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Mold Clearance Testing

clearance testing

One of the key parts of an effective mold remediation project is one that is often overlooked. “Post remediation verification” (PRV), or “clearance testing” is the process that evaluates the performance of a mold remediation project. This step should always be done by an unaffiliated, third-party testing company to assure an unbiased assessment. This assessment is so important that some states require it by law.  It is also key that this assessment is scheduled at the proper stage in a remediation project. A verification assessment should be done after all of the mold has been removed, but before the containment has been removed, antimicrobial coatings have been applied, and build-back of the building materials.

The specific steps taken for a post remediation verification assessment are dependent on the specific mold remediation project, however a few basic steps should be followed: assessing the containment, visual inspection for remaining mold growth or mold damaged materials, verifying there are no musty odors present, and checking that the work area is clean.  Although there is no consensus on sampling for clearance, air samples are commonly collected to see if the levels in the air have been returned to background amounts.

We occasionally get calls from clients who have been told by their remediation company NOT to have a post remediation verification inspection done. They typically say it is a waste of money.  These unscrupulous companies don’t want anyone to review their work because in our experience even the best companies often miss things. You can imagine what might be missed by companies who like to cut corners! In our experience, we find something that was missed in about 50% of all post remediation verifications. This can range from small areas of missed growth or a slight elevation of airborne fungal levels to large issues like major moisture problems and mold damaged materials remaining in place.

The key goal of a mold remediation project is to return the affected areas to a “pre-loss state”. This can help avoid future issues from a problem you thought was already addressed.  One of the most compelling reasons to have PRV testing done is to provide a “clearance letter”.  This is a document you can share with the future purchaser of your home when disclosing the past mold problem.  Having an independent evaluation determine that the project was successful can put everyone’s’ mind at ease.  For all these reasons, we strongly recommend having a post remediation verification assessment done.

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”

7 thoughts on “Mold Clearance Testing

    Hello Dylan,
    I would like to have your opinion on Indoor air quality -clearance test .
    As environmental consultant i have to give exact detail recommendation for contractors during the mould remediation.
    Env. companies are following procedures differently.
    Simply, I am asking when to do air clearance test after mould remediation, if scrubber is still on negative air after 24 hrs or on re circulation air after 24 hours. Also I have a dilemma, if sampling should be done when scrubber is on of off? before turning scrubber off, we are advising to seal inlet and outlet of the scrubber with plastic and tape. Usually I went and I sampled air when scrubber was off.
    recently I was told by some of contractors to test air when scrubber is still on on re circulation and sealed. But then it can brake a machine when opening are sealed?
    Could you please let me know , what is your the best experience?
    Thank you kindly,

    Note: my website is under rebuilding at this moment.

    Viktoria Bogucka,
    Edelweiss Environmental Inc.


    I will do my best to address many of your questions. At the end of the day, each project is going to be unique and there is no perfect standard on how to perform a verification testing.

    Ideally, negative pressure is preferred to recirculation. You should not sample with the scrubber on, and has been shut down as you described. I would not run an air scrubber with the openings sealed, that is a lot of stress on the motor. By sealing the openings before shutting down the machine this reduces the chance spores are “burped” back into the air after the machine is turned off.

    I had a mold test done and it shows a high mold count within my apartment. Are these counts an immediate danger? Can the apartment be mediated making the home free of mold? I just moved into a new apartment and I am getting sick.
    From the MoldREPORT
    Overall Mold Source Assessment mold score 293
    Penicillium/Aspergillus types mold score 102
    Cladosporium species spores mold score 100
    1) Chaetomium 2) Stachybotrys mold score 293
    1) Other brown 2) Alternaria mold score 242


    I can not interpret these results in any meaningful way for a few reasons. First, none of the numbers have an associated unit with them. The most common unit for measuring mold in air samples is spores/m3. Also, there is no reference sample to compare your indoor results with. An outdoor sample should be collected at the time of testing as a reference for what should be expected in the space.

    I have a compromised immune system as well as young children. We had our house tested for mold and below is the results. My main question is….will we take mold spore aith us on our possessions when we leave? I hear so many conflicting things about this. Of course we are having the company remediate clean the air conditiong system and retest the air but what does that mean for our beds couches and clothes etc? The family room is the highest but we know we jave a leaky back door and thats probably why. The basement is finished and totally dry with a humidifier altho somedays can get a little high moisture if i forget to run it. So back to my original question….Can our possesions be washed and steam cleaned to make sure we dont take mold spores with us? We had the outside air, family room air, and basement air tested. Here are the results. Cladosporium O-360, Fam-192, Bas-130. Penicillium and Aspergillius group O-13, Fam-7900, Bas-910. Alternaria O-0, Fam-0, Bas-27. Aureobasidum O- 27, Fam-27, Bas-40. Curvularia O- 0, Fam-27, Bas-0. Pithomyces O- 27, Fam-27, Bas-40. Epicoccum O-13, Fam-27, Bas-13. Nigrospora O-27, Fam-0, Bas-0. Smuts/ pericona/ myxomycetes group O- 360, Fam-67, bas-280. Total counts O- 790, Fam-8200, Bas-1400

    The only thing that sticks out on your results to me is the level of Asp/Pen in the family room. These levels are slightly elevated. Here are a few tips for what you can do to clean items so you do not bring residual spores with you if you move. So to start, cleaning should be done outside. This is to assure that the mold that is removed does not settle back onto cleaned items. Hard surfaces can be cleaned with a damp wipe and a solution of dish soap and water. Softer items such as couches, rugs, mattresses, etc can be shaken out and cleaned carefully with a HEPA vacuum. Clothing and smaller cloth items can be washed in a washing machine. One limitation is it will be hard to tell if things have been completely cleaned since mold is microscopic and there is no sure way to determine if there are residual spores inside an item.