Mold: More than a Number

Viable Air Sample for Mold

You may take air samples when trying to identify a hidden mold problem.  The total number of spores in the complaint area should be compared to indoor and outdoor controls, or more accurately, “references”.  For example, if you find 10,000 spores per cubic meter in the complaint area, and only 1,000 in the reference samples, there is a high likelihood of indoor amplification.

Although it’s important to look at the total numbers, it’s critical to also make comparisons of the types of mold.  Each type of mold is unique.  There are some types that will predominantly grow on leaves outdoors.  These don’t have an apetite for building materials and will rarely be found growing indoors.  Other types, however, do have the enzymes needed to digest common building materials in its quest for more food.

A few references can help you make a distinction between types of mold typically found outdoors and those that can grow on building materials.  I’ll summarize a few of these references below:

  • EPA BASE Study. In the 90’s, the Environmental Protection Agency carried out the Building Assessment Survey and Evaluation (BASE) study which performed a thorough indoor air quality assessment in 100 office buildings.  A document published from the study describes how the EPA categorized their air sampling results, placing each type into one of four fungal groupings.  Click Fungal Groupings to download the PDF from the EPA website.
  • IESO Standard.  The Indoor Environmental Standards Organization (IESO) published a non-ANSI standard in 2002 titled, “Standards of Practice for the Assessment of Indoor Environmental Quality”.  The standard identifies genera of mold that may indicate the potential for moisture and mold.  The list includes:
    • Aureobasidium
    • Aspergillus
    • Chaetomium
    • Fusarium
    • Penicillium
    • Trichoderma
    • Stachybotrys
    • Ulocladium
  • Sampling and Analysis of Indoor Microorganisms” is an excellent book edited by Chin Yang. In the chapter describing microscopic methods, the book identifies the following genera as water damage indicators:
    • Chaetomium
    • Stachybotrys
    • Memnoniella
    • Ulocladium
    • Aspergillus-Penicillium Group is also mentioned
  • ERMI.  Researchers from EPA and HUD developed the Environmental Relative Moldiness Index (ERMI) to help identify problem homes.  I’ll describe the whole ERMI process in a future post, but for now we’ll only look at its fungal categories.
    • Water damage indicators: Stachybotrys chartarum, Chaetomium globosum, Cladosporium sphaerospermum, Aspergillus versicolor, Eurotium (A.)amstalodami, Penicillium variabile, Aspergillus flavus, Aspergillus restrictus, Penicillium crustosum, Penicillium chrysogenum, Aspergillus niger, Aspergillus sclerotiorum, Penicillium purpurogenum, Aspergillus fumigatus, Penicillium corylophilum, Aureobasidium pullulans, Aspergillus ochraceus, Penicillium brevicompactum, Paecilomyces variotii, Aspergillus sydowii, Penicillium spinulosum, Wallemia sebi, Aspergillus unguis, Scopulariopsis brevicaulis, Scopulariopsis chartarum, Aspergillus penicillioides, Trichoderma viride.
    • “Normal” species: Acremonium strictum, Alternaria alternata, Aspergillus ustus, Cladosporium cladosporioides v1, Cladosporium cladosporioides v2, Cladosporium herbarum, Epicoccum nigrum, Mucor & Rhizopus group, Penicillium chrysogenum, Rhizopus stolonifer

Hopefully the references above will help you better distinguish common outdoor fungi and those that may indicate indoor air contamination.

Do you know of any additional references that discuss this topic?  Please leave a comment below!

By Ian Cull

I'm I.A.N. the Indoor Air Nerd. I'm a speaker and consultant on indoor air quality issues. To learn more about me, click "about" at the top of this page.

9 replies on “Mold: More than a Number”

How would you use the ERMI data in an investigation? If you have enough time to explain ERMI further I would appreciate it.

Thanks! Ryan


I am unable to find the blog regarding ERMI and answering Ryan’s question after scouring the website. Will you please provide a link to the blog you mentioned here?


I’ve done my own research over the years and worked with various types of mold tests for personal health issues. I wanted to share a my recent experience mold testing. I am not a professional, just a person with severely debilitating health issues and many related to mold exposure.

First, multiple trusted physicians pointed me to and that website talks about the ERMI, HERTSMI (or HERTSMI-2), and Mycometrics lab with much of the information provided by Dr. Ritchie Shoemaker. This website has some very useful information.

I moved cities, got rid of all my furniture and books, and uprooted my life due to significant problems with mold and got in touch with one of the “Shoemaker Protocol Certified Physicians” with a background at Harvard and Hopkins. She had recommended to just do a HERTSMI dust sample test to decide what apartments were likely safe/not safe for me and the website gives information on how to score the test here: with a disclaimer on a note “*Any score under 11 has been safe to date.”

Don’t stop reading yet if this applies at all to you!

I ran multiple HERTSMIs on different potential rentals and after ruling out a few due to high HERTSMI scores I found a place that was very mold-consious and proactive about preventing mold. I did a HERTSMI test and it got a score of 6 – okay, right? Well, I also had the lab test an additional species that I have not been able to find ranges on because I have a Class IV IgE allergy to it. The number seemed high although the HERTSMI (with a disclaimer) leads one to believe this place was “safe”.

Out of frustration regarding the additional species I spent an extra $300 and had the lab run a full ERMI, Environmental Relative Mold Index, (36 species as opposed to 6) and my results were shocking to me and the property management: 5.66, meaning according to this test over 75% of homes in the US have less mold than this one and definitely not recommended for someone concerned about mold.

So before you content yourself with running a HERTSMI if you have health concerns with mold, even if your mold-knowledgeable physician recommends it, consider that had I not tested and been concerned with a specific additional species, I (with my mold biotoxin illness, genes, and allergies) would have moved in confidently to a significantly moldy home.

My personal experience me leads me to recommend *in my non-professional opinion* to consider a different mold test option before using the HERTSMI as your only test to give you safety answers if you too have significant problems with mold.

I’m glad to provide my test results if someone would like to see them.

I have nothing negative to say about the lab or Dr. Shoemaker, just a warning from my personal experience about counting on the HERTSMI to give you a big enough picture for safety (the disclaimer is there for a reason and I never anticipated it being such a potentially big reason!).

Thank you and I wish you all the best.

In the Maryland tri-state area I can recommend a mold-inspector used by my primary care doctor and myself who was incredibly professional and thorough (mold dog and EMSL Labs with a air sample after visual inspection who provided practical recommendations without medical advice).

Tessa, thank you for making this detailed post. I ran an ERMI test on my house which failed with a 6.3 and I am in the process of relocating. This is invaluable info for me!!

Tessa, Just a quick comment while the HERTSM2 has its place, as individuals you have to understand that Dr Shoemaker is utilizing that as a tool, its not the complete tool kit but using an air sample as an indicator of exposure is very short sighted. There are a number of potentially pathogenic moulds which are not easily airborne and then you have bacteria growing sided by side and if you don’t culture the bacteria you wouldn’t even know that its there- some moulds also are infected by mycoviruses which can replicate and also be perhaps in some diseases of greater importance than high levels of moulds. What this is simply saying is that I love the HERTSME 2 but I only use it as one part of my investigations.
Downunder (where we spell mould correctly)

Ian, you call yourself a Professional Engineer but you are not commenting on the need of a control in mold testing.

All, be very careful running one of these tests yourself, there are a lot of people stealing your money off of these home tests. Do your research and see how one mold site may reference another site for testing….but then you find out all these people are in business together. I’m not saying this is the case for Ian, but the more I have gone down these paths, the more frustrating it is. You can not conclude anything from mold test without using the correct engineering experimentation techniques of having controls to compare against. Also be careful of so called acceptable ‘ranges’ out there, these are less than scientific. I could go on and on, but I will just say do your research and be careful with your money.

You must have missed the second sentence where I say, “The total number of spores in the complaint area should be compared to indoor and outdoor controls, or more accurately, “references”.

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