Manual Cressi GIOTTO (page 13 of 21) (English)

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CNS TOXICITY DISPLAY

PO2 ALARM

MODE

LONG

MODE

LONG

BEEP-BEEP

MODE

LONG

MODE

LONG

PRE DIVE

LOG BOOK

MODE

LONG

INDEX

IMPORTANT: Check the FO2 value (percentage of oxygen) set on the computer prior to diving! This can

be done on surface by means of the main screen PRE-DIVE and the DIVE SET screen which allow

visualisation of the previously set parameters.

IMPORTANT: Under the same dive conditions, a Nitrox mixture requires longer no decompression times

than air. It is recommended to comply with the maximum depth allowed by the selected Nitrox mixture.

DIVING WITH NITROX

During a Nitrox dive within the no decompression limits, all the information related to a standard dive with

air will be provided, as well as:

1) Nitrox dive indicator

2) Graph representing CNS O2 toxicity level

3) Indicator of the mixture used, MIX1 or MIX2.

The second screen, after pressing the right button, displays the same settings as the DIVE AIR but, of

course, concerning the nitrox mixture used in that moment (MIX1 or MIX2).

CNS TOXICITY DISPLAY.

The Giotto computer by Cressi is able to display a graph of the oxygen toxicity level for the Central

Nervous System (CNS). This is related to the Partial Oxygen Pressure and to the time of the diver's

exposure to high Partial Oxygen Pressure (PO2). The level of toxicity of the Oxygen is represented in the

display column consisting of a 5-segment bar, which show the increasing amount of accumulated oxygen.

When all the segments are lit up, it indicates that 100% of the maximum tolerance allowable to the CNS

has been reached and serious danger of hyperoxia exists.

It is important to be able to constantly monitor this data that, being function of the Partial Oxygen Pressure

and the time of exposition, should always be controlled. When the oxygen level reaches warning values,

next to the maximum allowable toxicity (corresponding to 5 segments out of 5 lit up), the graph starts

flashing along with the Nitrox writing and a temporary alarm starts sounding, showing the proximity of a

CNS toxicity level. If the situation remains unchanged or if it worsens (100% of allowable toxicity), the bar

and the writing continue to flash and the temporary sound alarm is repeated until, ascending, the Partial

Oxygen Pressure decreases below 0.6 atmospheres. At this point, the graph stops flashing, yet the alarm

is entered in the Logbook.

REMARK: The result of the oxygen pressure computation is approximated to the nearest whole number.

DANGER: do not use hyper-oxygenated mixtures in diving or decompression without having attended the

related training course. The Nitrox Basic license enables to use just the standard hyper-oxygenated

mixtures (Ean 32 and Ean 36, respectively called Nitrox 1 and Nitrox 2), within the non decompression

limits.

PO2 ALARM.

The computer is able to constantly monitor another basic parameter related to Oxygen: the O2 Partial

Pressure value (PO2). Oxygen toxicity may be caused both by an excessive exposure (CNS toxicity, seen

in the previous chapter) and by exceeding the maximum PO2, which is exceeding the maximum depth

allowed by the mixture used. As already seen, the PO2 limit value is set by the diver in a range between

1.2 bar and 1.6 bar. Giotto considers the 1.6 bar value as the Partial Pressure maximum allowable limit

and, according to the mixture used, automatically signals the maximum depth which may be reached.

Remember that, even by using air, you may reach the oxygen toxicity level. This limit varies according to

the PO2 set. Giotto is manufactured with a pre-set value of 1.4 bar, whose corresponding maximum depth

is 56.6 m. Of course, you can set the computer on other PO2 values, up to a maximum of 1.6 bar as long

as you are in the NITROX DIVE-S.

To warn the diver about the excess of PO2, the computer has an alarm. When reaching the limit depth

related to the PO2 set (from 1.2 bar to 1.6 bar), a sound alarm will go off while the PO2 icon will be flashing

indicating the current depth. As soon as you return to a depth shallower than the limit one, the sound alarm

will stop; the current depth and the PO2 icon will stop flashing. The latter remains lit up during the residual

part of the dive in the LOG BOOK and in the PRE DIVE screen.

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Cressi GIOTTO Manual

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