Environmental Engineering Reference
In-Depth Information
together are overcome. For small particles, both cohesive and adhesive forces
are very strong, but mechanical vibration may produce sufficient energy to
overcome these forces. Release of fibers by air erosion, even in return air
plenums with spray-applied ACBM, has been shown to be minimal.
Several studies have indicated that resuspension of surface dust is the
main source of airborne asbestos fibers indoors. Other studies have sug-
gested that the resuspension of asbestos-containing surface dust is of
minor, if not negligible, importance. Resuspension requires sufficient dis-
turbance to overcome the strong adhesive forces that exist between parti-
cles and surfaces.
6.
Indirect indicators of potential exposure
Measurements of indoor asbestos fiber concentrations are often made by
building managers in response to occupant asbestos exposure concerns. Such
one-time measurements are, at best, a snapshot of potential exposure in
sampled spaces. Concentrations vary significantly over time, depending on
the amount of ACBM/asbestos-containing dust disturbance. Consequently,
USEPA does not recommend, and even discourages, use of airborne asbestos
sampling to determine potential asbestos exposures in buildings.
Under USEPA regulatory requirements, asbestos hazard determinations
for school buildings are based on detailed inspections which include iden-
tifying potentially hand friable ACBM, collecting bulk samples, assessing
the extent of damage, and determining the potential for future damage.
Building asbestos hazard assessments are used to select abatement pri-
orities. Assessment methods in current use consider the accessibility and
condition of the ACBM. Assessment is based on the following premises: (1)
the likelihood of disturbance increases with accessibility, (2) damaged ACBM
is evidence of past disturbance and the potential for future disturbance, and
(3) damaged ACBM is more likely to release fibers when disturbed. In the
USEPA decision tree,
Figure 2.5
,
ACBM is given exposure hazard rankings
Figure 2.5
USEPA building asbestos hazard assessment decision tree.
