled. Stored items are not only contamination sources; their handling in
the computer room controlled areas can agitate settled contamination already in the
room.
Outside Influences
A negatively pressurized environment can allow contaminants from adjoining office
areas or the exterior of the building to infiltrate the computer room environment
through gaps in the doors or penetrations in the walls. Ammonia and phosphates are
often associated with agricultural processes, and numerous chemical agents can be
produced in manufacturing areas. If such industries are present in the vicinity of the
data center facility, chemical filtration may be necessary. Potential impact from
automobile emissions, dusts from local quarries or masonry fabrication facilities or
sea mists should also be assessed if relevant.
December 2012
Contaminant Properties and Sources
Controlling Contaminants 91
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