kevrumbo's Page

Dive History
Sipadan -luckily & unknowingly departed on the last boat out before the infamous Abu Sayyaf Raid, Easter Sunday April 23, 2000.
Indonesia -Lembeh, Halmaherah & Raja Ampat;
Papua New Guinea -Bismark Sea, Fathers Reef;
Thailand -Similans, Hin Daeng/Hin Muang Pinnacles;
Fiji -Bligh Straits;
Philippines -Balicasag Island, Tubbataha Reefs, Verde Island (Blackfish Corner)
Palau -Peleliu Corner & Express, Blue Corner, Big Drop-off et al;
Hawaii -Oahu & Big Island;
Mexico -Cozumel, Baja Calif./La Paz;
Grand Cayman & Little Cayman British West Indies;
US Virgin Islands -St. Thomas;
Galapagos Islands Ecuador and Cocos Island Costa Rica.

South China Sea/Singapore/Kuantan Malaysia -WWII Battleships HMS Prince of Wales & Repulse, Super Tanker Seven Skies;
Indian Ocean/Sri Lanka: WWII Aircraft Carrier HMS Hermes,
Banten Bay/Sunda Strait Indonesia: WWII Cruisers USS Houston & HMAS Perth,
Chuuk Lagoon -HIJMS Oite Destroyer, Aikoku Maru, San Francisco Maru, Nagano Maru, Shotan Maru, Amagisan Maru, Momokawa Maru, Unkai Maru, Seiko Maru, Fujisan Maru Tanker, Hokuyo Maru et al;
Palau -Helmet Wreck, IJN Iro, Chuyo Maru, Ryuko Maru, Teshio Maru;
Subic Bay Philippines -USS Rochester (New York), Sakura Maru, LST, F4 Phantom Jet Wreck;
Coron Bay Philippines -HIJMS Akitsushima, IJN Irako Wrecks et al.

Acute Dengue Viral Fever (mosquito vector) contracted in Papua New Guinea '01.
DCS type I Left Shoulder suffered in Chuuk '08 with successful Table 6 treatment in Chuuk and Honolulu, with additional work-up to rule out Deep Vein Thrombosis & Pulmonary Embolism: fully recovered with no residual effects --see link 264517-type-i-bends-hit-chuuk.html

Certification History
PADI Drager Dolphin Rebreather 1999 (Fred Colburn, Pacific Wilderness); GUE-Fundamentals 2001, 2007 (John Walker, Beach Cities Scuba, Michael Kane, Hollywood Divers); TDI Adv. Trimix 2005 (Chuck Mather/Keith Keizer, Dive Tek Hawaii); DSAT Trimix Blender 2005 (Dave Ross, Tech Asia); PADI Wreck Diver 2005 (Jo Hjelm, Island Divers Oahu); NAUI Wreck Penetration 1 2005 (Andrew Georgitsis, 5thD-X); NACD Cavern 2006 (German Yañez, Yucatech Expeditions); NAUI DPV 1 '06 (Joe Talavera, 5thD-X); IANTD Technical Wreck Diver '06 (Sam Collett, Tech Asia).
Candidate/Intern Certified Hyperbaric Technologist (NBDHMT); Volunteer Crew Intern, Catalina Hyperbaric Chamber --see link TOP.HTM
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Gas Planning/Ratio Deco Tools (written in Excel97):
rock_bottom_revA.xls
GasCalc_Liters_B.xls
GasCalc_CuFt_A.xls
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How to use the Metric System with 11 Litre Tanks (Double AL80's)::
http://www.scubaboard.com/forums/5607156-post3.html

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How to use a SPG in bar units to read remaining volume in cubic feet in a set of double manifolded LP95's:
Just look at the metric tank rating for a set of double manifolded LP95's:
30 litres/bar.
And there are 28.3 litres in one cubic foot;
So 30 litres/bar divided-by 28.3 litres/cubic foot equals:
1.1 cubic foot/bar.
Therefore, a SPG in bar units used with a set of double LP95's will also indicate remaining volume in cubic feet, to a reasonable approximation. . .
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How to tolerate sea sickness without medication:
http://www.scubaboard.com/forums/5367954-post40.html
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Some statistics on Diving Accidents from the Catalina Hyperbaric Chamber:
http://www.scubaboard.com/forums/4851589-post153.html

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DCS and the Immune System:

http://www.scubaboard.com/forums/attachments/ask-dr-decompression/90503d1299115977-dcs-immune-system-redux-rethinkingdcs-1-.pdf

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The "Real" Problem of Iso-Baric Counter Diffusion in Deco Gases:

From Ross Hemingway, developer of V-Planner program:

At my web site, I have some basic diagrams of the IBCD problem, and how it relates to deco times. Decompression myths and mistakes In V-Planner we suggest limiting the increase of inert pp to 0.5 between mixes. This is measured between the swap point depth - the inspired pp of each. . .

Quote:

If you're talking strictly about breathing gas, it's fine (and sometimes even beneficial) to switch from a helium-based bottom mix to an N2O2 decompression mix. Nitrogen and helium have different solubility coefficients, so the helium will diffuse out faster than the nitrogen can diffuse in, especially in the 70 foot range where the diver would be switching over to 50/50 nitrox.

This is the standard argument listed in medical journals. In normal deco dives with modest deco times we can all "get away with it" and turn the effect into a reduction of deco time benefit.

But its actually the root cause of IBCD in deep dives. For very deep dives with longer decompression, then we must avoid any spikes of N2 pp in deco. Allowing a big N2 spike mid way through deco, will bring on a gas reversal in the tissues. Helium will diffuses out at an uncontrolled rate, whiles N2 diffuses in at an uncontrolled rate. This happens mid way through your "controlled" decompression. The end result is that the body can not fully perform the reversal, deco is compromised from the mid point onwards. The diver has created an IBCD injury half up way through the deco schedule, which now requires a lot of extra deco time to counter and correct for. . .

You get a warning in [ V-planner] if the ppN2 or ppHe changes more than 0.5 between mixes in deco. There is also the pp graph that lets you see the pp values throughout the deco phase.

The warning will be a crimson highlight along the row of the gas switch exhibiting a counterdiffusion trend (as shown in V-planner on an old pocket PC).

For example, enter a dive in V-planner to a depth of 90m for 20min with a bottom mix of 12/60, and deco gases of 21/35 at 57m; 35/25 at 36m; Eanx50 at 21m; and Oxygen at 6m. There will be a red warning highlight along the row corresponding to the 21/35 gas switch, signifying a 0.5 or greater change in ppN2 in this instance. Note that you're going from an fN2 of 28 percent from the bottom mix of 12/60, to an fN2 of 44 percent in the intermediate deco mix of 21/35.

Check:
At 60m, your inspired ppN2 on backgas is: 0.28(7.0) = 1.96
Switch at 57m, your ppN2 on 21/35 is now: 0.44(6.7) = 2.94
Your ppN2 change is: 2.94-1.96/1.96 = 0.5 hence an ICD warning.

If you use an intermediate deco gas of 18/45 instead (fN2 of 37 percent):
Switch at 57m, your ppN2 would be: 0.37(6.7) = 2.47
Your ppN2 change: (2.47-1.96/1.96) = 0.26 , and the ICD warning clears. . .

Strategy for Minimizing Inspired N2 On Deco Gas Switches and avoiding potential Isobaric Counter-Diffusion (ICD):
http://www.subpacific.cl/icd.pdf
Deco_Strategies_Wkpp.pdf

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A More "Sensible" Explanation of the Oxygen Window. . .

On Diving acclimatization and DCS:
In summary, our results show that DCS induces a stress response, as confirmed by the expression of heat-shock protein in lung, liver, and heart tissue. DCS preconditioning reduced the neurological impairment caused by subsequent rapid decompression from exposure to high pressure. We conclude that bubble formation in tissues after decompression can activate a stress response and that the protective effects derived from this stress response may be the mechanism responsible for the phenomenon of diving acclimatization. . .
Diving acclimatization has been described as an adaptive response to decompression stress after repetitive exposure to pressure (7). This adaptation reduces a diver's susceptibility to DCS or the severity of DCS. The mechanism contributing to diving acclimatization, however, remains obscure. We proposed an "induction hypothesis," speculating that repetitive compression-decompression is a form of preconditioning that generates protective factors and reduces the severity of acute tissue injury during subsequent bubble formation. In the present study, our results further demonstrate that DCS induces a stress response and that this DCS preconditioning significantly alleviates the neurological impairment induced by subsequent exposure to high pressure. These results strengthen our induction hypothesis by explaining the mechanism underlying diving acclimatization. . .
DCS is a disease caused by gas bubble formation in tissues. Air bubbles produce their effects by mechanical obstruction, by altering the biochemical environment, or both. Bubble formation interrupts blood flow and compresses or disrupts tissues (22). Air bubbles can also initiate an air-liquid interface reaction in tissues, which activates plasma proteins, including clotting factors, enzymes, and immunoglobulins (15). The complement system, polymorphonuclear leukocytes, and oxygen metabolites are proven factors that mediate air-bubble-induced tissue injury (22). Protection from air-bubble-induced tissue injury may result from a smaller number of bubbles or from less tissue reaction to air bubbles. Wisloff and Brubakk (31) reported that endurance exercise reduces bubble formation and increases survival in rats exposed to hyperbaric pressure. It is not known whether DCS preconditioning reduces bubble formation after the next episode of decompression from a hyperbaric environment. Nevertheless, endurance exercise is a stressor that increases the expression of HSP70 and may represent a powerful preventative agent against tissue injury in several models (8, 23). These reports suggest that stresses such as endurance exercise can activate bioprotective mechanisms. Compatible with these reports, our results show that prior DCS is also a stress inducer, which may activate a bioprotective mechanism similar to that induced by endurance exercise. This suggests that this protection involves mechanisms more complex than a reduction in bubble formation. . .
http://ajpregu.physiology.org/cgi/content/full/287/5/R1214
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On adaptation to Deep Air and Nitrogen Narcosis:
"Moreover, our results suggest that experienced divers can discriminate between the behavioral and subjective components of narcosis. . .It has been proposed that the intensity of narcotic symptoms could be used by divers to gauge the extent of performance loss (10). The present results indicate that this advice is inappropriate for adapted divers because the two components of narcosis [behavioral and subjective] uncouple in a direction that could lead to an overestimation of performance capabilities --a potentially dangerous situation. On the other hand, the question arises as to whether adaptation confers any benefits on the diver, since performance efficiency is not directly improved and could be overestimated. In this regard, it could be argued that a reduction in symptom intensity reduces the possibility that attention will be focused on subjective sensations rather than the task at hand." [i.e. Subjective, sensations awareness vs. Situational, task-at-hand awareness??]
From:
p.9, Hamilton K, Laliberté MF, Fowler B. Dissociation of the behavioral and
subjective components of nitrogen narcosis and diver adaptation. Undersea Hyperb
Med. 1995 Mar;22(1):41-9. PubMed PMID: 7742709.
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"The Meyer-Overton hypothesis states that narcosis happens when the gas penetrates the lipids of the brain's nerve cells. Here it apparently interferes with the transmission of signals from one nerve cell to another. Exposure to nitrogen-oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anesthesia. . . and narcotic potencies of inert gases are attributed to their lipid solubility." (see PADI Encyclopedia of Recreational Diving Ch.5/p22)

Of interesting empirical note, from Wienke BUBBLE MODELS AND DECOMPRESSION COMPUTATIONS:
A REVIEW p.34:

Quote:
To track gas transfer across bubble boundaries, we need mass transport coefficients . . . Table 4 lists [mass transport coefficients] for the same lipid-aqueous surfaces, using Eisenberg [28], Frenkel [33], and Bennett and Elliot [10]

Table 4. RGBM Mass Transfer Coefficients. . .

Gas (μm2/sec fsw)
Ne 10.1 × 10−6
He 18.4 × 10−6
Ar 40.7 × 10−6
O2 41.3 × 10−6
N2 56.9 × 10−6
H2 72.5 × 10−6

Notice that helium has a low mass transport coefficient, some 3 times smaller than nitrogen.
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Helium offgassing rate

From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:

Quote:
Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.

Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.
RGBM_Eanx32_Helitrox_NDL.pdf
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Re-posting & quoting Joel Silverstein's (an old bold & bald NE Wreckdiver) anecdote post on extreme PO2 Exposure: