Contamination control is the primary design goal of any cleanroom. Any potential source of contamination into the cleanroom must be thoroughly evaluated and minimized. Lighting fixtures should be subjected to contamination evaluation. Unfortunately, there are no established standards to prequalify fixtures for a particular cleanroom class. The National Sanitary Foundation (NSF) does provide listing and testing of materials used in food, pharmaceutical, medical or other FDA applications. Fixtures used in these applications should be required to carry the NSF listing mark. Manufacturers often advertise fixtures as being suitable for cleanroom use with no data or standard qualifications to substantiate their claims.
The materials and construction types of cleanroom fixtures vary widely. Since no accepted standard exists for specific cleanroom classifications, it is up to the engineer or lighting designer to carefully evaluate any proposed fixture. In general, it is recommended that fixtures used in ISO Class 5 (Class 100) to ISO Class 3 (Class 1) cleanrooms be constructed of powder-coated steel, anodized aluminum or stainless steel.
In NFS/FDA applications, stainless steel is typically required.
In addition, the fixtures should have airtight seals around the lens and frames. Gasketing materials should be closely reviewed for outgassing and resistance to cleaning solvents. The overall fixture construction should feel solid, tightly joined or sealed in all areas, should not flake or shed particles when lightly scratched and be smooth to the touch.
Doorframes for recessed fixtures are commonly available in a variety of materials, construction details and closure methods. The frames may be of aluminum, carbon steel or stainless steel and may be formed in one piece or assembled from extruded components. Extruded aluminum doors are specified most often, when the cleanroom process will permit, due to their cost advantage. If the cleanroom activity requires frequent wash down, such as in NSF/FDA or animal research clinics, a one-piece stainless steel door is generally specified and door closure is accomplished with countersunk screws.
Lens material is generally acrylic, but glass is occasionally used. The lens should be inverted, with the smooth side down for positive sealing and ease of cleaning. A uniform prismatic structure is most common, but a combination structure providing symmetric/asymmetric light distribution is available for special applications. The lens projects light down and away for general illumination to supplement specific task lighting.
Cleanrooms present numerous challenges to designing and specifying lighting systems. The mission-critical nature of cleanroom processes requires thorough analysis, specification and placement of the lighting fixtures.
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