Generic Site Preparation Guide - Edition 6

resistance between connections, leading to equipment failures. High humidity can also have an

adverse affect on some magnetic tapes and paper media.

CAUTION: Low humidity contributes to undesirably high levels of electrostatic charges. This

increases the electrostatic discharge (ESD) voltage potential. ESD can cause component damage

during servicing operations. Paper feed problems on high-speed printers are usually encountered

in low-humidity environments.

Low humidity levels are often the result of the facility heating system and occur during the cold

season. Most heating systems cause air to have a low humidity level, unless the system has a

built-in humidifier.

Be aware when reviewing air quality that temperature and relative humidity can be a factor in

corrosive issues.

ESD Prevention

Static charges (voltage levels) are created when objects are separated or rubbed together.

Be aware that destructive ESD levels can exist very far below human thresholds. Extreme caution

must be used to protect contemporary microcircuitry that is manufactured densely and physically

smaller.

The voltage level of a static charge is determined by the following factors:

• Types of materials

• Relative humidity

• Rate of change or separation

Humidity Levels Influence the Creation of Static Charges

Table 1-2 compares the static charges generated by activities in different humidity levels.

IMPORTANT: Use ESD processes and ESD prevention equipment whenever equipment needs

servicing.

Table 1-2 Effect of Humidity on ESD Charge Levels

Humidity

and Charge Levels (voltages)

Personnel Activity

50%40%32%26%

3,700 V4,625 V5,750 V6,150 VPerson walking across a linoleum floor

11,100 V13,875 V17,250 V18,450 VPerson walking across a carpeted floor

14,800 V18,500 V23,000 V24,600 VPerson getting up from a plastic chair

1 Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell Laboratories, 1981)

2 For the same relative humidity level, a high rate of airflow produces higher static charges than a low airflow rate.

3 Some data in this table has been extrapolated.

For more information regarding ESD, see the HP ESD Standard HP-00005-04 at:

http://standards.corp.hp.com/smc/hpstd/pdf/F-HP0000504.pdf

Relative Humidity

Where possible, maintain a humidity range of 40% to 55%.

Static Protection Measures

Follow these precautions to minimize possible ESD-induced failures in the computer room:

24 General Site Preparation Guidelines