By Dave Tewel
The emergence of new technologies, new ergonomic standards, and increased public awareness of workplace health issues have combined to inspire a dramatic shift in console design. Today’s control workstations are smaller, more functional, and more aesthetically appealing than earlier generations.
The ergonomic approach to designing consoles into the layout of a control room should contribute to achieving the performance objectives established for the space in question, while ensuring that every aspect of interaction between human, machine, and the environment - from raised flooring to acoustical concerns, from indirect lighting to the overall well-being, health, and safety of each operator - is taken into account.
Top-Down Approach
A top-down approach provides a framework for ensuring that decisions on such matters as equipment selection, operating practices, working environments, and furniture choices all derive from operating demands. No matter how well designed a workstation might be, the overall system will fail if operators are overloaded, undertaking tasks for which they are poorly trained, or straining to read displays that are illegible. With a top-down approach, the limitations of the operator are automatically included and potential mismatches between operator capabilities and system demands are minimized.
The international standard known as ISO 11064 is the backbone of ergonomic design of control rooms. The essence of this approach can be defined within a single term: user-centered design.
The top-down approach requires that you first spell out the goals of the control center in various situations, including normal, off-normal, emergency, outage, and startup conditions. Determine what systems are required to accommodate these conditions, then list the functions best undertaken by machines (e.g. repetitive calculations), followed by those functions at which human operators are superior (e.g. coping with unexpected situations). The result will define system specifications for computers as well as those tasks to be conducted by human operators.
In addition to forcing an evolution in console design, revolutionary changes in technologies are also nurturing improved console aesthetics. The arrival of digital technologies, system integration, and flat-panel displays have enabled console makers to design a wider variety of consoles with smaller footprints. Simultaneously, console makers are also discovering more and more about the way people use control rooms. Sharing that knowledge with architects ensures that ergonomic factors will be designed into the larger control environment as well as into the consoles themselves.
Ergonomics
Ergonomics is the study of the relationship between workers and their environment. Most original console standards were set back in the 1960s, and have since been revised to accommodate both new technologies and new understandings of how our head, neck, and eyes operate.
Past ergonomic studies were done with a person in the “sitting tall position,” with his or her hips, shoulders, and ears in a straight, vertical line. Realistically, no one would sit in such an uncomfortable position, especially for the duration of an 8-hour shift. Because we now understand more about how the neck, head, and eyes operate, today’s ergonomic standards are based on more realistic assessments of how operators actually work at consoles. The latest ergonomic studies of people sitting in a relaxed position show that our heads tilt forward approximately 8 degrees at a viewing angle of minus 30 degrees to 35 degrees , with an average viewing distance of 30" to 35" from the screen. With that in mind, newer consoles are lowering the target angle of the primary viewing displays.
The average minimum viewing distance is largely determined by three factors:
- Eyesight accommodation is the distance at which our eyes focus when there is no object on which to focus. The eye muscles that focus the lens must work 21⁄2 times harder to focus at 12" than at 30", which contributes to eye strain.
- Convergence is when the eyes turn inward to focus on a near item. This actually contributes more to eye strain than accommodation.
- Depth of focus is the range of distances that do not require the eyes to refocus, which most frequently affects the over-40 operator, those of us requiring reading glasses.
The solutions to problems arising from all three factors are similar: Lower the monitor height, keep items and screens to be viewed at similar distances, increase task lighting on printed material, increase text size, and change tasks periodically. Accommodation and convergence are both shortened when the gaze is lowered. The average resting point of convergence is 35" at 30 degrees down angle, 45" at horizontal, and 53" at 30 degrees up angle. These data offer a significant justification for lowering monitor height. The other benefit of lower monitor height is a reduction in dry eye syndrome caused by eyelids opening wider when looking up.
The vertical and horizontal eye and head movement diagrams in Figure 1 demonstrate best viewing angles for an operator. Ideally, there is no head movement and minimal eye movement for the most important and most common tasks.
Figure 1
SOURCE: THE WINSTED CORPORATION
In the design of a console it is necessary to determine if the workstation will be used as an isolated unit or in conjunction with overview displays or other workstations. The height of the console should be calculated so that the smallest operator can see over the top of any mounted electronics to remote monitor walls or displays, and the clearance beneath the worksurface should allow for the tallest operator to sit comfortably. The eye height of the fifth percentile of operators may be as low as 42", depending on the range of chair adjustment.
Physical layouts should accommodate the use of non-electronic equipment and documents, such as log books, maps, and clipboards. An element of flexibility should also be allowed for positioning such items as telephones, keyboards, and writing areas. This will enable operators to change posture during their shift and minimize the effects of fatigue.
Displays/Monitors
When using the top-down approach to designing display layouts, start with management objectives rather than attempting to see how many monitors can surround an operator. Keep in mind that the amount of information that an individual can handle is limited. Maximizing operator performance requires that the designer know the amount of activity associated with each monitor image and the size of detail, both of which affect the detection of significant events. Even with as few as four monitors, accurate activity detection in a busy environment decreases to 83 percent.
Displays that are used for close image inspection should be positioned directly in front of the operator, with sizes typically ranging from 15" to 19". Displays outside the workstation and positioned at a greater distance or behind the console should range in sizes from 19" to 42" or larger.
The introductions of flat-panel displays and touch-screen technologies have had a significant impact on console design. Large cathode ray tube (CRT) monitors are rapidly being replaced with flat-panel screens that take up considerably less space, reduce power consumption, and require less cooling within the console. Every year the resolution, refresh rate, and size of LCD screens increase on a per-dollar basis. Today, it is difficult to find displays with native mode resolution as low as the long-standing VGA standard of 640 x 480 pixels. More commonly, today’s displays range from 800 x 600 (SVGA) to 1280 x 1024 (SXGA), 1600 x 1200 (UXGA), or even greater.
When screen resolution increases, it means the operator can get closer to the display and still not be able to detect the individual pixels. Still, it is important to keep in mind that there are practical limits to the size of displays. A quick rule of thumb for viewing video images is that the operator should be at least twice the distance from the screen as the height of the display. A more precise set of guidelines, based on screen diagonal size and image resolution, is explained in Figure 3 .
To calculate display height, remember that today’s displays often employ a 4:3 aspect ratio, though increasingly they are migrating toward the wide screen 16:9 high definition displays. Using a 3:4:5 ratio (height:width:diagonal), the height of a 20" diagonal screen will be 12" and the width will be 16". Moderate- to high-resolution monitors ranging from 15" to 21" diagonal measurements are typically appropriate for primary displays.
Touch-screen technology is also affecting the ergonomics of new console designs, especially in high-security or high-attention environments. While touch screens are not used in many applications, new studies show that when some operators get extremely nervous or come under high stress, they have trouble operating a mouse to find and click on an icon. But typically they have less trouble pointing with their finger to an element on a touch screen. As a result, touch screens are becoming more and more prevalent in high-security, high-stress, or control room applications. However, consoles incorporating touch-screen technology must offer a shorter distance between the operator and the screen - typically less than 28" from the edge of the console worksurface - so that the screen can comfortably be touched from a relaxed sitting position.
Whatever the hardware interface, the ideal is a design in which operator attention is focused on a single source of vital information relevant to each situation.
To minimize head and extreme eye movement, the primary images to be viewed, whether displayed locally or on a distant video wall, should be centered within a 30 degree cone. To calculate the minimum distance, multiply the width of the display times 1.87. Thus, using our previous 12:16:20 example, a 20" diagonal display will have a width of 16", meaning that the minimum distance from the display should be 30". If the design calls for two 50" displays, then the nearest operator needs to be at least 12'6" from the displays: 2(40 x 1.87).
Control Room Factors
Issues to consider when designing console placement in the control room include the room’s dimensions, the number of stations, the dimensions of each station, the dimensions of any video wall, and the width of the aisles.
The distance from which to view a large-screen display or group of displays should not be less than twice the display’s height or greater than eight times its height for normal video or as little as four times its height for text-intensive applications. However, if this is a primary monitor for the operator, where it should fit into the 30 degree cone of viewing, then the longer-range formula of screen width x 1.87, should take precedence as the minimum viewing distance.
Figure 2
SOURCE: THE WINSTED CORPORATION
As an example, consider a console that is 39" deep, and an aisle that is 42" wide, for a total of 81". If the plan is to use one 75" diagonal display (see Figure 2), here is how you would calculate the room layout:
The first row of operators will be 9'4" from the front (1.87 times the 60" width of a 75" diagonal screen).
The back row will be no more than 30' from the front
(8 times the 45" height of a 75" diagonal screen).
This will permit four rows of consoles and three aisles, to keep within the maximum distance. The first row at 112" deep may be up to 13'8" wide (2 x (distance from front - half the screen width) or 2 x (112 - 30)). The second row at 193" (112 + 81) may be up to 27'2" wide. The third row at 274" (112 + 81 + 81) may be up to 40'8" wide. Since a fourth row at 355" (29'5") would leave no room for operators, only three rows are practical.
Alternatively, you might be asked to determine the proper size for a large screen display, given certain room dimensions. The same formulas apply.
A command control room should be designed for more than just day-to-day operations. You need to consider every situation in the initial design and for future upgrades. Enough space should be maintained in and around the console so that multiple groups of personnel, from supervisors to security professionals, emergency service personnel, or even government officials, can view and analyze information quickly and efficiently. Design for crisis - hope for routine.
Environmental Design
The provision of an appropriate working environment is essential for control rooms that must accommodate auditory or visual tasks. Where speech communication is important, all auditory needs of the environment must be appropriately specified. Ambient noise levels need to be controlled by considering such factors as room and console finishes, noise output of equipment, and control of external sources of noise. Ceiling acoustics should strive to achieve an NRC (noise reduction coefficient, a measurement of sound absorption characteristics) of 0.65 to 0.75 or better and an AC (articulation class, a measurement of sound attenuation) of 40 to 44 or better.
Figure 3
SOURCE: THE WINSTED CORPORATION
Air quality and air temperature can play an important part in keeping operators awake and alert. One of the most common criticisms of control room design is a lack of consistent ambient temperature. An example of how environmental design can contribute directly to operator performance is an air-conditioning system that is automatically set to increase the ambient temperature to compensate for natural early-morning drops in body temperature. Room temperature should range from 70 degrees Fahrenheit, with relative humidity from 40 percent to 65 percent and minimal air movement not exceeding 4" to 6" per second.
To maintain the most consistent operator environment, a separate equipment room should be provided to house CPUs, servers, and other rack-mount equipment. This will remove the biggest sources of heat from disk arrays and processors and noise from cooling fans from the operators’ area. It also has the benefit of locating the most sensitive equipment in a secure, limited access area that is designed for proper cooling.
Wherever extensive arrays of displays are used, lighting within control rooms should be sufficient and suitable for all visual tasks. A lighting scheme largely based on indirect ambient lighting, where the ceiling reflects light down into the room, has been found to offer an effective solution. In designing a lighting scheme, attention needs to be given to the range of tasks undertaken as well as the ages of the operators. Low levels of lighting may be fine for image monitoring but can pose problems with paper-based tasks. Operators of all ages, but especially older workers, will require adjustable task lighting to conduct small-scale visual tasks.
Ceiling materials should offer moderate to high reflectance of 0.8 or more to improve light distribution throughout the room and reduce energy costs for lighting. Walls should be an off-white matte or flat finish with a reflectance range of 0.5 to 0.6. Floor materials should have a lower reflectance of 0.2 to 0.3 for carpet or 0.25 to 0.45 for floor tiles.
Operators typically do not like working in windowless environments. Unless proscribed for operational or security reasons, it is strongly recommended that north-facing windows be included in a control room, primarily for psychological reasons. However, such light sources also pose potential security challenges and can contribute to reflections and glare. Windows and doors should be off the primary field of view but visible from a seated position. Allow circulation space around doors to minimize congestion.
Although a rectangular room provides the most possible options for equipment, display, and console positioning, in general, rooms with sharply angled walls or with support columns should be avoided. Designing a control room of the right size and shape can go a long way toward achieving an efficient, comfortable operating environment.
Dave Tewel is Western Regional Manager for The Winsted Corporation.
