Presentation Abstract

Title: Comparison of Direct and Indirect Sample Preparation Methods for Asbestos Analysis

Authors: Leonard G. Burrelli and John W. Spencer

Presented at: AIHce 2001, New Orleans, LA

Industrial hygienists must clearly understand the procedures encompassed within the various analytical methods to properly conduct health hazard assessments. It is imperative that the industrial hygienist selects the appropriate standard analytical method for an assessment to obtain meaningful results; assures that the assessment was conducted in accordance with federally mandated guidelines; and obtains results that are conducted using verifiable and quality assured processes.

A study was conducted to compare the effect of a “direct” filter preparation technique (NIOSH Analytical Method 7400) with an “indirect” filter preparation technique (ASTM Method D5755-95) that utilizes ultrasonic treatment and re-deposition of collected particulate. The airborne sample materials used for the analysis were generated from non-friable asbestos-containing gaskets. The dust generation technique was developed only to produce material for collection on the filter cassette, and was not reflective of likely occupational airborne fiber values when working with the gasket products.

The results of the study showed that the use of the indirect sample preparation method as described in ASTM Method D5755-95, disassociated bound asbestos fibers from the non-friable gasket matrix material, and also dispersed fiber bundles rendering discreet “countable” asbestos structures. Analysis of the indirect sample preparations revealed an increase in the number of fibers detected and countable by phase contrast microscopy. Samples analyzed by the direct preparation methodology as required by OSHA showed that fibers were generally encapsulated in bundles and matrices.

Therefore, air samples prepared by an indirect analytical methodology presented results that were not reflective of the actual fiber concentration in the air. In all cases, the fiber in air concentration by indirect preparation exceeded the companion sample analysis prepared by the direct methodology by a factor of 20 to 26 times.

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