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September 17, 2007
Taking a handheld computer underwater
When I took that advanced NAUI class I was exposed to all sorts of disciplines. Night diving, light salvage, advanced buoyancy, navigation, deep diving, rescue, using scooters -- all were part of the training. On my own I also picked up the basics of underwater photography, learned how to go about high altitude diving and now have taken the Nitrox class. But I learned even more, and that is how to integrate scuba diving into my work, which is reviewing and writing about all sorts of gadgets and technology, from digital cameras to handheld computers to those ultra-rugged notebooks that the military or firefighters use.
How would diving come in handy for that? Well, with cameras it is obvious. There are many of them that you can take underwater. Most with housings, and now more and more that don't even need one as long as you don't go deep. So knowing camera technology and being a diver lets me take my reviews underwater, and that opened a whole new area for me, one that I greatly enjoy.
But computers? I am not talking dive computers here, the ones we take down to great depths, but just regular computers. So what's this all about? Well, manufacturers realize that not all PDAs and notebook computers will lead a sheltered life sitting on desktops and meeting room tables. Some are used outdoors, some are dropped, some are rained on, and some may even get banged around or crushed. The military, for example, needs the equivalent of a HumVee in a computer, and not some plasticky thing. Anyone who uses a computer as a tool for a job needs just that, a tool, and not a gleaming conversation piece with a panorama screen so that DVDs can be watched on it.
Which means that there is a significant industry out there that makes nothing but tough, rugged computers for special purposes. Panasonic for example, they are a household name with their TVs and electronics, but they also make the "Toughbook" line of notebooks that can take much more punishment than a standard laptop. Companies like UPS or FedEx buy hundreds of thousands of handheld computers they use on the job, to scan and track packages and capture signatures. Those handhelds must be pretty tough to survive all that, day after day and month after month.
There are some standards the industry uses to describe how rugged a computer is. Most come from the military and simply describe testing procedures. The MIL-STD (military standard) alone consists of hundreds of pages of how it's all done. Most countries have their own, and then there are some industry associations and institutes that also have standards, so it can get a bit confusing. Reading and deciphering those ruggedness specifications, and then figuring out what it means in real life, is part of my job. The one standard I think matters more than most is the IP rating. That stands for "Ingress Protection" and was defined by the International Electrotechnical Commission. A mobile computer's IP Rating is expressed as a two-digit number, like IP-56. The first number designates protection from solids (from 0 to 6), while the second number designates protection from liquids (from 0 to 8).
All dive computers would have an IP68 rating if they were tested for that. IP68 means they are completely protected from dust getting inside, and, of course, they are completely waterproof and protected from the effects of immersion. Regular computers are not. They don't have to be. But maybe they should, at least to a degree.
To make a long story shorter, there are some handheld computers with an IP67 rating, which means they can actually be immersed into water and survive. It's just baby steps for now, with immersion usually limited to about a meter and for no longer than 30 minutes or so. And even that is extremely rare. It so happens that I got one of those computers to review and test, a very tough handheld from a company called Tripod Data Systems. Their new Nomad computer is for the military, for surveyors, and others that need to computer and communicate in extreme conditions. It's a very sophisticated unit with a fast processor and a razor-sharp display that puts the Apple iPhone to shame. And it's rated IP67, with 30 minute immersion to a meter of water.
Needless to say, I had to check that out for myself. My regulator and BC had just come back from their first annual service and I was absolutely dying to get back underwater. If I had a dive buddy, I'd have gone up to Lake Tahoe to catch another dive or two before the water gets too cold up there. But I could not find one, and so it had to be my pool.
Preparing for the dive with the Trimble Nomad computer required some planning. First was the mental step in deciding to actually do it -- take an expensive piece of equipment underwater, one that I needed to send back to the manufacturer. What if it flooded? The second was to record the event, and for that I needed cameras. I decided to use a Casio Exilim EX-Z77, also here for review, for the above-water scenes as it includes a cool new "YouTube mode" which means it spits out video optimized for the YouTube video sharing service. For underwater I picked a SeaLife DC600, mounted on a regular tripod. My eleven-year-old son Morgan was my assistant and he certainly earned his pay (in chocolate-covered peanut pretzels).
So I am finally all geared up and wearing my new "Edge" 3-mil wetsuit. I do some preliminary tests by carefully immersing the computer into the water and watch for bubbles. On camera. No bubbles. Now Morgan joins me in the water with his snorkel gear. He holds the only slightly negatively buoyant tripod with the SeaLife camera on it steady and starts recording. I am going down, making sure not to descend deeper than three or four feet, holding the Nomad computer in my hand. I circle the pool, then stop in front of the camera and operate the computer with its stylus. The touch screen operates just fine. I bring up some menus, click here and there - no problem at all. The Nomad, like many handheld computers, has handwriting recognition, and so we try to capture that in a closeup. It works, but the screen is too reflective to get a good shot with the camera, and so that didn't quite pan out. I do a final underwater lap around the pool and surface, with Morgan capturing that on the Casio.
So that was diving with a handheld computer that was probably never meant to be used in scuba gear. But it could handle it, and now I wonder if perhaps we won't be seeing underwater computers sometime soon. They'd sure beat a white slate and a pencil. Perhaps. There are times when throwing expensive technology at a simple problem makes no sense, but I'd like to see it anyway. Imagine drawing, reading an eBook, emailing or testing, or even browsing the web during a long, boring deco stop. Or using the dive slate's built-in digital camera. The opportunities are endless.
As is, I got to dive again, and I got to do something new and exciting. I needed that. An event that I had looked forward to all year was recently cancelled. It was to be my first dive trip to a "real" exotic dive location. I had practically lived for that all this year, thought about it while falling asleep and dreamed how great it'd be, but due to circumstances beyond my control, it won't happen. So that totally threw me for a loop and left profound sadness that I have been unable to shake. I think diving and all that it means and includes is more than just a sport. I am not quite sure what it is, but I know it changed my life.
Posted by conradb212 at 11:20 PM
September 14, 2007
Nitrox certified
I was certified for Nitrox use on September 12, 2007 after completing the PADI course. Why PADI and not NAUI? Primarily because preparation includes a lot of work with dive tables, and once you become used to either the PADI or the NAUI method, it's difficult to change. The tables are, of course, based on the same principles, but just different enough to thoroughly confuse you. So I figured why add confusion to an already confusing thing like using dive tables?
It's interesting how those courses are conducted. You actually do all the studying beforehand with the coursebook in the crew pack. You also watch the DVD that covers the exact same material, but makes it all look nice and friendly. And you practice with the included dive tables. For the Nitrox class that's plastic dive tables for Nitrox with 32 and 36% of oxygen, and a table that shows equivalent air depth for mixtures with 30 to 40 percent oxygen. On the other side of that one is an Oxygen Partial Pressure table you use to calculate total allowable oxygen exposure for a day.
The course book is organized like the larger book for the initial PADI Open Water class. You read, you underline and you answer questions at the end of each chapter. The idea is not necessarily to memorize every word, but to grasp concepts and know where to look things up. The answers are always given, on the same page, in small print. At the end of each major section is a "knowledge review" that you fill out and sign. No answers given there. Studying and understanding all the materials takes some time, and then doing all the dive table examples takes some more. It's not necessarily very difficult, but it is important stuff that people from all walks of life need to understand before they go diving with Nitrox. Bottom line: you need to set aside several hours of concentrated worktime to prepare for the class.
The class itself was full. 12 people at least in a small but neat and well organized and equipped classroom. Our instructor was Rick Rowett, a PADI course director, which is as high as it gets in the PADI hierarchy, and also the manager of the Dolphin scuba store. And, as he later told us, a reverend. Rick was personable, knowledgeable and did a great job. The class essentially consisted of going through all questions of both Knowledge Review sections, with detailed explanations if someone had gotten it wrong or did not understand. A good approach, assuming everyone had indeed done their studies beforehand. Rick threw in a lot of explanations, advice, and anecdotes, making it all flow nicely and having great rapport with the class.
The second part of the Knowledge Review included several dive table questions, and we worked through each and every one of those in detail.
Once that was done, we signed a general liability release and were issued the final test that consisted of 25 multiple choice questions, including several that required the dive tables and a calculator. Those were not idiot questions and required some thinking. Once finished, you joined Rick in the next room where he demonstrated the use of an oxygen analyzer. You then got to use the analyzer yourself and entered the requisite data into a log book, just as you would when you get a Nitrox fill.
After everyone was finished and had done the hands-on with the oxygen analyzer, it was back to the classroom where we went over all the questions. Once again, Rick explained each answer and went into more detail if someone had gotten it wrong. I got 24 of 25 and stumbled over a trivial one. No big deal.
Thing is, unless you really, really goof, you can't fail. You no longer have to hand in the signed knowledge reviews that are part of the course book (and bound in). Apparently, you also cannot fail in the final test; at the bottom is a statement that says something like, "I have gone over the answers I got wrong and now understand the question and how to answer it properly," and then you sign that. And there are no dives involved. So you don't get to experience the difference between compressed air and Nitrox under the guidance of an instructor. No big deal, really, as Nitrox is becoming quite common.
I think I have mixed feelings on this. While Nitrox has been used for a hundred years or so, its use in recreational diving is relatively new. Initially and from what I am told, PADI and NAUI were quite opposed to it. Early course materials included true but rather discomforting statements like "you can die," and even the current course book has sort of a "not invented here" tone to it. It feels a bit like Nitrox is a subject that the certifying agencies were forced to include because the lure of longer bottom times (and feeling better after dives) were such that recreational divers simply wanted to do it.
If used improperly, Nitrox can be dangerous, but that goes for a lot of stuff in life. Anyone can walk into a car dealership and buy a 500-horsepower Corvette or Viper even though such vehicles can be vastly more dangerous than, say a Toyota Camry. There is no "Corvette" certification needed (actually, good thing PADI doesn't run the Department of Motor Vehicles...). So it comes down to common sense.
What makes it all a bit more confusing is dive computers. Sure, understanding the theory behind Nitrox use, and being able to figure out a problem on old-fashioned dive tables, is a good thing, but these days divers rely on dive computers. They may take a look at the maximum depth for their Nitrox mix, but then solely rely on what the dive computer says. And that's a big problem because dive computers are definitely not standardized. It can be next to impossible to even figure out if a dive computer can handle Nitrox unless you have the instructions at hand (and who does?) and that the instructions are halfway intelligible (they often aren't). So you take a class to learn Nitrox diving with dive tables, but then virtually everyone uses their dive computer and may not have a clue how to even set it to Nitrox. A definite weakness in the armor there.
In any case, I am hugely pleased that I finally have my Nitrox certification!
Posted by conradb212 at 11:19 PM
September 12, 2007
Nitrox
Today I am going to take the PADI Nitrox class. Attending the class and passing the exam will allow me to use Nitrox when I am diving. Interestingly, actual dives are not required with the class - it is all academics. You buy a "Nitrox crew pack" that consists of a textbook with questions, a DVD that illustrates what is in the textbook, and three special dive tables for Nitrox.
What is Nitrox? There are various definitions. Nitrox is something that almost no one who isn't a diver has ever heard of. And even if you explain it to a non-diver, the whole theory behind it is such that they're likely just going to shrug their shoulders. Hmmm... Nitrox. Interesting. If that.
So what is it? Well, it's a special air mix where the percentage of Oxygen versus Nitrogen is different from that of the regular air we breathe. Regular air consists of about 21% Oxygen, 78% Nitrogen, and one percent of various trace gases (mostly Argon, but also a tiny bit of Neon, Helium, Krypton, Methane and a good half dozen others). Divers generally consider Nitrogen an "inert" gas because our body does not metabolize it. A better description is that Nitrogen is generally inert. There are, after all, things like Nitrous oxide -- N2O -- which is also known as "laughing gas" because of the mild euphoria and analgesia it caused in dental patients. It's also been used as an aerosol in spray cans, and street racers use it to gain more power from their engines as it delivers more oxygen than regular air, and thus allows more fuel to more burned.
None of this matters to divers who do consider Nitrogen an inert gas. Unlike Oxygen, our body does not use it up. However, Nitrogen does play a very important part in diving anyway. That's because it is absorbed into our systems, and that absorption is pressure-related. This absorption is not an issue under atmospheric pressure. Our bodies are in a state of nitrogen saturation, our tissues absorb so and so much nitrogen and that is that. That all changes when the pressure on our bodies is increased or decreased. Decreasing pressure, as in going from sea level up to the top of a mountain where the air pressure is less is rarely an issue as pressure simply goes from one atmosphere, or roughly 14.7 pounds per square inch (psi), to maybe 10 or 12 psi at considerable altitude. It is very different when we dive. The pressure on our body increases by a full atmosphere for every 33 feet of depth. So if we dive down to 33 feet, it is already twice what we experience at sea level, and at 99 feet four times as much. And since dives don't generally last very long, we go from standard atmospheric pressure to several times that and then back within an hour or so.
What does that mean? Well, several things. When we dive, the air we breathe must counteract the water pressure pushing in on our bodies. So at 33 feet, though breathing feels no different, the pressure of the air supplied by the regulator is actually twice that on the surface. We don't really notice that due to Boyle's law that says as gas pressure increases, its volume decreases. The composition of the air, however, does not change. Even under pressure, it's still roughly 21% oxygen and 79% nitrogen. John Dalton figured that out over 200 years ago. Around the same time, another brainiac, William Henry, found that the amount of gas that will dissolve in a liquid is a function of its partial pressure and how easily the liquid absorbs gas. So what do we make of all that?
Well, if we go down to 33 feet, the compressed air we breathe still consists of 21% oxygen and 79% nitrogen, but its pressure is twice as much as on the surface. That means we now inhale twice as many oxygen molecules and twice as many nitrogen molecules. How does the body react to that? As far as oxygen goes, it simply takes what it always takes and the rest is breathed out by exhaling. Even at sea level, humans do not use all the oxygen we inhale in a breath. In fact, it's only a quarter of it or so (else doing mouth-to-mouth resuscitation wouldn't help at all). Down at our 33 feet, we still use about the same number of oxygen molecules, the rest goes to waste (a phenomenon which, of course, is exploited by rebreathers).
Nitrogen, that's another story. As a mostly inert gas it simply gets absorbed into our body tissues in compliance with Henry's law. So as we go deeper, more nitrogen gets absorbed into our body tissues. Not all absorb at the same rate -- some are "fast" tissues and others are "slow" tissues. The software program that I use with my UWATEC dive computer, for example, shows how the various tissue "groups" in my body absorb or release nitrogen during the various stages of my dives.
Now nitrogen, inert though it is considered, does two things. First, while absorbing more of it into our bodies during a descent doesn't do much, releasing the gas again as we ascend is another matter. If we ascend too quickly, the body "off-gases" the absorbed nitrogen in the form of bubbles. If all goes well, those bubbles are tiny and simply go through the blood stream into our lungs where they are safely exhaled. However, rapid pressure decrease can result in bigger bubbles and they can get stuck in the blood and block passages, or they can lodge in inopportune places like joints, the skin or elsewhere. That can have dire consequences. The dreaded "bends" is one. And the bends can range anywhere from discomfort to death.
The second thing nitrogen does is exhibit a narcotic effect if its partial pressure becomes too great. Partial pressure means the pressure the gas represents of the total pressure in a gas mix. Nitrogen's partial pressure is about 71% of the total pressure of air at sea level. As we dive, nitrogen's pressure stays the same in terms of percent, but at 33 feet that 71% is now twice as much in terms of absolute pressure, so we breathe in twice as many nitrogen molecules with each breath. As we go deeper yet, that partial pressure of nitrogen somehow interacts with our nervous system and causes a narcotic effect called "nitrogen narcosis" or, by more poetic souls, things like "rapture of the deep." While that may have its pleasant aspects, being what really equates to being kind of drunk while diving at, say 120 feet, isn't a very good thing.
So this is where Nitrox comes in. When most divers say "Nitrox," they mean air that has a larger percentage of Oxygen and a smaller percentage of Nitrogen. What does that do? Well, with less nitrogen in the breathing mixture, less will be absorbed into the body. If you dive with Nitrox to a certain depth, it's really like diving with air to a lesser depth. Anyone who took the basic open water diving certification classes is familiar with the dive tables. They are about how long you can stay under without having to make decompression stops so that the absorbed nitrogen can be released safely. With less nitrogen, less is absorbed. And that means you can stay down longer. If you stay down the same amount of time as with air, and at the same depth, and then come up, you have absorbed less nitrogen and need less of a surface interval, if that matters to you.
So it's all good, that Nitrox stuff. Well, yes, mostly. But everything comes at a price. With Nitrox it is not only the higher price of a tank refill (they need to create that different kind of air somehow; it cannot just be run through a standard air compressor), but also what another gas can potentially do to us. And that gas is Oxygen. Yes, life-giving Oxygen can also be toxic. How so?
As we go deeper and the partial pressure of Oxygen increases, it can have its own effects on the body. It can make you experience a bunch of syndromes such as tunnel vision, ear ringing, nausea, euphoria or anxiety, dizziness, and twitching or muscle spasms. Those are all warning signs of impending CNS, or central nervous system toxicity. That generally leads to convulsions and you drown. Very bad.
So we have to watch oxygen as well. The partial pressure of oxygen in air on the surface is 0.21 atmospheres. At 33 feet it's 0.42. And at 66 feet 0.63. It's been determined that the maximum safe partial pressure of oxygen is about 1.4 atmospheres, with brief "contingency" exposures of 1.6 acceptable. With compressed air, we get there well past the recreational diving depth limit of 133 feet, so it is not generally an issue when you dive with compressed air. With Nitrox, it's different. Two common Nitrox mixes contain 32 and 36% oxygen. With a 36% oxygen mix, usually called EANx36, we reach that 1.4 atmosphere barrier at just under 100 feet. You can see the problem here, and you can see why divers who want to use Nitrox and take advantage of the longer dive times it affords need to know about all this and the theory behind it. Sure, dive computers take care of it, but you need to understand how it all fits together.
And there's more. While air is air is air, with Nitrox there can be errors. If you think you're diving with 32% oxygen in your tank but, in fact, it's 42%, things can go real bad quickly if you go deeper than you should. So one of the cardinal rules of Nitrox diving is that the diver MUST test the Nitrox mix personally, with an oxygen tester. There are also mandatory records and labels to provide extra safety and accountability.
But even that is not all. Oxygen can be dangerous. It can ignite in pure form, or even when it is present in high concentration. The crew of Apollo 1 perished in a flash fire when a spark ignited the pure oxygen in their capsule. Some filling methods use pure oxygen which is then diluted until the proper mix is reached. So tanks used for Nitrox must be "oxygen-safe." Depending on the oxygen mix, other parts of the equipment, such as regulators, may also need to be oxygen-safe, though the kind of Nitrox recreational divers use does not require anything other than a dedicated Nitrox tank.
So I will soon find out about Nitrox and how it feels. Carol swears by it and uses it almost exclusively. Like many Nitrox divers, she feels less fatigue after a Nitrox dive, and she generally feels better. Me, I have only done a few dives and have not been subjected to to the rigors of lots of repeat dives, so I guess I'll find out.
Posted by conradb212 at 11:19 PM
