US Federal Standard 209 E

Yusuf Nawaz Khan

Reg. No. 11505342

The United States (U.S.) Federal Standard 209 (FS 209) was published by the Institute of Environmental Sciences and Technology (IEST).

FS 209 was approved for use by the U. S. General Services Administration (GSA) in 1963, making it obligatory for organizations doing work for the United States government.

INTRODUCTION

This document establishes standard classes, and provides air cleanliness for cleanrooms and clean zones based on specified concentrations of airborne particles.

It prescribes methods for verifying air cleanliness and requires that a plan be established for monitoring air cleanliness.

Airborne particulate cleanliness class is the level of cleanliness specified by the maximum allowable number of particles per cubic meter of air.

Calibration is the Comparison of a measurement standard of unknown accuracy with another standard of known accuracy to detect, correlate, report, or eliminate by adjustment any variation in the accuracy of the unknown standard.

Some Definitions

Clean zone is a defined space in which the concentration of airborne particles is controlled to meet a specified airborne particulate cleanliness class.

Cleanroom is a room in which the concentration of airborne particles is controlled and which contains one or more clean zones.

Ultrafine particles are particles in the size range from approximately 0.02 m to the upper limit.

As-built cleanroom is a cleanroom that is complete and ready for operation, with all services connected and functional, but without equipment or operating personnel in the facility.

At-rest cleanroom is a cleanroom that is complete, with all services functioning and with equipment installed and operable or operating, as specified, but without operating personnel in the facility.

Operational cleanroom is a cleanroom in normal operation, with all services functioning and with equipment and personnel, if applicable, present and performing their normal work functions in the facility.

Anisokinetic sampling is the condition of sampling in which the mean velocity of the flowing air stream differs from the mean velocity of the air entering the inlet of the sampling probe. This can cause the concentration of particles in the sample to differ from the concentration of particles in the air being sampled.

Isokinetic sampling is the condition of isoaxial sampling in which the mean velocity of the air entering the probe inlet is the same as the mean velocity of the unidirectional airflow at that location.

Sample location and number- i. For unidirectional air flow- sample locations shall be uniformly spaced

throughout the clean zone. The minimum number of sample locations

shall be the lesser of A/2.32 or Ax64/(10M)0.5

where A is the area of the entrance plane in m2

and M is the metric designator of class.

Monitoring of airborne particulate cleanliness

ii.For nonunidirectional air flow-Minimum number of sampling locations will be equal to

SI units : A x 64 / (10M) 0.5

where A is the area of the entrance plane in m2

and M is the metric designator of class.

Restrictions on sample locations – Minimum two locations shell be sampled. At least one sample shell be taken from

each selected location. Different number of samples may be

taken at different locations. A total of at least 5 samples shell be

taken in each zone. Sampling at more locations will result

more precision.

Sample volume and sampling time –i. Single sampling plan – Each sample of air tested at each location

shall be of sufficient volume such that at least 20 particles would be detected.

Volume = 20 particules/[class limit (particules/volume)]

The volume of air sampled shall be no less than 0.00283 m3 (0.1 ft3).

Results of calculations should not be round off.

A larger sample volume will decrease the variation between samples, but the volume should not be so large as to render the sampling time impractical.

Sample volumes need not be identical at all locations.

Sampling larger volume will result in greater precision.

Sampling time is calculated by dividing the sample volume by sample flow rate.

Statistical evaluation of particle concentration measurement shall be performed, to verify compliance of air to airborne particulate cleanliness class limits. Average particle concentration. Standard deviation of the averages. Standard error of the mean of the

averages. Upper confidence limit.

Interpretation of the data

After verification, airborne particulate cleanliness shall be monitored while the cleanroom or clean zone is operational.

Other environmental factors may also be monitored as specified to indicate trends in variables that may be related to airborne particulate cleanliness.

Monitoring of airborne particulate cleanliness

The method and equipment to be used for measuring airborne particle concentrations shall be selected on the basis of the particle size.i. Counting particles 5 micrometers

and larger By using optical microscopy. Discrete-particle counter (DPC).ii. Counting particles smaller than 5

micrometers Discrete-particle counter (DPC).

Methods and equipment for measuring airborne particle concentrations

Discrete-particle counters with unlike designs or operating principles may yield different data when used to sample air at the same location.

Caution should be used when comparing measurements from different instruments.

Since the sizing and counting of particles by optical microscopy defines size on the basis of a "longest dimension," while DPC's define size on the basis of "equivalent diameter," particle concentration data obtained from the two methods may not be equivalent and therefore shall not be combined.

Limitations of particle counting methods

All instruments shall be calibrated against known reference standards at regular intervals using accepted procedures, as specified.

Calibration may include, but is not limited to, airflow rate and particle size.

Calibration with respect to particle size shall be carried out for each size measured in verification.

Calibration of particle counting instrumentation

Minimum no of sampling location is more in larger area. Minimum number of locations required by ISO does not

depend on the cleanliness classification as it does in FS 209E. The ISO standard does require minimum one minute samples,

whereas the FS 209E allows shorter samples, especially at smaller particle sizes.

FS 209E does not make recommendation nor stipulate requirement to demonstrate continuing compliance, ISO 14644-2, gives requirements for monitoring a cleanroom or clean zone to provide evidence of its continued compliance with ISO 14644-1.

FS 209E left recommended tests entirely to the seller and buyer to ascertain the types of tests to be carried out, it did not address the type of tests required. ISO 14644-3 dedicated the entire volume to “Metrology and test methods”.

FE 209E VS ISO 14644

Chyan, Ir Liew Huey, Federal standard 209e for cleanroom - an obsolete document.

Federal standard 209E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones.

Reference

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