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100+ Free CMI Practice Questions

Pass your ACAC Council-certified Microbial Investigator (CMI) exam on the first try — instant access, no signup required.

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An inspector documents elevated indoor counts of a single 'Aspergillus restrictus group' species via qPCR but spore-trap counts are normal. What is the best interpretation?

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2026 Statistics

Key Facts: CMI Exam

100

Exam Questions

ACAC Candidate Handbook

75%

Passing Score

ACAC Candidate Handbook

3 hours

Exam Duration (closed-book)

ACAC Candidate Handbook

$500

Total Fee ($400 cert + $100 exam)

ACAC fees page

2 years

Field Experience Required (1 yr with degree)

ACAC

15 L/min

Air-O-Cell Standard Flow Rate

IICRC S520

40 RCs

Recertification Credits per 2-year Cycle

ACAC

The ACAC CMI (Council-certified Microbial Investigator) is the professional certification for mold/microbial investigators issued by the American Council for Accredited Certification (ACAC). It is broader than the residential-focused CRMI and serves investigators working across residential, commercial, and institutional settings. The 100-question, 3-hour, closed-book exam (75% passing score) covers microbial ecology and morphology, current sampling technology (Air-O-Cell spore traps at 15 L/min, Andersen N6 viable sampling, ERMI), instrument calibration, ANSI/IICRC S520, ANSI/IICRC S500, ASTM D7338, and professional ethics. Prerequisites: 2 years field experience in microbial sampling (1 year with a qualifying 2-year degree). Certification is valid for 2 years and requires 40 Recertification Credits for renewal.

Sample CMI Practice Questions

Try these sample questions to test your CMI exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which ANSI consensus standard is the primary reference for professional mold remediation in the United States?
A.ANSI/IICRC S500
B.ANSI/IICRC S520
C.ASTM D7338
D.ASTM E2418
Explanation: ANSI/IICRC S520 (Standard for Professional Mold Remediation) is the U.S. consensus standard for mold remediation, covering assessment principles, condition classifications (1, 2, 3), engineering controls, PPE, and post-remediation verification. CMI candidates must know its scope and terminology.
2Which ASTM standard provides a guide specifically for the assessment of fungal growth in buildings?
A.ASTM D7338
B.ASTM E1527
C.ASTM D6245
D.ASTM E2418
Explanation: ASTM D7338 (Standard Guide for Assessment of Fungal Growth in Buildings) describes the methodology for visual inspection, moisture assessment, sampling, and reporting in fungal investigations. CMIs use it as a procedural framework alongside ANSI/IICRC S520.
3Stachybotrys chartarum is best characterized as:
A.A xerophilic mold that grows readily on dry surfaces
B.A hydrophilic mold requiring prolonged wetness on cellulose substrates
C.A common outdoor mold rarely found indoors
D.A yeast rather than a filamentous mold
Explanation: Stachybotrys chartarum is hydrophilic (high water-activity demand, typically aw > 0.90) and grows on cellulose-rich materials such as paper-faced drywall, ceiling tiles, and wood after sustained wetting (often beyond 72 hours). It produces macrocyclic trichothecene mycotoxins.
4Which mycotoxin is most commonly associated with Aspergillus versicolor?
A.Aflatoxin B1
B.Sterigmatocystin
C.Trichothecenes
D.Ochratoxin A
Explanation: Aspergillus versicolor is well known for producing sterigmatocystin, a hepatotoxic and possibly carcinogenic (IARC Group 2B) mycotoxin. Finding A. versicolor in indoor environments often signals chronic water damage and warrants further investigation.
5An Air-O-Cell spore trap cassette is typically operated at what flow rate?
A.5 L/min
B.10 L/min
C.15 L/min
D.28.3 L/min
Explanation: Air-O-Cell cassettes are designed for 15 L/min, with typical sampling times of 5-10 minutes (75-150 L sampled volume). The flow must be calibrated with a primary standard (e.g., bubble meter) before and after sampling.
6When using an Air-O-Cell cassette at 15 L/min for 5 minutes, what is the sampled air volume?
A.15 L
B.30 L
C.75 L
D.150 L
Explanation: Flow × time = 15 L/min × 5 min = 75 L. This is a common default sample volume. Doubling the time to 10 minutes yields 150 L. The CMI must document calibrated flow, time, and resulting volume.
7The Andersen N6 single-stage impactor is most appropriate for which type of sampling?
A.Non-viable spore trap analysis
B.Viable (culturable) bioaerosol sampling
C.Surface tape lift collection
D.Bulk material sampling
Explanation: The Andersen N6 is a single-stage viable impactor that draws air through 400 calibrated holes onto a culture plate (e.g., MEA, DG18). It is used to enumerate culturable fungi (CFU/m³). It does not capture dead spores.
8Under ANSI/IICRC S520, which condition describes an indoor environment with actual mold growth and associated spores?
A.Condition 1
B.Condition 2
C.Condition 3
D.Condition 4
Explanation: S520 defines: Condition 1 = normal fungal ecology, Condition 2 = settled spores/fragments without actual growth, Condition 3 = actual mold growth and associated spores. There is no Condition 4 in S520.
9An indoor air spore trap shows Penicillium/Aspergillus at 4,500 spores/m³ while the simultaneous outdoor sample reads 200 spores/m³. What is the most appropriate initial interpretation?
A.Normal — indoor counts always exceed outdoor
B.Indoor amplification likely; investigate further
C.Sample is invalid because Pen/Asp is a single genus
D.The lab made an error; reject the result
Explanation: Healthy indoor environments typically show Penicillium/Aspergillus equal to or less than outdoor levels with similar genera distribution. A 22.5× elevation strongly suggests indoor amplification (a hidden moisture source). The CMI should investigate moisture, hidden cavities, and HVAC contamination.
10Which water activity (aw) threshold is generally considered the lower limit for most mold growth on building materials?
A.0.50
B.0.65
C.0.75
D.0.95
Explanation: Most molds require aw of approximately 0.75 or higher to grow. Xerophilic species (e.g., some Aspergillus, Wallemia, Eurotium) can grow at 0.75-0.80; hydrophilic species (e.g., Stachybotrys, Chaetomium) require aw > 0.90.

About the CMI Exam

The CMI credential certifies competency in microbial investigation including sampling technology, investigation methodology, mold ecology, lab interpretation, and professional reporting per ANSI/IICRC S520 and ASTM D7338.

Questions

100 scored questions

Time Limit

3 hours

Passing Score

75%

Exam Fee

$500 (certification + exam) (ACAC (American Council for Accredited Certification))

CMI Exam Content Outline

~25%

Microbial Ecology & Morphology

Indicator molds, water activity, xerophilic vs hydrophilic species, mycotoxins, fungal growth requirements

~25%

Sampling Technology & Methodology

Air-O-Cell spore traps (15 L/min), Andersen N6 viable sampling, surface sampling (tape lift, swab, bulk), ERMI/HERTSMI, calibration

~20%

Investigation Protocols & Building Science

Visual inspection, moisture mapping, infrared thermography, vapor drive, HVAC assessment, hidden mold

~15%

Standards & Reference Documents

ANSI/IICRC S520, ANSI/IICRC S500, ASTM D7338, EPA, NIOSH, NYC DOH guidance

~15%

Reporting, QA/QC & Professional Conduct

Chain of custody, lab QA/QC, report writing, sampling strategy, ACAC Code of Ethics, conflict of interest

How to Pass the CMI Exam

What You Need to Know

  • Passing score: 75%
  • Exam length: 100 questions
  • Time limit: 3 hours
  • Exam fee: $500 (certification + exam)

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

CMI Study Tips from Top Performers

1Master the ANSI/IICRC S520 mold condition classifications (Conditions 1, 2, 3) and corresponding PPE requirements — these are foundational exam concepts
2Know the Air-O-Cell cassette standard flow rate (15 L/min) and how to calculate sampled volume; understand the Andersen N6 viable sampler operation
3Understand water activity (aw) thresholds — xerophilic molds (Aspergillus, Penicillium) grow at lower aw than hydrophilic species (Stachybotrys, Chaetomium)
4Memorize the key indicator molds: Stachybotrys chartarum (hydrophilic, cellulose), Chaetomium globosum (hydrophilic), Aspergillus versicolor (sterigmatocystin producer)
5Study ASTM D7338 assessment methodology — visual inspection, sampling rationale, and report content requirements
6Understand QA/QC: field blanks, chain-of-custody, lab accreditation (AIHA-LAP, EMLAP), and analyst qualifications

Frequently Asked Questions

What is the CMI exam?

The CMI (Council-certified Microbial Investigator) exam is administered by ACAC (American Council for Accredited Certification). It tests competency in mold/microbial investigation including ecology, sampling technology, instrument calibration, ANSI/IICRC S520 standards, ASTM D7338 assessment methodology, and professional ethics.

How many questions are on the CMI exam?

The ACAC CMI exam contains 100 multiple-choice questions delivered as a 3-hour, closed-book examination through Kryterion testing centers. A score of 75% is required to pass.

What is the passing score for the CMI exam?

ACAC requires a score of 75% to pass the CMI exam. Scores are graded electronically at the testing facility and are available to candidates immediately upon completion.

What are the prerequisites for the CMI credential?

ACAC requires 2 years of documented field experience in microbial sampling, reduced to 1 year with a 2-year post-secondary degree (15 credit hours) in microbiology, engineering, science, architecture, industrial hygiene, or a related science. Candidates must also agree to the ACAC Code of Ethics.

How is the CMI different from the CRMI?

The CRMI (Council-certified Residential Mold Inspector) is focused on residential mold inspection, while the CMI (Council-certified Microbial Investigator) is broader in scope and applies to investigators working in residential, commercial, and institutional settings. The CMI has higher experience requirements and a more rigorous knowledge base.

How long is the CMI certification valid?

The CMI certification is valid for 2 years from the date of issue. Holders must accumulate 40 Recertification Credits (RCs) — each representing 1 hour of continuing education — prior to expiration to maintain the credential.

How long should I study for the CMI exam?

Most candidates prepare for 80-120 hours over 6-10 weeks. Focus on indicator molds and water activity, Air-O-Cell and Andersen N6 sampling protocols, ANSI/IICRC S520 condition classifications, and ASTM D7338 assessment methodology. Complete at least 100 practice questions before exam day.