longer than those that would be allowed by the U.S. Navy tables.
Compartments and Half Times
When you dive with the IQ-400, it measures and displays depths and times as
your dive progresses. It shows you available no-decompression time and possi-
ble decompression required based upon the following five factors:
1. your present depth,
2. excess nitrogen absorbed during earlier portions of the dive,
3. residual nitrogen remaining from previous dives,
4. the no-decompression limits that apply to that depth,
5. the personal/ altitude adjustment mode in use.
Back on the surface, the IQ-400 will continue to calculate the no-decompres-
sion dive times available for various depths on the next dive. As the surface
interval increases, so does the available dive time for the next dive.
To perform these calculations, the IQ-400 continuously models the absorption
and release of excess nitrogen from theoretical compartments. Each compart-
ment absorbs and releases nitrogen at a different rate. The compartments that
absorb and release nitrogen rapidly are believed to have a high tolerance for
excess nitrogen, whereas compartments that absorb and release nitrogen more
slowly are believed to be more sensitive.
The no-decompression limits in the U.S. Navy tables are based upon six theo-
retical compartments for single dives, and one compartment for surface inter-
vals and repetitive dives. If you are familiar with table theory, you may know
that they are characterized by half times (i.e. the time required for 50 % equili-
bration to a pressure change) ranging from 5 minutes to 120 minutes.
The IQ-400 includes the same six compartments, and two additional compart-
ments for an increased range of the mathematical model. The calculations are
based on all eight compartments for all phases of diving, including surface inter-
vals and repetitive dives. The IQ-400’s half times range from 2.5 to 320 minutes.
The multi-level tissue calculations are based on modified Haldanean principle.
38
WARNING
THE USER SHOULD BE AWARE THAT ANY DIVE,
INCLUDING ONES WITHIN THE U.S. NAVY TABLES
OR IQ-400 LIMITS, DOES CARRY SOME RISK OF
DECOMPRESSION SICKNESS.
