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• When & How to Inspect and Test after Mold Cleanup
• What building areas should be tested?
• How does a building "pass" a clearance inspection?

Here we explain and describe the post remediation mold clearance procedures and testing that should be used after a mold remediation or mold cleanup project. This document is a chapter of the Mold Action Guide which provides an easy to understand step-by-step guide for dealing with toxic or allergenic indoor mold and other indoor contaminants: what to do about mold "mildew," moisture, in your house or office, building-related illness, involving your physician, treatment, sick building investigators, reduction of irritants, and special products to help clean buildings and air. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

For each step in the process of diagnosing, identifying, removing, and preventing indoor mold problems in buildings, links to in-depth articles are provided. In some cases in this document I use excerpts from longer dissertations on these subjects. Where we do that we offer a link to the longer, more detailed original documents as well. Extensive, in-depth articles about mold and other indoor air quality concerns are organized at our Mold Information Center

This document discusses the importance of mold clearance inspection and testing following a mold cleanup or "mold remediation" project and gives advice on who should conduct mold clearance sampling, when clearance testing should be performed, and how to interpret the results of a post remediation mold clearance inspection and test. What should be involved in a mold remediation clearance inspection and test? Simple air testing alone may be quite unreliable.

Simple use of a mold remediation clearance test acceptable ratio (percentage of indoor versus outdoor spore counts) can be very unreliable too. A visual inspection for extent of work, cleanliness, and careful selection of screening samples of mold from surfaces, dust, and possibly air, inside and outside the work area are what's needed in a mold remediation clearance test if you want to trust the results. The purpose of a mold clearance inspection is to assure that the mold cleanup has been done correctly and effectively in the work area and to confirm that the cleanup did not accidentally distribute high levels of moldy dust and debris into other building areas or into its mechanical systems such as heating or air conditioning systems. To avoid conflicts of interest, mold clearance testing should never be performed by the mold remediation contractor nor by someone with any connection with such contractors.

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THE MOLD ACTION GUIDE
MOLD DOCTOR?
MOLD EXPERT, WHEN TO HIRE
DO IT YOURSELF MOLD CLEANUP
HOW TO FIND MOLD
MOLD CLEANUP GUIDE
MOLD KILLING GUIDE
FLOODS & MOLD CLEAN/PREVENT
CLEARANCE INSPECTIONS
  CLEARANCE PROCEDURES
  ACCEPTABLE MOLD LEVEL
  VISUAL CHARACTERISTICS
  SUCCESSFUL MOLD TEST
AFTER THE MOLD CLEANUP
MOLD PREVENTION GUIDE
OTHER IAQ ISSUES

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CLEARANCE PROCEDURES: to be Used After a Mold Cleanup / Remediation Project

There are no single accepted "pass-fail" criteria for clearance inspections. I examine remediated areas for mold or other allergens and I look in other building areas for evidence of spread of contaminated demolition debris or inadequate cleaning if cleaning was recommended for those areas. My evaluation combines a visual inspection of the extent of removal and cleaning of infected materials/areas with a microscopic examination of surface, dust, air, and/or vacuum samples collected at the property.

Visual Inspection for Demolition & Cleaning Completeness

A visual inspection is performed of both the cleaned area and other building areas. In the clean-up area we want to know that demolition has been sufficient - that no moldy materials remain, and that all surfaces appear to have been physically cleaned. If a fungicidal sealant was to be applied, we want to see that it was not simply sprayed atop mold and dirt or debris instead of first cleaning those surfaces.

Mold Screening Tests for Effective Cleaning in the Work Area

We will collect mold clearance inspection test samples of physical surfaces which appear to still be moldy or dirty; if all surfaces are clean we will collect at least one settled dust sample from a representative cleaned surface in each major area. We may also collect other screening samples by using air or vacuum sampling methods. But beware; air sampling alone is not a reliable means of screening a building for problems.

Mold Screening Tests for Cross Contamination Outside of the Work Area

Outside of the remediation area we will collect screening samples of suspect surfaces, settled dust, vacuum and/or air samples of representative areas in the building, paying special attention to areas (or equipment such as HVAC systems) which are at particular risk of having been cross-contaminated by inadequate dust containment measures during the cleanup.

General Property Condition

We will also report ongoing conditions which continue to put the building at extra risk of a new mold problem, such as failure to correct various causes of leaks, water entry, and high moisture.

Lab Processing of Test Samples

Test samples from the site examined in my laboratory using appropriate chemical/stain preparations and a light microscope at magnifications up to 1000X. My opinion regarding the level of cleanliness reflected by fungal samples is based on several existing studies of building contamination, a comparison with the original contamination levels, and my field and laboratory experience examining properties before and after remediation.

ACCEPTABLE MOLD LEVEL What are Acceptable Mold Levels in Buildings

Problems with indoor versus outdoor spore counts

Comparing indoor mold spore levels with outdoor mold spore levels

A common mold remediation clearance test plan specifies that the indoor mold level or spore counts should be no more than 50% of the outdoor level. This approach can generate nonsense, particularly in mold sampling reports I've reviewed in which the genera and species of the indoor mold spores were completely different from the outdoor mold spores. For example an outdoor "Pen/Asp" spore count of 1000 spores/M3 of air might be compared with an indoor "Pen/Asp" spore count of 500 spores/M3 of air.

But often the outdoor "Penicillium/Aspergillus" spores are not the same species as the indoor species, making such count comparisons completely meaningless. Worse, some labs include small basidiospores in their "Pen/Asp" count since often many small amerospores (small round featureless mold spores) like certain Penicillium spores and certain Basidiomycetes are difficult or even impossible to differentiate microscopically. If the indoor and outdoor Penicillium or "Pen/Asp" spores are different species from one another, you are evaluating the effectiveness of a mold remediation project by comparing "apples and oranges."

Examine the indoor mold genera and species

It is important therefore to look qualitatively as well as quantitatively at indoor mold spores after a mold remediation project. If there is a high level of indoor spores of the same genera (and species) as the problem-mold which was originally identified then the cleanup may have been incomplete, regardless of "outdoor spore count comparisons. A common example of incomplete work in which I find problem-levels of Penicillium or Aspergillus after a mold remediation is when mold-infected fiberglass insulation has not been removed because it "looked clean" to the naked eye of the mold cleanup crew. A simple vacuum sample of that material can indicate whether or not the insulation needs to be removed.

What indoor mold levels indicate a problem

After a mold remediation? It depends partly on site conditions. In a sealed room where moldy debris has been removed, testing immediately may disclose an abnormally high level of indoor problem mold which has remained airborne even though the cleaning has removed all of the original mold reservoir. In that case some additional surface cleaning and fresh air exchange may be all that's needed.

Mold counts versus mold Species: Even more questionable is the use of "generic" airborne mold spore counts without further attention to genera and species. A count of 200 Stachybotrys chartarum mold spores /M3 of air would be unusually high as this mold is not normally airborne. I'd be worried about where those spores came from. Conversely, a count of 200 Aspergillus sp. spores /M3 of air in the same circumstances might be considered very "clean".

What indoor mold spore level is considered "contaminated" then depends in part on what mold genera or genera and species have been identified. But if the indoor mold spore count/M3 of air is high enough, we may decide that more investigation or cleaning is needed regardless.

While there is no well-established quantitative standard for fungal spores on surfaces or in air, mold contamination is considered present in a building when the total mold spore concentration per cubic meter of air is above 10,000. (Baxter, ETS). Acceptable levels for individual species vary since species toxicity varies widely as does spore size, weight, and other features which affect risk to building occupants. E.g. Aspergillus/Penicillium in a "clean" residential building study was at a mean of 230, in buildings known to have a moisture or flooding problem it was at 2235 and in mold contaminated buildings the figure was 36,037.

Mold sample processing lab variation

Some writers also warn that mold labs have reliability problems. I agree that two experts counting the same slide will not provide precisely the same counts. My lab participates in a "round robin" quality assurance program in which a group of expert mold sample processing labs around the country "count" spores on the very same slide (we mail it around). We compare our count results as a method for checking on and refining our procedures.

While counts vary among labs, it is unusual for counts by expert labs following the same (agreed-on) count procedures to vary by as much as one order of magnitude. If the mold sample processing lab is actually using an expert to process the samples (rather high-volume part-time minimally-educated workers), then the variability in lab results is very much less than the variation in mold sample results caused by variations in sampling conditions I discussed below at "Mold Sampling Conditions Cause Wide Variation in Results".

Surface samples of mold:

Cultures of mold for Clearance Testing

Since only a small percentage of all molds (perhaps 10%) will grow in any culture at all under any condition, using a culture to screen for problematic mold is a questionable practice. There are uses for mold cultures but I question their application for building screening.

The mold level target is never zero except in special applications such as medical and drug facilities which operate in a "clean room" environment where no stray particles are permitted. Mold is a natural ingredient in outdoor air most of the time. We do not want to find higher indoor mold levels than outdoor, and we do not want to find high levels of problematic mold spores indoors.

Mold Sampling Conditions Cause Wide Variation in Mold Test Results

Warning: interpret all quantitative mold clearance test data with caution, particularly air samples. Individual samples of airborne mold (or any other airborne particles in a building) show tremendous variation from minute to minute, usually by many orders of magnitude, making "ok" mold clearance sampling test results a thing to view with care.

If the mold remediation clearance investigator did not document the sampling method, including where, when, and under what conditions a sample was collected, interpretation of sample results can be tenuous. Were building fans on or off? Were windows open or shut? Was work going on in the area? How long after completion of the mold remediation project did the investigator wait before testing? Turning on a ceiling fan in a room can increase the airborne particle level by a factor of 1000! In situations of particular risk (such as sensitive occupants) or ambiguously-conducted post mold remediation testing, additional or periodic testing should be considered.

More Reading

VISUAL CHARACTERISTICS of Successful Mold Remediation Sites

All suspect or mold-contaminated material, which cannot be cleaned, should have been removed. There should no demolition debris left in the building. Areas of removal such as remaining structural components, floors, and other surfaces should have been thoroughly cleaned, HEPA (High-efficiency particulate air filtering system) vacuumed, wiped, and sealed if a sealant was to be used. HEPA vacuuming is important since ordinary "shop vacuums" and most home vacuum cleaners will simply pass small mold spores right through the system, actually increasing the level of airborne mold.

Remediated areas should be free of visible mold. On previously infected structural members or surfaces, some remediators use fungicidal sealants as extra assurance against movement of remaining incidental spores and to reduce potential future moisture uptake in wood and thus future mold growth. I report the extent of such treatments if evidence of such is visible.

The most common mold cleanup mistakes I encounter are failure to maintain a working dust containment system for the cleanup area during the procedure, failure to actually clean up demolition dust and debris from every surface, and bringing in new building materials or actually beginning reconstruction of the building before a successful clearance inspection and test have been completed. This last "error" means that either the clearance inspection and test are limited in assuring the success of the job or that some of the new work has to be removed to permit inspection and testing.

More Reading:
Cleaning Mistakes people make when cleaning-up moldy building materials and surfaces:

SUCCESSFUL MOLD TEST: How do We Define Successful Post-remediation Mold Test Laboratory Results

In the living area we should find in surface, dust, air, or other samples no more than incidental occurrence of the problem mold or allergens previously found at the property. There should be no significant presence of toxic or allergenic spores or other allergens indicating a remaining mold reservoir.

Air tests, while not a reliable overall indicator of building condition, should, if used for mold screening, show indoor mold levels at or below typical outdoor levels or at levels associated with various studies of "clean" buildings.

Warning: some investigators risk making erroneous conclusions if they attempt to compare directly levels or counts of indoor Penicillium/Aspergillus spore levels with outdoor Penicillium/Aspergillus spore levels in air samples. With some exceptions, it is almost impossible to determine the species of these genera in an air sample. A previous report on a property I was asked to investigate showed that the indoor Penicillium/Aspergillus spore level was equal to the outdoor level and that both were at 8000 spores/M3 of air. But a detailed investigation of the samples disclosed that the outdoor spore level was in fact a species of Penicillium while the indoor species was Aspergillus niger which, at this level I considered an indicator of incomplete cleaning traced, ultimately to incomplete demolition. In this case the original "count comparison" of indoor to outdoor Penicillium/Aspergillus spores was like comparing apples and oranges. It was nonsense.

More Reading:
Mold Investigation and Mold Test Lab Reports: What A Valid, Useful Mold Investigation Report Should Include
Mold Classes, Levels - Mold Hazard levels, Mold Spore Count Validity, Interpreting Mold Counts, and Classes of Mold

AFTER THE MOLD CLEANUP: Addressing Other Leaky or Moldy Building Areas

Some building owners make the mistake of insisting that only limited areas of a moldy building be addressed, or they do not repair other building leaks. When leak-damage, mold, or suspect areas remain in a building following a mold related remediation, the insurance company, contractors, and inspector could express confidence only in the specific areas treated and only at the single point in time of the final successful clearance inspection. The building remains at risk of future discovery of a separate pre-existing or new mold or water damage problem caused by new moisture or leak problems and potentially exacerbated by mold inoculation from pre-existing un-remediated areas.

More Reading:
Mold Prevention: Avoiding Mold Problems in Buildings by Using Mold-resistant Construction Products & Practices
MOLD PREVENTION GUIDE list articles describing steps to reduce the chances of future mold growth in buildings.

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