The ISO global cleanroom standards — What do they really mean?

by Richard A. Matthews

Every manufacturer has some form of standard operating procedure (SOP) that dictates how his operation will run and the quality level it will produce. Some manufacturers, particularly those in the healthcare field, have to meet stringent regulatory criteria — another form of standards.

The new family of ISO Global Cleanroom Standards was written by experienced operations personnel whose practical experience had great influence over what is called for in those new standards.

ISO/TC209, the ISO Technical Committee on “Cleanrooms and associated controlled environments,” draws on well over 1,000 volunteers from 37 countries to create realistic standards for practical use in the global cleanroom community.

This is the first of a series of articles that will provide an understanding of what is in these 11 new standards and what they mean.

In this article we will explore the true value of ISO 14644-1.

TITLE: Cleanrooms and associated controlled environments. Part 1: Classes of Air Cleanliness.

SCOPE: Defines the classification of air cleanliness in cleanrooms and associated controlled environments exclusively in terms of airborne particles in sizes from 0.1 to 5.0 micrometer.

STATUS: Published as an official ISO Standard May 1, 1999.

In this document are some of the only mandatory criteria called for in these new ISO Cleanroom Standards. All other information provided is for guidance only. Suffice it to say, smart business and professional cleanroom people will follow this guidance, because it is in their best interest to do so.

This 18-page document defines the new international classes of air cleanliness measured in number of particles per cubic meter in six different particle sizes (See table). These classes of air cleanliness and how they are calculated is clearly defined in this document.

There are nine major classes of air cleanliness, which can be further divided into 1/10th increments from ISO Class 1 to ISO Class 9, thereby providing 81 separate classes for fine tolerance clean space design. For example, ISO Class 7.4 would allow up to 1,760,000 particles 0.5 micrometer and larger per cubic meter. (This would be comparable to a Class 50,000 under US Federal Standard 209E).

Under ISO 14644-1, air cleanliness can be determined in 3 different occupancy states – “as built”, “at rest” and “operational.”

It is important to know that ISO 14644-1 requires that air cleanliness be reported by ISO class number, by occupancy status and by specific particle size or sizes. Reported data must read as follows: ISO Class 5 “as built” at 0.2 micron and 0.5 micron.

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There are further provisions for defining air cleanliness based upon particles larger than 5.0 micrometers. These are called macroparticles or M descriptors. Macroparticles are necessary for defining relatively dirty clean environments where powders or heavy dusts are present as part of a controlled manufacturing process.

There are also provisions for particles smaller than 0.1 micrometer. These are called ultrafine particles or U descriptors. As certain research and manufacturing processes tend toward nanometer dimensions, U descriptors can be utilized to qualify and quantify clean space.

M descriptors and U descriptors cannot be used to define airborne particle cleanliness classes. However, they may be used independently or in conjunction with specific airborne particle cleanliness classes in Table 1.

ISO Standards by design have normative (mandatory) sections and informative (non-mandatory) sections. It is important to know the difference.

Mandatory criteria

Normative sections specify required or directive information. For example, the classes of air cleanliness are normative. How classes are determined is specifically spelled out by a clearly defined mathematical formula. This is also normative.

The basic document, which includes scope, definitions, classification of air cleanliness and demonstration for compliance, is all normative, i.e., mandatory in content.

In addition, two of the six annexes in this document are also normative, i.e., mandatory. They are:

Annex B: Determination of particle cleanliness classification using a discrete-particle-counting, light scattering instrument.

Annex C: Statistical treatment of particle concentration data.

Non-mandatory criteria

The other four annexes are informative and are provided for user guidance. They provide a relative graphical illustration of the air cleanliness classes, examples of classification calculations, consideration for counting and sizing both macroparticles and ultrafine particles as well as a procedure for sequential sampling.

General comments

There is basically no difference in the cleanliness quality of air when measured by ISO-14644-1 criteria or by US Federal Standard 209E. The air has not changed, only the measurement itself from the English system to the metric system.

The selection of the classification of air cleanliness for a specific clean space area is always per agreement between the customer and the supplier. ISO-14644-1 provides a comprehensive baseline for making this selection.

ISO14644-1 is the keystone for the full series of ISO global cleanroom standards. The use of this document became mandatory in the European Union on November 1, 1999. Other parts of the world have also adopted 14644-1 as their baseline cleanroom (clean space) classification document. ISO 9000-certified organizations are required to utilize ISO 14644-1 in defining their clean space.

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Richard A. Matthews is chairman of the ISO Technical Committee ISO/TC209 “Cleanrooms and associated clean environments.”


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