Dive Rite NiTek He Owner's Manual download pdf (Page 32)

NiTek

/NiTek

Owner’s Manual Page 32

In your entry-level Enriched Air Nitrox Diver training, you learned that among

the greatest risks Nitrox (EANx) use poses is that of CNS Oxygen Toxicity. One way

CNS Oxygen Toxicity can occur is when divers breathe Nitrox at depths where the

partial pressure of oxygen (PO

) exceeds safe limits.

The NiTek is designed to help divers avoid such situations by presenting

information and warnings regarding current PO

levels and cumulative exposure to

elevated PO2s. To do so, however, the NiTek must be set to an FO

that accurately

matches the concentration of oxygen in the gas mixture being breathed.

Similarly, the NiTek is designed to help divers avoid decompression illness

by providing No-Decompression Limits (NDLs) or mandatory decompression stop

information. Again, to do so, the NiTek must be set in a manner that accurately

matches the concentration of nitrogen in the breathing media.

When it lacks this information, the NiTek will attempt to protect divers by

basing its oxygen- and nitrogen-exposure calculations on a “worst case” assumption.

This is, that divers may be breathing a mixture containing up to 79 percent nitrogen,

or up to 99 percent oxygen. This is what we are referring to when we say that the

NiTek’s FO

setting is in “default.”

When and How FO

Default Occurs: One factor in determining if and when your

NiTek’s FO

setting will default is whether you set it for air or Nitrox.

➤ If you set your NiTek for air (an FO

of 21 percent), it assumes that subsequent

dives will be made using air as well. Thus, it remains set for air, dive after dive,

without defaulting.

➤ If, on the other hand, you set your NiTek for Nitrox or oxygen (FO

s of 22 to

99 percent), the computer assumes that subsequent dives may also be on Nitrox.

Thus, to protect you from accidentally diving a Nitrox mixture to which it cannot

accurately monitor, the NiTek’s FO

setting will default ten minutes after surfacing

from any dive in which it was set to an FO

other than air.

As discussed earlier, if you ascend above a depth of 5 ft/1.5m, then descend below

this depth within ten minutes, the computer will treat this descent as a continuation

of the same time, made using the same cylinder(s). Thus, the computer will hold its

current FO2 setting for the continuation of the dive.

On the other hand, if your surface interval (or time spent above a depth of 5

ft/1.5m) exceeds ten minutes, the NiTek will treat subsequent descents as a separate

dive. If the computer was previously set to an FO

of 22 percent or more, it will

assume you may have switched cylinders prior to descending. Thus, to protect you

from the consequences of diving a gas mixture whose FO

is unknown, the NiTek’s

FO2 setting will default.

There is one more way in which the NiTek’s FO

setting can default. Let’s

say you set the computer’s FO

to a value of from 22 to 50 percent, but do not

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Dive Rite NiTek He Owner's Manual Page 32

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