A buddy sent me a pointer to an interview at DEMA 2009 by Curt Bowen from Rebreather World and Advanced Diver Magazine with Bruce Partridge from Shearwater Research about the new Predator Dive computer.

I saw an interesting slide at the UHMS GLC meeting in October. It compared dive profiles that were virtually identical except for a very deep bounce at the beginning of what was otherwise a “square” profile. The presenter stated that there were less observed bubbles after the dive that began with the bounce than the one that didn’t.

That’s quite astounding. One would think that starting a dive with a bounce would increase the number of bubbles, not decrease it. This result seemed to support some of the claims made by bubble model proponents that neo-Haldanean compression models miss opportunities to exit from deep dives earlier. The effect is explained by the theory of micronuclei, which can be made up of very small bubbles that already exist in the bloodstream, which grow larger in the presence of supersaturated inert gas (i.e. Nitrogen or Helium) and cause problems. The deep bounce crushes these micronuclei to a degree where they do not easily accrete dissolved gases and grow to a size that would cause the diver problems.

Sounds intriguing, but I’m still not convinced that this is safe enough for my personal use. I worry that certain environmental conditions or dive profiles would result in a reversal of the effect and the onset of serious DCS. I’m probably full of “it” on this topic but if one model predicts I’m going to be fine and the other predicts I’m going to be writhing in agony, I’m going to err on the side of staying down a little longer.

It’s interesting that there is no agreement among agencies as to the exact definition of Respiratory Minute Volume (RMV) and Surface Air Consumption (SAC).

My original certification agency, NASDS, defined SAC as the surface equivalent number of PSI per minute on a dive, which is (PSI Consumed/Total Dive Time)/((33+Depth)/33).

IANTD does the same thing, and defines RMV as the SAC/(Working Pressure/Rated Cylinder Volume).

DSAT defines SAC as the same as IANTD and NASDS defines RMV, and defines RMV is the (Tidal Volume minus Respiratory dead air space) times breaths/minute. I added the parenthesis to what I read in the book (p42 Tec Deep Diver Manual) because otherwise it doesn’t make any sense. Oddly the Encyclopedia of Recreational Diving doesn’t seem to mention either term. Wikipedia’s definition of RMV is similar to DSAT but doesn’t factor Respiratory Dead Air Space.

In the SDI solo diving course SAC is defined as the volume per minute consumed at rest on the surface. They recommend breathing from a tank while sitting around watching TV or like activity to measure this. For me, consuming about 325 PSI of a 3000 PSI working pressure tank with a rated volume of 77.4 cubic feet in 30 minutes, this was about .28 cubic feet per minute. They call what IANTD and NASDS call RMV the SRMV, or Surface Respiratory Minute Volume. They then go on to recommend that before each dive the RMV by multiplying by the number of absolute atmospheres of pressure and also by a “Dive Factor”, which takes into account effort and should be at least 1.5 for an easy dive, and perhaps more than 3 for a high effort, cold or stressful dive.

Disconcertingly, their sister agency, TDI, recommends determining SAC using a swim at depth, the very thing that SDI says doesn’t work, and implies that RMV is just another term for SAC.

0.28 seems a bit low. I think having the reg in my mouth called attention to my breathing and slowed it down some. At 33 feet a tank would last over 2 hours at that rate, although my record is about an hour and 20 minutes on a reef dive (and 1h 40 in really shallow water) on a single 80 so maybe it’s not all that far fetched. I know when it’s cold and I’m working a bit hard the rate goes way, way up.

It would be nice to have a consensus between agencies on this topic. Maybe ISO will define it some day.

The Shearwater Predator, an upgrade to the already wonderful Shearwater Pursuit is on my Christmas list. Right after I get back from my upcoming trip to Florida I’m going to work on the upgrade. The 2 big changes to the Pursuit are:

1. A larger, OLED colour screen. The extra size and brightness should allow me to delay buying that prescription mask for at least a couple more years.
2. Bluetooth instead of Infrared communications to the computer. No more juggling my laptop and and dive computer on the train on the way to work. Just turn the computer on and put it back in my laptop back and download the dives.

I’m so glad the upgrade is available. If I were buying one now, I would have opted for the open-circuit only version that’s new in the Predator, as I’m doubtful I’ll ever get a rebreather, but the buyer’s remorse is way less from at least being able to upgrade it a reasonable price.

No, this isn’t a harangue about “same day, same ocean” dive buddies. I’ll save that for another time. On Saturday (October 30th) we headed up to Big Bay Point to finish our solo diving course. The purpose of the in-water exercises is to promote self sufficiency. For this reason, we spent some enjoyable moments having our air shut off, are masks removed, and ourselves entangled in line.

We all had our own issues. I’d not thought everything through properly. I took the backup reg set from my technical setup for the AL80 on my back, and one of my deco regs for the pony. I’d not realized that this would only give me one LP inflator, which meant that with my dry suit I’d have nothing to use for my BC. It had been 26 years since I’d dived using oral inflate only but rather than switching over to my recreational reg with its “extra” second stage, I decided it would be good practice to try it on this dive. Despite what you might read about *OMS) bungeed wings being impossible to inflate orally, I had no problem with it, although I did have to blow a little harder than with a regular wing.

After dropping my pony bottle (more like a quarter-horse bottle as I used my Faber steel 45) on the bottom, I did my giant-stride off the end of the dock and releasing the minimum amount of air to submerge, fetched it and hooked it on to my BC while swimming out to the descent line.

The first exercise was replacing my mask with my spare. I was glad to do this as while I always carry one, I’ve never actually practiced replacing it. I didn’t find it difficult, although it took a while to get the pocket open, retrieve the mask, orient it properly and put in on. The first time through this exercise we were on the bottom. Following that we did the out of air drills. This didn’t go so well. Inadvertently I’d looped the regulator hose around the bottom clip, so it would not pull out. So I had to lean forward to keep the reg in my mouth while I unclipped the tank to free the hose. Manageable, I suppose, but not something you’d want to have occur in a real out-of-air situation.

After that, we did the same drills while swimming, with our friendly divemasters shutting our air down or removing our masks at various times. The hardest thing was maintaining depth without a mask. I could feel the air expanding in my dry suit and quickly moved to dump some air. I felt like I was still ascending but emptied my lungs and found that I was at about the same depth once my mask was back on as when I started. Looking at my computer log it there only seems to be small incursions so my perceptions were no-doubt amplified by my imagination.

Solo Dive

We also had lines tied around us and masses of silt blinding our vision. Perfect for a day’s outing. Both the water and the air were about 11 degrees C (52-53 F). There was little evidence of a thermocline down to 63 feet, although I’m sure we would have hit one if we went a little deeper.

That’s fall diving in Ontario, and why we like our dry suits.

Anyway, congratulations to Marty, Steve, Rich and Carlos on becoming SDI solo divers.

I just watched, not for the first time, a Sea Hunters episode from 2005 on a search for several models of the famous Canadian fighter aircraft, the Avro Arrow, in Lake Ontario. In this episode, the crew took their boat from Port Dover in Lake Erie to Point Petre in Prince Edward County in Lake Ontario, where during the mid-to late 50s Avro Aircraft Limited shot models of their aircraft into the lake at supersonic speeds, on the nose of a rocket.

They didn’t find it. They found an unidentified sailboat from the mid 19th century in great condition at a depth of 200′. They also found a rocket which  they believed to be a Canadair rocket booster used to test the Velvet Glove Missile, which was being designed as armament for the  Arrow. This booster was designed in part by Gerald Bull, a Canadian engineer who was assassinated (reputedly by the Mossad) while working on Project Babylon, a supergun for the Iraqi government.

The show then rambled on into a rather pointless expedition off the Virginia coast  where the visibility was so back they could only feel the object they were trying to investigate.

Despite the squirrely storyline, the Sea Hunters is my favourite underwater TV show. It’s short on the wonders of the ocean environment and long on hard core diving and exploration (not that I’m against the environment, sharks or pretty fish, it just gets repetitive after a while). In Lake Ontario they were diving surface supplied trimix with a hardhat and ship to diver voice communications, running sidescan sonar, and a ROV. What could be more fun than that?

Yesterday (October 24th, 2009) I attended the 30th annual meeting of  the  Great Lakes Chapter of the Undersea and  Hyperbaric Medical Society. For reasons I’ll explain at another time, this is probably the last meeting of the chapter, due to reorganization of the parent society.

There were many interesting talks, but one thing really stuck in my mind about the state of hyperbaric medicine in Canada – and that is that it isn’t taken seriously enough. Hyperbaric medicine is used in the treatment of several ailments, including

1. Air  or gas embolism
2. Carbon monoxide poisoining
3. Clostridial  myositis and myonecrosis (gas gangrene)
4. Crush injury, compartment syndome and other acute ischemia
5. Decompression sickness
6. Enhancement of healing in selected problem wounds
7. Exceptional anemia
8. Intracranial abscess
9. Necrotizing soft tissue infections (like necrotizing fasciitis a.k.a. flesh-eating disease)
10. Ostemyelitis
11. Delayed radiation injury
12. Grafts and skin flaps
13. Thermal burns

One particular aspect of the above was in  the treatment of diabetic foot ulcers, which often would otherwise result in amputation. With the population (like me) aging, diabetes is becoming more common and the incidence of this problem will grow proportionately.

However, when we visited the Hyperbaric Facility at Toronto General Hospital and asked why it wasn’t in use at that time, the reply was that there was no funding to pay for technicians. Meanwhile it seems that private hyperbaric facilities are popping up all over the place for treatments that have no proven benefit, putting, as we heard, the situation as on where a clinic “can charge patients for hyperbaric oxygen therapy for conditions that is doesn’t work for, but cannot charge for condition for which it can”.

Per capita Canada has about 10% of the number of chambers as the US available for physician-prescribed HBOT. Part of this I’m sure is the stringent controls on private facilities  that  can avail themselves of  government funding,  and of public facilities  that can access private funds (i.e extra-billing  which was outlawed decades ago  by the government of Pierre Trudeau).  But it also seems there is a general ignorance and/or  scepticism with regard the to usefulness of HBOT, and the leaders of the  chapter are campaigning for greater awareness and education amongst the medical community.

Let’s hope they succeed. Access to recompression chambers for emergency use  is essential to divers, but actually provide greater benefits to the general public. That’s a double win.

A little off topic, but this one would be kind of fun, if only people would stop falling for these things. I’ve heard of this particular scam just recently. The premise is that someone you know has been mugged, arrested, sick, or whatever in some foreign country and now needs money. This one however is quite poorly executed.

By the way, for the first time ever, I replied to one of these (after stripping my contact details from my email signature). I said I’d be happy to help, and just send me details of the police report #, the hotel name, the airline and flight #, etc., and I would have a close friend in the RCMP help him out via the  local police department.

Of more  concern is how they got my friend’s email address, since the reply was requested through his legitimate address. I hope to find out soon. This comes less than 24 hours after another friend’s Facebook account was hacked… Let’s be careful out there in cyberspace!

This had to come in a hurry and it has left me in a devastating state.We are in some terrible situation and we really going to need your urgent help.Some days ago,unannounced,We came to visit a resort center in South Glamorgan UK,England…but we got mugged by some hoodlums and lost all our cash,credit cards,we are financially stranded right now and our return flight leaves in few hours time but we need some money to clear some bills,we didn’t bring our cellphone along since we did not get to roam them before coming over.So all we can do now is pay cash and get out of here quickly.we do not want to make a scene of this which is why we did not call my house,this is embarrassing enough.we was wondering if you could loan us some cash,will def refund it to you as soon as we arrive home just need to clear our Hotel bills and get the next plane home,As soon as we get home we will refund it immediately.Write me so we can let you know how to send it.

Somebody searched for this question and it’s an easy answer so here it is.

There’s a grey button on the back of the unit. Find something pointy but not sharp and use it to hold the button down for a second or two. There, you’ve done it.

But wait, you’ve just reset your computer. You will have to reset the time (press the mode button until you get to the TIME screen, and then use the left and right buttons to set the time – unless you’re over eighty you should be able to guess how to do this).

You will also have to set your computer to Imperial from Metric if that’s the way you dive. Use  the MODE button to go to the DIVE screen, and hold both the left and right buttons down for about 5 seconds to move from Metric to Imperial.

That’ll do it. You’ll have to reset your alarm preferences and enter your gas mixes as well if that’s what you need. You may also want to set it to fresh water from salt (also on the DIVE screen), and if you’re like me and using it with tables from DIVE to GAGE mode.  Logged dives will not be erased.

I picked up this pointer on the Ontario Diving web site.  It’s  the proceedings of the Baromedical and Environmental Physiology Group of the Norwegian University of Science and Technology, 18–19 December 2008, in Trondheim, Norway and looks pretty interesting, although it’s still downloading as I write this. It  has an appendix the entire seminal document on  decompression sickness (“The Prevention of Compressed Air Illness”) by John Scott Haldane, which makes up about a third of its almost 300 pages.

I was pleased to read the  following sentence in one of the papers: “Nevertheless, there is no clear evidence, to date, that diving, in the absence of serious acute damage, leads to long-term neurological dysfunction.”  That’s good news, I think.