- Which CMI This Sheet Covers
- The One-Glance Exam Snapshot
- The Six Official Domains at a Glance
- Fees, Terms and Renewal Numbers
- Eligibility and Application Facts
- The Reference Library to Know
- Pass Rate and Passing Score, Kept Separate
- Test-Day Logistics and Documented Conflicts
- A Domain-Ordered Review Sequence
- Quick Answers (FAQ)
- The exam is 100 multiple-choice questions in three hours, closed book, with a 75% passing score.
- Six official domains exist, and ACAC publishes no percentage weights for any of them.
- Initial cost is $500 for a two-year term: a $100 exam fee plus a $400 certification fee.
- ACAC's 2025 report shows 22 passes from 25 CMI exams (88%), including retakes and licensing-only sittings.
Which CMI This Sheet Covers
Several credentials share the acronym "CMI," so start by pinning down the one this page covers. Everything below concerns the Council-certified Microbial Investigator, issued 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). If you need a primer on the name itself, see What Does CMI Stand For? and What Is CMI Certification?.
The credential sits in the microbial consulting and investigation field. It is a written, computer-delivered exam, and no separate practical assessment is described. Mold inspector credentials from other issuers, and course-provider exams that carry their own titles, are different products. Do not mix their fees, dates or formats into your planning.
The One-Glance Exam Snapshot
| Item | Verified Fact |
|---|---|
| Issuer | ACAC, CMI Certification Board |
| Test vendor | Kryterion, Inc. |
| Questions | 100 multiple-choice, at least four answer options each |
| Time | Three hours, computer-delivered |
| Book policy | Closed book |
| Passing score | 75%, set with the Modified Angoff method |
| Scored vs. unscored split | Not published |
| Practical component | None described |
| Delivery | Proctored testing center or online with video proctoring |
| Results | Immediate electronic score and an emailed result |
The handbook describes a fixed question set with randomized question and answer order. Adaptive testing is not described. Calculator permission is unverified, so confirm it with ACAC before test day rather than assuming either way. For a deeper look at the format and what makes it demanding, read How Hard Is the CMI Exam?.
The Six Official Domains at a Glance
The current linked formal chart is titled "ACAC, CMC and CMI Examinations," approved February 21, 2024. It expressly applies to CMI and supplies six exam headings. Its columns numbered 1 through 7 hold subdomains, not seven extra domains. No official weights are published, so you cannot say which domain is "biggest." Some third-party sites list allocations such as 25/25/20/15/15; those describe the publishers' own practice resources, not the real exam.
Domain 1: Scientific knowledge of biological agents
The biology foundation for everything else.
- Be able to describe the organisms and biological contaminants encountered in indoor environments.
- Know how growth, amplification and dispersal relate to moisture and building conditions.
- Expect scenario questions that start from biology and end at a field decision.
Domain 2: Potential health effects and risks associated with exposure
Linking exposure to outcomes without overclaiming.
- Understand exposure routes and why susceptibility differs among occupants.
- Practice distinguishing what evidence can support from what it cannot.
- Be ready to word conclusions cautiously and defensibly.
Domain 3: Principles of Microbial Investigation
The investigative process from complaint to conclusion.
- Know how to structure an inspection and document observations.
- Understand building science context, including water intrusion and moisture sources.
- Practice forming a hypothesis, testing it and interpreting results.
Domain 4: Principles of Microbial Sampling
The heart of the eligibility requirement, since applicants must show they can design, conduct and interpret sampling regimens.
- Match the sampling method to the question being asked.
- Understand why sample design, controls and comparisons matter to interpretation.
- Know the limits of any single result.
Domain 5: Principles of Microbial Remediation
What good remediation looks like and how to evaluate it.
- Know the standards behind water damage restoration and mold remediation (see the reference list below).
- Understand containment concepts and how clearance is judged.
- Be able to tell a sound remediation plan from a weak one.
Domain 6: Health & Safety
Worker and occupant protection, tied to the respiratory-protection references.
- Know respirator selection logic and the elements of a respiratory protection program.
- Understand hazard recognition on investigation sites.
- Do not skip this domain: the handbook's shorter five-topic summary omits it, but the formal chart includes it, and the chart controls.
For subdomain-level detail, see the CMI Exam Domains Guide.
Fees, Terms and Renewal Numbers
| Item | Amount (USD) | Note |
|---|---|---|
| Examination fee | $100 | Part of the initial total |
| Certification fee | $400 | Includes a $100 nonrefundable processing fee, not an extra charge |
| Initial total | $500 | Covers the initial two-year term |
| Retake | $100 | Per retake |
| Renewal | $400 | Every two years |
No separate member versus nonmember fee schedule is published. Budget for the full $500 up front, plus the cost of your reference books and any prep materials. A fuller breakdown lives in the CMI Certification Cost guide.
Renewal in brief
Certification runs two years. ACAC's Recertification Procedures call for 40 recertification credits (RCs): 10 for continued field activity and 30 for professional development during the term. You attest and retain documentation in case of audit, and a current photo is requested.
Eligibility and Application Facts
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 experience.
- Experience-heavy route: a high school diploma or GED plus two years of consulting experience in microbial sampling.
Related fields include microbiology, engineering, science, architecture and industrial hygiene. ACAC's eligibility FAQ adds that at least one full year of actual field experience is required regardless of college credits. Candidates must demonstrate designing, conducting and interpreting microbial sampling regimens, and the application requires four project sheets, applicable academic evidence and experience verification.
Advanced education and experience pathways that belong to the CMC credential do not transfer to CMI, so ignore any CMC-specific guidance you encounter. No mandatory preparation course or minimum training-hour requirement is published for CMI. Full qualification detail is in CMI Requirements.
Application mechanics and where ACAC's pages disagree
| Topic | Current application page | CMI handbook |
|---|---|---|
| Overall timeline | Six months including the examination | 90 days |
| Forms | Online forms with required email verifications | Notarized forms and employer affidavits |
| Board approval | Unanimous board approval; board meets every four to six weeks | Board meets approximately every four weeks |
These discrepancies remain unresolved by the issuer. Plan for the longer timeline, and confirm the current requirements before you submit anything. One more important point: passing an exam solely for state licensing does not itself award CMI certification. For timing and scheduling, see CMI Exam Dates.
The Reference Library to Know
The handbook lists these bibliographic sources, including explicit edition alternatives:
- ACGIH, Bioaerosols: Assessment and Control, first edition (1999) or second edition (2024)
- AIHA, Field Guide for the Determination of Biological Contaminants, second edition (2005)
- ANSI/IICRC S500-2021, Standard for Professional Water Damage Restoration, fifth edition
- ANSI/IICRC S520-2015 and IICRC R520-2015 (Reference Guide for Professional Mold Remediation), third editions, or ANSI/IICRC S520-2024, fourth edition
- OSHA, Small Entity Compliance Guide for the Respiratory Protection Standard (2011)
- NIOSH, Respirator Selection Logic (2004)
Key Takeaway
These listings are bibliographic entries, not proof of an exam revision. Choose one edition option per title, use it consistently, and map each text to the domain it feeds: bioaerosols and field guide to Domains 1, 3 and 4; S500 and S520 to Domain 5; the OSHA and NIOSH respiratory documents to Domain 6.
Note that although the OSHA 2011 guide is on the CMI bibliography, the CMI study-guide section does not supply a section or page subset for it. Read it as a whole rather than hunting for a trimmed excerpt.
Pass Rate and Passing Score, Kept Separate
Candidates often blur two different numbers, so keep them apart.
- Passing score: 75%, the cut score set by the Modified Angoff method. This is what you must reach. See CMI Passing Score.
- Pass rate: ACAC's 2025 Exam Pass Ratio reports 88%, or 22 passes from 25 CMI examinations. This is what a group of test-takers achieved.
ACAC's activity report as of December 31, 2025 lists 25 CMI applicants, 59 recertifications and 166 current certifications. These are issuer counts of a specialized credential, not search-demand figures. It is a small, specialized community, which is worth knowing when you consider the job market. For earnings and career context, see the CMI Salary Guide, CMI Jobs and Is the CMI Certification Worth It?. No reliable salary survey specific to ACAC CMI holders was verified, so be skeptical of any single precise figure.
Test-Day Logistics and Documented Conflicts
Testing center
- Bring two government-issued IDs, including one photo ID.
- Arrival time: ACAC's Examinations page says 15 minutes early, while the handbook says 30. Aim for the earlier, longer buffer.
Online proctored
- Supply your own computer, an approved webcam and a private location.
- Internet speed must be at least 2 Mbps upload and download.
- Phones and tablets are excluded.
Run the system check well before exam day. A failed webcam or weak connection costs you focus you cannot afford in a three-hour sitting. The pacing math is simple: 100 questions in 180 minutes leaves roughly 108 seconds per question on average, so scenario questions that require reading a sampling plan or evidence summary deserve more time than recall questions, and you should bank time on the quick ones.
A Domain-Ordered Review Sequence
Since ACAC publishes no weights, spread effort evenly at first, then adjust to your own weak spots. Order matters because the domains build on each other. This sequence follows that logic.
Foundations: Domains 1 and 2
- Read the bioaerosols text for biological agents and exposure concepts.
- Write plain-language summaries of exposure routes and health-effect limits.
Method: Domains 3 and 4
- Work through the AIHA field guide on sampling design and interpretation.
- Draft sample plans for hypothetical complaints, then critique them.
Action: Domains 5 and 6
- Study S500 and S520 for remediation principles.
- Review the NIOSH and OSHA respiratory documents as a set.
Integration
- Take timed mixed-domain sets at the 100-question, three-hour pace.
- Revisit whichever domain produced your most missed items.
You can run timed sets and track domain-level misses on the main practice test site. If you are weighing outside courses, ACAC's accredited training directory lists providers, but a provider's own exam or course hours are not the CMI exam's format or duration. See also CMI Training for options.
Quick Answers (FAQ)
There are 100 multiple-choice questions with at least four answer options each, delivered by computer over three hours. The exam is closed book.
The passing score is 75%, set using the Modified Angoff method. ACAC does not publish how many of the 100 questions are scored versus unscored.
The initial two-year term costs $500: a $100 examination fee plus a $400 certification fee, which already includes a $100 nonrefundable processing fee. Retakes are $100 and renewal is $400.
No. The approved chart lists six domains with subdomains but gives no percentage weights, so any weights you see elsewhere reflect a publisher's practice materials, not the official exam. For a practice-side view, try the CMI practice tests.
No. They share an examination chart title and some documents, but they are separate credentials, and CMC's advanced pathways do not apply to CMI. Keep your fees, eligibility and study scope tied to CMI only.