Contamination Guidelines: Interpreting the Analysis
Nathanson, P. Eng.
Manager, Indoor Air Quality
PWGSC - Public Works &
Government Services - Canada
such as fungi, bacteria, viruses and pollen, are natural and ubiquitous
components of the outdoor and indoor environment. Fungi, often called
"mould", or "mildew", originate on plants, leaves and in soil. Yeasts
are also fungi. Over 100,000 species of fungi are known to exist and
many have yet to be classified; most produce spores that are designed to
be transported through the air.
evaluation of indoor air started in the late 1950s when secondary [nosocomial]
infections of patients were reported. Later, an industrial case of
exposure to airborne contaminated cutting fluids [Pontiac fever] and
cases of exposure to contaminated cooling towers [legionellosis,1976]
and humidifiers [humidifier fever] were documented. In Canada, microbial
contamination affects approximately 20% of buildings with indoor air
quality problems (8). The first measured case occurred in 1986.
should not grow in indoor environments. However, spores will germinate
anywhere where both moisture and nutrients exist. Therefore, strategies
to prevent microbial growth must include the avoidance of wet surfaces,
keeping relative humidity levels below 70%, effective filtration of
particulates, proper HVAC system operation and maintenance, and good
and leaks do occur in buildings and established procedures should be
followed to avoid contamination. When areas do become contaminated,
often the mould is not visible and odours may be absent. Release of
spores can take place months after water has disappeared. Air sampling
is undertaken in order to characterize the extent of the problem and to
establish a remediation plan.
Microbials can be measured by a variety of methods; bulk samples,
surface samples using a swab or tape, and air-borne samples using a
pump. The samples can be inspected microscopically or can be cultured on
a nutrient medium, or agar. The identification and numeration of species
should be done by an accredited laboratory. The Canadian federal
protocol uses a Reuter centrifugal sampler [RCS], Rose-Bengal agar, and
a 4-minute sampling time to measure viable air-borne microbials. A spore
trap is used to assess non-viable quantities. Swab samples are taken to
locate the source of contamination.
Interpretation of Results
no regulated exposure thresholds or standards for micro-organisms;
several reasons for this will be examined in the following section.
Using data collected since 1986 by PWGSC [over 3,000 samples in hundreds
of buildings], the Federal-Provincial Advisory Committee on
Environmental and Occupational Health in 1993 (1), and 1995 (1) (2),
published interpretation guidelines for microbial measurements in
building environments. Other cognizant authorities such as the World
Health Organization, The American Industrial Hygiene Association [AIHA,
1996] (3), and the American Conference of Governmental Industrial
Hygienists [ACGIH, 1999] (4), have referenced these Canadian guidelines.
basic, common-sense approach to interpretation is as follows;
Microbial growth within a building is not acceptable. Moisture
intrusion, visible mouldy, wet, or soiled surfaces must be
remediated following an established protocol. Good HVAC system
design, operation, and maintenance practices should follow current
standards to avoid microbial amplification.
Fungal quantities, measured as colony-forming-units per cubic meter
of air [CFU/m3], should be lower inside compared to outside, and the
"mix" [biodiversity] should be similar. Quantities of normal outdoor
[phylloplane] species greater than 500 CFU/m3 indoors, indicates
poor filtration or housekeeping. Dominance indoors by species of
mould that are not predominant outdoors indicates an interior
amplification site. This must be located and rectified. If no
contaminated site or moisture source is found, then "normal"
remediation is recommended; all hard surfaces wiped with a cleaning
solution, all fleecy surfaces vacuumed with a HEPA filtered unit.
The area should be re-sampled in 3 months.
confirmed presence of a toxigenic fungi [as defined in (5)],
indicates that further investigation is necessary. Visual
inspection, use of a moisture meter, and air/surface sampling is
usually done to locate the source. If none is found, normal
remediation is recommended, and the area should be re-sampled in 3
Health Canada's protocol for mould recognition and management (2),
follows the following phases; assess the magnitude of the health
problems, identify problems in the building environment,
identification of indoor fungal amplifiers, risk communication, and
remedial action. All cases lead towards remediation. New York City
guidelines (6) state, "Except in cases of widespread fungal
contamination that are linked to illnesses throughout a building,
building-wide evacuation is not indicated".
guidelines apply to bacterial samples. Bird and bat droppings must be
assumed to contain pathogenic fungi and must be removed under hazardous
no mandatory numerical limits for fungal exposure in any country.
Several reasons for this are as follows;
not possible to collect all bio-organisms using a single sampling
method. The methods used to collect, culture and analyze samples
vary greatly. For example, settle plates will collect only large
microbials, and centrifugal samplers are also size selective and
will miss the larger spores. Microbials may be culturable,
nonculturable, and non-viable. Fungal and bacterial fragments can be
allergenic. Different agars will support the growth of different
fungal species, depending on the agar formulation and moisture
availability. Incubation time and temperature also favor selective
Collection methods do not reflect actual human exposure. Microbial
concentrations in air will vary by several orders of magnitude in
one location and between sites. Short "grab" samples [4 minutes for
the RCS] cannot represent real exposure values over a work period.
Information relating both viable and non-viable micro-organisms is
presently insufficient to establish dose-response relationships.
Very few epidemiological studies have been done. The issue is
further complicated be the secondary by-products that many microbial
species produce, such as mycotoxins, endotoxins, volatile organic
compounds, antigens, -1,3-glucan, etc., that may be more potent that
the microbial itself. These "indicator" measurements do not
accurately reflect total exposure.
is a wide variation in individual susceptibility to microbials and
various factors such as genetics, age, personal habits, health,
pre-existing conditions, medication, and previous exposure, will
affect people's reaction. Furthermore, building occupants are
exposed to a large variety of complex and variable chemical and
biological mixtures at work, outdoors and at home. Consequently,
exposure information is imprecise because agents, other than those
identified and measured, will also be present and may be responsible
for some of the health responses by exposed persons. Biological
markers of exposure to fungi are largely unknown.
prevention and control of microbials are requisite conditions needed to
maintain a healthy and comfortable workplace, remediation is necessary
if there is an internal source. Depending on the species type and level
of contamination, there are protocols established by Health Canada (2),
New York City Department of Health (6), the Canadian Construction
Association (10), and other authorities, (4) (7).
that all building occupants should be protected from microbial exposure
during testing and remedial action must be followed. In this regard, the
extent of contamination [size] is accounted for by the use of different
containment strategies, equipment and methods. Another important related
consideration is the isolation of the air distribution system from the
remediation area so that microbials are not transported to other zones.
following general remediation principles apply.
control is recognized as the primary factor in controlling microbial
growth. If porous materials such as fibreglass insulation, carpets,
ceiling tiles, and plaster do become contaminated, it is usual to
discard these materials. Hard surfaces can be salvaged using a detergent
or a 6-10% bleach solution and clean-water rinse. Biocides and
antimicrobial agents may be used to decontaminate selective areas such
as ducts, water reservoirs, and condensate pans. However, occupants must
not be exposed to any residual compound.
damage from leaks, floods and plumbing failures should be repaired and
remediated within 24 hours. Wet materials should be dried,
sewage-contaminated porous materials must be discarded. Water
penetration or migration through the building envelope, and condensation
within the interior or exterior wall assembly is to be avoided. A
moisture meter is useful in detecting non-accessible or hidden wet
areas. Do not over-humidify the building during the winter. Dehumidify
supply air in summer to 60% maximum during occupied periods and to 70%
system can be a source of microbial contamination; avoid water vapour
reintrainment from roof-top cooling towers and condensers, maintain good
filter performance [small systems at 30% efficiency, large systems at
85%]. Avoid stagnant water within the system and clean condensate pans
and other wet areas such as drift eliminators, reservoirs, floors, etc.,
monthly. Wet porous material is to be avoided. There should be no
moisture or water vapour in front of the fan as this will carry through
into the supply ducts. Insure access to all components for scheduled
maintenance and cleaning. Keep a log of all activities.
sampling is not an infallible means of determining the existence of
fungal contamination and any survey must rely on the skill and
experience of the investigator. Information from a large data set has
produced practical guidelines on how to interpret measurement results
and how to effectively remediate the situation.
information on microbial contamination [and other IAQ and environmental
issues] increases, research and co-operation between the various
disciplines; architecture, engineering, industrial hygiene, mycology,
and medicine will evolve to increase our understanding of the issues.
The multi-disciplinary aspect of microbial assessment and remediation
has been already demonstrated at the Third International Conference on
Fungi, Mycotoxins and Bioaerosols, at Saratoga Springs, NY, in 1998,
where over 300 participants, many of them medical doctors, presented an
extraordinary range of papers (9). Until the magnitude of the population
risk is known, it would be prudent, based on current evidence, to
remediate indoor sources of microbials.
Indoor Air Quality in Office Buildings: A Technical Guide, A report
of the Federal-Provincial Advisory Committee on Environmental and
Occupational Health, Health Canada, 1993, revised 1995.
Fungal Contamination in Public Buildings: A Guide to Recognition and
Management, Federal-Provincial Advisory Committee on Environmental
and Occupational Health, Health Canada, 1995.
Guide for the Determination of Biological Contaminants in
Environmental Samples, American Industrial Hygiene Association,
Fairfax, Virginia, 1996.
Bioaerosols Assessment and Control, American Conference of
Governmental Industrial Hygienists, Cincinnati, OH, 1999.
Significance of Fungi in Indoor Air: Report of a Working Group,
Health and Welfare Canada working Group on Fungi and Indoor Air,
Canadian Public Health Association, 1987.
Guidelines on Assessment and Remediation of Fungi in Indoor
Environments, New York City Department of Health, 2000.
Managing Water Infiltration into Buildings, University of Minnesota,
Environmental health and Safety, 1998.
Indoor Air Quality Building Investigations, 1987-1994, Summary
Report, T. Nathanson, PWGSC, 1995.
Bioaerosols, Fungi and Mycotoxins: Health Effects, Assessment,
Prevention and Control, edited by Eckart Johanning, Eastern New York
Occupational & Environmental Health Centre, Albany, New York, 1999.
Mould guidelines for the Canadian Construction
Industry, 82-2004, Canadian Construction Association,