Electrostatic Discharge (Esd) Prevention; Table 2-1. Effect Of Humidity On Esd Charge Levels - HP rp8400 Series Manual

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 2-1 lists charge levels based on personnel activities and humidity levels.
Table 2-1 Effect of Humidity on ESD Charge Levels
Person walking across a carpeted
floor
Person getting up from a plastic
chair
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.
Chapter 2
Personnel Activity
Person walking across a
linoleum floor
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.
a b
Humidity
26%
6,150 V
18,450 V
24,600 V
Electrical and Environmental Guidelines
Environmental Elements
and Charge Levels (voltages)
32% 40%
5,750 V 4,625 V
17,250 V 13,875 V
23,000 V 18,500 V
c
50%
3,700 V
11,100 V
14,800 V
25