Thursday, August 30, 2012

Air Breaks… what are they, and do people take them for the wrong reason?

Thanks to doppler and his Tech Diving Blog

I find the concept of taking air breaks to manage oxygen toxicity while decompressing comparable to using a paper towel to mop up an incoming tide at the beach. Or put another way, air breaks in this context are about as useful as ashtrays on a motorcycle.

Allow me to explain. I believe oxygen toxicity is one of the biggest risks to recreational divers, especially technical divers, but air-breaks as commonly described and executed, are no substitute for proper CNS planning… and are useless as a CNS management tool in any event.

The first time I remember hearing the term air-breaks was in a conversation with a hyperbaric doctor over a bottle of wine and a grilled fish supper some years back. The context was a discussion about the practice of getting hyperbaric chamber patients on air after 20-minute spells breathing pure oxygen at a “dry depth” of 18 metres (60 feet). Of course, this therapy – part of the procedures called for in the US Navy Diving Manual – delivers an oxygen partial pressure of 2.8 bar, well in excess of the 1.6 bar recommended as a maximum for recreational divers… technical or otherwise. I have no clue how or who decided that this term was the right one to use to describe the practice of switching to a low-oxygen content gas after breathing oxygen during staged decompression stops in the water. Nor can I fathom what it can possibly have to do with managing central nervous system (or pulmonary toxicity, gods forbid) while recreational diving.

Oxygen toxicity is a condition resulting from the harmful effects of breathing oxygen at elevated partial pressures. The most serious form of oxygen toxicity has the potential to affect a diver’s central nervous system and is a result of breathing very high-partial pressures (more than one bar or atmosphere) for a relatively short period of time (less than a few minutes at extreme levels). This type of toxicity may result in a clonic-tonic seizure; which in the water usually means death by embolism or drowning. Historically, this central nervous system condition was called the Paul Bert effect. The less problematic whole-body or pulmonary condition – a function of breathing lower partial pressures (less than one bar) over much longer periods – goes under the name the Lorrain Smith Effect, after the researchers who pioneered its discovery and description in the late 19th century.

I have heard and read that divers manage both Paul Bert and even Lorrain Smith effects by taking a short “air-break” during moderately long decompressions. The typical scenario is this: A diver conducts a deep or deepish dive which earns her a lengthy series of staged decompression stops on her way back to the surface. She finishes her dive by breathing pure oxygen at 6 metres on up. In this scenario, the decompression schedule requires the diver to breathe oxygen for around 20 minutes. There are a pile of variations on this theme, but the common thread is a fair amount of time breathing a gas that is delivering around 1.6 bar of oxygen… by the way, the NOAA limit for exposure to 1.6 bar of oxygen for a diver is 45 minutes, so this type of exposure does load a diver with the potential for a CNS incident… there is no argument there.

The “air-break” myth goes something like this. At some point during her spell breathing pure oxygen – sometimes at the end and sometime mid-stream – the diver will “RESET” her CNS “clock” by switching from breathing oxygen to breathing bottom mix, air, a less oxygen-rich nitrox (typically the mix she was breathing during her ascent to her final stops). Let’s illustrate the air-break protocol with a dive profile calling for a final decompression stop for 21 minutes at six metres or 20 feet. In this example, the diver might use oxygen for ten minutes, and then switch to say an EAN50 for five minutes, and finally switch back to oxygen for eleven minutes to finish up their deco. Typically, as in this example, the time spent on an “air-break” is not credited against the decompression obligation.

What I have yet to hear fully explained is how a five-minute break from breathing pure O2 resets a diver’s CNS loading during this procedure. Actually, you may also read postings from divers who rely on the same technique to manage Lorrain Smith effect, which shows an even greater misinterpretation of the mechanism behind the syndrome*.

OK, let’s take a step back and turn on the logic filter. According to NOAA – the folks who literally set the standards for nitrox use in the recreational dive community – a period of 20 minutes breathing oxygen at 6 metres – a practice that delivers a partial pressure or oxygen depth of around 1.6 bar/ata – has a corresponding time limit of 45 minutes. When we calculate the CNS loading for a dive, we are taught to account for the CNS loading for ALL phases of the dive. That’s to say, every minute spent breathing elevated levels of oxygen. Let’s ignore whatever came before during our example dive, and let us just focus on what happens at six metres or 20 feet. In a nutshell: The diver has to account for 20 minutes on pure oxygen. The NOAA tables don’t give a rat’s behind whether those 20 minutes are accumulated in one lump or two… or three or four. Twenty minutes is 20 minutes and uses up about 44-45 percent of the total allowable time regardless! The five minutes breathing another gas – in our example we can say she used EAN50 delivering an oxygen partial pressure of about 0.8 bar – simply adds a little to the total CNS loading, albeit a very tiny about (less than one percent). There is nothing in the NOAA dive manual or any of Hamilton’s published work that tells us anything different.

Now, to set the record straight, faced with the situation outlined above and breathing pure oxygen for that long, the chances are that I would take an air-break and recommend taking one to my team-mates; however, it has NOTHING to do with CNS but rather to help optimize off-gassing.

Oxygen is a vasoconstrictor – it causes some blood vessels to shut or partially shut – which may have some effect on general perfusion levels. This does not seem like a great plan for those of us trying to eliminate dissolved inert gas.
The bottom line is this: Let’s agree to take a break from pure O2 during our deco, but let’s not confuse the issue by suggesting that doing so magically helps manage CNS toxicity. Better yet, let’s opt to employ a better option and a slightly more helpful gas. But more about that later.

* Prolonged breathing of gas with an Fio2 (Fractional Inspired Oxygen) greater than 60 kPa (0.6 bar/ata)can lead to pulmonary toxicity and eventually irreversible pulmonary fibrosis, but this takes many hours or days and does not constitute an issue for the rank and file technical diver. Most likely, the “burning” sensation and pulmonary toxicity like symptoms mentioned by technical divers breathing oxygen and oxygen-rich gas during recreational decompression is a function of breathing cold, dry air (the dew-point of oxygen in the cylinders in my fill station is marked as -40! That’s dry.) This air has the ability to dry the mucus membranes lining our lungs and bringing on something called dry-air asthma. A less far-fetched probable outcome than pulmonary toxicity.

Kathy Dowsett

Sunday, August 26, 2012

Basic Wreck Diving vs. Advanced Wreck Diving

Divers are often confused between basic and advanced wreck diving certifications and why there is a need for two courses. This is a good question considering a wreck is a wreck and diving is diving. All wrecks present the same risks. The single biggest difference is the diver and what they want to do during their dive on the wreck.

Basic Wreck Diving

Basic wreck dives would consist of swimming around the outside of the wreck, with the occasional peek in the wheelhouse or cargo hold. That does not mean there is not a lot to learn, even though the plan is to stay on the outside, or that there is not a lot to see. For divers wishing to survey the wreck or watch the marine life it attracts, this is the perfect spot. The outside of a wreck is also where we get those dramatic photographs of the bow stabbing towards the surface, hoping to sail again. For the diver wishing to view a piece of history, diving on the wreck can show you what some will only read about or see in pictures. This type of wreck diving has been enjoyed by many and for some divers this is as close as they want to get to a wreck.

The equipment needed for a basic wreck dive is pretty much the same equipment used for any dive. There are some pieces of additional equipment that may come in handy: a large slate for drawing the wreck and noting depths and features, a small reel, and a lift bag or surface marker buoy (SMB) just in case you lose track of the anchor line or get blown off the wreck.

Advanced Wreck Diving

Advanced wreck diving is really an extension of basic wreck diving. Advanced wreck diving starts on the exterior with a survey that familiarizes the diver with how the wreck is oriented: on its keel, on its side, separated into halves or with a twist. No two wrecks are the same and all suffer different damages due to how they sunk, how long their journey was to the bottom or the severity of the storms that have battered them over the years. There are even vertical wrecks and wrecks clinging to the side of walls. Learning how to effectively survey the wreck is an extremely important part of any wreck course. This visual image, is the only thing the diver will have to rely on, since his compass will not work. Even wooden wrecks tend to have massive hunks of metal or boilers, which send the compass into a spin. But here is the point where advanced wreck diving waves goodbye to basic wreck diving; it is where we go beyond “the light zone.”

The light zone is where ambient light enters an overhead area and artificial light is required in order to see. Once a diver enters an area in a wreck where a light is required, the rules of wreck diving change. A diver in this area must have the knowledge and skills they need to go into and come out of a wreck should the worse possible scenario, a complete silt out, occur. In order to do this, divers must know how to use a reel for navigation and how to properly tie off lines so they will not get cut during the dive. But this is also where the fun starts for wreck divers craving to study the more intimate details of the wreck or seeking that hidden artifact that no one else has seen.

Many wreck divers don’t feel they know all there is to know about a wreck until they have explored every room, seen the engines that pushed this once mighty vessel through thousands of nautical miles. There are also those who want to see the artifacts, some still lying in place as if the ship had never sunk. To some, the best part of the wreck dive started before they even entered the water, it was the hours of researching and planning that lead up to the dive. But before a wreck diver can see these sights they need to undergo serious dive training and have an experienced TDI Wreck Instructor explain the safety protocols. Remember that worst case scenario of silting out? For divers who spend their time on the outside of a wreck, this silt would only come from the fin thrust as it hits the bottom or deck of the boat. For divers entering the wreck, this silt comes from above and is called percolation silt, cased by the exhaled bubbles as they dislodge rust, insulation or other debris trapped on the ceiling.

Another big area of difference between basic and advanced wreck diving is the equipment needed. Advanced wreck divers should carry at a minimum two lights a primary and a back-up, two cutting devices, two reels, two lift bags and a redundant air supply. While this may sound like a lot of equipment, a TDI Advanced Wreck Instructor can teach divers where to stow this equipment and still keep very streamlined in the water.

Wrecks have a mysterious calling to many people. Wrecks that occurred due to war or sank because of a violent storm draw divers in, some say this is because it closes that chapter in our lives. Others would go there because they read about it in history books and they wanted to see it firsthand. Whatever the reason, or if you are going to view the wreck from the outside or inside, it is always best to take the course from an instructor who has been there and done it. Sometimes the best lesson learned from a course is not what is in the book or the skills you had to perform, it is merely what you learned by diving with and watching how an experienced instructor handled himself underwater.

Every wreck has a story, even the ones that were sunk intentionally. So do yourself a favor…find out what that story is! Safe diving!

Thanks :::: SDI TDI ERDI

Kathy Dowsett

Tuesday, August 21, 2012

Dive Travel to Malaria-Risk Regions

Fact: The world is full of mosquitoes. Fact: Asia Pacific has a few spots with heavier densities of mosquitoes carrying diseases like dengue fever, encephalitis and, most notably, malaria. Follow these tips and you can decrease the likelihood of contracting malaria.

The easiest way to avoid malaria is to avoid getting bitten by an infected mosquito:

1. Select a resort/live-aboard with screened windows.

2. Wear long sleeves and pants in neutral colours. As an extra precaution, treat clothing with permethrin (e.g., Sawyer Duranon Permethrin Insect Repellent).

3. Stay indoors at dawn and dusk.

4. Wear an appropriate strength DEET repellent (e.g., UltraThon 32%). Picaridin-based repellents also are quite effective and much less irritating to the skin and malodorous than DEET (e.g., Cutter Advanced Aerosol).

5. Avoid scented toiletries.

6. Upon arrival, treat your quarters with bug spray and retreat on a regular basis.

Next, consider taking an antimalarial:

1. The right medication depends upon the area you’re visiting, so check with your doctor.

2. Malarone (atovaquone + proguanil) is among the safest and most effective on the market.

3. Lariam (mefloquine) is also quite effective, but has potential side effects of concern to divers because they are dangerous and may mimic DCI — e.g., dizziness, sensory and motor abnormalities, headache and fatigue.

Thanks to Sport Diver for this information

Kathy Dowsett

Saturday, August 18, 2012

Giant Strides in Underwater Photography

Written by Katy Danca Galli for Scuba Diving

Well, I’m back from the Digital Shootout and am ready and patiently waiting for next year’s event to hurry up and get here. I learned a TON during my week at the Little Cayman Beach Resort with the Backscatter Underwater Video and Photography crew. Here is a list of the most important things I remembered:

Strobe placement should not require a protractor, compass or other mathematical device to figure out. According to Berkley White, position your strobes above and behind the dome port for best results. If you are shooting with a super wide angle lens (like I was) and want to achieve that close focus, wide angle look, keep your strobes the same distance away from your camera as your subject object is from the dome port.

Try losing weight. No, I don’t mean you should run to the nearest Jenny Craig or buy a StairMaster. I mean loose lead weight. I have ALWAYS dived with ten pounds in salt water, and I was down to six by the second day of the Shootout. Try loosing three pounds to start and then go from there.

As I’ve said in my day four blog — FIRE CORAL IS BAD. I went the entire week without a wetsuit, and boy did I live to regret it. If you think the water is too warm for neoprene (like it was for me in Little Cayman), at least wear a skin. It’ll keep down the ouchie factor 100 percent.

Marine creatures are a lot like cats — they are finicky and never do what you want them to do, ever. After spending multiple days trying to chase down all the sea life on Bloody Bay Wall and only managing to chase them away, I learned that the best method is to simply let them come to you. The squid I shot loved my camera strobes and approached to me to investigate. All I did was click the shutter to achieve success.
Lastly, use your shutter speed to control the exposure instead of your aperture. It completely un-complicates things and works like a charm the majority of the time. I realize this is not how many underwater photographers work, but almost every image I shot was exposed properly (so there).

Next year the Backscatter team is heading to Bonaire and sign-up has already begun. Check out for more information and coverage of past events. THANK YOU twenty times over to everyone from the Little Cayman Beach Resort for their amazing accommodations and food, Reef Divers and their awesome dive staff, everyone from Backscatter who helped me immensely and allowed me to join this awesome event, and all of the zany, wonderful people who participated and gave me advice. May the force be with you all and hope to see you next year.

Kathy Dowsett

Monday, August 13, 2012

Why hammerhead sharks have such funny heads

There are more than 360 species of sharks: Big ones, wee ones, aggressive ones, sweet ones, sleek ones, and …really awkward-looking ones — specifically, the nine species of hammerhead sharks. The scientific genus name of hammerhead sharks is Sphyma, which comes from the Greek word for hammer. And hammer it does resemble. Unlike the aerodynamic streamlined heads of most sharks, the hammerhead has a big clunky head that appears to be at odds with the rest of its body, like a showgirl with an extra-cumbersome headpiece.

Although sharks are fish (rather than marine mammals), they give birth to live young rather than hatching eggs. If you’re wondering about the physical logistics of the hammerhead in this scenario, take solace in knowing that when the pups are born, their heads are round. It’s not until they reach maturity that the hammer-shaped head is in full swing.

The question is: Why, in all of her infinite wisdom, would Mother Nature lead an animal down such a curious evolutionary path?

Well, these are sharks we’re talking about, so it’s little surprise that the answer has to do with finding prey. Hammerhead sharks are voracious predators and their mallet-shaped heads boost their ability to find that which they like to eat. The wide expanse of head allows for a broader spread of highly specialized sensory organs that they use to find food. And beyond smell and vision, these sensory organs are rather high-tech. The "ampullae of Lorenzini" group of organs allows the stealth hunters to detect electrical fields created by prey. The hammerhead's increased ampullae sensitivity helps it track down its favorite meal, stingrays, which are usually hidden under the sand.

In addition, that funny wide head allows for very special placement of the eyes which results in — as counterintuitive as it may seem — outstanding binocular vision. The position of the eyes also allows the sharks to see above and below them at all times. In the meantime, by moving their head sideways as they swim, they can observe much of what is behind them. All the better to help find those stingrays.

And once they find dinner, hammerheads use that brute head to pin the stingray to the seafloor for the kill.

The largest of the hammerhead species can grow to be up to 20 feet in length, although more commonly they are relatively small. They have few predators and are considered harmless to humans. For the stingrays, it’s another story.

thanks to mother nature network

Kathy Dowsett

Friday, August 3, 2012

The Survival of the Sea Turtle :: Video

Watch the miraculous journey of infant sea turtles as these tiny animals run the gauntlet of predators and harsh conditions. Then, in numbers, see how human behavior has made their tough lives even more challenging.

Lesson by Scott Gass, animation by Veronica Wallenberg and Johan Sonestedt.

Thanks to TedEd

Kathy Dowsett