Environmental Engineering Reference
In-Depth Information
preventing mold infestation is a rapid effort (within 24 to 48 hours) to repair
plumbing problems and dry the wet materials. The more quickly wet mate-
rials are dried, the less likely they will become infested.
HVAC system problems.
Leaks from AHUs are common. They, like other
water problems, must be repaired as soon as possible, and wet ceiling tiles
removed and dried or discarded.
One of the most common causes of significant mold infestation in schools
is improper operation of cooling systems during summer months. In many
cases, building spaces are cooled to temperatures of 70 to 74°F (21 to 23.5°C)
during daytime hours and the HVAC system is subsequently shut down
during nighttime, unoccupied hours. On high dewpoint days (75 to 77°F, 24
to 26°C), outdoor air infiltrates the building and condenses on cooler build-
ing surfaces which are below the dewpoint. Significant mold infestation
generally occurs, particularly on older topics. Such problems can be avoided
by operating cooling systems continuously or maintaining cooling temper-
atures at higher settings (78 to 80°F, 25 to 26°C).
Infestation of HVAC system filters is often associated with excessive dust
accumulation as a result of infrequent filter replacement. More frequent
replacement is desirable. Duct liner materials are porous and collect organic
dust, which has the potential for becoming infested, particularly near water
sources such as fan coil units. Insulating materials are best placed on the
exterior of ducts to avoid soiling and mold infestation.
Remediation measures.
Once a mold infestation problem has become
manifest, remediation measures are necessary to eliminate or reduce mold
growth and reduce occupant exposures. The most commonly used remedi-
ation measures are removal and disinfection.
Removal can be viewed in two contexts. These are the removal of mold
growth from an infested surface by application of cleaning measures and,
in the case of wood, scraping. Such cleaning and scraping of mold-infested
materials are commonly done on relatively hard surfaces such as window
frames, window glass, flooring, drywall, and wall cavity materials. It is
typically followed by other treatments to prevent reinfestation.
In the case of soft materials such as paper products, furnishings, carpet-
ing, and heavily infested structural timbers and gypsum board, the materials
themselves may be removed and replaced. Such removal is essential to
mitigating problems associated with toxigenic fungi such as
Stachybotrys
chartarum
. In the case of heavy infestations by tox-
igenic fungi, removal is conducted to the minimum standards of asbestos
removal, with a higher degree of worker supervision. Such abatements are
conducted under negative pressure enclosures with full respiratory protec-
tion and personal protective equipment for workers. The abatement must
meet clearance values using aggressive sampling for specific toxigenic fungi
before the contractor can be released. Clearance values of zero spores of
and
Aspergillus versicolor
S.
chartarum
on a 100% count of total mold spore samples are recommended.
Biocidal treatments are commonly used in mold mitigation activities. In
small infestations (such as a wall surface), cleaning is usually followed by a
