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.

Criticism of DIR Policy

DIR Policy	Rationale for DIR policy	Criticism of DIR policy
The snorkel is not acceptable equipment in the DIR configuration[1]	A snorkel is completely useless in an overhead environment A snorkel mounted on the mask interferes with the deployment of the long hose A snorkel mounted on the mask increases the risk of the mask being dislodged if the snorkel snags A snorkel stored on the leg (or other place off the mask) is an unacceptable entanglement hazard Surface swimming on the back in open water is an adequate substitute for a snorkel in all conditions	Generally accepted, but not all diving is in an overhead environment. A specific truth can not always be extended to a generality. Even when the major part of a dive is under an overhead, there may be periods of surface exposure where a snorkel could be a significant convenience or risk mitigation. This is true if the long hose is looped around the neck, which is a core DIR configuration policy. A snorkel on the mask is clearly incompatible with a neck looped long hose primary regulator. The snorkel is indisputably an increased snag hazard on the mask. The risk depends on whether the snorkel is likely to be near an object which could snag it during a dive. The DIR principle of consistant uniform configuration implies that if it can ever be a risk it is never acceptable. It is possible to provide an off-mask snorkel storage which is not an entanglement hazard. This would allow the use of the snorkel on the surface when needed, and risk-free storage during the dive. This would not be in logical conflict with the DIR configuration. (a) When surface swimming on the back, the diver is severely constrained in seeing where he/she is going. This is a major disadvantage when, for example, negotiating large kelp forests, swimming among shallow rocks and in the surf zone, where a snorkel can allow the diver to swim facing down or forward, where the obstacles are visible, to navigate more safely and efficiently, while conserving gas for the dive. (b) A snorkel can make surface swimming more comfortable and safer when strong winds blow spray around just above the water. This can not always be avoided, and the risk is significantly mitigated by the use of a snorkel. This also conserves gas for the dive, and allows continued breathing comfort after a dive even if all the remaining gas is used up on the return swim. DIR Option #1 - Don't dive is an overreaction to an avoidable problem.
Solo diving is generally prohibited under DIR policy of the unified team.[2]	Diving as a member of a well trained, well equipped and disciplined team is safer than diving solo It is obligatory to mitigate all risks to the lowest practicably achievable level. (Option #1 - Don't dive) There is no diving activity that can not be conducted more safely and enjoyably by a suitably competent and equipped team than by a solo diver The DIR configuration is unsuitable for solo diving as there is insufficient redundancy.	This is not in dispute. The dispute is over whether risk in solo diving can be acceptable. In reality, this can only be achieved by never diving at all. Even the statistically much safer surface supplied procedures required for most commercial diving operations do not entirely eliminate risk. A more realistic requirement would be to mitigate all risks to a personally acceptable level, as recreational diving is a voluntary activity. This is the de-facto standard of the developers of the DIR sysytem, who habitually engaged in extremely hazardous activities, but mitigated the risk to personally acceptable levels by use of what became the DIR system. Most survived. There are occasions where a team of suitably competent and equipped divers is logistically impracticable, and solo diving is the lowest risk alternative. In these cases, if the overall risk to the solo diver is significantly lower than the minimised risk which is nevertheless acceptable for a unified DIR team on a dive in a more hazardous environment, it would be hypocritical to condemn the solo dive and resort to Option #1 - Don't dive. Enjoyment is a personal matter and is up to the diver. (a) The DIR configuration does not prohibit the addition of task specific equipment to the core configuration.[3] The additional equipment required by a solo diver can be seen as task specific equipment, and need not conflict with the core configuration. It is unneccesary for team members to be familiar with the configuration when there are no team members involved. (b) Use of a short primary hose is acceptable in shallow open water environment.[4] When there is no foreseeable need for supplying a buddy with breathing gas, a similar arrangement should be acceptable. (c) On the basis of minimalist configuration, there should not be a requirement for a secondary second stage at all as in solo diving a fully independant bailout gas supply with it's own regulator is a more robust arrangement.
DIR policy is against the use of personal decompression computers	Divers tend to become dependant on dive computers and less aware of the depth and duration during the dive, particularly when new to decompression diving Dive computers inhibit proper dive planning and discourage divers from analysing the effect of variations in gas mixtures and decompression choices Dive computers do not benefit diver education as they do not promote proper questioning and planning discussions. Dive computers often use algorithms that use large conservatism factors, which can result in excessively long decompression. Dive computers are expensive. The money can be better spent on more important equipment Dive computers significantly reduce the probability that divers will keep track of their residual inert gas loading. Leaving them less informed if the computer fails. Most dive computers do not allow for use of helium based gases. Those which do are excessively conservative. Dive computers often require more decompression than "an astute, well-educated, experienced diver generates" Dive computers often confuse the diver by providing unneccesary information which may take attention away from the important information. Some computers become very difficult to use if a decompression stop is violated and will lock up completely, others will fail to provide information desperately needed by the diver to avoid serious injury or death. Computers do not allow the diver to modify the decompression profile to account for advances in knowledge, such as the use of deep stops. Divers who habitually rely on a decompression computer lose proficiency with tables, and may be handicapped if the computer is not available.	If this is true, it is an issue of training and self discipline, not a defect of the computer or the use thereof. This too is a matter of training and not a defect of the computer. There is nothing to stop the training agency from using other tools for training. Software that matches the algorithm used by the dive computer can be very useful in demonstrating the consequences of variations in gas choice, dive profile and other user selectable factors. There is a fairly large range of computers available, with a fair range of elective conservatism. The diver is free to pay his money and make his choice. Compared to other diving equipment computers are not that much more expensive, particularly for recreational range diving. A diver can not keep accurate track of inert gas loading during a dive without a computer, and only a few will display the information in real time. Estimates of inert gas loading based on manual tracking of depth and time are usually major overestimates due to assumed sqare profiles, or highly unlikely to be accurate if approximations and averages are used in the estimates. The computer will provide a much more reliable record of gas loading as it is making regular constant updates with accurate information on depth and time. A backup computer (carried by a dive buddy) is a more reliable source of information if the computer fails than anything the diver may have been working out on the fly. Several computers allow for helium based gases. Most have elective conservatism. Possibly none allow as aggressive a dive profile as used by some DIR divers. Most manufacturers are conservative to avoid lawsuits for negligence in the event of divers suffering decompression sickness when using their algorithm. Divers do occasionally get decompression sickness while staying within the limits of the algorithm, so this is not a frivolous point. If a diver wishes to push the margins of safety, it will have to be done without a computer. It is not specified where the "asture, well educated, experienced diver" gets his data to support the choice of decompression schedule. The published, peer reviewed science is used in the algorithms in dive computers. Empirical data may be relied on by these divers, and it may be empirical data based on someone else's experience. This is doing experimental work with oneself as the subject at best. It may work. Some may do so, others may not. The diver is free to make the choice of a computer which provides useful information. This is a valid objection to those computers which perform as described. They are dangerous as they let the diver down at his time of greatest need, whether or not the violation was intentional or negligent, cutting the data off that could help save the diver from serious injury or death is like a car switching off the airbag system if the driver exceeds the speed limit. Divers are free to buy computers that will not leave them in the lurch and should enquire about the failure modes before purchase. Decompression computers are not user programmable. Most divers are not competent to reprogram a dive computer. However, some models can have the software upgraded. Some also include deeper stops and elective conservatism and choice of algorithm. There is also nothing to stop a diver doing deep stops. The computer will however, not shorten the shallower decompression schedule to take advantage of the deep stop if the algorithm is incompatible, so deep stops will in these cases increase decompression times. The objective evidence in favour of deep stops is somewhat flimsy, and the jury is still out. The diver has the option of a backup computer, or learning to use the table, or even Option #1 - Don't dive. The same argument applies to any essential piece of equipment, but that is not a valid reason why it should not be used. For most recreational and technical divers the advantages of using a computer, even if it is not optimised for extreme exposure diving, outweigh the disadvantages.[citation needed]
Policy 4	Rationale for policy 4	Criticism /comment on rationale for policy 4

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 ^[1]. 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.

Notes and references

See also

Internal Links

• Ear clearing
• Valsalva maneuver
• Frenzel maneuver
• Toynbee maneuver

External Links

• Entraînement à la Béance Tubulaire Volontaire on the website of the Committee of apnea FFESSM

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.

Open circuit

Back mount

Backplate and wing

Stabiliser jacket

ABLJ and backpack

Side mount

Closed circuit

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."^[1] 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.^[2].

• 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.

^[3].

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 <p> 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^{[4] [5]}.

• 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 ^[6]

elastic work - work to overcome:

• lung elastic recoil
• thoracic cage displacement
• abdominal organ displacement

frictional work - work to overcome:

• air-flow resistance (major)
• viscous resistance (lobe friction, minor)

inertial work - work to overcome:

• 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 ∝ W_elastic + W_{inspiratory flow-resistive} + W_negative passive recoil of lungs overcomes the work of expiratory flow-resistance

decompression

decompression