Seating can affect operating results when workers spend most of their day seated at an assembly line, workstation or bench. Workers who sit in a chair or on a stool that is too high, too low, too hard or too difficult to adjust are placing fatiguing strain on their back, legs and stomach muscles. They increase the risk of musculoskeletal disorders, which account for more than one-third of work-related injuries in the U.S.
Ergonomic seating, selected to meet personal comfort needs of users, can help reduce this risk. Adjustable ergonomic seating can adapt to individual differences created by height, strength, body style and other factors. An ergonomic chair can support a balanced work posture and easily adjust to posture changes for all individuals who use the chair.
Adaptability is key
Purchasing personalized seating does not necessarily mean selecting a different chair model for each individual and task. Instead, look for products that are versatile and adaptable to specific needs. Versatility and adaptability can be provided through such features as adjustable seat and backrest controls or through options and accessories like special backrests, seats, controls, armrests and casters/glides. In addition, modular construction can make it easy to interchange parts, upgrade components, add options and “build†chairs to fit specific user and work requirements.
Here are some guidelines to consider when selecting ergonomic seating:
1) Backrest features
The chair’s backrest should provide lumbar support to maintain the back’s natural s-curve (low-back support may not be suitable for an individual with irregular spinal curvature). The backrest height and tilt should be adjustable to provide comfort and assure that the lumbar support fits the back.
Backrests in special sizes can meet special needs. For example, a taller and wider backrest may increase upper back support, while a narrow backrest (eight inches wide) can support the spine and lumbar area while providing upper-torso mobility, allowing a worker good range of motion without backrest restraint.
2) Chair seat
A chair seat’s width and depth need to accommodate the user. The seat pan should be wide enough for the hips and thighs on either side and deep enough (or shallow enough) to allow the user to sit with his or her back against the backrest without reducing circulation to the lower portions of the legs. To aid circulation and increase comfort, the seat pan should have a waterfall front (well-rounded front edge).The seat tilt should be adjustable. The seated worker needs to be able to adjust the angle between the seat pan and backrest to maintain even weight distribution and proper torso-to-thigh angle. Ergonomists recommend an angle between 90-105 degrees.
Seat height adjustability is also needed to work at the proper level and avoid awkward postures. Working at the proper level — rather than to be able to put feet flat on the floor — is the number one reason for adjusting seat height. Seat height mechanisms should be easy to operate and not require the user to leave the sitting position to make an adjustment. Use a footrest or footring if necessary for foot support.
3) Chair controls
On many chairs, the only control is for seat height. A chair needs to also offer seat tilt, backrest height and backrest tilt adjustability for full ergonomic benefits. These controls need to be within easy reach of the seated chair user.
Many chairs of modular construction can be retrofitted with other, more sophisticated types of controls such as a seat and back lock.
4) Armrests
Armrests can help relieve the strain of prolonged seated work on shoulders, back and neck. On the other hand, armrests have the potential for obstructing free movement and may not be suited for some work.Whether to use armrests depends on the application and user preference. Chairs of modular construction provide the flexibility to incorporate the most suitable armrest style or to add armrests in the future.
Chairs fit many more workers and work situations when the height and width of their armrests are adjustable.
5) Casters and glides
Casters or glides can reduce stress and fatigue when they easily move individuals as needed at their workstations. These parts need to be selected according to the application, including the type of floor surface (hard or carpeted) and requirements for resisting movement.
Locking casters can increase safety in tasks involving machinery, cutting tools, table saws or conveyor lines, and work well on tile, wood and other hard floors. Caster options include the ability to lock when the seat is occupied, wide casters for grated floors and non-skid glides.
6) Other alternatives
For ergonomic alternatives, look beyond traditional chairs and stools to other workplace solutions such as:
- Sit/stands that help prevent muscle strain for workers who normally stand for much of the day.
- Urethane ergonomic chairs that are easy to wash down and resist damage in harsh industrial settings.
- Ergonomic welding chairs with upholstery that is fire-retardant and resistant to high heat.
- Adjustable stools that are wall-mounted and swing out to a work position or under a conveyor to a production station.
Ergonomic seating, personalized for the application, can deliver on the bottom line in increased productivity, fewer and less traumatic injuries, fewer lost workdays, and a favorable impact on workers’ compensation and medical insurance costs. The result is risk control rather than risk financing.
SIDEBAR: The right seat height
Because of body differences, there is no single formula for determining the correct seat height for every individual and work situation. There is, however, a calculation that can serve as a guideline.Measure the real work level — not just the height of the work surface, but the entire distance from the floor to where the hands are performing a task. Then subtract 12 inches for the correct seat height. This height should be the midpoint of the chair’s seat-height adjustment range.
example: 36-3/4" (work level from floor to task height) - 12" = 24-3/4" (midpoint of seat-height adjustment range)
