Chapter 6. Safety and Comfort

This chapter gives you important information about setting up your Challenge rackmount server for maximum safety and comfort.

Human Factors Guidelines for Setting Up Your System

You can increase the comfort and safety of your work environment and decrease your chances of cumulative trauma disorders by following the guidelines given below using these guidelines. You can create a healthy and productive work environment by

  • properly choosing a site for your system and its components

  • setting up your desk and chair correctly

ANSI Standard for VDT Terminal Workstations

Table 6-1 shows recommended guidelines for furniture and system adjustment, as developed by the American National Standards Institute (ANSI). Adjustment parameters are defined in Figure 6-1. Guidelines are shown for small persons (standing height of 150 cm or 59 in.) and large persons (standing height of 185 cm or 73 in.). Midpoints are also interpolated for persons of average height.

Figure 6-1. Basic Guidelines for VDT Workstation Adjustment (Adapted From ANSI/HFS 100, 1988)

Table 6-1. ANSI/HFS 100 Guidelines for VDT Workplace Adjustment (1988)


Small Person
cm (in.)

cm (in.)

Large Person
cm (in.)

Seat pan height

40.6 (16.0)

46.3 (18.2)

52.0 (20.5)

Work surface height

58.5 (23.0)

64.75 (25.5)

71.0 (28.0)

Screen viewing height

103.1 (40.6)

118.1 (46.5)

133.1 (52.4)

Screen viewing distance

>30.5 (>12)

>30.5 (>12)

>30.5 (>12)

Screen viewing angle

0-60 degrees

0-60 degrees

0-60 degrees

Note: Local VDT guidelines issued by country, state, or municipality may apply and supercede the guidelines in Table 6-1.

CAD Operator Preferences

If you work on a CAD system, you may feel more comfortable using the ranges of adjustment shown in Table 6-2.

Table 6-2. Adjustments Preferred by CAD Users


Mean cm (in.)

Range cm (in.)

Seat pan height

54 (21.3)

50-57 (19.7-22.4)

Work surface height

73 (28.7)

70-80 (27.6 -31.5)

Monitor center above floor

113 (44.5)

107-115 (42.1-45.3)

Screen viewing distance

70 (27.6)

59-78 (23.2-30.7)

Work surface tilt

8.6 degrees

2-13 degrees

Monitor tilt

–7.7 degrees

–15 to +1 degree

Note: A negative tilt is a forward monitor inclination (top of the screen toward the operator). The information in Table 6-2 is derived from Grandjean, Etienne. Ergonomics in Computerized Offices. London: Taylor & Francis Ltd., 1987,
p. 148.

Tips for Setting Up and Using Your System

The following tips may be useful for setting up an ergonomic work environment that is safe, comfortable, and productive. Although you may be able to perform this procedure yourself, it is useful to work with a friend to achieve the best fit.

Facilities Selection

  1. A good work chair should swivel, and you should be able to adjust the seat height while sitting. The seat should have a rounded front edge. The chair should have a large enough base to remain stable when adjusted to its maximum height. It should have castors or glides. Many chairs rock, which may partially relieve the muscle tension from sitting in a fixed position. Some chairs can also be adjusted for seat tilt and depth, armrest height, back rest angle, and lower back support. Check the instructions that came with your chair to take advantage of its adjustability features.

  2. Select a work surface that provides enough space to do your work without excessive turning, twisting, or stretching. The height of the work surface should be adjustable and, if possible, the workspace should be wide enough to use the mouse and keyboard at the same height. This will help your neck, shoulders, and upper arms to stay relaxed while you work.

  3. Indirect lighting should be used, whenever possible, to prevent glare on the display screen. If you prefer lower levels of lighting (for example, 200–250 lux) than are usually found in offices, separate task lighting may be needed for reading documents. Wearing dark-colored clothing helps minimize glare reflections on the screen.

Adjusting Your Chair, Work Surface, and Terminal

  1. Adjust your chair first, from a seated position if possible. Your lower leg and thigh should form approximately a 90-degree angle at the knee, and your feet should rest flat on the floor. If you are short, you may want to use a footrest for better comfort.

  2. Once your chair is adjusted, raise or lower your work surface to a height that allows you to keep the wrists flat and straight while using the keyboard. The angle between your lower and upper arm should be 70–90 degrees at the elbow. If necessary, use a padded wrist rest under the keyboard to support your wrists.

  3. To minimize screen glare, position your terminal screen perpendicular to overhead lighting sources and windows. Do not set the terminal in front of or behind a window, or parallel to other sources of light. Tilting the screen slightly forward helps avoid glare. Adjusting the terminal controls to minimize brightness and maximize contrast may also reduce the effects of glare.

  4. Adjust your terminal height so your line of sight in your regular seated position is at or near the top the screen. You should be able to see the whole screen without tilting your head forward or backward, within a 60-degree viewing angle of the normal line of sight. With smaller terminals, this may require using a display stand under the terminal base. With larger terminals, it may require a longer viewing distance (refer to Table 6-2).

These adjustment steps should be done each time a different person uses the system.

System Usage

  1. When using the keyboard, or other input devices, keep your wrists flat as much as possible, and do not rotate your hands inward toward the thumbs or outward toward the fingers.

  2. Electronic keyboards and input devices do not require as much force to operate as manual typewriters. Type or click lightly on the keyboard.

  3. Document stands can be mounted on the work surface or swing out on an arm to position documents next to the display. These can be helpful in maintaining a healthy posture for using the workstation (head in approximately a straight line with the body).

  4. You may find it helpful to take rest breaks of several minutes every one to two hours. During breaks, focus your eyes on objects or scenery at least 30 feet away, stretch, and move around.

Electrostatic Discharge

Silicon Graphics designs and tests its products to be resistant to the effects of electrostatic discharge (ESD). ESD is a source of electromagnetic interference and can cause problems ranging from data errors and lockups to permanent component damage.

It is important that while you are operating your system, you keep all the covers and doors in place. The shielded cables that came with the system and its peripherals should be installed correctly, with all screws fastened securely.

To ensure the proper function and/or data integrity in your peripherals, precautions against electrostatic discharge when removing or replacing the front loading devices. You should use an ESD wrist strap along with antistatic packaging materials, whenever you transport or store peripherals.