Decompression Sickness vs Nitrogen Narcosis - What's the Difference?

Both Are Caused By Nitrogen, So What Is the Difference?:

During the open water certification course, student divers learn about both nitrogen narcosis and decompression sickness. I have noticed that students tend to get the two conditions confused because both decompression sickness and nitrogen narcosis are caused by nitrogen gas. Nitrogen narcosis and decompression sickness have very different symptoms and must be treated in very different ways.

What Is Nitrogen Narcosis?:

Nitrogen narcosis is an altered state of awareness caused by breathing a high partial pressure (or concentration) of nitrogen. The deeper a diver goes, the greater the partial pressure of nitrogen, and the stronger the diver's narcosis will be. Some divers have compared the feeling of nitrogen narcosis to being pleasantly drunk, while others find it terrifying. Nitrogen narcosis is one of the factors that will limit how deep a you can dive.

What Is Decompression Sickness?:

Decompression sickness is a physical condition caused by the formation of nitrogen bubbles in a diver's blood and tissues. Although they are generally quite tiny, these nitrogen bubbles can block blood flow to various parts of the body and may irreversibly damage tissues.

The Differences Between the Nitrogen Narcosis and Decompression Sickness::

1. The Causes of Nitrogen Narcosis and Decompression Sickness Are Different:

• Nitrogen narcosis is caused by breathing such a high concentration of nitrogen that the gas functions as a mild anesthetic. The nitrogen causing nitrogen narcosis remains dissolved in a diver's blood and tissues and does not form bubbles.

• Decompression sickness is caused by nitrogen coming out of solution (no longer dissolved in the body) and forming bubbles. Where do the bubbles come from? During every dive, a diver's body absorbs nitrogen from his breathing gas. As he ascends, the nitrogen expands according to Boyle's Law. Normally, the nitrogen travels in the diver's bloodstream until it reaches his lungs, where it is exhaled. However, if a diver stays underwater too long (past his no-decompression limit), or ascends too quickly, his body cannot eliminate the nitrogen effectively, and the excess nitrogen trapped in his body forms bubbles.

2. The Symptoms of Nitrogen Narcosis and Decompression Sickness Are Different:

• Nitrogen narcosis is most commonly described as a state of intoxication, similar to drunkenness. Fuzzy thinking, incoherent reasoning, confusion, and impaired manual dexterity are all symptoms of narcosis.

Divers experience nitrogen narcosis while underwater during deep dives.

• Like nitrogen narcosis, the symptoms of decompression sickness may include confusion and impaired thinking, but also may include pain, loss of feeling in an isolated area of the body, tingling, visual disturbances, vertigo, and paralysis (among many other symptoms). A bubble may even block blood flow to the point that body tissues and organs are permanently damaged.

Divers typically experience decompression sickness a few hours to one day after a dive, or during ascent from a very deep or long dive. Unlike nitrogen narcosis, the symptoms of decompression sickness are not noticeable during the deepest part of the dive.

Learn more about decompression sickness and nitrogen narcosis:
• Decompression Sickness
• Drunkenness and Confusion: Nitrogen Narcosis Part 1
• Sobering Up (Eliminating Narcosis): Nitrogen Narcosis Part 2

3. Procedures for Dealing With Narcosis and Decompression Sickness Differ:

• Nitrogen narcosis is related to a diver's depth. To treat nitrogen narcosis, a diver should simply ascend at a safe ascent rate until the symptoms abate. As long as he feels normal, the diver can continue diving, but should not return to the depth at which he experienced narcosis.

• Decompression sickness is caused by nitrogen bubbles. To treat decompression sickness, a diver must eliminate the nitrogen bubbles by undergoing re-compression therapy in a hyperbaric chamber. The longer the bubbles remain in a diver's body, the more damage they will cause. Decompression illness is dangerous and sometimes life-threatening.

Decompression sickness and nitrogen narcosis are often confused because they are both caused by nitrogen gas. However, when the specifics of each condition are understood, it is easy to see that the two conditions are very different!

Thanks to About.com

Kathy Dowsett
www.kirkscubagear.com

Friends share stories of diving beneath the ice

Brad Grecula could not see anything in the pitch-black water. Very slowly, something came into focus before him.

Grecula was looking at the Hopkins/Minnetonka shipwreck, which was once part of a fleet of six streetcar boats that transported people around Lake Minnetonka in the early 1900s.

When her sister boats were being dismantled and sunk in 1925, Capt. George Hopkins purchased it, renamed it Minnetonka and operated it as an excursion boat until 1949. At that time, it was sunk near her sisters north of Big Island. The state recognizes it as an archeological site, according to Maritime Heritage Minnesota.

As an outline of the wreck appeared before him, Grecula was sure it was the Hopkins/Minnetonka. After all, he and his friends had a GPS location on the shipwreck as they drove through a dense fog over the frozen lake, but diving through pitch-black water can mess with your mind.

“Your imagination can run away from you when you’re down there,” Brian Dahl said.

Divers going so deep that sunlight does not reach them can attest to what Grecula and Dahl are saying. What makes their tales even more harrowing is the only way they can escape the water is through a small hole in a thick sheet of ice.

Ice diving can be a deadly recreational activity if you are not properly trained and do not take the safety precautions seriously.

MyFox Twin Cities reported a story two years ago of a pair of ice fishermen hooking a scuba diver. The story had some comical elements to it because the fishermen thought they caught a big one. The diver was unharmed and offered a couple of beers as a peace offering, the fishermen told Fox news.

Dahl of Andover, Grecula of East Bethel, Art Gullette of Andover, John Oliver of Isanti and Nate Putbrese of Cambridge know this diver and this story was no laughing matter because several safety measures were not followed, they later learned. Ice divers are a fairly tight-knit group in Minnesota because there are so few of them, Gullette said.

The Professional Association of Diving Instructors is the not the only diving certification organization, but is the largest by far, said PADI spokesperson Bridget Evans. Over the last five years, more than 1,700 PADI ice diver certifications were earned throughout the whole U.S. In 2012, only 11.3 percent of all PADI certifications earned were for ice diving.

Mitigating the dangers

There are many safety measures to check off before going on an ice dive. The obvious first step is to make sure the ice is thick enough on which to drive a vehicle. Once on the site, they usually have a chainsaw to cut a triangle hole in the ice. They can cut a square, but a triangle takes less effort to cut because it has one less side.

They must be attached to a rope so they have an easier time finding the ice hole. Another step that can be taken is to clear snow in the shape of an arrow. Sunlight will highlight the arrow and give divers a bearing.

The most ideal situation is to have one person diving and another person on the ice in their gear in case the diver has to be rescued. There should be at least one and preferably two tenders in case both are in the water.

Ice diving is such a challenge that Dahl said PADI recommends a person have at least 50 dives before they can be trained.

According to Dahl, one of the most important traits he picked up from ice diving is the ability to remain calm and problem solve in tense situations.

A saying that stuck with Oliver is, “technical diving is the only sport where you can kill yourself and have half-an-hour to think about it.”

Gullette said this can be true of any type of diving, but the more logistically challenging the dive, the more true this is. There is a large difference between recreational and technical diving, he said.

Scuba diving in a river is beyond the level of most ice divers because “the current can take you into no-man’s land where there is no exit hole,” Oliver said. A second exit hole is a must for river ice dives, Gullette said.

If anybody feels nervous, a dive is called off without question.

Each of them has a different standard for calling a dive, however. Gullette is probably the most cautious, while Putbrese is the risk taker, to the chagrin of Gullette.

“When Nate calls it, I check my pulse because I may already be dead,” Oliver said.

Dahl, Gullette, Oliver and Putbrese know what a search and rescue feels like from the other side because they used to be volunteers for the Isanti County Sheriff’s Office dive team.

Isanti County does not have the budget for all the equipment so much of it is the diver’s own gear, said Chief Deputy Bill Guenther of the Isanti County Sheriff’s Office. Two men with their own gear recently volunteered to be the county’s only two dive team members, he said.

Although they may give Gullette a hard time for being such a stickler for the rules, he is deeply respected.

“I’ve done a fair amount of training through other instructors, but Art is hands-down the most thorough,” Oliver said. “It’s not that he wants to keep you there for an extra two hours. He wants to make sure you’re absorbing what he’s trying to tell you. I’ve told him before, when my daughter gets certified, he’s the one that’s going to do it.”

Some wild tales

Gullette first tried ice diving in 1975 and he swore he would never do it again, but he decided to give it a try when he met Putbrese in 2004.

“Nate and I have an interesting relationship. I keep Nate alive. He keeps pushing my comfort zone and envelope and keeping it fun,” Gullette said.

While they gave Putbrese some grief, Dahl was quick to note that Putbrese is very experienced and “dive smart.”

Dahl met Gullette through work at the Minnesota Department of Corrections and started diving around 2005. Oliver started ice diving in 2008 or 2009 just a year or two after celebrating his 40th birthday.

The four of them soon connected with Grecula, who began diving shortly after he graduated from high school in 2008. “Shortly after high school in 2008? Why do we let him hang out with us?” Dahl said while they all chuckled.

Their schedules do not always allow the five of them time to get together when they are not diving, but when they got together for an interview at Gullette’s Andover home, there was a lot of reminiscing, laughs and some head shaking.

One story Gullette really wanted to tell was the first time that Oliver was the unexpected rope tender on the surface. Oliver was still new to ice diving, so Gullette was training him on rope tending. Gullette was diving and Putbrese was supervising him on the ice.

Gullette suddenly came up to the surface all excited, telling them he found a wreck and giving them the coordinates so they knew where he was going. When he was surveying the wrecked boat, he looked to his left to see Putbrese swimming up to him. It turns out that Oliver was tending them both, which really made Gullette mad at Putbrese.

Another interesting tale was about a fisherman throwing his wedding ring down his ice hole on Mille Lacs Lake. The Isanti County dive team happened to be training in the area and Putbrese volunteered to recover the ring and, of course, document it.

Putbrese taped his descent and recovery of the ring and posted it on YouTube. Search “Nate Putbrese” to find his YouTube channel and the video. When he sees the ring, you hear him gurgling “my precious” in homage to the character Gollum from J.R.R. Tolkien’s “The Hobbit” and the “Lord of the Rings” trilogy.

Then there are the stories of Putbrese pushing the envelope. One time Gullette got out of the truck and walked to shore with his cell phone in hand and watched as Putbrese gunned the truck across the ice.

Oliver said Putbrese has graduated from “rock, paper scissors” to flipping a coin to determine if they should walk or drive across the ice. He will often throw these coins in the water to make a sacrifice to “the lake gods” and to see how long the coins are visible.

Thanks to ABC Newspapers

Kathy Dowsett

www.kirkscubagear.com

DAN Case Study

Reprinted with permission from Chantelle Taylor-Newman of Dive Medic


DAN Case study 8

This diver was a 61-year-old male in good health, taking no medications.

He was on a liveaboard dive vessel in the South Pacific, vacationing with his son. He had completed 700 lifetime dives over 35 years. On this trip he had performed 13 dives over a five day period breathing air (two or three dives per day). His deepest dive was to 148 fsw (45 msw) and he reported having no problems with any of the dives. This was his typical style of diving.

His final day of diving started with a 148 fsw (45 msw) dive for 37 min with a customary safety stop. Upon surfacing, he became disorientated and had numbness and weakness in both legs. He required help getting back into the boat. The only oxygen immediately available was a nitrox blend. He was able to get up and walk to his cabin without assistance after breathing the blend; but his symptoms had only slightly improved. He was then taken to a medical clinic and placed on 100% oxygen. From there he was transported to a remote chamber facility.

His only improvement to this point was a slight reduction in disorientation. Six hours after initial symptom onset he received his first USN TT6. A physician’s evaluation revealed numbness, weakness and hyperreflexia in his legs. His mental clarity issues resolved, but his other symptoms progressed to lower extremity paralysis, severe pain in the abdomen and legs and loss of bowel and bladder function.

His symptoms worsened by the next morning, whereupon he received a second USN TT6 and a USN TT5 each day for two more days. He was then transported to a second hyperbaric medical clinic and received two more wound healing treatments without improvement. He was then evacuated home.

Two years from the incident; his legs remain paralyzed with minimal movement, he had limited bowel and bladder function and was medicated for his chronic pain. Further diving was not possible for this individual.

kirkscubagear published this post not to scare divers, but strickly as an informative piece.

Kathy Dowsett

www.kirkscubagear.com

Return to Antikythera: Divers revisit wreck where ancient computer found

Thanks to:
Jo Marchant is the author of a book about the mechanism, Decoding the Heavens: Solving the Mystery of the World's First Computer

In 1900, Greek sponge divers stumbled across "a pile of dead, naked women" on the seabed near the tiny island of Antikythera. It turned out the figures were not corpses but bronze and marble statues, part of a cargo of stolen Greek treasure that was lost when the Roman ship carrying them sank two thousand years ago on the island's treacherous rocks.

It was the first marine wreck to be studied by archaeologists, and yielded the greatest haul of ancient treasure that had ever been found. Yet the salvage project – carried out in treacherous conditions with desperately crude equipment – was never completed. So this month, armed with the latest diving technology, scientists are going back.

Antikythera Mechanism

Between 1900 and 1901, the sponge divers retrieved a string of stunning antiquities, including weapons, jewellery, furniture and some exquisite statues. But their most famous find was a battered lump that sat unnoticed for months in the courtyard of Athens' National Archaeological Museum, before it cracked open to reveal a bundle of cogwheels, dials and inscriptions.

It has taken scientists over a hundred years to decode the inner workings of those corroded fragments, with x-ray and CT scans finally revealing a sophisticated clockwork machine used to calculate the workings of the heavens.

Dubbed the Antikythera mechanism, it had pointers that displayed the positions of the sun, moon and planets in the sky, as well as a star calendar, eclipse prediction dial and a timetable of athletics events including the Olympics.

It's a stunning piece of technology that revolutionises our understanding of the abilities of the ancient Greeks. Nothing close to its complexity is known to have been created for well over a thousand years afterwards, and the emergence of mechanical clocks in medieval Europe.

There are questions that remain unanswered, such as where it's from and who built it (Posidonius, a philosopher who lived on Rhodes during the first century BC, is one candidate, while the third century BC genius Archimedes may have invented this type of device). But one of the most intriguing mysteries relates to the wreck on which it was found. What's still down there?
The wreck lies in around 60 metres of cold, rocky, current-swirled water – not an easy place to visit. The sponge divers who salvaged its cargo worked in clunky metal diving suits with little understanding of the dangers of diving at such depth. By the time they abandoned their project, two of them had been paralysed by the bends, and one was dead. They left behind stories of abandoned treasures, including giant marble statues that rolled down the steep slope from the wreck and out of reach.

The undersea explorer Jacques Cousteau spent a couple of days at the wreck site in 1978 and brought up some precious smaller items, including some coins from the Asia Minor coast, which suggested that the ship sailed from there around 70-60 BC (probably carrying war booty from Greek colonies back to Rome). But even with their sleek scuba gear, Cousteau's divers could spend only brief minutes on the seabed without risking the bends.

No one has been back since. Now, after years of negotiations with the Greek authorities, Brendan Foley, a marine archaeologist based at Woods Hole Oceanographic Institution in Massachusetts, finally has permission to dive at Antikythera. He's working with Greek archaeologists including Theotokis Theodoulou of the Ephorate of Underwater Antiquities.

This week, the team begins a three-week survey using rebreather technology, which recycles unused oxygen from each breath and allows divers to stay deeper for longer. The aim is to survey the wreck site properly for the first time, to find out once and for all what has been left down there – and to check down the slope, to 70 metres depth or more, to see if those stories of runaway statues are true.
Any items found on the wreck site could provide further clues to the origin or ownership of the ship. And not all of the pieces of the Antikythera mechanism were ever found. It's a long shot, but those missing bits could still be on the seabed.

This isn't what gets Foley most excited about the project, however. His team will also dive around the entire island, a distance of about 17 nautical miles, using James Bond-style propellers to cover ground quickly. Foley hopes this could reveal a whole clutch of previously unknown wrecks.
The island of Antikythera sits in the middle of what has been a busy trade route since ancient times: a treacherous shard of rock notorious for downing ships in a storm. In Roman times, it was also an infamous centre for pirates. So it's a good bet that there are plenty of other wrecks here, from all periods of history.

On a two-day reconnaissance survey in June this year, Foley and his team discovered the wreck of a British warship called HMS Nautilus, lost in 1807, plus a range of ancient anchors, ceramics and a 19th-century naval gun.

This suggests the area hasn't been looted (which makes sense given the difficulty of diving here), so any new wrecks found could be pristine. "Everyone is very, very excited," Foley says of the upcoming mission. "This ought to be extraordinary."

He also points out that the Antikythera ship, with its valuable cargo, is unlikely to have been travelling alone. When it sank, others in its fleet may have gone down too. Could one of them have been carrying another Antikythera mechanism? For the past hundred years, this awe-inspiring device has stood alone, our only glimpse into a technology lost for millennia. That might – just might – now change.

Kathy Dowsett
www.kirkscubagear.com

Waters of Lake Michigan are a treasure trove of sunken wrecks

Roger Rice says the Bermuda Triangle, that polygon in the western Atlantic reputed to occasionally gobble up ships and aircraft, "has got nothin'" over the storm-battered waters off Wisconsin's Door Peninsula.

"Lake Michigan was a nautical superhighway for schooners and freighters in the 1800s and early 1900s, and a lot of them (hundreds, in fact) went down on the shoals off Door County, at Death's Door on the tip of the peninsula and over in Green Bay," said Rice, a veteran scuba diver.
And while the boats and aircraft that (supposedly) went down in the Bermuda Triangle have never been found, divers can explore at least three dozen ships off the Door Peninsula. Some are in relatively shallow water, so snorkelers can get an easy look; others are more than 100 feet down, requiring scuba tanks and training.

Rice, 69, lives at the tip of the peninsula in Gills Rock, Wis. He got his scuba certification eight years ago, after atrip to visit his son in Hawaii.

"It looked like so much fun that I had to try it, and I was a little peeved I couldn't dive with him because I didn't have my license," said Rice, who has logged more than 300 (and counting) dives since then off the Door and in California. He has no plans to slow down.

"There are wrecks out there all over the place," said Rice, whom I met while diving on the Frank O'Connor last summer. The O'Connor, a 300-foot wooden steamship, sank in 65 feet of water several miles off the Cana Island lighthouse. It was launched in 1892 and went down in 1919 after a fire.
"And really, the boats are what make diving interesting, because the bottom of the lake is so flat," he said. "It is really great to explore those old ships."

As we sped out to the wreck on a dive boat piloted by Jake Gransee, Rice said O'Connor is one of his favorite wrecks because its two large boilers and a 12-foot propeller remain intact.

"The thing burned and went straight down," he said. "So the old steam engine is just sitting there on the bottom."

Some 30 minutes later, I was geared up in a hefty wetsuit to keep out the Lake Michigan chill (it was about 50 degrees at 65 feet) and moving slowly down a buoy line toward the ship.

Just as Rice promised, the big propeller was still standing, connected to the steam engine. Unfortunately, the wooden sides of the boat had collapsed over the years and lay spread out on the bottom. Pieces of shiny coal used to fire the boilers nearly 90 years ago were scattered nearby.

The O'Connor was constructed by shipbuilder James Davidson, who built freighters in the late 1800s, when sailing was giving way to steamships. Davidson constructed his bulk carriers of wood rather than steel to save money. But they were fire traps and nearly all ended up burning.

As Gransee and I swam along the ship for the next 30 minutes, we could see layers of zebra and quagga mussels covering nearly every section of exposed wood and metal. Invaders from the Caspian and Black seas, these filter feeders are thought to have been brought to this country as ballast from tankers.

Since their colonization of the Great Lakes in the early 1990s, they have covered the undersides of docks, boats, anchors and spread into nearby streams. Widely despised, they can grow so densely that they block pipelines and clog water intakes of municipal water supplies and power plants.

But — for divers, anyway — they have an upside. Because they are filter feeders, they have greatly improved the visibility in the Great Lakes. The change has been dramatic, said Gransee, 38, who began diving when he was 14.

There are billions of these mussels in the Great Lakes, and studies show that they can filter roughly a quart of water a day.

"When I first dove on the O'Connor back in 1994, it was great to have 30-foot visibility, and 40 feet was considered phenomenal," he said. "Now it's not unusual to be able to see 100 feet, and it's a bad day when you can't see at least 50 feet. That's a huge change in less than 20 years."

Gransee, who grew up in Baileys Harbor on the Lake Michigan side of the Peninsula, said he began snorkeling around age 10 with a buddy.

"We went to a dive shop up in Gills Rock to get some gear, and the owner drew us a map of some wrecks in shallow water of around 12 feet in Baileys Harbor," he recalled. "I forget the name of the boats, but after that, we were hooked."

A self-described history buff, Gransee said he enjoys researching the wrecks he's visited and imagining what the conditions were like when the ships went down in storms.

"I also like introducing people to wrecks they haven't seen before," added Gransee, who dubbed his dive charter operation "Dark Side" after the 1973 Pink Floyd album "Dark Side of the Moon."
Gransee said he often takes divers to the O'Connor and then returns to the warmer and shallower waters of Baileys Harbor to examine the Emeline, a 111-foot-long schooner that sank in 1896 in less than 20 feet of water.

"It's a nice wreck for beginners to explore, and the water is considerably warmer than down where the O'Connor is located, where it can drop into the 40s," he said.

Gransee said he and his diving friends are always looking for new wrecks.

"There's a lot out there that hasn't been discovered," said Gransee, who uses sonar to map possible dive sites. He was planning to purchase a 'side scan" unit, which he said will "literally paint a picture of the bottom and really tell us what's down there."

"It would be great if we could find a new wreck in the 100- to 120-foot depth range," he mused. "That would really stimulate interest in diving up here again. It was more popular in the past. And way back in 1969, National Geographic did a big story on Door County and devoted a whole section to wreck diving."

In the meantime, he's content to lead customers to lakeside wrecks that start just a few miles south of Baileys Harbor and include the Ocean Wave, a scow schooner that sank in 110 feet of water in 1869.
And he can go 20 miles north to the infamous Death's Door, where three wrecks off Pilot Island went down so close together that they are touching. He also dives sunken ships on the Green Bay side of the peninsula and can even head north to islands off Michigan's Upper Peninsula.

If you enjoyed this blog, you will enjoy reading Ross Richardson's new book "Search for the the Westmoreland"

Thanks to the St Louis Dispatch

Kathy Dowsett

www.kirkscubagear.com

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

www.kirkscubagear.com

Diving into the mysteries of the deep

Some people like to read mysteries.

Ross Richardson likes to dive for them.

He traces his interest in shipwrecks back to a contest in first grade when he wrote about a wreck. That fascination quickly developed into a passion.

“I love solving mysteries,” says Richardson, who is from Lake Ann, Michigan, which is about 15 miles west of Traverse City. He has focused his interest on the Great Lakes, mainly on nearby Lake Michigan, and to a lesser extent on lakes Huron and Superior.

While serving on the sheriff’s public safety dive team of Michigan’s Benzie County, Richardson, 44, was doing ice-diving training on Higgins Lake in central Michigan with a woman whose father had disappeared there years before. Her story of her dad’s disappearance intrigued Richardson. So did the demise of up to 50 aircraft and countless ships in Lake Michigan.

He not only started diving for wrecks of ships and planes but established a website on the subject http://www.michiganmysteries.com/ and is writing a book. It is called “The Search for the Westmoreland, the legend, the history and the discovery of Lake Michigan's Treasure Ship.” He hopes to have the book published by this summer.

The Westmoreland sank during a severe snowstorm on December 7, 1854, off Lake Michigan’s Sleeping Bear Point, “probably the most notable landmark in the Lower Peninsula,” says Richardson. One of the early propeller-driven ships, the Westmoreland had lost its engine power during the storm. “They tried to get the sails up but one was imbedded in ice and the other was ripped apart (by the gale).” Hopes of bringing the ship to the safety of South Manitou Island’s harbour were dashed. Half of the 34 occupants of the ship died, while the others made it ashore in a lifeboat.

The ship had been the subject of many searches in the ensuing 150-plus years until Richardson located it on July 7, 2010, using Side Scan Sonar. Three days later he dove to the site and confirmed the finding. He found it was well preserved, a fact he attributes to its resting place in an uncharted hole near Sleeping Bear Dune that sheltered it from currents. It was sitting upright and was nearly intact.

Richardson’s sources in researching vanished ships and aircraft include old newspapers. Using Google news archives, digitalized newspapers can be searched using key words. “I get an amazing amount of information there. Half my information is from there,” he says. “The other half is from local historical societies and micro-film in libraries.”

Typically, for a ship missing for so long, the Westmoreland’s legend has grown to include unconfirmed stories that gold and 280 barrels of whiskey were among the cargo being transported. One story maintains that the lumberjacks on board, thinking they were going to die, started drinking the whiskey and belatedly tried to launch the last lifeboat. It was the largest lifeboat, but it was tipped over when the ship’s crane caught it on its side, dooming the lumberjacks. It is known, at least with more certainty, that the cargo included oats, flour, grass seed and beef quarters. Most of it was from Chicago but some came from Milwaukee.

Richardson has also located three uncharted wreck sites at Sleeping Bear Point near a 450-foot sand dune. He says there are big parts of a ship, an old schooner and the remains of an old sailing vessel with tons of artefacts around it. During an October gale in 2010 a large section of a shipwreck washed ashore, so he looked a couple of miles offshore and found the wreck sites.
“I think they have been there since the late 1800s,” Richardson says, adding that they are in the heart of the Manitou passage, which was “almost the highway of its day.” Sleeping Bear Point jutted out into this passage and became a hazard during storms.

One of the missing aircraft that intrigues him is a Northwest Airlines DC-4 that crashed into Lake Michigan on June 23, 1950 during a storm. All 55 passengers and the three crew members died but the aircraft has never been found. At that time, it was the largest death toll in an aircraft crash.

The National Underwater and Marine Agency (NUMA) team of novelist and marine archaeologist Clive Cussler has come for the last eight or nine years to search for the plane but has yet to locate it, says Richardson. “These guys are the best.”

His website also chronicles missing persons in the area of his research and bodies that have not been found.

A technical diver qualified to go to depths well beyond the range of recreational divers, Richardson’s major focus is on shipwrecks.

While he doesn’t have a problem with a museum or historical society having a relic from a shipwreck to display, he isn’t interested in it for himself: “I believe in conserving wrecks. I haven’t taken anything off a wreck.”

For Ross Richardson, the thrill is in the search: “It’s amazing how many missing things there are that are solvable mysteries.”

Read Michigan Mysteries by Ross Richardson

Kathy Dowsett

www.kirkscubagear.com

March 2012::Update::Ross is humbled to announce that he has signed a publishing deal with Arbutus Press for his upcoming book “The Search for the Westmoreland", Lake Michigan’s Treasure Shipwreck”, due to be out this summer.

Scuba Diving::::Is It An Extreme Sport?

How extreme do you want your sport to be?

What is your comfort level with risk?

When it comes to scuba diving, these are questions you will have to ask yourself if you wish to advance to some of the more extreme elements of the sport.

That is one of the strengths of scuba. It’s versatile. You can choose the level at which you wish to participate.

“Scuba is not extreme, but it lends itself to extremes,” says Catherine Donker, a dive master from St. Thomas, Ontario, Canada. “It is user friendly. You can take a casual approach if you are not looking for a lot of physical challenge or excitement. You can choose dives according to your level or interest. You can do 15-to-20 foot dives on top of a reef or if you’re getting into the extremes, a wreck such as the Andrea Doria.”

While approaching the coast off Nantucket, Massachusetts, the Andrea Doria and the eastbound freighter MS Stockholm collided. The Andrea Doria sank on July 26, 1956, resulting in 46 deaths. Diving to its wreck is difficult and dangerous and it involves depths beyond 200 feet. It is only for highly qualified technical-certified divers, whose certifications include training in the use of mixed gases.

For scuba divers who want to push the limits in other ways, there is cavern and cave diving.

PADI describes the cavern zone as the area near the entrance of a cave where natural light is always visible. Cavern divers always keep the entrance in sight and use a guideline to help them find their way back in case they lose sight of the entrance. However, cave divers will go much farther into the cave, sometimes thousands of yards.

The majority of scuba enthusiasts will probably never want to advance to cave diving. They are happy with what they set out to do – explore the underwater world of coral reefs and occasionally dive to a shipwreck that is accessible enough for the dive certification they hold.

There is no shortage of sites for either experience. Florida and the Florida Keys are popular destinations for people living on or near the U.S. Eastern seaboard.

“The Keys has both wrecks and reefs covered,” says Catherine. “There are hundreds of wrecks in Florida.”

Dive sites include the USS Oriskany, a former aircraft carrier that was sunk off Pensacola, and the USS Spiegel Grove, a former U.S. Navy dock loading ship that rests on the bottom offshore from Key Largo. Both of these dives can be done with an Advanced Open Water certification.

Viewing reefs and shipwrecks is more in line with what most divers envisioned when they began scuba lessons.

“I would say the most common reason people enrol in lessons is a reference from a friend. They’ve heard exciting stories of the incredible colours of the reefs and amazing aquatic life or maybe a compelling historical wreck,” says Catherine. “If you can get them to watch your video creations, people see what they’ve only seen before on National Geographic and they know that it really is accessible to anyone. They know you are not Jacques Cousteau, just a regular person.”

Kathy Dowsett

www.kirkscubagear.com

History of rebreathers

A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere. In the armed forces it is sometimes called "CCUBA" (Closed Circuit Underwater Breathing Apparatus).

Around 1620: In England, Cornelius Drebbel made an early oar-powered submarine. To re-oxygenate the air inside it, he likely generated oxygen by heating saltpetre (potassium nitrate) in a metal pan to emit oxygen. Heating turns the saltpetre into potassium oxide or hydroxide, which absorbs carbon dioxide from the air. That may explain why Drebbel's men were not affected by carbon dioxide build-up as much as would be expected. If so, he accidentally made a crude rebreather more than two centuries before Saint Simon Sicard's patent.

1808: The oldest known rebreather based on carbon dioxide absorption was patented in France by Sieur (old French for "sir" or "Mister") Touboulic from Brest, mechanic in the Napoleon's Imperial Navy. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver himself and circulating in a closed circuit through a sponge soaked in lime water. Touboulic called his invention Ichtioandre (Greek for 'fish-man'). There's no evidence of a prototype having been manufactured.

1849: Patent for the oldest known prototype of a rebreather also used an oxygen reservoir, granted to the Frenchman Pierre Aimable De Saint Simon Sicard.

1853: Professor T. Schwann designed a rebreather in Belgium; he exhibited it in Paris in 1878. It had a big backpack oxygen tank at pressure about 13.333 bars, and two scrubbers containing sponges soaked in caustic soda.

1878: Henry Fleuss invented a rebreather using stored oxygen and absorption of carbon dioxide by an absorbent (here rope yarn soaked in caustic potash solution), to rescue mineworkers who were trapped by water.

About 1900: The Davis Escape Set was designed in Britain for escape from sunken submarines. It was the first rebreather which was practical for use and produced in quantity. Various industrial oxygen rebreathers (e.g. the Siebe Gorman Salvus and the Siebe Gorman Proto, both invented in the early 1900s) were derived from it.

1903 to 1907: Professor Georges Jaubert invented Oxylithe, which is a form of sodium peroxide (Na2O2) or sodium dioxide (NaO2). As it absorbs carbon dioxide (e.g. in a rebreather's scubber) it emits oxygen.

1907: Oxylithe was used in the first filming of Twenty Thousand Leagues Under the Sea.

1907: This link shows a Draeger rebreather used for mines rescue.

In 1909 Captain S.S. Hall, R.N., and Dr. O. Rees, R.N., developed a submarine escape apparatus using Oxylithe; the Royal Navy accepted it. It was used for shallow water diving but never in a submarine escape.

1912: The first recorded mass production of rebreathers started with the Dräger rebreathers, invented some years earlier by an engineer of the Dräger company, Hermann Stelzner. The Dräger rebreathers, especially the DM20 and DM40 model series, were those used by the German helmet divers and German frogmen during World War II.

1930's: Italian sport spearfishers used rebreathers systematically. This practice came to the attention of the Italian Navy, which developed its frogman unit Decima Flottiglia MAS, which was used effectively in World War II.

World War II: Captured Italian frogmen's rebreathers influenced design of British rebreathers. Many British frogmen's breathing sets' oxygen cylinders were German pilot's oxygen cylinders recovered from shot-down German Luftwaffe planes. Those first breathing sets may have been modified Davis Submarine Escape Sets; their fullface masks were the type intended for the Siebe Gorman Salvus. But in later operations different designs were used, leading to a fullface mask with one big face window, at first oval like in this image, and later rectangular (mostly flat, but the ends curved back to allow more vision sideways). Early British frogman's rebreathers had rectangular breathing bags on the chest like Italian frogman's rebreathers; later British frogman's rebreathers had a square recess in the top so they could extend further up onto his shoulders; in front they had a rubber collar that was clamped around the absorbent canister, as in the illustration below.

Some British armed forces divers used bulky thick diving suits called Sladen suits; one version of it had a flip-up single window for both eyes to let the user get binoculars to his eyes when on the surface.

Early 1940s: US Navy rebreathers were developed by Dr. Christian J. Lambertsen for underwater warfare and is considered by the US Navy as "the father of the frogmen". Lambertsen held the first closed-circuit oxygen rebreather course in the United States for the Office of Strategic Services maritime unit at the Naval Academy on 17 May 1943.

Thanks to Wikipedia

Kathy Dowsett

www.kirkscubagear.com