Monday, April 16, 2007

VAT Article from our 2007 Spring Newsletter.


A study published in the 2003 issue of “Applied Occupational and Environmental Hygiene” magazine titled “Asbestos Release During Removal of Resilient Floor Covering Materials” by Marion Glenn Williams, Jr. and Robert N. Crossman, Jr. of the University of Texas Health Center indicated that worker's exposure to asbestos during vinyl asbestos floor tile (VAT) removal may be under reported. Because we work in New York (NYS), we are very familiar with the limitations of polarized light microscopy (PLM) analysis on VATs or for that matter on any nonfriable organically bound (NOB) material. Under NYS Environmental Laboratory Accreditation Program (ELAP) requirements materials that are considered NOBs must go through a multiple step process for analysis. This process ends with analysis by Transmission Electron Microscopy (TEM) for samples that are negative for asbestos. This method is required for VATs because the type of asbestos typically used was Grade 7 asbestos known as Shorts & Floats. Grade 7 asbestos is no longer sold and was the cheapest asbestos material sold. The dimensions of this grade of asbestos was ultra-fine. With fiber dimensions approaching the less than 5 micron range. This study was done to determine if there was fiber release at the less than 5 micron level that was not being analyzed by the Phase Contrast Microscopy (PCM). PCM is used for air sample analysis and only analyzes greater than 5 micron fibers with a 3:1 or greater length to width ratio. The study found the following issues:

  • When removing a non-asbestos sheet vinyl flooring with an asbestos felt backing the PCM method only reported 5-7% of the fibers counted by the TEM method.

  • When removing an asbestos containing 12x12 VAT with asbestos containing mastic the PCM method only reported 2-2.5% of the fibers counted by TEM.

  • When removing an asbestos 9x9 VAT with an asbestos mastic the PCM method reported 0-2.5% of the fibers counted by TEM.

  • When removing mastic using a mastic remover (TEM levels were between 1.319-1.749 structures/cubic centimeter (s/cc)) versus amended water (TEM levels were between 0.094-0.184 s/cc).

This study shows that air sample results are significantly underreported using the PCM method of analysis. When performing VAT removals asbestos air monitors and project monitors should be using TEM analysis for clearance (at the very least) and they should be running a few TEM samples during the actual removal of the VATs. These would give us a better understanding of what is happening during VAT removals and ensure that the asbestos abatement was thoroughly completed.

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