- Which CMC This Guide Covers
- The ACAC Exam at a Glance
- Qualifying Before You Study
- Working Through the Six Domains
- Reference Books and Edition Choices
- Question Style and Practice Material
- A Domain-Sequenced Study Plan
- Exam-Day Logistics and Source Conflicts
- Reading the Pass Rate Honestly
- After You Pass: Renewal and Career Value
- Frequently Asked Questions
- The exam is 120 multiple-choice questions in three hours, closed book, with a 75% passing score.
- ACAC publishes six unweighted domains, including Health & Safety, which the shorter handbook text omits.
- ACAC reported 16 passes from 17 attempts in 2025, but that figure is not first-attempt-only.
- Eligibility rests on documented microbial sampling experience, four project sheets, and unanimous board approval.
Which CMC This Guide Covers
Several credentials share the acronym "CMC," and candidates regularly end up studying the wrong material. This guide is about one credential only: the Council-certified Microbial Consultant, issued by the American Council for Accredited Certification (ACAC) through its CMC Certification Board. The program is accredited by the Council for Engineering and Scientific Specialty Boards (CESB).
If you are unsure whether you are in the right place, our explainers on what CMC certification is and what CMC stands for cover the naming question in detail. Management, nursing, and pharmaceutical credentials that abbreviate to CMC have nothing to do with this exam, and a provider's own mold-inspector test is not a substitute for the ACAC exam.
The ACAC Exam at a Glance
Knowing the container shapes how you prepare. Here is what ACAC's published information establishes:
| Feature | Official detail |
|---|---|
| Questions | 120 multiple-choice, each with at least four answer options |
| Time | Three hours, computer-delivered, closed book |
| Passing score | 75%, set using a Modified Angoff method |
| Scored vs. unscored items | Split not published |
| Practical component | None described |
| Delivery | Testing center or online video proctoring, scheduled through ACAC |
| Results | Immediate electronic score, followed by emailed results |
Three hours for 120 questions averages out to roughly 90 seconds per item, which is generous for recall questions and tight for scenario-based ones. The handbook describes the same question set delivered with randomized question and answer order, and adaptive testing is not described. Calculator permission is unverified, so do not build a strategy around having one; practice working sampling arithmetic by hand. For a deeper look at the cut score, see our breakdown of the CMC passing score.
Qualifying Before You Study
Unlike many exams, you cannot simply register and sit. ACAC requires an application approved by its board, and the pathway depends on your education and documented experience. Three alternatives exist:
- A related four-year postsecondary degree, or 30 qualifying college credits, plus four years of documented microbial sampling.
- A related two-year degree, or 15 qualifying credits, plus six years of documented microbial sampling.
- A high school diploma or GED plus eight years of consulting experience in microbial sampling.
Qualifying fields include microbiology, engineering, science, architecture, and industrial hygiene. ACAC's FAQ defines qualifying coursework and excludes social sciences, so check your transcript before assuming credits count. Candidates must demonstrate that they have designed, conducted, and interpreted sampling regimens, not merely assisted with collection.
The paperwork includes four project sheets, applicable transcripts, and experience verification. The handbook says experience should come from Building Sciences, Microbiology, and Microbial Risk Analysis, but that wording should not be read as a mandatory three-area rule. No minimum training-hour requirement or mandatory preparation course is published. Our full CMC requirements guide walks through each pathway.
Costs total $500 for the initial two-year term: a $100 examination fee plus a $400 certification fee (which includes $100 of nonrefundable processing). A retake costs $100 and renewal costs $400. No separate member and non-member schedule is published. The CMC certification cost breakdown has the full picture.
Working Through the Six Domains
The current formal domain chart, approved February 21, 2024, covers the CMC and the related CMI examination and lists six domains. ACAC publishes no percentage weights, so no domain can be declared the heaviest. Treat all six as fair game and study accordingly. For a domain-by-domain companion, read our complete guide to the CMC content areas.
Domain 1: Scientific knowledge of biological agents
This is the foundation. You need to recognize the organisms and biological contaminants encountered in built environments and understand how they grow, spread, and persist.
- Fungal, bacterial, and other biological agents relevant to buildings
- Moisture, substrate, and conditions that support amplification
- How biological material becomes airborne, which connects directly to bioaerosol principles
Domain 2: Potential health effects and risks associated with exposure
Expect questions that ask what exposure can and cannot be said to cause, and how to communicate risk responsibly without overstating certainty.
- Exposure routes and the range of potential health outcomes
- Susceptible populations and why exposure thresholds are hard to define
- The limits of what sampling data can say about individual health
Domain 3: Principles of Microbial Investigation
This domain is about the investigative process: building-science reasoning, hypotheses about moisture and contamination sources, and structuring a defensible assessment.
- Visual and building-envelope assessment logic
- Linking observations to likely moisture and contamination pathways
- Documenting findings so conclusions can be traced to evidence
Domain 4: Principles of Microbial Sampling
Because the credential is built on sampling experience, expect this domain to feel the most practical. You must know when to sample, how, and what the results do and do not tell you.
- Sampling design: objectives, number and placement of samples, controls
- Method selection, equipment calibration, and sample handling
- Data limitations and interpretation, including variability and comparison to reference conditions
Domain 5: Principles of Microbial Remediation
Know how remediation is scoped, contained, and verified. This is where the ANSI/IICRC standards listed in the handbook become central.
- Containment, cleaning, and removal principles
- Documentation of remediation work
- Post-remediation verification and what constitutes an acceptable outcome
Domain 6: Health & Safety
Do not skip this one. The handbook's shorter five-topic body-of-knowledge text omits standalone Health & Safety, but the formal domain chart includes it, so study it as a full domain.
- Respiratory protection programs and respirator selection
- Personal protective equipment and worker exposure control
- Regulatory expectations tied to the OSHA and NIOSH references
Key Takeaway
The exam objectives are official, but they are objectives, not a provider curriculum. When a prep site assigns equal percentages to categories, that is the publisher's allocation, not an ACAC weighting.
Reference Books and Edition Choices
The handbook names a specific reference set, and the exam assumes comprehensive knowledge of it. The listed materials are:
- 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, fifth edition
- ANSI/IICRC S520-2015 and R520-2015, third editions, or S520-2024, fourth edition
- OSHA Small Entity Compliance Guide for the Respiratory Protection Standard (2011)
- NIOSH Respirator Selection Logic (2004)
The handbook also states that its selected study-guide sections and page references are examples, not an exhaustive preparation plan. Reading only the flagged pages is a trap. Budget time to read each reference as a whole, and map what you read back to the six domains so nothing is orphaned.
Question Style and Practice Material
Questions are multiple choice with at least four options, and a meaningful share should be expected to be applied rather than purely definitional: a described building condition, a sampling objective, or a data set, followed by a question about the defensible next step or interpretation. Practice accordingly. Memorizing definitions will carry you through Domain 1 but not Domains 3 through 5.
When you choose practice resources, check them against official facts. Some publisher mock exams use a different length, time limit, or passing mark than the real exam (for example, shorter timed mocks with a lower pass threshold). Those are useful drills but should never replace your understanding that the real exam is 120 questions, three hours, and 75%. Several public sites also assert that ACAC does not publish pass rates, which is outdated given the 2025 report discussed below. You can start with our CMC practice tests and, once you have a baseline, return to the CMC cheat sheet for rapid review of the facts you keep missing.
To calibrate expectations, our guide on how hard the CMC exam is explains where candidates tend to struggle, and the CMC training overview covers the provider landscape. ACAC maintains a provider directory but requires no specific course.
A Domain-Sequenced Study Plan
Sequencing matters because the domains build on each other: you cannot interpret sampling data (Domain 4) without the biology and risk context (Domains 1 and 2). This is the one place where we suggest a calendar, and it is adjustable to your existing experience.
Biology and risk (Domains 1 and 2)
- Read the biological agent and health effects portions of the bioaerosols text and the AIHA field guide
- Build a one-page summary of agents, growth conditions, and exposure pathways
Investigation and sampling (Domains 3 and 4)
- Work through sampling design for several hypothetical buildings, writing the objective before choosing a method
- Practice interpreting data with stated limitations
Remediation and safety (Domains 5 and 6)
- Study S500 and your chosen S520 edition for scoping, containment, and verification
- Review the OSHA and NIOSH respirator references so Health & Safety is not neglected
Integration and timed practice
- Take full-length timed sets at 120 questions in three hours
- Re-study the domain where your errors cluster
Experienced practitioners may compress the early weeks but should expect to extend Weeks 5 and 6, because remediation standards and respiratory protection are often learned informally in the field and need to be checked against the written references.
Exam-Day Logistics and Source Conflicts
You schedule through ACAC, either at a testing center or by online video proctoring. Testing-center candidates need two government-issued IDs, including one with a photo. Online candidates supply their own computer, an approved webcam, and a private location, with at least 2 Mbps upload and download speeds; phones and tablets are excluded.
One conflict to be aware of: the current Examinations page specifies arriving 15 minutes early, while the handbook says 30. Plan for the longer window so the discrepancy never costs you. Run your technology check well ahead of time if you test online.
Reading the Pass Rate Honestly
ACAC's 2025 Exam Pass Ratio reports 94%, based on 16 passes from 17 attempts. That is encouraging, but read it carefully. The attempts include retakes and candidates taking the exam only for state licensing, so it is not a first-attempt figure for certification candidates, and the sample is very small. No 2026 rate has been verified. Part of the favorable picture is likely that the application gate screens candidates before they ever sit the exam. For full context, see our CMC pass rate analysis.
Also note that passing a licensing-only exam result does not itself confer CMC certification. Certification requires the approved application and the full process.
After You Pass: Renewal and Career Value
Certification lasts two years. Current recertification procedures call for 40 renewal credits: 10 for continued field activity and 30 for professional development, with attestation and retained evidence in case of audit. A current photo is requested. Other ACAC sources phrase the requirement differently (the handbook uses general 40-credit wording and the program page mentions 20 professional-development hours per year), so follow the current Recertification Procedures page. As of December 31, 2025, ACAC reported 288 current CMC certifications and 99 recertifications, a small, specialized community.
On earnings, be cautious. No reliable salary survey specific to ACAC CMC holders has been verified, and no causal pay premium is established, so treat any precise salary figure with suspicion. Our salary analysis, ROI discussion, and overview of CMC jobs explore the qualitative case: consultants who design and interpret sampling programs for building owners, remediation firms, and indoor environmental practices use the credential to document expertise.
Key Takeaway
The strongest preparation mirrors the credential itself: know the six domains, read the full reference set rather than sample pages, and be able to justify a sampling or remediation decision in writing, not just recognize a term.
Frequently Asked Questions
The exam has 120 multiple-choice questions with at least four answer options each, delivered by computer over three hours. It is closed book, and the passing score is 75%.
That cannot be established. ACAC's formal domain chart lists six domains but publishes no percentage weights. Prepare for all six, including Health & Safety.
No. ACAC publishes no mandatory preparation course and no minimum training-hour requirement. It does maintain a provider directory, but listing there is not a requirement for sitting the exam.
Not exactly. The 2025 figure of 16 passes from 17 attempts includes retakes and licensing-only candidates, the sample is tiny, and it is not first-attempt-only data. Use it as encouragement, not a forecast.
The handbook lists either edition for the ACGIH bioaerosols text (1999 or 2024) and for S520 (2015 or 2024). This shows acceptable references, not an exam revision date, so understand the concepts that both editions share.