- What the Four Letters Actually Mean
- Who Governs and Who Tests
- Why the Acronym Causes Confusion
- What the Credential Proves About a Nurse
- The Eligibility Pathway Behind the Title
- How the Exam Is Built
- The Sixteen Preparation Topics
- Fees, Registration, and Renewal Mechanics
- Where CHRNs Work
- Sequencing Your Preparation
- Frequently Asked Questions
- CHRN here means Certified Hyperbaric Registered Nurse: a nursing credential in hyperbaric oxygen therapy, not any other credential sharing the acronym.
- BNACB oversees nursing certification; NBDHMT administers and grades the exam at approved testing centers.
- The exam has 120 multiple-choice and true/false items, a two-hour limit, and a 70% passing threshold.
- Candidates need an unrestricted RN license, an approved 40-hour course, and 480 post-course patient-care hours.
What the Four Letters Actually Mean
CHRN stands for Certified Hyperbaric Registered Nurse. Each word does work. "Certified" signals a credential earned by examination rather than a job title assigned by an employer. "Hyperbaric" names the clinical environment: patients breathing oxygen at pressures above normal atmospheric pressure inside a treatment chamber. "Registered Nurse" establishes the license foundation, since only nurses holding an unrestricted RN license can pursue it.
If you have been reading about this acronym across several pages, the companion explainers on this site cover the same ground from different angles: What Does CHRN Stand For?, What Is CHRN?, and What Is A CHRN? This article focuses on what the meaning implies for the person holding the credential and for the candidate preparing to earn it.
Who Governs and Who Tests
Two organizations share responsibility for the credential, and knowing the split saves candidates from contacting the wrong office.
| Body | Role in the CHRN process |
|---|---|
| Baromedical Nurses Association Certification Board (BNACB) | Oversees nursing eligibility and certification standards |
| National Board of Diving and Hyperbaric Medical Technology (NBDHMT) | Administers and grades the examination at approved testing centers |
Testing takes place at a designated testing site. Any in-house proctorship requires NBDHMT approval, so candidates should not plan on default unproctored home testing. Registration guidance in the current application asks candidates to register 30 days before the test, which matters when you are lining up employer sign-offs. The scheduling details are covered in CHRN Exam Dates 2026: Testing Windows, Deadlines & Scheduling.
Why the Acronym Causes Confusion
Several unrelated credentials use the letters CHRN, and search engines blend them together. A candidate looking for hyperbaric nursing information can land on pages about a different field entirely, with different eligibility rules and different exam logistics. The practical rule: verify that any source discusses the BNACB and NBDHMT, hyperbaric oxygen therapy, and a hyperbaric clinical-hours requirement. If it does not mention those, close the tab.
Related but distinct credentials inside hyperbaric medicine also deserve a mention. Within CHRN materials, "CHT" means Certified Hyperbaric Technologist, a separate technical credential. Advanced or administrative pathways are not the same as the basic Certified Hyperbaric Registered Nurse certification. This article addresses only the basic CHRN. For a plain-language overview, see What Does CHRN Mean? and What Is CHRN Certification?
What the Credential Proves About a Nurse
Holding the CHRN tells a manager or medical director that a nurse has been tested on a specific body of knowledge and has documented hands-on experience in the chamber environment. That knowledge spans physics, physiology, decompression theory, accepted indications, complications, chamber operation, fire safety, and nursing management. The credential is not a general critical-care certification; it is narrowly focused on the care of patients exposed to hyperbaric conditions.
For nurses weighing whether the investment pays off, our analysis in Is the CHRN Certification Worth It? Complete ROI Analysis 2026 examines the tradeoffs, and CHRN Salary Guide 2026: Complete Earnings Analysis addresses compensation questions.
The Eligibility Pathway Behind the Title
The title is earned through a layered pathway, not a single exam sitting. Under the current requirements, a candidate needs:
- An unrestricted RN license.
- Two years of hospital or clinic experience, or one year of critical care experience.
- A recent active year of hyperbaric experience.
- An approved 40-hour introductory course, or applicable 40 Category A replacement credits.
- 480 post-course patient-care hours, approved by a qualified preceptor.
- An employer recommendation.
Full detail on documentation and sign-offs lives in CHRN Requirements 2026: Eligibility, Prerequisites & How to Qualify, and the training side is discussed in CHRN Training.
How the Exam Is Built
The examination consists of 120 items in multiple-choice and true/false formats, with a two-hour time limit. The manual explicitly excludes essays and short-answer questions. A 70% threshold determines passing. A pocket calculator is allowed, and supplemental dive tables are provided, which signals that computation and table-reading are fair game.
| Feature | CHRN detail |
|---|---|
| Items | 120 |
| Time | Two hours |
| Formats | Multiple-choice and true/false |
| Passing threshold | 70% |
| Tools | Pocket calculator allowed; dive tables provided |
| Setting | Designated testing site, not default home testing |
Some things are not publicly established: the scored versus unscored item split, whether the test is adaptive, and a current credential-specific pass rate. A historical combined-program figure exists but is not CHRN-specific, so treat claims about pass rates skeptically. Our pages on CHRN Pass Rate 2026: What the Data Shows, CHRN Passing Score 2026: Exactly What You Need to Pass, and How Hard Is the CHRN Exam? Complete Difficulty Guide 2026 unpack what is and is not known.
The Sixteen Preparation Topics
The current-linked June 2024 resource manual lists sixteen technical preparation topics in its study-guide contents. These are issuer study-guide competencies, not an authenticated weighted blueprint. Official percentage weights and a definitive domain count remain unverified, so do not assume any topic is "worth" a particular share of the 120 items. The sixteen topics are:
- 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
A deeper walkthrough appears in CHRN Exam Domains 2026: Complete Guide to All 16 Content Areas. Below are the areas where candidates most often need concrete, hands-on fluency.
Physical Aspects: The Math Domain
This is where the calculator and 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 hyperbaric scenarios.
- Convert temperatures among Fahrenheit, Celsius, Rankine, and Kelvin.
Decompression Theory: Table Literacy
The published objectives name specific US Navy tables.
- US Navy Standard Air Decompression Table.
- No-Decompression Limits and Repetitive Group Designation Table.
- Residual Nitrogen Timetable for Repetitive Air Dives.
- The limits of those tables in preventing decompression sickness, plus factors that raise susceptibility.
Therapeutic Mechanisms
Know six mechanisms of hyperbaric oxygen and be able to classify each accepted indication by mechanism.
- Antimicrobial effects, vasoconstriction, and hyperoxygenation.
- Neovascularization, attenuation of reperfusion injury, and gas bubble reduction.
Oxygen Toxicity and Complications
Distinguish the two classic presentations and manage them.
- Central nervous system toxicity (Paul Bert effect) versus pulmonary toxicity (Lorrain Smith effect).
- Methods to extend patient tolerance; prevention and management principles.
- Recognizing gas-filled spaces before compression, venting equipment, and spotting airway compromise during decompression.
Patient Safety and Assessment
Pre-exposure assessment is a recurring theme.
- Special risks for insulin and non-insulin dependent diabetics, seizure history or recent head injury, fever, chest surgery or penetrating chest injury, and reconstructive ear surgery.
- Patient preparation: removing static-producing clothing, hairpieces, recent nail polish, makeup, body lotions, loose dentures, hook-and-loop fasteners, and battery-operated devices such as hearing aids and Holter monitors.
- Recognizing pulmonary barotrauma of ascent and premonitory signs of CNS oxygen toxicity.
Environment, Fire, and Chambers
Facility knowledge blends engineering with clinical judgment.
- Acrylic versus steel-hulled vessels; monoplace versus multiplace advantages and disadvantages.
- Safe handling of compressed gas cylinders and the color codes for oxygen, air, nitrogen-oxygen mixtures, helium-oxygen mixtures, nitrogen, and helium.
- Measures that reduce chamber fire risk, including ancillary equipment, chamber materials, and personal items.
Fees, Registration, and Renewal Mechanics
The June 2026 initial application confirms three initial fee tiers, tied to membership evidence:
| Applicant category | Initial exam fee | Renewal fee (Aug 2025 form) |
|---|---|---|
| BNA member | US$250 | US$150 |
| UHMS or ACHM member | US$300 | US$200 |
| Nonmember | US$400 | US$250 |
The June 2024 manual lists US$100 for a repeat examination; no newer retake-fee override was found in the retrieved application, so confirm before budgeting. A lapsed renewal adds US$100 and removes member discounts. For a full budget view, see CHRN Certification Cost 2026: Complete Pricing Breakdown.
Renewal happens every four years and requires:
- An active RN license.
- 40 continuing education hours, including 20 Category A.
- Employer or medical director confirmation of at least one year of hyperbaric experience, including 480 hours within the previous 12 months.
Key Takeaway
The older manual's statement that ongoing hours need not be logged does not waive the newer renewal form's employer-validated recent-practice requirement. Plan to document your hyperbaric hours as you go.
Where CHRNs Work
The credential applies wherever hyperbaric oxygen therapy is delivered under nursing care: hospital-based hyperbaric departments and wound care centers, and outpatient hyperbaric facilities. Employers in these settings value nurses who can manage both the clinical picture, such as wound healing, critically ill or pediatric patients, and drug effects in a hyperoxic environment, and the physical environment of the chamber itself. The credential also signals familiarity with BNA nursing standards and NFPA chamber guidance. For role-specific listings and employer expectations, see CHRN Jobs and the broader CHRN Certification overview.
Sequencing Your Preparation
Because official weights are unverified, a sensible approach is to sequence by dependency rather than by assumed exam share. Physics and physiology underpin nearly everything else, so they come first. A sample plan:
Physical and physiological foundations
- Pressure terms and unit conversions with a calculator.
- Gas laws applied to chamber scenarios.
Decompression and therapeutic mechanisms
- Practice reading the provided dive tables.
- Map each accepted indication to its mechanism.
Toxicity, complications, and patient safety
- Contrast CNS and pulmonary oxygen toxicity.
- Rehearse pre-treatment assessment and prohibited items.
Facility, fire safety, monitoring, and nursing management
- Chamber types, gas color codes, NFPA concepts, TcPO2 procedure.
- Nursing process, pharmacology, wound healing, BNA standards.
For a fuller plan, read CHRN Study Guide 2026: How to Pass on Your First Attempt and keep CHRN Cheat Sheet 2026: One-Page Review of Must-Know Facts handy for last-week review. When you are ready to test yourself under exam-style conditions, our CHRN practice tests are built around the sixteen preparation topics above, and the main practice site lets you track weak areas topic by topic.
Frequently Asked Questions
CHRN stands for Certified Hyperbaric Registered Nurse, a nursing certification in hyperbaric oxygen therapy overseen by the Baromedical Nurses Association Certification Board, with testing administered and graded by NBDHMT.
No. Within CHRN materials, CHT refers to Certified Hyperbaric Technologist, a separate credential. The CHRN is specifically for registered nurses holding an unrestricted RN license.
The exam has 120 multiple-choice and true/false items with a two-hour limit and a 70% passing threshold. Essays and short-answer questions are excluded. A pocket calculator is allowed and dive tables are provided.
The June 2026 application lists US$250 for BNA members, US$300 for UHMS or ACHM members, and US$400 for nonmembers. The June 2024 manual lists US$100 for a repeat exam; confirm current retake fees before applying.
Every four years. Renewal requires an active RN license, 40 CE hours including 20 Category A, and employer-confirmed recent practice including 480 hours in the previous 12 months. A lapse adds US$100 and removes member discounts.