Document G5o0KOx9MxOVN24Ba6N9G08bN

FILE NAME: Flooring (FLR) DATE: 2002 DOC#: FLR019 DOCUMENT DESCRIPTION: Journal Article - Examination of Asbestos Floor Tile by White Light Interference Microscopy and Scanning Electron Microscopy Microscope Volume 50:4 173-177(2002) Examination of Asbestos Floor Tile by White Light Interference Microscopy and Scanning Electron Microscopy James R. Millette* , Richard S. Brown*, William M. Ewing** and Tod A. Dawson** KEY WORDS Surface profiler, depth, white light interference, floor tile, VAT, asbestos ABSTRACT This study involved the application of a scanning white light interference microscopy (SWLIM) surface profiler and scanning electron microscopy in the examination of the surfaces of asbestos-containing floor tiles after abrasion. Although asbestos-contain ing floor tiles are non-friable when new, it is evident that asbestos fibers are released from the tiles under certain circumstances. The mechanism involved in the release of asbestos fibers from a product in which a vinyl or asphalt binder is present has not been fully described. The results described here demonstrate the use of complimentary microscopy techniques to assess a mechanism by which asbestos fibers can be liberated from floor tile due to foot traffic. INTRODUCTION Vinyl asbestos tile (VAT) was manufactured by mixing dry ingredients, polyvinyl chloride (PVC) resin, copolymers, limestone filler, pigment (usually titanium dioxide), and asbestos fibers. The materials were heated and mixed with metal blades. Once the mixture reached a specified temperature and degree of plasticity, it was rolled to a predetermined thick ness and cut to size. A similar manufacturing process was used to make asphalt asbestos tile. Although asbestos-containing floor tiles are nonfriable (not easily crumbled to dust under hand weight) when new, it is evident that they wear with use (Figure 1). In 1982, French researchers (1) published the first measurement of elevated concentrations of indoor air borne asbestos associated with the weathering of asbestos floor tiles during their service life. They con cluded that the short chrysotile fibers present in the air of the building had escaped from the vinyl matrix of the floor tiles. The fact that the highest concentra tions were measured in the workshop on the third floor, where the activity was greatest, reinforced their conclusion. They hypothesized that, in this work shop, breakdown forces such as walking and other activities were higher. A study in 1984 also reported that increased airborne asbestos fiber concentrations could be present in buildings where the only known source of asbestos is floor tile (2). The release of asbestos fibers from the matrix of vinyl or asphalt tiles that have been partially pulver ized during sawing, drilling and chipping has been well documented. Work practices to prevent fiber release during these activities have been issued by the United States Environmental Protection Agency (3) and others (4-7). Less abrasive procedures such as buffing have also been shown to cause increased air borne asbestos concentrations (8, 9). The fact that the matrix does not totally encapsu late asbestos fibers in a product where a vinyl or asphalt binder is present has been noted previously (10). Although the outside of a fiber bundle or clump may be coated with the binder; once the coating is broken, asbestos fibers are available to be released upon further abrasion. In one study, the researchers found that; "Surface adhesive lift and cross-sectional bulk sample analysis indicated that the wax layer which had accumulated and had been replenished *MVA, Inc., 5500 Oakbrook Pkwy, Suite 200, Norcross, GA 30093 **Compass Environmental, 1751 McCollum Pkwy, Kennesaw, GA 30144 173 periodically on the surface of the VAT served as a sink or reservoir for asbestos structures and matrices which may have migrated from the tile as a result of physical wear and abrasion. The surface analysis clearly revealed the presence of free asbestos struc tures in the wax layer on the surface of the VAT."(11) STUDY PROCEDURES This study used a scanning white light interfer ence microscopy (SWLIM) surface profiler and scan ning electron microscopy to examine the surface of floor tile for asbestos fibers after abrasion. The investigation of floor tile asbestos fiber release involved two studies. In the first, floor tiles removed from buildings were subjected to a simula tion of abrasion (scratching and gouging by dirt parti cles). In the second, floor tiles extracted from build ings after a period of normal use were examined for evidence of abrasion. Both vinyl asbestos (VAT) tiles and asphalt tiles were tested. Study 1 Floor tiles that had been identified as having been manufactured by a number of companies were obtained from state and local government buildings. Samples of dirt were also obtained from those build ings, or immediately outside the buildings. In per forming the abrasive testing process of this study, a researcher wearing a moistened, flat, leather soled shoe stepped into dirt. With some dirt on the bottom of his shoe, the researcher then stepped onto the tile with weight measured to be approximately 100 pounds and rotated his foot ninety degrees ten times. He then stepped into dirt again and repeated the activity. The abrasive testing process was repeated 3 times for a total of 30 rotations on each tile. The tile surfaces were photographed at intervals during the process. After the testing process, portions of each tile were examined microscopically for information about the depth of scratch and pitting penetration and evi dence of asbestos fibers protruding. Study 2 Floor tiles were extracted from buildings belong ing to a state government. These tiles had been in place for a period of years and had seen the wear and tear of normal use. Portions of each tile were exam ined microscopically for information about the depth of scratch and pitting penetration and evidence of asbestos fibers protruding. METHODS AND EQUIPMENT The tile and dirt material samples were analyzed for asbestos by polarized light microscopy (PLM) uti lizing an Olympus BH-2 polarized light microscope. Transmission electron microscopy was used to ana lyze some of the floor tiles for asbestos. After the shoe abrasion testing, the tile sample surfaces were examined by stereomicroscopy utiliz ing a Zeiss Stemi 2000 stereomicroscope and by scan ning electron microscopy (SEM) using a JEOL 6400 coupled with an x-ray energy dispersive spectrometry (EDS) Noran Voyager system. Measurement of the depth of some of the indentations in the tested tiles was performed using a WYKO scanning white light interference microscope (SWLIM) surface profiler operated in the vertical scanning mode at a magnifica tion of 2.5 (12 and 13). The vertical scanning technique has a 500 pm range with a lateral resolution of 15 pm and a vertical resolution of 1 nanometer. RESULTS Samples of dirt were composed primarily of soil mineral and plant fragments. Some shards of glass were seen. No asbestos-containing material was detected. All the floor tiles used in the study were found to contain asbestos. It was found that floor tiles were damaged by a dirty shoe under weight. Particles in the dirt caused grooves to be ground into the tile surfaces (Figures 2 and 3). The light interference microscope scans showed varying depths of the grooves caused by abrasion testing. Surface scratches and gouges over 10 pm were common (Figures 4 and 5). In addition to similar scratches and gouges, as seen in the simulation study, the normal use tiles examined in Study 2 showed evidence of pits which were over 40 pm deep (Figure 6). In the scanning electron micro scope images, uncoated chrysotile fibers were visible in some grooves of the tiles (Figures 7 and 8). Some tiles in which shorter asbestos fibers were present required more analysis time than tiles that had longer fibers. The microscopical findings were similar for the floor tiles in Study 2 where the tiles had been sub jected to normal use in state buildings. DISCUSSION AND CONCLUSIONS Wax layers are reportedly 3 pm thick (14). Therefore, even with two layers of wax, the scratches and gouges occurring from the interaction between a floor tile and dirt on a shoe is sufficient to reach the 174 M1CROSCOPE(2002)50 JAM ES R. MELLETTE et.al Figure 1. An example of an area of asbestos-containing floor tile that had worn away completely. Figure 2. View of scratches on a floor tile surface caused by a dirty shoe under approximately 1 JO pounds weight. Magnification = approximately 30x. Figure 3. View of scratches on a floor tile surface caused by a dirty shoe under approximately 100 pounds loeight. Magnification = approximately 30x. Figure 4. Scanning white light interference microscope vieio o f scratches on a floor tile surface caused by a dirty shoe under approximately 100 pounds weight. Figure 5. Scanning white light interference microscope vieio of scratches on a floor tile surface caused by a dirty shoe under approximately 100 pounds weight. Figure 6. Scanning white light interference microscope view o f a pit and scratches on a floor tile surface from a tile taken from a building after years o f normal use. 175 REFERENCES 1. Sebastien, P., Bignon, J., and Martin, M. Indoor Airborne Asbestos Pollution: From Ceiling and the Floor. Science, Vol. 216, 25 June 1982.1410-1413 2. Dufour, G. "Indoor Asbestos Pollution from Floor Tiles." In: Workshop on the Monitoring and Evaluation of Airborne Asbestos Levels Following an Abatement Program. National Bureau of Standards, Gaithersburg, MD (1984) Figure 7. Scanning Electron Microscope view of uncoated asbestos fibers in scratches on afloor tile surface caused by a dirty shoe under approximately 100 pounds weight. 3. USEPA, Recommended Interim Guidance for Maintenance of Asbestos-Containing Floor Coverings ( J a n . 2 5 , 1990) 4. Brakett, K.A.; Hanna, J.L., Vincent, H.S. and Clark, P.J.; Engineering Control Practices for Reducing Emissions During Drilling of Asbestos-containing Flooring Materials,. EIA Tech. Monograph Series, Vol. 2,1997 5. Resilient Floor Covering Institute, Recommended Work Practices for the Removal of Resilient Floor Coverings, Rockdale MD, 1995 6. OSHA, Asbestos Advisor for Building Owners, Release 2.0, Section 6, Flooring Operations, http ://www.osha.gov/oshasoft/asbestos/asbwin3.html, 1997 Figure 8. Scanning Electron Microscope View of uncoated asbestos fibers, in scratches on a floor tile surface caused by a dirty shoe under approximately 100 pounds weight. asbestos fibers in the floor tile matrix. Pits and scratches occurring during the normal use of floor tiles can be deeper than the layers of wax that might be put on a tile. Asbestos fibers observed in the scratches, grooves, gouges and pits were not com pletely coated by the floor tile binder material. Breaking off of these fibers through additional wear of the tiles is one possible explanation for the increased airborne asbestos fiber concentrations reported in buildings where the only known source of asbestos is floor tile. This study demonstrates a mechanism by which asbestos fibers may be liberated from floor tile due to normal foot traffic. 7. Oberta, A.F. and Fischer, K.E. Negative Exposure Assessments for Asbestos Floor Tile Work Practices. Advances in Environmental Measurement Methods for Asbestos, ASTM STP 1342, M.E. Beard and H.L. Rook, Eds., American Society for Testing and Materials, 2000. 8. Wilmoth, R. C. and Hollett, B. A. Asbestos Operation and Maintenance Studies on Carpet Cleaning, High Efficiency Particulate Air Vacuum Use, and Tile Buffing. Appl. Occup. Environ. Hyj 1994, 9(ll):879-888 9. Kominsky, J.R., R.W. Freyberg, J.M. Bolani Airborne Asbestos Concentrations During Buffinj Burnishing and Stripping of Resilient Floor Til! Project Summary. August 1995, Documen EPA/600/SR-95/121 10. Millette, J.R., and Brown, R.S., "Scanning Electro Microscopy of Asbestos-Containing Material whei the Asbestos Fibers are Considered Locked in A 176 MICROSCOPE(2002)50 Binder", Proceedings, 51st Annual Meeting, Mic. Soc. of America, August 1993. 11. Demyanek, M.L., R.J. Lee, K.A. Allison, and G.R. Dunmyre, Air, Surface, and Passive Measurements in a Building During Spray-Buffing of Vinyl-Asbestos Floor Tile. Occup. Environ. Hyg. 1994, 9(ll):869-875 12. Church, E.L., "Direct comparison of mechanical and optical measurements of the finish of precisionmachined surfaces," Proc. SPIE 429, 105-112 (1983) 13. Caber, R. J., "An interferometric profiler for rough surfaces," Optical Society of America Topical Meeting on Surface Roughness and Scattering, Tucson, AZ (1992) 14. Personal communication, Wax Division, S.C. Johnson and Sons (2001). JAMES R. MILLETTE et.al periodically on the surface of the VAT served as a sink METHODS AND EQUIPMENT