Rebreather Diver Certification Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1.A diver using a closed-circuit rebreather (CCR) differs from a traditional
open-circuit scuba diver primarily because the CCR system is designed to do
which of the following?
A. Eliminate the need for breathing gas cylinders entirely
B. Recycle exhaled breathing gas by removing carbon dioxide and controlling
oxygen levels
C. Provide unlimited underwater endurance regardless of gas supply
D. Automatically prevent all forms of decompression illness
Correct Answer: B
A closed-circuit rebreather recycles the diver’s exhaled gas by chemically
removing carbon dioxide and adding oxygen as needed to maintain a
breathable mixture. It does not create unlimited gas or eliminate
physiological risks.
2. The primary purpose of the scrubber canister in a rebreather system is
to:
A. Increase oxygen concentration in the breathing loop
B. Remove nitrogen from exhaled gas
C. Absorb carbon dioxide from exhaled breathing gas
D. Regulate buoyancy during descent
,Correct Answer: C
The scrubber contains a carbon dioxide absorbent material, commonly
soda lime, which removes CO₂ from exhaled gas to prevent hypercapnia
and maintain a safe breathing mixture.
3. In a closed-circuit rebreather, oxygen sensors are primarily responsible
for:
A. Measuring the diver’s heart rate
B. Monitoring oxygen partial pressure within the breathing loop
C. Detecting water leaks in the breathing hoses
D. Measuring nitrogen narcosis levels
Correct Answer: B
Oxygen sensors measure the partial pressure of oxygen (PO₂) in the
breathing loop, allowing the diver and electronics to maintain an
appropriate oxygen concentration.
4. The term “setpoint” in CCR diving refers to:
A. The maximum depth rating of the rebreather
B. The desired oxygen partial pressure maintained by the system
C. The amount of bailout gas carried by the diver
D. The volume of carbon dioxide absorbed by the scrubber
Correct Answer: B
A CCR setpoint is the target PO₂ value that the system attempts to
maintain by adding oxygen or diluent gas.
5. A major advantage of a CCR compared with open-circuit scuba is:
A. It produces no bubbles under any circumstances
B. It completely eliminates decompression obligations
,C. It conserves breathing gases by recycling them
D. It requires no diver training after purchase
Correct Answer: C
CCR systems conserve gas because most exhaled breathing gas is reused
after carbon dioxide removal and oxygen adjustment.
6. A major hazard associated with excessive oxygen partial pressure
during CCR diving is:
A. Oxygen toxicity
B. Hypothermia
C. Dehydration
D. Nitrogen deficiency
Correct Answer: A
Excessive oxygen partial pressure can lead to central nervous system
oxygen toxicity, which may cause seizures underwater.
7. Before entering the water with a rebreather, a diver should first verify:
A. That the dive computer display is turned off
B. That the breathing loop is properly assembled, tested, and functioning
C. That the oxygen cylinder is completely empty
D. That the scrubber has been removed
Correct Answer: B
Pre-dive checks confirm correct assembly, leak integrity, gas supply,
electronics function, and breathing loop operation before exposure to
underwater hazards.
8. The most important reason for performing a positive pressure test on
a CCR loop is to:
, A. Increase oxygen concentration
B. Confirm the breathing loop does not leak
C. Reduce scrubber temperature
D. Calibrate the diver’s depth gauge
Correct Answer: B
A positive pressure test checks whether the breathing loop can maintain
internal pressure without losing gas through leaks.
9. A negative pressure test on a rebreather is primarily used to:
A. Detect leaks that allow gas to enter the loop
B. Determine maximum operating depth
C. Measure cylinder pressure
D. Activate bailout systems
Correct Answer: A
A negative pressure test helps identify leaks where outside gas or water
may enter the breathing loop system.
10. The function of the diluent gas in a CCR system is to:
A. Remove carbon dioxide from the loop
B. Provide volume control and adjust breathing mixture composition
C. Replace the scrubber material
D. Prevent all decompression requirements
Correct Answer: B
Diluent gas is used to maintain loop volume, control oxygen concentration,
and support safe operation at depth.
11. If a CCR diver experiences a sudden increase in breathing
resistance, the most appropriate initial response is to:
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1.A diver using a closed-circuit rebreather (CCR) differs from a traditional
open-circuit scuba diver primarily because the CCR system is designed to do
which of the following?
A. Eliminate the need for breathing gas cylinders entirely
B. Recycle exhaled breathing gas by removing carbon dioxide and controlling
oxygen levels
C. Provide unlimited underwater endurance regardless of gas supply
D. Automatically prevent all forms of decompression illness
Correct Answer: B
A closed-circuit rebreather recycles the diver’s exhaled gas by chemically
removing carbon dioxide and adding oxygen as needed to maintain a
breathable mixture. It does not create unlimited gas or eliminate
physiological risks.
2. The primary purpose of the scrubber canister in a rebreather system is
to:
A. Increase oxygen concentration in the breathing loop
B. Remove nitrogen from exhaled gas
C. Absorb carbon dioxide from exhaled breathing gas
D. Regulate buoyancy during descent
,Correct Answer: C
The scrubber contains a carbon dioxide absorbent material, commonly
soda lime, which removes CO₂ from exhaled gas to prevent hypercapnia
and maintain a safe breathing mixture.
3. In a closed-circuit rebreather, oxygen sensors are primarily responsible
for:
A. Measuring the diver’s heart rate
B. Monitoring oxygen partial pressure within the breathing loop
C. Detecting water leaks in the breathing hoses
D. Measuring nitrogen narcosis levels
Correct Answer: B
Oxygen sensors measure the partial pressure of oxygen (PO₂) in the
breathing loop, allowing the diver and electronics to maintain an
appropriate oxygen concentration.
4. The term “setpoint” in CCR diving refers to:
A. The maximum depth rating of the rebreather
B. The desired oxygen partial pressure maintained by the system
C. The amount of bailout gas carried by the diver
D. The volume of carbon dioxide absorbed by the scrubber
Correct Answer: B
A CCR setpoint is the target PO₂ value that the system attempts to
maintain by adding oxygen or diluent gas.
5. A major advantage of a CCR compared with open-circuit scuba is:
A. It produces no bubbles under any circumstances
B. It completely eliminates decompression obligations
,C. It conserves breathing gases by recycling them
D. It requires no diver training after purchase
Correct Answer: C
CCR systems conserve gas because most exhaled breathing gas is reused
after carbon dioxide removal and oxygen adjustment.
6. A major hazard associated with excessive oxygen partial pressure
during CCR diving is:
A. Oxygen toxicity
B. Hypothermia
C. Dehydration
D. Nitrogen deficiency
Correct Answer: A
Excessive oxygen partial pressure can lead to central nervous system
oxygen toxicity, which may cause seizures underwater.
7. Before entering the water with a rebreather, a diver should first verify:
A. That the dive computer display is turned off
B. That the breathing loop is properly assembled, tested, and functioning
C. That the oxygen cylinder is completely empty
D. That the scrubber has been removed
Correct Answer: B
Pre-dive checks confirm correct assembly, leak integrity, gas supply,
electronics function, and breathing loop operation before exposure to
underwater hazards.
8. The most important reason for performing a positive pressure test on
a CCR loop is to:
, A. Increase oxygen concentration
B. Confirm the breathing loop does not leak
C. Reduce scrubber temperature
D. Calibrate the diver’s depth gauge
Correct Answer: B
A positive pressure test checks whether the breathing loop can maintain
internal pressure without losing gas through leaks.
9. A negative pressure test on a rebreather is primarily used to:
A. Detect leaks that allow gas to enter the loop
B. Determine maximum operating depth
C. Measure cylinder pressure
D. Activate bailout systems
Correct Answer: A
A negative pressure test helps identify leaks where outside gas or water
may enter the breathing loop system.
10. The function of the diluent gas in a CCR system is to:
A. Remove carbon dioxide from the loop
B. Provide volume control and adjust breathing mixture composition
C. Replace the scrubber material
D. Prevent all decompression requirements
Correct Answer: B
Diluent gas is used to maintain loop volume, control oxygen concentration,
and support safe operation at depth.
11. If a CCR diver experiences a sudden increase in breathing
resistance, the most appropriate initial response is to:
