Advanced Nitrox Chapter 1-4 Flashcards
What % of gas exchange occurs in lower 1/3 of lungs?
70%
What is diaphragmatically initiated breathing?
‘ideal breathing’
Pull diaphragm down and away - pulls gas into lower lungs
Fill lungs to comfortably full
Pause and exhale, tongue to roof of mouth - exhalation should last longer than inhalation
Fill lungs from bottom and empty from top
What fundamental skills should you master?
Buoyancy, swimming, trim and breathing
What is the ideal swimming technique (working position)?
Don’t use hands
Allow time for glide after each kick
Use fins to make turns
Horizontal in water with slight arch to back so you can see forward, with knees slightly bent
When should you deviate from ideal breathing?
Using a rebreather - need shorter cycles
When correcting buoyancy - may need to cycle breathe quickly to keep lung volume high if suddenly descending
What is the ideal working position on descent?
Keep slightly negative
Angle head downwards
Planing of body will help with forward movement
Describe O2
Tasteless, odourless gas
Supports combustion
Diatomic molecule
How long can we live without O2?
4-6 minutes
Describe Boyle’s law
Inverse relationship between pressure and volume when temperature is constant
During descent, as a diver goes deeper, more gas is needed, volume gets smaller
Golden rule of diving (never hold breath) is related to Boyle’s law
Describe Dalton’s law
Each gas in a mixture will have a pressure that is directly related to its fraction in the mixture
Partial pressure of a gas is equal to its fraction of the total pressure of gas
What do we use Boyle’s law for?
Calculating pressure at any depth, amount of gas consumed at depth and how much the volume will increase by if they ascend from one depth to another
What do we use Dalton’s law for?
Calculating maximum operating depth, best mix and partial pressure calculations
Gas blending calculations
How much of each breathing gas a diver absorbs
What is EAD?
Equivalent Air Depth
Way for a diver to use any air table to calculate dive profiles
Dive profiles are linked to partial pressure of inert gases a diver breathes throughout dive
Increased O2 in mix reduces inert gas absorbed so the amount of nitrogen absorbed is the same as with air at a shallower depth
What is a hypoxic mix?
Mix with less than 0.21 ATA of oxygen
What low levels of oxygen become dangerous?
- 16 = hazardous
0. 12 = fatal
What does anoxic mean?
Gas absent mix
Why is the risk of hypoxia increased in shallow water?
Risk in CCR if oxygen is not being added to loop
Risk increased in shallow water as ppO2 can drop quickly
Can be accelerated during ascents due to drop in ppO2 caused by ascent
When must a diver track their oxygen exposure?
If they are exposed to over 0.5 ATA
Must track for each dive and for multiple dives through consecutive days
Why are you more at risk of oxygen toxicity in technical diving?
Exposure from air poses risk due to extended exposures and use of decompression gases
What are the 2 types of oxygen toxicity?
Short term high dose exposure
Long term lower dose exposure
Describe short term high dose exposure
Risk of dramatic problem - CNS toxicity
Tracked as a percentage of the allowed dose for each dive and the total of each day of diving
Describe long term lower dose exposure
Diver tracks this exposure with assistance of oxygen tolerance units (OTUs)
Used to track the whole body/ pulmonary exposures
What is the max oxygen exposure allowed?
- 4 ATA for working part of dive (sport or technical)
1. 5 or 1.6 for decompression phase of a technical dive or short, warm water sport dives
What are the symptoms of CNS toxicity?
Convulsions Visual disturbances Ear ringing Nausea Twitching/ tingling Irritability Dizziness (ConVENTID)
What is most common symptom of CNS toxicity?
Nausea
Can you acclimatise to oxygen toxicity?
No
What is the NOAA and what did they set up?
National Oceanic and Atmospheric Administration
Set up particular partial pressures of oxygen and the exposure limits for each one
How are the exposures measured?
Time dose concept
Higher the pressure of oxygen to which diver is exposed, the lower the allowable exposure time
Exposure is accumulated throughout the dive
How does exposure change when diving open circuit?
Exposure changes throughout the dive and is calculated for each pressure of oxygen experienced
Mixture the diver breathes is a fixed fraction of oxygen but gives a variable exposure level
How does exposure change when diving CCR?
Exposure doesn’t change much as rebreather maintains a constant pressure of oxygen
What is the most critical calculation with regards to exposure?
CNS oxygen exposure as it results in the greatest risk of immediate major consequences
How do you calculate CNS oxygen exposure?
Time of exposure/ total exposure allowed for each pressure of oxygen to which the diver is exposed
x100 to get percentage
All percentages experienced by diver are added up
Can allow for washout time
How do we calculate CNS oxygen exposure on open circuit?
Calculated using maximum depth of each phase of the dive and then for each decompression stop
Sport dive = maximum depth for the entire time of dive
How do we calculate CNS oxygen exposure for CCR?
Time exposed at chosen set point (pressure of oxygen) for total time of dive
How long does a washout effect take?
Oxygen exposure and washout effect takes 90 minutes for half of the exposure to be removed
When will you experience pulmonary oxygen exposure?
Breathing over 0.5 ATA for prolonged periods of time
Why do you get symptoms with pulmonary oxygen exposure?
Irritation and reactivity of oxygen with the body’s tissues
What are the symptoms of pulmonary O2 exposure?
Difficulty breathing, pain on inhalation, dry unproductive cough, soreness in lungs/ throat
How does pulmonary O2 exposure cumulate?
Allowed exposure drops for repeated days of diving
Important for CCR divers because they allow for fixed pressures of oxygen to be breathed for hours
How do we measure pulmonary O2 exposure (and give calculation)?
Oxygen Tolerance Units (OTUs) No washout allowed for Numbers are additive for each day One OTU is the equivalent of breathing oxygen at atmospheric pressure for 1 minute OTU = Tx (0.5 / ( PO2 - 0.5 )) ^0.833 Tx = time in minutes PO2 = oxygen partial pressure in bar
How do you work out PO2 for ascent?
Half distance between bottom depth and depth of safety stop - find PPO2 delivered by mix at that depth and multiply by number of minutes spent ascending
If PPO2 is less than 0.6 bar, you can disregard it
OR
Add 20 units to cover ascents from any dive - covers dives from a max of 45m at a standard speed of 9m per minute
What is the max one day dose of OTUs?
850 OTUs thought to reduce vital capacity by 4%
Impractical as this means 850 minutes at 1 bar or 440 minutes at 1.6 bar
What is max dose for multiple days?
300 OTUs
What is the NOAA 24 hour limit?
Used for multiple dive tracking of CNS toxicity
Tracking does not allow reduction of dose according to half-time calculations
24 hour values are calculated and added together to discover total daily CNS toxicity levels
What is the average ascent rate for divers after safety stop?
60m / minute
How can divers plan for the eventuality of a DCI event?
Be trained in first aid and O2 administration
Ensure the emergency O2 is available
Carry dive insurance
Continue education in rescue diving
Planning for decompression incidents on all dives
What is the accepted range for nitrogen narcosis exposure?
4.0 - 5.21 ATA of N2
What is narcosis?
Suppression of mental activity of brain
Amplify existing state of mind
What is the maximum narcosis exposure for dives in overhead environments?
4.0 ATA
As well as cold and dark waters
What is the oxygen narcosis effect?
Oxygen can cause narcosis too
Don’t dive with nitrox deeper than you would dive with air
What is CO2 toxicity?
Byproduct of metabolism
Can build up if diver is not breathing properly, is overexerting, has poorly performing equipment or is retaining CO2
CO2 can increase decompression risk
Increases oxygen toxicity risk
How can you reduce risk of CO2 toxicity in a rebreather?
Scrubber packing and duration logging are critical steps
What is CO toxicity?
Byproduct of incomplete combustion
Usually due to a bad gas source
Causes metabolic suffocation
Headaches, nausea, vomiting, altered levels of consciousness, cherry red lips and nail beds (not usually seen in divers)
What is the compliment complex?
Body has immune response to air bubble formation - creates an immune cascade throughout the body
Can cause thickening of blood
