01. What is the approximate composition of air?

• 79% nitrogen
• 21% oxygen

02. What is atmospheric pressure?

• The weight of air pressing against the earth’s surface

03. What, if any, is the relationship between depth and pressure?

• Any object submerged into water will be subjected to the pressure created by the weight of the water above the object

04. What is bar pressure at 20m 40m and 45m?

• 3 bar, 5 bar, 5.5 bar

05. What is the depth at 2 bar, 4 bar and 3.5 bar?

• 10m, 30m, 25m

06. What is ambient pressure?

• The pressure surrounding an object, such as gas and liquid

07. Explain your understanding of Boyles law?

• Pressure and volume
  • At a constant temperature, the volume of a given mass of gas varies inversely with the absolute pressure
• E.g. if the pressure on gas is doubled, the volume is halved

08. What body spaces may Boyles Law affect?

• Lungs, ears, sinuses, teeth

09. How does Boyle's Law affect the diver?

• During descent - Mask squeeze, ear clearing, loss of buoyancy, sinus squeeze
• During ascent - increase of buoyancy
• Air consumption - the higher the pressure (depth), the more air we consume

10. On ascent from approx. 25m, between what depths does the greatest change in volume occur?

• 10m to 0m (surface)
• E.g. The closer to the surface, the greater the change in volume

11. A balloon occupying a volume of 6L at the surface will occupy what volume at 10m?

• 3 litres

12. Explain your understanding of Dalton's Law, and how it could affect the diver?

• Partial pressure
  • In a mixture of gases each constituent gas exerts a partial pressure in proportion to its percentage of the mixture
• E.g. Partial pressure of oxygen at surface is 0.21 bar, and nitrogen is 0.79 bar, so at 10m, ambient pressure is doubled, and oxygen is 0.42 bar, nitrogen is 1.58 bar
• Dalton’s Partial Pressure law allows us to calculate and understand diving limits:
  • Decompression - nondeco and deco stops, residual nitrogen
  • Gas Toxicity - High partial pressures of oxygen (1.6 bar)
  • Breathing Mixtures - Mixture of oxygen, nitrogen and sometime other gases, such as helium, to avoid Nitrogen Narcosis
  • MOD / Maximum Operating Depths - Depth where the partial pressure of the mix exceeds acceptable limits
  • Nitrogen Narcosis - High partial pressures of nitrogen (2.33.4 bar)

13. Explain your understanding of Henry's law and how it could affect the diver?

• Solubility and partial pressure
  • The amount of gas that dissolves in a liquid is proportional to the partial pressure of the gas in contact with the liquid
• For instance:
  • Blood, as a liquid, comes in contact with air (oxygen and nitrogen), as a gas
  • When a diver ascends and pressure is reduced, the amount of gas that can remain in the blood is reduced
  • If ascending slowly, reduction in partial pressure releases the gases
  • If ascending quickly, the gases must leave quickly and form bubbles

14. Explain your understanding of Charles' Law, and how it could affect the diver?

• Temperature and gas volume
  • At constant pressure, the volume of a gas varies directly with the absolute temperature
  • At constant volume, the pressure of the gas varies directly with the absolute temperature
• If temperature is increasing, then either volume or pressure must increase
• A dive cylinder exposed to heat can explode or rupture
• A dive cylinder getting cold ( in water / at depth) will reduce its pressure

15. Explain, giving examples, your understanding of the term 'partial pressure' of a gas?

• Partial pressure of a gas means that the pressure is in proportion to its part of the mix, e.g.:
  • If the percentage of oxygen is 21% at 1 bar (the surface) then the partial pressure it exerts is 0.21, and at 10 meters (or 2 bar) it's 0.42, and at 3 bar it's 0.63, and so on
  • This means that we can calculate at what pressure specific gases affect us negatively, for instance when oxygen toxicity occurs, as we can calculate the partial pressure of the specific gas
  • It also means that we can change the gas mixes, and for instance increase oxygen (commonly to 32-36%) to reduce the risk of nitrogen narcosis as well as increasing bottom time, while at the cost of decreased MOD (Maximum Operating Depth)

16. Should a full diving cylinder be left out in the sunshine on a hot day? Why?

• No. It may increase the pressure of the gases inside the cylinder beyond working pressure to dangerous pressure levels, as the temperature increases the heat in the cylinder

17. Why would the pressure in an unopened dive cylinder, drop several hours after filling?

• Charles' Law - During filling, the temperature increase, and as such the pressure increase. As the cylinder cools down, the pressure drops

18. What happens when a carbonated drink is shaken and then immediately opened? Why?

• Gases rushes out, bringing liquid with it
• The turbulence creates excess pressure that forms bubbles that helps the gas escape quickly
• Excess gas is dissolved in the liquid, so when the cap is removed the high pressure is quickly reduced, forcing the gases to leave the drink quickly

19. Why is the bubbling of a gas in a liquid relevant to divers?

• If we ascend too quickly, gases must leave the body quickly, which leads to gas bubbles formed in the blood stream, which causes decompression sickness / the bends

20. At approximately what partial pressure does oxygen become toxic?

• 1.4 bar (at ~60 meters, when diving on air)

21. Two factors influence the absorption of gas in the body during a dive, what are they?

• Dalton's Law and Henry's Law:
  • Partial pressure of a given gas and its solubility with a liquid (blood) determines how much of the given gas is absorbed at a specific pressure

22. Blood absorbs and releases nitrogen faster than fat. True or false?

• True
• Blood is a fast compartment, whereas stored body fat is a slow compartment, while it can hold more dissolved nitrogen than a fast compartment

23. Why might a RIB's pontoons slightly deflate in the cool of the evening?

• Charles' Law - Under constant pressure, volume will drop as temperature drops

24. What is tooth squeeze?

• Pain in tooth caused by change in ambient pressure when air is trapped in a dental filling or cavity

25. What is mask squeeze? How is it alleviated?

• Boyle's Law - Mask squeeze is the change, e.g. decrease in air volume inside the mask as the ambient pressure increase during descent
• It is alleviated by gently breathing out through the nose, just enough to increase the air volume inside the mask

26. Why do divers not wear swimming goggles while diving?

• You can't equalise the pressure in the air space inside goggles

27. What happens to light when it passes from air to water?

• Light is refracted, e.g. it bends, when it passes from air to water

28. What effect does light passing from air to water have on the diver's vision?

• Objects appear:
  • 33% larger
  • 25% closer

29. Some coloured objects may appear grey at depth. Why is this so, and how can this be resolved by the diver?

• Water absorbs colour
• Colour is absorbed in the following order: Red, Orange, Yellow, Green Blue Violet, Grey
• Colour absorption can be resolved by using a torch

30. Does sound travel faster underwater or on land?

• Sound travel faster underwater - about 4 times faster (~330m/s * 4 = 1,320m/s)
• The denser the material, the faster sound travels

31. Is it easy for a diver to determine distance and direction of sound underwater?

• It is difficult, as the sound travels too fast
• In air, sound strikes one ear a little bit sooner and a little bit louder, which is how we can determine direction and distance
• In water, sound is detected by both ears at almost exactly the same time, as it travels so fast

32. Do different body tissues absorb gases at the same rate? Explain your answer

• No
• Some tissues are fast, such as blood
• Some tissues are slow, such as muscle and bone
• Essentially, the richer and faster the blood flow, the faster it can absorb gases
• NOTE: This does not refer to HOW MUCH gas the tissues can absorb, only at WHAT RATE (speed)

33. What is your understanding of Archimedes Principle?

• Any object which is partially or wholly submerged in a liquid will be buoyed by a force that is equal to the weight of the displaced fluid

34. What is positive, negative and neutral buoyancy?

• Positive buoyancy: object will ascend
• Negative buoyancy: object will descend
• Neutral buoyancy: object will neither ascend nor descend - it is neutral and will remain at the given depth

35. What is the ideal state of buoyancy for a diver?

• Neutral buoyancy

36. Why does a diver wear weights?

• Weights are needed to neutralise positive buoyancy, to stay in control of buoyancy

37. What factors cause a reduction in buoyancy in a diver?

• BCD
• Weights
• Exposure protection (wetsuit / dry suit)
• Other dive gear
• Tank pressure (tank buoyancy can go from almost 1 kg negative when full to almost 2kg positive at end of dive)
• Air in the lungs
• Salt vs Fresh Water
• Body composition - the more body fat ()as opposed to muscles), the greater the buoyancy

38. How does a diver compensate for this on descent?

• A properly weighted diver release air from BCD at surface and exhale
• During the descent the diver will regularly add short bursts of air into the BCD, to ensure the descent remains controlled

39. What can happen if a diver experiences dramatic loss of buoyancy during a dive?

• Dramatic loss of buoyancy can lead to an uncontrolled descent

40. What should a diver do to recover from dramatic buoyancy loss?

• Add air to BCD
• Add air to lungs - inhale
• Drop gear
• As last resort, drop weight belt (this can had the opposite effect - uncontrolled ascent)

41. What can happen if a diver experiences dramatic gain in buoyancy during a dive?

• Dramatic gain in buoyancy can lead to an uncontrolled ascent

42. What should a diver do to recover from dramatic buoyancy gain

• If you can't quickly identify and rectify the problem, swim down to something to hold on to, or signal your buddy to help control you, then:
  • Continuously exhale while ascending
  • Pull BCD air dump valves - they are faster than the low pressure inflator
  • Roll over face up
  • Get horizontal, extend arms, legs and fins parallel to the surface, like a cross - e.g. get big

43. What effect does increased depth have on the wet-suited diver?

• Increased depth leads to decreased buoyancy as the wetsuit gets thinner and thinner under pressure

44. In freshwater, will the diver wear more or less weight than in the sea? Explain your answer.

• Less weight in fresh water
• Salt water is denser than fresh water (salt increases density), and objects are as such more buoyant in salt water

45. Briefly explain the causes, signs/symptoms of nitrogen narcosis

• Causes of nitrogen narcosis
  • Produced by exposure to increased partial pressure of nitrogen
  • At shallower depths it's normally not as severe
  • It is not unseen that nitrogen narcosis affects divers already at 2.37 partial pressure
  • It is common that nitrogen narcosis affects divers at 3.16-3.95 partial pressure
• Signs/symptoms of nitrogen narcosis - resembles alcoholic intoxication:
  • Poor judgement
  • Short-term memory loss
  • Trouble concentrating
  • A sense of euphoria
  • Disorientation
  • Reduced nerve and muscle function
  • Hyper focusing on a specific area
  • Hallucinations

46. Briefly explain the treatment and prevention of nitrogen narcosis

• Treatment: Ascend to shallower depths
• Prevention: Dive at shallower depths - as per your own qualifications, ability and tolerance

47. Divers of many years' experience never get narcosis. True or false?

• False - you can't learn or circumvent nitrogen narcosis
• Though, apparently, some evidence exists that certain divers may become partially acclimated to the effects of nitrogen narcosis with diving frequency - this is not a rule

48. Compared to breathing rates at the surface, to what extent does air consumption at 30 m increase?

• Your air consumption is 4 times higher at 30 meter
• For instance, if you need 2 bars per minute at surface (12 litre x 2 = 24 litre), you'll need 2 bars x 4 ATA (30 meter depth) = 8 bars per minute at 30 meters