Based on widely published data by EPA researchers and HUD's 2006 American Healthy Household Survey, the test has been developed as a tool to assess the potential risk of indoor mold growth and the associated health effects on occupants.
To use this tool most effectively, the obtained ERMI should be compared to a national database. Rates were determined using this method for 1,096 homes in the U.S. as part of the 2006 HUD American Healthy Homes Survey. Individual rates, ranked from lowest to highest, were used to create a national mold index scale. relative (RMI).
In early USEPA studies, concentrations of different mold species were compared in “mold homes” (homes with visible mold growth or a history of water damage) and “reference homes” (homes without visible mold). Based on those results, mold species were selected and grouped into those with higher concentrations in homes with mold (group 1) and those with lower concentrations (group 2). To calculate the ERMI, the individual concentrations of the detected mold species are log transformed and the sum of the group 2 logs is subtracted from the sum of the group 1 logs.
List of mold species included in an ERMI report:
Group 1: Water Damage Molds
- Aspergillus flavus/oryzae
- Aspergillus fumigatus
- Aspergillus niger
- Aspergillus ochraceus
- Aspergillus penicillioides
- Aspergillus restrictus
- Aspergillus sclerotiorum
- Aspergillus sydowii
- Aspergillus unguis
- Aspergillus versicolor
- Aureobasidium pullulans
- Chaetomium globosum
- Cladosporiumsphaerospermum
- Eurotium (Asp. amstelodami
- Paecilomyces variotii
- Penicillium brevicompactum
- Penicillium corylophilum
- Penicillium crustosum
- Penicillium purpurogenum
- Penicillium Spinulosum
- Penicillium variabile
- Scopulariopsis brevicaulis/fusca
- Scopulariopsis chartarum
- Stachybotrys chartarum
- Trichodermaviride
- Wallemia sebi
Group 2: Common interior molds
- Acremonium strictum
- Alternaria alternata
- Aspergillus ustus
- Cladosporium cladosporioides1
- Cladosporium cladosporioides2
- Cladosporium herbarum
- Epicoccum nigrum
- Mucor amphibiorum
- Penicillium chrysogenum
- Rhizopus stolonifer
Ermi Chart
The following table helps interpret the graph.
| Quartile |
Zone |
Percentage |
ERMI value |
Relative Mold |
| Q1 |
Green |
25% household |
Between -10 to -4 |
Low |
| Q2 |
Amber |
25% household |
Between -4 to 0 |
Low to medium |
| Q3 |
Amber |
25% household |
Between 0 to 5 |
Medium to high |
| Q4 |
Red |
25% household |
Between 5 to 20 |
High |
|
Red |
|
Greater than 20 |
Very high |
Types of samples:
Swiffer Fabric Sampling
A clear limitation of ERMI vacuum sampling is that many homes do not have carpeting and many people who are susceptible to mold-related illnesses have chosen to have hardwood or tile floors. As a result, the “Swiffer Fabric Method” was developed. The important issue in sampling is that the procedure must collect dust that is representative of the area sampled, providing a sufficient quantity of dust so that laboratory analysis can be successful.
