Cleanroom ergonomic seating fills many roles setting the standard

05/01/2004

By James Frobose

Properly designed seating fills a multifaceted role in a cleanroom. Ergonomic chairs provide comfort and support for workers, helping them stay productive. These chairs also help maintain the integrity of the cleanroom, providing airborne particulate cleanliness and, in many applications, static control as well.

While improvements to lumbar support in chair backrests, seat height adjustability and backrest tilt mechanisms have been made, advancements in filtration and air exchange systems are minimizing contamination that can be caused by chairs, which are now being made to comply with worldwide cleanroom standards outlined in ISO 14644 for ISO Class 3 through ISO Class 5 environments.

ISO 14644 is an international cleanroom standard that establishes airborne particulate cleanliness classes. Though the ISO standard does not evaluate furniture used in a cleanroom, chair manufacturers focus on making cleanroom seating products that meet or exceed the standard's particulate cleanliness goals.

Posturing for position

So, what are the issues in designing an ergonomic chair? One consideration is the need to support a balanced work posture. The backrest must provide critical support for the lumbar area of the lower back. The torso and hips must be properly supported so that the torso serves as a firm anchor for the arms and legs. The seat height must promote circulation to the lower legs. The seat must be contoured for comfort, and the seat cushion must have plenty of density for support.

Another consideration is the work application. The designer should consider the type of work, the chair user's work movements, and the actual level of the work being done. The correct seat height is determined by the real work level, which incorporates not just the height of the work surface but the entire distance from the floor to where the worker's hands are performing the task.

Adjusting for the environment

The designer's challenge is to provide the optimum combination of chair components and adjustable controls to meet these considerations. Easy adjustability of backrest height and tilt, as well as seat height and tilt, are key advantages of ergonomic seating. Providing the proper adjustment ranges for the application is a major design issue.

What additional issues are involved in cleanroom chairs?

A chair must be designed to assure cleanroom compatibility at the level required for the class of cleanroom. Since air is expelled from the seat cushion during chair use, the cushioning material must incorporate a system to filter or capture particles so they can't escape into the cleanroom. For example, when someone sits in an ISO Class 3 or Class 4 chair, the air in the cushion discharges into an air reservoir. An ISO Class 5 chair's air filtration system within the seat traps particulates while allowing the seat to conform to normal body shapes.

Upholstery selection is also important. Most applications call for vinyl because it is better than fabric for controlling particle emissions. When static control is also an issue, designers can specify a vinyl with a carbon-impregnated undersurface to help drain static charges.

Use of vinyl necessitates special attention to the contour of the chair seat. The relatively slippery surface can combine with the slipperiness of cleanroom gown material to cause individuals to slide forward while working. An ergonomic seat with a backward tilt of approximately 3.5 degrees minimizes this concern and increases work comfort.

What are the R&D and testing processes for cleanroom ergonomic seating?

Seating used in a cleanroom must meet or exceed particulate cleanliness standards established in ISO/DIS14644-1. Manufacturers, like BioFit, worked with an independent laboratory to develop repeatable and accurate testing of upholstered chairs for compression particulate cleanliness, and subsequently made the testing procedure available to the cleanroom industry. BioFit also sponsors strength and durability tests to assure that its seating conforms with ANSI/BIFMA Standard X5.1-1993.

Another area of R&D involves the ergonomic design of the seat and backrest. Often times, prototypes are developed, and the manufacturer receives customer and end-user feedback on comfort factors of various designs.

The Business and Institutional Furniture Manufacturers Association established the ANSI/BIFMA standard as a means of evaluating the suitability of a furniture product for long-term use. Whereas ISO 14644 pertains to cleanliness, ANSI/BIFMA focuses on durability. Compliance with both standards is important in identifying a chair as a high-quality cleanroom product.

JAMES FROBOSE is engineering manager at BioFit Engineered Products (Waterville, Ohio; www.biofit.com).