- What the Six Official Domains Actually Are
- How the Domains Are Tested: Format and Logistics
- Domain 1: Scientific Knowledge of Biological Agents
- Domain 2: Health Effects and Exposure Risks
- Domain 3: Principles of Microbial Investigation
- Domain 4: Principles of Microbial Sampling
- Domain 5: Principles of Microbial Remediation
- Domain 6: Health & Safety
- Reference Books and Edition Alternatives
- Sequencing Your Preparation Around the Domains
- Source Conflicts and Look-Alike Credentials
- Frequently Asked Questions
- The ACAC domain chart approved February 21, 2024 lists six domains, and Health & Safety is the sixth.
- No percentage weights are published for the domains, so no domain can be called the heaviest.
- The exam is 120 multiple-choice questions in three hours, closed book, with a 75% passing score.
- The handbook's five-topic text omits standalone Health & Safety, but the formal chart includes it.
What the Six Official Domains Actually Are
The Council-certified Microbial Consultant credential is issued by the American Council for Accredited Certification (ACAC) through its CMC Certification Board, and the program is accredited by the Council for Engineering and Scientific Specialty Boards (CESB). The exam objectives are published in a formal chart titled CMC and CMI Examinations, approved February 21, 2024. That chart expressly covers the CMC and lists six domains in sequence:
- Scientific knowledge of biological agents
- Potential health effects and risks associated with exposure
- Principles of Microbial Investigation
- Principles of Microbial Sampling
- Principles of Microbial Remediation
- Health & Safety
Two clarifications save candidates confusion. First, the numbered columns inside the chart describe subdomains, not additional exam domains; the chart does not describe a seven-domain exam. Second, these are official exam objectives, not any training provider's curriculum. A provider course may organize material differently, so always reconcile your study notes against the ACAC chart itself. No separately labeled 2026 exam version has been verified, so the February 2024 chart is the current formal reference we can point to.
How the Domains Are Tested: Format and Logistics
All six domains are tested on a single written examination delivered by computer through Kryterion. The published facts are:
| Feature | What ACAC Specifies |
|---|---|
| Questions | 120 multiple-choice, at least four answer options each |
| Time | Three hours, computer-delivered |
| Book policy | Closed book |
| Passing score | 75%, set using a Modified Angoff method |
| Scored vs. unscored items | Split not published |
| Practical component | No separate practical assessment described |
| Delivery | Testing center or online video proctoring, scheduled through ACAC |
| Results | Immediate electronic score; results also emailed |
The handbook describes the same question set delivered with randomized question and answer order, and it does not describe adaptive testing. Calculator permission is unverified, so confirm it with ACAC before test day rather than assuming. Testing-center candidates bring two government-issued IDs, including one photo ID. Online candidates need their own computer, an approved webcam, a private location and at least 2 Mbps upload and download speeds; phones and tablets are excluded. Arrival guidance differs by source: the current Examinations page specifies 15 minutes early, while the handbook says 30, so plan for the longer window.
For the passing standard in detail, read our CMC passing score guide, and for scheduling mechanics see CMC exam dates and deadlines.
Domain 1: Scientific Knowledge of Biological Agents
This domain is the biology foundation for everything that follows. A consultant who cannot reason about what organisms are, how they grow and how they spread cannot design a defensible sampling plan or interpret results. Expect questions that ask you to apply organism biology to building scenarios rather than recite definitions.
Domain 1 Focus Areas
Build working fluency in the organisms and biological contaminants encountered in indoor environments.
- Fungal, bacterial and other biological contaminants relevant to the built environment
- Conditions that support growth, including moisture, nutrients, temperature and time
- How biological material becomes airborne and settles on surfaces
- Terminology you will need to read sampling and laboratory reports accurately
The AIHA Field Guide for the Determination of Biological Contaminants (second edition, 2005) is on the handbook's reference list and is a natural anchor for this domain, alongside the ACGIH bioaerosols text discussed below.
Domain 2: Health Effects and Exposure Risks
Domain 2 moves from the organism to the occupant. The exam title for this area is "Potential health effects and risks associated with exposure," which signals that you need to understand how exposure relates to health outcomes and, just as importantly, the limits of what a consultant can claim.
Domain 2 Focus Areas
Know the vocabulary and logic of exposure and risk.
- Routes of exposure and factors that influence whether exposure leads to a health effect
- Susceptible populations and why risk is not uniform across occupants
- The difference between establishing that contamination exists and attributing a specific health outcome to it
- How to communicate risk without overstating certainty
Questions here often reward caution. When a scenario tempts you toward a medical conclusion, the stronger answer typically stays within the consultant's scope: characterizing conditions and exposure potential rather than diagnosing illness.
Domain 3: Principles of Microbial Investigation
Investigation is where building science meets microbiology. The ACAC experience guidance for applicants references Building Sciences, Microbiology and Microbial Risk Analysis, and Domain 3 is where that blend shows up on the exam. The handbook wording is not converted into a mandatory three-area rule, but it is a useful lens for what the domain expects.
Domain 3 Focus Areas
Think like an investigator working from symptoms of a problem back to source and cause.
- Visual inspection and documentation practices, including recording what was and was not observed
- Identifying moisture sources, building envelope and HVAC contributors, and pathways of contamination
- Forming hypotheses before sampling so that sampling answers a defined question
- Recognizing the limits of an investigation and writing them into the report
Domain 4: Principles of Microbial Sampling
Sampling is the heart of the credential. Candidates must demonstrate designing, conducting and interpreting sampling regimens, and the eligibility pathways require documented microbial sampling experience, so this domain reflects daily professional work. It is also where many scenario questions concentrate their difficulty.
Domain 4 Focus Areas
Master the full sampling lifecycle: design, collection, handling and interpretation.
- Choosing sample types and methods that match the question being asked
- Equipment selection, calibration and verification before collection
- Chain of custody, sample handling and laboratory communication
- Controls, comparison samples and why outdoor or reference conditions matter
- Data limitations: variability, detection limits, and what a single result can and cannot show
- Interpreting results in context rather than against a single numeric cutoff
The ACGIH Bioaerosols: Assessment and Control text and the AIHA field guide are the primary references most relevant here. Practice explaining, in plain language, why you would choose one method over another for a given scenario; the exam rewards that reasoning. Our CMC difficulty guide explains why interpretation-heavy items feel harder than recall items.
Domain 5: Principles of Microbial Remediation
Remediation connects the consultant's findings to corrective action. Even when the consultant does not perform the work, the consultant specifies, oversees or verifies it, so the exam expects you to understand scope, containment, process and verification.
Domain 5 Focus Areas
Understand how remediation is scoped, controlled, documented and verified.
- Source correction: remediation fails if the moisture or contamination source remains
- Containment and engineering controls during work
- Remediation documentation and protocol development
- Post-remediation verification and what evidence demonstrates a successful outcome
- Applying the water-damage and mold remediation standards listed in the handbook references
The handbook lists ANSI/IICRC S500-2021 (fifth edition) and the S520 standard, with edition alternatives covered in the reference section below. Be able to connect a standard's principles to a scenario, not merely name the standard.
Domain 6: Health & Safety
This domain is the one candidates most often underestimate, because of a documentation quirk. The handbook's shorter five-topic body-of-knowledge text omits standalone Health & Safety, while the linked formal domain chart includes it as its own domain. Do not rely on the handbook summary alone; study Health & Safety as a full domain.
Domain 6 Focus Areas
Protect yourself, your team and building occupants during investigation, sampling and remediation.
- Respiratory protection program principles and respirator selection logic
- Personal protective equipment selection and use
- Hazard recognition on site, including hazards unrelated to the microbial concern
- Protecting occupants and adjacent spaces during sampling or remediation activities
The handbook lists the OSHA Small Entity Compliance Guide for the Respiratory Protection Standard (2011) and NIOSH Respirator Selection Logic (2004). These two documents map directly onto Domain 6 and are inexpensive to study relative to the large reference texts. If you want a quick consolidation tool near exam day, our CMC cheat sheet is built for that purpose.
Reference Books and Edition Alternatives
The CMC Candidate Handbook lists specific references, and several allow edition alternatives. These alternatives do not establish an exam revision date, and listing them does not mean you have free access to the full paid texts.
| Reference | Edition(s) Listed | Most Relevant Domains |
|---|---|---|
| ACGIH Bioaerosols: Assessment and Control | First edition (1999) OR second edition (2024) | 1, 2, 4 |
| AIHA Field Guide for the Determination of Biological Contaminants | Second edition (2005) | 1, 3, 4 |
| ANSI/IICRC S500 | 2021, fifth edition | 3, 5 |
| ANSI/IICRC S520 and R520 | 2015 third editions OR S520-2024 fourth edition | 3, 5 |
| OSHA Respiratory Protection Standard compliance guide | 2011 | 6 |
| NIOSH Respirator Selection Logic | 2004 | 6 |
The domain mapping in the right column is our own study-planning aid, not an official ACAC alignment. The handbook explicitly warns that its selected study-guide sections and page references are examples rather than exhaustive exam preparation, and that the exam assumes comprehensive knowledge of the listed references. Reading only the suggested pages is a known trap.
Sequencing Your Preparation Around the Domains
Because the domains build on one another, order matters more than intensity. The sequence below ties each phase to a domain pair and the reason for that ordering. Adjust the timeline to your own experience; someone with years of field sampling will compress Domain 4 and spend longer on Domain 2.
Domains 1 and 2: Biology and Risk
- Learn organism and contaminant fundamentals first, since every later domain uses this vocabulary
- Pair biology with exposure and risk so you practice staying within consultant scope
Domains 3 and 4: Investigation and Sampling
- Study investigation and sampling together; treat sampling as an answer to an investigative question
- Work through sampling design, calibration, controls and data-limitation scenarios
Domains 5 and 6: Remediation and Safety
- Study remediation verification and the S500/S520 principles
- Give Health & Safety a dedicated block rather than folding it in as an afterthought
Integration and Timed Practice
- Take timed, mixed-domain sets sized to the real three-hour, 120-question format
- Review misses by domain to find which of the six needs a second pass
You can run domain-tagged drills on our CMC practice test site. Third-party practice banks vary in scope and alignment, and any mock exam with a different length, time limit or passing mark than the official 120 questions, three hours and 75% should be treated as a practice resource only. Our full study guide covers pacing in more depth.
Source Conflicts and Look-Alike Credentials
Documented Conflicts Within ACAC Materials
ACAC's own documents are not perfectly consistent, and candidates should know where. The current Applications page describes online forms, required email verifications and a six-month timeline including the examination, with a board that meets every four to six weeks; the handbook instead describes 90 days and notarized forms or employer affidavits. This issuer conflict is unresolved, so confirm current procedures with ACAC directly. For the cost side, see the CMC certification cost breakdown: the initial two-year term totals $500 (a $100 examination fee plus a $400 certification fee), with a $100 retake and $400 renewal. Eligibility pathways are detailed in our CMC requirements guide.
Do Not Substitute Another Exam or Credential
The acronym CMC is shared by several unrelated credentials in management, nursing and other fields. This article concerns only the Council-certified Microbial Consultant. A provider's own mold-inspector examination, including a state or district licensing exam a training course may offer, is not the ACAC CMC exam, and a licensing-only result does not itself confer CMC certification. If you are unsure which credential a resource describes, our what is CMC certification explainer clarifies the scope.
Pass Rate Context
ACAC's 2025 Exam Pass Ratio reports 94%, based on 16 passes from 17 attempts. That sample is small, includes retakes and state-licensing-only candidates, and is not first-attempt-only data; no 2026 rate has been verified. It is also a different measure from the 75% passing score, which is the threshold on your own exam. See what the pass rate data shows for the full caveats.
Key Takeaway
Study to the six-domain ACAC chart, not to a provider's outline or the handbook's five-topic summary. Give Health & Safety its own block, read the full reference texts rather than only the sample pages, and verify any application-timeline detail with ACAC before committing to a date.
Frequently Asked Questions
ACAC's formal domain chart, approved February 21, 2024, lists six domains: scientific knowledge of biological agents, potential health effects and risks associated with exposure, principles of microbial investigation, principles of microbial sampling, principles of microbial remediation, and Health & Safety. The numbered columns in the chart are subdomains, not extra domains.
That cannot be established. ACAC does not publish percentage weights for the six domains, so no domain can be identified as the highest-weighted. Any weights you see on third-party sites are publisher allocations rather than official blueprint figures, so prepare for all six.
The handbook's shorter body-of-knowledge text omits standalone Health & Safety, while the linked formal domain chart includes it as a sixth domain. Because the chart is the more complete and current formal document, study Health & Safety as its own domain.
It is closed book: 120 multiple-choice questions over three hours, with a 75% passing score. It is computer-delivered either at a testing center or by online video proctoring scheduled through ACAC, and electronic scores are available immediately after testing.
The handbook lists edition alternatives, such as the 1999 or 2024 ACGIH bioaerosols text and the 2015 or 2024 S520 editions, but this does not establish an exam revision date. Familiarize yourself with the listed editions, and read our domain guide and CMC certification overview for related context.