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AGR-AQUA50-09 · Lesson 3 · 26 clock hours · theory

ADCI Commercial Diver Written Exam Domain Review

Objective. Learners correctly solve practice items in every ADCI written examination content area—dive physics, physiology, decompression theory, surface-supplied equipment, underwater work methods, ADCI/OSHA regulatory requirements, and emergency procedures—at a level consistent with passing the official exam.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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ADCI Commercial Diver Written Exam: Domain Overview

The ADCI Commercial Diver written examination tests knowledge across seven core content areas drawn from the ADCI Consensus Standards for Commercial Diver Training, the US Navy Diving Manual, and applicable federal regulations. Passing requires demonstrated competence in every domain, not just an acceptable overall average. This lesson walks through each domain, highlights the highest-yield concepts, and builds the calculation skills the exam requires.

Dive Physics

Commercial diving takes place in an environment governed by predictable physical laws. Boyle's Law states that at constant temperature, the pressure and volume of a gas are inversely proportional (P₁V₁ = P₂V₂). As a diver descends, gas spaces compress; on ascent, they expand—the mechanism behind lung over-expansion injuries if a diver holds their breath.

Dalton's Law states that the total pressure of a gas mixture equals the sum of the partial pressures of each component gas. Partial pressure (pp) = fraction of gas × absolute pressure. Oxygen partial pressures above approximately 1.6 ATA carry a risk of central nervous system oxygen toxicity—a critical safety limit in commercial work.

Absolute pressure at depth in seawater is calculated as: P(abs) = (depth in feet ÷ 33) + 1 ATA. In fresh water, use 34 feet per atmosphere. Gauge pressure excludes the surface atmosphere: P(gauge) = P(abs) − 1.

Dive Physiology

Nitrogen narcosis becomes significant below about 100 fsw and impairs judgment. Oxygen toxicity at high partial pressures causes convulsions without warning—convulsing underwater with a regulator is fatal. Carbon dioxide retention from skip-breathing elevates CO₂ faster than the diver perceives it, increasing narcosis risk and triggering hypercapnia. Carbon monoxide contamination of the breathing supply—a documented commercial diving fatality cause—demands that compressor intakes be positioned upwind and away from exhaust sources, and that CO monitoring be performed.

Decompression sickness (DCS) results from dissolved inert gas coming out of solution when ambient pressure is reduced too quickly, forming bubbles in tissues and blood. Type I DCS involves musculoskeletal pain and skin symptoms. Type II DCS involves neurological, pulmonary (chokes), or cardiovascular symptoms and is a medical emergency. Surface-supply of 100% oxygen at one atmosphere is the immediate first-aid treatment while arranging evacuation to a recompression chamber.

Decompression Theory and Tables

Commercial divers use the US Navy Dive Tables or approved equivalent. Key terms: bottom time (measured from leaving the surface to beginning ascent), repetitive dive, residual nitrogen time (RNT), and surface interval. Omitted decompression requires a defined response: the diver should return to the water at the first decompression stop depth if within a short window specified in the applicable table procedures, breathe oxygen if available, and receive emergency recompression at a chamber as soon as possible. The exact return window and procedure are dictated by the applicable dive plan and medical officer guidance—know the principle and the immediate actions.

Surface-Supplied Equipment

Surface-supplied diving (SSD) systems include a primary gas supply, backup supply, diving helmet or band mask, umbilical (gas hose, communications, pneumofathometer, and safety line), and a surface control panel (SCP). The pneumofathometer measures diver depth via the pressure required to free-flow a small gas stream from the diver's depth. The umbilical must be inspected before each dive and tagged with the date. The standby diver must be dressed in and ready to enter the water immediately whenever a diver is in the water—this is a regulatory requirement, not a suggestion.

Underwater Work Methods

Commercial divers perform inspection, construction, cutting, and welding tasks. Underwater wet welding and cutting produce hydrogen and oxygen gases at the work site—explosive combinations. The work area must be evaluated for confined spaces before the diver enters; lockout/tagout (LOTO) procedures must be applied to any machinery or piping that could be energized or start unexpectedly. PPE requirements include dry suits or wetsuits appropriate to water temperature, hard hats in overhead environments, and insulated gloves and electrode holders for electrical work.

ADCI and OSHA Regulatory Requirements

29 CFR Part 1910, Subpart T governs commercial diving operations in general industry. Key requirements include: a designated dive supervisor responsible for the operation; a written diving project plan and safe practices manual; pre-dive checklists; a diver's log recording depth, bottom time, and decompression; equipment inspection records; and immediate accident reporting. ADCI Consensus Standards complement these regulations and define team qualifications—diver, tender, dive supervisor, and standby diver roles and minimum training levels.

Emergency Procedures

Know these responses cold: (1) Unconscious diver in water—standby diver enters, secures the victim, surfaces, maintains airway, signals the team; (2) Suspected DCS on surface—lay victim flat, administer 100% O₂ by non-rebreather mask, keep warm, monitor, arrange chamber transport; (3) Out-of-air emergency—surface-supply systems include a bailout cylinder; the diver switches to bailout, signals tender, and ascends following the applicable decompression schedule; (4) Fire or gas leak at surface panel—supervisor shuts primary supply, switches to backup, evacuates diver following emergency ascent procedures.

Exam Strategy

Read each question stem completely before reading options. Eliminate clearly wrong answers first. For calculation items, write out the formula, substitute values, and check units before selecting an answer. Flag items you are unsure of, complete the rest of the test, and return to flagged items with remaining time.

Key terms8

Absolute pressureTotal pressure acting on a diver, including the weight of the atmosphere (1 ATA at sea level) plus water pressure. In seawater: P(abs) = (depth ft ÷ 33) + 1 ATA.
Partial pressureThe pressure contributed by a single component gas in a mixture, equal to its fraction of the mixture multiplied by the total (absolute) pressure. Used to assess oxygen toxicity and narcosis risk.
Decompression sickness (DCS)A disorder caused by nitrogen bubbles forming in body tissues and blood when ambient pressure is reduced too rapidly. Type I affects joints and skin; Type II involves the nervous, pulmonary, or cardiovascular systems.
Surface-supplied diving (SSD)A diving mode in which the diver's breathing gas is delivered from the surface through an umbilical, rather than from tanks carried by the diver. Allows longer bottom times and continuous communication.
PneumofathometerA device at the surface control panel that measures diver depth by reading the back-pressure required to free-flow gas from a capillary tube at the diver's level.
Standby diverA fully dressed and equipped diver stationed at the surface, ready to enter the water immediately to assist the working diver. Required under ADCI standards and 29 CFR Part 1910, Subpart T whenever a diver is in the water.
Omitted decompressionA situation in which a diver surfaces without completing all required decompression stops, increasing the risk of DCS. Requires a defined emergency response including possible in-water recompression and chamber evacuation.
Oxygen toxicityA potentially fatal condition caused by breathing oxygen at partial pressures above safe limits (generally above about 1.6 ATA). Central nervous system toxicity can cause convulsions without warning.

Worked examples4

1. A diver is working at 66 fsw in seawater. What is the absolute pressure at that depth, and what is the partial pressure of oxygen (ppO₂) if the diver is breathing air (21% O₂)?
  1. Step 1 – Calculate absolute pressure. Each 33 fsw of seawater = 1 ATA. Depth = 66 fsw. Pressure from water = 66 ÷ 33 = 2 ATA. Add surface atmosphere: P(abs) = 2 + 1 = 3 ATA.
  2. Step 2 – Calculate ppO₂ using Dalton's Law. ppO₂ = fraction of O₂ × P(abs) = 0.21 × 3 ATA = 0.63 ATA.
  3. Step 3 – Check: 0.63 ATA is well below the 1.6 ATA oxygen toxicity threshold, so air is acceptable at this depth.
Answer: Absolute pressure = 3 ATA; ppO₂ = 0.63 ATA.
2. A diver fills a flexible lift bag to 6 cubic feet at a depth of 99 fsw in seawater. Assuming temperature is constant, what will the volume of gas in the bag be when it reaches the surface?
  1. Step 1 – Find absolute pressure at 99 fsw. P₁ = (99 ÷ 33) + 1 = 3 + 1 = 4 ATA.
  2. Step 2 – Surface absolute pressure: P₂ = 1 ATA.
  3. Step 3 – Apply Boyle's Law: P₁V₁ = P₂V₂. Solve for V₂: V₂ = (P₁ × V₁) ÷ P₂ = (4 × 6) ÷ 1 = 24 cubic feet.
  4. Step 4 – Note the safety implication: a vented or open-bottom lift bag will spill the expanding gas; a sealed bag could burst or ascend uncontrollably if not vented.
Answer: The gas volume expands to 24 cubic feet at the surface.
3. A diver breathing a nitrox mix of 32% O₂ descends to 110 fsw in seawater. What is the partial pressure of oxygen at that depth, and does it exceed the generally accepted 1.6 ATA CNS toxicity limit?
  1. Step 1 – Calculate absolute pressure at 110 fsw. P(abs) = (110 ÷ 33) + 1 = 3.33 + 1 = 4.33 ATA (rounded to two decimal places).
  2. Step 2 – Calculate ppO₂ using Dalton's Law. ppO₂ = 0.32 × 4.33 = 1.39 ATA.
  3. Step 3 – Compare to limit: 1.39 ATA is below 1.6 ATA, so CNS toxicity limit is not exceeded at this depth with this mix. However, the diver and dive supervisor should confirm the maximum operating depth for this mix prior to the dive.
Answer: ppO₂ = 1.39 ATA; this does not exceed the 1.6 ATA CNS oxygen toxicity limit.
4. A diver at 33 fsw in seawater has a tank with 80 cubic feet of gas at 4 ATA absolute (measured at depth). The diver must ascend to the surface. Using Boyle's Law, what volume would that gas occupy at the surface? (Assume temperature is constant.)
  1. Step 1 – Identify known values. P₁ = 4 ATA (absolute at 33 fsw: (33÷33)+1 = 2 ATA — wait, re-read: the problem states the gas is measured at 4 ATA absolute, so P₁ = 4 ATA, V₁ = 80 ft³.
  2. Step 2 – Surface pressure: P₂ = 1 ATA.
  3. Step 3 – Apply Boyle's Law: V₂ = (P₁ × V₁) ÷ P₂ = (4 × 80) ÷ 1 = 320 cubic feet.
  4. Step 4 – Interpretation: The tank still physically holds 80 ft³, but the gas compressed inside would occupy 320 ft³ if released at the surface — illustrating why lung over-expansion injury is fatal if a diver holds their breath during ascent.
Answer: 320 cubic feet at the surface (1 ATA).

The math in this lesson2

Learners compute absolute pressure at 66 fsw and ppO₂ with Dalton's law (fraction × ATA).
A-SSE.1N-Q.1
Brush up in the math halls at newSchoolWorks.com:
In class: Complete a timed diagnostic practice test structured around the ADCI Commercial Diver consensus standards content areas; score by domain and rank areas for priority review, then work through instructor-led sessions on the lowest-scoring areas using the ADCI Consensus Standards for Commercial Diver Training document, US Navy Diving Manual (current revision) excerpts, and applicable OSHA commercial diving regulations (29 CFR Part 1910, Subpart T) as reference. · Drill applied calculation problems in small groups: absolute/gauge pressure conversions, gas volume changes at depth using Boyle's Law, equivalent air depth for nitrox, decompression stop planning using dive tables, and partial pressure calculations using Dalton's Law—matching the style and difficulty of ADCI exam items. · Participate in a facilitated question-and-answer review of ADCI regulatory content (diving team qualifications, standby diver requirements, equipment inspection logs, accident reporting) and emergency procedures (omitted decompression management, suspected DCS recognition and surface O₂ first aid, unconscious diver emergency), using scenario prompts to apply regulatory knowledge to realistic commercial dive job situations.
Materials: ADCI Consensus Standards for Commercial Diver Training (current edition), US Navy Diving Manual (current revision, Volumes 1–2), 29 CFR Part 1910 Subpart T reference printout, NOAA Diving Manual (current edition) as supplementary reference, calculator, gas law formula sheet, dive table sets, whiteboard
Check: Practice test domain scores reviewed individually; learner must reach a passing score on each domain practice set before the mock exam; instructor provides written remediation plan for any domain below passing with additional targeted drills completed within the lesson block.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Dive Physics
1. A diver is at 99 fsw in seawater. What is the absolute pressure at that depth?
ADCI/OSHA Regulatory Requirements
2. Which federal regulation governs commercial diving operations in general industry workplaces in the United States?
ADCI/OSHA Regulatory Requirements
3. A standby diver is required during surface-supplied diving operations. According to ADCI standards and applicable OSHA regulations, when must the standby diver be ready to enter the water?
Emergency Procedures
4. A diver surfaces without completing required decompression stops. Which of the following is the correct immediate action?
Dive Physics
5. Using Boyle's Law, a rigid container holding 3 cubic feet of gas at 4 ATA is raised to the surface (1 ATA). What is the volume of the gas at the surface?
Dive Physics
6. A diver breathing air (21% O₂) reaches a depth where the partial pressure of oxygen equals 1.26 ATA. What is the approximate depth in seawater?
Dive Physiology
7. Which symptom is most characteristic of Type II (serious) decompression sickness?
Underwater Work Methods
8. Before a diver enters water near energized machinery or piping, which safety procedure must be applied to prevent unexpected activation?
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