- How the 16 Content Areas Are Framed
- Exam Format and Registration Mechanics
- Foundations: History, Physics, Physiology, Decompression (Domains 1-4)
- The Therapy Core: Mechanisms and Indications (Domains 5-6)
- Oxygen Toxicity and Other Complications (Domains 7-8)
- Facility and Safety: Domains 9-12 and 16
- Monitoring and Nursing Practice (Domains 13-15)
- Sequencing Your Prep Around the Domains
- After the Exam: Renewal and Where the Credential Is Used
- Frequently Asked Questions
- The 16 areas mirror the topics in the NBDHMT CHRN Resource Manual's study guide; they are not an officially weighted blueprint.
- The exam has 120 multiple-choice and true/false items, a two-hour limit, and a 70% passing threshold.
- Initial application fees are USD 250 for BNA members, USD 300 for UHMS or ACHM members, and USD 400 for nonmembers.
- Dive tables are supplied and a pocket calculator is allowed, so unit conversions and gas laws are fair game.
How the 16 Content Areas Are Framed
The Certified Hyperbaric Registered Nurse (CHRN) credential is overseen by the Baromedical Nurses Association Certification Board (BNACB), while the National Board of Diving and Hyperbaric Medical Technology (NBDHMT) administers and grades the examination. The sixteen content areas in this guide reproduce the technical preparation topics listed in the study-guide contents of the NBDHMT CHRN Resource Manual (June 2024 update), excluding its Introduction.
One caveat shapes everything else in this article: these are unweighted study-guide competencies. The manual contains thirteen detailed body sections even though its introduction still refers to twelve, and neither number is an authenticated count of exam domains. A complete, current, percentage-weighted exam blueprint has not been verified, so no one can honestly tell you which domain is "worth the most points." Treat all sixteen as testable and prepare accordingly.
If you are still deciding whether to pursue the credential, start with What Is CHRN Certification? for the basics and CHRN Requirements 2026: Eligibility, Prerequisites & How to Qualify for the full eligibility picture. This guide assumes you are already committed and want a domain-by-domain map.
Exam Format and Registration Mechanics
Before diving into content, understand the container your knowledge must fit into. According to the current-linked June 2024 manual:
| Element | What the Published Materials State |
|---|---|
| Number of items | 120 |
| Time limit | Two hours |
| Item types | Multiple-choice and true/false; essays and short-answer questions are explicitly excluded |
| 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 | Not verified |
| Adaptive testing | Not established |
This is not default unproctored home testing, and unrestricted open-book testing is not established. For the scoring details, see CHRN Passing Score 2026: Exactly What You Need to Pass.
Fees and Timing
The June 2026 initial application confirms USD 250 for BNA members, USD 300 for UHMS or ACHM members, and USD 400 for other applicants, with membership evidence required. The June 2024 manual lists USD 100 for a repeat examination; no newer retake-fee override was found in the retrieved application. The application says to register 30 days before the test. For the full cost picture, including renewal, read CHRN Certification Cost 2026: Complete Pricing Breakdown, and for scheduling see CHRN Exam Dates 2026: Testing Windows, Deadlines & Scheduling.
Foundations: History, Physics, Physiology, Decompression (Domains 1-4)
The first four domains build the scientific vocabulary that every later domain assumes. Candidates who skim them often struggle later, because oxygen toxicity, complications, and safety questions all lean on gas laws and physiology.
Domain 1: History of Undersea and Hyperbaric Medicine
The published terminal objective asks you to identify the pioneering contributions and observations of a specific roster of figures and to understand the concurrent development of hyperbaric and diving medicine.
- Names to attach to contributions: Behnke, Bert, Boerma, Bond, Boyle, Brummelkamp, Fontaine, Haldane, Henshaw, and Yarborough
- Understand how diving medicine and hyperbaric medicine developed in parallel rather than as separate stories
- Expect recall-style items; build a one-line "who did what" list for each name
Domain 2: The Physical Aspects of Undersea and Hyperbaric Medicine
This is the most calculation-friendly area, and the calculator allowance exists for a reason.
- 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
Practice conversions until they are automatic. Many candidates lose points not on concept but on careless arithmetic, such as forgetting that absolute pressure is gauge pressure plus atmospheric pressure.
Domain 3: The Physiological Aspects of Undersea and Hyperbaric Medicine
Here the physics meets the patient.
- Normal respiration and circulation
- Medical terminology as it applies to diving and hyperbaric medicine
- Beneficial and potentially harmful direct effects of pressure during compression and decompression
- Indirect effects of pressure: oxygen toxicity and nitrogen narcosis
- Advantages and limitations of therapeutic gases: air, oxygen, nitrogen-oxygen, and helium-oxygen
Domain 4: Mechanisms and Theory of Decompression
This domain is where the supplied dive tables earn their keep.
- U.S. Navy Standard Air Decompression Table
- U.S. Navy No-Decompression Limits and Repetitive Group Designation Table for No-Decompression Air Dives
- U.S. Navy Residual Nitrogen Timetable for Repetitive Air Dives
- The limits of those tables in preventing decompression sickness
- Physiological and operational factors that raise susceptibility to decompression sickness
Note the dual demand: a working knowledge of how to use the tables, and a fundamental understanding of where they fail. Questions may probe both.
The Therapy Core: Mechanisms and Indications (Domains 5-6)
Domain 5: Therapeutic Mechanisms Associated with Hyperbaric Oxygen Exposure
The published objective lists six mechanisms produced by oxygen partial pressures above one atmosphere absolute:
- Antimicrobial effects
- Vasoconstriction
- Hyperoxygenation
- Neovascularization
- Attenuation of reperfusion injury
- Gas bubble reduction
The objective goes further: you should be able to classify each currently accepted indication by its proposed therapeutic mechanism. That is a connecting skill, not a memorization task. For each indication, ask which mechanism is doing the work.
Domain 6: Currently Accepted Indications for Hyperbaric Oxygen Exposure
Candidates must be able to list all the "Currently Accepted Indications" the Undersea and Hyperbaric Medical Society (UHMS) considers appropriate for referral, and to know the commonly used treatment protocols (absolute pressure, exposure time, and frequency) for each.
- Memorize the indication list as published by UHMS, not as remembered from older materials
- Pair each indication with its typical pressure, duration, and frequency
- Cross-link each indication to a Domain 5 mechanism
Oxygen Toxicity and Other Complications (Domains 7-8)
Domain 7: Oxygen Toxicity
Expect clinical-presentation differentiation and management principles.
- Distinguish central nervous system toxicity (the Paul Bert effect) from pulmonary toxicity (the Lorrain Smith effect)
- Know commonly used methods to extend patient tolerance to hyperbaric exposure
- Know prevention and management principles for both central and pulmonary forms
Domain 8: Other Potential Complications
This domain centers on barotrauma and airway vigilance.
- Recognize all anatomic and equipment gas-filled spaces or potential spaces before compression
- Minimize barotrauma risk through patient education, instruction, and appropriate venting of equipment before pressure changes
- Recognize potential airway compromise, particularly during decompression, and know the immediate management to reduce the risk of pulmonary barotrauma
- Understand how CNS oxygen toxicity and reactive airway disease complicate decompression
Domains 7 and 8 reward scenario thinking. A patient with a seizure history, reactive airway disease, and a sealed ear is a single case touching several domains at once.
Facility and Safety: Domains 9-12 and 16
Five of the sixteen areas concern the chamber, the environment, and the people in it. Domains 9, 12, and 16 overlap enough that studying them together is efficient.
Domain 9: The Hyperbaric Medicine Facility
Know each chamber type, including its respective advantages and disadvantages, and the operating characteristics of each.
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
This is one of the densest domains in the published scope.
- Effects of pressure change on gas-filled spaces in the body, in vascular access lines, and in patient support and monitoring equipment
- Special hazards for patients with known pulmonary pathology
- Special risks for insulin and non-insulin dependent diabetics, patients with seizure history or recent head injury, febrile patients, patients with chest surgery or thoracic procedures or penetrating chest injury, and patients with reconstructive ear surgery
- Pre-exposure assessment: pressure equalization education, anticipated temperature changes, and removal of restricted items such as static-producing clothing, hairpieces, recent nail polish, make-up, 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
Domains 12 and 16: NFPA Guidelines and Chamber Operation
The study guide lists understanding of the NFPA guidelines for hyperbaric chambers (Domain 12) and basic operation of all hyperbaric chambers, including monoplace and multiplace (Domain 16). The manual does not provide separate detailed chapter bodies for these entries, and their full current external standards have not been verified here.
- Obtain the current NFPA hyperbaric guidance yourself and read it directly
- Compare monoplace and multiplace operation: crew requirements, access to the patient, compression and decompression handling
- Link these to Domain 10's fire-prevention content, since the topics reinforce each other
Monitoring and Nursing Practice (Domains 13-15)
Domain 13: Transcutaneous Oxygen Monitoring
TcPO2 is a distinctive hyperbaric-nursing competency, and the published objectives are practical.
- TcPO2 technology and a working knowledge of the monitor and ancillary equipment
- Knowledge of the TcPO2 test consistent with current industry standards
- Obtaining the subject's consent for the procedure
- Inspection procedures for the equipment needed to conduct a study
Domain 14: Nursing Management of the Patient Undergoing Hyperbaric Oxygen Therapy
- Human responses to actual or potential problems related to altered health status: physiological, psychological, sociological, and cognitive
- Application of 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
Domain 15: Nursing Standards of Practice
The study guide points to the BNA Hyperbaric Nursing Standards found on the BNA website. The manual provides no separate chapter body for this entry, so go to the source and read the standards directly rather than relying on summaries.
Key Takeaway
Domains 11, 14, and 15 are where your nursing identity meets hyperbaric science. Practice turning each patient-risk list (diabetes, seizures, thoracic surgery, ear surgery) into a pre-treatment assessment you could actually perform at the bedside.
Sequencing Your Prep Around the Domains
Because no official weights exist, sequence by dependency rather than by points. Here is one CHRN-specific ordering; adjust for your own experience.
Physics First
- Domain 2: pressure terms, unit conversions, and the four gas laws with calculator practice
- Domain 1: build the names-and-contributions list
Physiology and Tables
- Domain 3 physiology and gas properties
- Domain 4: work the supplied-style dive table problems
Therapy and Toxicity
- Domains 5 and 6 together, mapping each indication to a mechanism
- Domains 7 and 8: compare CNS and pulmonary oxygen toxicity, then barotrauma scenarios
Facility, Safety, and Practice
- Domains 9, 10, 12, and 16 as one chamber-and-fire-safety block
- Domains 11, 13, 14, and 15, ending with mixed scenario practice
For a broader plan, see CHRN Study Guide 2026: How to Pass on Your First Attempt, and use CHRN Cheat Sheet 2026: One-Page Review of Must-Know Facts for last-week review. To calibrate how demanding the material is, read How Hard Is the CHRN Exam? Complete Difficulty Guide 2026. When you want exam-style repetition across all sixteen areas, the CHRN practice tests let you drill by topic. Keep in mind that practice-question allocation is editorial and does not reflect an official blueprint.
After the Exam: Renewal and Where the Credential Is Used
Certification lasts four years. The currently linked 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, and 40 CE hours over four years including 20 Category A hours. Renewal fees are USD 150 for BNA members, USD 200 for UHMS or ACHM members, and USD 250 for nonmembers; a lapse adds USD 100 and removes member discounts. The older manual's statement that ongoing hours need not be logged does not waive the newer form's employer-validated recent-practice requirement.
The credential is aimed at registered nurses working in hyperbaric medicine, typically in hospital-based and clinic-based hyperbaric and wound-care settings. For the employment side, explore CHRN Jobs; for earnings context, CHRN Salary Guide 2026: Complete Earnings Analysis and Is the CHRN Certification Worth It? Complete ROI Analysis 2026 go deeper. A current CHRN-specific pass rate is not publicly disclosed, and the historical 74% figure belongs to a combined program rather than to CHRN alone; CHRN Pass Rate 2026: What the Data Shows explains what can and cannot be concluded.
Frequently Asked Questions
No. They reproduce the technical topics in the June 2024 CHRN Resource Manual's study-guide contents. They are unweighted preparation competencies, and a complete current weighted blueprint has not been verified.
The manual's introduction says twelve sections while it contains thirteen detailed body sections. Neither number is an authenticated domain count, so rely on the sixteen listed preparation topics for scope.
A pocket calculator is allowed and supplemental dive tables are provided. Unrestricted open-book testing is not established, so don't assume you can bring your own references.
Use it to understand scope, but verify accepted indications, dosing, and safety standards against current sources. The manual still calls a 1992 indications report the most recent, while the UHMS 15th edition front matter is dated 2023.
Certified Hyperbaric Registered Nurse. If you need background on the term, see What Does CHRN Stand For? and the complete guide to all 16 content areas.