Must-haves vs. nice-to-haves: Selecting the right cleanroom construction materials
06/01/2006
Scott A. Kouri, Porta-Fab Corporation and Raymond K. Schneider, P.E., Clemson University
The question of modular versus conventional cleanroom construction is increasingly common in high-tech industries, and one that may have a different answer depending on each individual project. Speed to market, however, is critical for almost all manufacturing companies, and it’s particularly important for the pharmaceutical and biopharmaceutical industries, which need to maximize the patent protection period after what is usually a long and expensive product development cycle. It’s also crucial for the microelectronics industry where technology changes on a near-daily basis.
Facilities are also being designed and constructed for maximum adaptability and to provide for minimal operational disruption or downtime. In order to meet this need, facilities must be constructed of components that not only allow change but provide the utmost flexibility as needs change in the market. Moving forward, it will be important to fully understand a project’s requirements and to separate required functional needs (must-haves) from aesthetic preferences (nice-to-haves). This article will examine critical selection criteria for determining the most efficient and cost-effective cleanroom construction technique, with a particular emphasis on the potential benefits offered by modular construction.
Construction site factors
Construction activities invariably result in disruption to areas surrounding the construction site. For example, dust generation, increased personnel, noise and vibration, access restrictions and accidental damage can negatively impact any job site. Pharmaceutical and semiconductor facilities are particularly sensitive to the dust and debris generated by conventional construction, which can be carried by personnel into other areas or drawn into ventilation inlets.
Availability of skilled labor is another consideration. Adherence to a construction budget can be greatly affected by labor instability and poor availability of construction materials. For example, after hurricane Katrina, resources for sheet rock were scarce since all available materials were being purchased to rebuild affected areas. And, constrained laydown areas can also be a challenge. Lack of storage space can potentially delay the build process and impose additional costs.
Project schedule, cost
Whenever a new product introduction requires a new purpose-built facility, construction must be carried out as quickly as possible. One way to reduce construction time is to perform as many construction activities in parallel as possible. This might entail, for example, installing chase walls together with process and utility lines.
Project costs and economics can be assessed in two ways: cost assessment-costs of the actual construction; and financial assessment-benefits derived from the speed of construction and improved cashflow.
 Table 1: Cost estimate per ft2 installed |
In general, building materials used for modular construction are more expensive compared to traditional construction materials (see Table 1). Although modular construction is initially more expensive than conventional construction (finished drywall averages about $10 to $12 per ft2) and can be built with readily available materials, the disadvantages can sometimes outweigh these attributes. For example, conventional construction is permanent, making modifications to any room expensive, messy and disruptive to the current operation. Existing walls cannot be reused and require new materials and labor, increasing renovation costs. There are also no tax advantages associated with this type of construction.
Regulations and standards
Any construction project, whether cleanroom-related or not, is subject to building codes. Regardless of construction technique, the overall objective of a building project is the same: The components of the cleanroom facility must satisfy local and national building regulations for fire protection and structural design. Materials are required to meet minimal flame and smoke development requirements (Class A non-combustible) or have fire separation walls (1- or 2-hour fire-rated for hazardous areas).
Design guidelines for architectural finishes used in cleanrooms and controlled environments can vary according to room classification, room usage, and product manufacturing. Therefore, finishes should be carefully evaluated for specific compliance. Architectural finishes are required to meet building regulatory requirements and should be accompanied by written documentation and certified test data verifying compliance. Applicable testing may include ASTM E84 Flame Spread and Smoke Development Values.
As part of the overall design, architectural systems and finishes should meet project-specific health and safety requirements, state and/or local building codes, and local seismic codes. Architectural systems should also have the ability to integrate process equipment and process utilities via utility chases or stainless-steel utility panels.
Cleanroom facilities have typically been classified under two different occupancy classifications: F (Factory and Industrial) and H (High Hazard). In addition to adopting major codes and procedures, most jurisdictions write amendments to the model codes to adapt them to local needs. The designer should become familiar with the general code requirements and modified local codes to make sure all the applicable rules have been found. Engineering design guides can assist in the design and the planning of cleanrooms and controlled environment areas. These sources include FDA guidance documents, United States Pharmacopeia (USP), European regulations, and industry guidance documents (e.g., ISPE Baseline Guides®, and IEST guidelines).
Very few industries are as highly regulated as the pharmaceutical industry. In fact, because the industry is so regulated, it’s not uncommon, when a certain methodology works for a facility, for an “if it’s not broken, why fix it” mindset to develop. Whenever possible, quality should be designed into the facilities to avoid any adverse impact on the product itself. Although other industries may not be subject to such strict regulation, the quality standards are no less critical to the operation.
Design for flexibility
The density of mechanical and process services, such as HVAC ducting, utilities and pipework for clean utilities, in a microelectronics or pharmaceutical facility can result in a congested technical space. Flexibility must therefore be foremost to accommodate expansion and modification as well as the integration of new equipment and tools. Hand-in-hand with this requirement is the need for quick change-over of equipment to minimize downtime in order to increase productivity, reduce cost and minimize any chance of contamination. If buildings have expandability and flexibility designed in, the cost of future change can be reduced.
The chases within walls of pharmaceutical facilities can serve to house mechanical ductwork, electrical utilities, process work, and additional utilities. Due to the amount of services running within the walls, chases may vary in thickness from 6 inches to 12 inches to 18 inches in depth. Access to these chases must be available and allow for future piping expansion capability.
Since equipment is continually moved in and out of cleanrooms, especially within the microelectronics industry, it’s important that the user be able to penetrate the walls separating bays from chases in any location via bulkhead openings. These bulkheads can be created using components to “box” around the equipment and an extruded gasket can interface with the wall to seal around the equipment (see Fig. 1).
Functionality is another important feature especially with regard to the use of vertical battens to connect wall panels or use of a seamless-type wall system. The seamless-type wall system provides a smooth look and continuous appearance. Although this feature is aesthetically appealing, the functionality is not always practical. Seamless-type walls are more critical in biotech and pharmaceutical applications for eliminating crevices in which organic material can grow. This is not as much of a concern in semiconductor facilities, where the batten only protrudes from the wall 1/16 inch.
Most semiconductor facilities experience modifications not only after the cleanroom has been installed but even during installation. Most equipment doesn’t arrive at the job site until much later in the project, or the layout may be altered based on a change in the process. In either case, the batten wall systems provide more flexibility and consistent appearance for in-field modifications.
The ability to support and hang piping and racks from the walls is another important feature for clearing up floor space in the chases without having to run frequently accessed lines under the raised flooring. This can be achieved by attaching struts to vertical studs and hanging the lines, while other stud posts have a built-in “strut cavity,” which eliminates the need for a separate strut framework altogether.
Choosing a modular system
It’s important to understand a project’s requirements and separate the required must-haves from the aesthetic nice-to-haves (see Table 2). The design of classified spaces requires that architectural finishes be designed to be smooth, easy to clean, nonshedding, and have minimal ledges and joints. Life science applications require radius corners for ease of cleaning, nonporous surfaces, and resistance to microbial and fungal growth. The architectural finishes should also be able to withstand repeated cleaning and sanitization with various chemical solutions.
 Table 2: Approaches to cleanroom design |
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Panel-post designs
Panel-post design is a popular and commonly used approach because the systems can be moved, reconfigured and expanded cleanly and easily. Utilizing a nominal 4-foot wide panel with a stud post, the stud post dismantles into two pieces, allowing a panel to be removed without disturbing other panels. All of the components can be reused in new configurations, and raceways built into the system allow easy access to utilities without endangering the classification or causing a rise in particle counts. These systems can also easily accommodate rack-mount utilities on chase walls and bulkhead openings.
A wide variety of smooth materials are available for wall panels and make cleaning easy. Materials include vinyl, melamine, high-pressure laminate, fiberglass reinforced plastic (FRP), PVC laminate, stainless steel or aluminum, and painted steel. Core materials include polystyrene, polyisocyanurate, fiberglass and aluminum honeycomb. These systems can be designed as freestanding enclosures placed inside of a larger structure, creating a self-contained envelope structure (see Fig. 2). These envelope structures can even be designed with load-bearing decks to support maintenance loads or mechanical equipment.
 Figure 2. A freestanding cleanroom envelope with load-bearing mechanical platform deck. Photo courtesy of PortaFab Corp. |
The advantages include lower up-front materials cost ($7 to $16 ft2) and complete prefabrication at the factory, minimizing or eliminating on-site cutting. Also, field modifications are easy, and the freestanding structure eliminates the need to reinforce the existing building roof to support equipment and ceilings. In addition, users can apply for accelerated depreciation. The disadvantages are that the joints at stud post locations protrude from the wall about .0625 inch and there are minimal flush-mount accessories (such as doors, windows, grille openings).
Panel-panel designs
Used more within the pharmaceutical arena, these systems can provide non-progressive construction for removal of a single panel without disturbing adjacent panels. Panel edges are formed edges with dog-bone, tongue-and-groove or cam-lock mechanisms to connect a panel directly to another panel, eliminating the ledge of the panel-post design. Joints are sealed with a caulk joint or chemical weld, producing a wall system conducive to wash-down applications. Some systems offer raceways built within the panel itself; otherwise, utilities must be surface-mounted onto the face of the panel or fit-up at the chases. Radius coving at floor, ceiling and corner connections provide easily cleaned corners, and windows and door frames are flush-mount across the plane of the wall.
The panel-panel systems are not load-bearing as designed and require an internal support structure or reinforcement at panel joints. The most common surfaces include UPVC-coated steel, stainless steel and painted steel, which can withstand a variety of cleaning agents and exposure times. Cores include polystyrene, fiberglass and aluminum honeycomb.
Advantages include complete prefabrica-tion at the factory, minimizing or eliminating on-site cutting, and minimal ledges and joints, producing an easy-to-clean surface. Also, they offer good aseptic detailing and radius coves, and users can apply for accelerated depreciation. Some disadvantages are the higher material costs ($22 to $30 ft2), the expense of double-chase walls for utilities and returns, and field modifications are more difficult due to the finished vertical panel edge.
Chases can be created in both the freestanding panel-post and panel-panel designs by installing a double run of wall, creating the chase wall on either side of the utilities. This can become an expensive design, however, depending on the panel construction used. The double-wall approach has been seen as a more cost-effective approach because:
- The metal stud framework provides support and a means of attachment for utilities and processes.
- The panels supported off the metal studs on both sides are thinner and occupy less space within the cleanroom.
- Double-wall panels on metal studs are less costly.
- Contractors can frame out the metal studs up front and install utilities prior to panels arriving.
Double-wall designs
Double-wall designs offer a unique solution for pharmaceutical applications. These systems integrate with a metal stud framework by hanging off one or both sides of the studs, creating a utility chase with a more economical panel. Panels have formed or cut edges to connect panels directly to one another and they utilize a caulk joint, gel coat or chemical weld, creating a smooth panel transition across the surface of the wall. Individual panels can be removed by striking the joints and removing the panel from the framework. Panel thicknesses are between 0.50 inch and 0.625 inch, and can provide an alternative to creating a chase wall from two thicker panels, which can be very costly. The use of a metal stud framework can also provide separate utility and electrical support and panels can be prepped for all fit-ups.
Easily cleaned radius covings are provided for all connections, while doors and windows are an integrated part of the system for flush-mounting into the walls. Freestanding envelopes can be created by using structural metal studs or columns within the chases to carry beam loads.
A wide range of surfaces are available for these systems, including fiberglass-reinforced plastic, stainless steel, glassboard, painted steel or aluminum, and PVC-coated steel-all of which are chemically resistant to aggressive cleaning agents. Core materials include aluminum honeycomb, XP board and gypsum.
Furring wall designs
Furring wall systems can be attached to any solid wall or wall surface, including block, concrete and drywall. These systems are a good solution for upgrading existing areas in lieu of using a full freestanding panel, which can be very costly.
There are various attachment methods for securing panels to existing surfaces. Wall systems for microelectronic applications generally use an extruded aluminum batten every 4 feet between vertical panel edges and have concealed fasteners. Pharmaceutical systems may use a hanging “Z” clip attachment, which supports the panels and provides formed or cut edges in conjunction with a caulk joint, gel coat or chemical weld, creating a smooth transition from panel to panel.
Non-progressive construction with any of the systems allows panels to be removed without disturbing adjacent panels.
Spaces requiring a fire-rated perimeter often use a furring system to finish off walls with a cleanable, nonshedding surface. Column enclosure also benefits from using a furring system to finish onto drywall or to create return chases with strut or metal studs.
Panel thicknesses of 0.25 inch to 0.625 inch are available with painted aluminum or steel, fiberglass-reinforced plastic, stainless steel, and PVC-coated steel. Core materials include aluminum honeycomb, XP board and gypsum.
Conclusion
Project scope, design requirements, manufacturing processes, and construction schedule are all factors in the consideration and selection of construction materials for cleanroom environments. The material selection review process will ensure that the materials meet the design requirement for the specific manufacturing process and that these materials comply with accepted design and regulatory guidelines.
Scott Kouri is sales manager for Porta-Fab (Chesterfield, Mo.). He can be reached at [email protected].
Raymond K. Schneider, P.E., is the Interim Chair of the Department of Construction science and Technology at Clemson University. He can be reached at [email protected].
The case for modular construction
Modular cleanroom construction can offer a number of important advantages over conventional (stick-build) approaches. For example, modular walls are an inherently dry construction material with little or no modification required for installation, thus minimizing dust generation. Modular systems can also be manufactured from materials that are nonshedding and non-particulating.
Since modular construction creates little dust, a “clean build” approach can be taken by installing other critical processes along side it. Fit-outs can be cut into panels at the same time as the erection of the system, reducing the project schedule. For less complicated non-pharmaceutical projects, it has been shown that modular construction can reduce construction time by 20 to 40 percent through parallel construction. In addition, modular construction greatly enhances facility clean-up post-construction.
Modular construction can also offer a solution to a lack of skilled labor in any given market. Modular walls are manufactured to provide a consistent quality, which can vary with conventional construction from one section of a cleanroom to another depending on the skill level of the laborers. Since modular construction is prefabricated, the modular system manufacturer and contractor can also coordinate project schedules and have construction materials shipped in stages based on the portion of the facility being built. As that section is being built, the next group of materials can be staged and shipped to coordinate with the completion of the previous installation.
Although modular walls are more expensive up-front, costs can be offset by the savings achieved through greater productivity. For example, modular construction results in less construction material waste because of greater reliance on standard construction sizes and prefabrication of components. Since mterials are pre-engineered and cut to size at the factory, in many cases on-site cutting of materials can be completely eliminated. In addition, modular construction can be considered a piece of equipment in most states and therefore subject to accelerated depreciation and tax considerations.
Modular construction also offers advantages for meeting regulatory requirements and standards. Modular wall systems are manufactured with factory-controlled procedures, producing a consistent, quality product with no variation. This ensures that what has been successfully employed at one facility will perform the same in future installations The material must also be installed in a set manner, producing a consistent appearance.
Prefabricated wall systems incorporate the principles outlined in current engineering guidelines and apply them to cleanroom design and construction. Modular architectural systems have incorporated design criteria for system performance following good engineering practices, taking into account GMP, cGMP, safety, health, regulatory requirements, and industry guidelines.
Modular design also accommodates the need for flexibility. For example, non-progressive construction with demountable walls allows the removal of individual wall panels without disturbing adjacent panels, flooring or ceiling. In addition, modular systems can be disassembled and modules can be relocated to quickly create or expand cleanrooms, lowering the costs of expanding existing pilot plants or low-volume launches to high-volume operations.
Modular wall systems can be designed with access panels into the chases. Full-size panels can also be easily removed to access larger openings into the chases. Modular panel systems allow owners and contractors the ability to make field modifications during the process installation, offering additional installation flexibility and potential design cost savings. The ability to use standard components offers economic savings by decreasing design costs and increasing construction predictability.
Customers can buy or lease modular cleanrooms, which are considered a piece of equipment, not a part of the existing structure. This means significant financial advantages because they can be depreciated at an accelerated rate. For a company leasing space, a modular room remains the property of the lessee, while any conventional construction would remain with the space and be the property of the lessor.
Flexibility remains a key design option in the use of modular architectural systems, as well as the ability to incorporate only those materials that best suit the project scope and design requirements. Pre-engineered modular architectural systems for cleanrooms and critical environments can offer owners, architects, and engineers construction alternatives and flexibility while maintaining the design criteria and regulatory guidelines required for specialty cleanroom environments.