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by Tim Burke
While no actual standards exist at this time for multiple screen array environments such as PSAP (911), control room, command center and trading environments. I will take a practical view on these environments and apply some basic guidelines and principles on ergonomics offered by various bodies (ANSI/BIFMA, OSHA) etc.
1) Focal Adjustability - To be within the focal range of 95% of the US population, monitors should be adjustable between 20 and 40” with an arc (concave arrangement) that would accommodate an arm length reach to the middle of the screen for most users. Focal adjustability is necessary so the user will not need to lean in or strain their eyes to view information. This can be addressed in two ways, moving the screens to and from the user or by increasing/decreasing the screen resolution. Although focal has become a bit less important because of the rapid increase in screen size and resolution (See Figure 1). Screen sizes have grown steadily since 2009, from 15” to an average now of 22”, with many users going to 34” (computer monitors are measured the same way as TV’s, diagonally across the screen). Resolution has increased steadily as well from 720p to 1080 (full HD) with many users now deploying 4K. A monitor with 4K resolution effectively doubles the resolution of a 1080p monitor in each direction giving you four times the more on-screen real estate. This allows the user to leave the screen farther away while remaining comfortable viewing the information. (Resolution is measured as a set of numbers which measure the number of vertical lines of pixels side by side vs. the number of horizontal lines of pixels that are stacked on top of each other).
2) Screen height – To be within the proper screen height for the US population from the 5th – 95th percentile, the height adjustability (measured from the top of the monitor to the top of the work surface) would need to be between 19.6” and 22.75”, a difference of roughly 3.15”. This adjustment is even more important of height adjustable work surfaces and desks as the ration of the measurement from the monitor to the work surface remains constant. Eye height should rest within an inch of the top of the monitors viewable surface. Important Note: Bifocal users typically view the monitor through the bottom portion of their lenses. This will cause them to tilt their heads backward to see a monitor that would otherwise be appropriately placed. This can fatigue muscles that support the head and can lead to injury.
3) Monitor alignment – Usage of 4-8 screens is common in the PSAP/control/operations environments and if improperly aligned can cause discomfort and possible injury. The 2 primary viewing screens (continuously monitored) should be visible by an adjustment of the eyes only and should be placed directly in front of the user, parallel to the desk front edge. Secondary screens (monitored every few minutes) should be visible with a slight turn of the head should be placed above with slight down angle or to the immediate right and left of the primary screens. Tertiary screens, if more than 4 screens (those viewed only occasionally) should be placed further to the right or left. OSHA recommends that no monitor screen be placed at a distance of greater than 35 degrees angle from the user
4) Other Desktop technology and proper reach – Phones, tablets, secondary keyboards, touch screen turrets and radio consoles should be within a 20” reach of the user without extending the arm in the primary reach zone.
Items such as charging ports, Pen holders, desktop storage can be within the reach of the user by extending the arm, engaging the elbows and shoulder in the secondary reach zone. Other desktop storage, photos and rarely used items should be placed behind the viewable surface of the monitors.
5) Desk chair positioning – Feet should be flat on the floor (Foot rest should be used when appropriate), Feet should never dangle. Thighs should be parallel to the floor with knees at a right angle. Arm rests should be at a height to comfortably rest elbows when not typing (arm should not hang from the shoulder.