Issue



Setting the Standard: Evolution of an IEST Recommended Practice


03/01/2005







BY Charles Berndt, C. W. Berndt Associates

INTRODUCTION

The Institute of Environmental Sciences and Technology (IEST) is responsible for the origination, publishing, and revision of approximately 35 Recommended Practices (RPs) in topics of interest and value to the contamination control industry. The IEST working groups responsible for these documents meet regularly for lively discussions of best practices, and represent a wide range of experience and technical interests.

A case study in the process of producing an RP can be found in the evolution of the current IEST-RP-CC003.3 Garment System Considerations for Cleanrooms and Other Controlled Environments. IEST-RP-CC003.3 is the culmination of nearly 20 years’ work by IEST members developing successive guidelines to cleanroom apparel usage. This latest revision of the Recommended Practice crosses industry lines to provide a global aid to understanding and establishing an informed and effective cleanroom garment program.

CURRENT REVISION

Evolution

In May 1997, IEST Working Group CC-003 conducted a review of IEST-RP-CC003.2, “Garment System Considerations for Cleanrooms and Other Controlled Environments,” and voted unanimously to rewrite the document. An extensive rewrite of the document was undertaken, resulting in the release of IEST-RP-CC003.3 in August 2003. The 48-page revision is organized into four substantive main sections: product, processing, usage considerations, and quality management. Additionally, recommended garment configurations and test methods are presented in two appendices.

The Working Group began its review of IEST-RP-CC003.2 with a discussion concerning the Helmke Drum, NVR testing, as well as garment sizing issues. A steering committee was formed to thoroughly evaluate the document and suggest areas that would require updating. Emphasis was placed on the structure of the document, its relevance and usefulness for today’s contamination control needs and test methods. The committee concluded that a major rewrite was needed and undertook an exhaustive section-by-section review of the recommended practice. After further discussions during two Working Group meetings in early 1998, the restructure of the document was expanded and agreed upon. Sections were assigned to teams to write new material where necessary, consolidate information from the current RP, and consider the section-by-section input from the steering committee as well as comments from the Working Group. The results of these efforts were the central point of discussion at a November 1998 Working Group meeting in Chicago.

Subsequent changes and new items to look for

The Working Group committed to a comprehensive rewrite of the document and called for some additional revisions, including:

  • expanded sections on fabrics, material properties and testing, design and construction of apparel, and more information on apparel types;

  • processing considerations outlining responsibilities of the processor and the user;

  • usage considerations such as environmental guidelines for garment usage, processes to control contaminants from personnel, types of contamination from personnel, development of gowning system specifications, design of cleanroom gowning systems, and performance values;

  • quality management information covering quality protocols and application of a quality system;

  • appendices for recommended garment configurations as well as testing for particle penetration including equivalent pore diameter testing of fabrics, tests for apparel cleanliness such as releasable large particle testing, particle dispersion testing (body box), revised Helmke Drum testing, and microbial penetration testing.

    The revised Helmke Drum test now measures and classifies both 0.3-µm and 0.5-µm particles. The resultant data is now expressed as a particle emission rate. Further, very clear and specific details are provided for the configuration of the drum along with detailed procedures for conducting the test. As a point of information, some manufacturers and suppliers of Helmke equipment may suggest drum testing methods and equipment (design/configuration) that may not be consistent with the test as presented in IEST-RP-CC003.3. It is strongly suggested that all users of the test consult the new recommended practice for guidance.

    HISTORY

    Early garment usage guidelines

    IEST-RP-CC003.3 has its roots in garment usage guidelines going back nearly a half-century. The earliest reference we have found concerning the use of cleanroom apparel was in a 1955 article referring to the use of special “dust-proof” clothing made of nylon.1 More definitive detail regarding the use of cleanroom apparel can be found in Environmental Control in Electronic Manufacturing, published in1973.2 Garments are referred to as “people filters,” just as they are today. Garments consisted of smocks, >hats and, in some cases, face masks and shoe covers. Their effectiveness depended on their design, how well they were cleaned and how they were used. They were to be constructed of synthetic monofilament materials. Compromises were made in that the weave of the fabric was to be tight enough to prevent particles from sloughing off the wearer, but not so tight as to cause discomfort. Typical cleanroom garment requirements included:

  • The fabric should be of a synthetic type and should exhibit a very low electrostatic-generating property.

  • Smocks should be of a simple design with no pockets and as few seams as possible.

  • Seams should have no open ends of fabric.

  • Seams should be double-stitched with synthetic thread.

  • Smocks should have adjustable neckbands and cuffs.

  • Snap fasteners should be of a rustproof metal.

  • The cap should be of the style worn in hospital operating rooms, covering the hair.

  • Hoods, coveralls, and foot coverings should conform to these same general requirements.

  • The cleaning process required for these specialized garments was also defined. Some of the stipulations were:

  • Garments should be processed in a suitable environmentally controlled laundry.

  • Equipment should be reserved for cleanroom garments only.

  • The laundering process must be capable of producing a clean garment capable of passing all tests for cleanliness.

  • Cleaned garments should be neatly folded, individually packaged and sealed in clean plastic (polyethylene) bags.

  • The identification mark of each garment should be clearly visible without opening the bag.

    As can be seen, expectations for cleanroom garments and processors haven’t changed much in 30 years.

    IES-CC-RP-003-87T and IES-RP-CC-003-89

    Published in October 1987 as a “Tentative-For Trial Use” document, IES-CC-RP-003-87T completed work begun with a 1985 draft (RP-3-001-1985). IES-CC-RP-003-87T covered generalities about wearing garments to control human-sourced contamination. The document discussed basic fabric characteristics, including flammability and chemical effects; garment construction characteristics, including sewing thread, seams, seam joining, seam finishing, entrapment areas, findings and collar construction; and types of garments, including body coverings, head coverings, and footwear.

    IES-CC-RP-003-87T provided basic sizing information and controlled environment definitions per the now-defunct FED-STD-209. References to ESD were brief and deferred to the efforts of Working Group 022 on Electrostatic Charge in Cleanrooms and Other Controlled Environments. Basic recommendations concerning garment processing covered garment repair and inspection, sampling, testing, acceptance criteria, recommended garment usage and change frequency, packaging, shipment, processing contractor and customer responsibilities.

    Particulate cleanliness test methods presented in the document included the Helmke Drum test, modified ASTM F51-68 and the alternate method, particle penetration and equivalent pore diameter testing, particle containment (body box), and extractables testing. Most of the information in that early document was very general and basic in nature.

    In April 1989, the Working Group reviewed issues that had to be settled before the document could be published without the “Tentative” designation. These included lack of consistency and accuracy in the use of S.I. units, the need to upgrade tables, and the need to incorporate Standards and Test Methods appropriate to Class 1 and 10 environments. The corrections, which were slated to be distributed as IES-RP-CC-003-89, were never published. The untimely passing of the then Chairman, Richard Beeson, left the Working Group without continuity for a time.

    Evolution of RP 3.2

    In April 1990, a new initiative for rewriting the Recommended Practice was based on deficiencies identified following a section-by-section review of 87T. They included the previously identified errors as well as the following:

  • Section 4, Garment Requirements-Did not answer the most commonly asked questions by users relative to fabric and garment selection.

  • Section 5, Particulate Cleanliness-Contaminants other than particulates needed to be more fully addressed.

  • Section 6, Particle Penetration and Equivalent Pore Diameters-Filtration efficiency of fabrics and test methodology

    One major item intentionally excluded from RP 3.2 dealt with the validation process necessary to provide aseptic (sterile) garments. Instead, the supplement on aseptic garments was produced about a year after the release of RP 3.2.

    Round-robin testing attempts (Helmke Drum)

    The Helmke Drum has long been the accepted method for evaluating particle release in the submicron range. It has also been one of the most maligned. In developing IEST-RP-CC003.2, the Working Group attempted to establish levels by which fabric, garments, and even laundries could be compared. Round-robin testing was determined to be the most effective way to establish accuracy. The first test, arranged in November 1991, involved four laundries. Test results were skewed by a number of variables, so the Working Group decided to rerun the test. Six specific items needed to be reported, ranging from air cleanliness of the room where the drum was located to a confirmation as to how the garment was placed into the drum. The drum rotation speed was to be varied along with garment size. This time, six facilities participated in the testing. The results were normalized to a percentage of value of their respective averages. This allowed direct comparison of the behavior of each variable. After careful evaluation of the resulting data, the Working Group determined that the particle counts were too low to differentiate the true source. The members felt that they could not, with any authority, modify the protocol or adjust the count levels by which garments were classified. They did, however, feel that two caveats should be added:

  • The test should not be used to compare facilities.

  • Although the test has been used for processing trend analysis, particle densities less than 500 over a tumbling garment show statistical variability.

    The test will provide consistency only within the facility where it is performed. These types of results also made it very difficult for a user to stipulate a level by which garments should be qualified within a bid package. III

    Charles W. Berndt is the principal in C. W. Berndt Associates, Highland Park, Illinois, which provides advisory services associated with human-sourced contamination control. He spent eight years as group manager of the Araclean Division of ARA/Aratex Services (now known as ARAMARK Cleanroom Services). He serves on the Editorial Advisory Board of CleanRooms magazine, chairs the Editorial Board of the peer-reviewed Journal of the IEST, is Communications Vice President of IEST, and serves on IEST’s Executive Board. He chaired Working Group CC-003 during the development of IEST-RP-003.3. He currently chairs IEST Working Group CC-029, Contamination Control Considerations for Paint Spray Applications. Berndt is the recipient of the 2001 Willis J. Whitfield Award presented “for substantial contributions to the field of contamination control through published papers, studies and reports,” and the 2004 Monroe Seligman Award “for his diligence and perseverance in carrying out the mission of the Journal of the IEST.” Both awards were presented by IEST.

    ABOUT IEST

    IEST is an international technical society of engineers, scientists, and educators that serves its members and the industries they represent (simulating, testing, controlling, and teaching the environments of earth and space) through education and the development of recommended practices and standards. IEST is the Secretariat for ISO Technical Committee 209, Cleanrooms and associated controlled environments, charged with writing a family of international cleanroom standards. IEST is also an ANSI-accredited standards-development organization. For more information, contact IEST at iest@iest.org or visit the IEST website at www.iest.org.

    REFERENCES

    1. “Western Electric Develops Dust-Control to ‘nth-Degree’,” Industrial Laboratories Magazine, December 1955.

    2. Morrison, P.W., ed., “Personnel Control,” Chapter 13 in Environmental Control in Electronic Manufacturing, Western Electric Series (1973).

    Interested in IEST Working Groups? Several will be meeting in Chicago in conjunction with ESTECH 2005, the annual technical meeting and exposition of IEST. Meeting dates are May 1-4. Working Groups are open to all interested parties. Visit www.iest.org for details and registration information.

    Working Groups meeting at ESTECH 2005

    WG-CC001: HEPA and ULPA Filters

    WG-CC003: Garment System Considerations for Cleanrooms and Other Controlled Environments

    WG-CC006: Testing Cleanrooms

    WG-CC007: Testing ULPA Filters

    WG-CC008: Gas-Phase Adsorber Cells

    WG-CC009: Compendium of Standards, Practices, Methods, and Similar Documents Relating to Contamination Control

    WG-CC011: A Glossary of Terms and Definitions Relating to Contamination Control

    WG-CC012: Considerations in Cleanroom Design

    WG-CC013: Procedures for the Calibration or Validation of Equipment

    WG-CC019: Qualifications for Organizations Engaged in the Testing and Certification of Cleanrooms and Clean-Air Devices

    WG-CC024: Measuring and Reporting Vibration in Microelectronics Facilities

    WG-CC027: Personnel in Cleanrooms

    WG-CC032: Packaging Materials for Cleanrooms

    WG-CC034: HEPA and ULPA Filter Leak Tests

    WG-CC035: Design Considerations for Airborne Molecular Contamination Filtration Systems in Cleanrooms

    WG-CC036: Testing Fan-Filter Units

    WG-CC101: Forum on Air Cleanliness Technology

    WG-CC902: MIL-HDBK-406 Contamination Control Technology: Cleaning Materials for Precision Pre-Cleaning and Use in Cleanrooms and Clean Work Stations; and MIL-HDBK-407 Contamination Control Technology: Precision Cleaning Methods and Procedures