Cleanroom Design Considerations

Let's address some of the many considerations when designing and building a cleanroom. While an exhaustive list would be a thirty-page document, we can highlight some of the common issues, and nomenclature and view a chart with typical designations. Addressing some of the thoughts below early in the process can help your cleanroom be more effective and efficient.

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Are You Overthinking Your Cleanroom?

Be mindful of the tendency to over-engineer your space. You may have a very sensitive cleanroom, like an ISO 5 or lower; in this case, caution over budget or lead times is advised. However, many cleanrooms can be built faster and cost-efficiently with a dose of pragmatism. Do you need a VESDA system, or will smoke detectors near areas with potential flammability suffice? While Lighthouse-style electronic monitoring systems are excellent, do you need them for the single 800 ft2 cleanroom your organization monitors? I’ve installed these systems in many cleanrooms that needed them; however, you’ll want to address the use case and value of items like these with your internal experts and design/construction teams.

• Does your cleanroom need to be ISO or FED Certified? If so, see the chart below for classification levels. If a certification is not required, but you need a clean manufacturing or dust-reduced environment for your quality standards, you may consider building your space to the ISO 8 standard without certifying it. This can set the space up to provide the environment you need while allowing the option of future certification. Note that the last three cleanrooms built by the author, to ISO 8 standards, met the ISO 5 standards for particulate count. This situation isn’t uncommon when dealing with high-quality design and construction teams.?

• If you plan to build to the ISO 7, 8, or 9 Standard, some typical cleanroom componentry may not be required. You’ll need to address your goals before deciding which components you need. For example, you may not need a cleanroom ceiling grid rated ISO 6-1 when a less expensive grid system that accepts cleanroom grade gasket may be acceptable for your purposes. This is an example of the many considerations that should be discussed with a knowledgeable design and construction team.

• Does your maximum ISO requirement reflect the overall needs of your space? Do you have specific components that require ISO 6 or 7, while most of your work only requires ISO 8? This presents an opportunity to build an ISO 8 cleanroom with an additional modular unit inside that meets the higher standard for that specific ISO 6 or 7 need. This could lead to significant cost savings.

Will Your Environment Tolerate Silicone?

Silicone is a marvelous material, especially for caulking in cleanrooms. That said, many cleanrooms are utilized by aerospace, industrial, semiconductor manufacturing, and other industries sensitive to silicone off-gassing. This can be a game-changing factor for the design and construction of these spaces. You may initially think of clear caulking, but silicone can be present in many caulks, gaskets, adhesives, specific piping, plastics, etc. Ensure your design and construction team are clear about your silicone sensitivities.

Hidden Sources of Friable Particulate

Hidden sources of friable (easily shed and made airborne) material and particulates can often be found in even the newest cleanrooms. While it may take a keen eye to notice that galvanized exhaust fitting, the unpainted gray conduit that looks like the gray painted conduit, or that a pipefitter is using the white Teflon tape, in more sensitive cleanrooms, your particle counter might notice. ?Below, I’ll list some easily missed sources of unnecessary particles that you can look for as an owner or facilities professional.

• Galvanized components. These can be found among conduit or equipment fittings, electrical components, structural members, roof decking materials, screws and fasteners, HVAC ducting and related components, and plumbing or piping components. The worst offenders in the world of galvanization are items that are “hot-dipped” galvanized. Hot-dipped components are a source of quick shedding and airborne (friable) contamination. ?Galvanized components that are not hot-dipped can be mitigated with an encompassing coat of epoxy paint. Hot-dipped components should be removed from clean spaces.

• Teflon and other non-stick-treated components. As mentioned above, the white Teflon tape used to connect fluid and gas piping can produce friable particulate. Other leak-reducing tapes are available.

• Insulated ducting. While insulated ducting is excellent for sound attenuation, the insulation can cause several problems. One is that it can trap particulate that should be caught and removed by the filtration system. This may sound acceptable, but this entrapment is temporary and allows for the coupling of particles to create even larger particulates that will eventually break free. The second issue is the nature of insulation; it is prone to shedding. These issues can cause more rapid degradation of the HEPA filtration system and increase particle counts in the cleanroom.

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Can You Limit Dust-collecting Items That Are Surface-mounted?

The design of a cleanroom naturally focuses on smooth, cleanable, and non-porous surfaces. Significant effort is spent specifying components to meet these goals, from epoxy paints that are difficult to apply to smooth duct connections. Anti-static measures range from ESD (static dissipative) flooring to humidity control and de-ionized water systems, which are integrated to protect sensitive equipment from shock and help prevent particles from sticking to surfaces. These systems are necessary but can have their effectiveness limited by improperly planned or installed utilities that are surface mounted on the walls of the space. Utilities like power, VESDA or other smoke detection systems, monitoring apparatuses, safety features, and gasses are often surface-mounted, creating particle collection issues and barriers to proper cleaning. While these items may not be able to be avoided, early consideration within the design can mitigate their negative impact. For instance, cleanrooms utilizing multiple walls for in-wall plenum air returns are typically designed to have all components surface mounted. The logic behind this is that having conduits and other utility feeds inside a plenum creates dust-collecting surfaces that are difficult to access, and cleaning these can be problematic. Some additional questions or considerations at the design phase can help address these issues. Can the room accept thicker wall systems that allow a utility chase created by using a 1 5/8” metal stud separating the plenum-facing substrate from the material (possibly drywall with rated epoxy paint) that you will see, and your technicians will clean? This allows conduits and other supplies to be installed behind your clean wall while also being separated from your plenum. A design like this increases utility and wall construction time and expense. Still, it can save technician and cleaning crew person-hours for the life of the cleanroom while drastically limiting particle collecting or producing surface exposure to the space.

You can assess needs versus wants and the amalgamation of component supply utilities. Can an electrical busbar at worker height be installed versus installing multiple outlets? Individual outlets require individual conduits, while a busbar can accommodate many outlets with various power outputs with only one conduit input. Gas and liquid supplies can also be provided via manifolds with quick connections. This minimizes permanently installed supply locations while allowing flexibility for users and equipment configurations.

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Some Common Cleanroom Items and Definitions

• Magnehelic Gauge: This is a dial-style instrument that measures the internal pressure of the cleanroom using Pascals or inches of water. Cleanrooms need consistent positive pressure levels to maintain low particulate counts. The magnehelic gauge shows the level of positive pressure.

• HEPA Filters and or Fan Filters: These terms are often intertwined. HEPA filters are technically the filter medium that can be easily replaced. In contrast, the fan filter is the powered, ceiling-installed unit that contains the HEPA filter used to clean air pumped into the cleanroom. Together, these items help to create the positive pressure, air changes, and particulate-reduced environment of a cleanroom.

• Air Shower: An air shower is a component that disturbs and contains any particulates that may be on a technician before entering a cleanroom. The air shower is the last space one enters before accessing the cleanroom. These are typically sized for one person; imagine a 7’ tall by 4’ stainless steel rectangle with ingress and egress doors. This self-contained box blows high-pressure air onto the user from many ports along its vertical wall(s). The air (and any rouge particles) is sucked into the floor, ceiling, or both. The doors on an air shower should be electronically staggered, meaning that the entry door and exit door (into the cleanroom) should not be able to be opened at the same time. This is to avoid a pressure cascade from the cleanroom, as cleanrooms are designed to have significant positive pressure. Note that the air shower is typically a prebuilt component that can have very long lead times, needs to be installed into the cleanroom perimeter wall, requires power, and needs to be installed before ESD or other cleanroom flooring.

• ESD Flooring: Electrostatic Discharge Flooring. This is a floor coating, typically epoxy-based, that contains components like graphite, metal-coated particles, and/or conductive carbon. ESD flooring is designed to discharge or conduct static electricity that can build up from general movement, walking, and lower humidity environments. Static electricity that is not adequately discharged can damage sensitive electronic components. Humidity controls in cleanrooms can help limit static electricity as well. Note that the ESD floor must be grounded and have verifiable conductivity and thickness. Installing these floors is time and labor-intensive compared to standard epoxy flooring and does not allow other trades to work while they are being installed. These floors must be one of the last components installed in a cleanroom.

• Lighthouse Systems: This is a common name for cleanroom remote air quality monitoring systems, though they may go by other brand names or general verbiage. This system works similarly to a VESDA system, using a vacuum to bring air into a highly sensitive apparatus. The lighthouse apparatus can be specified to perform different functions based on need. These functions often include real-time updating of airborne particulate count and pressure readings. This gives the owner remote cleanroom status information. These systems typically utilize transparent hosing vs the conduit used in a VESDA system. Most of these systems do not function well with hose lengths more than 100’ from the sensor apparatus. The apparatus is typically not in the cleanroom but in a nearby central utility plant, control room, or other space.

• De-ionized Water Systems / DI Water: Deionized water is used in cleanrooms due to its lack of contaminants. Water that has been deionized absorbs contaminants from surrounding sources, making it attract dirt and dust from surfaces. With DI water being free of impurities, it does not leave spots or residue on surfaces. DI water and Isopropyl Alcohol (IPA) are the typical cleaning agents for ISO-rated cleanrooms level 8 and under.

• VESDA Systems: ‘Very Early Smoke Detection Apparatus.’ VESDA is a type of fire alarm system installed in spaces that need far more smoke sensitivity than typical laser interruption smoke detectors can provide and/or spaces that circulate or contain too much air for typical smoke detectors to function correctly. VESDA is a system of sealed conduit (usually orange in color) connected to a vacuum that actively pulls air into a highly sensitive particulate detection device. This device can alert users of fires or fire risks and rapidly detect smoke in areas with high ceilings or large open spaces and in areas with abnormally high rates of air turnover. VESDA systems can also have their conduits placed strategically when areas of greater risk are identified.??

I hope that this has given you some ideas to improve your cleanroom design and build. Many more considerations will be necessary for a fluid construction process and user experience. Caution is advised when determining your design and construction teams. Feel free to reach out for a discussion about your individual needs.

For more information about SCIFs, Cleanrooms, or other Advanced Technology design and construction, contact me at [email protected]

*This article was not written with A.I. Constructive criticism is always welcome!

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