Environmental Engineering Reference
In-Depth Information
bars embedded lengthwise in the pipe wall. If wire is used, it is wound
tightly to prestress the core and is covered with an outer coating of con-
crete. Prestressing is accomplished by manufacturing the pipe with a
permanent built-in compression force.
4.9.1.2.4 asbestos-Cement (a-C) Pipe
Asbestos-cement pipe is composed of a mixture of Portland cement
and asbestos fiber which is built up on a rotating steel mandrel and then
compacted with steel pressure rollers. This pipe has been used for over
70 years in the United States. Because it has a very smooth inner surface,
it has excellent hydraulic characteristics (McGhee, 1991). In wastewa-
ter operations, though, the ultimate removal and disposal of asbestos-
cement pipe pose a problem for operators; for example, consider an
underground wastewater line break that must be repaired.
Locating exactly where the line break is can sometimes be difficult,
because A-C pipe is not as easily located as conventional pipe. When
the line break has been located, the work crew must first excavate the
soil covering the line break, being careful not to cause further damage
(A-C pipe is relatively fragile). When the soil has been removed, expos-
ing the line break, the damaged pipe section must be removed. In some
instances, it may be more economical or practical to remove the damaged
portion of the pipe only and to install a replacement portion, girdling it
with a clamping mechanism (sometimes referred to as a
saddle clamp
).
To this point in the repair operation being described, the likelihood
of exposure to asbestos by personnel is small because, to be harmful,
asbestos-containing materials (ACMs) must release fibers that can be
inhaled. The asbestos in undamaged A-C pipe is not
friable
; that is, it
cannot readily be reduced to powder form by hand pressure when it is
dry. Thus, it poses little or no hazard in this condition. If, however, the
maintenance crew undertaking the pipe repair must cut, grind, or sand
the A-C pipe section, the nonfriable asbestos will separate. This type of
repair activity is capable of releasing friable airborne fibers, and herein
lies the hazard of working with A-C pipe. To guard against the hazard of
exposure to asbestos fibers, A-C pipe repairs
must be accomplished in a safe manner.
Operators must avoid any contact with an
ACM that could disturb its position or
arrangement, that could disturb its matrix
or render it friable, or that could generate
any visible debris.
Key Point:
The presence of visibly damaged,
degraded, or friable ACMs is always an indi-
cator that surface debris or dust could be
contaminated with asbestos. OSHA stan-
dards require that we assume that such dust
or debris contains asbestos fibers (Coastal
Video Communications, 1994).
In the A-C pipe repair operation described above, repairs to the
A-C pipe require that prescribed U.S. Environmental Protection Agency
(USEPA), Occupational Safety and Health Administration (OSHA), state,
and local guidelines be followed. General USEPA/OSHA guidelines, at a
minimum, require that trained personnel perform repairs on A-C pipe.
The following safe work practices are provided for those who must work
with A-C pipe (Spellman, 2001).
