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August 20, 1998
Should you be concerned about mold?
By BRAD PREZANT
Prezant Associates Joining asbestos, lead and PCBs, mold in buildings has captured the public's
attention as a potential health hazard requiring special care. We're all familiar with the costly mechanical and structural damage caused by the
presence of water in buildings. In recent years however, building owners,
managers and tenants have discovered that water damage (condensation, leakage
or entry during new construction) also creates genuine or perceived health hazards
to occupants. Recent attention to the issue of mold in buildings, particularly Stachybotrys, has
fueled a new level of concern. In some cases this attention is justified. In other
cases, the concern goes beyond the actual risk, resulting in difficult and sensitive
risk communication issues. Are there reasons to be concerned about mold in buildings? Yes, if excessive exposure might occur. Molds produce spores, very tiny particles
which become invisible airborne particulate, similar to asbestos or lead particles.
The spores sometimes contain chemicals, designed to kill other competing life
forms (remember, it's a jungle out there). These substances, known as mycotoxins,
adversely affect human health. Exposures occur when the spores containing these chemicals are inhaled.
Interestingly, it doesn't matter if the spores are dead or alive, since breathing the
spores doesn't cause an infection like breathing tuberculosis bacteria or common
cold viruses would. The spores' health effects include suppressing the immune
system because of the chemical toxins they contain. While not all molds produce such mycotoxins, all mold spores contain other
substances irritating to the human respiratory tract, and can elicit allergic
symptoms in sensitive individuals. Spores from numerous species of outdoor molds are typically found inside
buildings at levels ranging from 10 percent to 50 percent of their levels in outdoor 1 of 4 1/7/00 3:36 PM Should you be concerned about mold? http://www.djc.com/special/enviro98/10043980.htm air. The concern for mold in buildings is not related to these species or to the
outdoors as a source. Problems occur when uncommon species of molds grow
indoors on building materials, especially those containing cellulose. You may think of sheetrock as a
gypsum-and-paper sandwich. I
think of sheetrock as a sponge
with food pasted to both sides.
The gypsum insures a consistent
long-term source of moisture for
the non-outdoor molds growing
on the paper and deposited dust.
This provides an ideal
environment for molds to
reproduce. As they proliferate, these Mold looks nice growning in a petri dish . . .
non-outdoor molds release Photo by the Cohen Group
spores, creating immediate and
possibly future exposures for
occupants. Mold growing indoors is unacceptable; remediation requires identifying
and removing the porous substrate upon which they are growing, removing the
source of moisture and then cleaning up the residual spore-containing dust. How many spores are too much? This determination requires a situation-specific
evaluation, considering many factors including whether or not related health
effects are being experienced by occupants. A consensus has emerged among
microbiologists, certified industrial hygienists and other qualified health
professionals that it is unacceptable to have ongoing mold growth in occupied
buildings. Unlike other contaminants of indoor air, indoor sources of fungal growth can be
prevented and eliminated. Conducting site evaluations, sampling and interpreting
air monitoring data, and providing guidance on remediation is highly complex and
controversial, requiring specialized and experienced certified industrial hygienists. How mold gets into buildings From water entry during construction. A tilt-up concrete addition on a concrete
slab was assembled without protection from the rain. Six months later, employees
began to feel sick and evacuated the building. Investigation revealed extensive
mold growth on the plywood underside of the roof, throughout the 2 x 4 studs
used to support the interior sheetrock, and on the back side of the sheetrock. 2 of 4 1/7/00 3:36 PM Should you be concerned about mold? http://www.djc.com/special/enviro98/10043980.htm Employees recalled the
sheetrocker working in rubber
boots because the concrete slab
was wet during construction.
Sufficient moisture had been
retained within the structure
during construction to permit
extensive growth of Aspergillis
and Penicillium, with elevated
airborne levels of both. Remediation required extensive
. . . but not so nice growing on a wall. cleaning and demolition over a
Photo by Prezant Associates 12-month period. During construction of a large commercial building, numerous packaged fans were
rained on prior to the roof being installed. Insulation within these units became wet
and moldy. Construction was delayed and ultimately the units had to have the
internal insulation removed and replaced. Flooding. Floods in Western Washington in 1994 resulted in numerous buildings
being inundated with water. One flooded building, a one-story convalescent home,
was cleaned extensively and reoccupied after receiving 6 to 12 inches of water.
Water wicked up the sheetrock and mold grew within the wall cavities until the
sheetrock dried. While the mold was no longer alive, it left behind extensive spores
which were able to migrate through the wall and create unacceptable exposures to
building occupants. A kitchen located above an office had plumbing which repeatedly leaked water
over a one- to two-year period. Mold growth within the office resulted in
extensive illness and evacuation of the building. The masonry exterior of a school building was wet from a misplaced sprinkler
during the summer. The following fall, teachers noticed mold bleeding through the
sheetrock behind a cabinet. Water had been retained and slowly released for many
months by the wet masonry, providing ideal conditions for mold growth. Remodeling. Disturbance of the exterior of a hospital building during exterior and
interior renovation created airborne Aspergillis spores. Because Aspergillis is one
of a select few molds which can cause incurable infections in humans, extensive
isolation and verification was required to insure that immuno-compromised
patients were not exposed. Condensation. A building in a hot, humid climate was constructed without a
vapor barrier on the outside of the building. The air conditioning system was
creating a negative pressure indoors relative to outdoors, allowing hot, moist air to
migrate inward. The first vapor barrier reached was the vinyl-covered wall on the
occupied side of the sheetrock. Because the interior of the building was cold, the
humid air leaking inward cooled and released its water content on the back side of 3 of 4 1/7/00 3:36 PM Should you be concerned about mold? http://www.djc.com/special/enviro98/10043980.htm the sheetrock. Peeling the vinyl wall covering off revealed extensive growth of
Stachybotrys and other molds throughout the sheetrock. A building was constructed with ventilation supply ducting in the concrete slab.
Unfortunately, the slab was chronically wet. As a result, warm supply air picked up
moisture which condensed on the colder exterior surfaces of the building,
including windows and interior wall cavities at the cold exterior wall. Extensive
mold growth was present in the walls. In many of the above cases, removal of porous materials such as carpeting and
sheetrock, and cleaning of non-porous materials was required. These tasks, along
with removal of the water source and HEPA vacuuming of remaining dusts,
prevented potential mold spore exposures. Brad Prezant, CIH, CPE, principal of Prezant Associates, Inc. is board certified in Indoor
Environmental Quality by the American Board of Industrial Hygiene. Copyright © 1998 Seattle Daily Journal of Commerce. 4 of 4 1/7/00 3:36 PM |
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