Cleanroom Classes & Definitions
Historically, cleanroom cleanliness class has been defined by Federal
Standard 209. FS 209 class designations are based on a reference
particle size of 0.5 mm. The standard has been refined over the
years to include metric designations (the "M" numbers).
However, recently the International Standards Organization (ISO)
has adopted a new designation system that replaces the Federal Standard.
ISO 14644 is completely metric and is based exclusively on a particle
size of 0.1 mm.
What Makes a Cleanroom Clean? What makes a cleanroom dirty? Particles
(among other things). Particles come in all sizes. They can be made
of anything and they can come from anywhere: from air ducts, from
open doors, from the owner’s equipment inside the cleanroom,
and most prominently from us. Humans generate an average of 600,000
particles per minute from our skin, our hair and our breath. That’s
why we have to wear bunny suits whenever we are in a cleanroom.
But we also have to take steps to guard against particles from all
those other sources, too.
Essentially, there are two things that make a cleanroom clean:
filtration and air movement. Filtration removes contaminants from
the air that is supplied to the room. Air movement is used to carry
away contaminants that are generated inside the room. Almost all
cleanrooms today are built with vertical flow. Air is supplied at
the ceiling and removed near the floor level. There are many variables
that can be manipulated to control the cleanliness of a cleanroom.
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