Official notification of the withdrawal of the standard:
‘Federal Standard 209E is withdrawn with effect from 29 November 2001 and replaced by the International Organisation for Standardisation (ISO) standard.’
‘Cleanrooms and associated controlled environments, ISO 14644 Part 1: Classification of air cleanliness and ISO 14644 Part 2: Specification for testing and monitoring to demonstrate continued compliance with ISO 14644 Part 1.’(source: everyspec.com)
To briefly explain the context for all those who are not so deeply familiar with the subject, you should know that class ISO 1 and class ISO 2 are not considered in the US Federal Standard. Some people refer to the Federal Standard as class 0.1 or 0.01, but these classifications are not described there.
The same applies to class ISO 9 (this would correspond to a 1,000,000 – also not described). You should also not equate individual classes of the two standards, as there are minor differences which I will not discuss here. However, as a rough approximation, the: ISO 3 corresponds to class 1, ISO 4 to class 10, ISO 5 to class 100, ISO 6 to class 1,000, ISO 7 to class 10,000 and ISO 8 to class 100,000.
Some users of cleanroom technology are still very much stuck in the formulations of the 1980s and communicate with the terms commonly used at the time. It should not be the aim to ‘educate’ them to the standards that have been in place for almost 30 years. You shouldn't want to ‘ explain’ to a customer, if you do, then you should convince them. And just try to convince a potential customer in China, Malaysia or the USA of the wording of ISO 14644 – not easy.
If anyone does have this enthusiasm, they will fail at the latest when they try to explain to their American colleague that the metric system of measurement, to which the United States has also committed itself, is largely the only system that still applies.
Nevertheless, the users of cleanroom technology will be understood. You should only be careful if suppliers are not up to date with the latest standardisation and it becomes very critical if planning offices are still living in the ‘old’ world (see also misconception no. 15).
The US Federal Standard 209 has accompanied us for many years and for the first reason gave us the opportunity to classify and standardise air purity. Measurement results have become comparable and the world of cleanroom technology has been able to refer to a comprehensible standard.
But every technical achievement has its time. And I also regard standards as technical achievements. So the US Federal Standard 209 also had its successful time. But development continues and we should keep up with it and refer to real standards, including in communication.