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Unit 5: Decompression
Nitrogen and Diving. Dive Table Overview. Dive Table Organization. Dive Planning Worksheet. Maximizing Your Underwater Time. Special Rules. Using the NAUI Dive Time Calculator. Sample Problems. Using Dive Computers.
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rs • Describe how ingassing and outgassing of nitrogen affects the amount of time you can spend underwater.
• Describe the concept of residual nitrogen.• Plan a dive using the NAUI dive tables.• Keep track of dive information using the
NAUI dive planning worksheet.• State the procedure for a precautionary stop.• Plan a dive using the NAUI dive time
calculator.• List the benefits of using a dive computer.
Student Performance: By the end of the lesson students will be able to:
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Nitrogen and DivingNitrogen that dissolves in your tissues during a dive is the gas you must be concerned about when planning your dives.
Ingassing nitrogen: Offgassing nitrogen: Decompression Sickness:
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Residual NitrogenTo properly use dive tables and dive computers, you must understand the concept of residual nitrogen.
Residual nitrogen reduces your time limits for any given depth on your next dive.
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Review on In and OutgassingWhat have you learned so far?
Describe what your body does with nitrogen when under pressure.
Describe why bubbles will form during offgassing.
State the depth you can dive to without a dive time limit.
Explain residual nitrogen.
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Dive Table OverviewThe NAUI Dive Tables use a Letter Group designation to express the amount of residual nitrogen in your body.
The letters range from A to L.
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Dive Table TermsThe following apply to the NAUI Dive Tables:
Dive schedule. Maximum Dive Time (MDT). Decompression Stop.
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Dive Table TermsThe following apply to the NAUI Dive Tables: continued
Precautionary decompression stop. Required decompression stop. Actual Dive Time.
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Dive Table TermsThe following apply to the NAUI Dive Tables: continued
Residual nitrogen. Letter group designation. Surface Interval Time.
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Dive Table TermsThe following apply to the NAUI Dive Tables: continued
Repetitive dive. Residual Nitrogen Time (RNT). Adjusted Maximum Dive Time (AMDT). Total Nitrogen Time (TNT).
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Dive Table RulesYou must understand the following dive table rules completely.
Ascend no faster than 30 feet per minute. Use exact or next greater number listed for your
depth. Use exact or next greater number listed for your
time.
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Dive Table Rules continuedYou must understand the following dive table rules completely.
Use the deepest depth you reach during your dive. Always make your deepest dive first. Dives shallower than 40 feet are planned as 40 feet.
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Dive Table Rules continuedYou must understand the following dive table rules completely.
Surface interval time must be at least 10 minutes. Use the next greater dive time if it was cold or
strenuous. Avoid dives that take you to the no-decompression
limit.
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Review on Dive Table RulesWhat have you learned so far?
State the maximum rate of ascent according to NAUI dive tables.
List the minimum amount of time needed between dives and the recommended amount of time.
Describe the order dives should be made according to depth.
State the minimum depth used when planning for dives shallower than 40 ft.
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Dive Table OrganizationThe NAUI dive tables are composed of three tables.
Table 1: End of Dive Letter Group.
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Review on Dive Table 1What have you learned so far?
List the Group Letters for the following dive profiles:
If you do a dive to 60 feet for 42 minutes.
If you do a dive to 40 feet for 88 minutes.
If you do a dive to 120 feet for 9 minutes.
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Dive Table OrganizationThe NAUI dive tables are composed of three tables.
Table 2: Surface Interval Time (sit) Table.
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Review on Dive Table 2What have you learned so far?
List the new Group Letters for the following Surface Interval Times:
You have a group letter of I and your SIT is 2 hours and 36 minutes.
You have a group letter of C and your SIT is 3 hours.
You have a group letter of G and your SIT is 42 minutes.
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Dive Table OrganizationThe NAUI dive tables are composed of three tables.
Table 3: Repetitive Dive Timetable.
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Review on Dive Table 3What have you learned so far? Answer the following questions.
1. If you have a beginning Letter Group of D and you want to dive to 60 feet, your AMDT is _____ minutes.
2. If you have a new letter group of B and you want to dive to 90 feet, your AMDT is _____ minutes.
3. If you have a beginning letter group of G, you can dive to 80 feet for _____ minutes.
4. If you have a beginning Letter Group of E and you dive to 57 feet, your RNT is _____ minutes.
5. If you have a beginning Letter Group of G and you dive to 37 feet, your RNT is _____ minutes.
6. If you have a beginning Letter Group of C and you dive to 67 feet for 22 minutes, your TNT is _____ minutes.
7. If you have a beginning Letter Group of D and you dive to 54 feet for 18 minutes, your TNT is _____ minutes.
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Dive Planning WorksheetYou must systematically keep track of your dive information when working with NAUI Dive Tables.
Planning your dive. Finding your letter group. Recording your SIT and finding your new group letter. Planning your repetitive dive. Recording your repetitive dive.
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Review on Dive TablesWhat have you learned so far?Review the following problems using your planning worksheet.
1. Your first dive of the day was to 66 feet. You descended at 9:40, surfaced at 10:19, and completed a 3-minute precautionary decompression stop (ADT=36). Your second dive was to 46 feet. You descended at 12:32, surfaced at 1:13, and completed a 3-minute precautionary decompression stop (ADT=38). Your third dive was to 40 feet. You descended at 2:43, surfaced at 3:26, and completed a 3-minute precautionary decompression stop (ADT=40).
2. Your first dive of the second day of your trip was to 80 feet. You descended at 8:35, surfaced at 8:58, and completed a 3-minute precautionary decompression stop (ADT=20). Your SIT was 2 hours and 46 minutes. Your second dive was to 52.5 feet for 36 minutes including your precautionary decompression stop (ADT=33). You surfaced at 12:20. Your third dive was to 33 feet. You descended at 3:10, surfaced at 4:10, and completed a 3-minute precautionary decompression stop (ADT=57).
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rsMaximizing Underwater TimeMaximize your dive time by adjusting your SIT, depth,or ADT.
Limiting your dive time: Planning your surface
interval: Limiting your depth:
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Special RulesThere are a number procedures you must learn to handle special situations.
Decompression diving. Precautionary decompression stops. Required decompression. Omitted decompression. Cold or strenuous dives. Flying after diving. Altitude diving.
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Using Dive ComputersThe easiest way to determine how long you can dive is to use a dive computer.
Both dive tables and dive computers are only theoretical models of what happens in the human body.
The computer constantly recalculates as your depth changes during your dive.
A dive computer is an electronic device that can fail without warning.
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Dive Computer TermsYou must be familiar with the terms associated with dive computers.
Ceiling: Violating the ceiling: Scrolling:
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Displays and FunctionsThe layouts of the display screens differ among computers.
Display information. Initialization. Scrolling. Dive mode. Decompression. Planning repetitive dives. Safe to fly indicators. Logging your dives. Dive computer rules.
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Review on Dive ComputersWhat have you learned so far?
Explain the information a ceiling indicator displays. State the recommended maximum depth for a
repetitive dive when using a dive computer. State what a dive computer does when it is first
turned on. Explain what occurs when a dive computer is
scrolling. State what you risk by ascending above a ceiling
indicated on the a dive computer. List two ways a dive computer can warn you that you
have exceeded your ascent rate.
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Decompression End of Unit 5
Nitrogen and Diving. Dive Table Overview. Dive Table Organization. Dive Planning Worksheet. Maximizing Your Underwater Time. Special Rules. Using the NAUI Dive Time Calculator. Sample Problems. Using Dive Computers.
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rs • Describe how ingassing and outgassing of nitrogen affects the amount of time you can spend underwater.
• Describe the concept of residual nitrogen.• Plan a dive using the NAUI dive tables.• Keep track of dive information using the
NAUI dive planning worksheet.• State the procedure for a precautionary stop.• Plan a dive using the NAUI dive time
calculator.• List the benefits of using a dive computer.
Student Performance: By the end of the lesson students will be able to:
