Draft standard targets AMC control
BY STEVE SMITH
ROLLING MEADOWS, Ill.—An international standard, designed to be used by any industry impacted by airborne molecular contamination (AMC), is being circulated to International Organization for Standardization (ISO) members for comment, following its draft release late this spring by the Institute of Environmental Sciences and Technology (IEST; www.iest.org).
ISO 14644-8—Cleanrooms and associated controlled environments, Part 8: Classification of airborne molecular contamination—will assign ISO classification levels to specify the limits of AMC concentrations within a cleanroom or controlled environment where a product or process is at risk.
"This document looks at molecular contamination as a three-step event: generation, transport, and sorption," explains Gordon Ely, IEST board member/contamination control, and section leader for the Identifications and Packaging division of Nelson Laboratories Inc. (Salt Lake City, Utah; www.nelsonlabs.com).
"Generation is due to external sources, process leakage or construction, or human material outgassing," Ely elaborates. "Transport occurs as AMC in air. Sorption happens when the AMC is on the sensitive surface, and is quantified as a surface molecular contamination (SMC)."
IEST serves a Secretariat for ISO Technical Committee 209, which developed the AMC standard as part of a series of contamination-control documents. The standard defines AMC in terms of a specific chemical or compound species (individual, group or category). It considers AMC concentrations between 100 and 10-12 g/m3 under cleanroom operational conditions.
As stated in the draft standard's introduction, "For classification purposes, this part [of ISO 14644]…is limited to a designated range of AMC concentrations and provides standard protocols for specifying such concentrations with regard to chemical compounds, methods of test and analysis, and time-weighted factors."
Ely says that "compliance with classification requirements is verified by performing specified testing procedures," which are outlined in the draft standard's "typical methods of measurement." A wide variety of sampling, off-line analysis, and on-line monitoring methods are listed.
"This document," Ely says, "has four informative annexes: parameters that affect or contribute to AMC, typical contaminating chemicals and substances, typical methods of measurement and analysis, and considerations of specific requirements for separative enclosures."
Voting began April 15 and ends Sept. 15. Following comment and approval by two-thirds of ISO members, 14644-8 will be submitted as a Final Draft International Standard. It is hoped that final approval will be completed by mid-2005.
"Changes and modifications to the text, tables, and other information contained in the document may significantly change before the standard is published," notes Ely.
Copies of all ISO 14644 standards are available from IEST's Web site, or via e-mail: email@example.com