Dive Tables
Planning dives safely
Objectives
 Describe the function of the dive tables.
 Define common dive tables terminology and concepts.
 Plan repetitive dives not requiring stage decompression.
 Determine contingency mandatory decompression stops.
Main points
 Dive tables aid in planning safe dives by setting depth and time limits
 Must understand the terminology
 Must adhere to the rules
 Recreational diving does not involve decompression stops
 Decompression stops are listed for contingences purposes
 We utilize computer but understand the tables are still key to safe diving
Terminology
 Dive Profile
 statement of depth and time
 70 feet for 40 minutes
 Actual Dive Time (ADT)
 Surface to surface time
 Depth or max depth
 Deepest point of dive no matter how brief the time spent there.
 Maximum Dive Time (MDT)
 Maximum time you can spend on a dive to a given depth without requiring a mandatory
decompression stop.
Terminology
 End-of-Dive Letter Group
 Symbol representing amount of excess nitrogen in your body at the end of the dive.
 Surface Interval (SIT)
 Time on surface between dives.
 During the SIT you are getting rid of some excess nitrogen (off-gassing) and therefore your
letter group, will change.
 New Group
 Letter group at the end of the SIT
 Repetitive Dive
 Any dive made within 24 hours of a preceding dive.
Terminology
 Residual Nitrogen Time (RNT)
 Excess Nitrogen in your body after a dive
 Represented by your new group at the end of the SIT
 Adjusted Maximum Dive Time
 The maximum dive time for a repetitive dive to a given depth.
 Total Nitrogen Time (TNT)
 Represents total nitrogen load in your body at the end of a dive
 Determined by combining RNT +ADT = TNT
Terminology
 Safety Stop
 Voluntary stop at the end of every dive
 Facilitates outgassing of Nitrogen
 Reduces the likelihood of bubble formation
 Mandatory Decompression Stop (Deco stop)
 Required stop at 15 feet whenever MDT or AMDT has been exceeded
 Beyond the training of recreational diving
Rules for Using the NAUI Tables
 Rate of ascent
1/2 foot per second or slower.
 Dive sequence
 Deep to shallow recommended
 During the dive
 For any rep. dive
 Depth
Use exact or next greatest
number.
 Time
Use exact or next greatest
number
 SIT




Minimum recommended : 1hr
Minimum recognized : 10min
Keep activity to a minimum
Drink water
Rules for Using the NAUI Tables
 Sport Diving Maximum Depth 130ft
 Altitude Diving
 Special training/tables required when diving at altitudes above 1000 feet.
 Flying after diving
 1 recreational dive: 12 hours
 Multiple recreational dives: 18hrs
 Multiple dive/multiple days: 24hrs
 Mandatory deco stop: 24hrs
 Long, cold, strenuous dive
 Use next greater TNT
Safety stops
 Maintain depth of 15ft for 3mins
 Minimal activity throughout the stop.
 Deep stops: (different schools of thought)
 initial 1-minute stop at a depth equal to ½ the Max depth,
 followed by a 3-minute stop at a depth of 15 feet.
 For example, on a dive to 100 feet of seawater (FSW),
 make a 1-minute stop at a depth of approximately 50 feet,
 followed by 3-minute stop at a depth of approximately 15 feet.
Stage Decompression Diving
 Dives that require a mandatory decompression stop.
 Beyond the realm of sport diving
 However you should have contingency information and be familiar with the minimal emergency
procedures in case the maximum recreational dive time is exceeded.
 Omitted Decompression
 Missed mandatory decompression stop and no symptoms
 Rest, drink fluids, and watch for signs of DCS.
 Do not re-enter water for at least 24 hours.
 If signs/symptoms of DCS are present treat for DCS
Walking through the table
Table 1
 Find depth column
 Find dive time rows
 Find max time for 40ft, 60ft, 100ft
 Find max time for 44ft, 55ft, 81ft
Finding letter groups
 60ft/30min
 70ft/36mins
 81ft/22mins
Table 2 (SIT Times)
 Finding your next letter group
 Letter group E
 SIT for 1hr
 SIT for 1hr 20mins
 SIT for 2hrs
 Letter group H
 SIT for 30mins
 SIT for 1hr 8mins
 3hrs
Table 3: Repetitive dive table
 Starting off with a new letter group
 Find your planned Max Depth
 Top number is your RNT
 Bottom number is your AMDT
 Examples
 E diver: what's your AMDT for
 40ft
 60ft
 75ft
Lets get complicated
 Dive 1




60ft/40mins
Letter group?
2hr SIT
New letter group?
 Dive 2
 MDT for 50ft?
 SIT time for a 30min dive at 50ft?
 If SIT=2hrs; then dive = 50ft/30mins
 what’s my new letter group? (TNT calculation)
Mandatory Decompression Stops
 Found in table 1
 Boxes to the right of the circled numbers
 Top number
 Indicates ADT requiring Mandatory Deco stoop
 Bottom number
 # minutes that must be spent at 15 feet
 Example
 A diver has a dive schedule of 100 feet/23 minutes
 The diver must spend 5 minutes at 15 feet
 Note that any time from 22:01 – 25:00 requires this stop
Mandatory Decompression Stops
 The actual stage decompression tables for air diving are extensive. The
information provided here is for contingency purposes only.
 Stage decompression diving requires extensive training and equipment,
and is beyond the realm of recreational diving.
Before the Dive
Prior to entering the water for any dive you must ask yourself, and answer,
the following questions:
 How much excess Nitrogen, if any, do I have left in my body from previous
dives?
 Residual Nitrogen Time or RNT
 What will be the maximum depth of my dive?
 What is my time limit for the planned depth of the dive?
Post Dive
After the dive you must ask yourself, and answer, the following questions:
 What was the maximum depth of my dive?
 How long did I stay under water?
 Actual Dive Time (ADT).
 What is the total Nitrogen load in my body?
 Total Nitrogen Time (TNT).
 What is my end of dive letter group?