Scuba Diving Dive Planning and Tables 1 — Questions and Answers
Question 1: What is a no-decompression limit (NDL) in recreational scuba diving?
- Maximum time at a given depth before a decompression stop is required (Correct answer)
- Maximum depth allowed without special training
- Minimum surface interval between dives
- Maximum number of dives per day
Correct answer: Maximum time at a given depth before a decompression stop is required
The no-decompression limit is the maximum bottom time at a specific depth that allows a direct ascent to the surface without mandatory decompression stops.
Question 2: What is a 'pressure group' on PADI's recreational dive planner tables?
- A letter indicating the amount of residual nitrogen in the diver's body after a dive (Correct answer)
- The team of divers on a given dive
- A measure of the tank pressure used during the dive
- The depth group assigned at the start of a dive
Correct answer: A letter indicating the amount of residual nitrogen in the diver's body after a dive
A pressure group is a letter (A–Z) on the RDP table that represents the level of residual nitrogen remaining in a diver's tissues after a dive.
Question 3: What is a 'safety stop' and at what depth is it typically performed?
- A 3-minute pause at 15 feet (5 meters) to allow excess nitrogen to off-gas (Correct answer)
- A stop at the bottom to check equipment before ascending
- A mid-water pause to equalize ear pressure
- A surface rest period between repetitive dives
Correct answer: A 3-minute pause at 15 feet (5 meters) to allow excess nitrogen to off-gas
A safety stop is a precautionary 3-minute pause at 15 feet (5 meters) recommended at the end of every dive to allow additional nitrogen off-gassing before surfacing.
Question 4: What does 'residual nitrogen time' (RNT) account for in dive planning?
- Nitrogen still dissolved in tissues from previous dives that counts against the next dive's NDL (Correct answer)
- The time needed to refill tanks between dives
- Nitrogen released during a safety stop
- The rate at which nitrogen leaves tissues during ascent
Correct answer: Nitrogen still dissolved in tissues from previous dives that counts against the next dive's NDL
Residual nitrogen time is the equivalent bottom time already 'used' due to nitrogen left from prior dives, which is added to actual bottom time when planning repetitive dives.
Question 5: What is the recommended maximum ascent rate in recreational scuba diving?
- 30 feet (9 meters) per minute or slower (Correct answer)
- 60 feet (18 meters) per minute
- 100 feet (30 meters) per minute
- 15 feet (4.5 meters) per minute
Correct answer: 30 feet (9 meters) per minute or slower
Most training agencies recommend ascending no faster than 30 feet (9 meters) per minute to allow adequate nitrogen elimination and reduce decompression sickness risk.
Question 6: Why should the deepest dive of the day be planned first?
- To minimize residual nitrogen for subsequent shallower dives (Correct answer)
- Because air consumption is highest in the morning
- To get the hardest dive done while rested
- Because visibility is best at depth earlier in the day
Correct answer: To minimize residual nitrogen for subsequent shallower dives
Doing the deepest dive first minimizes the residual nitrogen carried into subsequent dives, allowing longer NDLs on the shallower dives that follow.
Scuba Diving Dive Planning and Tables 1
What is a no-decompression limit (NDL) in recreational scuba diving?