SCUBA Diving

Strange body positioning in an attempt to get the perfect shot of a Blue Shark (Prionace glauca), Azores Bank

SCUBA …”Self Contained Underwater Breathing Apparatus”

A History of Scuba Diving

Early attempts to breath underwater began with people using hollow reeds – an early form of the snorkel used today. This however had its limitations and experimenting with different apparatus soon began. The first written reports of people undertaking dives were produced by Aristotle in the 4th Century BC, he wrote of divers that descended with an upturned cauldron which trapped air inside.

The first recorded diagrams of an underwater breathing system came more than a 1000 years later by Leonardo Da Vinci in the 15th Century, although it is said that Da Vinci kept his designs secret (for fear of them being used by the military or by criminals).

By 1535, Guglielmo de Lorena created and used what is considered to be the first “modern” diving bell, it consisted on an airtight chamber, suspended upright and supported by slings, air is trapped inside the bell for the diver to breath. Between the 16th and 17th Century’s modifications were made to the diving bell, such as the addition of hoses supplying fresh air fed by pumps at the surface.

However, it wasn’t until 1825 that the first autonomous (self contained) diving apparatus which did not require lines and air hoses to the surface was invented by William Jones. This involved a circular iron reservoir containing compressed air, carried around the diver’s waist. Further developments ensued with the invention of a demand regulator in 1865 by Rouquayrol and Denayrouze. High pressure air cylinders charged to 200 Bar patented in 1918. Then finally the advent of more lightweight equipment, together with the development of “modern” masks and fins in the 1920’s – 1930’s.

The first commercially successful Scuba sets were born in 1942. The ‘Aqualung’ open-circuit units developed by Emile Gagnan and Jacques-Yves Cousteau, in which compressed air was inhaled from a tank carried on the backs of diver’s and then exhaled out into the water. They were developed as an alternative to the re-breathers currently being used, due to Cousteau experiencing oxygen toxicity in the closed circuit systems, oxygen toxicity can result in seizures and occurs as a result of the partial pressure of oxygen increasing to hyperoxic levels as a result of rising ambient pressure when descending. Modern versions of both these open-circuit and semi closed/closed-circuit (re-breathers) systems are still in use today.

Types of Scuba Diving

This can be broadly split into 2 categories: Recreational Diving and Professional Diving.

Recreational diving is undertaken purely for enjoyment, although depending on where your interests lie, a number of technical disciplines apply such as; cave diving, drift diving, wreck diving, deep diving, ice diving and night diving, all of which require specific skills.

Professional diving covers many disciplines but collectively it involves the employment of a diver to perform specific tasks underwater. Such as; civil engineering, naval diving, military diving, police diving, underwater photography, aquarium diving and scientific diving including marine biology and underwater archaeology.

Basic Dive Information

Note: – Anyone interested in learning to dive should undertake a course with a certified organisation, the information given below is very brief and serves just to give you a taste of what is involved.

  • 1kg/cm2 = approx 1 Bar = atmospheric pressure
  • Pressure of water increases by 1 bar every 10m
  • Absolute pressure = water + atmospheric pressure
  • Absolute pressure for any depth in meters can be found by moving the decimal point one place to the left and adding 1 e.g.: 25m (2.5 + 1) = 3.5 bar
  • Compressible air spaces e.g.: a balloon. Pressure increases = Volume decreases. Compression on descent, expansion on ascent. Ears, sinuses, mask space are all affected by compression.




Air Density

























  • Equalise ears to balance pressure (air enters Eustachian tube into the middle ear cavity). Exhale air through the nose on descent to prevent mask squeeze.
  • Never dive with a cold / sinus infection!
  • Never hold your breath on ascent!

Buoyancy: if the mass of the object is greater than the mass of water displaced, it will sink and vice versa. You want to be neutrally buoyant when diving. Seawater is denser than freshwater, and so you are more buoyant in seawater than freshwater and will usually require more weights to become neutrally buoyant.

Scuba Gear: Mask, snorkel, fins, weight belt, BCD, regulator, cylinder, instrument console, (pressure gauge, depth gauge, compass), dive computer, knife and depending on water temperature – swimwear/wetsuit / dry-suit.for scuba diving page equipment section

How to calculate a cylinder capacity: Water Capacity x Working Pressure e.g.: 12 litres x 232 bar = 2784 litres.

Senses: Underwater objects appear 33% larger and 25% closer. Sound travels 4x faster underwater. Water conducts heat 25x more efficiently than air.

Loss of colour: As you go deeper you lose colours as the wavelengths are unable to travel down.  See chart.

Buddy Check

A buddy check is always conducted before each dive – BWARF!!

  • BCD – connections, adjustments
  • Weights – correct weights, right hand release
  • Air – air on, quantity, breathe from buddy’s spare regulator
  • Releases – familiar with releases, ensure secure
  • Final check – overall inspection.

Abandon a dive if; equipment is faulty, you or your buddy feels ill, surface/underwater conditions deteriorate, if you lose your buddy.

Problems which can occur when diving

DCI: Decompression Illness. During the dive tissues absorb Nitrogen, as we ascend the N+ exits tissues and is expelled via the lungs, if we ascend too fast N+ bubbles can form in tissues causing disorders known as DCI or “the bends”.

Factors affecting Nitrogen absorption = overweight, alcohol, cold, fatigue, exercise, age

Mild DCI = itches, skin rashes, joint pain.

Severe DCI = Neurological (visual, weakness, paralysis), respiratory difficulties.

Any pain or unusual feelings/behaviour within 36 hours of diving should be considered as DCI.

Nitrogen Narcosis = Usually occurs at depths greater than 30m, with N+ producing a narcotic effect at depth.

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