Class 10,000 Clean Rooms: The Good Old Days
It almost seems like a shame that US FED STD 209E, the set of clean room standards developed by the US General Services Administration, was cancelled. People may disagree about this, but the system was simple and easy to remember, which tends to bode well in industry and commerce. Take the example of STD 209E Class 10,000. It’s as simple as it gets! According to STD 209E, a Class 10,000 clean room can be classified as such only if a cubic foot of filtered air sample taken from within the clean room was found to feature no more than 10,000 0.5 micrometer-sized particles. And that was it.
But STD 209E’s replacement isn’t so bad. ISO 14644-1, as the replacement set of standards is known, is equally sensible. It’s based on an ascending logarithmic scale instead of multiples of ten. For example, if a clean room has been found to have no more than 10 0.1 micrometer-sized particles per cubic meter of air, then that clean room’s ISO 14644-1 rating is considered to be ISO 1 (101 = 10). If that sample contained 100 particles, it would be ISO 2 (102 = 100), and the ratings go all the way up to ISO 9, which is considered to be equal in terms of particulate volume to the air outdoors in an urban area. For some reason, I still find the STD 209E standard to be simpler. I understand the argument for changing, though.
Maybe the principal value of the switch to the ISO standards is that ISO 14644-1 is a metrified standard. This may make the sale of clean rooms across international borders less difficult. Also, the more different industries that subscribe to ISO standards, there are fewer variables within industry to contend with generally, which simplifies buying and selling. Simple, it seems, is usually good.