PADI OPEN WATER DIVER EXAM BANK 350
QUESTIONS AND ANSWERS
Questions 1–50
1. If a flexible container holds 1 liter of air at the surface, what will its volume be
at 20 meters/66 feet in salt water?
A) 0.25 liters
B) 0.33 liters
C) 0.5 liters
D) 0.75 liters
Correct Answer: B
Rationale: At 20 meters, absolute pressure is 3 ATA. Boyle's Law states P1V1 =
P2V2. (1 ATA × 1 L) = (3 ATA × V2) → V2 = 0.33 L.
2. What is the primary function of the exhaust valve on a regulator second stage?
A) To release exhaled air into the water
B) To allow air to enter the mouthpiece
C) To connect to the BCD inflator
D) To measure cylinder pressure
Correct Answer: A
Rationale: The exhaust valve is a one-way rubber flap that lets exhaled breath
escape into the water while preventing water from entering the regulator.
1
,3. Which of the following is the most reliable method to confirm your buddy has
enough air for the dive?
A) Asking them verbally on the boat
B) Watching their pressure gauge during the dive
C) Checking their SPG before and during the dive
D) Estimating based on their cylinder size
Correct Answer: C
Rationale: The only reliable method is to visually check their submersible pressure
gauge (SPG) at the start and periodically during the dive to confirm remaining
pressure.
4. What is the primary physiological mechanism that triggers decompression
sickness?
A) Nitrogen bubbles forming in tissues and blood
B) Oxygen bubbles forming in the lungs
C) Carbon dioxide accumulation in the brain
D) Helium diffusing into joints
Correct: A
Rationale: DCS is caused by nitrogen coming out of solution as bubbles. 5. What
is the recommended action if your BCD inflator sticks in the "inflate" position at
depth?
A) Unhook the low-pressure inflator hose immediately
B) Swim rapidly to the surface
C) Hold the deflate button and disconnect the hose
D) Drop your weight belt
Correct Answer: C
Rationale: Hold the deflate button to vent air while disconnecting the inflator hose.
This stops the uncontrolled inflation and allows you to control buoyancy manually.
2
,6. At 30 meters/99 feet, the partial pressure of nitrogen in air is approximately:
A) 0.79 ATA
B) 1.58 ATA
C) 2.37 ATA
D) 3.16 ATA
Correct Answer: D
Rationale: At 30m (4 ATA), nitrogen fraction is 0.79. 4 × 0.79 = 3.16 ATA.
7. Why is it dangerous to dive with a full wetsuit that is too tight in the neck?
A) It restricts blood flow to the brain
B) It prevents proper equalization of the mask
C) It restricts breathing and can cause carotid sinus reflex
D) It makes the suit less buoyant
Correct Answer: C
Rationale: A tight neck can compress the carotid arteries, triggering the carotid
sinus reflex (slowing heart rate and reducing blood pressure), which can lead to
fainting.
8. What does the "ceiling" refer to on a dive computer display?
A) The maximum depth allowed for the dive
B) The shallowest depth you can ascend to without violating decompression
C) The depth of the safety stop
D) The surface
Correct Answer: B
Rationale: The "ceiling" is the depth above which you cannot ascend during a
decompression obligation without risking DCS. You must stay below it until the
deco clears.
3
, 9. Which of the following is a symptom of pneumothorax (collapsed lung) after
diving?
A) Pain in the shoulder or chest
B) Ringing in the ears
C) Itchy skin
D) Joint stiffness
Correct Answer: A
Rationale: A pneumothorax causes sharp chest pain, often radiating to the
shoulder, due to air leaking into the pleural space. This is a form of pulmonary
barotrauma.
10. How should you breathe from a regulator that is free-flowing uncontrollably?
A) Breathe normally; the flow won't stop
B) Breathe by sipping or gulping from the freeflow
C) Hold your breath and use the octopus
D) Purge the regulator repeatedly
Correct Answer: B
Rationale: You can breathe from a free-flowing regulator by "sipping" the air as it
flows past your mouth, or by placing it in your mouth and inhaling as the air rushes
out.
11. What is the primary purpose of the "residual pressure" kept in a scuba cylinder
after use?
A) To keep moisture out of the cylinder
B) To make it easier to attach the regulator
C) To maintain valve pressure for inspection
4
QUESTIONS AND ANSWERS
Questions 1–50
1. If a flexible container holds 1 liter of air at the surface, what will its volume be
at 20 meters/66 feet in salt water?
A) 0.25 liters
B) 0.33 liters
C) 0.5 liters
D) 0.75 liters
Correct Answer: B
Rationale: At 20 meters, absolute pressure is 3 ATA. Boyle's Law states P1V1 =
P2V2. (1 ATA × 1 L) = (3 ATA × V2) → V2 = 0.33 L.
2. What is the primary function of the exhaust valve on a regulator second stage?
A) To release exhaled air into the water
B) To allow air to enter the mouthpiece
C) To connect to the BCD inflator
D) To measure cylinder pressure
Correct Answer: A
Rationale: The exhaust valve is a one-way rubber flap that lets exhaled breath
escape into the water while preventing water from entering the regulator.
1
,3. Which of the following is the most reliable method to confirm your buddy has
enough air for the dive?
A) Asking them verbally on the boat
B) Watching their pressure gauge during the dive
C) Checking their SPG before and during the dive
D) Estimating based on their cylinder size
Correct Answer: C
Rationale: The only reliable method is to visually check their submersible pressure
gauge (SPG) at the start and periodically during the dive to confirm remaining
pressure.
4. What is the primary physiological mechanism that triggers decompression
sickness?
A) Nitrogen bubbles forming in tissues and blood
B) Oxygen bubbles forming in the lungs
C) Carbon dioxide accumulation in the brain
D) Helium diffusing into joints
Correct: A
Rationale: DCS is caused by nitrogen coming out of solution as bubbles. 5. What
is the recommended action if your BCD inflator sticks in the "inflate" position at
depth?
A) Unhook the low-pressure inflator hose immediately
B) Swim rapidly to the surface
C) Hold the deflate button and disconnect the hose
D) Drop your weight belt
Correct Answer: C
Rationale: Hold the deflate button to vent air while disconnecting the inflator hose.
This stops the uncontrolled inflation and allows you to control buoyancy manually.
2
,6. At 30 meters/99 feet, the partial pressure of nitrogen in air is approximately:
A) 0.79 ATA
B) 1.58 ATA
C) 2.37 ATA
D) 3.16 ATA
Correct Answer: D
Rationale: At 30m (4 ATA), nitrogen fraction is 0.79. 4 × 0.79 = 3.16 ATA.
7. Why is it dangerous to dive with a full wetsuit that is too tight in the neck?
A) It restricts blood flow to the brain
B) It prevents proper equalization of the mask
C) It restricts breathing and can cause carotid sinus reflex
D) It makes the suit less buoyant
Correct Answer: C
Rationale: A tight neck can compress the carotid arteries, triggering the carotid
sinus reflex (slowing heart rate and reducing blood pressure), which can lead to
fainting.
8. What does the "ceiling" refer to on a dive computer display?
A) The maximum depth allowed for the dive
B) The shallowest depth you can ascend to without violating decompression
C) The depth of the safety stop
D) The surface
Correct Answer: B
Rationale: The "ceiling" is the depth above which you cannot ascend during a
decompression obligation without risking DCS. You must stay below it until the
deco clears.
3
, 9. Which of the following is a symptom of pneumothorax (collapsed lung) after
diving?
A) Pain in the shoulder or chest
B) Ringing in the ears
C) Itchy skin
D) Joint stiffness
Correct Answer: A
Rationale: A pneumothorax causes sharp chest pain, often radiating to the
shoulder, due to air leaking into the pleural space. This is a form of pulmonary
barotrauma.
10. How should you breathe from a regulator that is free-flowing uncontrollably?
A) Breathe normally; the flow won't stop
B) Breathe by sipping or gulping from the freeflow
C) Hold your breath and use the octopus
D) Purge the regulator repeatedly
Correct Answer: B
Rationale: You can breathe from a free-flowing regulator by "sipping" the air as it
flows past your mouth, or by placing it in your mouth and inhaling as the air rushes
out.
11. What is the primary purpose of the "residual pressure" kept in a scuba cylinder
after use?
A) To keep moisture out of the cylinder
B) To make it easier to attach the regulator
C) To maintain valve pressure for inspection
4
