Environmental Engineering Reference
In-Depth Information
of exposure. In most cases, concentrations of fibers <5
µ
m are greater than
those
≥
5
µ
m.
2.
Persons exposed to asbestos in buildings
A variety of individuals may be exposed to airborne asbestos fibers. These
include general building occupants such as teachers, students, office work-
ers, and visitors; housekeeping/custodial employees who may come in
contact with or disturb ACBM or contaminated settled dust during their
work activities, and maintenance/construction workers who may disturb
ACBM during repair or installation activities. Asbestos abatement/remedi-
ation workers and emergency personnel such as firefighters may also
become exposed.
3.
Ambient (outdoor) concentrations
Samples collected from Antarctic ice indicate that chrysotile asbestos has
been a ubiquitous contaminant of the environment for at least 10,000 years.
Snow samples in Japan have shown that ambient background levels are one
to two orders of magnitude higher in urban than in rural areas. Higher
concentrations of airborne asbestos fibers are reported in urban areas where
there is more ACM and mechanisms of release (vehicles braking and weath-
ering of asbestos cement materials); concentrations in the range of 1 to
20 ng/m
m are rarely found in
rural areas. Ambient concentrations using TEM analysis have been based on
mass measurements.
have been reported. Fibers longer than 5
µ
3
4.
Asbestos concentrations in building air
Asbestos concentrations in buildings have been measured using a variety of
techniques. Representative samplings of asbestos fiber concentrations (f/cc)
determined by TEM with direct sample analysis are summarized in
Table
limit of detection to maximum concentrations approximately 1.5 to 2+ orders
of magnitude greater than the current 8-hour OSHA TWA occupational
standard of 0.1 f/cc. Average concentrations are 2 to 3 orders of magnitude
lower than the occupational permissible exposure limit (PEL).
Average building asbestos concentrations ranging from 0.00004 to
0.00243 f/cc have been reported in a study of 198 randomly selected ACBM-
containing buildings. Mean concentrations for schools, residences, and pub-
lic/commercial buildings were 0.00051, 0.00019, and 0.0002 f/cc, respectively,
with 90 percentile concentrations of 0.0016, 0.0005, and 0.0004 f/cc. The
higher asbestos fiber concentrations observed in school buildings may be
due to the greater activity there that disturbs ACBM and resuspends asbestos
fibers. The concentration of airborne asbestos fibers in buildings of all types
appears to be associated with the presence of occupants and their level of
activity. These data also indicate that asbestos fibers longer than 5
m rep-
resent only a small fraction of the total number of airborne asbestos fibers.
µ
