Site Preparation Guide, Third Edition - Server Expansion Unit

Appendix A
General Site Preparation Guidelines
Environmental Elements
23
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
Static Protection Measures
Follow these precautions to minimize possible ESD-induced failures in the computer room:
• Maintain recommended humidity level and airflow rates in the computer room.
• Install conductive flooring (conductive adhesive must be used when laying tiles).
• Use conductive wax if waxed floors are necessary.
• Ensure that all equipment and flooring are properly grounded and are at the same ground potential.
• Use conductive tables and chairs.
• Use a grounded wrist strap (or other grounding method) when handling circuit boards.
• Store spare electronic modules in antistatic containers.
Table A-1 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 (voltages)
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%
Person walking across a linoleum floor 6,150 V 5,750 V 4,625 V 3,700 V
Person walking across a carpeted floor 18,450 V 17,250 V 13,875 V 11,100 V
Person getting up from a plastic chair 24,600 V 23,000 V 18,500 V 14,800 V