Contaminant Types and Sources

Contaminant Types and Sources

There are two criteria for a substance to be considered a contaminant in relation to a data center environment:

• It must be potentially damaging to hardware or people.

• It must be able to migrate to areas where it can cause damage.

Contaminants that affect people and equipment are typically airborne , so, obviously, it is important to limit the amount of potential contaminants that cycle through the data center air supply to prolong the life of all electronic devices. Potential contaminants can also be settled, making them harder to measure. Care must be taken that these aren't agitated by people or mechanical processes.

Measures should be taken to prevent air contaminants such as metal particles, atmospheric dust, solvent vapors, corrosive gasses, soot, airborne fibers, or salts from entering, or being generated within, the data center. Airborne particulate levels should be maintained within the limits of Federal Standard 209e, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones, Class 100,000. This standard defines air quality classes for clean zones based on airborne particulate considerations. Class 100,000 is generally accepted as appropriate for data center environments. In the absence of hardware exposure limits, applicable human exposure limits from OSHA, NIOSH, or the ACGIH should be used. ASHRAE Standard 62 is an adequate guideline for both operator safety and hardware exposure. See Appendix B, "Bibliography and References," for more information regarding these agencies and organizations.

Gaseous Contaminants

Excessive concentrations of certain gasses can cause corrosion and failure in electronic components . Gasses are of particular concern because of the recirculating airflow pattern of the data center. The data center's isolation from outside influences can multiply the detrimental influences of any gasses in the air, because they are continually cycled through equipment for repeated attack.

Gasses particularly disruptive to electronic components include chlorine compounds , ammonia and its derivatives, oxides of sulfur and petrol hydrocarbons. TABLE 12-1 outlines limits for various gasses that could pose a threat to hardware. These should be used as guidelines and not as absolute limits. Numerous other factors, such as the moisture content of the air, can influence environmental corrosivity and gaseous contaminant transfer at lower levels. Higher concentrations of these levels should be a concern.

Table 12-1. Recommended Gas Limits

Chemical Name	Formula	ASHRAE	OSHA (PEL)	ACGIH	NIOSH
Acetic Acid	CH 3 COOH	Not defined	10 ppm	Not defined	Not defined
Ammonia	NH	3500 mg/m 3	350 ppm	25 ppm	Not defined
Chlorine	C1	2100 mg/m 3	31 ppm (c)	Not defined	0.5 ppm (c)
Hydrogen Chloride	HC1	Not defined	5 ppm (c)	Not defined	Not defined
Hydrogen Sulfide	H 2 S	50 mg/m 3	320 ppm (c)	10 ppm	10 ppm
Ozone	O 3	235 mg/m 3	30.1 ppm	Not defined	Not defined
Petrol-hydrocarbons	C n H n	Not defined	500 ppm	75 ppm	300 ppm
Sulfur Dioxide	SO2	80 mg/m 3	35 ppm	2 ppm	0.5 ppm (c)
Sulfuric Acid	H2SO40	Not defined	1 ppm	Not defined	1 ppm (c)
PEL = Permissible Exposure Limit
ppm = Parts Per Million
mg/m 3 = Micrograms Per Cubic Meter
(c) = Ceiling

Note

In the absence of appropriate hardware exposure limits, health exposure limits should be used.

Gasses From Outside

Many chemicals used in normal office cleaning can damage sensitive computer equipment. Out-gassing from these products or direct contact with hardware components can cause failure. Certain biocide treatments used in building air handlers are also inappropriate for data centers, because they are not formulated for the airstream of a recirculating air system.

Gaseous influences can also come from:

• Ammonia and phosphates from agricultural processes

• Chemicals from manufacturing processes

• Exhaust from nearby roads and freeways

• Moisture from sea mists

Particulate Contaminants

The most harmful contaminants are often overlooked because they are so small. Most particles smaller than 10 microns are not usually visible to the naked eye, and these are the ones most likely to migrate into areas where they can do damage. Particulates as big as 1,000 microns can become airborne, but their active life is short and they are typically arrested by most filtration systems. Submicronic particles are more dangerous to the data center environment because they remain airborne much longer and can bypass filters. Some of the most harmful dust particle sizes are 0.3 microns and smaller. These often exist in large quantities , and can easily clog the internal filters of components. They have the ability to agglomerate into large masses, and to absorb corrosive agents under certain psychrometric conditions. This poses a threat to moving parts and sensitive contacts. It also creates the possibility of component corrosion.

Measuring airborne particulate concentration in the data center is useful in determining air quality. Your HVAC contractor can probably help with this, or recommend an air quality engineer.

The removal of airborne particulate matter should be done with a filtering system, and the filters should be replaced as part of the regular maintenance of the data center. See "Filtration" on page 159 for more information.

Human Movement

Human movement within the data center space is probably the single greatest source of contamination. Normal movement can dislodge tissue fragments , dander, hair, or fabric fibers from clothing. The opening and closing of drawers or hardware panels, or any metal-to-metal activity, can produce metal filings. Simply walking across the floor can agitate settled contaminants.

All unnecessary activity and processes should be avoided in the data center, and access should be limited only to trained personnel. All personnel working in the room, including temporary employees and janitorial staff, should be trained in the basic sensitivities of the hardware and to avoid unnecessary contact. Tours of the facility are sometimes necessary, but these should be limited and traffic should be restricted to avoid accidental contact with equipment.

The best solution to keeping human activity to a minimum in the data center is to design in a Command Center with a view into the data center room. Almost all operations of the center will take place here, and those visiting the facilities can see the equipment from there. The data center should never be situated in such a way that people must go through the equipment room to get to unrelated parts of the building.

Subfloor Work

Hardware installation and reconfiguration involves a lot of subfloor activity, and settled contaminants can be disturbed, forcing them up into the equipment cooling airstreams. This is a particular problem if the subfloor deck has settled contaminants or has not been sealed. Unsealed concrete sheds fine dust particles and is also susceptible to efflorescence ( mineral salts brought to the surface of the deck through evaporation or hydrostatic pressure). It is important to properly seal the subfloor deck and to clean out settled contaminants on a regular basis.

Stored Items

The storage and handling of hardware, supplies , and packing materials can be a major source of contamination. Cardboard boxes and wooden skids or palettes lose fibers when moved and handled. Particles of these have been found in the examination of sample subfloor deposits. The moving and handling of stored items also agitates settled contaminants already in the room. Also, many of these materials are flammable and pose a fire hazard . All of these are good arguments for making a staging area for packing and unpacking an important design criteria.

FIGURE 12-1 and FIGURE 12-2 show unnecessary clutter and particulate matter in a data center room.

Figure 12-1. Unnecessary Items Stored in the Data Center

Figure 12-2. Particulate Matter and Junk on the Floor

Particulate From Outside

Air introduced into the data center can be a source of contamination, especially if the filtering system is inadequate. It is important to know what dust and airborne chemicals could possibly come in from the outside environment. In particular, consider local agricultural activities, quarries, or masonry fabrication facilities. With this knowledge, plan the data center filtering system to arrest these particulates.