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FS209E and ISO Cleanroom Standards

FS209E and 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 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.

In November 2001, Federal Standard 209E was superseded by the new ISO 14644-1 international standards. References to FS209E are still used; the comparison chart below illustrates the relationship between the two standards.

Cleanroom walls are made of durable, easy-to-clean, ISO-grade materials, as specified in FDA guidance documents. Combined with your cGMP processes, they will help you comply with operational requirements.

Airborne Particulate Cleanliness Class Comparison:

ISO 14644-1

FEDERAL STANDARD 209E

ISO Class

English

Metric

ISO 1

 

 

ISO 2

 

 

ISO 3

1

M1.5

ISO 4

10

M2.5

ISO 5

100

M3.5

ISO 6

1,000

M4.5

ISO 7

10,000

M5.5

ISO 8

100,000

M6.5

ISO 9

 

 

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

ISO1

10

2

 

 

 

 

ISO2

100

24

10

4

 

 

ISO3

1,000

237

102

35

8

 

ISO4

10,000

2,370

1,020

352

83

 

ISO5

100,000

23,700

10,200

3,520

832

29

ISO6

1,000,000

237,000

102,000

35,200

8,320

293

ISO7

 

 

 

352,000

83,200

2,930

ISO8

 

 

 

3,520,000

832,000

29,300

ISO9

 

 

 

35,200,000

8,320,000

293,000

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.

A Guide to Gowning Procedures
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

In addition to ISO 14644-1 and ISO 14644-2, eight other cleanroom standards documents exist, as well as three specific to biocomtamination applications.

ISO Document

Title

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 14644-9

Surface Cleanliness by Particle Concentration

ISO 14644-10

Surface Cleanliness by Chemical Concentration

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

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.

Rajan Jaisinghani, in his paper "Energy Efficient Low Operating Cost Cleanroom Airflow Design," presented at ESTECH 2003, recommended the following ranges based on FS209E classifications:

FS Cleanroom Class

ISO Equivalent Class

Air Change Rate

1

ISO 3

360-540

10

ISO 4

300-540

100

ISO 5

240-480

1,000

ISO 6

150-240

10,000

ISO 7

60-90

100,000

ISO 8

5-48

Jaisinghani’s recommendations concur with other recent studies of ACR, which criticize some existing air rate standards (developed in the 1990s) 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:

  • 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. Control can be performed manually or automatically.

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 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
m/s (ft/min)

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, We 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’ (3302 mm x 3302 mm x 2134 mm) cleanroom, with 1008 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 minimize disruptions to these cascading pressures when doors are opened, air locks are often specified between rooms of differing ISO cleanliness levels. Automated fan controls simplify pressure balancing by allowing fan speed adjustments at a centralized console panel. Why is pressure differential important and how is it measured?

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.

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