Scuba Diving Open Water 4 — Questions and Answers
Question 1: What does a dive computer's 'no-decompression limit' (NDL) tell a diver?
- How many dives can be done in a day
- The maximum time at current depth before required decompression stops are needed (Correct answer)
- The minimum surface interval required between dives
- The maximum depth the computer allows
Correct answer: The maximum time at current depth before required decompression stops are needed
The NDL is the maximum time a diver can stay at a given depth and still ascend directly to the surface with only a safety stop, without mandatory decompression stops.
Question 2: Which condition is caused by air entering the space between the lung and chest wall during a dive?
- Arterial gas embolism
- Pneumothorax (Correct answer)
- Decompression sickness
- Nitrogen narcosis
Correct answer: Pneumothorax
A pneumothorax occurs when air escapes into the pleural space, potentially collapsing a lung, and is a serious pulmonary barotrauma complication.
Question 3: When entering the water from a boat using a giant stride entry, which item should a diver check last before entering?
- That the tank valve is fully open
- That the area below is clear of divers and obstacles (Correct answer)
- That the fins are on correctly
- That the weight belt buckle is secure
Correct answer: That the area below is clear of divers and obstacles
A diver must always confirm the entry zone is clear of other divers and hazards immediately before jumping to prevent collisions.
Question 4: What is 'thermocline' in the context of open water diving?
- A type of dive table
- A sudden layer where water temperature drops significantly with depth (Correct answer)
- A surface current pattern
- A bottom composition of thermal vents
Correct answer: A sudden layer where water temperature drops significantly with depth
A thermocline is a distinct layer in the water where temperature drops sharply, which can affect buoyancy and surprise unprepared divers.
Question 5: How should a diver retrieve a dropped weight belt during a dive?
- Swim head-down and kick hard to reach it quickly
- Descend slowly while equalizing and maintaining control (Correct answer)
- Surface immediately and ask the dive master to retrieve it
- Leave it and complete the dive positively buoyant
Correct answer: Descend slowly while equalizing and maintaining control
The diver should descend in a controlled manner, equalizing and monitoring buoyancy, just as during any planned descent.
Question 6: What is the function of a tank valve's 'J-valve' system (if encountered on older equipment)?
- It releases tank pressure if overfilled
- It provides a reserve air supply that opens when pulled (Correct answer)
- It automatically closes when the tank reaches 500 psi
- It filters contaminants from the air supply
Correct answer: It provides a reserve air supply that opens when pulled
The J-valve held a spring-loaded reserve of air that was released by pulling a rod, alerting the diver to low air — now replaced by pressure gauges.
Question 7: A diver surfaces far from the boat in a moderate current. What is the best immediate action?
- Swim aggressively against the current toward the boat
- Inflate the BCD fully, signal with an SMB, and conserve energy (Correct answer)
- Remove the BCD to swim faster
- Dive back down to escape the current
Correct answer: Inflate the BCD fully, signal with an SMB, and conserve energy
Full BCD inflation keeps the diver afloat with minimal effort, while an SMB makes them visible to rescue; fighting a strong current wastes energy and can lead to exhaustion.
Scuba Diving Open Water 4
What does a dive computer's 'no-decompression limit' (NDL) tell a diver?