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BSA OT1 Manual

Adapting to the underwater world
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Ocean Diver
Adapting to the
underwater world
Module objectives
This module provides a basic understanding of air and water pressure and the
effects of the underwater environment on the diver. It also covers the purpose
and function of diving equipment, and the other specialist kit that divers need, and
introduces the concept of buoyancy. Heat loss from the body and how this can be
reduced through the proper choice of protective clothing is considered.
Achievement targets
At the end of this module students should:
•
Have a basic understanding of air and water pressure and the physical effects
on the diver of the underwater environment
•
Understand the purpose and function of basic equipment
•
Understand the purpose and function of scuba equipment
•
Understand buoyancy
•
Understand heat loss, body temperature control and thermal protection options
Additional visual aids needed
•
Mask, fins, snorkel, and weight systems
•
Scuba equipment – cylinder, regulator with alternative supply, and buoyancy
compensator
•
Wetsuits and drysuits
Copyright © BSAC 2017
Module OT1
01

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Summary of Contents for BSA OT1

  • Page 1 Module OT1 Ocean Diver Adapting to the underwater world Module objectives This module provides a basic understanding of air and water pressure and the effects of the underwater environment on the diver. It also covers the purpose and function of diving equipment, and the other specialist kit that divers need, and introduces the concept of buoyancy.
  • Page 2 Instructor Manual Ocean Diver Adapting to the underwater world Module content This module considers the effects of depth and pressure underwater, basic equipment, scuba equipment, buoyancy and thermal protection. Understanding air and water pressure and the physical effects on the diver in the underwater environment Explain that before discussing diving equipment, students need to have some understanding of the diving environment and its effects on divers and how equipment, both snorkelling and scuba, is designed with this in mind.

  • Page 3: Air Pressure

    Instructor Manual Ocean Diver Adapting to the underwater world Air pressure It is important that students have a basic understanding of air and water pressure and the effects that this can have on our bodies. The bodies of land-dwelling animals are acclimatised to life on the Earth’s surface and the need to breathe air to stay alive.

  • Page 4: Water Pressure

    Instructor Manual Ocean Diver Adapting to the underwater world Water pressure To understand the effects of the underwater environment on our bodies and our diving equipment, students should understand some basic properties of water. Water • Non-compressible liquid Water, unlike air, is a very dense medium and is not compressible. •...
  • Page 5 Instructor Manual Ocean Diver Adapting to the underwater world The compression of the air volume for every 10m water depth is easy to remember. At 10m, at an absolute pressure of two bar, the volume of air reduces to half of its original surface volume.
  • Page 6 Instructor Manual Ocean Diver Adapting to the underwater world Quiz 1 Instructors should routinely check for transfer of knowledge to the students. A diver is at a depth of 15m; what is the water pressure? • 1.5 bar What is the absolute pressure? •...
  • Page 7 Instructor Manual Ocean Diver Adapting to the underwater world • Flexible seal or ‘skirt’ The mask should have a flexible seal or ‘skirt’ that moulds easily to the face. Most are made of silicone rubber. • Nose pocket The mask skirt must enclose the nose. Remembering that a volume of air will compress even in shallow water, being able to breathe into the mask will enable a diver to equalise the pressure inside with that of the surrounding water.
  • Page 8 Instructor Manual Ocean Diver Adapting to the underwater world Features Fins come in a variety of shapes and sizes. Before buying a set of fins you need to consider whether the style of fin suits the type of diving being undertaken. •...
  • Page 9 Instructor Manual Ocean Diver Adapting to the underwater world Snorkelling equipment – snorkel Allows surface breathing The snorkel is a simple breathing tube to allow a diver to breathe while face down on the surface observing the underwater scenery or finning along. Snorkels can be worn under the mask strap or attached to the strap with a small clip.
  • Page 10 Instructor Manual Ocean Diver Adapting to the underwater world Breathing underwater Snorkelling equipment • Diver breathes gas at atmospheric pressure Using basic equipment, the diver breathes gas at atmospheric pressure on the surface and then breath holds during a surface dive. •...
  • Page 11 Instructor Manual Ocean Diver Adapting to the underwater world Components Scuba equipment comprises a • Cylinder • Buoyancy compensator • Regulator The cylinder The cylinder holds the diver’s supply of breathing gas. Features • Contains breathing gas at high pressure Dive cylinders are usually filled to either 232 bar or 300 bar pressure, from a suitable compressor.
  • Page 12 Instructor Manual Ocean Diver Adapting to the underwater world Testing Diving cylinders should be subject to a suitable inspection and test regime to ensure they are safe. • Hydrostatic test every 5 years Scuba cylinders require a hydrostatic test every five years. On successful completion, the date (year/month) of the test is stamped on the cylinder shoulder.
  • Page 13 Instructor Manual Ocean Diver Adapting to the underwater world • Air (21% oxygen) Standard air from the environment is compressed and filtered into scuba cylinders. Air has an oxygen content of 21% and contains 79% nitrogen. • Nitrox (32% or 36% oxygen) A nitrox mix has extra oxygen in it in place of some of the nitrogen.
  • Page 14 Instructor Manual Ocean Diver Adapting to the underwater world Pillar/cross-flow valves A-clamp The A-clamp or international fitting cylinder valve has an O-ring set into the valve outlet and the regulator clamps around it. Sometimes this is referred to as a yoke fitting. •...

  • Page 15: Buoyancy Adjustment

    Instructor Manual Ocean Diver Adapting to the underwater world Buoyancy adjustment Gas is added to or dumped from the BC to assist the diver with their buoyancy control. Students will learn in the pool/sheltered water how the BC is used to adjust a diver’s buoyancy.
  • Page 16 Instructor Manual Ocean Diver Adapting to the underwater world Regulator Delivers breathing gas The gas in a diving cylinder is at high pressure, anything up to 300 bar. It would be impossible to breathe directly from the cylinder so the regulator has been designed to reduce the pressure of the gas leaving the cylinder and deliver it to the diver at ambient pressure so that it is easy to breathe whenever the diver wants to.
  • Page 17 Instructor Manual Ocean Diver Adapting to the underwater world stages are a common method of identifying this backup system. Regulator first stages manufactured after 2014 will be stamped with an “A” if they are compatible to be fitted with an alternative supply. As a backup system, an alternative supply second stage should be of equal standard to the primary second stage.
  • Page 18 Instructor Manual Ocean Diver Adapting to the underwater world • Service to manufacturer recommendations Regulators should be professionally serviced at least once a year according to the manufacturer’s recommendations. Remember they are a diver’s ‘life line’. Problems with the gas supply, or a lack of it, are not conducive to happy diving. Weights The weights that divers need to take with them to maintain control of buoyancy can be of several types/...
  • Page 19 Instructor Manual Ocean Diver Adapting to the underwater world Care • Wash in fresh water Weight belts, harnesses and pockets should be washed in fresh water after the dive. • Dry before storing As with all equipment, they should be allowed to dry before being stored. Using scuba equipment As scuba equipment delivers breathing gas at ambient pressure, when divers ascend, regardless of depth,...
  • Page 20 Instructor Manual Ocean Diver Adapting to the underwater world • Creates an upwards force equal to the weight of water displaced The water pushes back in an upward force (upthrust) equal to the weight of water displaced by the object. Any object immersed in water therefore apparently loses weight.
  • Page 21 Instructor Manual Ocean Diver Adapting to the underwater world Positive buoyancy • Too light • Physically tiring Positive buoyancy makes you too light and the ensuing struggle to remain below the water is physically tiring. • Uncontrolled upward movement More importantly, being too light risks an uncontrolled ascent and possible over- expansion of the lungs as ambient pressure reduces quickly.
  • Page 22 Instructor Manual Ocean Diver Adapting to the underwater world During a dive • Compensate with BC or drysuit Having left the surface, the increasing ambient pressure during descent will compress the bubbles in the wet/semi-dry suit material or the gas held within the drysuit resulting in buoyancy loss.
  • Page 23 Instructor Manual Ocean Diver Adapting to the underwater world Body temperature control and heat loss Humans give off heat naturally due to the heat generated in the cells by the body’s metabolism. Core body temperature The core consists of the important body areas – brain, spinal cord, chest organs, abdomen and pelvis.
  • Page 24 Instructor Manual Ocean Diver Adapting to the underwater world • Hypothermia If nothing is done to remedy the situation and shivering stops, the body is sinking into a state called hypothermia, which can become a very serious condition as the body slowly shuts down. Heat loss (2) In water •...
  • Page 25 Instructor Manual Ocean Diver Adapting to the underwater world Features • Comfortable close fit The fit should be reasonably close but allow movement. Too loose and more water will flush through the suit drawing more heat from the body and leading to more rapid heat loss.
  • Page 26 Instructor Manual Ocean Diver Adapting to the underwater world • Membrane Membrane drysuits are made of other waterproof materials, such as rubberised fabric or a laminate constructed of hardwearing outer surfaces and waterproof rubber inner layers. Features • Comfortable fit Fit needs to allow for movement.
  • Page 27 Instructor Manual Ocean Diver Adapting to the underwater world Quiz 2 What are three main parts of a scuba set? • Cylinder, BC and regulator When breathing from scuba equipment; what must you never do? • Hold your breath While underwater, divers should maintain what type of buoyancy? •...