Microcontamination in the Computer Room
Types of Contamination
By Carol Blake, Access Floor Systems, Inc., Abita Springs, LA
The more intricate and sensitive the equipment and situation, the higher the need is to control
contamination. Ultraclean manufacturing facilities are at the top of the list. In these clean rooms,
technology demands clean and uncontaminated air. Devices which measure the quality of the
airborne particulates (that is particles flying around the airflow) are routinely used for particulate
control. Ultraclean manufacturing facilities bring us semiconductors, advanced circuit designs,
and precision industrial instrumentation. Another critical area is a hospital operating room.
Contaminated particles entering an operating room while a patient is undergoing surgery can be
fatal, or can cause infections. The third sensitive area is one we are all familiar with...the computer room.
The physical environment surrounding an operating or stored computer plays an important role in
the long-term reliability of electronic equipment and peripherals. Computer rooms, office areas,
and industrial sites present environmental conditions that may affect the operation of your computer
equipment. It is our intent to provide you with an awareness of the environmental parameters
associated with contamination that may need to be controlled at your facility.
There are three types of airborne contamination:
Gaseous contamination can contribute to the degradation of numerous materials in computer
systems including both metallic and nonmetallic materials. Gases such as chlorine, hydrogen sulfide,
sulfur dioxide, ozone, and nitrogen dioxide are some of the common contaminants that corrode
electronic components and equipment, resulting in decreased system reliability.
Organic contamination refers to contamination from airborne organic compounds commonly referred
to as hydrocarbons. The largest source of airborne organic contamination is the incomplete combustion
of fossil fuels. In addition to combustion, oxidation of plastics, rubbers and elastomers is another
source of this form of contamination.
Particulate contamination or simply "dust" is a form of contamination that is frequently overlooked
in many computer facilities. Dust contamination exists in a variety of concentrations, size distribution,
and compositions. The characteristics of dust are very dependent upon the dust sources. It is very
common to find clothing fiber, dirt and construction materials in computer facilities.
Less common dust sources also exist. Natural events, such as volcanic eruptions and dust storms
are some of the largest dust producing events possible. These events introduce a variety of different
constituents into the atmosphere that usually remain airborne for considerable periods of time. In
addition to natural events, specific industries may generate their own particulate contamination.
Particulate contamination can have one or more of the following characteristics:
Abrasiveness - abrasive particulate may contribute to wear as well as fretting and fretting corrosion.
Hygroscopic - many particulate contamination compositions have an affinity for water and readily
absorb water vapor in the air. If sufficient water vapor is available, the particulate
can become wet with water at temperatures above the bulk room dew point.
Corrosive Composition - the elemental composition of a particulate contamination may be corrosive
to materials within the computer system.
We will identify the common types of particulates that contaminate the environment and offer some
suggestions for reducing and controlling contamination in your facility.
Synthetic Fibrous Particulate:
Common sources: Clothing; Other sources: Carpet fibers, Insulated drop in ceiling tiles
Because synthetics have a low melting point, they may create a sticky surface to which other particulates
Metal dust enters the data center environment from a variety of sources. Common
culprits include worn air conditioning parts, new raised floors, rotor brushes in vacuum cleaner monitors
and printer component wear. Another common culprit is the electrician, who might be hardwiring and
leave metal debris behind. Metallic particulates conduct electricity. Because they conduct electricity,
they have an increased potential for creating short circuits. They are also magnetically attracted to
circuits because of the magnetic fields generated by computer equipment. This particulate usually shows
up as rust.
Carbon comes from automobile exhaust, tobacco smoke, printer toners and carbon
paper dust. In addition to being conductive, carbon dust is also combustible. This type of particulate can
be disastrous as metallic particulates because humidity transforms the fibers into electrically conductive
elements which also act as carriers of other particulates.
Fibrous Organic Particulates:
These are natural based fibers such as cotton and wool. These fibers usually
originate from clothing, but also from incorrect cleaning materials or packaging materials. These fibers
absorb moisture and cause major problems with electronic circuits. Once a short circuit has been caused
it is almost impossible to detect the cause of failure because this particulate disintegrates from the heat
of the short.
Paper dust and particulates can cause problems similar to the fibrous particulates. These
particulates are attracted to magnetic fields.
These particulates originate from the improper sealing of the concrete subfloor, the
eventual erosion of the concrete, sand, plaster, sheetrock, brick and wax. Because these particulates are
so fine, they fall in the raised floor plenum and become airborne. They may be ejected through perforated
floor tiles into the atmosphere or into floor cooled computer hardware at speeds of 500 linear feet per minute.
These particulates are extremely abrasive.
Excessive particulate contamination within computer equipment can contribute to several problems, including
corrosion, wear, heat transfer and failure of electrical contacts.