15
PO
2
LEVEL
Max Bottom Time (minutes)
(Based on CNS Exposure)
.5
1304
.6
719
.7
496
.8
379
.9
257
1.1
221
1.2
194
1.3
172
1.4
149
1.5
110
1.6
44
Your dive computer calculates CNS or OTU toxicity percentages and it issues a
unique, five double-beep audible alarm once per minute should you reach 75
percent of the associated maximum limit. In addition to this audible warning, the
WARNING legend will appear and flash AND the TEMPerature digits will be
replaced with the current calculated CNS Oxygen Toxicity percentage. This
warning will continue until the calculated toxicity percentage is less than 75
percent. For example, the maximum bottom time exposure for a PO
2
level of 1.4
is 149 minutes. Once you reached 112 minutes of bottom time with a PO
2
of 1.4,
this alarm would be issued since 112 minutes is 75% of 149 minutes. At a PO
2
of 1.5, this alarm would be issued at 82 minutes, etc.
NOTE: While all other audible alarms of the dive computer consist of
five long beeps, the toxicity audible alarm consists of short double-
beeps that sound for five seconds.
Pulmonary (Whole Body) Oxygen Toxicity
Another key function to recognize when breathing mixtures with an O
2
content
greater than 50 percent is Pulmonary Oxygen Toxicity, also called “Whole Body”
Toxicity. This is a cumulative development, which must also be tracked
accurately, and is of particular importance should the diver require
recompression therapy or have extended exposure to elevated levels of O
2
.
LIFEGUARD™
monitors and computes this longer-term effect as "Oxygen
Tolerance Units" ( OTUs ) based on Bill Hamilton’s MODIFIED REPEX method of
oxygen exposure management. The following chart illustrates how the OTU
function relates to diving activity:
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