**Science & Deep Sea Diving**

**Gases:** All gases have some weight and occupy space but have no fixed volume or shape. Compared with liquids they are very light and compressible. Atmospheric air, the air we normally breathe, is a natural mixture of almost 21 percent oxygen and 79 percent nitrogen, with a trace of carbon dioxide and other rare gases.

It also contains water vapors in an amount depending on the weather conditions. Since gases are compressible, the density of gas fluctuates according to the pressure applied. Thus, the density of the gas a diver breathes varies according to the depth at which they are working.

**Water Pressure:**

The pressure with which the** diver** is most directly concerned is the pressure of the surrounding water at their diving depth (ambient pressure). Pressure in liquids conforms to certain basic laws, which are as follows:

- The pressure on an object in liquid is produced by the weight of the liquid above the object.
- The pressure produced acts on the object from all directions.
- The pressure will act at right angles to any surface of the object.

- Water pressure increase at a constant rate because water is incompressible and its density remains the same at any depth.👇

and, as water is virtually incompressible, this density remains constant irrespective of depth or pressure variations. The pressure exerted is, therefore, directly proportional to the depth, i.e. the pressure exerted at 20 m is twice that exerted at 10 m, and so on.

#### Calculation of Pressure at any Depth in Seawater:

Consider the below image it represents a plate lying on the bottom at a depth of 10 m. The pressure on the plate is produced by the weight of water above it.

Weight of water above the plate

= vol of water above plate x density of seawater x g

= (10 m x 1 m x 1 m) x (1030 kg/m³) x (10 m/s²)

= 103000 N

and Pressure

= Weight of water* **/* Area of Plate

=103000 N * **/ **1m x 1m*

= 103000 N/m²

= 103 kN/m²

**Water Pressure**

- With this in mind, it is safe to say that for every meter the diver descends the pressure of water will increase by:

**Sea Water Pressure**

**Freshwater Pressure**

= 1m³ x 1000kg/³ x 10m/s² */ 1m²*

= 10000 N/m²

Therefore to calculate the pressure at any depth:

Pressure (N/ m²)= Depth (m) x Density (kg/m³) x gravity (g)

**Notes**

**❕**

**In this case, gravitational acceleration is assumed constant at Approx 10 m/s² (Normally 9.81 m/s²)****1000 N = 1 kN**