By Carol Blake
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 will adhere.
Metallic Particulate: 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.
Carbonaceous particulate: 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: Paper dust and particulates can cause problems similar to the fibrous particulates. These particulates are attracted to magnetic fields.
Construction Particulates: 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.