Cochran Lifeguard 04-150i User manual

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LIFEGUARD™
PO2MONITOR
User Manual
English Language - Imperial Units
Version 150i
USER INFORMATION
For your records, please fill in the following information.
SERIAL NUMBER OF UNIT:_____________________________
DATE OF PURCHASE: ________________________________
PLACE OF PURCHASE: ________________________________
ADDRESS: ___________________________________________
CITY: _______________________________________________
STATE: __________________________ZIP CODE: __________
PHONE NUMBER: ___________________________________

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TABLE OF CONTENTS
Table of Contents 2
Figures Index 4
Limited Warranty and Liability Statement 5
Product Certifications 7
Patient Information 8
Introduction 9
Overview 9
User & Environmental Adaptation 9
Altitude Acclimatization 10
Water Temperature Compensation 11
Microbubble Compensation 11
Intelligent Deep-Dive Compensation 11
Salt Water/Fresh Water (High/Low Conductivity) 11
Theory of Operation 12
Equivalent Air Depth 13
Oxygen Toxicity 13
CNS 14
Pulmonary Oxygen Toxicity 15
Installation 17
CTU and O2Sensor 17
Activation 18
Shut-Off 18
Operating Modes 20
Self Diagnostic mode 20
Explanation of Page Layouts 20
Surface Mode 21
Predive Prediction Mode 22
CNS/OTU Toxicity Screen Display 24
Battery/Altitude Screen Display 25
Programming Mode 26
Calibration Mode 30
Subsurface Mode 33
Emergency Decompression Mode 35
Gauge Mode 39
Logbook Mode 42
Ascent Rate Bar Graph 44
Post-Dive Interval 45
Sleep Mode 45
Explanation 46
Altitude Diving 46
Ascent Rate 46
Ascent Rate Bar Graph 47

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TABLE OF CONTENTS
(continued)
BATT 47
Bottom 48
Ceiling 48
Depth 48
Dive 49
Max Depth 49
Metric 50
Remain Time NDC 50
Remain Time DEC 50
Surface Time 50
Tank 50
Temp 51
Time-To-Fly 51
Audible & Visual Warnings 52
Maximum Depth 52
Two-Minute 53
Entering Deco 53
60 FT Deco Stop 53
Ceiling Violation 53
Low Battery 53
Ascent Rate 54
Gauge Mode 54
OTU 54
CNS 54
Max PO255
Min PO255
Questions & Answers 56
Care and Maintenance 58
Rinsing and Cleaning 58
O2Sensor Care 59
Battery Type and Replacement 59
Battery Care 60
Technical Specifications 61
Product Assistance & Maintenance 62
Replacement Parts 63
Analyst® Personal Computer Interface 64
Field Programmer 64

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FIGURES INDEX
Figure Page Number
1. Self-Diagnostic Mode 20
2. Surface Mode, Primary Screen, with Nitrogen 21
3. Surface Mode, Alternate Screen, with Nitrogen 22
4. PreDive Prediction Mode, Primary Screen 23
5. CNS/OTU Toxicity Display 24
6. Battery/Altitude Display 25
7. Logbook Mode, Primary Screen 43
8. Logbook Mode, Alternate Screen 43
9. Subsurface Mode, Normal Dive, Primary Screen 33
10. Subsurface Mode, Normal Dive, Alternate Screen 34
11. Subsurface Mode, Emergency Decompression Dive,
Showing STOP Time, Primary Screen 36
12. Subsurface Mode, Emergency Decompression Dive,
Showing TOTAL Time, Primary Screen 37
13. Subsurface Mode, Emergency Decompression Dive,
Alternate Screen 38
14. Subsurface Mode, Gauge Mode, Primary Screen 40
15. CNS/OTU Toxicity Warning Display 42
17. Connecting Field Programming Probe 27
18. Field Programming Mode (Setting Conservatism) 29
19. Field Programming Mode (Setting Depth Alarm) 29
20a. Calibration Mode (Sensor Exposed to Air) 30
20b. Calibration Mode (Sensor Stabilized with 100%) 31
20c. Calibration Mode (Calibrated & Showing 100%) 32
21. Ascent Rate Bar Graph 44

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LIMITED WARRANTY
To the original purchaser ("OWNER") only, Cochran Undersea Technology, a
division of Cochran Consulting, Inc. ("COCHRAN"), represents this Product to be
free of defects in materials and workmanship under normal SCUBA use for 12
months from the date of shipment to the Authorized Dealer from which it was
purchased. For purposes of establishing warranty eligibility, date of shipment to
Authorized Dealer is noted on the original Product package, or can be
determined by contacting COCHRAN.
Any defective Product, unless cause is specifically excluded in the "Warranty
Conditions and Limitations" section below, will, at the sole discretion of
COCHRAN, be repaired or replaced with a new or refurbished unit of comparable
or better function and condition. COCHRAN is not responsible for any incidental
or secondary damages as a result of Product malfunction
WARRANTY CONDITIONS and LIMITATIONS
Product must have been obtained from a COCHRAN Authorized Dealer.
Verification of Dealer status at the time of the purchase may be obtained by
contacting COCHRAN. This Limited Warranty is not transferable. Warranty
Registration card must be sent to COCHRAN within 15 days of purchase in order
to validate Limited Warranty.
Failure to provide proper care for Product will render this Limited Warranty null
and void. Damages or malfunction resulting from accidental or deliberate abuse,
tampering, battery leakage, exceeding maximum intended operating depth,
extreme heat or cold, or other conditions which COCHRAN may deem to be
outside the intended scope of this Limited Warranty are not covered. Any
modifications or repairs to Product performed by anyone other than a COCHRAN
Authorized Dealer will void this warranty. Plastics, O-rings, oxygen sensors, and
batteries are specifically excluded from this Limited Warranty.
This Limited Warranty will be rendered null and void if an attempt is made to
establish communication with computer with any hardware and/or software other
than the Cochran approved ANALYST®Interface.
OWNER is responsible for shipping this Product to COCHRAN for service, and
paying all associated costs including shipping, insurance and import duties.
OWNER may take Product to an Authorized Dealer to arrange for service under
terms of this Limited Warranty. COCHRAN will return Product to OWNER or
Dealer via a method and carrier of its choosing. Costs for requested expedited
return shipping will be the responsibility of OWNER. Product returned for service
under the terms of this Limited Warranty must be accompanied by a photocopy
of the original sales receipt in order for any warranty repair or replacement to be
performed if Warranty Registration Card is nor on file.

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STATEMENT OF LIMITED LIABILITY
A mathematical model is used by this Product to calculate physiological effects of
SCUBA diving related to use of compressed air or other breathing mixtures while
at depth. Such effects specifically relate to nitrogen absorption into and
elimination from body tissues, as well as effects of oxygen used in Enriched Air
Nitrox breathing mixtures. However, because of the number of variables and the
varying degrees to which they may affect individuals engaged in SCUBA diving,
COCHRAN DOES NOT IN ANY WAY GUARANTEE THAT USE OF THIS
PRODUCT WILL PREVENT DECOMPRESSION SICKNESS OR ANY OTHER
CONDITION OR INJURY INCURRED WHILE USING THIS PRODUCT.
These influencing variables may include but are not limited to dehydration,
obesity, age, old injuries or illnesses, or other physical conditions on the part of
the diver, or environmental extremes of heat, cold, or altitude, or diving practices
which may promote the onset of decompression sickness or other harmful
effects.
This Product is sold and intended to be used only as a guide, providing the
TRAINED and CERTIFIED diver the information needed to make his own
intelligent diving decisions. It is expressly understood that by buying and/or
using this Product the Diver assumes ALL RISK as to its operability, reliability,
quality, performance, accuracy, and suitability for his diving style. Furthermore,
Diver recognizes that this Product is an electronic instrument being used in a
hostile environment and is subject to failure, which may manifest itself in a
number of ways. COCHRAN and its distributors and retailers will not be held
liable for any personal injuries or other damages resulting from its use, even if
COCHRAN has been advised of such occurrences or damages.
These products must be handled with care and properly maintained to assure the
optimum performance. Users must possess the proper training for SCUBA
diving activities and should be fully educated in the operation of this product.
Users are encouraged to possess and utilize a redundant (backup) computer for
their dive planning and execution. Divers are always encouraged to dive with a
buddy at all times.
Cochran strongly supports and agrees with maximum depth limits of 130 feet for
recreational SCUBA diving, as established by recognized training and
certification agencies, and in no way encourages diving beyond these or any
prudent limits as may be necessitated by environmental, diver-specific, or other
conditions.
THE WARRANTY AND REMEDIES SET FORTH ABOVE ARE EXCLUSIVE
AND IN LIEU OF ALL OTHERS, WHETHER ORAL OR WRITTEN, EXPRESSED
OR IMPLIED. COCHRAN UNDERSEA TECHNOLOGY SPECIFICALLY
DISCLAIMS ANY AND ALL IMPLIED WARRANTIES, INCLUDING, WITHOUT
LIMITATION, WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE.

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No Cochran Undersea Technology dealer, agent, or employee is authorized to
make any modification, extension, or addition to this warranty.
CAUTION!!! ACCIDENTAL OR INTENTIONAL LOSS OF BATTERY POWER
WILL CAUSE ALL PREVIOUS DIVE NITROGEN LOADING TO BE LOST. THIS
MAY AFFECT NITROGEN CALCULATIONS ON NEAR-FUTURE DIVES.
AFTER A BATTERY CHANGE, CONFIRM THAT NO-DECOMPRESSION TIME
DATA IS REASONABLE DURING THE PRE-DIVE PREDICTION MODE. DIVE-
OF-DAY NUMBER GOING TO ZERO IMMEDIATELY AFTER CHANGING
BATTERIES IS ANOTHER INDICATION OF A LOSS OF NITROGEN LOADING.
IF LOSS OF NITROGEN LOADING OCCURS, COCHRAN STRONGLY
RECOMMENDS THAT A PERIOD OF 24 HOURS ELAPSES BEFORE MAKING
ANY SUBSEQUENT DIVES.
FCC Label
FCC ID: LYP744556-01
This device complies with Part 15 of the FCC Rules. Operation is subject to the
following two conditions: (1) this device may not cause harmful interference, and
(2) this device must accept any interference received, including interference that
may cause undesired operation.
Interference Statement
NOTE: This equipment has been tested and found to comply with both the limits
for a Class B digital device and an intentional radiator, pursuant to Part 15,
Subpart B/C of the FCC Rules. This equipment generates, uses, and radiates
radio frequency energy. If not installed and used in accordance with the
instructions, it may cause interference to radio communications. The limits are
designed to provide reasonable protection against such interference in a
residential situation. However, there is no guarantee that interference will not
occur in a particular installation. If this equipment does cause interference to
radio or television reception, which can be determined by turning the equipment
on and off, the user is encouraged to try to correct the interference by one or
more of the following measures:
•Reorient or relocate the receiving antenna of the affected radio or
television.
•Increase the separation between the equipment and the affected
receiver.
•Connect the equipment and the affected receiver to power outlets on
separate circuits.
•Consult the dealer or an experienced radio/TV technician for help.

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Modifications
Changes or modifications not expressly approved by Cochran Consulting, Inc.
could void the user’s authority to operate the equipment.
Shielded Cables
To maintain compliance with FCC Regulations, this product is designed only for
use with the ANALYST®interface cable (RS-232).
Patent Information
Protected under one or more Foreign or US patents. Other patents pending.
All specifications subject to change without prior notice. LIFEGUARD and
Analyst are registered trademarks of Cochran Consulting, Inc. Copyright 1999
Cochran Consulting, Inc.
(C) 1999 Cochran Undersea Technology
LIFEGUARD Manual
English - Imperial
Version 150i

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Introduction
The LIFEGUARD™ PO2Monitor from Cochran Undersea Technology is an
independent monitoring device designed to be integrated with the breathing loop
of most commercially available rebreathers. It provides oxygen level (PO2)
monitoring in addition to the functionality of a sophisticated dive computer. User-
programmable options accommodate a broad range of personal preferences and
diving conditions, yet the LIFEGUARD™ remains very simple to use. All
essential information is continually updated and presented on an informative and
easy to comprehend display, with minimal distraction. Audible alerts advise of
conditions, which require immediate attention. Throughout the course of each
dive vital data is stored internally for later retrieval and study via the ANALYST™
PC Interface System.
This manual is organized to provide the basic operating information first, followed
by more technical and detailed sections for reference. The LIFEGUARD™ user
is strongly encouraged to read this document thoroughly before attempting
any operation of the device.
We wish to thank Dr. Bill Hamilton for working with us and sharing his
considerable knowledge in the areas of decompression theory and oxygen
toxicity.
The LIFEGUARD™: Overview
USER & ENVIROMENTAL ADAPTATION
The LIFEGUARD™ is designed and intended for use with rebreather devices,
where a combination of factors drives the need for monitoring oxygen levels
(PO2) in the breathing mixture. Additionally, the LIFEGUARD™ is one of the
new breed of Dive Computers that adapts its algorithm to the user’s diving
environment and style as originally pioneered by COCHRAN. All of COCHRAN’s
newer dive computers incorporate this capability. The factors used for this
‘Adaptation’ in the LIFEGUARD™ are:
Altitude Acclimatization Water Temperature
Salt/Fresh Water Compensation Microbubble
User Conservatism Previous Dive Profile
Intelligent Deep-Dive Compensation
However, the LIFEGUARD™ allows the diver, via the optional Analyst®PC
Interface, to disable the Temperature compensation should the diver deem a
particular diving situation would so warrant. Calculation of Central Nervous
System Oxygen Toxicity (CNS), Mission Oxygen Tolerance Units (OTU's), and
the Partial Pressure of Oxygen (PO2) is yet another added feature of this
algorithm. Twelve half-time compartments ranging from 5 minute to 480-minute

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theoretical tissue groups are used. You will find that this unit is extremely user
friendly and can be customized to your individual diving conditions and practices.
Factors that influence the decompression algorithm of your LIFEGUARD™ are
detailed as follows.
Altitude Acclimatization
Driving or flying to a dive site significantly higher in altitude requires special
modifications to the "sea level" algorithm. The LIFEGUARD™ regularly samples
the ambient barometric pressure to determine these changes in altitude.
Accordingly, the decompression algorithm is changed to reflect these barometric
pressure changes. Note that temperature and weather systems also affect
barometric pressure and hence, apparent altitude. Using the Time To Fly digits,
the number of hours required to adapt to the new altitude is immediately known
to the diver. If a significant altitude change occurs, a minimum of one hour
should pass before diving to allow the unit to adapt to this new altitude. Rapid
changes in altitude should be avoided. The dive computer may interpret a rapid
change from a high altitude to a lower altitude as a dive. Should this occur,
removing the batteries for ten minutes would reset the computer, however, all
tissue nitrogen loading will also be lost.
Should it be desired to initiate a dive PRIOR to completing the adaptation time,
the LIFEGUARD™ will treat this dive as a repetitive dive in its algorithm, taking
into account the "residual" nitrogen present due to travel to altitude. There are
two methods of compensating for altitude. Via the Analyst®Personal Computer
Interface, ZONE or SEAMLESS compensation for altitude may be selected.
In ZONE, all altitudes less than 2,000 feet above sea level use the sea-level
algorithm. At altitudes greater than this, altitude compensation is seamless;
literally, every small fraction of gained altitude is considered in adjusting the
algorithm. ZONE will reduce the occurrences of obtaining slightly different
altitude readings and corresponding no-decompression (NDC) limits when diving
within a given area. ZONE reduces the accuracy of altitude compensation for the
first 2,000 feet above sea level, treating altitudes below 2,000 feet as sea level.
The advantage in ZONE is that changes in apparent altitude (due to temperature
or weather changes at sea level) will not affect NDC computations.
In SEAMLESS, the algorithm is adjusted for extremely small changes in altitude.
A difference in altitude may be seen from day-to-day at a given dive site due to
temperature or weather systems and their effect on barometric pressures.
SEAMLESS will provide the most accurate altitude compensation algorithm, but
normal variations in atmospheric barometric pressure may affect the no-
decompression time which is more predominantly seen in the Pre-dive Prediction
forecast.

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WARNING: While your LIFEGUARD™ will automatically adjust its no
decompression algorithm for altitude, you should NOT attempt to dive
at altitudes greater than 1,000 feet above sea level without first
completing a sanctioned altitude diving course from a recognized
training agency for recreational diving. The LIFEGUARD™ should not
be used for this type of diving by anyone without this important
training.
WATER TEMPERATURE
Diving in cold water can lower a diver's core and skin temperature, affecting the
gas exchange rate of the body’s tissues. The LIFEGUARD™ progressively
makes its nitrogen algorithms more conservative as the water temperature
declines below 75 degrees F. Above this water temperature, there is no
temperature compensation. If the diver is wearing an insulated dry suit and is
relatively warm even in cold water, this temperature compensation factor may be
turned off at the divers discretion using the Analyst®PC software.
MICROBUBBLE
There are several theories regarding the method by which a nitrogen bubble
forms from a microbubble which was formed from micronuclei. Currently, the
predominant theory states that more rapid ascents accelerate bubble formation.
The LIFEGUARD™ accounts for this by progressively increasing its
compensation as the diver’s ascent rate exceeds 30 feet-per-minute (fpm).
Intelligent Deep-Dive Compensation
Research has established that successive dive profiles in a given dive day
should be progressively shallower to minimize susceptibility to decompression
sickness (DCS). Avoiding inverted; square or "sawtooth" dive profiles also
greatly decreases the risk of DCS symptoms. Intelligent Deep-dive
Compensation provides real-time real-condition adjustments to the nitrogen level
calculations in all 12 half-time compartments as the LIFEGUARD™ monitors
activity during the course of a dive day. Should the dive patterns result in
elevated risk of DCS, displayed information on remaining no-decompression
(NDC) time (or decompression time) will be adjusted accordingly.
Sea Water/Fresh Water Recognition (High/Low Conductivity)
There is approximately a three-percent difference in depth readings taken in
fresh water versus seawater. Some dive computers are calibrated in feet of fresh
water and some are calibrated in feet of salt water. Diving in a medium different
from what the dive computer is calibrated will cause apparent depth errors. Only
COCHRAN dive computers, including the LIFEGUARD™,actually determine the
type of diving medium and compensate the depth reading accordingly. This is
accomplished by measuring the conductivity of the water during a dive. Caution
must be taken in interpreting this reading since some apparent fresh water is

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actually high in minerals or contaminants and is correctly compensated as salt
water (high conductivity). This commonly occurs in some caves, springs and
lakes.
THEORY OF OPERATION
The LIFEGUARD™ is designed to constantly monitor and display Partial
Pressure of Oxygen (PO2) in addition to the conventional dive computer
information. This PO2value is directly sensed from the breathing loop, and is
used for no-decompression/decompression calculations, oxygen toxicity tracking,
and other related functions. The diver is able to maintain continual awareness of
this essential "raw value" as well as the derived computations.
The LIFEGUARD™ consists of three component parts, the Computer-
Transmitter Unit (CTU), the Wrist Unit (WU), and the PO2Sensor. The CTU
contains the computer’s electronics, the WU displays the information to the diver,
and the PO2Sensor measures the PO2of the loop gas.
Wrist Unit
The Wrist Unit consists of a Liquid Crystal Display (LCD) screen that Is the
primary method of conveying information to the Diver. The information is
presented in an easy to read and understand layout. The Wrist Unit is supplied
with TACLITE™, the night vision safe red Backlight. Two ENERGIZER®brand N-
Cell Size Alkaline battery power the WU. The WU will receive information from
the LIFEGUARD™ CTU from approximately 36 inches; the actual distance will
vary depending on the orientation of the WU to the CTU. When the WU is
beyond the communications range of the CTU the WU’s display will flash. When
the WU is back in communication with the CTU the display will cease flashing.
Computer-Transmitter Unit
The CTU contains the PO2Sensor connector cable, the Depth/Altitude Sensor,
and the computer’s electronics. The CTU performs all of the time-depth
calculations and also stores the detailed statistics and profile information. The
CTU transmits all information to the WU once per second where it is displayed.
Four ENERGIZER®brand AA-cell batteries power the TU; the batteries should be
Alkaline, non-tester.
NOTE: The WU and CTU contain NO USER SERVICABLE PARTS, If the
lens is removed from the WU and/or the lid from the CTU it will VOID
the limited warranty.

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PO2Sensor
The LIFEGUARD™ is supplied with one of two versions of PO2Sensors. One
version is supplied with a bulkhead connector and sensor. The other version is a
"tee" designed to be installed in the inhalation side breathing hose. The "tee" is
avaliable in two different diameters.
Equivalent Air Depth
Your LIFEGUARD™ uses Equivalent Air Depth (EAD) in determining the no-
decompression limits for each individual dive. A standard NOAA equation is
used to determine the EAD based on the oxygen percentage entered. This
equation is:
METRIC IMPERIAL
EAD = ( 1 - O2% ) X ( D + 10 ) - 10 EAD = ( 1 - O2% ) X ( D + 33 ) - 33
.79 .79
Where O2% is entered in decimal form and Dis the actual depth in meters/feet.
For example, if you were diving with NOAA II (36% oxygen) to 21 meters / 70
feet, the EAD used for determining your no-decompression would be:
METRIC IMPERIAL
EAD = ( 1 - .36 ) X ( 21 + 10 ) - 10 EAD = ( 1 - .36 ) X ( 70 + 33 ) - 33
.79 .79
EAD = .64 X 31 - 10 = 15.11m EAD = .64 X 103 - 33 = 50.44
.79 .79
Therefore, the no-decompression time for this example would be derived from an
EAD of 15.1 meters/50.4 feet.
Oxygen Toxicity
While oxygen is, of course, necessary to sustain life, its effects at increased
ambient pressures can be quite harmful. It is generally agreed that oxygen
toxicity manifests itself in two forms. Of the two, Central Nervous System (CNS)
toxicity is the more immediate and potentially dangerous condition. Pulmonary
(or "whole-body") toxicity is a longer-term, cumulative effect, which also needs to
be monitored. The LIFEGUARD™ provides audible and visual warnings to alert
the diver to buildup of both types of toxicity.
Similar to decompression issues, oxygen toxicity is as much theoretical as it is
practical, and many varying factors influence the degree and symptomatic
presentation of this condition. But research in recent years has led to
development of mathematical models, which can generally predict onset of
oxygen toxicity in both its main forms before serious harm is done. It is with

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these provisions in mind that the following information is presented. The
discussion is intended only as a brief overview to the extent necessary for
explanation of the LIFEGUARD™ product's functionality. Neither this information
nor the product is intended to take the place of extensive training and
certification necessary for safe use of rebreathers and enriched air breathing
mixtures.
Central Nervous System (CNS) Oxygen Toxicity
Maximum allowable exposure time calculations for a given depth are based on
Partial Pressure of Oxygen (PO2). Exceeding a PO2of 1.6 greatly increases the
likelihood of immediate onset of CNS Oxygen Toxicity symptoms. The
LIFEGUARD™ calculates CNS toxicity percentages and issues a unique, five
double-beep audible alarm once per minute should the diver reach or exceed 75
percent of the associated maximum limit. In addition to this audible warning, the
WARNING legend will flash on the Wrist Unit (WU) and the TEMPerature digits
will be replaced with the current calculated CNS Oxygen Toxicity percentage.
This warning status will continue until the calculated toxicity is less than 75
percent.
Maximum exposure time for a given depth is calculated based on the Partial
Pressure of Oxygen (PO2). The following formula is used to determine the PO2.
METRIC IMPERIAL
( D + 10 ) X O2% = PO2(
D + 33 ) X O2% = PO2
10 33
For example, if you were diving to 31 Meters/100 Feet with NOAA II (36% O2)
your PO2level would be:
METRIC IMPERIAL
( 31 + 10 ) X .36 = 1.48 ( 100 + 33 ) X .36 = 1.45
10 33
which gives a (rounded up) PO2value of 1.5.
Exceeding a PO2of 1.6 will greatly increase the probability of the immediate
onset of CNS Oxygen Toxicity. While various training organizations have
established maximum PO2limits, the maximum exposure times and their
associated PO2levels used in this dive computer's calculations are shown on the
following table:

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PO2LEVEL 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 PO2level of 1.4
is 149 minutes. Once you reached 112 minutes of bottom time with a PO2of 1.4,
this alarm would be issued since 112 minutes is 75% of 149 minutes. At a PO2
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 O2content
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 O2.
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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REPEX MAXIMUM DAILY OTU CHART
DAY Daily Dose Period Total
1 850 850
2 700 1400
3 620 1860
4 525 2100
5 460 2300
6 420 2520
7 380 2660
8 350 2800
9 330 2970
10 310 3100
11 300 3300
12 300 3600
13 300 3900
14 300 4200
15 - 30 300 N/A
OTUs are an exponential function of oxygen partial pressure. The time-
dependent limit varies with the number of days that the diver continues to dive
without full recovery. The recovery portion of the whole body effect algorithm is a
linear reduction of OTUs over time. The Mission OTU Clock continues running
as it tracks cumulative Oxygen exposure. Depending on frequency of dives and
other determining factors, as well as between-dive recovery time, this clock may
run for several weeks. The clock resets to 0:00 when the OTU level has dropped
to 0.
Symptoms of Pulmonary O2Toxicity include burning in the throat and chest,
coughing, and shortness of breath. Should any of these symptoms be
experienced, discontinue diving immediately and consult a Doctor.
NOTE: While most other audible alarms of the dive computer consist
of five long beeps, the OTU, PO2, and CNS audible alarm consists of
short double-beeps that sound for five seconds.
WARNING: It is possible in certain diving circumstances to reach an
Oxygen Toxicity limit well before reaching a no-decompression limit.
For this reason and many others, only a diver who has successfully
completed a sanctioned REBREATHER diving course from a
recognized training and certifying agency should conduct
REBREATHER diving.

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Installation
CTU and O2Sensor
The O2Sensor should be mounted in the inhalation side of the breathing loop,
located where it will not be subjected to water contamination. In most designs the
CTU connects, by means of the watertight bulkhead connector, to the O2Sensor
or by the T adapter which is designed to be placed in line on the breathing hose.
This allows for easy removal of the CTU from the rebreather when necessary.
Note: Press the CTU cable into the bulkhead adapter or "Tee". Finger
tighten the ring and press in and finger tighten again. Repeat this process
of press and tighten until the connection 'bottoms out'. DO NOT USE
TOOLS FOR THIS PROCEDURE.
The CTU should be secured in a protected area of the rebreather to prevent
snagging and impact with objects, which could damage it.
The object is to secure the bulkhead fitting to the outer case with the wires and
Molex connector passing through into the counterlung, where the Molex plug
attaches to the O2Sensor with the moisture barrier cap (“boot”) pressed down
over the back of the sensor.
Bulkhead Mounting Kit Parts List:
1- bulkhead connector assembly consisting of
•three-pin external bulkhead fitting with O-ring on back side
•three-wire harness terminating in 3-hole Molex connector,
with moisture barrier cap (“boot”)
1- retaining nut for bulkhead fitting
1- long cable tie
1- short cable tie
O2Sensor
1- Sensor
OR
1- Tee including Sensor
Wrist Unit (WU)
The Wrist Unit (WU) may be worn on the wrist or attached to the rebreather by its
strap or the optional retractor sold by Cochran, as long as it remains within its
intended operating range of approximately 3 feet.

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Activation
The CTU will automatically activate when it senses an Oxygen level at or above
the turn-on set point programmed by the user or by using the power activator
area (the “PWR” symbol inside the circular, crosshatched imprint on the left side
of the case lid). A sharp rap on this area with the edge of a coin works best. The
CTU will issue five "beeps" when it activates using either method.
NOTE: If the CTU is in the Altitude Adaptation Mode, four beeps, rather
than five, will be issued.
NOTE: The CTU must be in less than 3 feet of water in order to
activate. At depths below three feet the CTU will not turn on manually
or by sensing elevated O2 levels. It is strongly recommended that the
LifeguardTM is activated on the surface shortly before beginning the
dive, so that its proper operation can be confirmed at the same time
other routine equipment checks are performed.
Shut-Off
You cannot manually turn the CTU off. The CTU will turn off:
1. After 30 minutes if no elevated PO2is sensed and no dive is made
2. The Oxygen level drops below the preset activation threshold.
3. All 12 nitrogen half-time compartments are completely "off-gassed" on
repetitive dives.
After a dive the LifeguardTM CTU will remain on for 40 minutes before
automatically enter a "sleep" mode to conserve battery life. During this sleep
mode, all off-gassing calculations continue to run, but the CTU does not transmit
this data. To view current surface interval, time-to-fly, and other data, re-activate
the CTU just as would be done when first turning it on. Once “awakened” from
its sleep mode, the CTU will remain in active mode for one hour before
reentering the sleep mode. This assumes, of course that no repetitive dive is
initiated between each wake-up.
NOTE: The LIFEGUARD™ will not enter the Sleep Mode or turn off as
long as the PO2sensor is exposed to an oxygen level above the user
programmed turn-on set point.
To activate the WU, perform one of the following for five seconds (or until the
display becomes active): (1) rotate your wrist or (2) tap continuously on the lower
left corner of the face. Care has been taken to reduce the occurrence of the WU
being accidentally activated during transport, the WU may have to be rotated or
tapped for a longer period of time. The same rotating or tapping action is used to
select the alternate screen. The alternate screen is shown for three seconds
before returning to the normal screen. The TACLITE™ active backlighting for the

19
WU display is also activated whenever the alternate screen is selected.
TACLITE™ will remain illuminated for approximately 10 seconds.
Since all diving calculations are made by the TU, it is possible to activate the WU
underwater should you mistakenly forget to do so prior to the dive. Once
activated, the WU will immediately display the current diving data being
calculated by your TU. During the dive, it is not possible to turn the WU off.
Once back on the surface, you can manually turn the WU off. This is
recommended as a battery saving measure since all calculations are being
performed by the TU. To turn the WU off on the surface, continuously tap the
WU, in the same manner as that used to activate the unit, until the display goes
blank. With a little practice, you will learn how much tapping is required to turn
off the WU.

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OPERATING MODES
Self-Diagnostic Mode
At turn-on, both the CTU and WU complete self-diagnostic tests before
displaying current information. During these tests, all of the legends and digits
on the WU illuminate for approximately 5 seconds. During these tests if an error
or malfunction is detected, the unit will turn itself back off. Some of the reasons
are: 1. Altitude over 15,000 feet
2. Battery voltage too low
3. Internal diagnostic fault
Upon completion, the LIFEGUARD™ enters Surface Mode.
Fig-1
Self-Diagnostic Mode
Explanation of Page Layouts
The following pages provide a snapshot of the screen displays for each of the
computers various functional modes, showing:
1. An illustration of the WU screen
2. The LEGEND displayed
3. The MEANING of that legend
4. The VALUE depicted under that legend
Any WARNINGS or NOTES about that mode will be displayed on this page.