- The Exam at a Glance
- Registration and Fee Quick Reference
- Eligibility Checklist in One Pass
- Physics and Gas Law Essentials
- Physiology, Oxygen Toxicity and Complications
- Decompression and Dive Tables
- HBO Mechanisms and Accepted Indications
- Safety, Facility and Chamber Knowledge
- Nursing Management and TcPO2
- History: The Names to Recognize
- Scheduling the Sixteen Topics
- Renewal Cheat Sheet
- What This Cheat Sheet Cannot Tell You
- Frequently Asked Questions
- The CHRN exam is 120 multiple-choice and true/false items in two hours, with a 70% passing threshold.
- Initial application fees are US$250 for BNA members, US$300 for UHMS or ACHM members, and US$400 for nonmembers.
- Dive tables are provided and a pocket calculator is allowed, so practice pressure conversions and gas-law math.
- Renewal is every four years: 40 CE hours (20 Category A) plus 480 hyperbaric practice hours in the prior 12 months.
The Exam at a Glance
This page condenses what a Certified Hyperbaric Registered Nurse candidate needs on one screen. The credential is specific to nurses working in hyperbaric medicine. The Baromedical Nurses Association Certification Board (BNACB) oversees nursing eligibility and certification, while the National Board of Diving and Hyperbaric Medicine Technology (NBDHMT) administers and grades the test. If you want the full narrative version of this material, the CHRN study guide walks through a complete first-attempt plan.
| Exam Element | What the Published Materials Say |
|---|---|
| Number of items | 120 |
| Time limit | Two hours |
| Item types | Multiple-choice and true/false; no essays or short-answer items |
| Passing threshold | 70% |
| Aids | Pocket calculator allowed; supplemental dive tables provided |
| Testing location | Designated testing site; any in-house proctorship requires NBDHMT approval |
| Scored vs. unscored items | Split not verified in published sources |
| Pass rate | Not publicly disclosed for the CHRN specifically |
Two points deserve emphasis. First, this is not default unproctored home testing; plan around a designated site. Second, the 70% line over 120 items is a useful planning anchor, but because the scored/unscored split is not documented, treat every item as if it counts. For a deeper look at the number itself, see CHRN passing score: exactly what you need to pass.
Registration and Fee Quick Reference
The June 2026 initial application confirms the following fee tiers, and it requires membership evidence for the discounted rates. The application also advises registering 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 |
- Repeat examination: The June 2024 manual lists US$100 for a repeat exam. No newer retake-fee override turned up in the retrieved initial application, so confirm the current figure with NBDHMT before you pay.
- Lapsed renewal: A lapse adds US$100 and removes member discounts.
- Registration timing: Submit at least 30 days before your intended test date.
Because the membership tier changes the bill noticeably, compare the cost of joining against the discount before applying. The CHRN certification cost breakdown covers the full pricing picture, and the CHRN exam dates guide covers scheduling windows and deadlines.
Eligibility Checklist in One Pass
The published requirements are layered, and missing one item stalls the whole application. Use this as a checklist, then confirm details in CHRN requirements: eligibility, prerequisites and how to qualify.
- Unrestricted RN license.
- Nursing experience: two years in a hospital or clinic, or one year in critical care.
- Recent active hyperbaric year.
- Approved 40-hour introductory course or applicable 40 Category A replacement credits.
- 480 post-course patient-care hours with preceptor validation.
- Qualified preceptor approval and an employer recommendation.
- Membership evidence if you are claiming a discounted fee tier.
Physics and Gas Law Essentials
The physical aspects of undersea and hyperbaric medicine are where a calculator and the provided dive tables earn their keep. The published terminal objectives are explicit about what you must be able to do.
Domain 2: The Physical Aspects of Undersea and Hyperbaric Medicine
You are expected to differentiate pressure terms and convert freely between units.
- Pressure terms: atmospheric, barometric, absolute, gauge and hydrostatic.
- Unit conversions: ATA, FSW, PSI, MSW and mmHg.
- Gas laws: Dalton's, Henry's, Boyle's and Charles' Laws applied to undersea and hyperbaric scenarios.
- Temperature conversions: Fahrenheit, Celsius, Rankine and Kelvin.
Practical advice: build a one-line reminder for each law and attach a clinical example to it. Boyle's Law explains why gas-filled spaces change volume with pressure, which feeds directly into barotrauma questions. Dalton's Law governs partial pressures of breathing gases, which links to oxygen toxicity. Henry's Law connects dissolved gas to decompression sickness. Charles' Law explains chamber temperature changes during compression. When you can tie each law to a bedside consequence, the calculation questions stop feeling abstract.
Physiology, Oxygen Toxicity and Complications
Three of the sixteen topics cluster around what pressure and oxygen do to the human body. They overlap heavily, so study them together.
Domain 3: The Physiological Aspects
Expect questions bridging normal physiology and hyperbaric effects.
- Normal respiration and circulation.
- Medical terminology as used in diving and hyperbaric medicine.
- Direct effects of pressure during compression and decompression, both beneficial and harmful.
- Indirect effects: oxygen toxicity and nitrogen narcosis.
- Advantages and limitations of therapeutic gases: air, oxygen, nitrogen-oxygen and helium-oxygen.
Domain 7: Oxygen Toxicity
The key skill is telling the two forms apart and managing both.
- Central nervous system toxicity is the Paul Bert Effect.
- Pulmonary toxicity is the Lorrain Smith effect.
- Know commonly used methods to extend patient tolerance to hyperbaric exposure.
- Know prevention and management principles for both forms.
Domain 8: Other Potential Complications
This topic is dominated by barotrauma prevention and airway vigilance.
- Recognize all anatomic and equipment gas-filled spaces or potential spaces before compression.
- Minimize barotrauma through patient education and appropriate venting of equipment before pressure changes.
- Recognize potential airway compromise, particularly during decompression, and know the immediate management to reduce pulmonary barotrauma risk.
- Understand how CNS oxygen toxicity and reactive airway disease complicate decompression.
Decompression and Dive Tables
Because supplemental dive tables are provided at the test, the skill being assessed is reading and applying them, not memorizing them. The published objectives for Domain 4 name three specific US Navy references.
Domain 4: Mechanisms and Theory of Decompression
- US Navy Standard Air Decompression Table.
- US Navy No-Decompression Limits and Repetitive Group Designation Table for No-Decompression Air Dives.
- US Navy Residual Nitrogen Timetable for Repetitive Air Dives.
- The limitations of these tables in preventing decompression sickness.
- Physiological and operational factors that increase susceptibility to decompression sickness.
Rehearse reading each table with a timer so the lookups are fast on test day. The limitations question is easy to overlook: the tables reduce risk but do not eliminate decompression sickness, and you should be able to explain why.
HBO Mechanisms and Accepted Indications
Domain 5: Therapeutic Mechanisms Associated with Hyperbaric Oxygen Exposure
Exposure to oxygen partial pressures above one atmosphere absolute produces six named mechanisms:
- Antimicrobial effects
- Vasoconstriction
- Hyperoxygenation
- Neovascularization
- Attenuation of reperfusion injury
- Gas bubble reduction
The published objective goes one step further: you should be able to classify each currently accepted indication by its proposed therapeutic mechanism. That classification skill is a natural fit for a self-made table, with indications down one side and mechanisms across the top.
Domain 6: Currently Accepted Indications for Hyperbaric Oxygen Exposure
- List all indications considered appropriate for hyperbaric medicine referral by the Undersea and Hyperbaric Medical Society (UHMS).
- Know the commonly used treatment protocols for each: absolute pressure, exposure time and frequency of procedures.
Safety, Facility and Chamber Knowledge
Four of the sixteen preparation topics deal with the physical environment and the standards governing it. Several have no detailed chapter bodies in the manual, so plan to use outside references for them.
Domain 9: The Hyperbaric Medicine Facility
- Each hyperbaric chamber type, including working knowledge of advantages and disadvantages.
- The operating characteristics of each chamber type.
Domain 10: Hyperbaric Safety I. Protecting the Environment
- Chamber design and configuration, including 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.
- Measures to reduce chamber fire risk, covering ancillary equipment, chamber materials and personal items.
Domain 11: Hyperbaric Safety II. Protecting the Patient
- Effects of pressure changes on gas-filled body spaces, vascular access lines, patient support equipment and monitoring equipment.
- Special hazards in patients with known pulmonary pathology.
- Special physiological risks in insulin and non-insulin dependent diabetics, patients with a seizure history or recent head injury, febrile patients, patients with chest surgery or thoracic procedures, penetrating chest injury, and a history of reconstructive ear surgery.
- Pre-exposure assessment: education on pressure equalization, anticipated chamber 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 and symptoms of pulmonary barotrauma of ascent and the warning signs of CNS oxygen toxicity.
Nursing Management and TcPO2
Domain 13: Transcutaneous Oxygen Monitoring
- TcPO2 technology and the monitor with its ancillary equipment.
- Test procedure consistent with current industry standards.
- Obtaining the subject's consent for the procedure.
- Inspection procedures for equipment used in a TcPO2 study.
Domain 14: Nursing Management of the Patient Undergoing HBOT
- Human responses to actual or potential problems related to altered health status: physiological, psychological, sociological and cognitive.
- Applying the nursing process to a patient care plan.
- Pharmacology, including drug interactions and altered drug effects in the hyperbaric hyperoxic environment.
- Wound healing and adjunctive therapies that stimulate or enhance healing.
- Care of critically ill and pediatric patients.
This is the area where your bedside experience pays off. Wound healing, pharmacology and critical care questions reward nurses who connect hyperbaric physiology to patient assessment. If you are weighing how this knowledge translates into employment, the CHRN jobs overview and CHRN salary guide cover the career side.
History: The Names to Recognize
Domain 1: History of Undersea and Hyperbaric Medicine
The published objective asks you to identify the pioneering contributions and observations of ten figures and to understand how hyperbaric and diving medicine developed in parallel.
- Behnke
- Bert
- Boerma
- Bond
- Boyle
- Brummelkamp
- Fontaine
- Haldane
- Henshaw
- Yarborough
Make a flashcard per name with a single signature contribution. Several connect to topics elsewhere on the list: Bert to CNS oxygen toxicity, Boyle to the gas law, and Haldane to decompression theory. Those links make history easier to retain than isolated trivia.
Scheduling the Sixteen Topics
The published sources do not provide official percentage weights, and the manual does not authenticate a domain count: its contents list gives sixteen technical preparation topics, thirteen detailed body sections, and an introduction that still says twelve. So the sixteen topics here are an unweighted study scope, not a blueprint. Given that, sequence your preparation so foundations come before applications. The complete guide to all 16 content areas goes deeper on each one.
Foundations: Physics and Physiology
- Pressure terms, unit conversions, four gas laws, temperature scales.
- Respiration, circulation, direct and indirect effects of pressure.
Decompression and Oxygen Effects
- Navy tables with a timer; limitations of tables.
- Paul Bert versus Lorrain Smith; complications and barotrauma.
Therapy: Mechanisms and Indications
- Six mechanisms mapped to each accepted indication.
- Protocol pressures, times and frequencies from current UHMS sources.
Safety, Chambers and Standards
- Gas color codes, fire prevention, patient restrictions.
- NFPA guidance, BNA standards, monoplace and multiplace operation.
Nursing Practice, TcPO2, History and Timed Practice
- Pharmacology, wound healing, critical and pediatric care, TcPO2 procedure.
- Ten historical names; full-length timed sets of 120 items.
Foundations go first because physics and physiology are prerequisites for understanding toxicity, decompression and safety. Finish with timed, full-length sets on the CHRN practice test site to build pacing for the two-hour limit, which works out to roughly one minute per question. For a sense of how demanding the exam feels, see how hard the CHRN exam is.
Renewal Cheat Sheet
Certification does not end at the exam. Renewal runs every four years, and the August 2025 renewal form sets specific requirements.
- Active RN license.
- 40 CE hours over four years, including 20 Category A hours.
- Employer or medical director confirmation of at least one year of hyperbaric experience, including 480 hours in the last 12 months.
- Fees: US$150 BNA, US$200 UHMS or ACHM, US$250 nonmember.
- Lapse penalty: adds US$100 and removes member discounts.
Whether the ongoing commitment pays off is a personal calculation; the CHRN ROI analysis lays out the factors to weigh.
What This Cheat Sheet Cannot Tell You
Honest preparation means knowing the gaps in the public record. Based on the materials reviewed:
- No verified weighted blueprint. The current official percentage weights and the largest weighted domain are unverified. A nursing program webpage describes a forty-percent nursing versus technical balance while recounting the early 1990s exam design, but that is historical narrative, not a current 40/60 weighted blueprint, and it supplies no weights for the sixteen topics.
- No credential-specific pass rate. A historical combined-program figure of 74% exists, but it is not specific to the CHRN, so do not treat it as your odds. The CHRN pass rate discussion explains what the data does and does not show.
- Unknown adaptive status and scored/unscored split. Unrestricted open-book or adaptive testing is not established.
- Manual sample questions are not live content. Do not treat them as actual exam items.
- Scope differs from related credentials. This sheet covers the basic Certified Hyperbaric Registered Nurse certification only, not advanced or administrative pathways.
If you are new to the credential itself, what CHRN certification is and what CHRN stands for cover the basics. The same one-page summary is also hosted at the CHRN cheat sheet page for quick reference.
Frequently Asked Questions
The exam has 120 multiple-choice and true/false items with a two-hour time limit. Essay and short-answer questions are explicitly excluded, and the passing threshold is 70%.
A pocket calculator is allowed and supplemental dive tables are provided. You should still practice reading the US Navy tables quickly and be ready to convert pressure units and apply the gas laws.
The June 2026 application lists US$250 for BNA members, US$300 for UHMS or ACHM members, and US$400 for nonmembers, with membership evidence required. A repeat exam was listed at US$100 in the June 2024 manual, so confirm the current figure before paying.
Not in the sources reviewed. The manual lists sixteen unweighted technical preparation topics, and a complete current weighted blueprint remains unverified, so study all sixteen areas rather than betting on a favored few.
Renewal is every four years. You need an active RN license, 40 CE hours including 20 Category A, and employer confirmation of at least one year of hyperbaric experience including 480 hours in the previous 12 months. A lapse adds US$100 and removes member discounts.