Site Preparation Guide, Eighth Edition - Superdome HP 9000 Systems

Chapter 2
Electrical and Environmental Guidelines
Environmental Elements
52
Special precautions are necessary if the computer room is near a source of air pollution. Some air pollutants,
especially hydrogen sulfide (H2S), are not only unpleasant but corrosive as well. Hydrogen sulfide damages
wiring and delicate sound equipment. The use of activated charcoal filters reduces this form of air pollution.
Zinc Particulate Contamination
Metallic particulates can be especially harmful around electronic equipment. This type of contamination may
enter the data center environment from a variety of sources, including but not limited to raised floor tiles,
worn air conditioning parts, heating ducts, rotor brushes in vacuum cleaners or printer component wear.
Because metallic particulates conduct electricity, they have an increased potential for creating short circuits
in electronic equipment. This problem is exaggerated by the increasingly dense circuitry of electronic
equipment.
Over time, very fine whiskers of pure metal can form on electroplated zinc, cadmium, or tin surfaces. If these
whiskers are disturbed, they may break off and become airborne, possibly causing failures or operational
interruptions. For over 50 years, the electronics industry has been aware of the relatively rare but possible
threat posed by metallic particulate contamination. During recent years, a growing concern has developed in
computer rooms where these conductive contaminants are formed on the bottom of some raised floor tiles.
Although this problem is relatively rare, it may be an issue within your computer room. Since metallic
contamination can cause permanent or intermittent failures on your electronic equipment, Hewlett-Packard
strongly recommends that your site be evaluated for metallic particulate contamination before installation of
electronic equipment.
Electrostatic Discharge (ESD) Prevention
Static charges (voltage levels) occur when objects are separated or rubbed together. The voltage level of a
static charge is determined by the following factors:
• Types of materials
• Relative humidity
• Rate of change or separation
Table 2-2 lists charge levels based on personnel activities and humidity levels.
Table 2-2 Effect of Humidity on ESD Charge Levels
Personnel Activity
a
a. Source: B.A.Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell
Laboratories,1981)
Humidity
b
and Charge Levels (volts)
c
b. For the same relative humidity level, a high rate of airflow produces higher static charges
than a low airflow rate.
c. Some data in this table has been extrapolated.
26% 32% 40% 50%
Walking across a linoleum floor 6,150 5,750 4,625 3,700
Walking across a carpeted floor 18,450 17,250 13,875 11,100
Getting up from a plastic chair 24,600 23,000 18,500 14,800