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Hose Routing for Twin Tanks

posted Mar 4, 2012, 12:07 AM by Derek Quek   [ updated Jul 22, 2013, 2:52 AM ]

In technical and extended range diving, twin tank sets are used to provide not only additional gas for longer bottom time, but also redundancy in case of failures in the gas supply system.

Hose Routing Considerations

Considerations for your hose configuration will determine what kind of functionality will be available during failure of one or more points in the gas delivery system. Here are some key points that a diver should consider:

  • Primary and secondary regulators should come from different 1st stages to cater for 1st stage failure. If there is a BCD and drysuit inflator, they should similarly be on different 1st stages.
  • Most important connections should be connected to the right post: a ceiling rub/roll-off will turn the tank valve toward the “on” position, in the worst case, breaking the knob and resulting in a full on position. These connections would be the primary 2nd stage and the BCD inflator.
  • The lesser important connections would go to the left post. This would be the secondary 2nd stage and the SPG, and drysuit inflator.
  • Minimise hose ‘cross-overs’ where possible.
  • Minimise hoses sticking out of your profile as this increases risk of snagging onto coral, wreck, etc. Hoses leading downward from the 1st stage are ideal.
  • A team-wide standardised hose configuration will make it easier for a buddy to spot problems or render assistance.

Suggested hose lengths

Back Gas:
Primary reg 7ft/210cm
Secondary Reg 24"/60cm (22" ideal for singles*)
SP Gauge 24"/60cm (22" ideal for twins*)
BCD inflator 24"/60cm (22" ideal for singles*)
*Although shorter hoses may be ideal in some configurations, but a negligible extra 2 inches would provide better flexibility between single and twins configurations.

Stage:
SP Gauge 6"/15cm
Primary reg 39"/100m *
*This reg length allows the hose to route around your neck to reduce front clutter during travel/deco.

Based on the above considerations, the diagram on the right offers some suggested hose connection configurations for Apeks first stages.

Primary Lights

posted Mar 4, 2012, 12:06 AM by Derek Quek

What is it?

The primary light has one major purpose: communication. Beyond that, it also provides illumination in dark environments, from night diving to overheads, such as cave and wreck. Finally, it assists in bringing the colors to light, depending on the technology.

Why should I have one?

A primary light is one of the most indispensable pieces of gear because it allows the team to stay together with much greater ease and safety. Instead of being constrained to visual contact of the divers, the primary light allows a diver to broadcast their presence over greater distances. Now, instead of having to look for the diver, a teammate can simply look for the light beam or spot. And that makes all the difference in the world when it comes to smoother buddy diving.

What are the important characteristics?

As the primary role of the light is communication, it needs a few basic requirements.

1) Bright focused spot light

2) Dive time appropriate for planned dive

3) Enough power to illuminate area and cut through murky water.

4) Usable in either hand, with some facility to allow use of hands with light

Some nice to haves:

1) Light weight design for hand-holding

2) Easy attachment points

With that said, you have a huge catalog of choices to ponder.

HID vs. Halogen

In the early days of lighting, halogen reigned supreme. It's durable, low cost, and can powerful enough for most environments. It does not, however, have an accurate white color temperature, taking on much more orange cast to its light. It also is not a very efficient power source, requiring large amounts of battery capacity.

HID is much more efficient, allowing a much longer burn time as compared to halogen. It also is much brighter, roughly 5x the brightness for an equivalent watt halogen bulb. Finally, it's much whiter, making for better video lighting and easier to see. However it also has it's drawbacks, namely cost. Along with being 5X as bright, the bulb is also 5X as much. And as it is a much more complex technology, it is more complicated, requiring ballasts to regulate voltages to go along with those gas-filled bulbs. It requires a greater degree of care and maintenance when compared to the beater halogen lights.

Clearly, HID is the winner in current lighting trends, but it would be nice to get back some of the qualities of the halogen. . .

Lead Acid vs. NiMH

Traditional, power was provided by lead acid batteries, the same that power cars, motorcycles, and more throughout the world. As with halogen, the main benefits are cost and reliability. The sealed lead-acid battery pack is maintenance-free, in the sense that all you have to do is charge it. Memory effect is minimal, if you maintain the charging cycle on the battery, and the battery charges equally as per the voltage. The main drawback is weight: the lead in the lead-acid is obviously dense metal. Along with the weight, the packs are bulky, requiring larger canisters for the larger batteries.

NIckel Metal Hydride batteries are new on the scene, and possess some great qualities, namely lighter weight and greater capacity. My Pro-14 amp battery pack weighed in at ~12"+ long, and about 18 lbs out of the water. Meanwhile, the Helios 13.5 amp battery pack is roughly half the size. The main drawback is fragility, as the individual cells of the battery packs are not as sturdy as their lead-acid counterparts. Furthermore, the more complicated design of some packs has lead to some charging issues. But with that in mind, Nickel Metal Hydride offers a usable alternative.

Which One Should I Get??

WIth all that said, the choice of a primary light is up to you. Many primary lights possess the basic characteristics that make the light most practical.

Light Beam

The light beam should be focusable to allow for the beam size to be adjusted to provide the best spot in all conditions. Barring that, a fixed focus of reasonable size may also be used, provided the spot is bright enough for easy signaling.

Light Head

The light is best when compact with a Goodman handle of some variety. The smaller the head, the more easily it disappears on your hand. Lights with larger ballasts, namely 18 watt and higher, often interfere with dry glove rings, but most don't mind with the increased light. The goodman handle provides an easy way for the light head to remain on your hand, yet still allow you to perform tasks, such as putting in your backup, adjusting your buoyancy, etc. The Goodman handle is best when adjustable, as you ought to be able to open you hand, and not have the light head slip off. Finally, it ought to provide a simple means to attach bolt snaps or loops, to allow for easy stowage when broken/not in use.

Light Cord

The light cord allows the battery to be carried on the waist, reducing the weight of the light head, and reducing the dynamic instability that would be caused by swinging that battery around on your hand. It also means that you won't lose your light head when it inevitably falls off your hand. It should be long enough to travel from the canister to the left hand with a minimum of tension.

Canister

The canister ought to mount out of the way, and in easy reach. It must also be removable to allow for ditchable weight. Traditional location is on the right side of the waist belt, where the lack of fixed buckle allows easy ditching, and where it can conveniently hold your long hose in place as well. A second buckle can be used to keep the canister in place, which facilitates getting out of the harness in the water (such as is required for smaller boats, etc.)

With these initial characteristics sorted, which one should you get???

Get the brightest light you can afford, but be realistic about your needs, especially when it comes to burn time. If you're just starting out, a dive longer than 2 hours is not a reasonable need. If you go with lead acid technology, it is reasonably affordable to purchase a 2nd battery that can be switched between dives. The smaller lead acid canisters are a nice alternative to the pricier NIMH

If you have the scratch, a NiMH battery is very very sexy, with the small size and ease of transportation. I would recommend the 9 amp version, as the increased length makes for simpler storing of the long hose. Just mind the charging issue (which can be remedied by unplugging/ replugging the battery every time you see the charger on the green light is a cheap (albeit annoying) fix. The 4.5 amp version provides 4 hours of burn with a 10 watt head, and is free of the charging issue.

How Do I Rig It?

For non-use, i.e. getting on and off the boat, the light should be stored in the up position, meaning the bulb facing toward the head of the diver. This provides the most protection for the light head, and also keeps the diver relatively streamlined, preventing a dangling light head from entangling in line, etc. IT SHOULD NEVER BE CLIPPED IN THE UP POSITION WHILE THE LIGHT IS ON! That ought to do it. ..

When on, the light should be clipped in a downward direction. This is accomplished via an attachment point at the back of the light. It allows you to illuminate what you may be doing below you, but more importantly, it prevents you from blinding (or "welding) or your buddies as you would if you clipped off with the light facing forward. This can be done for SMB deployment, stage switches, note taking, or any reason. It also allows you to have your light on during ascent, leaving it available for signaling your buddies should you need to, yet prevents you from welding them during deco. It also may draw up curious creatures from the deep, either mola mola's (good) or great whites (bad).

Attachment

There are many different methods to attaching your light. Perhaps the first thing to remember is who will be affected by the way your light is clipped off: you. I hope that my buddy isn't so inept as to allow my light head rigging technique to affect his ability in the water. With that key point in mind, there are many variations.

1) Dual bolt snaps

I used this for many moons, but then realized that I would never use both attachment points at the same time. I kept getting line caught on it, and it made my light head look like a fishing jig. So while it was very easy to access either attachment point, it was a bit of overkill, and not very streamlined.

2) One bungee loop, and one bolt snap

The logic behind this was that removing the bolt snap from the front end allowed for more streamlined use, as you didn't get that "jingle bells" effect when signaling. It, however, allowed for simple clipping with the fixed bolt snap on the rear. Meanwhile, a small bungee loop attached by cave line allowed me to use a double ender to secure the front of the light. When in use, I could remove the double ender for nice free front end. I liked this method, but not as much as the next.

3) Two bungee loops, one double ender.

Two loops are attached to the light head: one in front, and one in rear. This allows you to use one double ender for attachment at either end. Use the front loop for stowage, use the rear loop for clipping while the light is on. Usually, I get in, unclip and activate the light, and then attach the double ender to the rear loop. It's now ready for clipping for 95% of the tasks I'd need to clip for during the dive, as my light will be on for the majority of the dive. When it comes time to turn the light off, I'm most likely in a non-stressful situation where I can use both hands to move the double-ender to the front loop. The only drawback to this system is the fact that the light hangs lower than it would with a bolt snap, but it's minimal interference when compared to the versatility and ease of use.

Regardless of which method you choose, realize that you need some forethought into how you use it. More important is to remember that you need to prevent blinding your buddies, so use the appropriate attachment points.

How Do I Use It?

Entire volumes could (and should) be written on the proper and non-annoying use of primary lights. But that's another topic for another EE. For now, keep the light out of your buddies' eyes, but keep it where they can see it. Try and keep it as steady as possible to avoid throwing odd light signals. And make your light signals slow and obvious, with exception of "emergency" which ought to be fast and obvious. The more distinction you can make between the two, the better you'll be understood.

How do I maintain it?

Check the sealing surfaces pre-dive. Always check the battery post-dive as any leak will be worse if you just leave it in your bucket. As always, rinse with fresh water post diving. Be sure to get the lead-acid batteries on a charge as soon as reasonably possible to prevent any long term memory issues. When not in use for an extended period of time, just leave on the charger. Perform a burn test every 6 months or so to monitor condition of the battery, and also to prevent any nasty surprises when you're three jumps into a cave, and have to come crawling out at night on a backup light with the ranger peeking over the edge, wondering why you're keeping him from steak dinner.

If any issues appear, first check to make sure the battery is charged. Be careful opening up the light; while not rocket science, it makes it harder to get the manufacturer to fix a flaw if you've gone mucking around inside.

Credits for this article go to the X-Forum at:

http://www.5thd-x.com/xducation/xeducindex.html

Apeks O-rings

posted Mar 4, 2012, 12:05 AM by Derek Quek

This article lists the O-Rings used for servicing Apeks regulators for the following models:

* First stages: US4, DS4, UST, DST, FST(ATX100), FSR(ATX200) 
* Second stages: T20, TX40/50/100/200, AT20, ATX40/50/100/200

Only o-ring are listed here. Additional parts such as diaphrams and seats are not listed here.

Material

There are several common materials used for SCUBA o-rings.

MaterialDescription
Acrylonitrile-Butadine Copolymers
(NBR, Nitrile or Bunan) 'N'
Most O-rings used in SCUBA are made from Nitrile, a hydrocarbon based synthetic rubber. Nitrile offers excellent resistance to many oils and acids and has good physical properties. However, Nitrile is not a very oxygen resistant material and is not considered oxygen compatible. Nitrile is also often referred to as Buna-N.
Fluorocarbon Elastomers
(FKM or Viton Fluorel) 'V'
O-rings made of FKM are more costly but are a preferred choice for oxygen and nitrox compatibility in SCUBA diving applications. FKM is an elastomer with excellent oil and oxygen resistance at high and low temperatures, very good chemical resistance. Even for use with ordinary air, most experts agree that FKM O-rings outperform common Nitrile O-rings. Viton is DuPont Dow's brand name for FKM. FKM has a higher heat tolerance, but emits a highly toxic gas if combusted.
Ethylene Propylene Diene Monomer
(EPDM) 'E'
EPDM O-rings are becoming more common in SCUBA because some people feel it's a safer material for use in breathing air systems. EPDM is a elastomer with excellent weatherability, heat resistance, dielectric qualities and odor-free characteristics. EPDM is not recommended for use with petroleum derivatives.

Starting from 2001, Apeks o-rings are based on EPDM with a hardness rating of 80 Shore-A.

Size 

Most scuba o-rings are based on imperial British Standards (BS) using a three-digit identifier. The first digit denotes the O-ring cross section width: 0xx = 1/16-inch, 1xx = 3/32-inch, 2xx = 1/8-inch. The other 2 digits are used to reference the diameter of the o-ring.


Apeks IDBSCross SectionInner diam.SCUBA Application Seal
-0031/161/16High-Pressure Hose/SPG swivel
AP64030041/165/64High-Pressure Hose/SPG swivel (less common)
AP12990061/161/8Apeks HP seat (1st stage)
AP11540101/161/4Low-Pressure Hose/2nd Stage Regulator
Cylinder Valve Stem
Apeks crown (2nd stage)
AP14090111/165/16Standard Low-Pressure Port/Hose (3/8 UNF)
Apeks adjusting screw (2nd stage)
Apeks conical filter (1st Stage)
Apeks FSR HP crown (1st stage)
Power Inflator quick disconnect oring
AP14450121/163/8High-Pressure Port/Hose (7/16 UNF)
Manifold and Manifold Port Plugs
AP14100131/167/16Large Low-Pressure Port/Hose (1/2 UNF)
Apeks balance plug inner (1st stage)
AP11590141/161/2Standard Yoke Regulator/K-valve
Apeks ATX adjuster screw (2nd stage)
AP12670151/169/16Apeks value spindle (2nd stage)
Cylinder Valve Bonnet Nut
AP14380191/1613/16Apeks Venturi (2nd stage)
Apeks turret bolt (1st stage)
AP14200241/161-1/8Apeks Turret (1st stage)
AP11661113/327/16Apeks DIN Regulator/Valve
Apeks Yoke spare (2nd stage)
Note:Yoke valves often use BS112 or BS014
-2141/81Cylinder with Large Neck/Valve
(3/4 NPS - All Aluminum, most Steel cylinders)
AP20412x1(606)1mm2mmApeks shuttle valve (2nd stage)
AP57112.5x1 (607)1mm2.5mmApeks ATX adjuster screw nib (2nd stage)
AP130015x1.51.5mm15mmApeks HP balance plug outer (1st stage)
-0062.9mm1.78mmPower Inflator spindle (Polyurethane)
-0121/163/8Power Inflator cylinder inner oring (Buna)
-1123/321/2Power Inflator cylinder outer oring (Buna)
-2041/83/8Power Inflator oral inflate oring (Buna)
Adjustments, servicing, disassembly and assembly of scuba equipment should be performed only by individuals who have attained appropriate training and certification by the equipment manufacturer.

Diving Accident at Indian Springs

posted Mar 4, 2012, 12:03 AM by Derek Quek

by Bill Gavin

There's a lot of talk these days about the need for experience in conducting technical dives without an real clarification of what being an "experienced diver" really means. Some equate it to an individual's years in diving. Others equate it to the number and types of dives the conducted or certifications earned. Ultimately perhaps it is a measure of a diver's ability to function effectively under pressure when everything goes wrong.

When Bill Gavin's account of the freak accident that resulted in Parker Turner's death first appeared in the NACD Journal (Vol.23 No. 4, 4th Qt. 1991) it caused a number of us to reexamine our own experience in light of the test that was put to Gavin and Parker. Their skill and experience as a team was probably the only thing that prevented this tradegy from turning into a double fatality.

This article has now become a part of the training manual at the Key West Technical Diving Center and is required reading for everyone beginning a gas course. How do you rate something as elusive as experience?

This is an account of the diving accident at Indian Springs on November 17, 1991, that resulted in the death of Parker Turner. It is an account of the experiences of the dive team and not of the surface personnel or support divers that were present that day. That information is included in a separate report.

Our dive at Indian Springs was the first in a series of exploration dives that had been in the planning stages for nearly two years. Because of the unique profile of the cave and the extreme depth at the point at which actual exploration would take place special decompression tables had been generated by Dr. R.W. Hamilton. The dive plan consisted of a 40 minute transit at 140 FSW while breathing an EAN 27 travel mix (27% oxygen, balance nitrogen), a descent and exploration at 300 FSW using trimix 14/44 (14% O2, 44% He, balance N2) followed by the return 40 minute transit to exit the cave. The deep working phase of the dive was expected to last 20 to 25 minutes. The 140 FSW penetration and exit was done using two 80 cubic feet "stage" bottles, while the deep portion was accomplished using back mounted double 104's.

The dive went almost exactly according to plan during the penetration. The deep section known as "Wakulla Room" was explored in three different directions. None of these yielded any going tunnel or evidence of flow. We began our exit at 63 minutes into the dive. At this time I had 2300 psig in my double 104's and I assume that Parker had the same or slightly less. We reached our nitrox bottles at the top of the room in two to three minutes, began breathing them, and did not use our doubles again until we encountered the obstruction at what is known as the "Squaws Restriction." After picking up our second stage bottle during the exit, Parker signalled that his Diver Propulsion Vehicle seemed to be running slow. We linked up via a tow strap and I increased the speed setting on my DPV to maximum. We were only about 1500 feet from the entrance, so this did not present a serious problem.

There is a distinctive arrow marker at the upstream/downstream junction which is about 500 feet from the entrance. As this arrow came into view, I remember estimating that our bottom time was going to be somewhere between 105 to 110 minutes. We made the left turn at this arrow and immediately noticed that the visibility in the cave had decreased. The floor was completely obscured by billowing clouds of silt, but the line was still in clear water near the ceiling. As we got closer to the entrance, the visibility got progressively worse. Finally, we had to stop using the DPV and swim while maintaining physical line contact. When we got to where I thought the restriction should be, the line disappeared into the sand on the bottom of the cave. We began pulling the line out of the sand, but some reached a point where it was buried too deep. Visibility in this area was 1 foot or less. I heard Parker shout into his regulator, "What's this?" We backed up out of the low area and removed our stage bottles and scooters. At about this time, the second bottle that I had been breathing during the exit ran out. Realizing that the situation was not going to be quickly resolved, I elected to switch immediately to my doubles, which still had about 2000 psig of gas. There were two lines running parallel in the cave at this point. We tried following both of them, but each time got to a point where the line could not be pulled from the sand which had covered it.

I secured the line from the reel that we had carried with us to the end of the permanent line (where it was buried) and tried to search for a way out. The restriction seemed to be completely blocked with sand and perhaps rock. The visibility was so bad that we could not really figure out exactly where we were or what had happened. However, there was flow and I tried to follow that. After finding no way past the blockage, I began to have doubts about our exact location. It seemed as though we must have made some mistake. While Parker continued to search, I swam about 300 feet back into the cave until I saw the upstream/downstream arrow marker. Though this marker is quite distinctive, I had to stare at it for a few seconds to convince myself that I really knew where we were. I swam back to the point where we had left our bottles and scooters. Parker was waiting there.

I am not sure how many attempts we made to retrieve the buried line, but at least 45 minutes passed while we sought in vain for some way out. At one point Parker showed me his pressure gauge which indicated about 400 psig of gas remaining in his doubles. He wrote on his slate, "What do we do?" I knew he was hoping I had some idea, but the only thing I could think to write back was "Hold on. I'll go look."

I went back to search using my reel and sweeping left and right. Finding no exit, I decided to return to the stage bottles, which at least had a little more gas to offer. I had been gone for less than five minutes. When I returned to the bottles, Parker was not there. I found my second stage bottle, which had about 600 psig left in it. I began breathing it while trying to think of some plan. After about four minutes it ran out and I switched back to my doubles, which now had less than 300 psig of gas. With no other alternative, I decided to try one last effort at finding an opening. As I started back out I saw that another line had be "Tee'd" into the permanent line. I followed it without really understanding how it had gotten there. I reached a point at which the cave seemed to open up and saw something hanging down on the edge of my vision. As I swam under the object it dimly occurred to me that it was the second stage of a scuba regulator. By now my doubles were almost empty and my regulator caught on my manifold as I passed. I rolled to my left to free it. At this point, I looked up and saw the permanent line rising at a sharp angle. I realized that I had cleared the restriction and raced to our decompression bottles, which were hung at 100 feet. I was almost holding my breath by the time I unclipped the second stage and began breathing from my first decompression bottle. Parker was not at the bottles and I realized at this time that he had drowned.

The regulator that had caught on my manifold was from his doubles, which he had removed and dragged through the small opening. I had no idea where Parker was and the visibility was still less than two feet. Numbly, I waited for support personnel to find me. In the confusion that followed, many lines were laid throughout the cavern area by our support divers in attempt to locate Parker's body. Despite their efforts, he was not found until the following morning when visibility had increased to about 10 feet. It had been 60 feet or better when we started our dive.

During the four hours of decompression that followed, I was gradually filled in on the situation by our support crew. Without their efforts, I think I would have gone mad wondering what had happened. For a long time I did not know if the entire entrance to the cave had collapsed or if anyone else was missing. I also had no idea what kind of decompression to follow. Though I fully expected to suffer decompression sickness, I emerged from the water with no physical damage. Apparently the fact that we had been shallower than expected during our deep exploration saved me from that malady.

After going over the incident countless times we were able to deduce what probably happened during those last minutes. While waiting for me, Parker must have decided to take his tanks off and try to squeeze through the blockage. Running short on gas, he probably decided that he couldn't wait any longer. He Tee'd in his safety spool and, dragging his tanks, was able to find a way through the blockage. Perhaps in doing so he caused the sand to shift enough that I was able to pass through a few minutes later with my doubles still on. After making it through the restriction he ran out of gas just 30 feet short of our decompression tanks. When he passed out, he dropped his doubles and floated to the ceiling about 15 to 20 feet above. His tanks landed on the permanent line and hung there. The line from the safety spool was tangled around his tanks. Whether this contributed to his death is impossible to say. Certainly it would have been difficult to lay line while dragging tanks and fighting extreme positive buoyancy from his drysuit. Miraculously, this combination of events, the line tangling on his tanks which then caught on the permanent line, placed the line from his spool in the only location large enough for a diver in doubles to squeeze through. I believe that even a one minute delay in my exit would have been enough to prevent me from ever reaching the decompression bottles.

It is still a mystery as to what caused the collapse at Indian. The actual physical event was that an unstable debris slope slid downhill filling the small restriction with sand. At about the same time, surface personnel witnessed a drop in the water level in the basin of approximately one foot, and a reversal of the spring run leaving Indian. Within 30 minutes, the water had dropped and returned to its normal level. Perhaps 100,000 gallons of water has rushed into the cave and several tons of sand had moved downhill several yards. The rush of water into the cave was great enough both in magnitude and duration to affect visibility 500 feet from the entrance.

I will not attempt to describe the effect this accident has had on myself or Parker's many friends and family. To say that we have lost a good friend, that we will miss him, that his place in our lives can never be filled is all true and also inadequate. Grief is a personal emotion, difficult to completely comprehend, and for me, not easily shared. To the many friends that have helped me through this, I offer a thanks the depth of which only they can understand. In all times to follow, whether diving together or in moments shared on other pursuits or when far apart, I will not forget any of you.

Bill Gavin is a veteran cave explorer and one of the individuals responsible for pioneering the use of mix technology in cave diving. He can be contacted at: 2113 Pebble Beach Blvd, Panama City, FL 32407. 


Re-published on 16 Oct 2007 with kind permission from the National Association for Cave Diving committee. 

This article should not be quoted or copied without prior permission from the National Association for Cave Diving.

Exercise and Diving

posted Mar 3, 2012, 8:54 PM by Derek Quek

Dave Chamberlin's post:

After chowing down on some donuts, pastries, cheeses and other goodies provided by the GUE conference organizers, I headed in to the conference room and sat down next to one of the numerous bowls of candies, also courtesy of the conference. And thus began the lecture on "fitness and diving". :-)

The over-riding theme I gleaned from the various lectures on fitness was that it definitely does not pay to be a rat - at least not one involved in DCS studies. :-)

The benefits of fitness on reducing decompression were well-covered by all the speakers. Cameron's book and the wealth of e-mails he and others have written in the past cover the topic rather thoroughly so I won't go in much detail here. I'll cover a few quick points though.

There was a study done whereby they compared both mice and pigs that trained on a tread-mill for 2 weeks prior to an aggressive decompression event. In the case of the mice, the treadmill mice experienced a 40% incidence of DCS whereas the control group experienced an 80% incidence. The results with the pigs were very similar, with 42% for the treadmill pigs and 74% for the control group.

Clearly this did not have much to do with body composition as that did not change much in the short period of training time, nor were the animals high in body fat to begin with. At this point GI chimed in that the primary reason for this is likely the exercise within 24 hours of diving, not that they had been training for 2 weeks.

He continued, saying that the Navy found that there was an enzyme release that reduces bubble nuclei generation. As it turns out, the slides presented later confirmed what GI had said. Note that the bubble nuclei generation tied in with Erik Baker's decompression lecture later.

There were 2 interesting points on the exercise-before-diving topic.

  1. The exercise had to be within 20 hours of diving to provide the beneficial effect.
  2. If the exercise is within 30 minutes of diving, not only does it not provide any benefits, but it actually *negates* the benefits of exercising within 20 hours.

I didn't hear any theories to explain the latter effect. I wonder if the exercise ends up creating more bubble nuclei through cavitation and/or mechanical stresses and the extra nuclei cancel out the beneficial effects of the enzyme release? Anyway, it'd be interesting to hear about more studies on this.

With exercise after diving, they found that weight lifting more than doubled the cases of DCS. The results for low-impact, aerobic exercise was less conclusive. But clearly weight-bearing exercise after diving is a bad idea - keep that in mind when climbing onto the boat in full gear after doing a deep dive ....

There were also some studies done on exercise *during* diving. With moderate exercise (swimming) at depth, it took almost 3 times the amount of decompression to eliminate cases of DCS. The rationale given for this is that the exercise increases the perfusion to the tissues and thus increases the gas burden in the tissues.

There was another study that looked at exercise during decompression. What they found was with moderate-light exercise during decompression, on a 100FSW dive they were able to decrease the length of decompression without affecting the number of DCS cases. On the same test to 150FSW they were able to reduce the length of decompression even further. Again, the rationale relates to perfusion of the tissues. The increased activity during decompression increases the perfusion, facilitating offgassing.

Thus the ideal would be very little activity during the dive and then light activity during decompression. If they had put the scooter workshop right after this lecture, one might have argued that it was partly a sales pitch. :-)

Note that in another lecture, a similar effect was shown but with temperature. Being warm during the dive, then cold during decompression greatly reduces the efficacy of the decompression. Reversing that and being cold during the dive and warm during decompression has the opposite (desirable) effect. Reinhard and Michael commented that this is the reason they do not turn on their heated undergarments during the dive - they only turn them on during decompression.

And just to tie back to the comment about Erik's talk and bubble nuclei ... Erik pointed out that creating bubbles in a liquid is actually pretty difficult purely through pressure differentials. Thus there must be a reason that bubbles are created much more easily in the body. David Yount found that under normal conditions there are surfactants in the blood and tissue.

Surfactants are molecules which are called "amphiphiles" which means they are hydrophilic on one side and hydrophobic on the other. As a result, they tend to clump together, forming a surface between fluid an air - which means they will in essence create bubbles (and in fact it's the surfactants that keep the bubbles from collapsing).

These little bubbles become nuclei for larger bubble formation with pressure differentials. Thus the presence/absence of the bubble nuclei has a very large effect on the number of bubbles that are generated during decompression.

Some studies that NASA did researching decompression when going into space showed that if you increase pressure first before dropping it, bubbles were less likely to form. The theory is that a number of the bubble nuclei get crushed during the inital pressure increase and thus the number of bubble nuclei present during decompression is reduced, reducing the likelihood of bubble formation.

-Dave

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