8 FURNITURE
8.3 Design Specifications
8.3.2 SURFACES
8.3.2.4 Input-Device Support Surface
Input-device support surfaces may be designed for use while seated only, standing only, or while seated or standing. The reader’s attention is directed to the requirements for placement of input devices within the recommended space specified in Section 5.2.3.4.
All input-device support surfaces shall
• Adjust in height, or a combination of height and tilt The manufacturer of an input-device support surface shall
• Provide information regarding the range of height adjustment
• Provide information regarding tilt adjustments All input-device support surfaces should
• Adjust fore and aft in the horizontal plane
• Adjust in side-to-side placement within the optimal area for input devices
• Tilt
8.3.2.4.1 Sit-Only Working Postures
The installed input-device support surface designed for sitting working postures only shall
• Comply with the clearance requirements specified in Section 8.3.2.0
• Have a surface height adjustment that includes at least the range of 56 cm to 72 cm (22 to 28.3 in.) as measured from the floor to the top of the surface.
If tilt adjustable, the tilt adjustment should
• Provide tilt adjustment to include the range between –15 degrees and +20 degrees including 0 degrees
8.3.2.4.2 Stand-Only Working Postures
If height adjustable only, the installed input-device support surface designed for standing work postures only shall
• Place the support surface at standing elbow height by adjusting in height between 95 cm and 118 cm (37.4 and 46.5 in.) as measured from the floor to the surface at the front edge of the support
Or, if both height and tilt adjustable, the input-device support surface shall
• Provide height adjustment to include some portion of the range between 78 cm and 118 cm (30.7 and 46.5 in.) and to include height adjustability in the range 89 cm to 110 cm (35 to 43.3 in,) as measured from the floor to the surface at the front edge of the support
• Provide tilt adjustment to include some portion of the range between 20 and –45 degrees, including the range 0 to –15 degrees
• Combine height and tilt within the specified ranges as defined by Equation 8-1
If tilt adjustable, input-device support surfaces designed for standing-work postures only should
• Allow tilt adjustment that includes the range between –45 degrees and +20 degrees
• Allow height adjustment that includes the entire range between 78 cm and 118 cm (30.7 and 46.5 in.) as measured from the floor to the surface at the front edge of the support
Standing input-device support surface height + sin (elbow angle relative to horizontal) x elbow-wrist length
A + sin (B) x C = input device height (8-1)
(Add product of sin (B) and elbow-wrist length to standing elbow height if angle is positive;
subtract if angle is negative)
Figure 8-4. Method of combining height and tilt for input-device support surfaces
Height adjustment, or a combination of height and tilt adjustment, is necessary to successfully accommodate the desired range of users. The interaction between height and tilt is illustrated in Figure 8-4. Acceptable height and tilt angle combinations may be calculated according to the procedures described in Appendix A. Tilt angles greater than 20 degrees above horizontal or more than 45 degrees below horizontal are not acceptable.
8.3.2.4.3 Sit/Stand Working Postures
If height adjustable only, the input-device support surface designed for both sitting and standing work postures shall
• Adjust in height between 56 cm and 118 cm (22 and 46.5 in.) as measured from the floor to the surface at the front edge of the support.
• Comply with the clearance requirements specified in Section 8.3.2.1 when used in the seated position
If height and tilt adjustable, the input-device support surface designed for both sitting and standing work postures shall
• Accommodate seated workers by adjusting in height in some portion of the range between 56 cm and 72 cm (22 and 28.3 in.) as measured from the floor to the surface at the front edge of the support
• Accommodate standing workers by providing additional height adjustability (greater than 72 cm [28.3 in.]) when combined with tilt as described in Equation 8-1
• Adjust in tilt in some portion of the range between +20 and –45 degrees, to include 0
• Comply with the clearance requirements specified in Section 8.3.2.1 when used in the seated position
A seated 5th percentile female will be accommodated at the 56 cm height and 0 degree tilt angle. A standing 95th percentile male will be accommodated at a 96 cm height with a surface that is tilted 45 degrees below horizontal; see Figure 8-4. Tilt angles greater than 45 degrees below horizontal are not acceptable.
The location of the input device on its support surface is a complex issue that integrates the recommended positions of the shoulder, upper arm, elbow, forearm, wrist, and hand with provision of clearance space for the legs underneath. Height and/or tilt adjustments are necessary to accommodate different sizes of workers and different working postures. Moreover, height and tilt requirements interact. These issues can be jointly addressed by an input-device support surface that supports placement of the input device or devices within a three-dimensional space or volume. Such an input- device support surface benefits from adjustability in both height and tilt. (See Section 5.2.4 for specification of the location of input devices relative to the user.)
Research suggests that input devices are most comfortable to use, and place less demand on the shoulder, when they are located so as to minimize shoulder abduction (Harvey & Peper, 1997;
Karlqvist et al., 1996; Paul & Nair, 1996). This is achieved when the devices are located approximately within the shoulder span of the user and within forearm reach. Similarly, users report equal comfort and productivity for a wide range of elbow angles (Cushman, 1984: Grandjean et al., 1983; Miller & Suther, 1981; Weberet al., 1984). Tilting support surfaces for input devices facilitates neutral wrist postures (Berqvist, Wolgast, Nilsson, & Voss, 1995; Hedge, Morimoto, & McCrobie, 1999; Hedge & Powers, 1995).
Research supports the benefits of alternating between seating and standing postures (Dainoff, Paasche, Simons, & Terlaga, 1999; Nerhood & Thomson, 1994; Paul & Helander, 1995). Accordingly, the standard specifies minimum height and tilt adjustment ranges for sit/stand input-device support surfaces. Finally, research indicates that placement of input devices at multiple levels represents a viable solution to the location of multiple input devices within the recommended space (Paul & Nair, 1996). However, care must be taken that the postural design criteria of Section 5.2.1.1 are followed when multi-tiered input-device supports are used.