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May the best mat win …

To the Editor:

I would like to respond to the article “Polymeric flooring demonstrated particle retention properties” that was printed in the November 1996 issue. This article, was contributed to CleanRooms magazine by Dr. Geoffery Barrett, a paid consultant for a large manufacturer of polymeric flooring, as pointed out at the end of the article.

The article attempts to build a case that this type of flooring is superior to “peel-off” mats in controlling foot or wheel borne particulates from coming into the cleanroom. The case is built by citing several studies, all from the United Kingdom, that according to Barrett prove his point. This argument not only unravels but completely explodes if any of these studies are actually examined in full. The results of these tests show results very different from the results that Barrett cites.

The complete studies that are cited in Barrett`s article show that both types of mats can function in controlled tests at levels comparable to each other. The size, consistency and concentration of particles all effect what type of mats work best in ideal situations. The tests show varying results, with each type of mat besting the other in certain circumstances. The results in the real world however, are normally very different.

For the two types of mats to continue to function at similar rates, the dirt must be removed from both at similar intervals. A “peel-off” mat accomplishes this with a 10 to 15 second maintenance procedure. At some facilities this may, depending on foot traffic, take place every hour, every shift or anywhere in between. For a polymeric floor to continue functioning at a comparable rate, it must be washed, squeegeed and dried at these same intervals. This may take 10 to 15 minutes, and because of this, it is normally only done once every 24 hours. Its ability to function is deteriorating throughout this period. Any user who has ever installed a polymeric system will confirm that it is totally impractical to try to clean, and thus close down the entrance to, a million-dollar cleanroom at multiple times in the day.

Both of these product groups have been in the marketplace for over 20 years. The market has determined a preference of almost 10 to 1 in favor of the peel-off product compared to the polymeric or washable matting.

Dennis K. Baldwin

Vice president, director of sales

ALMA Inc. (Palm Springs, CA)

Author`s Response:

On behalf of both myself and Dycem Ltd., I am would like to offer a few comments in reply to Dennis Baldwin`s letter.

As Mr. Baldwin points out, both product groups have been on the market for over 20 years.

The results of research on this subject have been reported regularly at meetings of the ICCCS including conferences held in Paris, Milan and Tokyo over this period and are consistent in terms of general conclusions with those of the more recent studies reported in the CleanRooms` article, “Particle retention properties demonstrated by polymeric flooring,” to which Mr. Baldwin refers and which were presented in more detail at my presentation to CleanRooms East `96 in Boston last April — this was far from being a “one-off” exercise.

During this period polymeric flooring has established itself as an integral part of contamination control systems operated by manufacturers of semiconductors, medical devices and pharmaceuticals in over 50 countries worldwide.

The importance of the results I presented in my article lies in the fact that they were carried out in the “real world” — in a practical trial undertaken in strictly controlled scientific conditions in a real cleanroom environment, whereas earlier studies had largely been based on laboratory experimentation and test procedures simulating particulate collection from feet and cart wheels. As noted earlier, the research was carried out at The University of Bath, England, in a Class 10,000 cleanroom sponsored by Glaxo, and the experimental protocol and measurements were undertaken by Kennet Bioservices, a company with an international reputation in this field.

In this “real world” the conclusions of our work, if examined in detail, cannot be disputed in that, under the test conditions employed, which were genuinely chosen to simulate practical operating use, the polymeric flooring product:

is more efficient than peel-off mats on removal of particulate over a range of all particle sizes;

is very much more efficient than peel-off mats in the removal of small particulate and on prevention of microbiological contamination from viable particulates;

retains its efficiency to a higher degree when subjected to the same degree of contamination than is the case with peel-off mats.

In tests recently completed, and yet to be reported, we have also demonstrated that after over a year of use, these advantages in performance are largely retained and performance in particulate removal is superior to peel-off mats.

As Mr. Baldwin also points out, however, there are many practical considerations in normal commercial use which have a bearing on the selection of products within a controlled environment — and certainly polymeric flooring needs to be cleaned regularly. When applying the approved cleaning procedures, common sense and control of personnel movement avoids the possibility that facilities have to be shut down at any time of the day, let alone on multiple occasions as Mr. Baldwin would have your readers believe.

There are, of course, other considerations which have to be borne in mind — “cost in use” is certainly one where polymeric flooring systems have demonstrated advantages in a wide range of practical operating situations. This should not, perhaps be the subject of debate within these columns. Conservation of resource and environmental considerations are, however, worth a mention.

Peel-off mats are energy intensive products to manufacture, both in terms of the base substrate and the “tacky coating;” also they cannot be effectively recycled. The continued use of such products with the inherent waste of energy and raw materials runs totally contrary to contemporary culture and trends in industrial practice, where systems which offer low energy costs in use and which can be recycled at the end of their product life — like polymeric flooring — will increasingly be preferred.

It is in the nature of research that one series of investigations lead to questions which require further answers; this is a course which we are currently pursuing with new investigations which we shall report fully in the future.

Dr. Geoffrey F.C. Barrett, B.Sc, Li.B., Asst. S.P.E.

Gloucester, England