NAUI Dive Tables
Objectives
• Describe the function of the dive tables.
• Define common dive tables terminology
and concepts.
• Explain the function and use of each
individual table within the dive tables.
• Plan repetitive dives not requiring stage
decompression.
• Calculate the minimum Surface Intervals
for repetitive dives.
• Determine contingency mandatory
decompression stops.
Purpose of the dive tables
• Track the amount of Nitrogen you
accumulate in your body during a series of
dives.
• Minimize the risk of Decompression
sickness.
• Set time and depth limits such that you
can make a direct ascent to the surface
with minimal increase in the risk of
decompression sickness (DCS)
Tables terminology and concepts
• Dive Schedule/Dive Profile
– Abbreviated statement of depth and time
– 70/40=70 feet for 40 minutes
• Actual Dive Time (ADT)
– Surface to surface time, not including safety stop.
• 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.
• 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 (outgassing) and therefore your letter group,
will change.
• New Group
– Letter group at the end of the SIT
• Repetitive Dive (Rep Dive)
– Any dive made within 24 hours of a preceding dive.
• 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 = T NT
• 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.
• Depth
– Use exact or next greatest number.
• Time
– Use exact or next greatest number
• Dive sequence
– Deep to shallow recommended
• During the dive
• For any rep. dive
• SIT
–
–
–
–
Minimum recommended
Minimum recognized
Keep activity to a minimum
Drink water
1 hour
10 minutes
• Depth limit recommendations
– Sport Diving Maximum Depth 130”
• Altitude Diving
– Special training/tables required when diving at
altitudes above 1000 feet.
• Flying after diving
– 1 recreational dive
– Multiple recreational dives
– Mandatory Decompression dive
• Long, cold, strenuous dive
– Use next greater TNT
12 hours
18 hours
24 hours
Safety stops
• Maintain mouth at 15'
– Minimal activity throughout the stop.
– Protocols:
• Dives with a max depth of 40 feet
– 3-minute stop at a depth of approximately15 feet.
• Dives with a max depth deeper than 40 feet
– initial 1-minute stop at a depth equal to ½ the Max depth,
– followed by a 2-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 2-minute stop at a depth of approximately 15 feet.
Stage Decompression Diving
• Dives that require a mandatory decompression
stop.
• Considered beyond the realm of sport diving
– risk and special equipment considerations.
– 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
Table 1 End-of-Dive Letter Group
• Function
– Provide MDT for initial dive in sequence
– Provide end of dive letter group after any dive
• Use
– Find depth of dive in left hand column
– Follow row for that depth to the right and find TNT
– Follow column for TNT down to find end of dive letter
group
– Circled numbers indicate the maximum TNT you can
accumulate for a dive to a given depth without the
need for a mandatory decompression stop
• Either for one dive or over a series of dives
Table 2 Surface-Interval-Time (SIT) Table
• Function
– Track SIT
•
Use
– Follow column for end of dive letter group
designation down until you find the block of
time that includes the time spent on the
surface.
– Follow that column to the right to your new
group designation in table 3.
Table 3 Repetitive Dive Timetable
• Function
– Provide new letter group designation
– Provide Adjusted Maximum Dive Time (AMDT)
– Provide Residual Nitrogen Time (RNT)
• How to Use Table 3
– Find the row for your new group designation.
– Follow this row to the left to the column for the
planned depth of repetitive dive.
– The box at the intersection of the column for planned
depth and the row for new letter group designation
provides:
• RNT
• AMDT
Top number
Bottom number
– Use this information to plan your dive.
Determining the End-of-Dive letter group
designation for a rep dive
• Based on
– Actual depth of the dive
– TNT (RNT + TNT)
• Go to Table 1 End-of-Dive Letter Group
– Find the actual depth of your dive in column 1
– Follow the row for that depth to the right until
you find the TNT.
– Follow this column down to find your end of
dive letter group.
Planning a minimum SIT
• This process involves working backward
from table 3.
– Used when you must plan a minimum SIT
between rep dives.
• For example at the end of your dive you
are an F diver and you want to go to 80
feet for 20 minutes. How long must you
wait.
• Look at table 3 Repetitive Dive Timetable
– Find the column for 80 feet
– Follow the column down until you find the
AMDT closest to but still greater than 20
minutes.
• Remember the AMDT is the bottom number in the
box.
– In our example it is the third box down which
shows
• RNT 13
• AMDT 22
• Follow that row to the right to find the highest
letter designation that will allow 20 minutes at 80
feet.
– In our example it is the letter C.
• Continue working to the right until you find the
intersection for the row C (the letter designation
you must become), and the column for letter F at
the bottom of table 1. (F is your current
designation as given in the example.)
• The box at the intersection of row C from table 3
and column F from table 1 indicates the SIT
necessary to change from an F diver to a C
diver. In this case it is 2:59 – 4:25, so we must
wait a minimum of 2:59.
• SIT of less than 10 minutes
• Two dives separated by a SIT of less than
10 minutes are considered one dive on the
tables.
• For example:
Dive 1
SIT
Dive 2 = on the tables
60/40
0:08
50/30 = 60/70
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
• A diver has a dive schedule of 100 feet for
35 minutes
– The diver must spend 15 minutes at 15 feet.
– Any time from 25:01 – 40:00 requires this
stop.
• 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?
– First dive in a sequence Maximum dive time (MDT).
– Repetitive dives Adjusted Maximum Dive Time
(AMDT).
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?
Proper use of the dive tables includes:
• Using the tables pre-dive to plan the dive.
• Using the tables post dive to determine
end-of-dive letter group.
• Maximizes Bottom time or minimizes SIT
• Minimizes the risk of DCS