Comparison of Mineral Wool Insulations in the Forensic Laboratory: Second Collaborative Study

Abstract

Abstract A method for comparing mineral wool insulationswas collaboratively studied a second time.Specimens are examined microscopically forcolor, disposition of resin, fiber diameters,quantity of slugs, and other gross microscopiccharacteristics. The resin is burned off and thefibers are annealed at 500°C. The heat-cleanedfibers are examined for shortwave ultravioletfluorescence, microscopic appearance, solubilityin HCI, and indices of refraction according to45.002-45.007. Ten collaborators examined 9specimens of mineral wool, 4 of which werefrom one large lot of Owens-Corning Fiberglasand 2 of which were from a single Johns-Manville ceiling tile. The other 3 were fromdifferent sources. Eight collaborators correctlyconcluded that the Owens-Corning samplescould have had a common origin, that theJohns-Manville samples could have had a commonorigin, and that the others were of independentlydifferent origins. Two collaboratorsin the same laboratory, using other than therecommended equipment, concluded that theOwens-Corning samples were one class, that theJohns-Manville samples were one class, andthat the others were of different origin, but theyfound slight differences in the refractive indicesof the Johns-Manville samples and did not concludecommon origin for them. The method hasbeen adopted as interim official first action.