Ocean Diver Lectures Flashcards
Benefits of BSAC Membership
Largest club in world Internationally recognised qualifications Diving Manual SCUBA magazine 3rd party Insurance Member's prices in shop
Benefits of diving with a branch
Branch support Planned diary of dives Range of diving buddies and interests Sharing the experience Branch dive trips and holidays
Aim of OD course?
Train a diver who can use 21%, 32% and 36% O2 mixes in controlled conditions to a depth of 20m under the supervision of a DM
Describe the OD course
7 lectures, theory assessment, 5 sheltered water, 5 open water
Describe atmospheric pressure
Weight of air in 1cm square column of the atmosphere
=1kg/cm^2
=1 bar
What is water pressure?
Water exerts pressure of 1 bar for every 10m of depth
What is absolute pressure?
= gauge pressure + atmospheric pressure
Describe the structure of a mask.
Has tempered glass, a frame and a flexible seal with adjustable strap
How big is a snorkel?
40-45cm long
20mm diameter
What is Boyles Law?
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume
What does SCUBA stand for?
Self Contained Underwater Breathing Apparatus
Describe when a cylinder is tested and to what standard.
BS/EN standard
Has a working and a test pressure
Hydraulic testing every 5 years
Visual every 2.5 years
What is the composition of our exhaled breath?
17% oxygen
4% CO2
79% nitrogen
What happens with a breath hold dive with hyperventilation?
O2 level to support consciousness begins high and drops, because CO2 level for stimulus to breathe doesn’t reach threshold
Describe the effects of diving on the ear.
Sound travels faster underwater - direction difficult to identify
Air spaces - ear drum, middle ear and Eustachian tube
Describe heat loss when diving.
25 times faster than air
Cold water increases rate of heat loss
End dive if getting cold
When do we need thermal insulation when diving?
20C+ = no suit required 10-20C = wetsuit or drysuit required 0-10C = drysuit required
What is sinus squeeze?
When there is no equalisation between sinuses and ambient pressure
Mucus membranes swell to relieve pressure
Blood vessels burst
Sinus pain
If a diver feels pain in sinuses during descent they should abort dive (indicative of damage to sinus nerves)
What is Archimedes Principle?
When an object floats in water it displaces a weight of water equal to its own weight
What are the 2 most important considerations in planning a dive?
1) nitrogen management
2) ensuring sufficient breathing gas
Describe nitrogen absorption on a dive.
Increase in ambient pressure results in more nitrogen being absorbed - on gassing
Fast tissues = good blood supply
Slow tissues = poor blood supply eg fat
What is the maximum descent and ascent rate?
Descent = 30m/ minute
Ascent = 15m/min up to 6m
1 minute from 6m to surface
What is current tissue code?
Body’s present level of nitrogen saturation
What is surfacing code?
Represents a change to CTC at end of dive
Flying before diving?
Tissues off gas
10 hour recovery before diving
Flying after diving?
Increased level of off-gassing - DCI
Need CTC of A or B
What do you need to plan a dive with tables?
Depth gauge
Dive watch
Dive slate
What are the functions of dive computers?
Theoretical body tissue models to calculate nitrogen on and off gassing Timer and pressure sensor Planning info eg depth and time Audible/ screen warnings Stored log of previous dives Temp sensors
How many dives can you do in 24 hours?
3
Advantages and disadvantages of nitrox?
Advantages: safety factor, reduced risk of DCI
Disadvantages: can still get DCI, special equipment, oxygen toxicity
What is an EAD calculation?
Equivalent Air Depth
Calculated using nitrox tables NOT 88 - removes errors of calculation
Nitrox analysing essentials
Calibrate prior to use Keep flow rate even and low Avoid windy conditions Avoid moisture Analysis must be within +/- 1% of your target mix
What is the rule of thirds? (and specific to 10L cylinder filled to 210 bar)
1/3 gas for descent to half way point
1/3 gas for second half of dive
1/3 gas as reserve
210/3 = 70 bar for each 1/3
140 bar for dive
When does gas consumption increase?
Physical effort increases
Divers cold or anxious
Why do we dive with a buddy?
Monitor each other and assist
Help in kitting up, entry and exit
Develop skills with more experienced buddies
What is a DM responsible for?
All diving on site
Selecting site
Arranging buddy pair
Gives dive brief
Info given on a DM brief?
Dive site info
Hazards to avoid
Surface support, assistant DM
Separation procedure
What does A flag mean? What is the American version?
Divers down, stay clear and reduce speed
USA: American Sports Divers Flag - divers below, stay clear
Describe the depths that colour absorbs at?
Red = 5m Orange = 10m Yellow = 15m Green = 20m Blue = 25m Indigo = 30m Purple = 40m
What reduces vis?
Suspended particles
Turbidity
Reduces light
What is the cause of DCI?
Inadequate elimination of nitrogen during ascent - bubbles
Gas embolism during ascent
Effects of DCI?
Bubbles can form in tissues - compress and damage vessels, reduces O2 delivery
Bubbles can form in/ enter blood and block flow
What is the cause and effect of DCI - lung damage?
Cause: ascent too fast, breath hold
Effects: over expansion, physical damage to lung tissue
DCI S&S?
Chest pain Voice change - crepitation SOB Itches/ rashes Joint aching N&T N&V Headache and confusion Weakness + paralysis
Narcosis - cause and signs?
Cause: nitrogen under pressure affects nerve impulse transmission
Signs: effects of alcohol
Signs of o2 toxicity?
Visual/ auditory disturbances
Muscle twitching
Convulsions
Cause and detection of contaminated breathing air?
Cause: problems with compressor
Detection: Oily taste
Effects of contaminated breathing gas?
Nausea, headaches, dizziness
Cause and resolution of out of air situation?
Cause: failure to monitor gas supply, equipment failure
Resolution: AS, dive aborted
Cause and resolution of CBL?
Cause: unconscious buddy
Resolution: get casualty to surface, ensure buoyant on surface
