User:Pbsouthwood/Scratchpad 2

Does the DIR system optimally satisfy all the requirements of the full range of scuba applications?
Deep cave diving and conventional open water recreational diving have significant differences in some of the things that are likely to occur during most dives. Long surface swims typically found in open water ocean diving is one of these differences. This difference drastically changes the arguments concerning the relative usefullness of a snorkel.

As a substitute for:


 * The claimed lack of benefits likely stems from DIR's historical context of being cave diving centric: caves rarely have air pockets to breathe from in the event of running out of breathing air.
 * Similarly, the snagging concerns also are cave diving centric: the head/mask concern stems from the snorkel interfering with the deployment of the 'long hose' regulator; the leg snag alludes to a risk of breaking a guideline used in cave diving (guide lines minimize the risk of getting lost from a silt-out). 
 * Surface swims (dive exits) in cave diving often occur in highly-protected calm waters, where such floating is both of short duration/swim distance and the water surface is predictably benign due to lack of wind to make waves. Open water conditions are not as reliably benign.
 * Overall, the snorkel illustrates that what can be an excellent risk-assessment based decision for one specific diving environment (here, cave diving), such a conclusion is not automatically transferable to all other environments without due consideration.

Invitation to contribute on WikiTravel Dive guides
Hi (insert name here), I see that you are a Scuba diver and underwater photographer, so I would like to invite you to take a look at the dive guide project on WikiTravel such as the Cape Town regional guide at Diving the Cape Peninsula and False Bay. I am trying to encourage other divers to contribute on regional guides and site guides such as Coral Gardens (Oudekraal) for areas that they know. Cheers,

Voluntary opening of the eustachian tubes

Voluntary opening of the tubes (French: béance tubaire volontaire (BTV) ) is a method of equalising or clearing the ears described by doctor Georges Delonca and used in scuba diving and freediving. It aims to rebalance the pressure between the external ear and middle ear. the subject must either exercise a voluntary control of the muscles opening the eustachian tubes, or move the jaw to open the tubes when necessary.

This is less easy to execute than the Valsalva maneuver, but the BTV is the gentlest method to clear the ears. However, not all divers can perform this manoeuvre. It may be necessary to engage in ear training exercises to re-educate the muscles to perform this manoeuvre.

Internal Links

 * Ear clearing
 * Valsalva maneuver
 * Frenzel maneuver
 * Toynbee maneuver

Scuba configurations
Diving breathing apparatus may be configured in several ways to provide a self contained source of breathing gas to the diver. One of the primary distinctions is between open circuit, where the gas is breathed once and then exhausted to the surroundings, and closed circuit, also known as rebreathers, where the gas is passed through absorbent material to remove the carbon dioxide, and oxygen is added to compensate for that consumed by meatbolic processes.

Semi-closed circuit rebreathers
A subset of the closed circuit configuration is the semi-closed circuit rebreather, where an oxygen enriched gas is supplied at a rate which compensates for the metabolic use of the oxygen content and scrubbed to remove the carbon dioxide.

Constant mass flow
Sonic orifice: Fixed orifice Needle valve

Passive feed rebreathers
Bellows type - proportional volume make-up proportional mass make-up

Back mount Chest mount Side mount

Comments to HowieKor on DIR edits
1) Since there is so much controversy about the edits to this section, you will have to be very careful when paraphrasing to ensure that there is no change of meaning. This is difficult, as a change of meaning is often in the mind of the reader.

2) Truth does not come into the equation. Verifiability is paramount, and relevance is also important. You can be challenged on both.

3) In line links are considered undesirable. Rather use a footnote.

I have quoted a section from the article and commented in line below.

DIR - Criticisms and Controversies
For a system that had attempted to consolidate and promote many useful diving practises into one comprehensive system and philosophy it may seem surprising that the DIR system has sparked such controversy and negative comment by many critics. In the exact words
 * Avoid in line links. preferred style is footnote, even for website links as far as I understand the MoS

of Casey McKinlay, Project Director for the Woodville Karst Plain Project - "I recognize the WKPP for numerous reasons has never been popular with many segments of the diving community." Controversy is reflected in the fundamental DIR text "Doing It Right: The Fundamentals of Better Diving by Jarrod Jablonski which catagorises all other divers and diving agencies - "Today, there are dozens of diving agencies, offering many more different certification courses, in skill-sets ranging from basic open water to advanced Trimix instructor. Though divers emerging from these courses often possess vastly different skill and experience levels, nonetheless, the fact is that most seem to lack sound fundamental diving skills." Reaction to such charges is reflected in counter-criticism and counter-charges that the proponents of DIR have no direct experience or understanding of the diving conditions in which alternative forms of diving is carried out and are unqualified to make such charges e.g. The British Cave Diving Group..
 * looks like a fair comment with acceptable ref to me.

Other controversies extend to arguments regarding DIR position, DIR diving practise or DIR behaviours:
 * This may be challenged, but you should be able to find refs. It would help if you clarified what you meant by DIR behaviour and DIR position.

Universality – can “one size fit all?”
The DIR system is, at its core, an approach to procedures and equipment configurations designed for some very advanced diving – deep cave penetration.
 * Actually P67 par 1 specifically states that DIR system was designed to work in all situations. Whether it succeeds is opinion in the absence of data. Opinion must be 3rd party citable. Ours is not admissable.

An operative philosophy in extending this DIR system to other forms of scuba diving follows the argument “if it’s safest for that extreme, it must be safest elsewhere”
 * This is not actually what Jablonski says on p67. The quotes suggest that it is.

.

Critics of DIR say this is not necessarily the case.
 * Who, where, when. I dont doubt it, but can you cite it?

From a purely mathematical point of view this criticism echoes the fact that any optimal solution cannot exist in all possible changes in system variables, but is confined to a more limited set of these variables.
 * Jablonski claims that DIR is a system that is adequately safe in all situations, not that it is optimal in all of them. He does however say it is "perfect" in zero viz and crystal clear waters, which is sticking his neck out somewhat.

But proponents of the DIR system maintain that optimality can be achieved over all variations of condition without allowing modification of configuration or practise.
 * That is not my interpretation of the article. I see it as that DIR is the best system available when the requirement to retain the same basic configuration in all situations is applied (quite a significant constraint). I.e., for a fixed configuration it is the most versatile, and since they also strongly support a consistant configuration, it is the optimum when these constraints are applied. I am not a mathematician but I think, as an engineer, that this is not in conflict with the concept of optimisation.

In Jarrod Jablonski's words " DIR is a holistic system and although incorporating one part of it into another system is possible, it is not DIR. It is also likely to be fraught with complications. The same is true within the equipment configuration itself. Divers who opt to make changes to any part of the equipment configuration are likely to upset the carefully arranged components that are structured to complement one another."
 * As it happens, I completely agree with this statement, but also suspect that there are possible improvements, and that it may not be possible to get to some of them by gradual evolution. DIR may be at or near the peak of an optimal system and the adjacent possible may be mostly or entirely downslope. "You cant get there from here". This doesnt mean there are no other peaks in configuration space - like eye evolution.

In the diving world, where more non-academic criticism applies, critics address two other more specific concerns:


 * ''Most Wikimedia editing avoids the use of  markup. (a minor point, but I may as well mention it) We normally use an extra line break. This also makes reading the code easier, particularly for those of us who are not very familiar with html.

Controversy over unacceptability and risk of other diving practise
All diving practises put divers at some level of risk. As Bob Halstead put it  “As soon as you step near a full scuba cylinder you are at risk…..every step that you take getting to, on and into the water increases that risk”. The general risks accepted as part of DIR deep cave diving, even when mitigated by specific DIR practises and gear configuration, are high, but are found acceptable to DIR practitioners. Solo diving however is specifically “banned” by DIR conventions. In a detailed study of risk in diving(Scuba Diving -a quantative risk assessment) DAN figures showed that the fatality rate for solo diving was 3.8% (of the total fatalities studied?)
 * 3.8% is given as the DAN figure, 8% for BSAC figure and 4.5% overall, for Solo diving as principal cause of fatality. I dont find any indication of the skill levels or equipment used by the divers, so difficult to draw many useful conclusions from the data.

and that of penetration diving (cave diving being the major proportion of this) was 14.8%. (of the total fatalities studied?)
 * Of 19 fatalities, 10 were untrained/inadequately equipped, 7 were trained and got lost, 9 were group fatalities, 10 were alone at the time of loss of consciousness. No figures available for the total number of cave dives by the sample population during the period, so the risk may be highly skewed
 * I doubt that the figures prove much at all, but I am not a statistician.

From these figures it becomes quite illogical to object to an alternative form of diving with a different but lesser set of risks,
 * Can you show how the figures prove a lesser risk for Solo diving vs Cave diving?

when to mitigate those risks a totally different equipment configuration is required.
 *  I dont have these refs, so can't comment

I dont know whether this is what you were asking for, so have stopped here in case I got it wrong. If this is what you wanted, let me know and I will do the rest. Peter (Southwood) (talk): 14:10, 10 December 2011 (UTC)

Work of breathing
Components of Work

elastic work - work to overcome: frictional work - work to overcome: inertial work - work to overcome:
 * lung elastic recoil
 * thoracic cage displacement
 * abdominal organ displacement
 * air-flow resistance (major)
 * viscous resistance (lobe friction, minor)
 * acceleration and deceleration of air (negligible due to low mass of air)
 * acceleration and deceleration of chest wall and lungs (negligible due to overdamping)

work = force * distance ≈ pressure * volume / 2 elastic work ∝ area a-b-c-a inspiratory flow-resistive work ∝ area a-i-b-a expiratory flow-resistive work ∝ area a-b-e-a negative work ∝ area a-e-b-c-a (tone on inspiratory muscles during expiratory air flow) total work ∝ Welastic + Winspiratory flow-resistive + Wnegative passive recoil of lungs overcomes the work of expiratory flow-resistance

decompression