Cleanroom construction is nothing new in the literal sense, dating back more than a hundred years to hospital environments. The process was later applied to industrial manufacturing during World War II as a means for safeguarding instrumentation during the production of munitions, tanks, and aircraft. However, the evolution of cleanroom construction and the expanded applications for these projects today have helped create a renaissance business, equal in stature to sustainable design and green construction.
The cornerstone of cleanroom development is, of course, the control of contamination, specifically airborne particulate matter that naturally occurs, such as dust, dirt, pollen, bacteria, and other microorganisms, even sea mist. Industrial functions, office activity, and workplace personnel, too, contribute significantly to airborne contamination, including particulates generated from combustion processes, chemical vapors, and friction in manufacturing equipment and contaminate particles emitted in the form of skin flakes, lint, cosmetics, and respiratory gases.
In most instances, the required standard of cleanliness of a room area depends on its purpose. Federal Standard 209E, considered the benchmark for cleanliness for many industries, defines a cleanroom as that in which the concentration of airborne particles is controlled to a specified maximum number of particles 0.5 microns in size per cubic foot (or cubic meter) of sampled air. Usually, cleanroom cleanliness is expressed in terms of classification areas or numbers, such as Class 100 or Class 100,000. For example, those classifications would denote there should be no more than 100 or 100,000 particles, respectively, larger than 0.5 microns per cubic foot of air during the sampling period.
The more susceptible a product or procedure is to contamination, the more stringent the FS 209E requirements become. And as technology advances, the purposes for cleanrooms increase, too. Aside from hospital health care, cleanroom construction has carved niches into numerous other industries: electronics, semiconductors, micromechanics, optics, biotechnology, pharmaceuticals, medical devices, and food and beverages.
Today, a substantial number of manufacturing or production processes require that area spaces be designed and constructed to control particulate and microbial contamination, while maintaining reasonable installation and operating costs. Not surprising, the key stakeholders in modern-day cleanroom construction have become the mechanical engineers who must design and build HVAC systems sophisticated enough to satisfy FS 209E requirements.
Professional Engineer Abraham Marinelarena, a specialist in cleanroom development and senior mechanical engineer for Bath Consulting Corp. in
Texas, notes that cleanrooms have evolved into two major types, differentiated by their method of ventilation—turbulent air flow and laminar air flow. The general method of ventilation used in turbulent air flow cleanrooms is similar to that found in general building and plant construction, with air supplied by an air-conditioning system through diffusers in the ceiling structure. However, a cleanroom differs from an ordinary ventilated room in three ways: increased air supply, use of high-efficiency particulate air filters, and room pressurization.
Laminar air flow, Marinelarena explains, is used when low airborne concentrations of particles or bacteria are required. This air flow pattern is in one direction, usually horizontal or vertical and at a uniform speed of between 60 to 90 feet per minute throughout the entire cleanroom area. The air velocity must be sufficient to remove relatively large particles before they settle onto surfaces and must take into account practical situations, such as room obstructions and personnel moving around. Any contaminant released into the air can be immediately removed by laminar air flow, whereas turbulent air flow ventilation relies on mixing and dilution to remove contamination.
Although air flow design is critical, Marinelarena emphasizes that it alone does not guarantee that cleanroom conditions will be satisfied. “Construction finishes, personnel and clothing, materials and equipment, and points of egress are other sources of particulate contamination that must also be controlled,” he says. In particular, room construction and material finishes are a significant part of cleanroom design, he points out, because not only is it vital to exclude outside contaminants, it is also important that material finishes not contribute to particle generation in the cleanroom space itself.
Benchmark Engineering Group Inc. of Toledo, Ohio, recognized cleanroom consultants, also stresses the importance of carefully selected construction materials and products that meet cleanroom standards, including walls, floors, ceiling tiles, lighting fixtures, doors, and windows. Benchmark’s clean construction guidelines cite the maintenance of ventilation as paramount, noting, “Contamination of the existing house ventilation can be prevented by isolating supply air dampers in the construction areas to prevent a positive pressure within the construction space.” Maintaining construction in a state of negative pressurization should always be the primary goal.
“A cleanroom requires the highest standards of construction,” says Space Industries Ltd. of
England. “The construction materials used to build cleanrooms can differ greatly from those used in non-cleanroom construction.” For example:
A cleanroom should be built with an airtight structure.
The internal surface finish should be smooth and suitable for cleaning.
The internal surface finish should be sufficiently tough to resist chipping or powdering when impacted or abraded.
Some process chemicals, cleaning agents, disinfectants, and water may attack or penetrate conventional finishes.
In some cleanrooms, electro-dissipative construction materials will be required.
In some cleanrooms, construction materials that give a minimum of “outgassing” will be necessary.
Additionally, materials that are used for cleanroom construction should be smooth on the surface facing the inside of the cleanroom, and all butts and joints as seen from the inside of the cleanroom should not show openings that may harbor, and then disperse, dirt.
All cleanrooms, as expected, have their own specific protocols for construction and operation. When designing and constructing a pharmaceutical cleanroom, for instance, the International Journal of Pharmaceutical Compounding says several critical factors must be considered, such as policies and procedures, employee training, aseptic technique and process validation, ongoing environmental monitoring, facility maintenance, and compliance auditing. If these factors are not properly addressed, problems of quality, operation, or maintenance will result. It is often suggested that professional independent consultants be retained who can serve as project managers for constructing cleanrooms for specific industries.