Summary of FS 209E and ISO 14644-1 and ISO 14644-2

The cleanliness classification levels defined by FS209E and ISO 14644-1 are approximately equal, except the new ISO standard uses new class designations, a metric measure of air volume and adds three additional classes - two cleaner than Class 10 and one beyond than Class 100,000. The second new ISO standard, ISO 14644-2, gives requirements for monitoring a clean-room or clean zone to provide evidence of its continued compliance with ISO 14644-1.

The following table compares FED STD 209E to the new ISO 14644-1 classifications.

   Airborne Particulate Cleanliness Class Comparison
ISO 14644-1FED STD 209E
ISO ClassEnglishMetric

The ISO standard also requires fewer sample locations, especially as the clean-room/area size increases; however, the ISO standard does require minimum one minute samples, whereas the Federal Standard allows shorter samples, especially at smaller particle sizes.

For example, to certify an FS Class 10 clean-room (ISO class 4), with 250 square feet (7.08 square meters), classified at 0.3 micron with a 1 cf/m flow rate particle counter, the required number of sample locations, sample volumes, and sample times would be as follows:

FS209E requires 10 sample locations, 19.6 liter minimum sample volume (0.85 cf), and a sample time of 51 seconds. This yields a total minimum sample time of 510 seconds and 10 equipment moves.

ISO 14644-1 requires 3 sample locations, 19.6 liter minimum sample volume (0.85 cf ), but also a minimum sample time of one minute yielding three samples of one cubic foot. This yields a total sample time of 180 seconds and three equipment moves.

The precise count levels required by ISO 14644-1 for each classification, by particle size, are given below.

   Airborne Particulate Cleanliness Classes (by cubic meter)
Number of Particles per Cubic Meter by Micrometer Size
ISO 1102
ISO 210024104
ISO 31,000237102358
ISO 410,0002,3701,02035283
ISO 5100,00023,70010,2003,52083229
ISO 61,000,000237,000102,00035,2008,320293
ISO 7352,00083,2002,930
ISO 83,520,000832,00029,300
ISO 935,200,0008,320,000293,000

ISO 14644-2 determines the type and frequency of testing required to conform with the standard. The following tables indicate which tests are mandatory and which tests are optional.

   Required Testing (ISO 14644-2)
Schedule of Tests to Demonstrate Continuing Compliance
Test ParameterClassMaximum Time IntervalTest Procedure
Particle Count Test<= ISO 56 MonthsISO 14644-1 Annex A
>ISO 512 Months
Air Pressure DifferenceAll Classes12 MonthsISO 14644-1 Annex B5
AirflowAll Classes12 MonthsISO 14644-1 Annex B4

   Optional Testing (ISO 14644-2)
Schedule of Additional Optional Tests
Test ParameterClassMaximum Time IntervalTest Procedure
Installed Filter LeakageAll Classes24 MonthsISO 14644-3 Annex B6
Containment LeakageAll Classes24 MonthsISO 14644-3 Annex B4
RecoveryAll Classes24 MonthsISO 14644-3 Annex B13
Airflow VisualizationAll Classes24 MonthsISO 14644-3 Annex B7