The School District of Palm Beach County in Florida planned to demolish a three-building school campus. Prior to demolition, all friable asbestos-containing materials had to be removed to comply with the USEPA asbestos NESHAP regulation. In this instance, this included wall plaster in all buildings, as previous sampling had found the plaster to be asbestos-containing. However, the results of this prior sampling were inconsistent, indicating that different plaster types may be involved. The District asked us to more accurately determine the asbestos-content of the plaster.
We knew from our prior experience that accurate analysis of plaster is difficult, and that commercial laboratories following standard analysis methods will typically have random errors of 3% to 5%. This level of error makes it impossible to determine if plaster genuinely has an asbestos content greater than 1%, which would make it a regulated material under the NESHAP regulation. On this project we collaborated with Chatfield Technical Consulting in Canada, who are able to analyze plaster to 0.01%. We core drilled the plaster and collected separate sets of samples from each building. The cores were cleaned and each layer of plaster classified by use of a stereo microscope with color corrected lighting. Each individual layer was categorized by cement and aggregate type, and then analyzed for asbestos, and cement composition. This analysis allowed us to determine that there were different plaster types on the inside surface of exterior walls, and on interior partitions. Plaster on the inside surface of the exterior wall was a Portland cement plaster, and did not contain asbestos. Interior plasters had two layers, having a base and finish coat. In two of the buildings the outside layer of plaster contained 0.5% asbestos, and as such was not regulated by the NESHAP regulation. All base coat plasters, and all plasters in the third building were asbestos free.
Determining the exact composition accomplished two things. First, worker protection requirements could be tailored to the actual asbestos content that would be encountered. Second, the scope of removal work required prior to demolition was greatly reduced. Separate plaster removal was not required for compliance with the NESHAP. In the worst case, where there was 0.5% asbestos in the plaster, only OSHA required worker protection was required.