Environmental Engineering Reference
In-Depth Information
4.
Encapsulation
Encapsulation is widely used to reduce fiber release from asbestos-contain-
ing SM such as spray-applied acoustical plaster and similar materials. Encap-
sulants are designed to bind asbestos fibers to ACM and/or assure adherence
of ACM to building substrates. Bridging encapsulants are applied to asbes-
tos-containing SM to form a strong membrane that prevents fiber release.
Penetrating encapsulants are designed to enter ACM to bind fibers to the
ACM matrix and substrate.
Use of these two types of encapsulants depends on ACM characteristics.
A bridging encapsulant is recommended for moderately friable ACM found
on cementitious materials and complex surfaces such as pipes, ducts, and
beams. Penetrating encapsulants are recommended for moderately friable
ACM that is <1” (2.54 cm) thick. They are not recommended for painted or
previously encapsulated surfaces.
Bridging encapsulants are widely used on acoustical plaster. The most
common encapsulant is latex-based paint. Bridging encapsulants have sev-
eral disadvantages: (1) they do not enhance adhesion to substrate surfaces;
(2) they often significantly increase the weight of ACM; and (3) they make
it more difficult and costly to remove ACM when it becomes necessary when
the building is to be renovated or demolished.
Encapsulation is an appropriate asbestos control measure when ACM
(1) retains its bound integrity, (2) is granular or cementitious, (3) is unlikely
to become damaged, and (4) is highly-to-moderately accessible. If applied
to ACM in poor condition, the material may delaminate, resulting in the fall
of ACM onto horizontal surfaces with subsequent fiber release.
Since the source remains, encapsulation is not considered a permanent
asbestos control method by USEPA. As a consequence, encapsulated ACM
will require periodic inspection and possible reapplication of the encapsulant.
The cost of encapsulation varies. Under AHERA (see Chapter 13) school
regulations, USEPA requires engineering controls and work practices similar
to those used for asbestos removal. As a consequence, application costs are
relatively high (approximately 50% of the cost of removal). Under OSHA
asbestos construction industry rules, encapsulation is treated much like a
repair and is classified as Class III asbestos work. Under this work classifi-
cation, engineering controls and work practices may be significantly less
demanding than for USEPA-regulated school abatement activities; therefore,
encapsulation costs are significantly lower.
5.
Removal
Removal is widely used as an asbestos abatement measure in buildings. Tens
of thousands of asbestos abatement removal projects are conducted in the
U.S. each year. In most cases, removal is conducted to comply with USEPA
regulations that require removal of friable or potentially friable ACM when
buildings are being renovated or demolished. Less often, ACM removal is
prescribed to reduce potential exposures to building occupants or service
