the international en iso 14644-1 standard (classes 1 to 9) is used for the classification of air cleanliness. this is the official standard, but the us federal standard 209e (classes 1 to 100 000)is also widely spread.

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The international EN ISO 14644-1 standard (classes 1 to 9) is used for the classification of air cleanliness. This is the official standard, but the US Federal standard 209E (classes 1 to 100 000)is also widely spread.