- What CHRN Means: Certified Hyperbaric Registered Nurse
- Who Governs and Who Administers the Credential
- Who Can Sit for the Exam
- What the Exam Looks Like
- What You Must Know: The Sixteen Preparation Areas
- Fees, Registration, and Timing
- Keeping the Credential: The Four-Year Renewal Cycle
- Where CHRNs Work and Why Employers Value It
- Sequencing Your Preparation Around the Content Areas
- Frequently Asked Questions
- CHRN means Certified Hyperbaric Registered Nurse: a nursing credential in hyperbaric oxygen therapy, not any other credential sharing the acronym.
- The exam has 120 multiple-choice and true/false questions, a two-hour limit, and a 70% passing threshold.
- Eligibility requires an approved 40-hour course plus 480 post-course patient-care hours with preceptor approval.
- The June 2026 application lists exam fees of $250 (BNA members), $300 (UHMS or ACHM members), and $400 (nonmembers).
What CHRN Means: Certified Hyperbaric Registered Nurse
CHRN stands for Certified Hyperbaric Registered Nurse. It is the certification for registered nurses who deliver care to patients receiving hyperbaric oxygen therapy (HBOT), where patients breathe oxygen at pressures greater than one atmosphere absolute inside a monoplace or multiplace chamber. The credential tells employers, medical directors, and patients that a nurse has demonstrated working knowledge of pressure physics, oxygen physiology, chamber safety, and the nursing management particular to this specialty.
The acronym is shared by several unrelated credentials in other fields, so it pays to be precise. This article covers only the hyperbaric nursing certification. If you want the same answer phrased other ways, see our short explainers on what CHRN stands for, CHRN meaning, and what CHRN certification is.
Who Governs and Who Administers the Credential
Two organizations share responsibility, and candidates often blur them together:
- Baromedical Nurses Association Certification Board (BNACB) oversees nursing eligibility and certification. Think of it as the body that governs the nursing credential itself.
- National Board of Diving and Hyperbaric Medical Technology (NBDHMT) administers and grades the examination at approved testing centers.
The practical consequence is that testing happens at a designated testing site rather than by default on your home computer. Any in-house proctorship arrangement requires NBDHMT approval, so do not assume you can sit the exam unproctored at home.
Who Can Sit for the Exam
The CHRN is not an entry-level credential you can attempt straight out of nursing school. Eligibility is built around real hyperbaric experience, which is why the pool of test-takers is specialized. Candidates need:
- An unrestricted RN license.
- Two years of hospital or clinic experience, or one year of critical care experience.
- A recent active hyperbaric year of practice.
- An approved 40-hour introductory hyperbaric course, or applicable 40 Category A replacement credits.
- 480 post-course patient-care hours.
- Approval from a qualified preceptor and a recommendation from your employer.
What the Exam Looks Like
The format is straightforward, and knowing it removes one source of test-day anxiety:
| Feature | CHRN Detail |
|---|---|
| Number of questions | 120 |
| Question types | Multiple-choice and true/false (no essays or short-answer) |
| Time limit | Two hours |
| Passing threshold | 70% |
| Calculator | Pocket calculator allowed |
| Dive tables | Supplemental dive tables provided |
| Setting | Designated testing site, administered by NBDHMT |
A few details remain unverified in public sources: the split between scored and unscored items, whether the test is adaptive, and a current CHRN-specific pass rate. Be wary of any site that quotes a precise pass rate as though it were official. A historical combined-program figure exists in older materials, but it is not specific to CHRN. We discuss what is and is not known in CHRN pass rate: what the data shows, and the scoring threshold in CHRN passing score: exactly what you need to pass.
The calculator and provided dive tables tell you something important about question style: expect applied problems, not just recall. You may need to convert pressures, work a gas-law scenario, or interpret a decompression table. Practicing these mechanics before test day matters far more than memorizing definitions. If you are wondering about overall difficulty, how hard the CHRN exam is gives a candid breakdown.
What You Must Know: The Sixteen Preparation Areas
The issuer's June 2024 Resource Manual lists sixteen technical preparation topics. These are unweighted study-guide competencies; a complete current weighted blueprint has not been verified, so avoid trusting claims about exact percentage weights per area. Here is how those areas break down in practice. The full tour is in our complete guide to all 16 CHRN content areas.
Foundations: History, Physics, and Physiology
Domain 1: History of Undersea and Hyperbaric Medicine
Candidates should recognize the pioneering contributions of Behnke, Bert, Boerma, Bond, Boyle, Brummelkamp, Fontaine, Haldane, Henshaw, and Yarborough, and understand how hyperbaric and diving medicine developed side by side.
Domain 2: The Physical Aspects of Undersea and Hyperbaric Medicine
This is the calculation-heavy area, and the calculator is there for it.
- Differentiate atmospheric, barometric, absolute, gauge, and hydrostatic pressure
- Convert among ATA, FSW, PSI, MSW, and mmHg
- Apply Dalton's, Henry's, Boyle's, and Charles' Laws to physical and physiological scenarios
- Convert temperatures among Fahrenheit, Celsius, Rankine, and Kelvin
Domain 3: The Physiological Aspects of Undersea and Hyperbaric Medicine
Normal respiration and circulation, relevant medical terminology, and the direct effects of pressure during compression and decompression. It also covers indirect effects (oxygen toxicity and nitrogen narcosis) and the advantages and limits of therapeutic gases: air, oxygen, nitrogen-oxygen, and helium-oxygen.
Decompression and Therapeutic Mechanisms
Domain 4: Mechanisms and Theory of Decompression
Working knowledge of the U.S. Navy Standard Air Decompression Table, the No-Decompression Limits and Repetitive Group Designation Table, and the Residual Nitrogen Timetable for Repetitive Air Dives. Equally important: understanding the limits of these tables in preventing decompression sickness, and the factors that raise susceptibility.
Domain 5: Therapeutic Mechanisms Associated with Hyperbaric Oxygen Exposure
The six mechanisms by which oxygen above one atmosphere absolute produces benefit:
- Antimicrobial effects
- Vasoconstriction
- Hyperoxygenation
- Neovascularization
- Attenuation of reperfusion injury
- Gas bubble reduction
You should also be able to classify each accepted indication by its proposed mechanism.
Domain 6: Currently Accepted Indications for Hyperbaric Oxygen Exposure
Be able to list the indications considered appropriate for referral by the Undersea and Hyperbaric Medical Society, and know commonly used treatment protocols (absolute pressure, exposure time, and frequency) for each.
Complications and Risk Management
Domain 7: Oxygen Toxicity
Differentiate the clinical presentation of central nervous system toxicity (the Paul Bert effect) from pulmonary toxicity (the Lorrain Smith effect). Know commonly used methods to extend patient tolerance, and the prevention and management principles for both forms.
Domain 8: Other Potential Complications
Barotrauma risk is the heart of this area.
- Recognize anatomic and equipment gas-filled spaces or potential spaces before compression
- Reduce barotrauma risk through patient instruction and venting equipment before pressure changes
- Recognize potential airway compromise during decompression and the immediate management to reduce pulmonary barotrauma risk
- Understand how CNS oxygen toxicity and reactive airway disease complicate decompression
Facility, Safety, and Equipment
Domain 9: The Hyperbaric Medicine Facility
Each chamber type, its operating characteristics, and its respective advantages and disadvantages.
Domain 10: Hyperbaric Safety I. Protecting the Environment
Chamber design and configuration (acrylic and steel-hulled vessels), safe handling of compressed gas cylinders, color codes for oxygen, compressed air, nitrogen-oxygen mixtures, helium-oxygen mixtures, nitrogen, and helium, and the measures that reduce chamber fire risk, including ancillary equipment, chamber materials, and personal items.
Domain 11: Hyperbaric Safety II. Protecting the Patient
This area is where nursing judgment meets physics.
- Effects of pressure changes on gas-filled spaces in the body, vascular access lines, and monitoring and support equipment
- Special hazards in patients with pulmonary pathology
- Physiological risks in insulin- and non-insulin-dependent diabetics, patients with seizure history or recent head injury, febrile patients, and those with chest surgery, penetrating chest injury, or reconstructive ear surgery
- Pre-exposure assessment: pressure equalization education, expected temperature changes, and removal of restricted items such as static-producing clothing, hairpieces, fresh nail polish, makeup, body lotions, loose dentures, Velcro attachments, and battery-operated devices like hearing aids and Holter monitors
- Recognizing signs of pulmonary barotrauma of ascent and premonitory signs of CNS oxygen toxicity
Domain 12: NFPA Guidelines for Hyperbaric Chambers
The manual lists NFPA hyperbaric-chamber guidance as a preparation topic but gives no separate detailed chapter body for it, so plan to consult the current standard directly.
Domain 13: Transcutaneous Oxygen Monitoring
TcPO2 technology, the monitor and ancillary equipment, test conduct consistent with current industry standards, obtaining the subject's consent, and inspecting the equipment needed for a TcPO2 study.
The Nursing-Specific Core
Domain 14: Nursing Management of the Patient Undergoing Hyperbaric Oxygen Therapy
Human responses to actual or potential problems from altered health status (physiological, psychological, sociological, and cognitive), the nursing process applied to care planning, pharmacology and drug interactions in the hyperoxic hyperbaric environment, wound healing and adjunctive therapies, and care of critically ill and pediatric patients.
Domain 15: Nursing Standards of Practice
Anchored to the BNA Hyperbaric Nursing Standards published on the BNA website. As with NFPA, the manual lists this topic without a separate detailed chapter body.
Domain 16: Basic Operation of All Hyperbaric Chambers
Operation of both monoplace and multiplace chambers.
Key Takeaway
Do not treat the sixteen areas as equal in weight; official weights are unverified. Instead, spend extra time wherever you are weakest and where applied problems appear, especially pressure conversions, gas laws, decompression tables, and patient-safety screening.
For a compressed review, the CHRN cheat sheet distills the must-know facts, and the CHRN study guide maps them into a preparation plan.
Fees, Registration, and Timing
The June 2026 initial application confirms three fee tiers, determined by membership evidence submitted with your application:
| Applicant Category | Initial Exam Fee |
|---|---|
| BNA member | US$250 |
| UHMS or ACHM member | US$300 |
| Nonmember | US$400 |
The June 2024 manual lists US$100 for a repeat examination; no newer retake-fee override turned up in the retrieved initial application, so confirm the current retake fee before you rely on that figure. The application also says to register 30 days before the test. Because the exam is delivered at approved sites, plan scheduling early rather than assuming you can book at the last minute.
Keeping the Credential: The Four-Year Renewal Cycle
CHRN certification renews every four years. The August 2025 renewal form requires:
- An active RN license.
- Employer or medical-director confirmation of at least one year of hyperbaric experience, including 480 hours within the last 12 months.
- 40 continuing education hours across the four years, including 20 Category A hours.
Renewal fees are US$150 for BNA members, US$200 for UHMS or ACHM members, and US$250 for nonmembers. A lapse adds US$100 and removes member discounts. Note that the older manual's statement that ongoing hours need not be logged does not waive the newer form's employer-validated recent-practice requirement. If you let your hyperbaric practice hours slip, renewal can become a problem even if your CE credits are complete.
Where CHRNs Work and Why Employers Value It
Hyperbaric nurses are most often found in hospital-based wound care and hyperbaric centers, outpatient wound-healing programs, and facilities that operate monoplace or multiplace chambers for accepted indications. Because the exam content ties directly to chamber safety, patient screening, and complications like barotrauma and oxygen toxicity, employers value the credential as evidence that a nurse can safely deliver treatment in an environment where errors carry unusual risk. The employer-recommendation requirement for eligibility also means many nurses pursue the CHRN as part of a deliberate career path in their program.
For market-facing details, see CHRN jobs and the CHRN salary guide. Salary figures vary by region and employer, and this article does not cite specific numbers. To weigh the investment, read is the CHRN certification worth it?.
Sequencing Your Preparation Around the Content Areas
The sixteen areas build on one another, so order matters more than hours logged. Here is one sensible progression, using the domain numbers above:
Physics First (Domains 1-2)
- Drill ATA/FSW/PSI/MSW/mmHg conversions until automatic
- Work gas-law problems with the pocket calculator you will bring
- Skim the history figures; return later for retention
Physiology and Decompression (Domains 3-5)
- Practice the Navy tables you will be given on exam day
- Memorize the six therapeutic mechanisms and tie each to indications
Indications, Toxicity, and Complications (Domains 6-8)
- Verify indications and protocols against current UHMS sources
- Contrast CNS and pulmonary oxygen toxicity presentations
Safety, Equipment, and Nursing (Domains 9-16)
- Build a pre-treatment patient screening checklist from Domain 11
- Read the NFPA and BNA standards directly, since the manual gives no chapter body for them
Finish by taking full-length timed practice sets: 120 questions in two hours leaves roughly one minute per item, so pacing is a skill you should rehearse. You can try our CHRN practice tests to simulate that format and identify weak domains, and the main practice site lets you review answer rationales afterward.
Frequently Asked Questions
CHRN stands for Certified Hyperbaric Registered Nurse. It is the credential for registered nurses practicing in hyperbaric oxygen therapy. See also what is a CHRN.
The exam has 120 multiple-choice and true/false questions with a two-hour limit. The passing threshold is 70%. The scored versus unscored split is not publicly confirmed.
Not by default. NBDHMT administers testing at designated testing sites, and any in-house proctorship requires NBDHMT approval. Unrestricted home testing is not established.
You need an unrestricted RN license, qualifying hospital, clinic, or critical care experience, a recent active hyperbaric year, an approved 40-hour course (or applicable Category A replacement credits), 480 post-course patient-care hours, preceptor approval, and an employer recommendation.
Renewal is every four years. It requires an active RN license, 40 CE hours including 20 Category A, and employer-validated recent practice including 480 hours in the previous 12 months. Fees are US$150, US$200, or US$250 by membership group, and a lapse adds US$100.