US standards for Cleanroom environments

[NG CHEUK WAI DAVID]

Hi, sorry if this is the wrong group...

Does anyone know where I can get documentations,
or more information on the US standards for
cleanroom environments?...
eg. class 100, class 10,000 etc.

I'm particularly interested in the biological
limits... eg. collony counts, etc. and
also how they came up with the standard.

Hope some can provide me some info on this
or points me a direction...

Thanks in advance,

David
ngcheuk at ecf.toronto.edu