Test Method 435 - Determination of Asbestos Content of Serpentine Aggregate

This page last reviewed December 20, 2012

Test Method 435 (M435), a method to quantify the asbestos content of aggregate, was adopted by the Air Resources Board (ARB or Board) in April 1990 in support of an Airborne Toxic Control Measure (ATCM) aimed at reducing public exposure to naturally occurring asbestos (NOA) by limiting the asbestos content of surfacing material. A second ATCM, focusing on construction, grading, quarrying, and surface mining operations that can disturb and entrain naturally occurring asbestos fibers into the air, was adopted later and also referenced M435 as an approved asbestos bulk test method.

ARB staff conducted a M435 interlaboratory study (ILS) which identified variability in equipment used and procedures followed among the participating laboratories and demonstrated that these differences can significantly affect the reported asbestos content of rock and soil samples.  In response to these ILS findings, ARB staff conducted workshops, sent out surveys, fielded numerous comments, and conducted method testing to seek ways to improve the accuracy and repeatability of M435 results. 

In lieu of making formal regulatory revisions to M435, staff plans to develop a “good practices” guidance document that should help both field and laboratory personnel produce more accurate and repeatable asbestos content determinations using M435. A draft guidance document will be made available for comment before being finalized. 


Public Workshop - June 10, 2008

Public Workshop - January 24, 2008

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For more information about the M435 revision activities, please contact Jeff Wright at (916) 322-7055 or Rebecca Neumann at (916) 324-1145.

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