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6
Prevention and Remediation
of Damp Indoor Environments
Among the concerns that people face when dealing with indoor mois-
ture problems are how to prevent microbial growth from starting and how
to get rid of established growth safely and effectively. This chapter discusses
prevention strategies, published guidelines for the removal of fungal growth
(remediation), remediation protocols, and research on the effectiveness of
various cleaning strategies. It also identifies weaknesses in the literature on
remediation and offers suggestions for further research. The chapter does
not offer guidance on which interventions are appropriate in which circum-
stances--this is beyond the scope of the report.
The chapter focuses on mold because most of the pertinent literature
deals with mold. The observations offered here are also likely to be relevant
to other indoor microbial exposures, but, because they have not been well
studied, it is not possible to make definitive statements about them.
PREVENTION
The most effective way to manage mold in a building is to eliminate or
limit the conditions that foster its establishment and growth. Every organ-
ism has strategies for locating a hospitable environment, obtaining water
and nutrients, and reproducing. Intervention in one or more of those strat-
egies can improve the resistance of the environment against microbial
contamination.
The key to prevention in the design and operation of buildings is to
limit water and nutrients. The two basic methods for accomplishing that
270
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PREVENTION AND REMEDIATION 271
are keeping moisture-sensitive materials dry and, when wetting is likely or
unavoidable, using materials that offer a poor substrate for growth. Specifi-
cally, design and maintenance strategies must be implemented to manage
· Rainwater and groundwater, preventing liquid-water entry and acci-
dental humidification of buildings.
· The distribution, use, and disposal of drinking, process, and wash
water, making equipment and associated utilities easily accessible for main-
tenance and repair.
· Water vapor and surface temperatures to avoid accidental condensation.
· The wetting and drying of materials in the building and of soil in
crawl spaces during construction.
Existing buildings have more limited options for water and moisture
control than new construction because the systems that manage drinking,
process, and wash water and that control rainwater, groundwater, water
vapor, and heat flow have already been selected and installed. Flawed
constituents of existing systems must be repaired, replaced, or addressed
through routine operations and maintenance. Operations and maintenance
procedures that reduce the likelihood of mold growth include cleaning
mold-resistant materials that routinely get wet in the course of ordinary
operations (floors in entryways, showers, and condensate systems or cool-
ing coils) and quickly drying mold-prone materials that accidentally get wet
through plumbing leaks, rainwater intrusion and the like.
Little scientific information on the efficacy and impact of prevention
strategies is available, perhaps in part because it is easier to study problems
than their absence. Moreover, little of the practical knowledge acquired
and applied by design, construction, and maintenance professionals has
been committed to print or subject to thorough validation; this complicates
the study and dissemination of best practices. Chapters 2 and 7 address that
topic and offer recommendations for research and for education of building
professionals and others.
PUBLISHED GUIDANCE FOR MOLD REMEDIATION
Efforts to remediate microbial contamination involve direct interven-
tion with building occupants, the source of the contaminant (the mold or
other microbial agent), or the transport mechanism, (that is, the means by
which a contaminant moves within a building environment). For example,
moving people during intense remediation activities is an intervention that
involves occupants, removing fungal growth and remediating the moisture
problem are interventions that involve the source, depressurizing a moldy
crawl space with fan-powered exhaust intervenes in the transport mecha-
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272 DAMP INDOOR SPACES AND HEALTH
nism, and filtration and increased dilution ventilation intervene in contami-
nant transport by lowering airborne concentrations in general.
This section addresses similarities and differences in various published
contamination-remediation guidelines, and the section that follows it is an
extended discussion of the steps to be taken in remediation.
Indoor mold has historically been treated as a nuisance contaminant.
Two decades ago, there was little guidance for responding to fungal con-
tamination in buildings beyond the general instruction to clean it up. That
began to change as more became known about the potential hazards of
mold exposures and the practice of remediation. In 1980, allergists sug-
gested removing mold-contaminated materials and cleaning affected areas
(Kozak et al., 1980). In the same year, the U.S. Department of Agriculture
published a bulletin advising people to control dampness and to treat con-
taminated materials with bleach (USDA, 1980). Four years later, Morey et
al. (1984) recommended moisture control, improved filtration, and ventila-
tion with outdoor air to prevent mold problems. Intervening in the mois-
ture dynamic, cleaning contamination from hard-surface materials, and
carefully discarding contaminated porous materials were suggested for deal-
ing with existing problems. For the first time, respirators were proposed for
workers performing remediation. No recommendations for containment
were included.
In 1989, the Bioaerosols Committee of the American Conference of
Governmental Industrial Hygienists (ACGIH) released Guidelines for the
Assessment of Bioaerosols in the Indoor Environment (ACGIH, 1989).
Those guidelines included recommendations for the design and operation
of buildings and equipment and remediation of contaminated materials.
Cleaning with detergent and high-efficiency particulate air (HEPA) vacu-
uming were suggested for removing biologic contamination, and cautious
use of biocides was suggested for disinfection. For containment, the guide-
lines recommended that air-handling equipment be turned off during reme-
diation. The 1992 booklet Repairing Your Flooded Home published by the
American Red Cross and the Federal Emergency Management Agency pro-
vided guidance for drying, cleaning, and rebuilding a flood-damaged home
but did not specifically address mold growth or exposure to dampness-
related contaminants (ARC and FEMA, 1992). And in 1993, the Canadian
Mortgage and Housing Corporation published a mold-cleanup guide for
homeowners (CMHC, 1993). It recommended water and bleach cleanup,
discarding some materials and using a hypochlorite-based sanitizer. Respi-
rators and gloves were recommended during cleanup. Containment was not
discussed.
While the issue was receiving more attention in both the federal and
private sectors, the late 1980s also saw an increase in attention from re-
searchers. A 1989 study discussed containment during the remediation of
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PREVENTION AND REMEDIATION 273
fungal contamination in buildings (Light et al., 1989). Containment con-
sisted of turning off heating, ventilating, and air-conditioning (HVAC)
equipment, excluding occupants from the work area, and identifying criti-
cal leakage sites and sealing them with plastic film. Contaminated materials
were either to be cleaned with HEPA vacuuming, washed with a detergent
disinfectant solution, or discarded. Worker protection was not mentioned.
Criteria for assessing whether the remediation effort was successful--called
"clearance" criteria in many guidance documents--were also discussed.
In 1992, an American Society of Heating, Refrigerating and Air-Condi-
tioning Engineers (ASHRAE) conference paper used a series of case studies
to outline guidelines for occupant and worker protection during fungal
remediation (Morey, 1992). These greatly increased the attention and detail
devoted to this aspect of remediation. For a case with a high potential for
dispersing spores, isolating work areas by using barriers over air leaks and
HVAC openings was recommended, as was paying attention to possible
bypass of leaks through ceiling and floor plenums (enclosed spaces in which
air pressure is higher than outside). Airlocks and clean rooms were recom-
mended at entries to prevent contaminant transport from the work area
during entry and exit. HEPA-filtered exhaust was advised as a means to
maintain the work area at a pressure 0.02 in. of water column (WC) lower
than surrounding spaces. The ASHRAE paper recommended that refuse be
double-bagged before removal from the work area and that HEPA vacuum-
ing be used for cleaning. The adequacy of containment was to be docu-
mented by monitoring air-pressure relationships and collecting bioaerosol
samples from occupied spaces. Air samples were to be used to document
clearance after remediation activities but before containment barriers were
removed.
In 1993, the New York City Department of Health (NYCDOH) con-
vened a panel of experts to develop guidance for the assessment and reme-
diation of Stachybotrys atra (chartarum) (NYCDOH, 1993). The resulting
document included a systematic set of steps to be undertaken for investiga-
tion, including evaluation of medical issues, visual inspection, sampling,
and interpretation. The second half of the document provided guidance for
containment, worker protection, and training requirements for abatement
personnel. Four levels of contamination were described, and identifying
and eliminating the moisture source supporting mold growth was required
for all four levels. Level I was for areas with less than 2 ft2 of contaminated
material, Level II for areas with 230 ft2, Level III for areas with over 30 ft2,
and Level IV for the remediation of contaminated HVAC equipment. Lev-
els I and II required respiratory protection for building-maintenance per-
sonnel with very little containment or clearance testing. Levels III and IV
required full containment, including air-pressure management, isolation of
HVAC equipment, and dermal and respiratory protection for workers. Air
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274 DAMP INDOOR SPACES AND HEALTH
sampling was required to document containment and to provide a basis for
reoccupancy.
Since the 1993 NYCDOH document was produced, a number of other
guidance documents have been written, including
· Fungal Contamination in Buildings: A Guide to Recognition and
Management (Health Canada, 1995).
· Control of Moisture Problems Affecting Biological Indoor Air Qual-
ity (Flannigan and Morey, 1996).
· Bioaerosols: Assessment and Control (ACGIH, 1999).
· Guidelines on Assessment and Remediation of Fungi in Indoor Envi-
ronments (NYCDOH, 2000).
· Mold Remediation in Schools and Commercial Buildings (U.S. EPA,
2001).
· Report of the Microbial Growth Task Force (AIHA, 2001).
Table 6-1 compares those guidelines with regard to how they were
developed, events that would trigger a fungal assessment or remediation,
assessment methods, remediation activities, and prevention actions.1
The seven documents were each developed by a group of people with
identified expertise in building and engineering issues, mycology, and occu-
pant health assessment. Topics are not uniformly covered by the docu-
ments--for example, the ACGIH document provides extensive coverage of
health effects, health assessment, and sampling, but some of the other
documents do not provide information on these subjects.
The documents agree that
· Mold should not be allowed to colonize materials and furnishings in
buildings.
· The underlying moisture condition supporting mold growth should
be identified and eliminated. Only the International Society of Indoor Air
Quality and Climate (ISIAQ) and ACGIH guidelines discuss moisture dy-
namics, identifying problematic moisture or remediating moisture prob-
lems. The Environmental Protection Agency (EPA) guidelines contain spe-
cific recommendations for a variety of water-damaged materials.
· The best way to remediate problematic mold growth is to remove it
1After this report was completed, the Institute of Inspection, Cleaning, and Restoration
Certification published IICRC S520: Standard and Reference Guide for Professional Reme-
diation (IICRC, 2003). This document, which was not reviewed by the committee, also ad-
dresses fungal assessment and remediation, and clearance criteria.
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PREVENTION AND REMEDIATION 275
from materials that can be effectively cleaned and to discard materials that
cannot be cleaned or are physically damaged beyond use. Managing mold
growth in place is not considered by any of the documents.
· Occupants and workers must be protected from dampness-related
contaminants during remediation. All the guidelines agree that some mold
situations present a small enough exposure potential that cleanup does not
require specific containment or worker protection but that other situations
warrant full containment, air-pressure management, and full worker pro-
tection. Situations between those extremes need intermediate levels of care.
Guidance for selecting appropriate containment and worker protection for
different situations lacks clarity within and between documents.
· HVAC systems are special cases. But the documents disagree on how
to respond to contamination in HVAC systems.
The documents are divided on the use of disinfectants. Four recom-
mend that disinfectants be used sparingly, in appropriate locations, for
specific purposes, and with caution. The original NYCDOH guidance re-
quires the use of biocides, whereas ISIAQ suggests it for hard surfaces. Only
two of the documents--those of ISIAQ and ACGIH--discuss the preven-
tion of mold growth in buildings to any substantial degree.
The American Industrial Hygiene Association (AIHA) document differs
from the others in several respects. It identifies itself as supplementary to
other guidance, and it is the only document that specifically reviews other
guidelines, identifying common ground, disagreements, strengths and weak-
nesses in the evidence, and gaps in knowledge. It also offers recommenda-
tions for best practices. The AIHA document focuses on 11 questions:
1. When should microbial growth found in occupied buildings be
remediated?
2. What amounts of mold should indicate what degrees of remediation?
3. What remediation methods should be used?
4. Should biocides be used in remediation?
5. Under what circumstances should buildings be evacuated and work
areas isolated?
6. How should remediation work areas be isolated?
7. How should water-damaged items be treated?
8. What quality-assurance principles should be followed to ensure that
mold remediation is successful?
9. What personal protective equipment is recommended during
remediation?
10. Is personal air sampling appropriate to determine worker expo-
sure during mold remediation?
11. What medical evaluation is recommended for remediators?
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276 DAMP INDOOR SPACES AND HEALTH
TABLE 6-1 Comparison of Seven Mold-Remediation Guidance
Documents
Flannigan and
NYCDOH, Health Canada, Morey, 1996
1993 1995 (ISIAQ)
General Guidance specific Fairly In addition to
to Stachybotrys comprehensive remediation
atra; earliest best- discussions with guidance, problem
practice cohesive logic tree moisture sources
remediation for assessment and and indoor fungal
document to give remediation of ecology receive
guidance on indoor microbial substantial
selecting contamination treatment
containment and
worker protection
Process Summary of Sections written by Written by
recommendations members of members of Task
from expert panel federal-provincial Group 1,
working group after International
literature review Society of Indoor
Air Quality and
Climate
ASSESSMENT
Triggering events Visible mold, Not specifically Not specifically
water damage, identified but by identified, but by
symptoms implication visible implication
consistent with mold growth, observation of
exposure accumulations of sampling that
bird droppings, or confirms
evidence of fungal colonization by
growth from mold, mites, or
sampling bacteria
Health assessment Conditional; brief Conditional/ No specific
discussion extensive coverage discussion of
assessment
included
Visual inspection Required; identify Required; extensive
and building extent of mold coverage
history growth and water
damage
Intrusive Not discussed Conditional;
inspection cautions on
disturbance
Fungal Bulk sampling to Conditional;
sampling document S. atra; coverage for many
air, not routinely methods
unless HVAC
contaminated
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PREVENTION AND REMEDIATION 277
ACGIH, 1999 NYCDOH, 2000 U.S. EPA, 2001 AIHA, 2001
Most extensive Expands original Primarily schools and Reviews existing
discussions of scope from single commercial buildings; guidance, basis for
health effects, species to molds in has specific section on recommendations,
sampling strategies, general; provides planning remediation information gaps,
and data analysis detailed guidance and specific remediation and recommenda-
on assessments, methods for different tions for 11 key
containment, and materials issues
worker protection
Written by Based on literature Prepared by Indoor Review of existing
members of review and Environments Division guidance by
Bioaerosols comments from of EPA; internal and Microbial Growth
Committee of expert review panel external review process Task Force of
ACGIH AIHA; minority
report included
Visible fungal Presence of mold, Not specifically Consensus of
growth identified water damage, or identified, but by published guidance:
in remediation musty odors implication visible visible mold growth
section; other identified in mold growth and moisture
sections give assessment section damage; hidden
insight into medical growth may be
and environmental important but may
sampling not be immediately
obvious
Conditional; Conditional; brief Conditional; brief Not covered
extensive coverage discussion reference
Required; extensive Required; brief Assumed; brief Not specifically
coverage discussion reference covered but implicit
in many sections
Brief discussion; Brief reference Discussion of hidden Includes appendix
cautions on mold; caution on on making holes;
disturbance disturbance cautions on spore
release
Conditional; Conditional; part of Conditional; part of Discusses dust
extensive coverage medical evaluation, medical evaluation, sampling and cavity
for many methods suspect HVAC suspect hidden mold, sampling; other
contamination, litigation methods extensively
suspect hidden mold discussed in AIHA,
1996
(continued on next page)
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278 DAMP INDOOR SPACES AND HEALTH
TABLE 6-1 continued
Flannigan and
NYCDOH, Health Canada, Morey, 1996
1993 1995 (ISIAQ)
Interpretation Bulk for presence Coverage for many
of S. atra; air, methods
differential
Analysis Screen Not covered
laboratories
for experience
with indoor
environmental
mycology
REMEDIATION
Moisture problem identify; intervene identify; intervene identify; intervene
Area 1 <2 ft 2 <3.23 ft2 (0.3 m 2) <2.15 ft2 (0.2 m 2)
Containment Special Clean material Carefully remove
containment not before removal materials
needed; bag
refuse
Worker Full respiratory Mask and gloves No specific
protection protection; guidance
29 CFR 1910.134
Training Building Trained personnel No specific
maintenance with guidance
some mold-
cleanup training
Area 2 230 ft2 3.2332 ft2 2.132.3 ft 2
(0.33.0 m 2) (0.23.0 m 2)
Containment Bag refuse; cover Clean before Bag refuse; local
adjoining surfaces removal containment;
with poly HEPA-filtered
exhaust air
Worker Full respiratory Half-face Proper respiratory
protection protection; respirators and protection
29 CFR 191O.134 gloves
Training Building Trained personnel Building-
maintenance with maintenance
some mold- personnel
cleanup training
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PREVENTION AND REMEDIATION 279
ACGIH, 1999 NYCDOH, 2000 U.S. EPA, 2001 AIHA, 2001
Extensive coverage Species ID for Use trained Dust sampling and
for many methods medical; differential professionals; cautions cavity sampling
for hidden mold on uncertainty
EMLAP accredited
laboratories,
interpretation by
experienced
professional
identify; intervene identify; intervene identify; intervene identify; intervene
Minimal 10 ft2 <10 ft2 Recommends:
Source Vacate work area; None required, use containment based
dust suppression, no professional judgment on combining
special containment, innovative
bag refuse, damp professional
wipe area judgment with
N95 mask and N95 mask, gloves, N95 mask, gloves, and areas defined by
gloves and eye; eye; use professional NYCDOH (2000);
29 CFR 1910.134 judgment worker protection
Building Not covered based on ACGIH
maintenance with recommendations;
some mold-cleanup health evaluation of
training workers advised by
NYCDOH (2000)
recommended
Moderate 1030 ft2 10100 ft 2
Local; HEPA- Vacate and cover Poly sheeting around
filtered exhaust work area with poly; area; HEPA-filtered
air dust suppression; exhaust air; block
bag refuse; HEPA- HVAC
vacuum and damp-
wipe area
N95 mask, full- N95 mask, gloves, N95 mask or half-face
body covering and eye; HEPA coverall, eye
and eye 29 CFR 1910.134
Building Not covered
maintenance with
some mold-cleanup
training
(continued on next page)
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280 DAMP INDOOR SPACES AND HEALTH
TABLE 6-1 continued
Flannigan and
NYCDOH, Health Canada, Morey, 1996
1993 1995 (ISIAQ)
Area 3 >30 ft2 >108 ft 2; area >32 ft2
between 32 and
108 ft2 does not
seem to be directly
addressed
Containment Full; HEPA- Full; HEPA-filtered Full; HEPA-
filtered exhaust exhaust air; critical filtered exhaust
air; critical barriers; airlocks; air; critical
barriers, airlocks; HVAC barriers; air locks;
HVAC HVAC
Worker Full-face HEPA, Full-face HEPA, Full-face HEPA,
protection coverall, and eye coverall, and eye coverall, and eye
implied but not
specified
Training Hazardous waste Trained personnel Hazardous waste
Area 4 NA NA NA
Containment
Worker
protection
Training
HVAC
Containment Full; HEPA- Unclear Depends on area
filtered exhaust as above
air; critical
barriers; airlocks;
HVAC
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300 DAMP INDOOR SPACES AND HEALTH
should be fixed and materials in the building should be dry, no methods for
establishing whether materials are dry are offered. Remediation failures due
to regrowth of mold frequently occur, and this is of particular concern and
needs to be addressed in future research. Regrowth often occurs because a
faulty moisture dynamic was not mended or because a damaged area was
reassembled before materials were completely dry; for example, the surface
of porous materials, such as wood and concrete, may be dry while the
interior remains damp.
"Clean" in the context of a clearance inspection means that the remed-
iated area is free of residual microbial contamination. However, it is pos-
sible to ascertain that only if all potentially contaminated visible and hidden
spaces have been inspected. All spaces would have to be subjected to close
inspection for dust, debris, fungal contamination, and dampness. Only in
this unusual case could thorough examinations and measurements be easily
made. The greater the chance of hidden dampness or contamination, the
more difficult it is to determine whether a remediation can be defined as
successful by this criterion.
Even when visible contamination has been removed, air or surface
measurements might detect mold or bacteria because fungal and other mi-
crobial material is ubiquitous. Their presence alone thus does not indicate a
contamination problem, so it is difficult to set quantitative standards for
evaluating when and whether a space is clean.
There is no agreement on requirements for, methods of, or interpreta-
tion of microbiologic sampling for clearance purposes. One could under-
take a sampling campaign after the completion of remediation identical
with that before the remediation and document whether there was a
decrease in microbial contamination as a result of the remediation. Such a
decrease in concentrations and microbial diversity to those of a reference
building has been reported in some studies (Meklin et al., 2002). How-
ever, as discussed in Chapter 3, sampling may present an incomplete
picture.
A small number of studies report decreases in symptoms experienced
by occupants after remediation of moisture damage. The Savilahti et al.
(2000) and Meklin et al. (2002) studies took place in Finnish schools, and
both used questionnaires before and after renovation in combination with
fungal sampling. In the Meklin et al. study, a comparison was made with a
control building. A third study (Jarvis and Morey, 2001) looked at a new
building in a hot, humid climate. Biologic sampling and questionnaires
were used before and after remediation. The study found that the occur-
rence of illness was reduced after remediation was completed.
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PREVENTION AND REMEDIATION 301
Reassemble the Space to Prevent or Limit the Possibility of Recurrence by
Controlling Sources of Moisture and Nutrients
When portions of the building are reassembled after remediation, they
must be modified so that the chance of recurring moisture damage and
fungal growth is reduced. That may require
· Adding rainwater drainage elements.
· Back-venting for cladding.
· Elimination of intentional or unintentional water-vapor retarders.
· Air sealing and changes in air-handling equipment or operation to
manage air-pressure relationships.
· Improvements in the dehumidification unit of the air-conditioning
equipment.
· Removal of humidification equipment or controls of humidification
or process-water systems.
· Replacement of materials that offer superior nutrient and substrate
for fungal growth with materials that are resistant to microbial growth
(ceramics, concrete products, stainless steel, and the like).
· Encapsulation of surfaces that have been dried and substantially
decontaminated but cannot be completely decontaminated (for example,
between floor joists and subfloors).
There is very little guidance for planning, installing, and determining
acceptability of the renovation in the guidance documents. The ISIAQ and
ACGIH documents provide the best discussion of these issues, but they are
limited in scope.
EFFECTS OF AIR AND SURFACE CLEANING AND VENTILATION
Ventilation, air cleaning, and surface cleaning can influence exposure.
Airborne spores can be removed from a building with the out-going venti-
lation airflow or trapped in a particle filter and thus removed from the air.
Spores can also be removed from surfaces by washing or vacuuming.
Model predictions indicate that normal variations in house ventila-
tion rates when windows are closed will have only a moderate influence
on indoor airborne concentrations of fungal spores 210 µm in aerody-
namic diameter (IOM, 2000; Chapter 10). For example, an increase of a
factor of 8 in the ventilation rate from 0.25 to 2 air changes per hour
would be expected to reduce airborne concentrations of 5-µm-diameter
spores by 60%. The decrease in concentration of 2-µm spores would be
larger (~70%); the decrease in 10 µm spores smaller (40%). In most
buildings, the practical increase in ventilation rates would be considerably
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302 DAMP INDOOR SPACES AND HEALTH
smaller than a factor of eight, with correspondingly smaller decreases in
airborne spore concentrations.
When air enters a building through small cracks and holes, only a
fraction (characterized by the penetration factor) of the particles will pen-
etrate to the indoor air, and the remainder will deposit on the surfaces of
the leaks. Considerable data indicate that the penetration factor for PM 2.5
(particle matter less than 2.5 µm) is close to 1.0 (Thatcher et al., 2001).
However, the penetration factor for particles of 210 µm in air leaking into
buildings is not well understood and varies with the size of holes through
which the air leaks. In studies of particle penetration through simulated
0.5-mm-wide cracks, the penetration factor was less than 0.1 (Mosley et al.,
2001). Particle penetration factors for the cracks in commercial windows
were 0.61.0 for 5-µm particles and 0.60.8 for 8-µm particles (Liu and
Nazaroff, 2002). Thus, the natural particle losses that occur during air
infiltration provide a substantial but still uncertain amount of protection
from outdoor fungal spores.
Opening windows can cause large increases in ventilation rates, de-
pending on the weather and how often and how long the windows remain
open. That ventilation will reduce exposures to indoor-generated spores.
However, large increases in indoor concentrations of spores from the out-
doors may occur. The rate of flow of spore-laden outdoor air into a house
will increase dramatically with open windows, and few spores will be lost
by deposition on surfaces (such as window sills) as the air passes through a
window.
Predicted reductions in indoor airborne concentrations of spore-size
particles by filtering were discussed in the 2000 Institute of Medicine report
Clearing the Air. Reductions in spore concentrations by recirculation of air
through filters in household furnace and air-conditioning systems--includ-
ing filters with a much better efficiency than the common see-through
furnace filter--will normally be less than 50% for 5-µm-diameter spores.
Portable fan filter units can reduce spore concentrations more, but only
with high rates of airflow through the filtration unit (10 room volumes per
hour). Few measurement data are available for evaluating those model
predictions. It seems likely, however, that normal variations in ventilation
rates and filtration in buildings with closed windows will have a moderate
effect on inhalation exposure to mold spores.
Surface cleaning, such as vacuuming, can remove spores, potentially
preventing their resuspension and inhalation and reducing the probability of
exposure dermal contact and incidental ingestion. A number of studies have
been performed on surface cleaning to evaluate the reduction in total dust or
lead on surfaces, fewer on the removal of dust-mite allergens, and fewer still
on the removal of fungal matter. However, some data imply, but do not
clearly demonstrate, that improved surface cleaning could reduce exposure to
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PREVENTION AND REMEDIATION 303
fungi. Cole et al. (1996) found that concentrations of fungi and bacteria in air
correlate with concentrations of fungi and bacteria on indoor nonfloor sur-
faces (r = 0.6 for fungi) and correlate with concentrations on floor surfaces
(no statistic provided). Intervention studies have demonstrated that improved
surface cleaning can reduce the loading of uncharacterized dust, lead, and
mite allergen on surfaces. Reductions of 8090% in dust, lead, and mite
allergen on surfaces were achieved by Roberts et al. (1999) after vacuuming
carpets for 645 min/m2 of carpet surface. Kildesų et al. (1998) compared
nine cleaning practices and found that the quantity of dust remaining on floor
surfaces where people walked varied by a factor of 2. In a cross-sectional
study of schools that improved cleaning practices for floors, classrooms
cleaned primarily with wet mopping had more airborne viable bacteria but
less settled dust than classrooms cleaned primarily with dry methods (Smedje
and Norbäck, 2001). Franke et al. (1994) reported a substantial reduction in
fungal spores on surfaces after a period of deep cleaning; however, the reduc-
tion was temporary, and the benefits of the cleaning were not easily distin-
guishable from natural variation.
A few studies have also found that surface cleaning practices or fre-
quency can influence airborne concentrations of particles or microorgan-
isms. In a conference paper, Skyberg et al. (1999) described a study com-
paring 49 offices that received improved cleaning with 55 control offices
that received superficial cleaning. The concentration of inhalable dust de-
creased by about one-third in the intervention offices and increased slightly
in control offices (significance level not reported). In another conference
paper, White and Dingle (2002) found that airborne PM 2.5 and PM 10
concentrations were decreased by about 50% (p < 0.01) after 14 weeks of
intensive5 vacuum cleaning of 19 houses, but airborne particle concentra-
tions were not significantly changed in 17 control houses. Kemp et al.
(1998) reported an 85% reduction (p < 0.04) in respirable suspended par-
ticles on two floors of an office building after improved surface cleaning
(9% reduction on control floors) but initial particle concentrations were
unusually high. In a cross-sectional study of classrooms, Smedje and
Norbäck (2001) found that cleaning practices were associated with concen-
trations of airborne viable bacteria (p = 0.013 in a multivariate regression);
however, no association of cleaning practices with airborne fungal concen-
trations was reported.
Finally, a few studies (Kemp et al., 1998; Skyberg et al., 1999; Wålinder
et al., 1999) have reported significant improvements in subjective or objec-
tive health measures with improved surface cleaning or lower concentra-
5Carpets were cleaned every 2 weeks for 4 min/m2 in the first cleaning, 2 min/m2 in the
second cleaning, and 1 min/m2 in five additional cleanings. Upholstered sofas and beds were
cleaned every 2 weeks for 1 min/m2.
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304 DAMP INDOOR SPACES AND HEALTH
tions of dust on surfaces, which is indirect evidence of reductions in expo-
sure to unidentified agents.
In summary, the normal variations in ventilation rates, air-filtration
rates, and surface-cleaning practices of homes may under some circum-
stances substantially affect exposure to fungal spores and other dampness-
related microbial bioaerosols. Improved surface cleaning appears to have
the largest and most practical potential for bringing about large reduc-
tions in exposure; however, further research is needed to characterize its
effectiveness.
FINDINGS, RECOMMENDATIONS, AND RESEARCH NEEDS
On the basis of its review of the papers, reports, and other information
presented in this chapter, the committee has reached the following findings
and recommendations and has identified the following research needs re-
garding the prevention of moisture problems and the remediation of build-
ings that have water damage or microbial contamination.
Findings
· The most effective way to manage a biological agent, such as mold,
in a building is to eliminate or limit the conditions that foster its establish-
ment and growth.
· There are several sources of guidance on how to respond to various
indoor microbial contamination situations. However, determining when a
remediation effort is warranted or when it is successful is necessarily subjec-
tive because there are no generally accepted health-based standards for
acceptable concentrations of fungal spores, hyphae, or metabolites in the
air or on surfaces.
· Remediation must identify and eliminate the underlying cause of
dampness or water accumulation. If the underlying causes are not ad-
dressed, contamination may recur.
· Valuable information can be acquired from architects, builders, oc-
cupants, and maintenance staffs regarding health complaints, the use his-
tory of the building, moisture events, and locations of problems. Both
expert assessment of the building's condition and knowledge of its history
and current problems are needed to make a thorough evaluation of poten-
tial dampness-related exposures and an effective plan for remediation.
· Fungal and other microbial material is present on nearly all indoor
surfaces. There is a great deal of uncertainty and variability in samples
taken from indoor air and surfaces, and it may be difficult to discern which
organisms are part of the natural background and which are the result of
problematic contamination. However, the information gained from a care-
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PREVENTION AND REMEDIATION 305
ful and complete survey may aid in the evaluation of contamination sources
and remediation needs.
· The potential for exposure to microbial contaminants in spaces such
as attics, crawl spaces, exterior sheathing, and garages is poorly under-
stood.
· Disturbance of contaminated material during remediation activities
can release microbial particles and result in contamination of clean areas
and exposure of occupants and remediation workers.
· Containment has been shown to prevent the spread of molds, bacte-
ria, and related microbial particles to noncontaminated parts of a contami-
nated building. The amount of containment and worker personal protec-
tion and the determination of whether occupant evacuation is appropriate
depend on the magnitude of contamination.
· Very few controlled studies have been conducted on the effectiveness
of remediation actions in eliminating problematic microbial contamination
in the short and long term and on the effect of remediation actions on the
health of building occupants.
· Available literature addresses the management of microbial con-
tamination when remediation is technically and economically feasible. There
is no literature addressing situations where intervening in the moisture
dynamic or cleaning or removing contaminated materials is not practicable.
Recommendations
· Homes and other buildings should be designed, operated, and main-
tained to prevent water intrusion and excessive moisture accumulation
when possible. When water intrusion or moisture accumulation is discov-
ered, the sources should be identified and eliminated as soon as practicable
to reduce the possibility of problematic microbial growth and building-
material degradation.
· When microbial contamination is found, it should be eliminated by
means that limit the possibility of recurrence and limit exposure of occu-
pants and persons conducting the remediation.
Research Needs
· Research is needed to characterize
-- The effectiveness of remediation assessment and remediation meth-
ods in different contamination circumstances.
-- The dynamics of movements of contaminants from colonies of
mold and other microorganisms in spaces such as attics, crawl spaces,
exterior sheathing, and garages.
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306 DAMP INDOOR SPACES AND HEALTH
-- The effectiveness of various means of protection of workers and
occupants during remediation activities
· Research should be performed to develop
-- Methods for finding microbial contamination in HVAC systems,
and in crawl spaces, attics, wall cavities, and other hidden or seldom-
accessed areas.
-- Building materials that, when moist, are less prone to microbial
contamination.
-- Standard methods of assessing the potential of new materials,
designs, and construction practices for dampness problems.
-- Standardized, effective protocols for cleaning up after flood-
ing and other catastrophic water events that will minimize microbial
growth.
-- Methods that can distinguish between naturally-deposited spores
and active microbial growth in wall cavities.
· Research should be performed to determine
-- How free of microbial contamination a surface or building mate-
rial must be to eliminate problematic exposure of occupants (in particular,
how concentrations of microbial contamination left after remediation are
related to those found on ordinary surfaces and materials in buildings
where no problematic contamination is present).
-- Whether and when microbial contamination that is not visible
to the naked eye but is detectable through screening methods should be
remediated.
-- The risk of microbial contamination in the building but outside
the general air circulation of the building--in crawl spaces, attics, wall
cavities, building sheathing, and the like.
-- The effectiveness of managing contamination in place by using
negative air pressure, encapsulation, and other means of isolation.
-- The best ways to address microbial contamination in situations
where remediation is not technically or economically feasible.
-- The best ways to open a wall or other building cavity to seek
hidden contamination while controlling the release of spores, microbial
fragments, and the like.
-- How to measure the effectiveness and health effects of a remedia-
tion effort.
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