- What CHRN Means and Who Governs It
- Who Qualifies to Sit for the Exam
- Exam Format and Testing Mechanics
- Application Fees and Registration
- What the Exam Covers: The Sixteen Preparation Topics
- Where Nursing Judgment Meets Chamber Physics
- Sequencing Your Preparation Around the Content
- Keeping the Credential: Renewal Every Four Years
- Where the Credential Gets Used
- Frequently Asked Questions
- CHRN means Certified Hyperbaric Registered Nurse; BNACB governs nursing certification while NBDHMT administers and grades the exam.
- The exam has 120 multiple-choice and true/false items, a two-hour limit, and a 70% passing threshold.
- Eligibility requires a 40-hour introductory course plus 480 post-course patient-care hours with preceptor approval.
- The June 2026 application lists fees of $250 (BNA), $300 (UHMS or ACHM), and $400 (nonmember).
What CHRN Means and Who Governs It
CHRN stands for Certified Hyperbaric Registered Nurse. It is a specialty nursing credential for registered nurses who care for patients receiving hyperbaric oxygen therapy (HBOT), the clinical use of oxygen at pressures above normal atmospheric pressure inside a treatment chamber. If you have seen the acronym attached to other credentials elsewhere, set those aside: on this page, CHRN refers only to the hyperbaric nursing certification. For a quick orientation on the acronym itself, see our short explainers on what CHRN stands for and CHRN meaning.
Two bodies split responsibility for the credential. The Baromedical Nurses Association Certification Board (BNACB) oversees nursing eligibility and certification. The National Board of Diving and Hyperbaric Medical Technology (NBDHMT) administers and grades the testing at approved centers. That division matters in practice: your eligibility questions and your exam logistics may route to different places, and the exam is not a default take-it-at-home event.
This article is a hub-style overview. For deeper dives, our CHRN certification page and the guide on what CHRN certification is cover adjacent angles, while the sections below walk through eligibility, format, fees, content, and renewal.
Who Qualifies to Sit for the Exam
The CHRN is not an entry-level exam you can attempt straight out of nursing school. The prerequisites are layered, and several of them involve time spent actually working in hyperbaric medicine. Based on the issuer's published materials, a candidate needs:
- An unrestricted RN license.
- Two years of hospital or clinic experience, or one year of critical care experience.
- A recent active hyperbaric year of experience.
- Completion of an approved 40-hour introductory course, or applicable 40 Category A replacement credits.
- 480 post-course patient-care hours, with approval from a qualified preceptor.
- An employer recommendation.
Notice the sequencing. The 40-hour course and the 480 experience hours are prerequisites. They are not part of the exam itself and have nothing to do with the exam timer. Candidates sometimes blur these together; the 40 hours is training you complete beforehand, the 480 hours is supervised clinical practice you log afterward, and only then do you register to test. Our CHRN requirements guide breaks down how to document each item, and CHRN training covers the course side.
Exam Format and Testing Mechanics
The published CHRN resource manual specifies the exam structure plainly:
| Feature | What the issuer states |
|---|---|
| Number of questions | 120 |
| Item types | Multiple-choice and true/false (no essays or short-answer) |
| Time limit | Two hours |
| Passing threshold | 70% |
| Tools | Pocket calculator allowed; supplemental dive tables provided |
| Testing location | Designated testing site; any in-house proctorship requires NBDHMT approval |
Two things are worth stating honestly about what is not known. The split between scored and unscored items has not been published in the materials reviewed, and unrestricted open-book or adaptive testing is not established. Treat the exam as a fixed-length, closed-style test and prepare accordingly. The page on the CHRN passing score explains how the 70% threshold translates into question counts you can aim for.
On difficulty and pass rates, be cautious about numbers floating around. A current CHRN-specific pass rate is not publicly disclosed, and an older combined-program figure is not specific to this exam. Our write-ups on the CHRN pass rate and how hard the CHRN exam is discuss what can and cannot be concluded from the available data.
Application Fees and Registration
The June 2026 initial application lays out a tiered fee structure tied to membership:
| Applicant category | Initial exam fee |
|---|---|
| BNA member | US$250 |
| UHMS or ACHM member | US$300 |
| Nonmember | US$400 |
The application asks for membership evidence, so if you are claiming a discounted rate, have your proof ready. It also says to register 30 days before the test, which means you should work backward from your intended exam window rather than treating registration as a last-minute step. The June 2024 manual lists a US$100 fee for a repeat examination; no newer retake-fee override turned up in the retrieved application, so confirm the current repeat fee with the issuer before you budget around it.
The fee difference between nonmember and BNA member status is large enough that comparing membership cost against the savings is a reasonable exercise before you apply. For the full picture, including the course and renewal costs, see the CHRN certification cost breakdown, and for scheduling details check CHRN exam dates.
What the Exam Covers: The Sixteen Preparation Topics
Here is where candidates most often get tripped up by loose claims online. The issuer's study-guide contents list sixteen technical preparation topics. These are unweighted issuer study-guide competencies. An official exam-domain count and official percentage weights for each area remain unverified, so nobody can honestly tell you "domain X is 20% of the test." The manual also contains thirteen detailed body sections while its introduction still says twelve; neither number is an authenticated domain count. For that reason, this site presents the sixteen topics as a preparation scope, not a scored blueprint. Our CHRN exam domains guide explores each in more depth.
The sixteen topics, in the order the study guide presents them:
- History of Undersea and Hyperbaric Medicine
- The Physical Aspects of Undersea and Hyperbaric Medicine
- The Physiological Aspects of Undersea and Hyperbaric Medicine
- Mechanisms and Theory of Decompression
- Therapeutic Mechanisms Associated with Hyperbaric Oxygen Exposure
- Currently Accepted Indications for Hyperbaric Oxygen Exposure
- Oxygen Toxicity
- Other Potential Complications
- The Hyperbaric Medicine Facility
- Hyperbaric Safety I: Protecting the Environment
- Hyperbaric Safety II: Protecting the Patient
- Understanding of the NFPA guidelines for hyperbaric chambers
- Transcutaneous Oxygen Monitoring
- Nursing Management of the Patient Undergoing Hyperbaric Oxygen Therapy
- Nursing Standards of Practice (BNA Hyperbaric Nursing Standards)
- Understanding of basic operation of all hyperbaric chambers, including monoplace and multiplace chambers
The foundational science block
History of Undersea and Hyperbaric Medicine
The stated objective is to identify the pioneering contributions of figures including Behnke, Bert, Boerma, Bond, Boyle, Brummelkamp, Fontaine, Haldane, Henshaw, and Yarborough, and to understand how hyperbaric and diving medicine developed together.
- Match each name to the discovery or clinical observation associated with it.
- Expect recognition-style items rather than deep narrative.
The Physical Aspects of Undersea and Hyperbaric Medicine
This is the quantitative core, and it is where the pocket calculator and provided dive tables earn their place.
- 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.
Mechanisms and Theory of Decompression
Candidates need 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.
- Understand the limits of these tables in preventing decompression sickness.
- Know the physiological and operational factors that raise susceptibility to decompression sickness.
Where Nursing Judgment Meets Chamber Physics
What separates the CHRN from a pure technologist exam is the nursing layer. The clinical topics ask you to reason about a specific patient inside a pressurized environment, which is a different skill from recalling a gas law.
Therapeutic mechanisms and indications
The therapeutic mechanisms topic asks you to appreciate how oxygen partial pressures above one atmosphere absolute produce six effects: antimicrobial action, vasoconstriction, hyperoxygenation, neovascularization, attenuation of reperfusion injury, and gas bubble reduction. Beyond naming them, you are expected to classify each currently accepted indication by its proposed therapeutic mechanism. The indications topic then asks you to list the accepted indications recognized by the Undersea and Hyperbaric Medical Society and to know the commonly used treatment protocols (pressure, exposure time, and frequency) for each.
Oxygen toxicity and complications
Oxygen Toxicity
You must distinguish central nervous system toxicity (the Paul Bert effect) from pulmonary toxicity (the Lorrain Smith effect), and know how to extend patient tolerance and how to prevent and manage both forms.
- Recognize pre-monitory signs of CNS oxygen toxicity before a seizure develops.
- Know that tolerance-extending methods are part of the stated objective.
Other Potential Complications
Barotrauma dominates here. The objectives center on recognizing anatomic and equipment gas-filled spaces before compression, minimizing risk through patient education and venting of equipment, and recognizing airway compromise during decompression.
- Understand how CNS oxygen toxicity and reactive airway disease complicate decompression.
- Know the immediate management that reduces the risk of pulmonary barotrauma.
Protecting the patient
Hyperbaric Safety II is arguably the most nursing-flavored topic. It covers how pressure changes affect gas-filled spaces in the body and in vascular access lines, patient support devices, and monitoring equipment, along with special risks for patients with pulmonary pathology. The stated risk groups include insulin and non-insulin dependent diabetics, patients with a seizure history or recent head injury, febrile patients, those with prior chest surgery or penetrating chest injury, and those with a history of reconstructive ear surgery.
The pre-treatment assessment requirements are concrete and testable: teaching pressure equalization methods, anticipating chamber temperature changes, and removing restricted items such as static-producing clothing, hairpieces, recently applied nail polish, make-up and body lotions, loose dentures, Velcro attachments, and battery-operated devices like hearing aids and Holter monitors. Expect scenario items built on exactly this kind of checklist thinking.
Facility, fire safety, and monitoring
The facility and environment topics cover chamber types and their advantages and disadvantages, acrylic versus steel-hulled vessel design, safe handling of compressed gas cylinders, color codes for oxygen, compressed air, nitrogen-oxygen mixtures, helium-oxygen mixtures, nitrogen, and helium, and the measures needed to reduce chamber fire risk, including ancillary equipment, chamber materials, and personal items. Transcutaneous oxygen monitoring (TcPO2) is its own topic, covering the technology, the monitor and ancillary equipment, inspection procedures, and obtaining consent for the procedure.
Nursing Management of the HBOT Patient
This topic ties the nursing process to a care plan and adds pharmacology in the hyperbaric hyperoxic environment.
- Apply the nursing process to develop a patient care plan.
- Understand drug interactions and altered drug effects under hyperoxia.
- Know wound healing and adjunctive therapies that stimulate or enhance healing.
- Understand the care of critically ill and pediatric patients.
Sequencing Your Preparation Around the Content
Because no official weights exist, a sensible plan front-loads the material that everything else depends on. The physics and physiology topics underpin decompression, toxicity, and barotrauma, so learn them first. The timeline below is one editorial suggestion, not an official schedule. For a fuller plan, see our CHRN study guide, and keep the CHRN cheat sheet handy for last-week review.
Pressure and gas laws
- Drill ATA/FSW/PSI/MSW/mmHg conversions until they are automatic.
- Work Boyle, Dalton, Henry, and Charles problems with the calculator you plan to use.
Physiology and decompression
- Review respiration, circulation, and the effects of compression and decompression.
- Practice reading the Navy tables, including repetitive group designations.
Mechanisms, indications, toxicity, complications
- Classify each accepted indication by therapeutic mechanism.
- Contrast Paul Bert and Lorrain Smith effects; rehearse barotrauma recognition.
Safety, facility, nursing management, standards
- Study the NFPA guidance and BNA standards directly, since the manual does not detail them.
- Run patient-preparation and risk-group scenarios, then take timed mixed practice sets.
When you are ready to test yourself under realistic conditions, our CHRN practice tests let you rehearse the 120-item, two-hour format, and the full practice question bank helps you find which topics need another pass.
Keeping the Credential: Renewal Every Four Years
Certification is not permanent. Renewal happens every four years, and 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 previous 12 months.
- 40 CE hours over the four-year cycle, including 20 Category A hours.
One subtlety: an older manual statement suggested ongoing hours need not be logged, but that does not waive the newer form's employer-validated recent-practice requirement. Follow the newer form. 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, so renewing on time is meaningfully cheaper than recovering from a lapse.
Where the Credential Gets Used
CHRN-certified nurses work wherever hyperbaric oxygen therapy is delivered: hospital-based hyperbaric departments, outpatient wound care and hyperbaric centers, and facilities operating monoplace or multiplace chambers. The credential signals that you can manage the intersection of nursing assessment and chamber safety, which employers in those settings value because a single mistake can involve fire risk, barotrauma, or an oxygen-toxicity event.
Specific compensation figures are not established in the materials behind this article, so we will not quote any. For current thinking on earnings and listings, see our CHRN salary guide, browse CHRN jobs, and weigh the tradeoffs in whether the CHRN certification is worth it.
Key Takeaway
Treat the CHRN as a clinical-plus-safety credential. Master the physics and physiology first, then spend your remaining time on patient-specific scenarios, because that is where nursing judgment is tested hardest.
Frequently Asked Questions
CHRN stands for Certified Hyperbaric Registered Nurse, a specialty certification for registered nurses who care for patients receiving hyperbaric oxygen therapy. BNACB oversees nursing certification and NBDHMT administers and grades the exam.
The exam has 120 multiple-choice and true/false questions, a two-hour time limit, and a 70% passing threshold. It does not include essay or short-answer items, and a pocket calculator is allowed with dive tables provided.
You need an unrestricted RN license, two years of hospital or clinic experience or one year of critical care, a recent active hyperbaric year, an approved 40-hour introductory course, 480 post-course patient-care hours with preceptor approval, and an employer recommendation.
Per the June 2026 application, the fee is US$250 for BNA members, US$300 for UHMS or ACHM members, and US$400 for nonmembers, with membership evidence required. The June 2024 manual lists US$100 for a repeat exam, so confirm the current retake fee before budgeting.
Renewal is every four years. It requires an active RN license, employer or medical-director confirmation of recent hyperbaric practice including 480 hours in the previous 12 months, and 40 CE hours with 20 in Category A. Fees run US$150, US$200, or US$250 depending on membership.