- The Short Answer: What a CHRN Actually Is
- Who Oversees It and Who Tests It
- What a CHRN Does at the Chamber Door
- The Road to Eligibility
- What the Exam Looks Like
- What You Must Master: The Sixteen Content Areas
- Fees, Registration and Renewal
- Where CHRNs Work
- Sequencing Your Preparation by Domain
- Credentials Often Confused With It
- Frequently Asked Questions
- CHRN means Certified Hyperbaric Registered Nurse: a nursing credential for RNs who deliver hyperbaric oxygen therapy.
- BNACB governs nursing certification, while NBDHMT administers and grades the exam at approved testing sites.
- The exam has 120 multiple-choice and true/false items, a two-hour limit, and a 70% passing threshold.
- Eligibility requires an unrestricted RN license, a 40-hour introductory course, and 480 post-course patient-care hours.
The Short Answer: What a CHRN Actually Is
A CHRN is a Certified Hyperbaric Registered Nurse: a registered nurse who has earned a specialty certification in hyperbaric nursing. The credential shows that the nurse understands the physics, physiology, safety requirements, and patient care demands of delivering hyperbaric oxygen therapy (HBOT), in which patients breathe oxygen at pressures greater than one atmosphere absolute inside a pressurized chamber.
Other credentials share the same four letters. This article covers only the nursing certification in undersea and hyperbaric medicine. If you want shorter explainers on the terminology, the pages on what CHRN stands for and CHRN meaning cover the basics. Here we go deeper into what the certification involves, how it is earned, and what it asks of a nurse.
Who Oversees It and Who Tests It
Two bodies share responsibility for the credential, and candidates often blur them together.
| Body | Role in the CHRN process |
|---|---|
| Baromedical Nurses Association Certification Board (BNACB) | Oversees nursing eligibility and certification |
| National Board of Diving and Hyperbaric Medical Technology (NBDHMT) | Administers and grades the examination at approved testing centers |
The practical consequence is that you do not sit for this exam by default at home on your own computer. Testing takes place at a designated site, and any in-house proctorship arrangement requires NBDHMT approval. Plan your logistics accordingly, and read CHRN exam dates, testing windows and scheduling before choosing a target date.
What a CHRN Does at the Chamber Door
The certification content mirrors the job. A hyperbaric nurse is responsible for far more than starting a treatment, and the published scope of the certification reflects that. Typical responsibilities include:
- Pre-treatment assessment: checking each patient before every exposure, teaching pressure-equalization methods, and explaining expected chamber temperature changes.
- Patient preparation: removing restricted items such as static-producing clothing, hairpieces, recently applied nail polish, makeup, body lotions, loose dentures, Velcro attachments, and battery-operated devices like hearing aids and Holter monitors.
- Risk recognition during compression and decompression: spotting signs of barotrauma and the early warning signs of central nervous system oxygen toxicity.
- Equipment awareness: understanding how pressure changes affect gas-filled spaces in vascular access lines, patient support devices, and monitoring equipment.
- Wound and adjunctive care: since many referrals involve problem wounds, nurses need working knowledge of healing and therapies that support it.
- Medication awareness: understanding how drugs behave, or interact, in a hyperoxic, hyperbaric environment.
The Road to Eligibility
The CHRN is not an entry-level credential you can attempt straight out of nursing school. The prerequisites are layered and require documented hyperbaric experience. In summary:
- An unrestricted RN license.
- Two years of hospital or clinic experience, or one year of critical care.
- A recent active year in hyperbaric practice.
- An approved 40-hour introductory 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.
For a full checklist with documentation tips, see CHRN requirements: eligibility, prerequisites and how to qualify. If you are still deciding on the introductory course, the overview at CHRN training is a useful starting point.
What the Exam Looks Like
The format is fixed and straightforward, and it is worth knowing before you start practicing.
| Feature | CHRN detail |
|---|---|
| Number of questions | 120 |
| Item types | Multiple-choice and true/false (no essays or short-answer items) |
| Time limit | Two hours |
| Passing threshold | 70% |
| Calculator | Pocket calculator allowed |
| Reference materials | Supplemental dive tables are provided |
| Setting | Designated testing site, not default home testing |
Two items on that list shape how you should study. First, the calculator and dive tables mean you should expect computation: pressure conversions and decompression-table lookups are fair game. Second, two hours for 120 items works out to an average of one minute per question, so fluency with the math matters as much as recall.
Some details are not publicly confirmed. The split between scored and unscored items is unknown, and the current CHRN-specific pass rate is not publicly disclosed. A historical 74% figure refers to a combined program and should not be read as a CHRN pass rate. For a careful look at what is and is not known, see CHRN pass rate: what the data shows and CHRN passing score: exactly what you need to pass.
Key Takeaway
Do not rely on unverified pass-rate claims or on assumptions about adaptive testing. What is established is a 120-item, two-hour, 70% exam with multiple-choice and true/false items only. Build your preparation around that.
What You Must Master: The Sixteen Content Areas
The preparation scope comes from the issuer's study-guide contents. The sixteen areas below are unweighted study-guide competencies. Official percentage weights for each have not been verified, so do not treat any single area as proven to dominate the exam. The full breakdown is in CHRN exam domains: a complete guide to all 16 content areas; here is a concentrated tour.
Foundations: history, physics and physiology
Domain 1: History of Undersea and Hyperbaric Medicine
Candidates should recognize the pioneering contributions of figures including Behnke, Bert, Boerma, Bond, Boyle, Brummelkamp, Fontaine, Haldane, Henshaw, and Yarborough, and understand how hyperbaric and diving medicine developed together.
Domain 2: The Physical Aspects of Undersea and Hyperbaric Medicine
This is the quantitative core of the exam.
- Distinguish 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
Expect normal respiration and circulation, relevant medical terminology, the direct effects of pressure during compression and decompression, and the indirect effects: oxygen toxicity and nitrogen narcosis. You should also understand the advantages and limitations of air, oxygen, nitrogen-oxygen, and helium-oxygen.
Decompression and therapeutic science
Domain 4: Mechanisms and Theory of Decompression
Working knowledge of three U.S. Navy resources is called for: the Standard Air Decompression Table, the No-Decompression Limits and Repetitive Group Designation Table, and the Residual Nitrogen Timetable. You should also understand the limits of these tables in preventing decompression sickness and the factors that increase susceptibility to it.
Domain 5: Therapeutic Mechanisms Associated with Hyperbaric Oxygen Exposure
Know how oxygen at more than one atmosphere absolute produces six mechanisms:
- 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 therapeutic mechanism.
Domain 6: Currently Accepted Indications for Hyperbaric Oxygen Exposure
Candidates need to list the accepted indications recognized by the Undersea and Hyperbaric Medical Society and know the commonly used protocols: absolute pressure, exposure time, and frequency of treatments.
Complications and risk
Domain 7: Oxygen Toxicity
Differentiate the presentation of central nervous system toxicity (the Paul Bert effect) from pulmonary toxicity (the Lorrain Smith effect). Know the methods used to extend patient tolerance and the prevention and management principles for both.
Domain 8: Other Potential Complications
- Recognize every anatomic and equipment gas-filled space or potential space before compression.
- Reduce barotrauma risk through patient instruction and proper venting of equipment.
- Recognize potential airway compromise, especially during decompression, and know 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
Know each chamber type, its advantages and disadvantages, and its operating characteristics.
Domain 10: Hyperbaric Safety I. Protecting the Environment
This domain covers acrylic and steel-hulled chamber 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 that reduce chamber fire risk, including ancillary equipment, chamber materials, and personal items.
Domain 11: Hyperbaric Safety II. Protecting the Patient
Special attention goes to patients with specific risk factors.
- Pulmonary pathology and its pressure-related hazards.
- Insulin- and non-insulin-dependent diabetes.
- Seizure history or recent head injury.
- Fever.
- Prior chest surgery, thoracic procedures, or penetrating chest injury.
- History of reconstructive ear surgery.
You should also know the signs of pulmonary barotrauma of ascent and the premonitory signs of CNS oxygen toxicity.
Domain 12: Understanding of the NFPA guidelines for hyperbaric chambers
NFPA guidance is listed in the study-guide contents, but the manual does not give it a separate detailed chapter. Use the current NFPA material directly rather than assuming the manual covers it fully.
Monitoring, nursing practice and operations
Domain 13: Transcutaneous Oxygen Monitoring
Know TcPO2 technology, the monitor and its ancillary equipment, testing consistent with current industry standards, obtaining patient consent, and inspecting equipment before a study.
Domain 14: Nursing Management of the Patient Undergoing Hyperbaric Oxygen Therapy
This area covers human responses to actual or potential health problems (physiological, psychological, sociological, and cognitive), the nursing process in care planning, pharmacology in the hyperbaric hyperoxic environment, wound healing and adjunctive therapies, and care of critically ill and pediatric patients.
Domain 15: Nursing Standards of Practice
The reference here is the BNA Hyperbaric Nursing Standards published on the Baromedical Nurses Association website. As with NFPA, the manual lists this topic without a detailed chapter body, so go to the source standards.
Domain 16: Understanding of basic operation of all hyperbaric chambers
This includes both monoplace and multiplace chambers.
Fees, Registration and Renewal
The initial application, as published for June 2026, sets fees by membership status and requires membership evidence. Registration is expected 30 days before the test.
| Item | BNA member | UHMS or ACHM member | Nonmember |
|---|---|---|---|
| Initial exam application | US$250 | US$300 | US$400 |
| Renewal (August 2025 form) | US$150 | US$200 | US$250 |
The June 2024 manual lists US$100 for a repeat examination. No newer retake-fee override was found in the retrieved initial application, so confirm the current figure with NBDHMT before you budget. A lapsed certification adds US$100 on renewal and removes member discounts. For a full budgeting walk-through, see CHRN certification cost: complete pricing breakdown.
Renewal in brief
The credential is renewed 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 previous 12 months.
- 40 continuing education hours over the four years, including 20 Category A hours.
Key Takeaway
An older manual statement that ongoing hours need not be logged does not override the newer renewal form's employer-validated recent-practice requirement. Keep your hours and CE documentation organized from day one of each four-year cycle.
Where CHRNs Work
CHRNs work wherever hyperbaric oxygen therapy is delivered. That generally means hospital-based hyperbaric departments, outpatient wound care and hyperbaric centers, and facilities operating monoplace or multiplace chambers. Because so many HBOT referrals involve problem wounds, nurses with wound-healing knowledge are especially well positioned. Employers care about both the credential and demonstrated chamber experience, which is why the eligibility path requires documented hours and a preceptor and employer sign-off.
For a closer look at the hiring landscape, see CHRN jobs. For earnings context, the CHRN salary guide is the place to start, and the CHRN return-on-investment analysis helps weigh cost against career benefit. Pay varies by region, facility type, and experience, so treat any single figure with caution.
Sequencing Your Preparation by Domain
Because the exam mixes calculation and recall, the order in which you tackle domains matters. One workable approach follows the logic of the content itself:
Physics first (Domain 2)
- Drill ATA, FSW, PSI, MSW, and mmHg conversions until automatic.
- Work gas-law problems with a pocket calculator, since one is permitted.
- Practice temperature conversions among all four scales.
Physiology, decompression and oxygen toxicity (Domains 3, 4, 7)
- Learn the direct and indirect effects of pressure.
- Practice with U.S. Navy table lookups.
- Separate the Paul Bert and Lorrain Smith presentations.
Therapeutics and patient safety (Domains 5, 6, 8, 11, 14)
- Match each accepted indication to its mechanism.
- Build checklists for pre-treatment assessment.
- Verify indications against current UHMS material.
Facility, fire safety and standards (Domains 9, 10, 12, 13, 15, 16)
- Review chamber types, gas color codes, and fire-risk measures.
- Read the NFPA guidance and BNA standards directly.
- Finish with timed mixed sets of multiple-choice and true/false items.
Front-loading the math pays off because it underpins later topics: you cannot reason about decompression or barotrauma without pressure and gas-law fluency. For a fuller plan, see the CHRN study guide for passing on your first attempt, and keep the one-page CHRN cheat sheet handy for last-week review. If you are wondering about difficulty before committing, the CHRN difficulty guide offers perspective. To check your readiness under realistic conditions, use the CHRN practice tests, and revisit weak domains afterward. Practice-question allocation on any study site is editorial, not an official blueprint, so use it to find gaps rather than to predict exact exam weighting.
Credentials Often Confused With It
The basic Certified Hyperbaric Registered Nurse certification is distinct from related and similarly named credentials. Do not substitute ACHRN, CHRNC, or an administrative renewal pathway for it. Within CHRN documents, CHT refers to Certified Hyperbaric Technologist, the technologist credential in the same field. It has no connection to any other credential using those letters outside hyperbaric medicine.
If you landed here searching for another "CHRN," double-check the issuing organization. The Certified Hyperbaric Registered Nurse credential is overseen by BNACB and tested through NBDHMT. For more definitional resources, see what CHRN certification is and the CHRN certification overview.
Frequently Asked Questions
CHRN stands for Certified Hyperbaric Registered Nurse. It is a nursing certification for RNs who provide care to patients receiving hyperbaric oxygen therapy. It is overseen by the Baromedical Nurses Association Certification Board, with testing administered and graded by the National Board of Diving and Hyperbaric Medical Technology.
The exam has 120 items in multiple-choice and true/false formats, with a two-hour limit. The passing threshold is 70%. Essays and short-answer questions are explicitly excluded. A pocket calculator is allowed, and supplemental dive tables are provided.
Yes. 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 or applicable replacement credits, 480 post-course patient-care hours, preceptor approval, and an employer recommendation.
The June 2026 initial application lists US$250 for BNA members, US$300 for UHMS or ACHM members, and US$400 for nonmembers. A repeat examination was listed at US$100 in the June 2024 manual, but confirm the current retake fee with NBDHMT before budgeting.
Every four years. Renewal requires an active RN license, 40 CE hours including 20 Category A hours, and employer or medical director confirmation of recent practice, including 480 hours in the previous 12 months. Renewal fees are US$150, US$200, or US$250 by membership group, and a lapse adds US$100 while removing member discounts.