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ERMI Testing Vs. Air Samples

Very often we receive calls from very concerned people that need help determining if they need an Environmental Relative Moldiness Index (ERMI) test or not.  The range of knowledge in the general public for this type of test varies.  In this post, I will highlight a few points to keep in mind when deciding on doing an ERMI test.First, let me provide some information per the Environmental Protection Agency’s (EPA) website on ERMI testing.  ERMI stands for Environmental Relative Moldiness Index.  The analysis from this test can be used by researchers to estimate the levels and types of mold inside a property.  The test is done by collecting a dust sample.  Since mold spores can settle onto dust, the DNA from the mold in the dust can be identified, thereby providing information on what types of mold are present.  However (and this is highlighted in bold lettering on the EPA website), “the ERMI should be used only for research.  The ERMI has not been validated for routine public use in homes, schools, or other buildings.”  The EPA also recommends that water damage is assessed during the inspection since moisture issues are what cause most mold problems.  

Our company performs several types of mold tests including ERMI and air samples.   Air samples differ from ERMI because no settled dust is used.  Instead, air is drawn through a cassette and any spores present are deposited onto a glass slide in the cassette and ultimately viewed through a microscope.  The laboratory analysis can tell us the concentration of mold that was found in the air along with the types of mold (generally, down to the genus level).  

So the main difference is that ERMI collects spores and DNA from dust, whereas air samples collect spores from the air.  What’s the big difference?  The spores settled in the dust provide more historical information and air samples provide more current information.  Is one better?  Not really, they are just different.  Analysis between the two types is another main difference with ERMI detecting DNA via polymerase chain reaction and most air samples being analyzed via the microscope.

ERMI tests use a statistical formula to provide a single ERMI number.  Interpreting that ERMI number can be a big challenge.

When potential clients ask us to perform an ERMI test, we first recommend that we do a visual inspection and moisture evaluation.  We recommend that they also do more traditional spore trap testing alongside ERMI.  This way we can provide them with both historical and current information regarding the mold levels in their home.   

This blog article is just scratching the surface about ERMI.  Please leave a comment if you have any questions.

EPA Website: https://www.epa.gov/sites/production/files/2016-01/documents/moldiness_index_1.pdf

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