PADI Diving Theory & Safety 4 — Questions and Answers
Question 1: What is the purpose of an alternate air source (octopus) in recreational diving?
- To provide a backup regulator if the primary fails mechanically
- To supply air to a buddy who has run out of breathing gas (Correct answer)
- To inflate the BCD orally if the low-pressure inflator fails
- To sample air quality from different parts of the tank
Correct answer: To supply air to a buddy who has run out of breathing gas
The alternate air source (octopus) allows an out-of-air diver to breathe from their buddy's tank during a controlled ascent.
Question 2: When equalizing ear pressure during descent, a diver should:
- Wait until feeling discomfort, then equalize forcefully
- Equalize early and often before discomfort occurs (Correct answer)
- Only equalize at the bottom of the descent
- Pinch the nose and blow as hard as possible
Correct answer: Equalize early and often before discomfort occurs
Equalizing early and frequently during descent prevents barotrauma by keeping the eustachian tubes open before pressure builds.
Question 3: A diver at 20 meters depth on air is breathing at what absolute pressure?
- 1 ATA
- 2 ATA
- 3 ATA (Correct answer)
- 4 ATA
Correct answer: 3 ATA
Absolute pressure = surface pressure + water pressure = 1 ATA + (20m/10m per ATA) = 3 ATA.
Question 4: What does a BCD (Buoyancy Control Device) primarily help a diver achieve?
- Thermal protection in cold water
- Neutral buoyancy at depth and positive buoyancy at surface (Correct answer)
- Protection against aquatic life
- Air supply management during a dive
Correct answer: Neutral buoyancy at depth and positive buoyancy at surface
The BCD allows divers to achieve neutral buoyancy underwater for effortless hovering and positive buoyancy at the surface for resting.
Question 5: If a diver surfaces with a headache, fatigue, and cherry-red skin coloration after filling tanks from a vehicle exhaust source, the cause is likely:
- Decompression sickness
- Carbon monoxide poisoning (Correct answer)
- Nitrogen narcosis
- Hyperoxia
Correct answer: Carbon monoxide poisoning
Cherry-red skin, headache, and fatigue are classic signs of carbon monoxide poisoning from contaminated breathing gas.
Question 6: What is the significance of the 'surface interval' between dives?
- It allows the diver to eat and rehydrate
- It allows residual nitrogen to off-gas and reduces DCS risk on subsequent dives (Correct answer)
- It allows the BCD to dry properly
- It is required by law in the United States
Correct answer: It allows residual nitrogen to off-gas and reduces DCS risk on subsequent dives
Surface intervals allow dissolved nitrogen to off-gas, reducing the residual nitrogen load before the next dive and lowering DCS risk.
Question 7: Which of the following is a contraindication to scuba diving?
- Being over the age of 40
- Spontaneous pneumothorax history (Correct answer)
- Mild myopia requiring corrective lenses
- A history of mild seasickness
Correct answer: Spontaneous pneumothorax history
A history of spontaneous pneumothorax is a contraindication because the same mechanism can cause pulmonary barotrauma during ascent.
PADI Diving Theory & Safety 4
What is the purpose of an alternate air source (octopus) in recreational diving?