- How to Read the Five Domains
- Domain 1: Supervisor Responsibilities, Qualifications and Certification
- Domain 2: Surface-Supplied Mixed-Gas Diving (HeO2)
- Domain 3: Underwater Operations
- Domain 4: Life-Support Equipment
- Domain 5: Emergency Procedures, Assessments and Reporting
- Domain Comparison at a Glance
- Sequencing Your Study Across the Domains
- Frequently Asked Questions
- The five domains are editorial groupings of ADCI Consensus Standards edition 6.5, not an official weighted exam blueprint.
- Section 3.6 (mixed-gas supervisor duties, qualifications, card requirements) is the backbone of Domain 1 and informs every other domain.
- Section 4.4 anchors Domain 2: surface-supplied mixed-gas operational personnel and equipment requirements.
- Candidates need 350 field days, 150 working dives and 30 days as assistant mixed-gas supervisor before the card.
How to Read the Five Domains
The Mixed Gas Diving Supervisor credential is tied to the Association of Diving Contractors International (ADCI) and its HeO2/mixed-gas supervisor examination. Unlike many professional certifications, ADCI does not publish a weighted exam blueprint with percentages beside each content area. What it does publish is the ADCI International Consensus Standards, edition 6.5, which the issuer homepage currently links as a PDF with a July 27, 2025 revision filename. That document is the real source of truth for exam preparation.
The five domains in this guide are an editorial map of the relevant standards sections. They are a practical way to organize your reading, not an official list of exam domains, and they are not proof that every exam question falls neatly into one bucket. If you see another site claiming exact domain percentages for this exam, treat that claim with suspicion; none are established.
For a broader preparation roadmap, pair this domain breakdown with our Mixed Gas Diving Supervisor Study Guide 2026. If you want to gauge how demanding the material is before committing, see How Hard Is the Mixed Gas Diving Supervisor Exam?
Domain 1: HeO2/Mixed-Gas Diving Supervisor Responsibilities, Qualifications and Certification
This domain draws primarily on section 3.6 of the Consensus Standards, which defines who may supervise a mixed-gas dive and what that person is answerable for. It is the most identity-defining part of the credential, and because supervisor duties thread through every operational section, it rewards deep, line-by-line reading.
Qualifications and card requirements
The path to the mixed-gas supervisor card is a stack of prerequisites, each of which is fair game for exam questions:
- Passing the specific ADCI HeO2/mixed-gas supervisor examination
- At least 350 field days as an air or mixed-gas diver
- At least 150 working dives
- At least 30 working days as assistant mixed-gas supervisor
- Prior qualification as an air-diving supervisor
- Employer vetting and a written assignment to the role
- A mode-specific supervisor card
- Medical fitness before hyperbaric exposure
- Valid CPR and first aid
The current issuer certification page lists an online exam as required and shows $275 for the supervisor card category. That figure should not be read as an independently verified exam-only fee; treat it as the card-category listing and confirm details with ADCI directly. For fuller eligibility detail, see Mixed Gas Diving Supervisor Requirements 2026, and for a cost breakdown, Mixed Gas Diving Supervisor Certification Cost 2026.
The supervisor's responsibility list
Section 3.6 reads like a job description, and exam questions often test whether you know what the supervisor personally owns. The responsibilities cover:
- Compliance with regulations and the employer's manual
- Life-support equipment readiness
- Immediate supervisory control of the dive
- Coordination with vessels and work sites
- A suitable surface location for supervision
- Pre-dive and post-dive checks
- Emergency and medical communications
- Job safety analysis and dive planning, including gas supplies
- Team duties and fitness
- Equipment suitability, compliance and inspection
- Keeping current manuals, decompression and treatment information available
- Team briefings and operation-specific procedures
- Depth, time and gas profiles
- Continuous tending of the diver
- Termination criteria for the dive
- Post-dive observation and recognition of symptoms
- Chamber availability and post-treatment arrangements
- Incident reports, maintenance records and log verification
What to Master in Domain 1
Know the distinction between duties the supervisor performs and duties the supervisor verifies.
- The full prerequisite chain, including the three numeric thresholds (350, 150, 30)
- Why employer vetting and written assignment are separate from the card itself
- Which pre-dive and post-dive checks fall to the supervisor
- The termination-criteria and post-dive observation responsibilities
If you are still orienting yourself on the role itself, What Is a Mixed Gas Diving Supervisor? gives useful background before you dive into the standards text.
Domain 2: Surface-Supplied Mixed-Gas Diving (HeO2)
Domain 2 centers on section 4.4, which sets out requirements for surface-supplied mixed-gas operational personnel and equipment. Where Domain 1 asks "who is responsible," this domain asks "what must be in place for a surface-supplied HeO2 dive to proceed."
Expect to study the composition of the dive team, the roles each member fills, and the equipment configuration that distinguishes mixed-gas work from routine air diving. Helium-oxygen operations introduce considerations that air diving does not: gas supply planning across bottom mixes and emergency gas, communication quality, and decompression obligations that make chamber access a planning issue and not an afterthought.
What to Master in Domain 2
Be able to describe a compliant surface-supplied mixed-gas dive setup from personnel to gas supply.
- Operational personnel requirements under section 4.4
- How gas supply planning feeds into dive planning (a Domain 1 duty)
- The relationship between depth, time, gas profile and decompression
- Why chamber availability is a planning requirement, not a contingency
Domain 3: Underwater Operations: Procedures, Checklists and Guidelines
Domain 3 draws on the operational material in sections 5, 6 and 7 as they apply to mixed-gas work. This is where abstract responsibilities become sequences of actions: how a dive is planned, briefed, executed and closed out.
Questions in this area tend to test whether you know the order and purpose of procedural steps, not just their names. A candidate who has only memorized lists will struggle when a scenario asks what should happen before a particular step, or what a missed check implies.
Operational themes worth drilling
- Planning and job safety analysis: how hazards, gas supplies and team capabilities are assessed before the dive
- Briefings: what the team must understand before anyone enters the water
- Launch, recovery, entry and egress: the controlled movement of the diver to and from the work site
- Tending and monitoring: continuous attention to the diver, timekeeping and gauges
- Termination and post-dive: criteria for ending the dive and the observation period afterward
- Coordination: working with vessel or site operators so that other activities do not endanger the diver
What to Master in Domain 3
Think in sequences: plan, brief, check, dive, tend, terminate, observe, record.
- Pre-dive and post-dive checklist logic
- Operation-specific procedures versus general procedures
- Log verification and record-keeping obligations at close-out
Domain 4: Life-Support Equipment: Requirements, Maintenance and Testing
Equipment is where many candidates lose points because the detail is dense and the standards expect precision. This domain covers the hardware that keeps a mixed-gas diver alive and the maintenance and testing regimes that keep that hardware trustworthy.
The equipment sections span:
- Diver dress and emergency gas
- Helmets and masks
- Hoses and umbilicals
- Compressors and air purity
- Manifolds and regulators
- Launch and recovery systems, and entry and egress equipment
- Gauges and timekeeping devices
- Compressed-gas equipment
- Pressure vessels for human occupancy
- Maintenance and testing requirements for the above
The supervisor connection matters here: under section 3.6, the supervisor is responsible for equipment suitability, compliance and inspection, and for verifying maintenance records. So equipment questions are rarely purely technical; they often ask what the supervisor must confirm before the dive proceeds.
What to Master in Domain 4
Know the purpose, inspection expectations and record-keeping linked to each equipment category.
- Emergency gas provisions and their role in dive planning
- Gas purity and compressor requirements
- Pressure vessels for human occupancy, which tie directly to chamber availability
- Maintenance and testing documentation the supervisor must verify
Domain 5: Emergency Procedures, Assessments and Reporting of Accidents
The emergency material is where a supervisor's judgment is tested hardest, and it is also where the standards connect most visibly back to Domain 1's responsibilities for emergency communications, chamber availability and incident reporting.
Scenarios the standards address include:
- Loss of breathing media
- Loss of communications
- A trapped diver
- An injured diver
- Umbilical damage
- Fire
- Equipment failure
- Adverse conditions at the work site
Beyond the immediate response, the domain covers assessment and reporting: documenting what happened, completing incident reports, and ensuring logs and maintenance records are verified. A candidate who knows the rescue sequence but not the reporting obligations has only half the domain.
What to Master in Domain 5
Connect each emergency to the supervisor duty it exercises.
- Immediate actions for each emergency type
- Emergency and medical communication responsibilities
- Chamber availability and post-treatment arrangements
- Incident reporting and record verification
Domain Comparison at a Glance
| Domain | Primary Standards Anchor | Core Question It Answers |
|---|---|---|
| 1. Supervisor responsibilities, qualifications and certification | Section 3.6 | Who may supervise, and what are they accountable for? |
| 2. Surface-supplied mixed-gas diving (HeO2) | Section 4.4 | What personnel and equipment must be in place? |
| 3. Underwater operations | Sections 5, 6 and 7 (operations) | How is the dive planned, run and closed out? |
| 4. Life-support equipment | Equipment sections; maintenance and testing | What equipment is required and how is it kept reliable? |
| 5. Emergency procedures, assessments and reporting | Emergency preparation sections | What happens when something goes wrong, and how is it documented? |
Remember that these groupings are editorial. The table shows where to look in the standards, not how many questions each area carries. For more on how the exam is weighted and scored, see Mixed Gas Diving Supervisor Passing Score 2026, which explains what is and is not established, and Mixed Gas Diving Supervisor Pass Rate 2026.
Sequencing Your Study Across the Domains
Because Domain 1 underpins everything, start there and return to it. A sensible order builds from accountability to hardware to crisis response.
Domain 1: Responsibilities and Qualifications
- Read section 3.6 end to end and list each supervisor duty in your own words
- Memorize the prerequisite chain and the 350 / 150 / 30 thresholds
Domain 2: Surface-Supplied Mixed-Gas Diving
- Work through section 4.4 personnel and equipment requirements
- Flag any saturation-specific wording so you do not over-apply it
Domains 3 and 4: Operations and Equipment
- Map the dive sequence from planning to post-dive observation
- For each equipment category, note testing, maintenance and what the supervisor verifies
Domain 5 and Integration
- Rehearse each emergency scenario and its reporting obligations
- Tie emergencies back to Domain 1 duties, then test yourself on mixed questions
Finish with timed practice on scenario-style questions, which is where integration across domains shows up. You can work through the mixed gas diving supervisor practice tests to check whether you can move between responsibilities, equipment and emergencies without losing the thread. A one-page refresher is also available in the Mixed Gas Diving Supervisor Cheat Sheet 2026.
Key Takeaway
Treat the standards document, not third-party summaries, as your primary text. Use the five domains to organize your reading, then cross-reference: nearly every emergency or equipment topic traces back to a section 3.6 supervisor duty.
Frequently Asked Questions
No. They are editorial groupings built from relevant sections of the ADCI International Consensus Standards edition 6.5. ADCI has not published a weighted exam blueprint, so the groupings help you organize study but do not indicate question counts or percentages.
The question count, time limit, passing score and pass rate are not established in the sources this guide relies on. Avoid any resource that states them as fact, and confirm current details with ADCI directly.
The standards call for at least 350 field days as an air or mixed-gas diver, 150 working dives, and 30 working days as assistant mixed-gas supervisor, plus prior air-diving supervisor qualification, employer vetting with written assignment, medical fitness and valid CPR and first aid.
No. This credential is the ADCI HeO2/mixed-gas supervisor examination, and ADC-UK or IMCA examinations are not substitutes. Their procedures and terminology differ, so base your preparation on the ADCI Consensus Standards.
The issuer's certification page lists an online exam as required and shows $275 for the supervisor card category. That should not be read as an independently verified exam-only fee, so confirm the current breakdown with ADCI. Our certification cost guide covers the details.