- What the Title Actually Means
- Who Issues the Credential
- What a CMI Does in the Field
- The Six Exam Domains
- Who Qualifies to Apply
- Exam Format and Test-Day Logistics
- Fees and the Two-Year Cycle
- CMI Compared With Look-Alike Credentials
- What the Published Pass Data Does and Does Not Say
- Sequencing Your Preparation by Domain
- Frequently Asked Questions
- CMI here means Council-certified Microbial Investigator, issued through the American Council for Accredited Certification (ACAC).
- The exam has 100 multiple-choice questions, three hours, closed book, with a 75% passing score.
- Six formal domains run from biological agents through Health & Safety; ACAC publishes no domain weights.
- The initial two-year term costs $500: a $100 exam fee plus a $400 certification fee.
What the Title Actually Means
A CMI is a Council-certified Microbial Investigator: a professional who has been vetted by a certification board to design, conduct and interpret microbial sampling regimens in indoor environments. The acronym is crowded. Other fields use "CMI" for entirely unrelated credentials, so a quick search can send you to the wrong place. This article covers only the ACAC credential, and everything below refers to that one.
If you want a quick orientation on the terminology before going deeper, our short explainers on what CMI stands for and what CMI certification is cover the basics. This piece goes further into what the credential demands and how the exam is built.
Who Issues the Credential
The certification is administered by the American Council for Accredited Certification (ACAC) through its CMI Certification Board. The program carries accreditation from the Council for Engineering and Scientific Specialty Boards (CESB), which matters because it signals that the program's exam development and governance have been reviewed by an outside accrediting body rather than simply self-declared.
Exam delivery is handled by Kryterion, Inc. ACAC and Kryterion play different roles: ACAC decides who is eligible and who is certified, while the testing vendor handles the proctored sitting. Passing the exam alone does not make you a CMI. The certification board must also approve your application, and ACAC states that approval is unanimous-board approval after review of your documentation.
What a CMI Does in the Field
The certification centers on the investigative side of indoor microbial work: deciding what to sample, how to sample it, what the results mean, and what a sensible response looks like. That puts the credential in the orbit of several kinds of practitioners:
- Industrial hygienists and environmental consultants who evaluate buildings after moisture events
- Mold assessors and inspectors who plan sampling and write findings
- Engineers, architects and building-science professionals who diagnose moisture and contamination problems
- Restoration-industry professionals who need to interpret sampling data and verify that remediation worked
The common thread is that a CMI is expected to reason about evidence. A candidate must be able to explain why one sampling approach suits a particular building question, how to interpret results against what would be expected in a comparison location, and how to communicate limitations honestly. If you are exploring where this leads professionally, see our overview of CMI jobs. We do not cite a CMI-specific salary figure, because no reliable survey isolating ACAC CMI holders has been verified; our CMI salary guide explains how to think about compensation without leaning on invented numbers.
The Six Exam Domains
ACAC's formal exam-domain chart for the CMC and CMI examinations, approved February 21, 2024, applies to the CMI and lists six headings. The numbered columns in that chart are subdomains, not additional domains. ACAC does not publish percentage weights, so any site claiming an "official" weighting for a given domain is not citing the issuer. For a longer walkthrough, see our complete guide to all six CMI content areas.
Domain 1: Scientific knowledge of biological agents
The foundation: what the organisms are, how they grow and what conditions support or limit them.
- Fungal and bacterial characteristics relevant to indoor environments
- Moisture, nutrients and conditions that drive amplification
- How biological agents become airborne or settle on surfaces
Domain 2: Potential health effects and risks associated with exposure
Connecting exposure to human health without overstating what sampling data can prove.
- Common exposure pathways and susceptible populations
- The difference between hazard and risk
- What an investigator can and cannot say about causation
Domain 3: Principles of Microbial Investigation
The reasoning layer: how an investigation is framed before any sample is taken.
- Building and occupant history, visual inspection and moisture assessment
- Forming hypotheses about sources and pathways
- Documenting findings so conclusions are traceable
Domain 4: Principles of Microbial Sampling
The core technical domain and the one that mirrors the eligibility requirement directly, since applicants must show they can design, conduct and interpret sampling regimens.
- Choosing air, surface and bulk approaches for the question being asked
- Controls, comparison samples and sampling strategy
- Handling, chain of custody and laboratory interaction
- Interpreting results and recognizing their limitations
Domain 5: Principles of Microbial Remediation
What a defensible response looks like once a problem is identified, and how to judge whether it worked.
- Water-damage response concepts and mold remediation principles
- Containment, source removal and drying
- Post-remediation evaluation
Domain 6: Health & Safety
Protection of workers and occupants during investigation and remediation, with respiratory protection as a recurring theme.
- Respirator selection logic and respiratory protection programs
- Hazard recognition on investigation sites
- Protective measures proportionate to conditions
Who Qualifies to Apply
Eligibility is built around documented field experience, and it is stricter than many first-time candidates expect. There are two pathways:
- Education plus sampling experience: a related two-year postsecondary degree, or an equivalent 15 qualifying college credits, plus at least one year of documented microbial sampling.
- Diploma plus consulting experience: a high school diploma or GED plus two years of consulting experience in microbial sampling.
Related fields named by ACAC include microbiology, engineering, science, architecture and industrial hygiene. ACAC's eligibility FAQ adds an important clarification: at least one full year of actual field experience is required regardless of how many college credits you hold. Credits cannot substitute for that year.
The application also requires four project sheets, applicable academic evidence and experience verification. The project sheets are where you demonstrate designing, conducting and interpreting sampling regimens on real work. Start gathering these early, since they depend on your own case records rather than on study time. The more advanced education and experience pathways that exist for ACAC's related credential in microbial consulting do not transfer to the CMI. For full details, see our CMI requirements guide.
Exam Format and Test-Day Logistics
| Element | What ACAC and its testing vendor specify |
|---|---|
| Delivery vendor | Kryterion, Inc. |
| Length | 100 multiple-choice questions, at least four answer options each |
| Time | Three hours, computer-delivered |
| Book policy | Closed book |
| Passing score | 75%, set by the Modified Angoff method |
| Practical component | None described |
| Scoring split | Scored versus unscored items not published |
| Delivery modes | Proctored testing center or online video proctoring |
The handbook describes a fixed question set with randomized question and answer order, an immediate electronic score and an emailed result. Adaptive testing is not described. Calculator permission could not be verified, so confirm with ACAC before test day rather than assuming either way. For more on the cut score, see what you need to pass.
Testing-center and online requirements
- Testing-center candidates need two government-issued IDs, one of them a photo ID.
- Online candidates supply their own computer, an approved webcam and a private location.
- ACAC specifies at least 2 Mbps upload and download speed for online delivery, and excludes phones and tablets.
- Arrival guidance conflicts: ACAC's exam page says 15 minutes early, while the handbook says 30. Plan for the longer window.
Because there is no practical assessment, the written exam carries the whole technical-judgment load. Questions reward applied reasoning (what would you sample, what does this result support, what is the safest next step) more than pure recall. To get used to that style, work through the scenario-based items on our CMI practice test site.
Fees and the Two-Year Cycle
| Item | Amount (USD) |
|---|---|
| Examination fee | $100 |
| Certification fee | $400 (includes a $100 nonrefundable processing fee) |
| Initial two-year term total | $500 |
| Retake | $100 |
| Renewal | $400 |
The $100 processing fee sits inside the $400 certification fee; it is not an additional charge. ACAC publishes no separate member and nonmember schedule. See our pricing breakdown for budgeting detail.
Application timing and a documented conflict
The application is completed online with required email verifications, and ACAC's application page describes a six-month window that includes the exam, with unanimous board approval and board meetings every four to six weeks. The candidate handbook instead describes 90 days, notarized forms or employer affidavits, and board meetings roughly every four weeks. These issuer discrepancies are unresolved, so confirm the current rules directly with ACAC before you start and build in extra time. Our exam dates and scheduling guide covers planning around this.
Renewal
Certification lasts two years. ACAC's recertification procedures specify 40 recertification credits (RCs) per term: 10 for continued field activity and 30 for professional development, with an attestation and retained documentation in case of audit. Other ACAC materials word this differently (the handbook speaks generally of 40 RCs, and the program page refers to 20 professional-development hours per year), so rely on the detailed procedures document and confirm the current requirement.
CMI Compared With Look-Alike Credentials
Candidates often confuse the CMI with neighbors in the same field. Keep the distinctions straight:
| Credential | Relationship to the CMI |
|---|---|
| ACAC CMI (this article) | Investigation and sampling focus; the credential covered here |
| ACAC CMC | A sibling credential sharing the same published domain chart; its advanced education/experience pathways do not apply to the CMI |
| Other issuers' mold inspector credentials | Separate programs with their own bodies, exams and fees; not interchangeable with the CMI |
| Provider-run mold inspector courses | Training products with their own tests; a course exam is not the ACAC CMI exam |
One practical trap: some training providers describe multi-day mold inspector classes that end in the provider's own exam. Course hours and a provider exam are not the CMI written exam's duration, and they are not a separate CMI practical assessment. If a course is part of your plan, check ACAC's accredited-training directory and verify that the content maps to all six official domains.
What the Published Pass Data Does and Does Not Say
ACAC's 2025 Exam Pass Ratio reports an 88% pass ratio for the CMI, with 22 passes from 25 examinations. That is an issuer-published figure, which makes it more trustworthy than third-party claims, but read it carefully:
- The sample is small (25 sittings), so a single result shifts the percentage noticeably.
- The report includes retakes and state-licensing-only examinations, and does not disclose how many CMI sittings fall into either category.
- It therefore is not a first-attempt pass rate and does not predict your individual result.
- No 2026 pass rate has been verified.
Do not confuse the 88% observed pass ratio with the 75% passing score. The first describes how a group performed in 2025; the second is the cut score you must reach on your own exam. Some third-party sites claim ACAC publishes no CMI pass rates, which is incorrect. For deeper context, see what the pass-rate data shows and our difficulty guide.
ACAC's activity report as of December 31, 2025 lists 25 CMI applicants, 59 recertifications and 166 current certifications. That shows a small, specialized credential community rather than a mass-market certification, which is useful context when judging whether the credential is worth it for your career.
Sequencing Your Preparation by Domain
Because there are no official weights, avoid allocating study time based on a publisher's percentages; those describe the publisher's practice materials, not the exam. A sensible approach is to follow the dependency order of the content, since later domains assume earlier ones. Here is one four-week arrangement; adapt it to your own strengths and to how much of the reference list you have already read. Our full CMI study guide expands on resources.
Biological agents and health effects (Domains 1-2)
- Build the vocabulary and growth-condition logic that everything else leans on
- Practice separating hazard from risk in written explanations
Investigation and sampling (Domains 3-4)
- Spend the most hands-on time here; it mirrors the sampling experience your application already requires
- Work scenario questions on method selection, controls and interpretation
Remediation (Domain 5)
- Read the water-damage and mold-remediation standards in your chosen editions
- Connect remediation steps back to what sampling should show afterward
Health & Safety, then mixed review (Domain 6)
- Drill respirator selection logic and the respiratory protection standard guidance
- Finish with timed, mixed-domain sets sized like the real 100-question, three-hour sitting
Key Takeaway
Run at least one full-length timed set before test day. Three hours for 100 questions is generous on paper, but scenario items reward careful reading, and a timed rehearsal shows you whether your pacing holds. A one-page fact review is useful for the final day, and the practice questions on our main site let you check your readiness domain by domain.
Frequently Asked Questions
It stands for Council-certified Microbial Investigator, a credential issued through the American Council for Accredited Certification (ACAC) and its CMI Certification Board. It is unrelated to other certifications that happen to share the acronym.
ACAC describes only the written examination: 100 multiple-choice questions over three hours, closed book. No separate practical assessment is described. Your hands-on competence is evaluated through the four project sheets and experience verification in the application.
No. ACAC requires at least one full year of actual field experience in microbial sampling regardless of college credits. The alternative route is a high school diploma or GED with two years of consulting experience in microbial sampling.
The initial two-year term totals $500: a $100 examination fee plus a $400 certification fee that includes a $100 nonrefundable processing fee. A retake costs $100 and renewal costs $400.
No. The 2025 figure of 22 passes from 25 examinations includes retakes and state-licensing-only sittings, so it is not a first-attempt rate and cannot predict an individual outcome. Your result depends on your preparation and on reaching the 75% passing score.