Chapter 6 - Open Water Diving Flashcards
What are the surface breathing rates?
25 L per minute - light work
40 L per minute - moderate work
70 L per minute - hard work
How do you calculate the actual breathing rate?
Surface breathing rate x absolute pressure at depth
What is the reserve air?
Should be enough to cover unforeseen emergencies
Should cover ascent and decompression stops
Should be based on the worst case scenario.
What is the worst case scenario?
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.
What are the methods of calculating air requirements?
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
How long will my cylinder last?
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
How much air do I need for a dive?
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
How much air do I need for a decompression dive?
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
How do you calculate your own breathing rate?
Record bottom time
Depth
Air in
Air left
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?
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
What is a quick method of calculating reserves?
Calculate the total air required to breathe x 4/3
Subtract air required for dive
What does a skipper do?
Responsible for safety of vessel and people
Final say in matters relating to safety
What does a dive supervisor do?
Controls all people
Controls all safety aspects
Responsible for the completion of the contracted work
Must liaise with skipper
What are small crafts?
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
What is the preparation for small crafts?
Help to launch Load vessel Adequate thermal protection Buoyancy aids Stay sitting whilst underway Keep a look out
What do you do on site and diving?
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
What are the large crafts?
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
What is the preparation for large boats?
Lid vessel
Ensure all equipment is onboard
Use transit time to prepare as much of the diving as possible
Divers fully kitted
What do you do whilst diving from a large boat?
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
What are some useful signals?
Flag Alpha - diver down keep we’ll clear at low speeds
Vessel restricted in ability to manoeuvre
Vessels engaged in underwater operations
What are the problems with deep dives?
More incidents of decompression illness More air required Greater distance to safety Gas narcosis probability increases Loss of light Mental stress Cold
What are the safeguards for deep dives?
Decompression tables
Carry enough air
Have a standby diver
Build up the dives to the depth of the contracted work
What are the problems of drift diving?
Divers can’t stop May be separated from vessel Ascents and descents May be too fast May be cold Hit objects Become entangled
What are the safeguards of drift diving?
Research the area Check seabed profile Check direction of current Talk to locals Check weather and sea conditions Use a lifeline
What are the problems of diving on a fixed worksite in moving water conditions?
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
What are the safeguards for stationary platforms?
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
What are the problems with low or nil visibility?
Hard to find and complete task
Orientation
Hard to avoid underwater obstructions
What are the safeguards for low or nil visibility?
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
What are the problems with no clear surface?
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
What are the safeguards for no clear exit?
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
What are the problems with night diving?
Separation from safety cover
Torch failure
Disorientation
What are the safeguards for night diving?
2 torches
Mark exit point with light signal
Use a shot line to the site
What are the problems with cold water diving?
Hypothermia
Equipment failure
What are the safeguards under ice?
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
What are the problems for tropical waters?
Sunburn
Dehydration
Coral and venomous creatures
Hyperthermia
What are the safeguards for tropical waters?
Wear environmental protection
Ensure well hydrated
What are the problems for isolated locations
Chamber availability
Ems availability
Logistics support
What are the safeguards for isolated diving?
Chamber on board vessel
No decompression dives
On site medical staff
Nitrox diving
