HP Integrity rx7620 Site Preparation Guide, Fourth Editon - HP Integrity rx762 - Page 55

General Site Preparation Guidelines Environmental Elements Metallic Particle Contamination Metallic particulates can be especially harmful around electronic equipment. This type of contamination can 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 worn printer components. 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 can 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 might be an issue within your computer room. Since metallic contamination can cause permanent or intermittent failures on your electronic equipment, HP strongly recommends that your site be evaluated for metallic particulate contamination before installation of electronic equipment. Electrostatic Discharge 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 B-2 lists charge levels based on personnel activities and humidity levels Table B-2 Effect of Humidity on ESD Charge Levels Personnel Activitya Humidityb and Charge Levelsc 26% 32% 40% 50% Walking across a linoleum floor 6,150 V 5,750 V 4,625 V 3,700 V Walking across a carpeted floor 18,450 V 17,250 V 13,875 V 11,100 V Rising from a plastic chair 24,600 V 23,000 V 18,500 V 14,800 V a. Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell Laboratories, 1981) 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. Static Protection Measures Follow these precautions to minimize possible ESD-induced failures in the computer room: • Install conductive flooring (conductive adhesive must be used when laying tiles). • Use conductive wax if waxed floors are necessary. Appendix B 41