01. Explain your understanding of decompression sickness.

• Decompression sickness refers to injuries caused by rapid decrease of ambient pressure, which can occur when a diver ascends incorrectly, e.g. too fast.
• If the partial pressure of nitrogen in the tissues exceeds the ambient pressure of nitrogen (by a ratio of 1.3:1 to 2.3:1, depending on fast/slow tissues), the nitrogen will form gas bubbles to escape the tissues
• The formed gas bubble can cause pain in the skin and joints (Type 1) and in severe cases the Central Nervous System (Type 2)

02. What are the symptoms of decompression sickness?

• Type 1:
  • Discolouring, blistering, itching, or othe3r skin reaction after a dive
  • Pain and difficulty moving joints - in particular knees and shoulders
• Type 2:
  • Any abnormality in behaviour
  • Numbness and/or weakness in any part of the body
  • Poor sense of balance
  • Paralysis of arms and legs
  • Double vision
  • Disorientation or mental confusion

03. What are some of the predisposing factors to decompression sickness?

• Alcohol in the body
• Smoking
• Dehydration
• Fatty tissues
• Fatigue
• Drugs and medication
• Cold water dives
• Heavy exercise during or after a dive

04. What is the treatment of decompression sickness?

• Recompression in a chamber under strict medical supervision

05. How long may it take for 90% of the symptoms to occur?

• 6 hours

06. What % of these symptoms occur in the first hour?

• 50%

07. What gas is generally involved in decompression sickness?

• Nitrogen

08. What is the only treatment for decompression sickness?

• Recompression in a chamber under strict medical supervision

09. What first aid can be given in the case of decompression sickness?

• Lie the subject down on the left side
• Give 100% oxygen while maintaining clear airway
• Keep warm and reassure the subject

10. A diver has just completed a long deep dive and exceeded his/her correct rate of ascent. His/her buddy complains of a severe headache, is stumbling uncharacteristically and fails to recall the correct details of the dive. What should the diver do?

• Immediately notify emergency services
• Lie the buddy down on the left side
• Give 100% oxygen while maintaining clear airway
• Keep warm and reassure the subject
• Watch for symptoms on him/herself and be prepared to give 100% oxygen to him/herself

11. What is pulmonary barotrauma? How is it caused?

• Burts lung
• It is caused by air trapped in the lungs - by holding breath, chest infections or other lung disorders - while ascending, causing the trapped air increase in volume (Boyle's Law) and "burst" the lung

12. What is an air embolism? How is it caused?

• Air embolism is the most severe case of burst lung
• It occurs when air escapes from the ruptured alveoli directly into the blood vessles surrounding the alveoli
• The air will in form of bubbles travel via the heart into the carotid artery
• During ascent, the bubbles will continue to expand (Boyle's Law), lodge in the capillaries of the brain and block blood from reaching the brain cells

13. What are the symptoms and first aid of an air embolism?

• Symptoms:
  • Bloody, frothy sputum at the mouth
  • Possible chest pain and coughing
  • Staggering
  • Confusion or difficulty with vision
  • Paralysis or weakness of limbs
  • Convulsions
  • Cessation of breathing
  • Cyanosis
  • Collapse and unconsciousness
  • Death
• First aid:
  • Recover the victim from the water
  • Administer 100% oxygen, to assist oxygenation of blood and tissues
  • Contact emergency services
  • Immediate removal to a recompression chambre is essential
  • If necessary commence Cardio-Pulmonary Resuscitation

14. What is pneumothorax?

• Pneumothorax is caused by over-expansion and rupturing of the lung alveoli
• Bubbles are not confined to entering the bloodstream
• A rupture also occurs in the lung surface resulting in air entering the space between the lungs and the chest wall lining, known as pleura
• On ascent, trapped will continute to expand and collapse the affected lungs, forcing the lung and heart to the back of the chest
• This impairs function of the heart and breathing cycle

15. What are the symptoms and first aid of a pneumothorax?

• Symptoms:
  • Sharp pain in chest, made worse by deep breathing
  • Shortness of breath and rapid shallow breathing
  • Cyanosis
  • Evidence of pain, favouring affected side of chest
• First aid:
  • Recover the victim from the water
  • Administer 100% oxygen, to assist oxygenation of blood and tissues
  • Contact emergency services
  • Immediate removal to a recompression chambre is essential
  • If necessary commence Cardio-Pulmonary Resuscitation

16. Air embolism and pneumothorax: name one other pulmonary barotrauma type.

• Mediastinal Emphysema - escaped air will follow the bronchioles, bronchi and surrounding blood vessels into the mediastinum
• Subcutaneous Emphysema - escaped air will travel from the mediastinum upward along the trachea into the neck

17. List at least three causes of burst lung.

• Irregular breathing
• Holding your breath during ascent
• During emergency ascents in out-of-air situations
• In near panic situations when exhaling goes against instincts

18. What is the advantage of CPR for a casualty?

• It's an effective method of introiducing oxygen into the lungs of a person who ahs stopped breathing
• It maintains the circulation of blood when the heart has stopped

19. How would a diver know that a casualty is not breathing?

• After turning the victim on their back and tilting the head back, to open the airway:
  • Look for the rise and fall of the chest as the casualty breathes
  • Listen and feel for exhalation of breath by keeping ear close to the casualty's mouth

20. What is the first thing that should be done, immediately after it is established that the casualty is not breathing?

• Contact emergency services

21. What is the correct ratio of compressions to breaths for a single operator?

• 30 compressions at a rate of 100 compressions per minute (~18 seconds), and then give two breaths

22. List the things to be done for the casualty in the Recovery Position.

• Check safety of subject and self, and shout "Are you OK"
• If there is no response, get someone to send for emergency services, or if on your own leave the casualty and go for help
• Open the airway (victim in back position, head tilted back, no obstacles in mouth) and check breathing
• If no breathing, begin CPR at 30:2 compression:breath ratio
• When defibrillator arrives, attach to casualty and execute accordingly (place pads per diagram, follow machine prompts, no-one touching the victim)
• This is followed by early advanced life support by paramedics, advanced paramedics, etc., and early post resuscitation care

23. What will failure to observe the limits of depth and time during a dive lead to?

• It will eventually lead to a decompression incident, and possibly out-of-air and other emergencies

24. Define the following terms: Bottom Time, Safety Stop, NDL, Repetitive Dive, Surface Interval; and Repetitive Group.

• Bottom Time: Time taken from leaving the surface until commencing final ascent at recommended ascent rate
• Safety Stop: 3 minute stop at 3-5 metres after every no-decompression dive
• NDL: No Decompression Limit - maximum time which can be spent at a given depth without mandatory stage decompression
• Repetitive Dive: Any dive carried out within 12 hours of a previous dive
• Surface Interval: Time spent from surfacing from a dive to commencing the next descent
• Repetitive Group: The measure of the excess nitrogen remaining in the body after a dive

25. What is the correct rate of ascent?

• 10 metres per minute

26. When buddies record different depths and time during their dive what should they do?

• Take the deepest and longest readings for calculating decompression

27. When buddies dive with dive tables and a computer respectively, which should be followed?

• Always follow the most conservative readings

28. What should a diver do in the event of computer failure during a dive?

• Abort the dive safely, by ascending to 6m at the standard ascent rate and perform a safety stop for either 5 minutes if still inside NDL, or for as long as possible if on mandatory deco time
• Also keep in mind that even if your dive buddy has a dive computer, you may not have the same profile, repetitive group, etc

29. What are the recommendations for cold working dive?

• Use the decompression and repetitive group prescribed for the next longest time increment
• e.g. for an 18m dive for 33mins that puts the diver in R.G. D, use the info for an 18m dive for 44mins that puts the user in R.G. E
• This also means that the NDL is decreased by one time increment while keeping the R.G. of the longer time (in this case E)
• e.g. a cold dive to 27m would have an NDL of 18min with an R.G. of E
• In summary, you prescribe the next increment R.G. while keeping the original shorter time

30. What are the recommendations regarding Intensive and Repetitive diving?

• A break from diving of half a day should be taken every three days to prevent build-up of excess nitrogen in the slow tissues
• The dive sequence each day should be to do the deepst dive first and the shallowest dive last

31. During a dive the deepest part should be attempted early or late in the dive?

• The deepest part should be attempted early so excessive nitrogen can be released during the later part of the dive

32. The plan is to make two dives on one day. The proposed depths are 30m and 15m respectively. What is the order of the dives and the surface interval? Why?

• The deeper dive is undertaken first, or the diver will be exposed to significantly greater risk of decomression sickness
• For example:
  • A 30m dive for 17 minutes puts you in R.G. D
  • After 30 mins you're in R.G. A
  • A second dive to 15min in R.G. A gives you an R.N.T. (Residual Nitrogen Time) of 16 mins
  • Normally a 15m dive has a limit of 75min
  • Your new NDL is 75min less 15min, meaning 59min

33. Describe briefly the ideal dive profile.

• Descend to planned depth immediately
• Dive at depth for the duraration of the bottom time
• Ascend to safety stop at a rate of 10m/min
• Perform a 3min safety stop at 6m (3-6m)
• Ascend to surface

34. What is recommended for decompression diving?

• A club diver is not qualified to carry out planned decompression diving
• In an incident where you end up in deco, the dive computer will calculate the required deco stops

35. How might a diver interpret the time allowed for a particular depth on a computer, if she experiences fatigue during the dive?

• The diver may decide to end the dive 5 minutes early from the NDL

36. What is maximum NDL for a 21 m dive? Repetitive group?

• Maximum NDL for 21m is 34min, which gives R.G. E

37. For a 42m dive with a Repetitive group D, what is the maximum bottom time?

• Maximum bottom time for a 42m dive and R.G. D is 9min

38. What is the max NDL for a dive to 16m? Repetitive group?

• Max NDL for a 16m dive is 47min which puts you in R.G. F - calculated from 18m as this is the next highest from 16m

39. For a dive to 25m with a Repetitive group of C, What is the maximum bottom time?

• Maximum bottom time for a 25m dive with R.G. C is 18min - calculated from 27m as this is the next highest from 25m

40. What is the repetitive group for a dive to 20m for 33mins?

• The R.G. for a 33min dive to 20m is E - calculated from 21m and 34min, as those are the next highest values from 20m and 33min

41. What is the repetitive group for a dive to 10m for20mins?

• The R.G. for a 10m dive for 20min is B - calculated from 12m and 25min, as those are the next highest values from 10m and 20min

42. In March and in Irish waters, what would be the RG for a dive to 20m for 22mins?

• The R.G. for a 22min dive to 20m is normally R.G. C - calculated from 21m as this is the next highest from 20m
• In March it's a cold dive, so we count the next R.G., which is D, while maintaining the original bottom time of 22min

43. Fighting a current on a dive to 16m what would be the: max bottom time if the RG was C?

• At 16m the normal max bottom time for R.G. C is 25min - calculated from 18m as this is the next highest from 16m
• However, as we're fighting a current, we look at the bottom time of the previous R.G. group, which gives us a max bottom time of 17min

44. What stops should be done on a dive to 34m for15mins?

• A 34m dive for 15min is calculated in the 36m group
• 15min is beyond the max NDL of 12min
• This means you get two mandatory deco stops - first 2min at 6m, followed by 5min at 3m

45. A diver with a RG of B wishes to dive again in an hour, what is the Residual Group?

• While R.G. B reaches R.G. A in 20min the diver will still be in R.G. A after an hour, as it takes 2h to reach "0" from R.G. B

46. What is the RNT for a dive to 12m if the previous dive, had a RG of C, and a Surface Interval of 15mins?

• R.G. of C with S.I. of 15min leaves the diver in R.G. B, as it takes 25min to reach R.G. A from R.G. C
• The R.N.T. at 12m and R.G. B is 25min

47. What is the RNT for a dive to 11 m if the previous dive; had a RG of C, and a Surface Interval of 15mins?

• The next shallower depth from 11m for repetitive dives is 9m
• R.G. of C with S.I. of 15min leaves the diver in R.G. B, as it takes 25min to reach R.G. A from R.G. C
• The R.N.T. at 9m and R.G. B is 37min

48. What is the max bottom time for a dive to 18m when the RG is A?

• R.G. A gives a 14min R.N.T. for an 18m dive
• Max bottom time for an 18m dive is 47min less the R.N.T. which gives 47min - 14min
• Max bottom time for an 18m dive is 33min when R.G. is A

49. What are the decompression stops, if a diver takes 5mins to ascend from 36m with a 12min bottom time? (hint: slowed ascent)

• 12min at 36m is the max bottom time
• With a slowed ascent, 5min to 6m safety stop, you're 2min slow in the ascent
• These extra 2min should be added to the bottom time
• This means the bottom time was not 12min but 14min
• Therefore you perform the two mandatory deco stops as prescribed for the next level - first 2min at 6m, followed by 5min at 3m

50. What should be done if a diver only does a 3min safety stop, having had a dive to 30m for 18mins?

• A 30m dive for 18min requires a deco stop at 3m for 5min
• Only 3min safety stop means the diver is risk of decompression sickness, and need to be monitored for symptoms over the following 48 hours and in particular the first 6 hours after the dive

51. How soon could a diver fly, if s/he did a lot of shallow intensive diving?

• Shallow intensive diving has a greater impact on nitrogen loading of the slow tissues
• The break before flying should therefore be at least 24 hours

52. What is the max bottom time for a dive to 17m when the RG is A?

• The next highest group is 18m, and is therefore calculated based on 18m:
  • R.G. A gives a 14min R.N.T. for an 18m dive
  • Max bottom time for an 18m dive is 47min less the R.N.T. which gives 47min - 14min
  • Max bottom time for an 18m dive is 33min when R.G. is A