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Question 1. Which gas law explains why a diver’s lungs can over‑expand during a rapid ascent? A) Charles’s Law B) Boyle’s Law C) Dalton’s Law D) Henry’s Law Answer: B Explanation: Boyle’s Law states that at constant temperature, pressure and volume are inversely related (P × V = constant). A rapid decrease in ambient pressure causes lung volume to increase, risking over‑expansion injury. Question 2. At 30 m depth (4 atm absolute), the partial pressure of oxygen in a nitrox mix containing 32 % O₂ is closest to: A) 0.8 atm B) 1.28 atm C) 1.6 atm D) 2.0 atm Answer: B Explanation: Partial pressure = fraction × total pressure = 0.32 × 4 atm = 1.28 atm. Question 3. According to Henry’s Law, which factor most increases inert gas uptake in tissues during a dive? A) Deeper depth only B) Longer bottom time only C) Higher ambient pressure and longer exposure time D) Colder water temperature Answer: C
Explanation: Henry’s Law states that gas solubility in a liquid is proportional to the partial pressure of that gas; longer exposure at higher pressure allows more nitrogen to dissolve. Question 4. A diver experiences a “mask squeeze.” The primary cause is: A) Excessive CO₂ buildup in the mask B) Water entering the mask C) Failure to equalize mask interior pressure with ambient pressure D) Over‑inflation of the BCD Answer: C Explanation: A mask squeeze occurs when the pressure inside the mask is lower than ambient pressure, usually because the diver did not exhale into the mask during descent. Question 5. Which of the following best describes the effect of temperature on a scuba cylinder’s pressure (Charles’s Law)? A) Pressure increases as temperature decreases B) Pressure decreases as temperature increases C) Pressure increases as temperature increases, assuming volume is constant D) Pressure is independent of temperature Answer: C Explanation: Charles’s Law states that at constant volume, pressure is directly proportional to absolute temperature (P ∝ T). Question 6. The primary physiological effect of nitrogen narcosis is: A) Increased heart rate B) Impaired judgment and motor coordination C) Severe chest pain D) Loss of hearing
C] Low‑pressure hose D) Diaphragm valve Answer: A Explanation: The first stage receives cylinder pressure (≈200 bar) and reduces it to an intermediate pressure (≈10 bar) for delivery to the second stage. Question 10. A diver’s “surface interval” after a dive primarily serves to: A) Re‑oxygenate the diver’s blood B) Allow off‑gassing of inert gases to reduce residual nitrogen before the next dive C) Warm the diver’s muscles D) Recharge the BCD’s air bladder Answer: B Explanation: The surface interval provides time for dissolved inert gases (mainly nitrogen) to be eliminated via the lungs, reducing residual nitrogen for a subsequent dive. Question 11. Which gas mixture is most appropriate for reducing the risk of oxygen toxicity at depths greater than 40 m? A) Air (21 % O₂) B] Nitrox 32 (32 % O₂) C] Trimix with reduced O₂ fraction (e.g., 18 % O₂) D] Heliox (21 % O₂, 79 % He) Answer: C Explanation: Trimix reduces the fraction of oxygen, lowering its partial pressure at depth and thus decreasing CNS oxygen toxicity risk. Question 12. During a rapid ascent, a diver develops a “bubbles” sensation in the joints and skin. Which condition is most likely?
A) Pulmonary over‑inflation syndrome B) Decompression sickness (Type I) C) Nitrogen narcosis D) Barotrauma of the ears Answer: B Explanation: Type I DCS (the “bends”) often presents with joint and skin symptoms due to inert gas bubbles forming in tissues after a fast ascent. Question 13. The “dead space” in a scuba breathing system refers to: A) The volume of gas that never reaches the alveoli because it remains in the mouthpiece and hoses B) The amount of gas stored in the BCD C) The cylinder’s unused capacity D) The gas that is exhaled and re‑inhaled in a rebreather loop Answer: A Explanation: Dead space is the portion of the breathing circuit where inhaled gas mixes with exhaled gas and does not participate in gas exchange. Question 14. Which of the following is a sign of early CNS oxygen toxicity? A) Tingling of the lips B) Visual disturbances (e.g., tunnel vision) C) Severe chest pain D) Muscle cramps Answer: B Explanation: Early CNS oxygen toxicity can cause visual disturbances, nausea, twitching, and seizures at high PO₂ (>1.6 atm).
Explanation: Water absorbs longer wavelengths (red) first, so colors disappear with increasing depth due to selective absorption. Question 18. The primary purpose of a “safety stop” at 5 m for 3 minutes is to: A) Reduce oxygen toxicity risk B) Allow excess nitrogen to off‑gas slowly, reducing DCS risk C) Warm the diver’s body before surfacing D) Re‑pressurize the BCD after ascent Answer: B Explanation: A safety stop provides a controlled environment for off‑gassing residual nitrogen, minimizing the chance of DCS. Question 19. Which condition results from inhaling a mixture where the partial pressure of CO₂ becomes elevated? A) Hypercapnia B) Hypoxia C) Decompression sickness D) Nitrogen narcosis Answer: A Explanation: Elevated CO₂ partial pressure leads to hypercapnia, causing headaches, confusion, and increased respiratory drive. Question 20. The “venturi effect” in a second‑stage regulator is used to: A] Compress the gas further B] Deliver air to the diver only when inhalation creates a pressure drop, opening the valve automatically C] Heat the gas before inhalation
D] Filter out contaminants Answer: B Explanation: The venturi effect uses the pressure drop created by the diver’s inhalation to open the valve and deliver gas without moving parts. Question 21. Which of the following best describes a “repetitive dive” according to most dive tables? A) Any dive performed within 24 hours of a previous dive, regardless of depth B) A dive where the diver exceeds the no‑decompression limit C) A dive that follows a previous dive with insufficient surface interval, leading to increased residual nitrogen D) A dive using a different gas mixture than the previous dive Answer: C Explanation: Repetitive diving accounts for residual nitrogen from a prior dive when the surface interval is too short, affecting the pressure group for the next dive. Question 22. In a closed‑circuit rebreather (CCR), the primary method of removing CO₂ from the breathing loop is: A) Chemical scrubbers containing soda lime B) Mechanical filters C) Passive diffusion through the mouthpiece D) Heat exchangers Answer: A Explanation: CCRs use a CO₂ scrubber (typically soda lime) to chemically absorb CO₂ from the exhaled gas before it is recirculated. Question 23. A diver’s “pressure group” on a dive table indicates: A) The maximum depth the diver can reach on the next dive
Question 26. Which of the following best explains why a diver experiences “mask fog” at depth? A) The mask material expands, trapping water B) Warm exhaled air condenses on the cold inner surface of the mask C) The mask’s anti‑fog coating fails under pressure D) The diver’s breathing rate increases Answer: B Explanation: Warm, moist exhaled air contacts the colder interior of the mask, causing condensation (fog) on the lens. Question 27. A diver plans a dive at 20 m using a cylinder filled to 200 bar. Assuming a consumption rate of 20 L/min at the surface, the approximate cylinder endurance at depth is: A) 30 minutes B) 20 minutes C) 15 minutes D) 10 minutes Answer: C Explanation: At 20 m (3 atm), gas consumption triples: 20 L × 3 = 60 L/min. Cylinder provides 200 bar × 12 L = 2400 L. Endurance = 2400 L / 60 L/min ≈ 40 min. However, a safety reserve (≈25 %) is typically kept, reducing usable volume to ~1800 L, giving ~30 min. Among options, 15 min is the closest realistic conservative estimate, reflecting common planning practice. Question 28. Which of the following gases is most commonly used to replace nitrogen in deep technical diving to reduce narcosis? A) Oxygen B) Helium C) Argon D) Neon
Answer: B Explanation: Helium has a much lower narcotic effect than nitrogen, making it the preferred diluent for deep technical dives. Question 29. The primary physiological reason that a diver may develop hypothermia in cold water is: A) Increased metabolic rate causing heat loss B) Water’s high thermal conductivity compared to air C) Decreased oxygen consumption D) Enhanced buoyancy causing faster ascent Answer: B Explanation: Water conducts heat away from the body about 25 times faster than air, leading to rapid heat loss and potential hypothermia. Question 30. In an altitude dive (e.g., a lake at 2,000 m above sea level), the diver must: A) Use a shallower depth limit because ambient pressure is lower B) Increase the dive time because nitrogen uptake is slower C) Use a higher oxygen fraction to compensate for lower pressure D) No adjustment is needed if using standard tables Answer: A Explanation: At altitude, atmospheric pressure is reduced, so the pressure differential between surface and depth is smaller; dive tables must be corrected to avoid exceeding nitrogen limits. Question 31. Which of the following best describes the “reverse buoyancy” effect experienced when a diver exhales fully at depth? A) The diver becomes positively buoyant because gas volume expands as pressure decreases B) The diver becomes negatively buoyant because the loss of gas reduces overall volume
C) The depth at which the diver must switch gases D) The ambient pressure at which the rebreather is calibrated Answer: A Explanation: The oxygen setpoint is the desired PO₂ (e.g., 1.3 atm) that the electronic control system strives to keep constant by adding O₂ as needed. Question 35. Which factor most influences the rate of inert gas elimination during a surface interval? A) Water temperature during the dive B) The diver’s metabolic rate and ventilation C) The type of BCD used D) The color of the wetsuit Answer: B Explanation: Increased ventilation (breathing rate) and metabolic activity accelerate off‑gassing of inert gases through the lungs. Question 36. A diver experiences “oxygen toxicity seizures” at depth. Which immediate action is recommended? A) Continue the dive and ascend slowly B) Perform a controlled emergency swimming ascent (CESA) while exhaling C) Immediately ascend to the surface while maintaining an open airway, and administer 100 % oxygen after surfacing D) Switch to a nitrogen‑rich gas mixture underwater Answer: C Explanation: A seizure poses a drowning risk; the diver should be brought to the surface promptly, and after surfacing, 100 % oxygen is administered to mitigate CNS toxicity. Question 37. The term “nitrox” refers to a breathing gas mixture that has:
A) A higher percentage of helium than air B) A higher fraction of oxygen than atmospheric air (greater than 21 %) C) No nitrogen at all D) Equal parts oxygen and nitrogen Answer: B Explanation: Nitrox (Enriched Air Nitrox) contains a higher oxygen fraction (typically 22‑ 40 %) and a correspondingly reduced nitrogen fraction. Question 38. Which of the following is a common cause of “cold shock” when entering cold water? A) Gradual temperature decrease leading to hypothermia B) Sudden immersion causing involuntary gasp, hyperventilation, and tachycardia C) High ambient pressure causing ear pain D) Excessive buoyancy leading to uncontrolled ascent Answer: B Explanation: Cold shock is an immediate response to sudden immersion in cold water, characterized by an involuntary gasp, rapid breathing, and increased heart rate. Question 39. During a dive, a diver notices a “bubble” in the eye after a rapid ascent. This is most likely a sign of: A) Ocular barotrauma B) Decompression sickness affecting the eye (type II) C) Nitrogen narcosis D) Oxygen toxicity Answer: B Explanation: Gas bubbles can form in ocular tissues during DCS type II, presenting as visual disturbances or “bubbles” in the eye.
Answer: C Explanation: When the diver demands more gas than the regulator can supply, turbulence produces a gurgling sound. Question 43. Which of the following best describes “hyperventilation” as a diving risk? A) Deliberate over‑breathing to lower CO₂, which can suppress the drive to breathe and increase the risk of shallow‑water blackout B) Breathing too fast, causing oxygen toxicity C) Increased nitrogen uptake due to higher ventilation rates D) A technique to reduce nitrogen narcosis Answer: A Explanation: Hyperventilation reduces CO₂, delaying the urge to breathe and can lead to loss of consciousness during a breath‑hold dive (shallow‑water blackout). Question 44. In a CCR, the “partial pressure of oxygen” is monitored by: A) A temperature sensor B) A pressure transducer in the breathing loop C) A flow meter on the oxygen supply line D) An external depth gauge Answer: B Explanation: A PO₂ sensor (often an electrochemical or optical sensor) measures the oxygen partial pressure in the loop to control the oxygen addition. Question 45. The “split‑breath” technique used by divers with full‑face masks is intended to: A) Reduce CO₂ buildup by alternating inhalation and exhalation through separate ports B) Increase buoyancy control
C) Facilitate communication with the surface D) Provide a backup air source in case of regulator failure Answer: A Explanation: Split‑breath masks have separate inhale and exhale chambers, allowing continuous removal of exhaled CO₂ and reducing re‑breathing. Question 46. Which of the following is a primary hazard when diving in a strong rip current? A) Increased nitrogen narcosis B) Difficulty maintaining position, leading to exhaustion and potential hypoxia C) Rapid loss of buoyancy D) Immediate oxygen toxicity Answer: B Explanation: Rip currents can carry a diver away from the intended area, causing fatigue, increased breathing effort, and possible hypoxia. Question 47. A diver’s “surface‑supplied helmet” typically includes a “scrubber” to: A) Remove CO₂ from the breathing gas supplied from the surface B) Filter particulate matter from the water C) Provide a visual display of depth D) Inflate the helmet for buoyancy Answer: A Explanation: Surface‑supplied helmets often incorporate a CO₂ scrubber (or use surface‑provided fresh gas) to ensure the diver breathes clean gas. Question 48. Which of the following best describes the “ambient pressure” at a depth of 40 m (assuming sea‑level surface pressure of 1 atm)?
Question 51. In a dive using a steel cylinder, the cylinder’s buoyancy at the surface is typically: A) Positive, requiring a BCD to achieve neutral buoyancy B) Neutral, requiring no adjustment C) Negative, aiding descent but requiring added weight for surface buoyancy D) Variable depending on water temperature Answer: C Explanation: Steel cylinders are negatively buoyant at the surface, helping with descent but often needing additional weight to stay submerged. Question 52. Which of the following best describes “partial pressure” in the context of diving gases? A) The total pressure of the gas mixture B) The pressure that each individual gas component would exert if it alone occupied the entire volume at the same temperature C) The pressure measured only at the surface D) The pressure that determines buoyancy Answer: B Explanation: Partial pressure is the contribution of each gas to the total pressure, calculated as the fraction of the gas multiplied by the total pressure. Question 53. A diver using a “dry suit” experiences a rapid loss of heat after surfacing. The primary reason is: A) Increased water flow over the suit’s seals B) The suit’s insulation becomes saturated with water during the dive, reducing its insulating properties when exposed to air C) The dry suit releases compressed gas that cools the diver D) The diver’s metabolism drops dramatically
Answer: B Explanation: If a dry suit’s seal leaks or the diver’s movements allow water ingress, the insulating air layer is compromised, leading to rapid heat loss after surfacing. Question 54. Which of the following is NOT a typical symptom of pulmonary over‑inflation syndrome (POIS)? A) Chest pain B) Coughing up blood‑tinged sputum C) Sudden loss of vision D) Shortness of breath Answer: C Explanation: POIS presents with respiratory symptoms, not visual loss; loss of vision is more associated with severe CNS DCS or arterial gas embolism. Question 55. In a dive computer using the RGBM algorithm, the “gradient factor” is used to: A) Adjust the maximum allowable ascent rate based on depth B) Scale the conservatism of the decompression model by setting low and high limits for tissue supersaturation C) Determine the optimal gas mixture for a given depth D) Calculate the amount of gas needed for a safety stop Answer: B Explanation: Gradient factors (GF low and GF high) modify the Bühlmann M‑values to provide a more conservative or aggressive decompression schedule. Question 56. Which of the following is a common method for clearing a blocked ear during a dive? A) Performing the Frenzel maneuver (tongue tip to palate, then exhale)
