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Tarheel Divers

Dive Tables Terms and Rules

Dive Schedule: This is an abbreviated statement giving the depth and time of the dive
Maximum Dive Time: This is the time you may spend at a given depth without having to do a required decompression stop during the ascent. Also known as Maximum Allowable Dive time or No Decompression Limit.
Decompression Stop: The point in a dive where you stop at a specified depth for a specified time during ascent to allow for Nitrogen offgassing.
Precautionary Decompression Stop: This is a stop at 15 feet for 3 minutes as a safety precaution when you have NOT exceeded the Maximum Dive Time. It is also known as a Safety Stop.
Actual Dive Time: This is the elapsed time from the moment you begin your descent from the surface to the time you return to the surface. Time spent during the ‘Safety Stop’ does not need to be included when determining your letter group.
Residual Nitrogen: This is the excess Nitrogen remaining in your body after any dive made before you have completely offgassed.
Letter Group Designation: This letter symbol identifies the amount of Residual Nitrogen you have in your system. The closer the letter is to the beginning of the alphabet the less Residual Nitrogen you have in your body.
Surface Interval Time: This is the time spent on the surface between dives. During this time your body is eliminating excess Nitrogen.
Repetitive Dive: This is any dive you make before you have completely offgassed from any dive or dives. Or, any dive within 24 hours of a previous dive.
Residual Nitrogen Time: This is the amount of time you must consider as already having been spent for a planned repetitive dive.
Adjusted Maximum Dive Time: This is the Maximum Dive Time minus the Residual Nitrogen Time for a repetitive dive for a given depth.
Total Nitrogen Time: This is the sum of your Residual Nitrogen Time and your Actual Dive Time following a given dive. Use this time to determine your letter group after a given Time.

1. Ascend no faster than 30 feet per minute.

2. Use the exact or next greater number on the Dive Table for your depth. If you exceed a number in the table use the next greater number.

3. Use the exact or next greater number on the Dive Table for your time. If you exceed a number in the table use the next greater number.

4. Use the deepest depth you reached during your dive to determine the Dive Schedule for your dive.

5. Always make your deepest dive first when making a series of dives.

6. Plan each of your repetitive dives to a shallower depth than your previous dives.

7. Consider any dive shallower than 40 feet to be a 40 foot dive when planning your dives.

8. Surface Interval Time must at least be 10 minutes between dives. One hour is the recommended amount of time for a Surface Interval.

9. Use the next greater dive time if your dive is particularly cold or strenuous.

10. Avoid dives that take you right to the decompression limit for any particular depth and time combination.