9-5 TABLE SELECTION

TABLE SELECTION

Decompression Tables Available

The decompression tables available for U.S. Navy air diving operations are:

• Unlimited/No-Decompression Limits and Repetitive Group Designation Table for unlimited/no-decompression air dives
• Standard Air Decompression Table Surface Decompression Table Using Oxygen
• Surface Decompression Table Using Air
• Residual Nitrogen Timetables for Repetitive Air Diving
• Sea Level Equivalent Depth Table

These tables contain a series of decompression schedules or depth corrections that must be rigidly followed during an ascent from an air dive. Each table has specific conditions that justify its selection. These conditions are: depth and duration of the dive, altitude, availability of an oxygen breathing system within the recompression chamber, and environmental conditions (sea state, water temperature, etc.).

The Residual Nitrogen Timetable for Repetitive Air Dives provides information for planning repetitive dives.

The five air diving tables and the criteria for the selection and application of each are listed in Table 9-2. General instructions for using the tables and special instructions applicable to each table are discussed in paragraphs 9-6 and 9-7, respectively.

TABLE 9-2 Air Decompression Tables Selection Criteria.

Selection of Decompression Schedule

The decompression schedules of all the tables are usually given in 10-foot depth increments and 10-minute bottom time increments. Depth and bottom time combinations from dives, however, rarely match the decompression schedules exactly. To ensure that the selected decompression schedule is always conservative, always select the schedule depth equal to or next greater than the maximum depth of the dive and always select the schedule bottom time equal to or next longer than the bottom time of the dive.

For example, to use the Standard Air Decompression Table to select the correct schedule for a dive to 97 fsw for 31 minutes, decompression would be selected for 100 fsw and carried out per the 100 fsw for 40 minutes (100/40) schedule.

When planning for surface-supplied dives where the diver will be exceptionally cold or the work load is expected to be relatively strenuous, Surface Decompression should be considered. In such case, conduct decompression from the normal schedule in the water and then surface decompress using the chamber stop time(s) from the next longer schedule. When conducting dives using Standard Air Decompression Tables, select the next longer decompression schedule than the one that would normally be selected.

If the divers are exceptionally cold during the dive or if the work load is relatively strenuous, select the next longer decompression schedule than the one that would normally be selected.

For example, the normal schedule for a dive to 90 fsw for 34 minutes would be the 90/40 schedule. If the divers are exceptionally cold or fatigued, they should decompress according to the 90/50 schedule. This procedure is used because the divers are generating heat and on-gassing at a normal rate while working at depth. Once decompression starts, however, the divers are at rest and begin to chill. Vasoconstriction of the blood vessels takes place and they do not off-gas at the normal rate. The additional decompression time increases the likelihood that the divers receive adequate decompression.