Advanced Nitrox Chapter 9-11 Flashcards
What are pre-dive checklists?
Need to be confirmed by dive buddy and instructor
Will vary depending on the type of dive
What is a START check?
Stress analysis prior to dive is important especially with a new team or new equipment
S Drill = out of air drill, bubble checks
Team = buddy equipment checks
Air = gas matching
Route = entry/ exit and planned path underwater
Tables = depth, duration, waypoints and schedule
Describe an ideal descent
Should be conducted as a team
Prepare for optimum performance during bottom phase
Ideal breathing should be focus
Observation of buddy’s kit is critical
Reasonable pace to allow for equalisation and to avoid build up of CO2 from overworking
Team should level off in advance of bottom and buoyancy should be locked in prior to reaching bottom
Describe an ideal ascent
Should be slow and allow for safety stops
Gas switches may be conducted - may need extra cylinders which can complicate logistics and affect streamline
When should you safety stop?
1 at 4m for 3-5 minutes
1 at half of bottom depth for 1 or 2 mins
1 at half this depth for 1 or 2 mins
What is a bailout procedure?
Diver should carry enough gas to make a direct ascent to surface with a shallow safety stop from the deepest portion of the dive
Gas consumption should take into account less than ideal breathing
What is partial pressure blending?
Simplest method, all equipment must be O2 cleaned
Add oxygen to cylinder and then top up with air to get to desired mix
Labour intensive and slow
What is continuous blending?
Mixes nitrox prior to gas being compressed
Uses pure oxygen and ambient air
Less labour intensive but more equipment intensive
Cylinders do not require an O2 clean for mixes less than 40%
What is the membrane separation system?
Membrane is used to remove nitrogen from air (membrane differentiates between size of nitrogen and oxygen molecules)
Allows use of cylinders that have not been O2 cleaned
What is premix?
Requires no blending
Gas supplies delivers premixed blends of nitrox which can be pumped directly into cylinders
Can be wasteful and more expensive
Allows for cylinders that have not been O2 cleaned
What is the molecular weight method?
Reserved for mixing large quantities of gas - use weight of component gases to make exact mix based on weight of gas introduced to pressure vessel
Rarely used in diving as it requires use of large scales
