Chapter 6 - Open Water Diving

Question 1

What are the surface breathing rates?

Answer 1

25 L per minute - light work
40 L per minute - moderate work
70 L per minute - hard work

Question 2

How do you calculate the actual breathing rate?

Answer 2

Surface breathing rate x absolute pressure at depth

Question 3

What is the reserve air?

Answer 3

Should be enough to cover unforeseen emergencies
Should cover ascent and decompression stops
Should be based on the worst case scenario.

Question 4

What is the worst case scenario?

Answer 4

Air you need to bailout with a total loss of air.

The worst case is reaching the end of the planned bottom time when max deco obligations have been reached.

Question 5

What are the methods of calculating air requirements?

Answer 5

How long will the cylinder last
How much air do you need for the dive
How much air do you need for a decompression dive
What is my own breathing rate

Question 6

How long will my cylinder last?

Answer 6

With a reserve of 50 bar how much time will you get from a 10L cylinder with a gauge pressure of 200 bar at 10m whilst doing light work

Air available to breathe = gauge pressure - reserve
200 - 50 = 150 bar

Air available (litres) = gauge pressure x water column 
150 bar x 10 L = 1500 L

Actual breathing rate = 25L/minute x 2 bar (10m) = 50 L/minute

Air available/ actual breathing rate = 1500L / 50 = 30 minutes

Question 7

How much air do I need for a dive?

Answer 7

30m for 20 minutes doing light work - what size cylinder do they need?

Actual breathing rate = 4 x 25 = 100 L/min
Total air required = 100 L x 20 mins = 2000L
Add air reserve = 2000 + 500 = 2500L
Cylinder size? = air required / working pressure

2500/232 = 10.77 L = 12 litre cylinder

Question 8

How much air do I need for a decompression dive?

Answer 8

40 m for 26 mins doing light work. What cylinder size is required?

Actual breathing rate = 5 x 25 = 125L/min
6m safety stop ABR = 25 x 1.6 = 40L/min

Air required = 125L x 26 mins = 3250 L
Air for stop = 40L x 44 = 1760 L
Reserve air = 500 L

Total air = 5510L
Cylinder size = total air / water pressure
5510/232 = 23.75 L - 2x12L cylinders

Question 9

How do you calculate your own breathing rate?

Answer 9

Record bottom time
Depth
Air in
Air left

Question 10

What would your breathing rate be on a 30 minute 10m dive with a pressure of 230 bar ending on 80 bar and a 10L cylinder?

Answer 10

Air used = (230-80) x 10 = 1500L
Actual breathing rate = 1500L/30mins = 50 L/min
Converting actual breathing rate to sur face breathing rate = 50/2 = 25L/min

Question 11

What is a quick method of calculating reserves?

Answer 11

Calculate the total air required to breathe x 4/3

Subtract air required for dive

Question 12

What does a skipper do?

Answer 12

Responsible for safety of vessel and people

Final say in matters relating to safety

Question 13

What does a dive supervisor do?

Answer 13

Controls all people
Controls all safety aspects
Responsible for the completion of the contracted work
Must liaise with skipper

Question 14

What are small crafts?

Answer 14

RIBS and inflatables
Ribs - fast and easy to use
Inflatables - not as fast but easy to use

Cramped, exposed to elements
Expensive fuel
May be transported by trailer to the launch site
Used for inshore work on a daily basis

Question 15

What is the preparation for small crafts?

Answer 15

Help to launch
Load vessel
Adequate thermal protection 
Buoyancy aids
Stay sitting whilst underway
Keep a look out

Question 16

What do you do on site and diving?

Answer 16

Dress and fallout standby diver
Dress and callout divers
Anchored and secured
Remove weight belt and hand it in followed by scuba unit knee mouthpiece in place until releases unclipped
Keep fins on 
Continue as per supervisors instructions

Question 17

What are the large crafts?

Answer 17

Good for offshore diving 
More space / shelter available
Slower speeds
More expensive
People more prone to seasickness
Live aboard facilities may be available
Can be equipped with more equipment

Question 18

What is the preparation for large boats?

Answer 18

Lid vessel
Ensure all equipment is onboard
Use transit time to prepare as much of the diving as possible
Divers fully kitted

Question 19

What do you do whilst diving from a large boat?

Answer 19

Use entry method specified
Swim clear of vessel if using lifelines and surface marker buoys
Signal all well after dive
Climb aboard with mask and mouthpiece in place
Fins may need to be removed
Stow equipment and continue to work as a tender or deck hand

Question 20

What are some useful signals?

Answer 20

Flag Alpha - diver down keep we’ll clear at low speeds

Vessel restricted in ability to manoeuvre

Vessels engaged in underwater operations

Question 21

What are the problems with deep dives?

Answer 21

More incidents of decompression illness
More air required
Greater distance to safety
Gas narcosis probability increases
Loss of light
Mental stress 
Cold

Question 22

What are the safeguards for deep dives?

Answer 22

Decompression tables
Carry enough air
Have a standby diver
Build up the dives to the depth of the contracted work

Question 23

What are the problems of drift diving?

Answer 23

Divers can’t stop
May be separated from vessel
Ascents and descents May be too fast
May be cold
Hit objects
Become entangled

Question 24

What are the safeguards of drift diving?

Answer 24

Research the area
Check seabed profile
Check direction of current
Talk to locals
Check weather and sea conditions
Use a lifeline

Question 25

What are the problems of diving on a fixed worksite in moving water conditions?

Answer 25

Reaching worksite and staying there 
Dislodged equipment 
Completing the task
Getting hit by moving objects 
Entrapment 
Holding depth for decompression stops 
Recovering diver to platform

Question 26

What are the safeguards for stationary platforms?

Answer 26

Check to see if work can be completed from land
Postpone dove if the water movement is more than 0.5 knots
Full face masks
Lifelines
Guideline thick enough to hold onto
Avoid dives that involve mandatory decompression stops

Question 27

What are the problems with low or nil visibility?

Answer 27

Hard to find and complete task
Orientation
Hard to avoid underwater obstructions

Question 28

What are the safeguards for low or nil visibility?

Answer 28

Use a shot line
Descend feet first
Use a tended lifeline
Use a full face mask
Move slowly
Sweep hand over the seabed to find the task or obstructions

Question 29

What are the problems with no clear surface?

Answer 29

Low visibility may decrease to zero
No line signals possible
Hard to locate exit
No direct line of escape
Malfunctioning regulator if under ice
Sharp metal edges if in wreck
Trapped inside weak structures

Question 30

What are the safeguards for no clear exit?

Answer 30

Full face mask
Tended lifeline
Hold lifeline and use as guide
Position a diver underwater to tend the lifeline at the point of entry to the wreck 
Carry a torch/lantern 
Move slowly
Wear and overall to protect the drysuit
Wear gloves to protect hands
Use environmentally protected regulators in cold water

Question 31

What are the problems with night diving?

Answer 31

Separation from safety cover
Torch failure
Disorientation

Question 32

What are the safeguards for night diving?

Answer 32

2 torches
Mark exit point with light signal
Use a shot line to the site

Question 33

What are the problems with cold water diving?

Answer 33

Hypothermia

Equipment failure

Question 34

What are the safeguards under ice?

Answer 34

Ensure ice can hold the weight of the workstation
Uses heated structure to cover the entry point
Use environmentally protected equipment
Don’t breathe from regulator until submerged
Carry sufficient air
Tended lifeline
Train divers in survival techniques
Train divers in ice search techniques
Wear adequate thermal protection
Provide seat for standby diver
Don’t enter water via tide cracks

Question 35

What are the problems for tropical waters?

Answer 35

Sunburn
Dehydration
Coral and venomous creatures
Hyperthermia

Question 36

What are the safeguards for tropical waters?

Answer 36

Wear environmental protection

Ensure well hydrated

Question 37

What are the problems for isolated locations

Answer 37

Chamber availability
Ems availability
Logistics support

Question 38

What are the safeguards for isolated diving?

Answer 38

Chamber on board vessel
No decompression dives
On site medical staff
Nitrox diving