The evolution of ISO cleanroom standards
05/01/2001
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by Richard A. Matthews
This is the second in a series of articles on the new ISO Global Cleanroom Standards. This month we will explore ISO 14644-2; which is the close companion document to ISO 14644-1 discussed in the April issue of CleanRooms.
TITLE: Cleanrooms and associated controlled environments - Part 2: Specification for testing and monitoring to prove compliance with ISO 14644-1.
SCOPE: Specifies the requirements for periodic testing of a cleanroom or clean zone to prove its continued compliance with ISO 14644-1 classification of airborne particulate cleanliness.
ISO 14644-2 draws its strength from ISO 14644-1, which was published in May 1999. ISO 14644-2 spells out the mandatory and non-mandatory tests that must be performed to prove compliance with ISO 14644-1. Although short, only eight pages, this document holds lots of clout.
The three mandatory tests that must be performed to prove compliance with ISO 14644-1 are:
a) classification of air cleanliness
b) pressure difference
c) airflow (either volume or velocity)
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Tables 1 and 2 (below) from ISO 14644-2 indicate the mandatory time interval between tests and also reference the proper test methods from ISO-14644-3 "Metrology and Test Methods." Please note that the maximum time interval varies by air cleanliness classification, with shorter time intervals for cleaner levels of air.
ISO 14644-2 also describes four owner optional tests that are non-mandatory. However, use of some or all of these tests may be appropriate for evaluating clean space performance. These additional four tests are:
a) installed filter leakage
b) airflow visualization
c) recovery time
d) containment leakage
Table A.1 (above) from ISO 14644-2 indicates the time intervals between these owner optional tests and references the proper test methods from ISO 14644-3.
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It is significant to note that if an installation has a continuous or frequent monitoring of airborne particle concentration and air pressure difference, the maximum time intervals expressed in Tables 1 and 2 may be extended, provided that the results of this continuous or frequent monitoring remain within the specified limits. This is one of the major user cost benefits provided by the new ISO Global Cleanroom Standards, for it reduces the requirements for periodic test frequency when there is a written monitoring plan rigorously followed.
Monitoring — whether continuous or frequent — must be performed according to a written plan. Such a plan shall be based upon risk assessment to the installation. This plan should include predetermined sample locations, volume of air per sample, duration of measurements, number of measurements per sample location, time interval between measurements, particle sizes to be counted, count acceptance limits, and if appropriate, the count alert, action and exclusion limits.
As pointed out last month with regard to ISO 14644-1, all classes of air cleanliness must be reported by occupancy state — as built, at rest or operational — and by specific particle size or sizes. Monitoring must reflect this criteria.
Generally, ISO 14644-1 and ISO 14644-2 require fewer sample locations for air cleanliness classification than is the case with US Federal Standard 209E, thereby providing cost savings at no sacrifice to air cleanliness quality.
The FDIS version of ISO 14644-2 is significantly different from the DIS version. The time intervals between tests have a new flexibility not available with the DIS version or with US Federal Standard 209E. The monitoring plan option based upon risk assessment allows for user-friendly flexibility, but such a plan must be carefully and thoroughly thought out.
ISO 14644-2 may be a short document, but it is very potent. It may well become part of an end-user Standard Operating Procedure (SOP) as well as part of the validation process in government-regulated industry facilities.
Editor's note: Copies of ISO 14644-2 in its FDIS version are available now from the Institute of Environmental Sciences and Technology (IEST), 940 East Northwest Highway, Mt. Prospect, IL 60059 (Phone 847-255-1561 or Fax 847-255-1699). The final published ISO 14644-2 Standard will also be available from the IEST sometime after July 2000.
Richard A. Matthews is founder of Filtration Technology Inc. (Greensboro, NC) and president of Micron Video International. He is chairman of the International Organization for Standardization Technical Committee ISO/TC209 "Cleanrooms and associated clean environments," and past president of the Institute of Environmental Sciences and Technology. He is on the CleanRooms Editorial Advisory Board.