Cleanrooms by United is the leading expert in the design and fabrication of critical-environment applications. We offer a complete range of equipment, furnishing and supplies for cleanroooms and laboratories. Following are the stringent standards to which United adheres.
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 14644-1 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By law, Federal Standard 209E can be superseded by new international standards.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 14644-1.
Airborne Particulate Cleanliness Class Comparison
|FEDERAL STANDARD 209E|
Airborne Particulate Cleanliness Classes (by cubic meter):
|CLASS||Number of Particles per Cubic Meter by Micrometer Size |
|0.1 micron||0.2 micron||0.3 micron||0.5 micron||1 micron||5 microns|
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 14644-2 describes the type and frequency of testing required to conform to certain standards. The following tables indicate mandatory and optional tests.
Required Testing (ISO 14644-2)
|Schedule of Tests to Demonstrate Continuing Compliance|
|Test Parameter||Class||Maximum Time Interval||Test Procedure|
|Particle Count Test||<= ISO 5||6 Months||ISO 14644-1 Annex A|
|> ISO 5||12 Months|
|Air Pressure Difference||All Classes||12 Months||ISO 14644-1 Annex B5|
|Airflow||All Classes||12 Months||ISO 14644-1 Annex B4|
Optional Testing (ISO 14644-2)
|Schedule of Additional Optional Tests|
|Test Parameter||Class||Maximum Time Interval||Test Procedure|
|Installed Filter Leakage||All Classes||24 Months||ISO 14644-1 Annex B6|
|Containment Leakage||All Classes||24 Months||ISO 14644-1 Annex B4|
|Recovery||All Classes||24 Months||ISO 14644-1 Annex B13|
|Airflow Visualization||All Classes||24 Months||ISO 14644-1 Annex B7|
Today, in addition to ISO 14644-1 and ISO 14644-2, 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 14644-1||Classification of Air Cleanliness|
|ISO 14644-2||Cleanroom Testing for Compliance|
|ISO 14644-3||Methods for Evaluating and Measuring Cleanrooms and Associated Controlled Environments|
|ISO 14644-4||Cleanroom Design and Construction|
|ISO 14644-5||Cleanroom Operations|
|ISO 14644-6||Terms, Definitions and Units|
|ISO 14644-7||Enhanced Clean Devices|
|ISO 14644-8||Molecular Contamination|
|ISO 14698-1||Biocontamination: Control General Principles|
|ISO 14698-2||Biocontamination: Evaluation and Interpretation of Data|
|ISO 14698-3||Biocontamination: Methodology for Measuring Efficiency of Cleaning Inert Surfaces|
The USA source for ISO documents is:
Institute of Environmental Sciences & Technology (IEST)
5005 Newport Drive, Suite 506
Rolling Meadows, IL 60008-3841
Phone: (847) 255-1561
Fax: (847) 255-1699
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 19111
Phone: (215) 697-2667
Fax: (215) 697-2978
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 14644-1 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 for cleanliness 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.
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 1219 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:
|Class||Ceiling Coverage (Percentage)|
|ISO 8 (Class 100,000)||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 1-2||80 – 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 146144-1 (Federal Standard 209E)||Average Airflow Velocity|
|Air Changes Per Hour||Ceiling Coverage|
|ISO 8 (Class 100,000)||0.005 – 0.041 (1 – 8)||5 – 48||5 – 15%|
|ISO 7 (Class 10,000)||0.051 – 0.076 (10 -15)||60 – 90||15 – 20%|
|ISO 6 (Class 1,000)||0.127 – 0.203 (25 – 40)||150 – 240||25 – 40%|
|ISO 5 (Class 100)||0.203 – 0.406 (40 – 80)||240 – 480||35 – 70%|
|ISO 4 (Class 10)||0.254 – 0.457 (50 – 90)||300 – 540||50 – 90%|
|ISO 3 (Class 1)||0.305 – 0.457 (60 – 90)||360 – 540||60 – 100%|
|ISO 1 – 2||0.305 – 0.508 (60 – 100)||360 – 600||80 – 100%|
Before deciding on the appropriate velocity and air changes for your application, United 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
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 gage 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.
Please contact one of our Controlled Environment Application Specialists to discuss your specific needs!