Environmental Engineering Reference
In-Depth Information
The ban on friable asbestos-containing materials used in building con-
struction and requirements for removal prior to demolition or renovation
were intended to minimize exposure of individuals in the general commu-
nity to contaminated ambient (outdoor) air. Potential exposures to building
occupants from fibers released from building products in the course of nor-
mal activities had not been addressed. In 1978, public attention was drawn
to the large quantities of friable or potentially friable ACBM that was used
in school construction as well as other buildings.
A. Mineral characteristics
Asbestos is a collective term for fibrous silicate minerals that have unique
physical and chemical properties that distinguish them from other silicate
minerals and contribute to their use in a wide variety of industrial and
commercial applications. These include thermal, electrical, and acoustic insu-
lation properties; chemical resistance in acid and alkaline environments; and
high tensile strength, which makes them useful in reinforcing a variety of
building products.
Asbestos comprises two mineral groups which are distinguished by their
ure 2.1
), the most widely used asbestos mineral, has a layered crystalline
structure with the layers rolling up on each other like a scroll or “tubular
fibrils.” The amphiboles, which include amosite, crocidolite, anthophyllite,
actinolite, and tremolite, have a crystalline structure characterized by double-
chain silicate “ribbons” of opposing silica tetrahedra linked by cations.
Individual asbestos fibers have very small diameters, high aspect
(length:width) ratios, and smooth parallel longitudinal faces. Asbestos fibers
are defined for exposure monitoring as any of the minerals in
Table 2.1
that
have an aspect ratio
≥
3:1, lengths >5
µ
m and widths <3
µ
m. In actual practice,
Figure 2.1
Chrysotile asbestos fibers under microscopic magnification. (Courtesy of
Hibbs, L., McTurk, G., and Patrick, G., MRC Toxicology Unit, Leicester, U.K.)
