Environmental Engineering Reference
In-Depth Information
Table 2.3
Airborne Asbestos Concentrations in Buildings Determined by
Transmission Electron Microscopy
Asbestos fibers
>5
ยต
m (f/cc)
Sample
#
Description
Range
Mean
Nonlitigation
19 Canadian buildings with spray-applied
ACBM
63
ND-0.003
0.00042
12 United Kingdom nonresidential buildings
with ACBM
96
ND-0.0017
0.00032
37 U.S. public buildings with damaged ACBM
256
ND-0.00056
0.00005
19 U.S. schools with ACBM
269
ND-0.0016
0.0002
Litigation
121 schools and universities
1008
ND-0.0017
0.00046
Source:
From Health Effects Institute-Asbestos Research,
Asbestos in Public and Commercial Build-
ings: A Literature Review and Synthesis of Current Knowledge
, Cambridge, MA, 1991. With permission.
Data based on arithmetic mean averages are likely to overestimate asbes-
tos exposure in buildings. Asbestos fiber concentrations are not normally
distributed and, as a result, geometric mean or median values are more
appropriate than arithmetic means. Arithmetic means have often been
reported in studies because 50% of airborne building asbestos values are
below the limit of detection; as a consequence, the median value would be
zero. Arithmetic means are very sensitive to a few very high values and thus
are likely to overestimate occupant exposure.
Higher exposures can be expected for custodial workers whose activ-
ities may resuspend settled asbestos fibers and structures on a regular basis,
and disturb ACBM on occasion. Comprehensive exposure studies associ-
ated with custodial activities have not been reported. Higher exposures can
also be expected for maintenance workers who damage ACBM during their
work. Elevated episodic exposure concentrations of >1 f/cc (determined
by phase contrast microscopy) have been reported for a variety of mainte-
nance activities.
5.
Factors contributing to asbestos fiber release and potential airborne
exposure
When fibers or asbestos structures from ACM become airborne, the process
is called primary release. Primary release mechanisms include abrasion,
impaction, fallout, air erosion, vibration, and fire damage. Secondary release
occurs when settled asbestos fibers and structures are resuspended as a
result of human activities. In unoccupied buildings or during unoccupied
periods, fiber release typically occurs by fallout or is induced by vibration
or air erosion.
Impaction and abrasion are likely to be the major causes of increased
airborne fiber levels. Fallout occurs when cohesive forces that hold ACM
