Altitude Diving; Oxygen Exposure - Suunto D4 User Manual

10.2.3. Altitude diving

The atmospheric pressure is lower at high altitudes than at sea level. After traveling
to a higher altitude, you will have additional nitrogen in your body, compared to the
equilibrium situation at the original altitude. This "additional" nitrogen is released
gradually over time and equilibrium is restored. It is recommended that you acclimatize
to a new altitude by waiting at least three hours before making a dive.
Before high-altitude diving, the instrument must be set to the Altitude Adjustment mode
to adjust the calculations for the new altitude. The maximum partial pressures of nitro-
gen allowed by the mathematical model of the dive computer are reduced according
to the lower ambient pressure.
As a result, the allowed no-decompression-stop limits are considerably reduced.

10.3. Oxygen exposure

The oxygen exposure calculations are based on currently accepted exposure time
limit tables and principles. In addition to this, the dive computer uses several methods
to conservatively estimate the oxygen exposure. For example:
the displayed oxygen exposure calculations are raised to the next higher percentage
•
value
for recreational scuba diving, the recommended upper limit of 1.4 bar PO
•
as a default
the CNS % limits up to 1.6 bar are based on 1991 NOAA Diving Manual limits
•
the OTU monitoring is based on the long-term daily tolerance level and the recovery
•
rate is reduced
is used
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