Cleanroom Classifications

Cleanrooms are classified according to the number and size of particles permitted per volume of air. Large numbers like &#;class 100&#; or &#;class &#; refer to FED_STD-209E, and denote the number of particles of size 0.5 mm or larger permitted per cubic foot of air. The standard also allows interpolation, so it is possible to describe e.g. &#;class .&#;

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Small numbers refer to ISO -1 standards, which specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per cubic meter of air. So, for example, an ISO class 5 cleanroom has at most 105 = 100,000 particles per m3.

Both FS 209E and ISO -1 assume log-log relationships between particle size and particle concentration. For that reason, there is no such thing as zero particle concentration. Ordinary room air is approximately class 1,000,000 or ISO 9.

ISO Cleanroom Standards

Before global cleanroom classifications and standards were adopted by the International Standards Organization (ISO), the U.S. General Service Administration&#;s standards (known as FS209E) were applied virtually worldwide. However, as the need for international standards grew, the ISO established a technical committee and several working groups to delineate its own set of standards.

FS209E contains six classes, while the ISO -1 classification system adds two cleaner standards and one dirtier standard (see chart below). The "cleanest" cleanroom in FS209E is referred to as Class 1; the "dirtiest" cleanroom is a class 100,000. ISO cleanroom classifications are rated according to how much particulate of specific sizes exist per cubic meter (see second chart). The "cleanest" cleanroom is a class 1 and the "dirtiest" a class 9. ISO class 3 is approximately equal to FS209E class 1, while ISO class 8 approximately equals FS209E class 100,000.

By law, Federal Standard 209E can be superseded by new international standards. It is expected that 209E will be used in some industries over the next five years, but that eventually it will be replaced internationally by ISO -1.

ISO is an independent, non-governmental international organization with a membership of 162 national standards bodies. Through its members, it brings together experts to share knowledge and develop voluntary, consensus-based, market relevant International Standards that support innovation and provide solutions to global challenges.

Airborne Particulate Cleanliness Class ComparisonISO -1FEDERAL STANDARD 209EISO ClassEnglishMetricISO 1ISO 2ISO 31M1.5ISO 410M2.5ISO M3.5ISO 61,000M4.5ISO 710,000M5.5ISO ,000M6.5ISO 9

Airborne Particulate Cleanliness Class (by cubic meter):CLASSNumber of Particles per Cubic Meter by Micrometer Size0.1 microns0.2 microns0.3 microns0.5 microns1 micron5 micronsISO ISO ISO 31,ISO 410,,,ISO ,,,,ISO 61,000,,,,,ISO ,,,930ISO 83,520,,,300ISO 935,200,,320,,000

In cleanrooms, particulate concentration changes over time &#; from the construction and installation of equipment to its operational status. ISO delineates three cleanroom classification standards: as-built, at-rest and operational. As instruments and equipment are introduced and particulates rise, an "as-built" cleanroom becomes an "at-rest" cleanroom. When people are added to the matrix, particulate levels rise still further in the "operational" cleanroom.

ISO -2 describes the type and frequency of testing required to conform to certain standards. The following tables indicate mandatory and optional tests.

Required Testing (ISO -2)

Schedule of Tests to Demonstrate Continuing ComplianceTest ParameterClassMaximum Time IntervalTest ProcedureParticle Count Test<= ISO 56 MonthsISO -1 Annex A> ISO 512 MonthsAir Pressure DifferenceAll Classes12 MonthsISO -1 Annex B5AirflowAll Classes12 MonthsISO -1 Annex B4

Optional Testing (ISO -2)

Schedule of Additional Optional TestsTest ParameterClassMaximum Time IntervalTest ProcedureInstalled Filter LeakageAll Classes24 MonthsISO -1 Annex B6Containment LeakageAll Classes24 MonthsISO Annex B4RecoveryAll Classes24 MonthsISO -1 Annex B13Airflow VisualizationAll Classes24 MonthsISO -1 Annex B7

Today, in addition to ISO -1 and ISO -2, eight other cleanroom standards documents are being prepared. Many are in the final voting stage and can be legally used in the trade (see chart).

ISO DocumentTitleISO -1Classification of Air CleanlinessISO -2Cleanroom Testing for ComplianceISO -3Methods for Evaluating and Measuring Cleanrooms and Associated Controlled EnvironmentsISO -4Cleanroom Design and ConstructionISO -5Cleanroom OperationsISO -6Terms, Definitions and UnitsISO -7Enhanced Clean DevicesISO -8Molecular ContaminationISO -1Biocontamination: Control General PrinciplesISO -2Biocontamination: Evaluation and Interpretation of DataISO -3Biocontamination: Methodology for Measuring Efficiency of Cleaning Inert Surfaces

The USA Source for ISO documents is:

Institute of Environmental Sciences & Technology (IEST)
Newport Drive, Suite 506
Rolling Meadows, IL -
http://www.iest.org
: (847) 255-
Fax: (847) 255-

The source for FS209E documents at the General Services Administration is:

Standards Order Desk
Naval Publications and Forms Center
700 Robbins Avenue
Section D BLD4
Philadelphia, PA
: (215) 697-
Fax: (215) 697-

ISO and Federal Air Change Rates for Cleanrooms

A critical factor in cleanroom design is controlling air-change per hour (ACH), also known as the air-change rate, or ACR. This refers to the number of times each hour that filtered outside air replaces the existing volume in a building or chamber. In a normal home, an air-conditioner changes room air 0.5 to 2 times per hour. In a cleanroom, depending on classification and usage, air change occurs anywhere from 10 to more than 600 times an hour.

ACR is a prime variable in determining ISO and Federal cleanliness standards. To meet optimal standards, ACR must be painstakingly measured and controlled. And there is some controversy. In an appendix to its ISO -1 cleanliness standard, the International Standards Organization addressed applications for microelectronic facilities only. (ISO classes 6 to 8; Federal Standards 1,000, 10,000 and 100,000.) The appendix contained no ACR standards for pharmaceutical, healthcare or biotech applications, which may require higher ACR regulations.

According to current research, case studies and experiments, using an ACR range (rather than one set standard) is a better guideline forcleanliness classification. This is true because the optimal ACR varies from cleanroom to cleanroom, depending on factors such as internal equipment, staffing and operational purpose. Everything depends on the level of outside contaminants trying to enter the facility versus the level of contaminants being generated on the inside.

The breadth of these ranges reflects how dramatically people and processes affect cleanliness. Low-end figures within each contamination class generally indicate air velocity and air change requirements for an as-built or at-rest facility &#; where no people are present and no contaminating processes under way. When there are people and processes producing contaminants, more air changes are required to maintain optimal cleanliness standards. For instance, some manufacturers insist on as many as 720 air changes per hour to meet Class 10 standards.

Determining the appropriate number of air changes for a particular application requires careful evaluation of factors such as the number of personnel, effectiveness of garbing protocol, frequency of access, and cleanliness of process equipment.

Rajan Jaisinghani, in his paper "Energy Efficient Low Operating Cost Cleanroom Airflow Design," presented at ESTECH , recommended the following ranges based on FS209E classifications:

FS Cleanroom ClassISO Equivalent ClassAir Change Rate1ISO -ISO -ISO -,000ISO -,000ISO 760-,000ISO 85-48

Jaisinghani&#;s recommendations concur with other recent studies of ACR, which criticize some existing air rate standards (developed in the s) as being unscientific because they are based on fans and filters inferior to today&#;s models. So when these older standards are applied, the resulting ACR is often too high. In fact, some studies have found that reducing the ACR (and its attendant air turbulence) can result in a cleaner atmosphere.

This was demonstrated in a study conducted by Pacific Gas and Electric (San Francisco) and the Lawrence Berkeley National Laboratory (Berkeley). The study measured air change rates in several ISO Class-5 cleanrooms and came to the conclusion that there is "no consistent design strategy for air change rate, even for cleanrooms of the same cleanliness classification."

ACR rates have critical design implications, especially when considering desired cleanliness, fan size and lower energy costs. The PG&E/Berkeley study caused many designers to reduce fan sizes. In short, a lower ACR often resulted in cleaner air.

The study revealed three abiding principles:

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• Lower air change rates result in smaller fans, which reduce both initial investment and construction cost.
• Fan power is proportional to the cube of air change rates or airflow. A 30-percent reduction in air change rate results in a power reduction of approximately 66 percent.
• By minimizing turbulence, lower airflow may improve cleanliness.

The study focused on Class-5 cleanrooms, concluding that an ACR range of from 250 to 700 air changes per hour is standard, but that "actual operating ACRs ranged from 90 to 625." It added that all of these optimized cleanrooms were certified and performing at ISO Class-5 conditions with these lower ACRs. Finally, the study concluded that rarely does a Class-5 facility require an ACR of more than 300.

The study also found that the "[b]est practice for ACRs is to design new facilities at the lower end of the recommended ACR range," with variable speed drives (VSDs) built in so that air flow adjustments can be made under actual operating conditions.

In his report "An examination of ACRs: An opportunity to reduce energy and construction costs," Peter Rumsey, PE, CEM, essentially concurred with the PG&E-commissioned study by Berkeley. Rumsey issued a caveat, then brushed it aside by citing research subsequent to Berkeley&#;s: "Air cleanliness is a critical component of any cleanroom, far outweighing energy saving priorities. Designers and operators need evidence from others who have tried similar strategies in order to address the perceived risks of lowering air change rates."

Rumsey then went on to cite studies done by International Sematech (Austin, Texas); the Massachusetts Institute of Technology (Cambridge, Mass.); Intel (Santa Clara, Calif.); and Sandia National Laboratories (Albuquerque, N.M.), which echoed the Berkeley study.
In summary, current research and thinking on air change rates indicate that some existing standards are too high and can be lowered while still meeting all ACR criteria.

Federal and ISO Ceiling Fan Coverage Specifications

Achieving the optimal air change rate requires proper ceiling fan coverage. The cleanest modular cleanroom incorporates filter/fan units (FFUs) in every 2&#; x 4&#; (610 mm x mm) ceiling bay. This near-100% coverage provides a laminar flow of filtered air to quickly remove contaminants from the room, thus meeting FS209E standards for Class 10 and ISO Class 1 standards.

Such coverage, especially in a large cleanroom, can lead to higher energy consumption, thus increasing costs for both initial construction and ongoing operation. In most cases, a smaller percentage of ceiling coverage produces adequate cleanliness.

This table illustrates the percentage of ceiling coverage recommended for each cleanliness class, again as a range:

ClassCeiling Coverage (Percentage)ISO 8 (Class 100,00)5 &#; 15%ISO 7 (Class 10,000)15 &#; 20%ISO 6 (Class 1,000)25 &#; 40%ISO 5 (Class 100)35 &#; 70%ISO 4 (Class 10)50 &#; 90%ISO 3 (Class 1)60 &#; 100%ISO 1 &#; 280 &#; 100%

Federal and ISO Airflow Velocity Standards

In addition to ACR and ceiling coverage, the third factor integral to maintaining cleanliness is fan-generated air speed. Again, higher airflow velocity results in a "cleaner" cleanroom. The term "ventilation efficiency" refers to the speed of filtered air passing through the cleanroom in addition to the number of air changes per hour (ACH or ACR).

An earlier chart showed a range of recommended air change rates (ACRs) for different classes of cleanrooms. Ranges are given because as-built and at-rest facilities require a smaller ACR than an operational cleanroom, where both people and equipment are actively engaged. Non-operational cleanrooms are found in the lower range; operational cleanrooms higher.

Combining all three factors &#; ACR, ceiling coverage and airflow velocity-results in the following table:

Class ISO -1 (Federal Standard 209E)Average Airflow Velocity m/s (ft/min)Air Changes Per HourCeiling CoverageISO 8 (Class 100,000)0.005 &#; 0.041 (1 &#; 8)5 &#; 485 &#; 15%ISO 7 (Class 10,000)0.051 &#; 0.076 (10 &#; 15)60 &#; &#; 20%ISO 6 (Class 1,000)0.127 &#; 0.203 (25 &#; 40)150 &#; &#; 40%ISO 5 (Class 100)0.203 &#; 0.406(40 &#; 80)240 &#; &#; 70%ISO 4 (Class 10)0.254 &#; 0.457 (50 &#; 90)300 &#; &#; 90%ISO 3 (Class 1)0.305 &#; 0.457 (60 &#; 90)360 &#; &#; 100%ISO 1 &#; 20.305 &#; 508 (60 &#; 100)360 &#; &#; 100%

Before deciding on the appropriate velocity and air changes for your application, Terra Universal recommends careful evaluation of factors such as number of personnel, effectiveness of garbing protocol, access frequency and cleanliness of process equipment. Once the required air change figure is established, the number of required FFUs can be determined using this formula:

No. of FFUs = (Air Changes/Hour ÷ 60) x (Cubic ft. in room ÷ 650*)
*CFM output of a loaded FFU

Meeting Class 100 standards using the low-end air change recommendation (240/hour) inside a 12&#; x 12&#; x 7&#; ( mm x mm x mm) cleanroom, with cu. ft. of volume, requires 6 FFUs. To meet the same standard using the high-end air change recommendation (480/hour) requires 12 FFUs.

Positive Pressure

Cleanrooms are designed to maintain positive pressure, preventing "unclean" (contaminated) air from flowing inside and less-clean air from flowing into clean areas. The idea is to ensure that filtered air always flows from cleanest to less-clean spaces. In a multi-chambered cleanroom, for instance, the cleanest room is kept at the highest pressure. Pressure levels are set so that the cleanest air flows into spaces with less-clean air. Thus, multiple pressure levels may need to be maintained.

A differential air pressure of 0.03 to 0.05 inches water gauge is recommended between spaces. In order to ensure that pressure differentials remain constant when doors are opened, or other events occur, control systems must be in place.

Laminar and Turbulent Air Flow

ISO 5 (Class 100) and cleaner facilities rely on unidirectional, or laminar, airflow. Laminar airflow means that filtered air is uniformly supplied in one direction (at a fixed velocity) in parallel streams, usually vertically. Air is generally recirculated from the base of the walls back up to the filtering system.

ISO 6 (Class 1,000) and above cleanrooms generally utilize a non-unidirectional, or turbulent, airflow. This means the air is not regulated for direction and speed. The advantage of laminar over turbulent airflow is that it provides a uniform environment and prevents air pockets where contaminants might congregate.

How Can You Keep Your Clean Room Free of Contaminants?

Here are five ways you can minimize the contaminants in a cleanroom:

1. Practice Good Hygiene

One of the biggest threats to cleanrooms is personnel-generated contamination. Every work environment should encourage standard cleanroom methods and protocols like:

Use of Proper Gowning Garments

Gravity pulls particulates downwards and garments are influenced by the pull of gravity. As a result, it is important that you do protective garments that will prevent contaminants from reaching clean parts of the garment.

Cleanroom garments are designed to provide coverage and ensure control of microbial contamination. They also protect you, the work environment, and manufactured products from contamination. Cleanroom garments may include hooded barrier coveralls designed to protect personnel from hazardous solutions and barrier gowns used for the administration of cytotoxic medication.

Cleanroom smocks and pocket coveralls can be used in less critical clean room areas.

Move Slowly

Rapid movement in the cleanroom can lead to the spread of particles and contaminants. Cleanroom personnel should move slowly and deliberately around the workstation when entering or exiting the cleanroom. Slow movement can also prevent slips, falls, and injuries.

2. Temperature and Humidity

Most cleanrooms have humidity specifications ranging between 30% and 40% RH and temperature specifications of 21 °C (or 69.8°F) + 2°C. This humidity and temperature level creates an ideal cleanroom environment that prevents bacterial growth. It also creates an ideal environment for employees, ensuring their comfort in work inside this clean space for longer period.

3. Use the Right Supplies

Office supplies are one of the most overlooked contamination sources in a cleanroom. Purchase cleanroom-compliant versions of office supplies like mouse pads, paper, notebooks, and pens.

It is important that you keep these supplies in the cleanroom; you can contaminate the cleanroom environment by simply moving a pen from an office to a cleanroom. Also avoid posting anything on the walls like sticky notes, as these can release particles.

4. Avoid Unnecessary Conversations

Every spoken word produces and expels saliva particles into the air. Although cleanroom personnel often wear facemasks, they are not always 100% effective. While speaking is necessary to perform certain tasks in the cleanroom, avoiding unnecessary talk can reduce the emission of saliva particles, which ultimately reduces the risk of contamination.

5. Use the Right Cleaning Materials

Cleaning supplies like swabs, wipes, mops, and brooms used to keep cleanroom flooring, coving and other parts of the cleanroom should be rated for your ISO class before use in the cleanroom.

Using just any cleaning material can compromise the sterility of a cleanroom. It is also important that you ensure that cleaning materials for the cleanroom are only used in the cleanroom.

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