Forensic Applications Consulting Technologies, Inc.
Is Testing for Moulds Necessary?
Caoimhín P. Connell
Forensic Industrial Hygienist
What do my samples really mean…?
1) Is sampling necessary?
2) What do the sample results mean?
3) Are my sample results high?
4) Are my sample results valid?
These are some of the common questions we receive from home owners and
facility managers regarding the results of mould (mold) testing. The short
answers are:
1) Almost never.
2) Probably nothing.
3) The results are probably uniterpretable.
4) Generally, “No.”
With the elevated public awareness and unfounded fear of indoor moulds has
come a new type of consultant, the “Mould Inspector.” Generally speaking,
these consultants are poorly versed in microbiology, mycology, the occurrence
of moulds, their assessment, and their significance. Based on our experience,
the credibility of the “certified mould inspector” is almost exclusively found in
the collection of “samples” and the production of “laboratory reports.” The
samples collected by most “mould inspectors” are unscientific, uninterpretable,
and largely meaningless, but which are often printed on impressive and official
“Laboratory Reports.” Such lab reports are usually replete with fancy Latin
names and apparently scientific notations. It is the possession of the
“Laboratory Report” that provides the credibility to the consultant – yet the true
credibility of the Laboratory Report rests exclusively within the consultant’s
data quality objectives (DQOs) – and the validity of the DQOs are incumbent
on the expertise of the consultant. A “Laboratory Report” has no intrinsic value
and the interpretation of the report can only occur in the context of the
inspector’s expertise, DQOs and hypothesis testing.
Most “certified mould inspector's” believe they are collecting a sample to
assess moulds in an house. However, the “mould inspector” usually fails to
meet the stated objectives in that the inspector fails to evaluate the building’s
fungal loading within any known degree of confidence, and usually relies on an
unscientific and unfounded comparison of indoor to outdoor spore
concentrations.
Many “mould inspectors” reference the US EPA document titled “Mold
Remediation in Schools and Commercial Buildings” (2001) and identify the
document as an applicable Industry Standard. Yet, in that document, the EPA
recommends against performing the very kind of sampling conducted by most
“mould inspectors”. In the referenced document, the EPA states:
Is sampling for mold needed? In most cases, if visible mold
growth is present, sampling is unnecessary.
The EPA warns:
Sampling for mold should be conducted by professionals with
specific experience in designing mold sampling protocols,
sampling methods, and interpretation of results.
In our experience, we have never encountered a mould inspector who has ever
designed or used any kind of legitimate protocol with valid DQOs. In the EPA
document the EPA states:
Sample analysis should follow analytical methods recommended
by the American Industrial Hygiene Association (AIHA), the
American Conference of Governmental Industrial Hygienists
(ACGIH), or other professional guidelines.
However, the ACGIH, states that the primary emphasis on indoor mould
assessments should rest with a thorough visual inspection of the property. 1
Last year, the AIHA 2 sponsored a publication titled “Recognition, Evaluation,
and Control of Indoor Mold” 3 (generally referred to as “The Green Book.”)
The Green Book is an hodge-podge of conflicting presentations from various
authors that presents both insightful, technically astute discussions alongside
technically inaccurate and unsupportable myths and misconceptions. However,
in the publication, the authors clearly state that a legitimate mold expert can
adequately identify a mould or contaminated building material by merely
looking at it.
Other professional guidelines, constituting industry standards, would include
the 2000 publication titled Guidelines on Assessment and Remediation of Fungi
in Indoor Environment (prepared by the New York City Department of Health,
Bureau of Environmental & Occupational Disease Epidemiology), and
considered by many industrial hygienists to represent a good practical
approach. In that publication, the NYC guidelines states:
A visual inspection is the most important initial step in identifying
a possible contamination problem.
Regarding air sampling, the NYC document specifically states:
Air sampling for fungi should not be part of a routine assessment.
This is because decisions about appropriate remediation
strategies can usually be made on the basis of a visual inspection.
The US Department of Health and Human Services, Centers for Disease
Control (CDC) Mold Work Group report, 4 Chapter 2 “ Assessing Exposure to
Mold” states (in part):
Sampling for mold is not part of a routine building assessment. In
most cases appropriate decisions concerning remediation and
need for personal protection equipment (PPE) can be made solely
on the basis of visual inspection. (sic)
The CDC document also recognizes the frivolity of the type of sampling
normally conducted by “mould inspectors” when it stated:
Other than in a controlled, limited, research setting, sampling for
biological agents in the environment cannot be meaningfully
interpreted and would not significantly affect relevant decisions
regarding remediation, reoccupancy, handling or disposal of
waste and debris, worker protection or safety, or public health.
In the EPA document referenced above, the EPA states:
Inadequate sample plans may generate misleading, confusing,
and useless results.
For someone without experience, sampling results will be difficult
to interpret. Experience in interpretation of results is essential.
Sampling should be done only after developing a sampling plan
that includes a confirmable theory regarding suspected mold
sources and routes of exposure. Figure out what you think is
happening and how to prove or disprove it before you sample!
This is known as “hypothesis testing” and the sampling plan is a statement of
“data quality objectives.”
SAMPLING DATA QUALITY OBJECTIVES
As a professional standard, an investigator performing any kind of sampling
should be capable of determining the errors and uncertainties associated with
their sampling and, pursuant to standard industry practice, place the reported
values in their proper perspective. This is the purpose of the “sampling plan”
mentioned by the EPA and also mentioned by the Centers for Disease Control
who stated: 5
If you do decide to pay for environmental sampling for molds,
before the work starts, you should ask the consultants who will do
the work to establish criteria for interpreting the test results. They
should tell you in advance what they will do or what
recommendations they will make based on the sampling results.
In our experience, we have never encountered a “mould inspector” that has
ever established a priori criteria used for the collection or interpretation of their
samples.
We frequently hear “mould inspectors” repeat the misconception that sampling
for moulds is new, and as such, there are no standards to be followed. This is
simply not true, since the concepts of sampling theory have been around for
decades and apply to all kinds of sampling and human exposure assessments. In
our corporate library, we still reference our original copy of William Wells'
1955 Airborne Contagion and Air Hygiene and the 1977 NIOSH Occupational
Exposure Sampling Strategy Manual, which clearly describe appropriate
sample collection considerations.
Pursuant to decades-old, fundamental industrial hygiene (IH) practices and
procedures, prior to the collection of any kind of sampling, the IH must
establish a priori DQOs 6, otherwise the validity of the data is at best
unreliable, and at worst, misleading. In our experience, all samples collected by
Home Inspectors and “certified mould inspectors” on mould related projects
were collected in the absence of DQOs, and therefore lack confidence, cannot
be interpreted by anyone and are largely meaningless and misleading. This is
not a disparaging remark about Home Inspectors. In our experience, Home
Inspectors who perform visual inspections for moulds are quite adequately
trained to provide sound advice on the subject matter, provided they are not
performing any kind of sampling. Also, in our experience, those Home
Inspectors who perform mould sampling and mould testing are the least
competent to perform mould consultation, and are often “certified” by a second
rate laboratory which merely pushes sampling to increase its own revenues.
The establishment of DQOs is the quality assurance, quality control (QA/QC)
part of a larger hypothesis testing or decision making process; the results of
sampling and analysis will either support or not support the hypothesis but only
in the context of the DQOs. This is part of the “sampling plan” mentioned by
the EPA.
The DQOs ensure, through their prescription, that tenable and statistically valid
results ensue. The DQOs ensure that a statistically sufficient number of samples
will be collected from statistically representative locations in an acceptable
manner by a validated method or method whose uncertainties are sufficiently
characterized. The DQOs further specify that the samples are submitted to a
laboratory capable of proficiently analyzing the samples to within a definable
uncertainty, using valid methods.
The parameters of the DQOs themselves are based on statistical confidence
needed to answer the a priori questions. The DQOs are what make laboratory
results meaningful (and tenable). Without DQOs, one does not have data on a
laboratory report; one has numbers and names on the laboratory report that
cannot be interpreted by anyone (especially the laboratory), since the
“numbers” have no intrinsic meaning outside of the context of the a priori
decision criteria.
Furthermore, contrary to good science and standard assessment protocols, most
“mould inspectors” leave the interpretation of their air sampling data to
personnel at the analyzing laboratory. In our experience, Laboratory personnel
never visit any of the subject properties from whence samples are collected,
and have no knowledge whatever of site conditions. Permitting a laboratory to
interpret one’s analytical results has never been an acceptable industrial
hygiene practice, and is almost exclusively used by consultants who lack the
technical competency to interpret their own samples. According to the US
Centers for Disease Control: 7
The results of samples taken in your unique situation cannot be
interpreted without physical inspection of the contaminated area
or without considering the building’s characteristics and the
factors that led to the present condition.
The DQO process is so entrenched in good environmental sampling that it is
the underpinning of all such sampling and is discussed in great detail in many
broad-spectrum environmental sampling protocols and Industrial Hygiene
sampling protocols. For example, one of the “bibles” of general environmental
sampling is the US EPA SW846 8 geared toward environmental sampling. The
sampling precepts and the QA/QC foundations are recognized as being
applicable to all kinds of sampling. The SW 846 describes DQOs thusly:
Data quality objectives (DQOs) for the data collection activity
describe the overall level of uncertainty that a decision-maker is
willing to accept in results derived from environmental data. This
uncertainty is used to specify the quality of the measurement data
required, usually in terms of objectives for precision, bias,
representativeness, comparability and completeness. The DQOs
should be defined prior to the initiation of the field and laboratory
work. The field and laboratory organizations performing the work
should be aware of the DQOs so that their personnel may make
informed decisions during the course of the project to attain those
DQOs.
Interpreting Data – PARCC Parameters
From an industrial hygiene perspective, the interpretation and reporting criteria
for airborne constituents, including moulds, are commonly referred to as
“PARCC” parameters: (precision, accuracy, representativeness, comparability,
completeness). At the end of the sampling and testing, the IH should be able to
answer each of the PARCC parameters.
Precision: How reproducible are measurements; has the variance been
characterized?
Axiom 1: All samples exhibit uncertainty.
Axiom 2: All analysis results exhibit uncertainty.
These statements are true regardless of the parameter being sampled or
analyzed. The precision of the data collected by “mould inspectors” is entirely
unknown because “mould inspectors” and Home Inspectors generally fail to
develop and/or follow a sampling plan that would determine the precision. It is
an established and industry accepted fact that particle migration is mainly
influenced by particle properties, ventilation conditions and airflow patterns. 9
Particle concentrations in general, 10 and spore concentrations in particular 11
within a structure exhibit extremely large spatial variations 12 which tend to be
compartmentalized within a given space.
This is to say that if an inspector were to lay out ten identical samplers within a
room, and collect ten identical samples at exactly the same time, they would
end up with ten completely different sample results; the spore counts would be
wildly different and even the types of organisms identified would be wildly
different. Yet, each sample came from the exact same room at the exact same
time!
Furthermore, the air samples collected by "mould inspectors” are exclusively
short-term samples (three to ten minutes in duration). It is a well established
and standard sampling precept that short term samples exhibit extremely large
temporal variations. 13
This is to say that if an inspector were to collect ten identical samples within
the same room, but at different times of the day (or year), they would end up
with ten completely different sample results; the spore counts would be wildly
different and even the types of organisms identified would be wildly different.
Yet, each sample came from the exact same room!
We can speak of the variability in terms of “deviation” which indicates the
amount of “spread” of results about an “average” concentration (actually a
“mean” concentration). Generally, the geometric standard deviation (GSD) of
interday and intraday airborne concentrations lie between 1.2 and 2.5 geometric
standard deviations. 14 These large variations are similar to those seen by other
authors, specific to airborne mould concentrations 15, 16, 17 some of whom have
reported even higher fungal variations in indoor air. 18
Classic industrial hygiene sampling strategy indicates that reasonable
confidence in estimating an average ambient airborne concentration is achieved
when at least 70% of the exposure time is measured, 19 and states that random
“grab samples” are the least desirable technique for estimating the average
exposure. 20 It is in fact “grab samples” that are exclusively collected and
reported by “mould inspectors” during their “mould surveys.” In our
experience, “mould inspectors” exclusively use single random grab sample
methods from selected areas (including outdoors). The total sampling time for
each grab sample is usually much less than 1% of the anticipated exposure time
for the exposed population (the home owner or building occupant). This error is
known as the “sampling design error,” and if uncharacterized produces huge
uncertainties in the reported results.
Although considered a “counsel of perfection,” a concept called “Shannon’s
Sampling Theorem” 21 estimates that the number of measurements needed to
achieve “perfect information” about airborne concentrations is roughly 250,000
measurements per cubic meter per hour. More practical foundational and
accepted classic industrial hygiene references22, 23 have estimated that for each
daily study period (usually expressed as any eight hour period for a work place
or 12 hours for a residential setting) between eight and eleven random grab
samples are needed from each study area (each room, crawlspace, outdoors,
etc.), to obtain adequate confidence in determining the variance associated with
the study area for that day. Without knowing the variance, one cannot know the
average concentration, and certainly one cannot know the average
concentration based on a couple of samples.
Some authors24 state that as many samples as necessary to determine the
distribution should be taken. As such, one sample (or indeed two or three)
collected from each study area, such as those collected and reported by Home
Inspectors or “certified mould inspectors” cannot provide adequate confidence
in estimating the spore concentration in a subject property.
It is a well established fact that spore counts of airborne fungal entities exhibit a
lognormal distribution throughout the day. 25 This means that the variation
between one or two samples can be huge and skewed in one direction. 26 As an
example, the following spore trap data are real data and are very typical and
from a Colorado home.
Air Monitoring Data
Time of Sample Spore Count
08:00 213
09:30 1,195
11:00 393
12:30 567
14:00 900
15:30 3,257
Table 1
Typical Distribution of Spores In a Colorado Home 27
In viewing this table, one may ask: “Which sample represents the spore
concentration for the home?” Answer: “They all do; they are all correct, and
none of them are contradictory.” So if mould testing personnel collected the
sample at 08:00, they would very likely have a different conclusion about this
home than if they collected the sample at 15:30. And yet, these are the same
variations expected to be present at all study locations. Samples collected
pursuant to proper DQOs will define the variance and determine the validity of
any one, or a set, of sample data. 28
It is for this reason, the airborne concentrations for a study area cannot be
adequately characterized by collecting just a few samples. Due to the temporal
and spatial lognormal distribution almost always seen in indoor and outdoor
spore concentrations, and the short sample time29 associated with sample
collection techniques, the single short-term samples collected in each study
area have a low probability of representing the actual airborne fungal loading in
that area, in the home in general or outdoors.
Remarkably, contrary to simple mathematics, most “mould inspectors” and
other poorly trained consultants attempt to derive the arithmetic mean from
their samples. An arithmetic mean would be appropriate if the data exhibited
Gaussian distribution. However, most “mould inspectors” never determine the
distribution, and there is no reason to believe that the distribution would be
Gaussian or anything other than lognormal. 30, 31 Even taking the mean of the log
transformed data would be a better representation of an “average,” 32 but would
still only approximate the median value and not the true “average.”
Summary of Precision
The air samples collected by “mould inspectors” are usually entirely unusable
since there is no confidence in the data based on precision.
Accuracy: Accuracy asks “How close is the reported value to the true value? ”
The lack of precision associated with reported data would shift the emphasis for
ensuring confidence toward accuracy. That is, in the absence of precision, one
may rely upon highly accurate data to aid in the interpretation of the data. Each
sampling method has only a limited inherent ability to enumerate specific types
of spores. The types of samplers used by most inspectors are spore traps (such
as the Air-O-Cell®cassette), and it’s collection efficiency is very well
established. 33
Each sampler has a specific and known physical limitation known as the “cut-
size.” The “cut-size” is the aerodynamic diameter, in micrometers of a
theoretical spherical particle of unit density that has a 50% chance of being
captured and is designated “d50.”
Generally, at the recommended flow rate of 15 liter of air per minute, at normal
temperature and pressure, the d50 for the Air-O-Cell® cassette is reported as 2.5
µm. 34 This means that a mould spore whose diameter is approximately 2.5 µm
has only a 50% chance of being captured. Most of the fungal conidia found in
indoor environments are at or near this aerodynamic diameter; therefore,
immediately, the accuracy of the results must have error statements wherein the
confidence of the result lies within one half to twice the reported values. This is
not a flaw with the sampling devices, but rather places additional emphasis on
the expertise of the consultant to understand what the limitation means, and
design DQOs that will take the cut-off values into consideration.
Having said this, often then samples were not collected under standard
conditions, since in many situations, the samples are collected at altitude (such
as in Denver) or at very warm or very cold temperatures. Each deviation from
the ideal temperature at sea level shifts the d50 one way or another. Although
some early authors suggested that real collection efficiency curves may be
approximated with a sloping straight line (which would aid in increasing the
interpretive value of the reported data), more recent information indicates the
collection efficiency is much more complex and as sampling altitude increases,
and/or the sampling temperature increases, the cut-size also increases; as the
airflow rate through the sampler increases, the cut-size decreases35 and even
more curious, the actual effective cut-size for the common slit impactor spore
trap can change as the mixture of spore sizes changes. 36
The net result is that the untrained “mould inspector” doesn’t realize that a
spore trap result of say, 1,000 spores per cubic meter of air could come from an
atmosphere containing fewer spores than a sample collected by an identical
spore trap of the same area with a result of say 500 spores per cubic meter of
air. 37 This is because the “total spores” reported on the laboratory report is not
the actual total loading per unit of air, but is rather just a representation of the
proportion of those spores which may have been trapped – which changes for
each spore type.
To illustrate this point consider the following scenario (See the data table
below)- The air in an home contains the spores from 12 different kinds of
fungi. Each genus and species produces spores in a narrowly defined size
range, so the spores from each species is a different size.
Spore Size Effects on Air Monitoring Data
Scenario #2
Scenario #1
Spore Scenario #1 Scenario #2 Reported
Collection Reported
Species Size Actual Spore Actual Spore Spore
Efficiency Spore
(µm) Concentration Concentration Concentratio
Concentration
n
Spore A 1 0.1 100 10 520 52
Spore B 30 0.9 100 90 29 26
Spore C 1 0.1 100 10 389 38.9
Spore D 2 0.3 100 30 289 86.7
Spore E 1.5 0.2 100 20 378 75.6
Spore F 5 0.7 100 70 37 25.9
Spore G 2 0.3 100 30 198 59.4
Spore H 10 0.7 100 70 41 28.7
Spore I 2.5 0.5 100 50 48 24
Spore J 2.5 0.5 100 50 60 30
Spore K 15 0.9 100 90 22 19.8
Spore L 1.5 0.2 100 20 365 73
Total spore
1,200 540 2,376 540
concentrations
Table 1A
Comparison of Reported Values to Actual Values
Now, in the first scenario, the spores from each genus are present at exactly 100
spores per cubic meter of air. Therefore, there are 1,200 spores present per
cubic meter of air. However, since the sizes of the spores are different, the
collection efficiency of each species is different, and so the proportion of
spores trapped and retained is different. In this case, the laboratory analyzes the
sample and reports finding 540 spores per cubic meter of air. The laboratory
report is correct! Now it is up to the consultant to understand why 540 spores
per cubic meter of air could have come from an atmosphere containing 1,200
per cubic meter of air.
But spore concentrations don’t neatly appear in equal concentrations, rather,
they are present in unpredictable proportions (called a profile). So in Scenario
Number 2, the air in the house contains a mixture of spores present at different
concentrations. The total concentration of the spores in the air is 2,376 per
cubic meter of air. But because of the collection efficiency of the spore types
present at the specified profile, the laboratory still reports the concentration as
540 spores per cubic meter of air. The laboratory report is right! Now it is up to
the consultant to understand why a laboratory report stating 540 spores per
cubic meter of air could be from an atmosphere containing either 540 spores or
1,200 or 2,376 or …? It is likely that the first time a “certified mould inspector”
has any idea that this is happening to their samples is when they read this page.
Summary of Accuracy
The up-shot is that not only is the precision of the data generated and reported
by “mould inspectors” extremely poor, the accuracy of the data is also
extremely poor due to the inherent limitations of the samplers used in the
absence of DQOs. We have never encountered a “mould inspector” who
actually understands that the accuracy of their data is very limited. In our
experience, “certified mould inspectors” view the laboratory report as some
kind of magical document which represents absolute truth. In fact, the
laboratory report is a meaningless document, if the consultant cannot place the
values within the context of his Data Quality Objectives.
Relevancy: Relevancy asks: “Do the data speak to the a priori question being
asked?”
Contrary to good sampling protocols, such as described by Dr. Harriet Burge, 38
in our experience, we have never observed where a Home Inspector or
“certified mould inspector” has actually asked an a priori question, developed
an hypothesis to test, or provided any point of relevancy to the collection of
their samples.
Indeed, based on the conclusions provided by most “mould testers,” none of the
samples or sample results provide any information that was not already known
prior to sampling, but frequently provide misleading conclusions that are not
substantiated by valid samples.
In their reports, Home Inspectors and mould testers never actually explain how
their samples are used or could be used to support their conclusions.
Comparability (Points of reference):
Comparability is the reference point against which one may answer the
question “Are the results high? Low? Normal? Abnormal? According to
whom? By which metric/standard? Is the metric or standard accepted, and if so,
by whom? Decisions about air contaminants can often be based by comparing
the qualified results against a regulatory requirement, nationally accepted
guideline, or confidently characterized guidelines. As stated in the EPA
recommendations, those criteria should be explicitly identified prior to the
collection of the samples. We have never seen where a mould inspector
exercised any valid comparisons, but, as already mentioned, most inspectors
rely on popular myth and misconceptions (such as comparing indoor to outdoor
concentrations) or other sloppy thinking to interpret the data.
In their reports, most “mould inspectors” use a method of comparison that is
popular amongst poorly trained consultants who presume their single indoor
datum is valid, and is then compared to a single outdoor datum, which is
similarly presumed (erroneously) to be valid.
However, this comparison is generally considered argumentum ad populum in
the light of state-of-knowledge. Essentially the consultant makes the case that
“since everyone seems to be doing it, it must be correct.” In fact, in making the
comparison, “mould inspectors” never provide any support for the comparison,
but rather shift the responsibility of interpretation to the analyzing laboratory.
The previously referenced EPA document explicitly states:
The results of samples taken in your unique situation cannot be
interpreted without physical inspection of the contaminated area
or without considering the building’s characteristics and the
factors that led to the present condition.
We have never seen a situation where laboratory personnel visited a study site
and performed a physical inspection. Therefore, laboratories have absolutely no
basis to perform the interpretation and therefore, usually only lower quality labs
engage in this kind of behavior.
It has long been known that there is no correlation between indoor and outdoor
spore concentrations in the circumstances under discussion, and investigators
who practice such indoor/outdoor comparisons are exclusively poorly trained
practitioners who lack a legitimate understanding of indoor aerobiology.
It is possible that the myth regarding indoor v. outdoor comparisons started
with notable, well respected researchers who alluded to indoor/outdoor
generalities39 and those generalities were then taken out of context and
referenced inappropriately in subsequent texts.
For example, in the 1998 edition of NIOSH’s Manual of Analytical Methods,
QA/QC Chapter J, NIOSH40 partially quoted a reference and stated:
In general, indoor microflora concentrations of a healthy work
environment are lower than outdoor concentrations at the same
location.(Macher & Burge 1995) If one or more genera are found
indoors, in concentrations greater than outdoor concentrations,
then the source of amplification must be found and remedied.
In the above statement NIOSH references the source as: Macher JM, Chatigny
MA, Burge HA [1995]Sampling airborne microorganisms and aeroallergens.
In: Cohen BS, Hering SV, eds. Air sampling instruments for evaluation of
atmospheric contaminants, 8th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, Inc., pp. 589-617.
However, if one goes to the original source (Macher & Burge, 1995), we see
that the referenced material does not support the statement as presented. The
authors Macher & Burge made the fist observation (the general comment about
indoor v. outdoor concentrations), but did not make the et sequitur conclusion –
rather that was an unsupported misinterpretation by NIOSH.
Placing the comments of the original cited authors back into context challenges
the fundamental legitimacy of performing indoor/outdoor comparisons and is
contrary to what the author wrote elsewhere on indoor/outdoor concentration
issues wherein the same original author (Burge) also in 1995, observed: 41
Indoor/outdoor relationships: Unless there is an indoor source for
specific bioaerosols, concentrations indoors will generally be
lower than outdoors. This effect is related to the reasons for
occupying enclosures, which are designed to protect us from
adverse weather and intrusion by vermin or other unwelcome
(sometimes human) visitors. The outdoor aerosol penetrates
interiors at rates that are dependent primarily on the nature of
ventilation provided to the interior. Indoor/outdoor ratios of
specific particle types (of outdoor origin) are highest (tending
toward unity) for buildings with “natural” ventilation where
windows and doors are opened to allow entry of outdoor air
along with the entrained aerosol As the interior space becomes
more tightly sealed, the ratio becomes lower and lower.
Therefore, the indoor/outdoor ratio of airborne moulds is primarily a function
of building systems, and the indoor to outdoor ratio will rise and fall with the
normal ventilation infiltration rate and other factors not related to indoor mould
growth. Unless one has evaluated the infiltration/exfiltration characteristics for
the structure, one cannot know how close to unity one may expect the structure
to be (even if one has data that exhibits statistical confidence).
Over the course of time, untrained “mould inspectors” have repeated the
NIOSH quote which has grown out of context and is now misconstrued to a
point of perverse “normality” exclusively through tautology, but the oft
repeated sentence still remains without foundation.
As mentioned, the spatial and temporal variations in spore concentrations
already described are equally large outside as inside (but for slightly different
reasons). Furthermore, the concentrations of outdoor spores vary enormously
with species, location, altitude, season, climate and time of day, and indeed,
many organisms exhibit relatively predictable increases and decreases with
time of day. 42
Therefore, similar to indoor samples, unless one has collected a sufficient
number of samples to properly characterize the outdoor population distribution,
one lacks the necessary precision to compare that sample with a
contemporaneous indoor sample.
That is - while the indoor spore concentrations (and specific genera and
species) are fluctuating wildly, the outdoor spore concentrations (and genera
and species constituents) are also fluctuating wildly, but at different times, in
different locations and for different reasons.
Furthermore, when legitimate sampling protocols, such as those found in
official NIOSH reference documents, make allusions to the comparisons of
indoor to outdoor concentrations, 43 they axiomatically are indicating that one
has actually measured, with confidence, the actual concentration used in the
comparison, and not simply taken one or two or three unreliable grab samples.
Grab samples merely represent a “snap-shot” and not the overall concentration.
Therefore, where NIOSH recommends comparing indoor to outdoor samples,
they also state: 44
Select at least three sites, one each to represent complaint area, a
noncomplaint area and outdoors.
In turn at each site, sample simultaneously for fungi, mesophilic
bacteria, and thermophilic actinomycetes.
Before moving to the next site, repeat twice to obtain triplicate,
consecutive samples.
Collect another complete set of samples and blanks on the next
day.
Therefore, at the end of the sampling period, the consultant would have
collected six samples for fungi, mesophilic Bacteria, and thermophilic
actinomycetes from each study area, six samples of the same from an indoor
control area and six samples from the outside. This is a far cry from the
protocol usually seen with “mould inspectors” collecting one or two
meaningless samples from an indoor area and comparing that with one or two
meaningless samples (inappropriately “averaged”) from the outdoors.
In the earlier referenced document,45 the EPA states:
Keep in mind that air sampling for mold provides information
only for the moment in time in which the sampling occurred, much
like a snapshot. Air sampling will reveal, when properly done,
what was in the air at the moment when the sample was taken.
For someone without experience, sampling results will be difficult
to interpret. Experience in interpretation of results is essential.
We know that if one collects a three minute sample from a specific location,
three minutes later, the airborne spore count will be wildly different in the same
location. In the table below, we have presented very typical instantaneous
indoor/outdoor collocates taken from a normal Colorado home.
Air Monitoring Data
Time Indoor Spore Count Outdoor Spore Count
10:00 971 6
13:15 16 112
15:23 33 102
18:06 426 133
Table 2
Indoor versus Outdoor Spore Counts 46
As can be seen from the above data, the indoor counts are showing the
expected large variation (lognormal distribution), and simultaneously, the
outdoor samples are similarly showing their expected large variation
(lognormal distribution).
Comparing one-on-one samples is a meaningless pursuit; and, as demonstrated
in the typical example above, if one used that decision criteria, the home in the
above example would have “elevated” spore counts (and thus a mould
problem) at 10:00 a.m. and 6:00 p.m, but would be considered normal at 1:15
p.m. and half past three in the afternoon.
In a similar example, the table below presents another actual data set from a
normal residential setting in Colorado during the month of July.
Air Monitoring Data
Time Data Set A Data Set B Data Set C
08:45 419 1,306 2,629
10:20 290 4,4,84 3,000
12:12 452 2,306 3,000
14:15 484 14,065 3,468
16:16 742 7,339 3,048
16:45 210 5,290 3,242
MVUE 434 5,858 3,064
Table 3
Indoor versus Outdoor Spore Counts
In this case, a “Toxic Mould Expert” (who is still practicing mumbo-jumbo
mould testing) had frightened an elderly couple with slit-impactor sampling
methods. The “consultant” managed to frighten the couple into leaving their
home. FACTs performed scientifically valid sampling in the “contaminated”
home, in the outdoors and in another home in the area (not experiencing any
mould related problems) as a control. The windows and doors in the study
home were closed and the occupants maintained closed-building conditions.
The occupants of the control home kept the all the windows in the building
open during summer months. The MVUE47 listed in the table is the actual
“average” based on the lognormal distribution. The “MVUE” is the statistic
considered to best represent a point estimate of the true “mean” for lognormally
distributed values. The MVUE is preferred over the geometric mean, especially
when sample populations are small.
Do the data in the above table intrinsically identify which home had a mould
problem? Or do the data identify which home was the healthy control home or
which data set represents the outdoor samples? No. In the above table, Data Set
A was collected from the “contaminated” home; Data Set C was collected from
the healthy control area; and Data Set B were samples collected from the
outdoors.
Regarding indoor versus outdoor comparisons, too many broad statements are
made without due consideration for building conditions and regional and
microclimate changes which can greatly alter the variations in concentrations
and can greatly alter the relationship between the indoor environment and the
outdoor environment.
For example, in Colorado our seasonal changes are so large, that on some days,
we may open our doors and windows permitting not just direct communications
between indoor and outdoor spore concentrations, but actual equilibrium of the
outdoors spore concentrations with the indoor air spore concentrations. 48
Extensive data collected by FACTs indicate that for samples collected under
“closed building conditions,” regardless of the region, there is poor correlation 49
between indoor and outdoor fungal profiles (genera, species and total counts)
whether the building is a “problem” (symptomatic) building or a “healthy”
(non-symptomatic) building. Studies by other researchers5 have made similar
conclusions regarding outdoor versus indoor influences, particularly with
regard to particulates. 51
In the graphic below, we have presented data for indoor and outdoor fungal
concentrations for both symptomatic (problem) buildings and non-symptomatic
(healthy) buildings collected in Colorado. 52
Figure 1
Indoor to Outdoor Spore Concentrations
Comparisons for Colorado Homes
As can be seen from the above graph, there are clearly times when “problem”
homes have spore concentrations less than outdoor concentrations and when
healthy homes have spore concentrations higher than outdoors. Some studies
purporting to demonstrate correlations between indoor and outdoor air, 53
however, exhibit fatal flaws upon closer scrutiny, and those studies do not
survive scientific rigor. 54
Furthermore, in temperate zones it is a well accepted fact that outdoor spore
concentrations change dramatically with seasons, and exhibit a bi-modal
distribution whose peaks are in the early spring and early autumn. And
although our definition of season (summer, autumn, etc.) is based upon the
equinoxes, moulds, being living organisms, are more interested in mean diurnal
temperatures, precipitation levels, sun light cycles, relative humidity and so
forth, for their living and growth conditions.
In the data set graphic below, for Colorado, winter outdoor MVUE fungal
counts are about 209 spores/3, with individual counts exceeding 900 spores/m3
approximately 10% of the time. Spring counts are approximately 900 spores/m3
with individual counts exceeding 900 spores/m3 approximately 40% of the
time. The summer counts average about 3,500 spores/m3 with individual counts
exceeding 900 spores /m3 approximately 72% of the time. And yet, non-
symptomatic closed-mode indoor counts remain roughly the same throughout
the year (horizontal central line).
Figure 2
Outdoor Spore Counts Vary With Seasons
Therefore, in Colorado, the representative indoor spore count in normal,
healthy houses will exceed the outdoor counts almost four months of the year.
Laboratories and consultants, who claim that a problem exists if the indoor
counts exceed outdoor counts ignore the fact that the spore counts in healthy
houses stay relatively stable, but the outdoor seasonal counts fluctuate around
the indoor concentrations. Therefore, according to the criteria found in some
“standards” (such as the IESO “standard,” which is not recognized by
legitimate microbiological experts as a "standard"), healthy houses contain
excessive levels of moulds in the winter but are normal in the summer, even
though the spore counts in the houses may not have changed.
Most “mould consultants” make a special point of noting that the genus
Stachybotrys may be identified in the indoor sample. Stachybotrys is the
“bogeyman” used by the toxic mould charlatan to frighten people, and its
presence is notable only to those who don’t realize that it is ubiquitous in ALL
houses.
Summary of Comparability
The comparisons made by mould testers are usually entirely untenable and the
conclusions drawn from those comparisons, are usually without validity.
FACTs has performed valid air sampling and developed an extensive database
of spore counts that permits direct comparison of other valid samples. Based on
our in-house database of total fungal counts (spores and fragments), as
determined by the spore trap Air-O-Cell® sample method, the fungal counts for
indoor samples in temperate zones, for closed building conditions 55, in
buildings not experiencing fungal problems usually have an MVUE of less than
about 500 spores per cubic meter (spores/3). However, even in those properties,
the indoor concentrations exceed 900 spores/m3 12% of the time. This means
that even in perfectly clean houses, during closed-mode conditions, one out of
every 10 samples will exceed 1,000 spores per cubic meter of air and a finite
probability that any one sample will exceed any given elevated value.
By contrast, the MVUE total fungal counts in buildings with fungal problems,
is greater than 40,000 spores/m3 and fungal concentrations exceed 900
spores/m3 66% of the time. 56
Essentially, this means that in even the “cleanest” house with no mould
problem, there is a finite and high probability that a single sample (or two or
three) will exceed even, say, 3,000 spores per cubic meter of air; and that in
even the mouldiest of houses, a single sample may be as low as 3,000 spores
per cubic meter of air.
At this point, it is probably important to address the following myth:
Myth Number 1: Airborne spore concentrations correlate to the amount of
mould present in a building.
Truth Number 1: There is NO correlation between air concentrations and the
amount of mould, hidden or otherwise in a building.
Some of our lowest air sample sets have come from properties with thousands
of square feet of visible, actively growing moulds. Some of our highest data
sets have come from properties with NO mould problems, (hidden or
otherwise).
This makes sense, since it is a myth that the number of spores present in an area
is somehow related to the size of the vegetative mass – but that simply isn’t
true. As a mould is actively growing, and using its resources (food and water),
it is in a mad rush to colonize and fight off competition – it doesn’t have time
to be engaged in reproductive activities! Result: Lots of vegetative mould
growth, not many mould spores in the air.
Air sampling, even properly conducted air sampling is entirely incapable of
quantifying the amount of mould in a structure and is entirely incapable, except
under extremely unusual circumstances, consisting of some very stringent
DQOs, of confirming the presence of “hidden” mould. Generally, these kinds
of assessments are very expensive, and virtually never needed.
The American Academy of Allergy and Immunology (AAAI) classifies general
allergic responses as follows: 57
AAAI Classification
Total
Allergy sufferers who are allergic to these pollens or
Spore Classification
moulds may experience symptoms of hay fever
Count
0 Absent No Symptoms
Only individuals extremely sensitive to these pollens and
1- 6,499 Low
moulds will experience symptoms
6500 - Many individuals sensitive to these pollens and moulds will
Moderate
12999 experience symptoms.
13000 - Most individuals with any sensitivity to these pollens and
High
49999 moulds will experience symptoms.
Almost all individuals with any sensitivity at all to these
50000 Very High pollens and moulds will experience symptoms. Extremely
sensitive people could have severe symptoms.
Table 5
Symptom and Spore Count Guidelines of the
American Academy of Allergy and Immunology
Therefore, in comparing indoor to outdoor, and maintaining the position that
the indoor environment does not have a mould problem if indoor spore
concentrations are less than outdoor spore concentrations then, according to
these same inspectors, indoor concentrations should not be of concern until
about 13,000 spores per cubic meter. Other researchers have reported “allergic
thresholds” for specific moulds such as 3,000 CFU/m3 for the ubiquitous genus
Cladosporium.58 We do not see how “mould inspectors” maintain these
conflicting and incongruous positions in the face of overwhelming published
data, accepted knowledge, logic and common sense to the contrary.
Completeness: Have all the DQOs been met; i.e. are the data reliable and do
they exhibit confidence?
Since no DQOs are ever established by “mould inspectors”, no DQOs can be
met.
Hidden Mould
There is a misconception that mould may be hidden in wall cavities and that the
hidden mould presents an exposure problem. However, mould hidden in wall
cavities does not present a significant exposure threat. FACTs has performed
several hundreds of building assessments for moulds and Bacteria. We have
never encountered a single project where sampling (air sampling or bulk
sampling) was successful in discovering a hidden mould problem that was
overlooked by normal, thorough visual inspection.
Furthermore, we have never encountered a situation where mould hidden in
wall cavities that ever resulted in the degradation of the indoor air in a
structure. When the front door of a residence is opened on a nice spring day in
a temperate zone, approximately two cubic meters of air are displaced and
mixed into the structure in an instant. At a moderate spore concentration of just
5,000 spores per cubic meter, the occupant has just introduced 10,000 mould
spores into the home in a matter of seconds.
By contrast, based on our tests using ventilation fume at various penetrations,
the air movement through a wall cavity, capable of carrying mould spores or
other fungal entities is so small as to be entirely insignificant by comparison.
Since the route of migration is insignificant, the source, however large or small,
becomes unimportant since there is no reasonable way for the source to get to
the recipient. In any event, in general, it is recognized by the cognizant
scientific community that colonization of mould inside wall cavities does not
present an exposure issue : 59
…it is reasonable to infer that small amounts of mold enclosed in
walls, floors, or ceilings will not have a large impact on the
indoor air quality.
The Wisconsin Department of Health and Family Services investigated the
relationship between mould on surfaces of oriented strand board siding and
mould levels inside the home; the results of the study indicated mould levels in
the affected homes were not significantly higher than those measured in “non-
exposed” homes. 6
As such, to our knowledge, there is no compelling reason to address mould
inside wall cavities based on mere presence. This is consistent with the opinion
of one of the world’s leading experts on mould, Dr. Harriett Burge who stated:
61
However, removal based on the mere fact of its presence, or
based on nonspecific symptoms that are not related to mold
exposure, is often not appropriate.
We have seen several studies wherein authors have claimed that air monitoring
or other sampling techniques have discovered hidden moulds. However, upon
review of the studies, the air monitoring in those cases were usually poorly and
improperly conducted and merely augmented the visual inspections, and in no
cases discovered hidden mould that would not have been otherwise found by a
normal visual inspection performed by an experienced investigator. One of the
authors62 of the The Green Book similarly makes this observation:
Some investigators have used air samples collected inside wall
and ceiling cavities to document the extent of hidden mold, but
this technique is controversial and interpretation is uncertain.
And elsewhere, the author explains that:
Finding hidden mold is difficult and expensive. If there are no
smells (sic) no complaints, and no indication of significant
moisture damage, we can reasonably be sure that there is no
problem and no reason for further investigation.
Studies and investigations performed by this author (Connell), consistent with
other researchers, have not observed a correlation between mould hidden in
walls and a degradation of indoor air quality or a correlation between mould
hidden in walls and an increase in spore counts in occupied spaces. Even
properly conducted airborne mould sampling is generally incapable of
determining when hidden mould may be present.
FINAL CLEARANCE SAMPLING
FACTs has been involved in mould remediation and correction activities for
hundreds of residences and commercial buildings. We have never seen a single
situation where a mould inspector performed proper sampling techniques for
final clearance activities. Furthermore, we have never seen a single situation
where sampling, including properly conducted sampling, has ever demonstrated
the efficacy of a mould remediation activity that was not readily known by a
visible inspection.
In short, there is no such thing as valid “clearance testing” for molds, as
commonly conducted by “mould inspectors” and mould remediators. No such
tests, as commonly conducted, are scientifically valid, and none stand up to
scientific scrutiny. The Green Book addresses “final clearance sampling”
thusly:
18.5.2
Current mold remediation guidelines support the concept that
project success depends on verification primarily through
inspection that visible mold growth and associated debris and
dust were appropriately removed63,. 64, 65
The AIHA publication continues with:
The primary objective of mold remediation, based on guidelines
published between 199366 and 200467 68 is to remove visible mold
growth and return material surfaces to a satisfactory condition.
The section concludes with:
A difficulty associated with using air sampling as the primary
means of achieving final clearance is the absence of numerical
guidelines for airborne fungi and for bioaerosols in general. 69, 70,
71
IOM72 concluded that, although there is an association between
respiratory health effects and dampness, the exact causal agents
of irritation and respiratory disease are obscure. Thus, from a
health effects viewpoint it remains uncertain whether the EHS
investigator should sample during final clearance for total spores,
culturable spores, hyphal fragments, specific allergens, glucans,
endotoxins, or other agents.
Therefore, in an effort to ensure that one is using valid standard industry
practices, from legitimate medical and scientific sources, legitimate mould
assessors should continue to exclusively perform visual inspections as the
preferred method of final clearance. Naturally, there will be some isolated
(rare) cases, wherein an Industrial Hygienist will need to perform (expensive)
air sampling to meet specific a priori DQOs.
BULK SAMPLES
Bulk samples usually provide virtually no useful information in assessments
over and above that which can be identified by a cognizant expert by the naked
eye. Bulk samples are seldom collected by cognizant experts. During our
assessments, without the collection of any samples, we are usually able to
provide the same information by merely looking at building materials. Even
then, knowing the genus or species of a mould is usually of no value since the
genus or the species of mould does not alter any subsequent decisions.
In general, we find that the bulk samples collected by “certified mould
inspector”s and Home Inspectors are meaningless and useless, and are never
actually used in any kind of decision making process. We have never seen a
report by a mould tester that actually explained why knowing the genus was
important to the process or how the genera involved impacted the remediation
in anyway.
The same PARCC parameters (precision, accuracy, comparability, etc)
described above for air samples also apply for bulk samples (tape lifts, bulks
and swabs).
CONCLUSION
Sampling and testing in mould assessments is virtually never needed, and
virtually never provides any information that is not otherwise immediately
available to a legitimate Industrial Hygienist.
Overall, most legitimate mould experts seldom see a need to collect any kind of
samples. Usually, the only consultants who routinely collect mould samples or
conduct mould tests are those consultants who need the laboratory report to
achieve an image of credibility with the client, since they otherwise lack
legitimate knowledge in the subject area.
Knowing the species and/or genus is virtually never useful information.
It is impossible, outside the context of a priori DQOs, to compare indoor
samples and outdoor samples.
Virtually ALL of the hundreds of samples FACTs has reviewed over the years
collected by Home Inspectors and “certified mould remediators” or “certified
mould inspectors” were useless or meaningless (or both), and always
unnecessary.
References
1 Macher JM, Chatigny MA, Burge HASampling airborne microorganisms and
aeroallergens. In: Cohen BS, Hering SV, eds. Air sampling instruments for evaluation of
atmospheric contaminants, 8th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, Inc., pp. 589-617.
2 American Industrial Hygiene Association
3 Recognition, Evaluation, and Control of Indoor Mold, Prezant E; Weekes, DM; Miller
JD (Eds.) American Industrial Hygiene Association 2008
4 The CDC Mold Work Group, National Center for Environmental Health, National
Center for Infectious Diseases, National Institute for Occupational Safety and Health,
Centers for Disease Control and Prevention, October 2005
5 US Centers for Disease Control, Mold: General Information: Basic Facts | CDC
APRHB, 2007, http://www.cdc.gov/mold/faqs.htm
6 Watson JG, Turpin BJ Chow JC, The Measurement Process; Precision, Accuracy and
Validity, Chapter 10 in Air Sampling Instruments for Evaluation of Atmospheric
Contaminants (ACGIH, 2001)
7 US Centers for Disease Control, Mold: General Information: Basic Facts | CDC
APRHB, 2007, http://www.cdc.gov/mold/faqs.htm
8 US EPA Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, 1996 is
OSW's official compendium of analytical and sampling methods that have been evaluated
and approved for use in complying with the RCRA regulations.
9 Li Y; Heng J; and Chen Z Study Of Particle Movement In Ventilation System
Proceedings: Indoor Air 2002 Anaheim California, 2002
10 Keady PB; Mainquist L; Tracking IAQ Problems to Their Source, Occupational
Health & Safety, September 2000
11 Connell CP, Field Measurements for Moulds: Spatial and Temporal Variations,
Presented at the ASTM International Conference: Bringing Science to Bear on Moisture
and Mold in the Built Environment, Colorado University, Boulder 2006
12 Macher JM, Chatigny MA, Burge HA Sampling airborne microorganisms and
aeroallergens In: Cohen BS, Hering SV, eds. Air sampling instruments for evaluation of
atmospheric contaminants, 8th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, Inc., pp. 589-617.
13 Ayer HE; Burg J, Time Weighted Averages Vs. Maximum Personal Sample (Presented
at the AIHA Conference, Boston, MA, 1973)
14 NIOSH Occupational Exposure Sampling Strategy Manual, HEW Publication Number
77-173 (1977)
15 Spurgeon, J; Data submitted to the ASTM D22.08.02 Committee for review, October
2005
16 Connell, CP, Sample results: What do they really tell us? Presented at the IAQ in
Schools Lecture Series, Corpus Christi, TX, 2003
17 Eudey L, Su HJ, Burge HA. Biostatistics and bioaerosols. In Bioaerosols, Burge HA,
ed. Boca Raton: Lewis Publishers, pp. 269-307. 1995.
18 Reponen T, Nevalainen A, Jantunen M, et al, Normal Range Criteria for Indoor Air
Bacteria and Fungal Spores in a Subarctic Climate; Indoor Air, 2:26-31 (1992).
Referenced by Macher JM, Chatigny MA, Burge HA. Sampling airborne
microorganisms and aeroallergens. In: Cohen BS, Hering SV, eds. Air sampling
instruments for evaluation of atmospheric contaminants, 8th ed. Cincinnati, OH:
American Conference of Governmental Industrial Hygienists, Inc., pp. 589-617, but not
reviewed by this author (Connell).
19 NIOSH Occupational Exposure Sampling Strategy Manual, HEW Publication Number
77-173 (1977)
20 Ibid.
21 As referenced in Rock JC; Occupational Air Sampling Strategies, Chapter 2 of Air
Sampling Instruments for Evaluation of Atmospheric Contaminants (ACGIH, 2001)
22 NIOSH Technical Information Exposure Measurement Action Level and
Occupational Environmental Variability, HEW Publication 76-131, Cincinnati OH,
45226, (1975)
23 NIOSH Occupational Exposure Sampling Strategy Manual, HEW Publication Number
77-173 (1977)
24 Macher JM, Chatigny MA, Burge HA Sampling airborne microorganisms and
aeroallergens. In: Cohen BS, Hering SV, eds. Air sampling instruments for evaluation of
atmospheric contaminants, 8th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, Inc., pp. 589-617.
25 Ibid.
26 Shapiro-Wilk W test (used to determine the most appropriate data distribution curve)
greater than 0.9500.
27 In the above closed-mode building data set, the one-tail percentage point of the W test
=0.7880; the Shapiro-Wilk W test (goodness of fit) is 0.9890, indicating lognormal
distribution (Gaussian distribution is rejected since W for normal is 0.7800). There is
95% confidence any single randomly collected sample will exceed 1,000 spores/m3 65%
of the time; the MVUE is 1,058 spores/m3 with a GSD of 2.6
28 Generally speaking, and certainly at FACTs, because of the expected variations, we
express the “average” value as the MVUE.
29 Based on the air volumes reported in typical laboratory reports, collected single 3-
minute samples.
30 Heber AJ, Bioaerosol Particle Statistics in Chapter 5, of Cox CS, Wathes CM
Bioaerosols Handbook 1995
31 Macher JM, Chatigny MA, Burge HA Sampling airborne microorganisms and
aeroallergens. In: Cohen BS, Hering SV, eds. Air sampling instruments for evaluation of
atmospheric contaminants, 8th ed. Cincinnati, OH: American Conference of
Governmental Industrial Hygienists, Inc., pp. 589-617. 1995
32 Ibid.
33 Macher J. Burge HA, Sampling Biological Aerosols Chp. 22 in Air Sampling
Instruments for Evaluation of Atmospheric Contaminants (ACGIH, 2001)
34 Alegro Industries, Operator’s Manual, IS013 Rev E 7-7-05 (Allegro Industries, 7221
Orangewood Avenue, Garden Grove, CA 92841)
35 Saulius T, Willeke K, Reponen T, Trunov M, Particle Cut-Size Evaluation –Final
Report Nov 1998, Internal Report by Zefon International-Analytical Accessories, 2860
23rd Ave, St. Petersburg, FL, 33713
36 Cadle RD The Measurement of Airborne Particles (1975), (referencing seminal work
by Ludwig, FL Env. Sci. Technology 2, 1968).
37 Connell CP, Sample Results: What do they really tell us? IAQ Sampling Myths 13th
Annual AIHA/ASSE OEH&S Conference, “Exchanging Knowledge – New Times, New
Ideas” Denver, CO October 2007
38 Burge HA, Bioaerosol Investigations, Chapter 1 in Bioaerosols Burge HA (ed), 1995
39 Burge HA Bioaerosols in the Residential Environment , Chapter 21 in Bioaerosols
Handbook (Cox CS, Wathes CM eds), 1995
40 NIOSH is the US Department of Health and Human Services, Centers for Disease
Control, National Institutes of Occupational Safety and Health. spud
41 Muilenburge ML, The Outdoor Aerosol, in Chapter 9 of Bioaerosols, (Burge HA, ed)
1995
42 Madelin TM, Madelin MF Biological Analysis of Fungi and Associated Molds;
Bioaerosols Handbook, Cox and Wathes, Eds. (1995)
43 Chapter J - Sampling and Characterization of Bioaerosols; NIOSH Manual of
Analytical Methods (NMAM®), 4th ed. DHHS (NIOSH) Publication 94-113 (August,
1994), 1st Supplement Publication 96-135, 2nd Supplement Publication 98-119, 3rd
Supplement 2003-154
44 NIOSH Method 0800, BIOAEROSOL SAMPLING (Indoor Air) Culturable
organisms: bacteria, fungi, thermophilic actinomycetes, Issue 1, January 1998
45 Mold Remediation in Schools and Commercial Buildings U.S. Environmental
Protection Agency
46(EPA 402-K-01-001, March 2001 updated June 25, 2001)
47 Connell CP, Field Measurements for Moulds: Spatial and Temporal Variations,
Presented at the ASTM International Conference: Bringing Science to Bear on Moisture
and Mold in the Built Environment, Colorado University, Boulder 2006
48 The statistic known as a “minimum variance unbiased estimate” (MVUE) is
considered to be a statistic that best represents a point estimate of the true “mean” for
lognormally distributed values. The MVUE is preferred over the geometric mean,
especially when sample populations are small.
49 Muilenburge ML, The Outdoor Aerosol, in Chapter 9 of Bioaerosols, (Burge HA, ed)
1995
50 Least squares fit, r2 = 0.058
51 Cooley J.D.; Wong W.C.; Straus D.C.; Jumper C.A. Correlation between the
prevalence of certain fungi and sick building syndrome, Occupational and Environmental
Medicine, September 1998, vol. 55, no. 9, pp. 579-584(6)
52 El-Hougeiri N., El-Fadel M.IAQ Characterization In Urban Areas: Indoor To
Outdoor Correlation Proceedings: Indoor Air 2002
53 Connell CP, Field Measurements for Moulds: Spatial and Temporal Variations,
Presented at the ASTM International Conference: Bringing Science to Bear on Moisture
and Mold in the Built Environment, Colorado University, Boulder 2006
54 Shelton BG, Kirkland KH, Flanders WD, Morris GK, Profiles of American Fungi in
Buildings and Outdoor Environments in the United States Applied and Env.
Microbiology April 2000 pp 1743-1753
55 Connell CP, Indoor Fungal Concentrations http://www.forensic-
applications.com/moulds/mvue.html
56 Closed mode conditions.
57 n=136. Data exceeding the upper quantifiable limit (estimated to be 1.7E6 spores/3)
were censored to 1.7E6 spores/3.
58 American Academy of Allergy and Immunology
http://www.aaaai.org/nab/index.cfm?p=reading_charts
59 Gravensen, S. Fungi as a cause of allergic disease Allergy (34): 135-154, 1979; as
reported in Ren P; Jankun TM; Leaderer BP; Comparisons of seasonal fungal prevalence
in indoor and outdoor air and in house dusts of dwellings in one Northeast American
county Journal of Exposure Analysis and Environmental Epidemiology (9) 560-568;
1999
60 Robbins C, Morrell J; Mold, Housing and Wood(Article prepared for the Western
Wood Products Association), Jan 2006.
61 Daggett DA, Chamberlain M, Smith W. Effects of Exterior Decay and Mold on Indoor
Mold and Air Quality. Proceedings of the 2nd Annual Conference on Durability and
Disaster Mitigation: November 6, 2000; Madison, WI (Cited by Robbins as referenced
here, but not reviewed by this author (Connell))
62 Burge, H. Can Mold Be Safely Left Inside Walls? The Environmental Reporter, Vol. 3,
No. 11, November 2005
63 Recognition, Evaluation, and Control of Indoor Mold, Prezant E; Weekes, DM; Miller
JD (Eds.) American Industrial Hygiene Association 2008, Section 2, Chapter 9
64 Health Canada: Fungal Contamination in Public Buildings: Health Effects and
Investigation Methods. Health Canada, Ottawa, ON (2004)
65 Canadian Construction Association; Mould Guidelines for the Canadian Construction
Industry; CCA; Ottawa, ON; 2004
66 Guidelines on Assessment and Remediation of Fungi in Indoor Environment; New
York City Department of Health, Bureau of Environmental & Occupational Disease
Epidemiology, 2000
67 Guidelines on Assessment and Remediation of Fungi in Indoor Environment; New
York City Department of Health, Bureau of Environmental & Occupational Disease
Epidemiology, 2000
68 Health Canada: Fungal Contamination in Public Buildings: Health Effects and
Investigation Methods. Health Canada, Ottawa, ON (2004)
69 Canadian Construction Association; Mould Guidelines for the Canadian Construction
Industry; CCA; Ottawa, ON; 2004
70 US Environmental Protection Agency, in its booklet “Mold Remediation in Schools
and Commercial Buildings, EPA 402-K-01-001 March 2001 (updated 6/25/01)
71 American Conference of Governmental Industrial Hygienists, (ACGIH), Data
Interpretation, In Bioaerosols: Assessment and Control, Macher J (Ed), Cincinnati OH,
1999
72 Storey E; et al Guidance for Clinicians on the Recognition and Management of Health
Effects Related to Mold Exposure and Moisture Indoors, Farmington CT, University of
Conn. Health Center, 2004
73 Institute of Medicine (IOM) Damp Indoor Spaces and Health, DC, IOM, 2004
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