Φιάλες και απόθεμα Β μέρος

Άρθρο: Γιώργος Πέτρου

Photo: Greek Diver Archive & George Petrou

Calculating the gas reserve & choosing the volume/pressure of our cylinder always remains a topical and very critical issue. No one wants to experience an air shortage incident.

Για αυτό καθόμαστε με την ησυχία μας σπιτάκι μας και υπολογίζουμε τι θα χρειαστούμε στη επικείμενη κατάδυση υπό τις πλέον δυσμενείς συνθήκες - WCS (Worst Case Scenario). Σε ένα οποιοδήποτε υποβρύχιο περιστατικό η επάρκεια αερίου αποτελεί καθοριστικό παράγοντα που μας προσφέρει ηρεμία και δυνατότητα επίλυσης του προβλήματος. Σε αυτό το άρθρο δίνονται πολύ βασικές πληροφορίες.

Pressure/Volume of bottles

We all know that there are cylinder volumes such as 2, 3, 6 liters, etc. Clearly, these cylinders are for specific uses (mainly support) and under no circumstances can they be used to carry out a complete dive, even in its simplest amateur form. We will see larger cylinder volumes with which we can do from a simple sightseeing dive to an advanced deep dive. Also, in the table below we will see their capacity in liters by filling these cylinders with a specific pressure.

First of all, let's remember that when we say that a bottle has a volume of 10 liters (at 1 ata pressure) we mean that if I fill it with water, it will hold 10 liters of water.

Bottle Pressure

100 bar 200 bar 300 bar

 10 λίτρα

 1000

 2000

 3000

 2 Χ 10 λίτρα

 2000

 4000

 6000

12 liters

 1200

 2400

 3600

 2 Χ 12 λίτρα

 2400

 4800

 7200

   15 λίτρα

 1500

 3000

 -

2 X 15 liters

 3000

 6000

 -

18 liters

 1800

3600 liters

 -

2 X 18 liters

 3600

 7200

 -

How do I calculate how much gas is required for a dive?

Τα στοιχεία τα οποία απαιτούνται για να υπολογίσω το πόσο αέριο απαιτείται για μια κατάδυση είναι:

Gas quantity

• for the descent
• για παραμονή 
• for emergence
• για αποσυμπίεση
• for stock (reserve)

The formula we use to calculate each of these elements is: P x T x SCR x MOD. To this, a reserve law can be added such as 1/3 (with or without subtraction of MOD), etc.

Where: P/Pressure = Absolute depth pressure

T/Temperature = Time SCR/Surface Consumption Rate = Surface Consumption Rate MOD/Modifiers= Project Production Factors

What criteria will I use to decide how much gas to stock?

Criteria or elements are:

The depth we will dive in combination with the required ascent time. For example, if 50 bar may be enough to cover our needs, one ascent and one mandatory decompression stop for preventive reasons after diving to a depth of 18 meters, if we dive deeper it will not be enough.

The decompression time combined with the depth at which it is performed

The possible unmeasured factors that can occur:

- Hypothermia increases the consumption rate. - Does our reserve cover the case that our partner runs out of gas and asks for support from us? Our reserve is reduced by half and anxiety increases, increasing our consumption rate. - The production of work, for example, such as swimming against a strong current - The loss of gas from a leak in the pressure regulator, buoyancy regulator or from a shutter, etc. - Exceeding the plan and increasing the mandatory decompression time. - I am diving with air and I have to perform a decompression, e.g. 3 minutes at 6 meters and 10 minutes at 3 meters with an Enriched Air Nitrox 32. Suddenly, for some reason, I cannot use this tank. Now I have to do the decompression with air. Inevitably, we have an increase in decompression time.

Have we calculated the necessary reserve of air gas?

Is there an easy way to calculate the volume of the tank I need, knowing how much gas I will need for a dive, while also ensuring the necessary reserve?

Let's assume that for a dive we need 2000 liters of gas e.g. 70 bar of gas as a reserve.

To see what volume of bottle we will need, we do the very simple thing:

We divide the total gas volume by the filling pressure of our cylinder, subtracting the pressure of the reserve we desire.

Παράδειγμα:

2000 liters / (200 bar - 70 bar reserve) = 2000 liters / 130 bar = 15 liters (15.384 to be exact)

Άρα μόλις εγώ χρησιμοποιήσω τα 2000 λίτρα θα έχω ένα απόθεμα 70 bar το οποίο μεταφράζεται σε 70 bar x 15 λίτρα φιάλη = 1050 λίτρα

The correct mindset of always surfacing with a reserve of at least 50 bar on the SURFACE is lifesaving.