Clean Room Design Standards
For those companies that need to adhere to specific design standards, they must understand that clean rooms can be built and operated to meet different cleanliness classifications, depending on the environmental conditions required for their use.

The primary authority for clean room classifications is the International Organization for Standardization or ISO.

ISO 14644 classifies a clean room based on the size and number of airborne particles per cubic meter of air. Prior to the implementation of ISO 14644, Federal Standard 209E set the industry guidelines for clean room classification. Both standards are displayed in the table at right.

Airflow Design Patterns
To achieve the required environmental conditions, the air in a clean room is purified using High Efficiency Particulate Air (HEPA) filters. Air is forced through the filters, which remove particles as small as 0.5 microns. The filtration system depends upon the required level of cleanliness.

Single Pass Design
In "single pass" design, ambient air is filtered into the cleanroom and transferred out into the surrounding building space.

Single pass designs are commonly used in environments that do not require temperature and humidity control.

Recirculating Air Design
In "recirculating" air designs, air handling units condition the air, which is drawn through low wall returns and into the ceiling plenum.

These designs are typically used for cleanrooms with temperature or humidity requirements, and to isolate the environment for greater process control. .

Design for Flexibility
The density of mechanical and process services in a microelectronics or pharmaceutical facility (i.e. HVAC ducting, utilities and pipework) can result in a congested technical space. Flexibility must therefore be integrated into the overall design of the cleanroom in order 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 cleanrooms are designed with expandability and flexibility in mind, the cost of future change will be reduced.

Chase Walls
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.

Bulkheads
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 image at right).

Seamless Walls (where needed)
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.

Batten Walls
Most semiconductor facilities experience modifications not only after the cleanroom has been installed but even during installation. Often times, equipment may not arrive at the job site until much later in the project, or the layout may need to be altered based on a change in the process. In either case, the batten wall system provides more flexibility and a consistent appearance for in-field modifications.

Struts
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 Cleanroom System
It’s important to understand a project’s requirements and separate the required must-haves from the aesthetic nice-to-haves (see table below). The design of clean rooms and classified spaces requires that architectural finishes be designed to be smooth, easy to clean, non-shedding, 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 sanitizing with various chemical solutions.

Common Design Configurations
Below are four common types of clean room configurations that can be used for a variety of different cleanroom applications.

Panel-post Cleanrooms
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 image at right). These envelope structures can even be designed with load-bearing decks to support maintenance loads or mechanical equipment.

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 Cleanrooms
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 prefabrication 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 Cleanrooms
Double-wall clean room 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 Cleanrooms
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, non-shedding 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.