20 Open Water Diver practice questions
In short
20 practice questions for the Open Water Diver level, one per lesson of the Octo app, each with its answer and explanation. Tap an answer to check yourself. These are original questions written for the app, not taken from any agency’s exam; the app has six per lesson, spaced review and a 30-question practice exam.
Your final exam is on Saturday and the chapters have started to blur. Answer these 20 questions cold, one per lesson, before you open any explanation. The ones you miss are your study list for the week. Trying to recall an answer, then checking it, strengthens the memory even when you get it wrong. Units are shown in metric with imperial in brackets. The theory behind each question is on the Open Water Diver course page.
The 20 questions, lesson by lesson
What Open Water lets you do
Open Water depth limit
1As a newly certified adult Open Water Diver, what is your recommended maximum depth?
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Answer B. Open Water training prepares you for dives to 18 m (60 ft). 12 m (40 ft) is the limit for juniors aged 10 and 11, 30 m (100 ft) comes with Advanced training, and 40 m (130 ft) is the limit of recreational diving.
Mask, fins, snorkel and exposure suit
why the mask covers your nose
2Why must a scuba mask enclose your nose?
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Answer D. Blowing out through your nose lets you equalize the mask on the way down and push water out of it. Swimming goggles can’t do either.
BCD, regulator, alternate air source and gauges
first and second stage
3Which part of the regulator fits onto the tank valve?
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Answer B. The first stage fits on the valve, by yoke or DIN fitting, and lowers the tank’s pressure. The second stage, in your mouth, gives you air when you inhale.
Setting up and the pre-dive check with your buddy
valve not fully open
4During the pre-dive check, the gauge needle dips each time you inhale and springs back when you stop. What does it mean?
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Answer C. A dipping needle means air isn’t flowing freely, usually because the valve isn’t fully open. At depth, you’d struggle to get enough air.
Pressure and volume
absolute pressure
5What is the absolute pressure at 20 m in sea water?
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Answer B. 20 m of sea water adds 2 bar, plus 1 bar of air at the surface: 3 bar absolute. Forgetting the air above gives the tempting wrong answer.
Equalizing ears, sinuses and mask
when to equalize
6When should you start equalizing your ears?
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Answer A. Equalize before the pressure difference builds. Waiting for pain means the tube may already be squeezed shut.
Never hold your breath
why breath-holding is dangerous
7What is the main danger of holding your breath while ascending on scuba?
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Answer B. Lungs full of compressed air can’t hold the extra volume as the pressure drops: the tissue can tear. This lung overexpansion injury can kill.
Buoyancy and weighting
neutral buoyancy
8Underwater, you neither sink nor rise. Your buoyancy is…
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Answer B. Neutral buoyancy means the upward push equals your weight. It’s the goal: no effort to stay level, less air used.
Air consumption and depth
dive time and depth
9A tank would last you 60 minutes at the surface. At the same effort, roughly how long would it last at 20 m?
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Answer B. at 20 m, the absolute pressure is 3 bar, so each breath takes three times as much air: 60 ÷ 3 = 20 minutes.
Hand signals and communication
thumbs up
10Underwater, your buddy gives you a thumbs up. What does it mean?
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Answer B. Underwater, the thumbs up means “up”: end the dive and ascend. “OK” is the ring made with thumb and index finger.
Descending, ascending and the safety stop
safety stop
11What is the recommended safety stop?
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Answer D. 3 minutes at 5 m (15 ft), on every dive unless an emergency prevents it. It adds a margin against decompression sickness.
Monitoring your air and your reserve
reserve
12Unless the briefing sets a higher figure, with how much air should you reach the surface?
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Answer B. Plan to surface with at least 50 bar (500 psi). That reserve covers the unexpected at the end of the dive.
Losing your buddy
lost-buddy procedure
13You’ve lost sight of your buddy. What’s the usual procedure?
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Answer C. A short search, then both divers go up and meet at the surface. Searching longer wastes air and can take you both in different directions.
Out of air: your options
best out-of-air option
14At 12 m (40 ft), you run out of air. Your buddy is right beside you. What’s your best option?
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Answer B. With a buddy close by, sharing air lets you ascend slowly and normally. The other options are for when that’s not possible.
Stress, overexertion and cramps
signs of stress
15Which of these is a typical sign of a stressed diver?
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Answer A. Fast breathing, wide eyes and rushed movements are early signs of stress. Spot them early, in yourself and your buddy.
Decompression sickness and nitrogen narcosis
cause of decompression sickness
16What causes decompression sickness?
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Answer D. Nitrogen absorbed at depth forms bubbles if you rise too fast or stay too long. A held breath causes a lung injury, a different accident.
Cold, heat, seasickness and fatigue
shivering underwater
17During a dive, you start shivering and can’t stop. What should you do?
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Answer C. Uncontrolled shivering is a warning sign: you’re losing heat faster than you make it. End the dive and warm up. Water usually gets colder with depth.
Dive computers and no-decompression limits
what the NDL is
18What does your computer’s no-decompression limit (NDL) show?
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Answer B. The NDL is how long you can stay at your current depth and still ascend directly, without mandatory decompression stops. It says nothing about your air.
The dive environment: currents, waves and aquatic life
starting into the current
19On a dive that returns to its starting point, which way do you go first in a current?
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Answer A. At the end of the dive you’re more tired and lower on air, so let the current do the work then.
Dive planning, logbook and flying after diving
flying after several days of diving
20After a week of diving, two dives a day, what’s the minimum wait before flying under DAN’s guidelines?
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Answer C. Several dives a day or several days of diving call for at least 18 hours. Your computer’s no-fly time may be longer: follow the longer one.
Frequently asked questions
Are these the real Open Water Diver exam questions?
No. These are original practice questions written for the Octo app. They cover the theory of the Open Water Diver level, but they are not taken from any training agency’s exams, knowledge reviews or manuals, and Octo is not affiliated with PADI or any other agency.
How many Open Water Diver questions does Octo have?
Octo has six questions for each of its 20 Open Water Diver lessons, 120 in all, each with the right answer and an explanation, plus a 30-question practice exam for the level that includes real-life scenarios, with an optional timer. See how Octo works.
What should I do with the questions I get wrong?
Reread the explanation, say in one sentence why the right answer is right, then try the question again a day or two later. In Octo, spaced review does this for you: a missed question comes back the same day, then at longer and longer intervals until you know it. Our guide to studying for the Open Water exam turns this into a two-week plan.
Which Open Water questions trip students up?
Pressure is the classic trap: at 20 m (66 ft), the absolute pressure is 3 bar (3 ata), not 2, because the air above the water counts. Others: a held breath is most dangerous near the surface, a thumbs up means “go up”, and the NDL shows time at depth, not air. Our article on the questions new divers get wrong explains each one.
