Pre-wetted wipers eliminate at least one problem in the cleanroom. The gloves that are a mandatory part of the gowning procedure prevent tactile feedback from a wiper as a wiper is wetted. This makes it difficult to know how much liquid to dispense onto a wiper from a squirt bottle. The optimum wetting level for wipers is about 50 to 60% of capacity – i.e. about half the amount of liquid that the wiper could hold at saturation. But without getting a feel for the wetting level (and no, it is not permissible to remove gloves in the cleanroom to get that feel), it’s hard to know whether too much or too little liquid is being dispensed onto the wiper. Human nature, being what it is, leads to excessive amounts of liquid dispensed onto the wiper and consequently, over-wetting the wiper. This in turn leads to sub-optimum removal of contaminants from surfaces, since the excess liquid on the wiper just moves the contaminants around. Conversely, too little liquid on the wiper makes it difficult to remove contaminants from surfaces. In a cleanroom, Goldilocks prefers pre-wetted wipers because they’re ”just right” (as far as wetting levels are concerned).

Recently, in the Cleanroom Cleaning group an inquiry was posted concerning action and alert levels for environmental monitoring measurements (i.e. measurement of bacterial levels) in ISO Class 7 & 8 environments in a medical device manufacturing facility.
While colony forming unit (CFU) measurements in ”controlled environments” display the typical negative exponential histogram character usually seen for particle measurements, in ”dirtier” environments, the histogram changes to a ”normal” i.e. a Gaussian distribution.
In a controlled environment, one would expect alert levels of 3*mean and action levels of 4.6*mean, In ISO Class 7&8 environments the alert levels change to mean +1.65*std dev’n and action levels change to mean +2.33*std dev’n. This information is described in a 2004 Cleanrooms East Conference paper. copy of Cleanrooms Magazine may be able to supply a copy of the full paper “Establishing and Environmental Monitoring Program”.
Other information sources on this topic include:
1. NSF publication “Environmental Monitoring” available at http://www.cerhb.ufl.edu/pdf/edcenter/environmental_monitoring.pdf/
Action and alert levels for ISO Class 7 & 8 environments are presented on page 25 of this document.
2 “Microbial Limit and Bioburden Tests: Validation Approaches and Environmental Limits” 2nd ed., Lucia Clontz, Taylor and Francis Group, 2009.
3. US-American Pharmacopoeia (USP), “Microbiological Evaluation of Clean Rooms and Other Controlled Environments”, USP 26 .