Pre-Wetted Wipers:  Convenient and Effective Cleaning

This article deals with the benefits of pre-wetted wipers for cleaning and maintaining cleanroom surfaces.  Companies using pre-wetted wipers have reported better protocol adherence (most likely due to the convenience factor), lower overall wiper usage, lower volatile organic compound (VOC) levels, reduced fire hazards and more reproducible wetting levels on wipers as compared to the use of dry wipers with squirt bottles.

Convenience

The factor that makes pre-wetted wipers so well-accepted for household cleaning tasks is the same factor that makes them so popular for use in maintaining cleanrooms surfaces[1].  And that factor is convenience.  A single package of pre-wetted wipers, provides everything needed for the cleaning task at hand – the wipers and the optimum level of filtered cleaning solvent.  Gone are the bags of wipers and the (routinely-missing) squirt bottles that have traditionally been used for cleaning operations.

Not frequently recognized is the fact that pre-wetted wipers actually promote routine cleaning.  How can this be?  Supervisors in critical environments are well aware of a simple maxim:  Cleaning is more likely to be done when cleaning supplies are conveniently available.    By eliminating the squirt bottle, the cleaning solvent and the dispensing equipment to fill the squirt bottle, pre-wetted wipers simplify cleaning tasks (while simultaneously simplifiying the purchasing and receiving operations).  Thus, pre-wetted wipers promote cleaning through convenience.

Squirt Bottles

Let’s spend some time considering the often missing squirt bottles – they evaporate just like the solvent they’re supposed to hold. Trying to find a filled squirt bottle to dampen a wiper in a cleanroom is like trying to find a taxi when it’s raining – they’re both missing in action.

And if you are lucky enough to locate one, you can be certain that it will be empty. Squirt bottles have been compared to orphans – nobody owns them.  Logic holds that if nobody owns them, nobody is responsible for filling them.  Hence the located, but empty squirt bottle.

Filling an empty, located squirt bottle is a task that nobody likes since it requires locating a supply of the appropriate cleaning solution and dispensing that into the squirt bottle without spilling.  If the cleaning solution is comprised of a flammable solvent, the dispensing operation raises safety issues as well.  Pre-wetted wipers begin to look better and better.

Four other factors argue against the use of squirt bottles. 

As supplied, typical low-density polyethylene (LDPE) squirt bottles contain additives such plasticizers used to enhance the physical, mechanical and chemical properties.  Rarely are new squirt bottles rinsed with several portions of the cleaning agent to remove surface additives from the bottles.  Also, there is the possibility that over time, these additives may leach into the cleaning solution in the bottle.  Obviously, these additives will contaminate the surfaces to be cleaned.

After the cleaning solution is dispensed onto the wiper, the bottle will aspirate cleanroom air back into the bottle; this introducing the possibility of bringing air-borne particles into the remaining cleaning solution.  These particles could then be dispensed onto the wiper and contaminate the surfaces to be cleaned.

The dispensing operation to fill squirt bottles is unlikely to incorporate in-line filtering to remove particles within the cleaning solution.  Again, these particles, if not filtered out, will be transferred into the squirt bottle and ultimately find their way onto cleanrooms surfaces.  The filling operation to manufacture pre-wetted wipers always incorporates in-line filtering.

Squirt bottles containing highly volatile solvents (e.g 100% isopropyl alcohol), may exhibit “spontaneous dispensing” i.e.  solvent dispensed without any squeezing action.  This can occur if the bottle is placed in a warm area.  Safety issues and elevated volatile organic compound (VOC) levels are thus an issue with this phenomenon.

Wetting Levels

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).