- How the Eleven Content Areas Are Organized
- Format and Rules That Shape How You Study
- Domains 1-3: The Foundation Layer
- Domain 4: Regulations
- Domains 5-7: Equipment, Technique, and Review
- Domains 8-9: Noise Control and HPD Fitting
- Domains 10-11: Counseling, Records, and the Team
- Sequencing the Domains Around Your Course
- Where the Skills Get Used
- Frequently Asked Questions
- The CAOHC handbook lists eleven blueprint headings but publishes no percentages, so no domain can be called highest-weight.
- Initial certification requires a 20-hour approved course, two practicums, and a written exam with a 75-minute timer.
- The passing standard is 70%, on four-option, single-best-answer questions offered in English or Spanish.
- Initial question counts differ between CAOHC sources (55 versus 50), so rely on the Course Director for your exam.
How the Eleven Content Areas Are Organized
The Occupational Hearing Conservationist credential, awarded by the Council for Accreditation in Occupational Hearing Conservation (CAOHC), carries the COHC designation. The eleven content areas below come from the exam blueprint printed on pages 6-8 of the OHC Handbook and Instructions (revised February 2023). The handbook labels these headings as the exam blueprint, but it omits percentage weightings. That matters for how you prepare: any article, video, or forum post claiming "Domain X is 25% of the exam" is going beyond what CAOHC has published for this credential.
The eleven areas, in the handbook's order, are:
- Hearing Conservation (Overall)
- Anatomy, Physiology and Diseases of the Ear
- Hearing and the Physics of Sound and Performing and Explaining a Hearing Test
- Federal and State Regulations Related to Occupational Noise-Induced Hearing Loss
- Audiometer and Testing Environment
- Audiometric Techniques and Testing
- Audiometric Review and Evaluation
- Noise Measurement and Control
- Hearing Protection Device (HPD) Fitting
- Counseling and Training
- Recordkeeping and the Hearing Conservation Team
Notice the shape of the list. It moves from the big picture (why hearing conservation programs exist), through the science of hearing, into the regulatory framework, then the hands-on technician skills (testing, reviewing results, measuring noise, fitting protectors), and finishes with the human and administrative side (counseling, records, teamwork). That arc mirrors what a working hearing conservationist actually does during a shift, and it is a useful way to organize your own notes. For a broader look at how all this fits into a study plan, see the OHC Study Guide 2026: How to Pass on Your First Attempt.
Format and Rules That Shape How You Study
Before diving into content, it helps to understand the container the content arrives in. Here is what CAOHC's published materials establish for initial certification:
| Element | What CAOHC Specifies |
|---|---|
| Course requirement | Minimum 20-hour approved course |
| Practicums | Satisfactory audiometric practicum and hearing-protection-fitting practicum |
| Written exam timer | 75 minutes (initial exam) |
| Question style | Four-option, single-best-answer multiple choice |
| Minimum passing mark | 70% |
| Language | English or Spanish |
| Attempts | Maximum of three; retakes arranged with the Course Director within 30 days of the previous attempt |
| Enrollment prerequisites | None for the course itself |
Two administrative details deserve attention. First, the timer cannot be paused, although you can flag questions and return to them. That favors a first pass that answers everything you know quickly and leaves flagged items for the end. Second, tuition and course registration go through your Course Director, who also arranges proctoring and any retake logistics, and retakes may carry proctoring fees. For the money side, see OHC Certification Cost 2026: Complete Pricing Breakdown, and for the 70% line, OHC Passing Score 2026: Exactly What You Need to Pass.
Domains 1-3: The Foundation Layer
Domain 1: Hearing Conservation (Overall)
Hearing Conservation (Overall)
This is the umbrella content area. Expect questions that test whether you understand why a hearing conservation program exists and how its components fit together, rather than the fine mechanics of any single component.
- The purpose of a hearing conservation program and the problem it addresses: preventing occupational noise-induced hearing loss
- The core program elements as a connected system: noise assessment, audiometric monitoring, hearing protection, training, and recordkeeping
- How each element supports the others, such as monitoring audiograms revealing whether controls and protectors are working
Treat this domain as the scaffold on which the other ten hang. If you can explain how a finding in audiometric review triggers action in counseling, HPD fitting, or noise control, you are already thinking the way the exam expects.
Domain 2: Anatomy, Physiology and Diseases of the Ear
Anatomy, Physiology and Diseases of the Ear
Candidates need working knowledge of how the ear is built, how sound travels through it, and what can go wrong. The point is practical: you must recognize patterns that matter during testing and referral decisions.
- Outer, middle, and inner ear structures and their roles in transmitting and transducing sound
- The difference between conductive and sensorineural loss, and why it matters when reviewing results
- How noise damages the inner ear compared with other causes of hearing problems
- Conditions that are not noise-related and might prompt a referral rather than routine monitoring
Domain 3: Hearing and the Physics of Sound and Performing and Explaining a Hearing Test
This combined heading is worth reading carefully, because it pairs science with communication. You need the physics vocabulary (frequency, intensity, the decibel concept, how sound behaves) and you need to be able to explain a hearing test to the person sitting in the booth. Questions here may test whether you can describe the testing process in plain, accurate language, since a worker who misunderstands the task produces unreliable thresholds. Practice stating each concept in one or two clear sentences.
Domain 4: Regulations
Domain 4 covers federal and state regulations related to occupational noise-induced hearing loss. The wording "federal and state" is deliberate: a hearing conservationist works inside a legal framework, and some jurisdictions layer their own requirements on top of federal rules. Rather than memorizing a single table of numbers from a prep sheet, make sure you can do three things:
- Identify which requirements apply to a given workplace scenario and what triggers them
- Describe what a compliant program must provide to employees in terms of monitoring, protection, training, and records
- Recognize that state rules may add to or differ from the federal baseline, and know to check the governing rule rather than assume
Domains 5-7: Equipment, Technique, and Review
These three areas are where the credential's technician identity shows most clearly. They also connect to the audiometric practicum, so your hands-on course time and your exam preparation reinforce each other.
Domain 5: Audiometer and Testing Environment
Audiometer and Testing Environment
Valid results depend on equipment that performs as intended and a space quiet enough to measure thresholds accurately.
- Components of the audiometer and what each does during a test
- Calibration concepts and the role of routine checks in keeping data trustworthy
- Ambient noise in the test space and why it can compromise thresholds
- Biological listening checks as a day-to-day verification habit
Domain 6: Audiometric Techniques and Testing
Audiometric Techniques and Testing
This is the procedural core: how a competent tester actually conducts a pure-tone air-conduction test and manages the person being tested.
- Patient preparation, instructions, and positioning of earphones
- The step-by-step threshold-finding approach and the rationale behind it
- Recognizing inconsistent or unreliable responses and responding appropriately
- Documenting what happened during the test so the record is usable later
Domain 7: Audiometric Review and Evaluation
Once the audiogram exists, someone must interpret it in context. This area focuses on comparing current results against a baseline, recognizing meaningful change, and deciding what follows. Expect scenario-style items where you read a described result and select the best next step. Understand the difference between a result that needs a retest, one that needs follow-up within the program, and one that suggests a referral for professional evaluation. Connecting this to Domain 2 (ear disease) and Domain 10 (counseling the employee) is what turns isolated facts into exam-ready judgment.
Domains 8-9: Noise Control and HPD Fitting
Domain 8: Noise Measurement and Control
Noise Measurement and Control
The best hearing protection is less noise. This domain asks whether you understand how exposure is measured and how it can be reduced at the source.
- Basic noise measurement instruments and what they report
- The idea of exposure averaged over time versus instantaneous levels
- The hierarchy of controls: engineering and administrative approaches ahead of reliance on personal protection
- How measurement results feed decisions about who is enrolled in the program
Domain 9: Hearing Protection Device (HPD) Fitting
This area parallels the second practicum, the hearing-protection-fitting practicum. Know the common categories of HPDs, how each is inserted or worn correctly, and the typical reasons fits fail: wrong size, poor insertion technique, damaged devices, or incompatibility with other gear. You should also understand that rated attenuation figures describe laboratory performance, and real-world protection can fall short without a good fit. When a scenario describes a worker complaining of discomfort or poor sound blocking, the best answer usually involves refitting, retraining, or choosing a different device, not simply telling them to tolerate it.
Domains 10-11: Counseling, Records, and the Team
Domain 10: Counseling and Training
Hearing conservation succeeds or fails on whether workers actually change behavior. This domain tests your ability to deliver information that is clear, respectful, and motivating. Think about explaining audiogram results in non-technical terms, encouraging consistent protector use, addressing common objections ("I can't hear my coworkers," "they're uncomfortable"), and structuring training so it covers the effects of noise, the purpose of protection, and how to use it. Because items are single-best-answer, the correct choice is typically the response that is both accurate and supportive of the employee's understanding.
Domain 11: Recordkeeping and the Hearing Conservation Team
The final area covers the documentation trail and the roles of the people around you. Records matter because they establish baselines, support trend analysis, and demonstrate compliance. The team element reminds candidates that a conservationist rarely works alone: employers, supervisors, safety professionals, and licensed professionals who review certain results all have defined responsibilities. Know what belongs in the record, who needs access to what, and when a case moves beyond your scope to someone else on the team.
Key Takeaway
The eleven domains are not eleven separate subjects. A single exam scenario can touch regulations, audiometric review, counseling, and records at once. Study the connections between domains, not just each in isolation.
Sequencing the Domains Around Your Course
Since there is no published weighting, a sensible plan spreads effort across all eleven headings and front-loads the areas you will also perform in the practicums. The timeline below assumes you are preparing alongside or just after your approved course; adjust it to your Course Director's schedule and your own exam date (see OHC Exam Dates 2026: Testing Windows, Deadlines & Scheduling).
Foundations and Law
- Domains 1 and 2: program overview and ear anatomy/disease
- Domain 4: map federal rules and note where your state may differ
Science and Testing
- Domain 3: physics vocabulary and practice explaining a test aloud
- Domains 5 and 6: equipment, environment, and test technique, ideally while rehearsing for the audiometric practicum
Interpretation and Exposure
- Domain 7: work through described audiograms and decide next steps
- Domain 8: noise measurement and control hierarchy
People, Paper, and Practice
- Domains 9, 10, and 11: fitting, counseling, and records
- Timed practice sets against the 75-minute limit, flagging and returning to uncertain items
You can run timed sets on the OHC practice test site to rehearse the single-best-answer format, then revisit any domain where your errors cluster. If you want to gauge how demanding this might feel, read How Hard Is the OHC Exam? Complete Difficulty Guide 2026, and for background on what reported results do and do not tell you, OHC Pass Rate 2026: What the Data Shows.
Where the Skills Get Used
Because the credential is built around technician-level hearing conservation work, the domains map onto workplaces where employees are exposed to hazardous noise: manufacturing, construction, utilities, transportation, military-affiliated operations, and mobile or contracted hearing testing services. Employers use certified conservationists to run on-site audiometric testing, fit protectors, deliver training, and maintain program records. Job titles vary, and many people hold the credential as an added qualification alongside safety, nursing, or industrial hygiene responsibilities rather than as a standalone role. For realistic expectations on titles and openings, see OHC Jobs, and for the financial picture, OHC Salary Guide 2026: Complete Earnings Analysis and Is the OHC Certification Worth It? Complete ROI Analysis 2026.
Frequently Asked Questions
No. The handbook labels its eleven headings as an exam blueprint but omits percentages, so there is no supported way to name a highest-weight domain. Prepare across all eleven.
CAOHC's handbook says 55 and its online exam guide says 50, and the published materials do not reconcile the two. Confirm with your Course Director and plan around the 75-minute timer, which cannot be paused.
You need at least 70% on the four-option, single-best-answer questions. You may attempt the exam up to three times, with retakes arranged through your Course Director within 30 days of the previous attempt; proctoring fees may apply.
There are no course-enrollment prerequisites. Certification itself requires completing a minimum 20-hour approved course, passing both practicums, and passing the written exam. See OHC Requirements 2026: Eligibility, Prerequisites & How to Qualify for details.
Without published weights, avoid skipping any area. If you must triage, lean on the domains tied to your practicums (Domains 5, 6, and 9) while keeping regulations (Domain 4) and audiometric review (Domain 7) sharp, since scenario questions often combine them.