- CMI Defined: One Credential, One Issuer
- Who Issues It and Who Stands Behind It
- What the Credential Is Meant to Prove
- The Six Exam Domains
- Exam Format and Testing Conditions
- Eligibility Pathways and the Application
- Fees, Validity and Renewal
- The Reference Library Behind the Exam
- What the Published Pass Data Does and Does Not Say
- CMI Compared With Look-Alike Credentials
- Where the Credential Fits in a Career
- Sequencing Your Preparation Around the Domains
- Frequently Asked Questions
- CMI here means Council-certified Microbial Investigator, issued through the American Council for Accredited Certification (ACAC).
- The exam is 100 multiple-choice questions in three hours, closed book, with a 75% passing score.
- Six official domains apply, 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.
CMI Defined: One Credential, One Issuer
Search for "CMI" and you will find several unrelated credentials sharing the same three letters. This article is about exactly one of them: the Council-certified Microbial Investigator, a professional certification for people who design, conduct and interpret microbial sampling in the built environment. If you came looking for a different credential that happens to abbreviate to CMI, the details here (issuer, fees, exam format, references) will not carry over.
A Council-certified Microbial Investigator is, in practical terms, a person trusted to answer questions like: Is there a microbial problem in this building? How should it be sampled? What do the results mean? And what does that imply for occupants and for remediation? That combination of fieldwork, laboratory-data interpretation and health-aware judgment is what the certification is built around. For other plain-language explanations of the term, see our short pieces on what CMI stands for and what CMI certification is.
Who Issues It and Who Stands Behind It
The credential is issued by the American Council for Accredited Certification (ACAC) through its CMI Certification Board. The program is accredited by the Council for Engineering and Scientific Specialty Boards (CESB), which matters because third-party accreditation of the certifying program is one of the signals employers, clients and attorneys look for when weighing a credential's credibility.
ACAC's examination is delivered through Kryterion, Inc., the testing vendor. The exam content is organized in a formal chart that ACAC shares with its related Council-certified Microbial Consultant (CMC) examination. The chart was approved on February 21, 2024, and it expressly applies to CMI. No separately labeled 2026 exam version was verified, so treat the February 2024 chart as the current published framework.
What the Credential Is Meant to Prove
ACAC's eligibility language centers on one demonstrable skill: candidates must show they can design, conduct and interpret microbial sampling regimens. That wording is worth internalizing, because it shapes both the application and the exam. This is not a vocabulary test about fungi. It is an assessment of whether you can choose appropriate sampling strategies, understand what the data can and cannot tell you, and connect findings to health risk and remediation decisions.
The credential also carries a practical boundary: passing an examination solely for state licensing purposes does not itself award CMI certification. If your jurisdiction requires a licensing exam, that is a separate track from the ACAC certification process.
The Six Exam Domains
ACAC's approved chart organizes the exam under six official headings. The numbered columns (1 through 7) in the chart contain subdomains, not seven extra domains. Importantly, ACAC does not publish percentage weights for these domains, so no domain can be declared "highest-weighted." Be skeptical of any third-party site that presents precise allocations as if they were official. For a deeper walkthrough, see our complete guide to all six CMI content areas.
Domain 1: Scientific knowledge of biological agents
The biological foundation: what organisms are involved, how they grow, spread and persist indoors, and what conditions favor them.
- Characteristics of fungi, bacteria and other biological agents relevant to buildings
- Growth requirements, moisture relationships and indoor reservoirs
- How biological material becomes airborne or settles on surfaces
Domain 2: Potential health effects and risks associated with exposure
The connection between a finding and a person. Investigators must understand exposure without overstating or understating risk.
- Categories of health effects associated with microbial exposure
- Factors that make some occupants more vulnerable than others
- The limits of what sampling data can say about individual health outcomes
Domain 3: Principles of Microbial Investigation
The investigative method: how a building assessment is structured from first complaint to written conclusion.
- Building inspection, moisture assessment and hypothesis building
- Interviewing occupants and reviewing building history
- Documenting observations and forming defensible conclusions
Domain 4: Principles of Microbial Sampling
The core technical domain, mirroring the credential's central skill: designing, conducting and interpreting sampling.
- Selecting sample types and methods to answer a specific question
- Collection technique, controls, chain of custody and laboratory communication
- Interpreting results in context, including comparison to outdoor or reference conditions
Domain 5: Principles of Microbial Remediation
Even though investigators are not necessarily the ones performing cleanup, they must understand remediation well enough to specify scope and verify outcomes.
- Containment, source correction and removal principles
- Water damage response as it relates to microbial growth
- Post-remediation evaluation and clearance concepts
Domain 6: Health & Safety
Protecting the investigator, the occupants and the workers. Note that ACAC's shorter five-topic handbook summary omits this domain, but the formal approved chart includes it, and the chart controls.
- Respiratory protection selection and program fundamentals
- Personal protective equipment and hazard awareness during inspection
- Reducing cross-contamination and exposure during fieldwork
Because Domain 6 is easy to under-prepare (it is absent from the handbook's summary), build it into your plan deliberately. The respiratory-protection references listed by ACAC, covered below, are the natural anchor.
Exam Format and Testing Conditions
| Feature | CMI Exam Detail |
|---|---|
| Delivery vendor | Kryterion, Inc. |
| Questions | 100 multiple choice, at least four answer options each |
| Time | Three hours, computer-delivered |
| Reference materials | Closed book |
| Passing score | 75%, set using the Modified Angoff method |
| Practical component | None described |
| Question order | Fixed question set with randomized question and answer order |
| Results | Immediate electronic score and an emailed result |
Several details are unpublished: ACAC does not state how many of the 100 items are scored versus unscored, adaptive testing is not described, and calculator permission is unverified. Don't assume; confirm with ACAC before test day. For more on the scoring standard, read our breakdown of the CMI passing score.
Test-Day Logistics
- Delivery options: proctored testing center or online video proctoring.
- Testing center: two government-issued IDs are required, including one photo ID.
- Online: you supply the computer, an approved webcam and a private location. ACAC specifies at least 2 Mbps upload and download speeds and excludes phones and tablets.
- Arrival time: ACAC's exam page says 15 minutes early, while the handbook says 30. Plan for the longer figure to be safe.
Eligibility Pathways and the Application
ACAC offers two routes into the CMI, both requiring documented, hands-on microbial sampling experience:
- Education-plus-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: 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 FAQ is explicit that at least one full year of actual field experience is required regardless of how many college credits you hold. Note that the CMC's advanced education and experience pathways are separate and do not transfer to the CMI. The full details are in our CMI requirements guide.
What You Submit
- Four project sheets documenting your sampling work
- Applicable academic evidence
- Experience verification
- Online forms with required email verifications
Documented Conflicts in the Issuer's Own Materials
ACAC's pages and handbook do not fully agree on the process, and candidates should verify current rules directly. The application page describes a six-month window including the examination, unanimous board approval and a board meeting every four to six weeks. The handbook instead describes 90 days, notarized forms with employer affidavits and board meetings roughly every four weeks. Until ACAC reconciles these, treat the more conservative timeline and paperwork as your planning baseline. Our exam dates and scheduling guide covers how to plan around this.
Fees, Validity and Renewal
| Item | Amount (USD) |
|---|---|
| Examination fee | $100 |
| Certification fee | $400 (includes a $100 nonrefundable processing fee, not an extra charge) |
| Total initial cost (two-year term) | $500 |
| Exam retake | $100 |
| Renewal | $400 |
ACAC publishes no separate member versus nonmember fee schedule. A full cost discussion, including indirect costs like references and training, is in our CMI certification cost breakdown.
Staying Certified
Certification lasts two years. ACAC's recertification procedures specify 40 recertification credits (RCs): 10 for continued field activity and 30 for professional development during the term. You attest to your credits and keep documentation in case of audit, and a current photo is requested. Be aware that the handbook's general 40-RC wording and the program page's mention of 20 professional-development hours per year differ from the detailed procedure; the detailed procedure is the most specific source, but the discrepancy is real, so confirm with ACAC when your term begins.
The Reference Library Behind the Exam
ACAC's handbook lists the references the CMI draws on. Several allow a choice between editions:
- 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, Standard for Professional Mold Remediation, 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)
Map these to the domains: the ACGIH and AIHA texts support the biological-agent, sampling and investigation domains; the IICRC standards support remediation and water-damage understanding; and the OSHA and NIOSH respirator documents anchor Health & Safety. The handbook's study-guide pages are explicitly illustrative, not exhaustive, so candidates need comprehensive command of the reference texts rather than just the excerpted pages. Also note that the handbook's detailed study-guide section does not provide an OSHA section or page subset for CMI, so read the OSHA guide in full rather than hunting for a shortcut. Our CMI study guide turns this reading list into a plan.
What the Published Pass Data Does and Does Not Say
ACAC's 2025 Exam Pass Ratio report lists 22 passes from 25 CMI examinations, an 88% ratio. That is real issuer data, but it deserves careful reading:
- It includes retakes and state-licensing-only examinations, and does not disclose how many CMI sittings fall into either category.
- It is therefore not a first-attempt success rate.
- With only 25 examinations, small shifts move the percentage a lot.
- It cannot predict any individual candidate's result.
- No 2026 pass rate was verified.
Don't confuse the 88% observed ratio with the 75% passing score. One describes how a group performed; the other is the cut score you must reach. See our full treatment in the CMI pass rate analysis, and for a candid look at difficulty, how hard the CMI exam really is.
ACAC's Accredited Certification Activity report as of December 31, 2025 lists 25 CMI applicants, 59 recertifications and 166 current certifications. That gives a sense of scale: this is a small, specialized credential community rather than a mass-market certification.
CMI Compared With Look-Alike Credentials
| Credential | How It Relates to This Article |
|---|---|
| Council-certified Microbial Investigator (CMI) | The subject here: ACAC-issued, built around designing, conducting and interpreting microbial sampling |
| Council-certified Microbial Consultant (CMC) | Related ACAC credential sharing the same approved exam-domain chart; has its own advanced pathways that do not transfer to CMI |
| Other issuers' mold inspector certifications | Separate programs with their own bodies, fees and exams; outside this article's scope |
| Provider-owned mold-inspection exams | Course-end assessments run by training companies; not the ACAC written exam |
This distinction matters when you evaluate training. Some providers list ACAC-related courses whose own examinations, hours and licensing purposes differ from the CMI written exam. A 24-hour class and a provider's end-of-course test are not the three-hour, 100-question ACAC examination, and ACAC publishes no mandatory preparation course or minimum training-hour requirement. See our overview of CMI training options for how to evaluate providers.
Where the Credential Fits in a Career
The CMI suits people whose work involves assessing indoor environments for microbial problems: independent consultants, industrial hygiene and environmental health practitioners, building-science professionals, and personnel at restoration, engineering or architectural firms who evaluate moisture and mold conditions. The credential signals that your sampling methodology and interpretation have been reviewed against a recognized, CESB-accredited standard, which can help in client-facing, insurance-related and dispute-prone situations where credibility is everything.
On compensation, be cautious. No reliable salary survey specific to ACAC CMI holders, and no causal earnings premium from holding the credential, was verified. Pay in this field depends heavily on region, employer type, whether you are salaried or running your own practice, and your underlying experience. Our CMI salary guide, CMI jobs overview and ROI analysis separate occupational compensation from the narrower question of what the certification itself adds.
Key Takeaway
Treat the CMI as evidence of method and judgment, not as a guaranteed pay raise. Its strongest value is credibility in situations where someone must defend a sampling plan and its interpretation.
Sequencing Your Preparation Around the Domains
Because ACAC publishes no domain weights, spread effort evenly and adjust based on your own field gaps. Experienced samplers often find Domain 4 comfortable but underestimate Domain 2 (health effects) and Domain 6 (Health & Safety). A sensible sequence for a six-week lead-in:
Foundations: Domains 1 and 2
- Read the ACGIH bioaerosols text on organisms, growth and exposure
- Write your own summary of exposure-versus-risk limits
Method: Domains 3 and 4
- Work through the AIHA field guide on sampling design and interpretation
- Practice explaining why you would pick one sample type over another
Response: Domains 5 and 6
- Study IICRC S500 and S520 for water damage and remediation
- Read the OSHA and NIOSH respirator documents in full
Integration
- Take timed, closed-book practice sets across all six domains
- Review misses by domain and reference, not just by question
Quick-reference material helps in the final days; our CMI cheat sheet condenses the must-know facts, and you can find more practice on the main CMI Exam Prep practice test site. When using third-party question banks, remember that publisher-assigned topic allocations are not official exam weights, and that complete accuracy and alignment of paid banks was not independently verified.
Frequently Asked Questions
It stands for Council-certified Microbial Investigator, a certification issued through the American Council for Accredited Certification (ACAC). It is distinct from other credentials that share the same acronym.
The exam is 100 multiple-choice questions delivered by computer over three hours, closed book. The passing score is 75%, set using the Modified Angoff method.
The initial two-year term costs $500: a $100 examination fee plus a $400 certification fee that includes a $100 nonrefundable processing fee. A retake is $100 and renewal is $400.
Not necessarily. You can qualify with a related two-year degree (or 15 qualifying college credits) plus one year of documented microbial sampling, or with a high school diploma or GED plus two years of consulting experience in microbial sampling.
Two years. Renewal involves 40 recertification credits, 10 for continued field activity and 30 for professional development, with attestation and retained documentation in case of audit.