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Diving with Hydrogen – It’s a Gas

When most people think of hydrogen, they think of the fuel that stars burn in their nuclear fires, the hydrogen bomb, or the Hindenburg disaster. Hydrogen is known for its combustibility and explosiveness. Not many people would think of diving underwater with it.

Technical divers breathe various gas blends, using mixtures of nitrogen, oxygen and even helium. But leave it to the ever inventive Swedes, makers of some of the best diving equipment in the world, to use hydrogen as an experimental diving gas as early as the 1940s.

Hydrogen will not burn under two conditions; if there is too little hydrogen, or too much hydrogen and not enough oxygen. A gas mixture (air or oxygen) with less than 4% hydrogen will not burn, and with more than 94% hydrogen in oxygen (or 75% hydrogen in air), the gas mixture will also not burn. So 100% hydrogen will not burn, unless it leaks out of its container and gets diluted in air. And then if there is an ignition source, woosh, a la Hindenburg.

 

A diver with supposed nitrogen narcosis. Photo credit, Daniel Kwok on flickr.

So why would anyone consider breathing hydrogen? When diving deeper than a few meters, you need a so-called diluent gas to mix with oxygen. Air is a mixture of nitrogen and oxygen, and when compressed, that nitrogen becomes narcotic, leading to nitrogen narcosis, or “rapture of the deep”. When air is compressed it also becomes dense, making it more difficult to breathe than air is at the surface.

Helium, often used by deep diving Navy and technical divers, is less dense than nitrogen and therefore is easier to breathe at depth. Furthermore, it is not narcotic, so no more “rapture of the deep”.

But for seriously deep diving, greater than about 450 msw (~1500 fsw), even a mixture of helium and oxygen becomes dense enough to impede breathing. One solution is to use an even lighter gas, hydrogen.

Experimental hydrogen-helium-oxygen gas mixtures have been used by COMEX in France to slightly exceed, at 2290 fsw (701 msw), the U.S. deep diving record (2250 fsw, 686 msw) set using a mixture of helium, nitrogen and oxygen.

Hydrogen has one annoying property — it is narcotic. It is far less narcotic than hyperbaric nitrogen, and some narcosis seems to be necessary to counteract the deleterious effects of the High Pressure Nervous Syndrome (HPNS). However, unlike nitrogen narcosis, which is akin to mild alcohol intoxication, hydrogen narcosis is reported to be psychotropic, inducing at great depth altered realities akin to those produced by LSD.

I once was conducting medical research on a 450 msw dive at the German GUSI deep diving chamber, and one of the divers was a French diver who had been a subject on the French hydrogen dives. He reported, without going into detail, that he did not like the effects of hydrogen at all. It was strange, he said. On the other hand, the same diver did very well on the helium-nitrogen-oxygen gas mixture used at GUSI and Duke University.

That some exotic gases on deep experimental dives would be considered strange is an understatement. Deep hydrogen has been reported to produce out of body experiences, something that a person as well grounded as a professional diver would consider frighteningly bizarre.

Swedish diver Arne Zetterström

The Swedes, and Arne Zetterström in particular, were interested in hydrogen diving during World War II for a simple reason; they wanted to dive deep, without the effects of nitrogen narcosis, but did not have access to helium. Most helium comes from gas wells in the United States and Russia. So, looking for another diluent gas other than helium, Zetterström briefly considered two constituents of intestinal gas (flatus), namely methane and hydrogen. Arguably, it was easy for the Swedes to produce plenty of methane and hydrogen. Just how they planned to do that is something I never asked.

Eventually, hydrogen was chosen for the Swedish dives simply because hydrogen was less dense than methane.

In principle, hydrogen could be used by a deep technical diver, but only at depths deeper than 132 fsw (5 atmospheres), a depth which would turn the noncombustible 4% oxygen in hydrogen gas mix into a so-called normoxic gas mixture, meaning it would have about as many oxygen molecules per breath as air at the surface. If the diver attempted to come shallower on that same gas mixture, he would lose consciousness due to hypoxia.

Since helium is not a combustible gas it does not have gas mixture restrictions. As long as  a helium-oxygen gas mixture contains the right amount of oxygen (not too much and not too little), then it will be safe. Both nitrogen and helium are therefore far preferred over either of the flammable gases methane and hydrogen  for use in breathing gas mixtures for diving.

Nevertheless, as divers continue to explore ways of diving deeper, it is certainly possible that hydrogen and other exotic gases may eventually play a role in deep life-support. Who knows, perhaps a perfect gas mixture will involve a blend of hydrogen and methane along with oxygen. If so, perhaps we could call it, oh I don’t know, maybe … Flatogen!

 

 

 

 

 

What I Would Miss on Mars

When I first saw images from NASA’s various Mars rovers, I was almost crawling out of my skin with excitement. As I spoke at a NASA sponsored conference where scientists and engineers were discussing plans for a Mars mission and colonization, I was enthralled with the thought that humans are actually planning for mankind to leave our planet for a foreign world.

Lately, I’ve been thinking about what I would miss if I were a colonist on Mars. I’ve decided, what I would miss the most is something we take for granted in most places of the world; water.

Of course, Martian pioneers would have to have abundant stockpiles of drinking water. But I sure would miss Earth’s oceans; their awe inspiring breadth and depth, their multitudes of sea life, and the gentle shades of blue-green in clear water along sandy coasts.

I would miss the sound of the surf, the laughter of children chasing and being chased by harmless but persistent waves.

I would miss the sound of clicking shrimp, and the clicking of dolphins corralling schools of fish.

I would miss being able to open the windows on a perfect day. I would miss feeling a breeze on my bare face.

I would miss never having to wonder if I had enough oxygen to breathe. I’d miss not worrying that toxic carbon dioxide would seep into my tiny house and suffocate me and my family in our sleep, or that my home’s pressure barrier would fail and our blood would essentially boil, releasing a flood of deadly bubbles stopping our hearts.

I am concerned that those attempting to colonize Mars woud sink into a chronic melancholy simply because the water that pleases and sustains so many of us is absent on Mars. Could these homesick astronauts survive, and even thrive?

If the first wave of colonizers did survive, procreate, and nurture the next generation, the first generation of true Martians, then I suspect that generation would fare much better psychologically than the first. After all, they would never have known the verdant forests and splendorous seas of Earth.

As I pondered what it would be like to be a third and fourth generation colonist on Mars, growing up knowing nothing else, I realized that rather than space exploration being a guaranteed and common place activity at that time in the not too distant future, a bleaker possibility exists.

It is entirely possible that war, disease, asteroid and comet collisions, or even the failure of mismanaged banking systems could so impoverish the Earth that space travel to the Martian colony might not remain economically sustainable. Eventually, to the stranded Martians our Earth could be little more than a distant memory, perhaps even a legend. Martian children might grow up on the red planet hearing tales of Sky People who came to Mars from a far away place, a world of indescribable beauty, with colors of blue and green that are not even imaginable on Mars.

Some native Americans have in the past recounted tales of Sky People coming to Earth. Wouldn’t it be ironic if the next generation of Earthlings becomes the fabled Sky People that populate the planet Mars?

If offered the chance to be one of those Sky People on a one-way trip to Mars, would I sign up for the mission? Frankly I don’t think I could leave the most beautiful planet in the solar system, perhaps in the galaxy, even for something as exotic as a trip to Mars. 

 

Computer Simulation as Art — or Rorschach Test

No one has ever confused me for an artist.

I might have been visually gifted as a 3rd-grader, as my parents told it, at least compared to my peers. However, I never seemed to progress beyond that point. I think my progress slowed about the time I saw my first Rorschach test.

I realized then that some people’s art is someone else’s diagnosis. After all, it is no fun to look at an ink blot abstraction, to voice an opinion about it, only to have an authority figure nod his head and write in his notebook as he says, “I see,” when obviously he didn’t.

Clinical trauma aside, I now know that all humanity looks instinctively for visual patterns and searches for meaning in patterns whether they be random or not. There is a survival aspect to that of course; if we detect a tiger’s stripes partly hidden in a confused background of woodland scenery, that offers a potential survival benefit.

Sometimes, even the most mundane things turn out to be “pretty”. Such were the images I saw being formed on my computer screen the other day. The more I looked at them, the more interesting they became. They were like my own Rorschach test, in a very literal way. They were random patterns based on random processes, but my brain refused to look at them that way. They appeared to me as images of natural things, representing anything except what they truly were.

The image to the left, for instance, looked to me like a view through a telescope of a star field with at least one galaxy situated near the center axis.

Or in a very biological way, it might be the view through an immunofluorescence microscope.

The next image looked to me like a view of a placid star seen in ultraviolet light. I could almost feel the blistering heat radiating through space.

Alternatively, it might be a view of a human egg waiting patiently for fertilization, an altogether different interpretation, but like the first, being a necessary component of creation.

The final image looked to me like a cooler star but with clearly visible solar prominences, magnetic storms arcing over the hellish nuclear surface.

I have no idea what others might see in these images, if anything, but I’m guessing each image can be interpreted differently based on one’s own life experiences.

And that after all is the whole point of art, and Rorschach tests.

 

 

The above images were created as part of a random, or stochastic, simulation of rebreather scrubber canisters. They are a view of the upstream end of an axial canister, and shows the state of the canister as heat producing carbon dioxide absorption reactions are beginning.

The cooler looking the canister, the less the amount of exhaled carbon dioxide entering the canister.

The simulation tracks chemical reactions and heat and mass transfer processes in an array of 272,000 finite elements making up a simple absorbent canister. Slicer Dicer and 3VO software (PIXOTEC, LLC) were used to visualize the three-dimensional data set acquired during one moment in time shortly after the simulated reactions began.

 

 

Another Rebreather Scrubber Thermokinetic Simulation

Compared to the previously posted video of a segment of a rebreather scrubber, this video shows a much larger, and therefore more realistic scrubber with axially aligned, CO2 rich gas flow passing from left to right. Due to the larger size of the simulation space, more widely distributed heat patterns are noticeable, as are fluctuations in heat. The flow of those fluctuations are most noticeable along the simulated boundary of the cylindrical scrubber bed.

The assumptions of this simulation are that CO2 production (diver workload) is constant throughout the simulation run, ventilatory flow through the canister is constant, the surrounding water temperature is constant at 50° F, and the canister was chilled to the water temperature before the “diver” started breathing through it.

The previous simulation conditions were similar except that the canister was toasty warm prior to immersion in frigid water.

To fully appreciate the fine detail of the imagery, click on the video frame then expand the video to full screen size (lower right symbol immediately after “You Tube”) and play back in 1080p High Definition mode.

 

 

 

 

The Mysterious Physical Attraction of Slash Pine Seeds to … Anything

Pine cones are falling from the sky and smacking the roof with a thud, with all the earnestness of a piece of reentering space debris. The sound reverberates among the rafters, giving the impression of a large falling limb, sending us scurrying outside searching for damage to the roof.

It is October in the Florida Pan Handle, the time of year when pine cones eject their winged pine seeds.  Once emptied, the cones are rejected by their parental trees like useless appendages.

Those seeds had begun their race towards destiny high in the outstretched branches of 100-foot tall slash pines, being nestled by the overlapping leaves of their natal cones. But once ejected from their nest, they were on their own, distributed by gravity, winds, and those always tricky helicopter aerodynamics.

Walking outside this morning I could see those seeds helicoptering down to the ground, or the pool. Those landing fruitlessly, without hope on the concrete were distributed forlornly like bodies on a battle field. But those landing in a pool, being swept towards the uncaring maw of the pool skimmer, did something interesting.

It reminded me of illustrations of the attempted fertilization of human eggs by sperm; all lined up, jockeying to be the first to the prize. The heavier seed end of the wing seemed to be attached to the pool ladder as if by magic, although I suspected some subtle electrical charge interaction with the metal.

This was not occurring in still water; there was a considerable flow carrying unattached seeds swiftly past those clustered around the ladder.

Click to enlarge.

But then I saw the seeds clustering around other objects, the walls of the pool, and in an almost Oedipal fashion, a pine cone floating in the pool. One cluster of seeds were touching their ends together as if in some group incest.

Keep in mind, each seed fluttered down on its own, singly. Yet when they met in the water they had an unexplained physical attraction, literally.

 

The last two photos made me suspicious that the attraction was not based on electrical charge, but on surface tension — somehow. In the photo of the pine cone you can see dimples in the water around the wings and seed, an observation that positively screams surface tension.

Just how surface tension works to orient these seeds in the way they do is unclear to me. However, I see an evolutionary benefit.

Concrete pools are not of nature. In nature, seeds falling in water might be benefited if surface tension orients the seed end towards the edge of whatever stream or pond the seeds fall into. If the seed ends can touch the soil of the earthen banks, then they have a chance to germinate.  If the seed ends pointed away from the soil, they would eventually become water logged and sink, thus drowning the potential pine seedling.

In the following short video clip we see the strange maneuvering of three separate seeds, unattached except through some invisible force, moving to and fro in the eddy behind a pool ladder in a relatively swift current.

[youtube id=”CDmWVLZOpu4″ w=”525″ h=”439″]

 

One of the many joys of being human is discovering the beauty and mystery in nature. You don’t have to understand it to appreciate it.

 

 

 

 

 

I Dreamed about Flying Last Night

I rarely dream about flying, but I did last night.

I seem to have a propensity for thinking about flying. I’ve written about flying hybrids, as in James Patterson’s Maximum Ride series about a flock of flying kids, which is, as I’ve said before, “some of the most interesting reading a bird man (aka aviator, pilot) is likely to find in an airport bookstore.”

I’ve written about flying whales, and I’ve written about flying airplanes. But until now I haven’t written about flying dreams.

One reason is simple: no one wants to hear about other people’s dreams. But flying dreams are part of our collective experience. Everyone has them at some point, usually when young. As I grow older I find them occurring less frequently, and therefore find them all the more enjoyable for their rarity.

Flying dream artwork by Joseph Kemeny (www.josephkemeny.com)

Last night my arms were initially wings, but I quickly realized that I lacked the strength to fly with wings like a bird, or like Maximum Ride. I solved that problem by reverting back to my old dream style, flying with outspread arms, effortlessly.

I was standing on a 3rd story window ledge in a home where a young boy was close by, and I accidentally knocked a small pumpkin sitting on that ledge to the ground. It splattered.

Feeling some sense of responsibility for the child’s welfare, I told him not to try what I was about to do, for his head would splatter like the pumpkin. And then I stepped off the ledge and flew.

It was foggy, but instinctively I knew how to get where I was going, without aid of charts or GPS. I knew I could navigate based on some primordial signal in my brain, like a migrating bird.

It was wonderful.

It was undoubtedly a lucid dream because I was aware of a certain biological need that I consciously resisted because I did not want to break out of the dream. I knew I would never regain the dream once it was broken.

The strangest flying dream I had was only seconds long but memorable. I was viewing a glass city, with tall glass spires reaching far into the sky. It was clearly not of this earth, and I can’t swear that I was even human. But I launched myself from near the top of one of those tall glass buildings, and swooped downward, gaining speed, then glided on without effort, like an eagle.

In my college days I told my roommate about a flying dream where I was trapped underneath trolley lines in Atlanta (yes, they used to have electric trolleys downtown in the 60’s) and he found that amusing, but I did not. It was peculiar, but frustrating.

Reportedly it’s common to encounter barriers like electrical wires, and this time I sure enough found those blocking my way at one point, but unlike before I was able to ascend vertically till free of them, then continue on my way.

Sigmund Freud made much ado about dream interpretation, and would no doubt see physical barriers in flying dreams as symbols of psychological barriers existing in the dreamer’s waking world. But the fact that flying dreams are so common, even archetypal in a Jungian sense, and typically so enjoyable, makes me wonder if they might be more than some complex mental fiction that requires a highly paid professional to interpret. Perhaps they are nothing more than memories.

While you digest that thought, I suggest you enjoy the wonderful flying sequence below, generated by a computer game. For full effect, play it in high definition and full screen.

 

 

A Look Inside Rebreather Scrubber Canisters, Part 2

Computer modeling allows you to see things that are invisible in real life.

The previous posting showed the complex thermal profiles generated in a rebreather canister found in closed-circuit underwater breathing apparatus during the CO2 absorption process. But heat generation is just part of the absorption process. Simulation allows you to see how the end product of CO2 absorption, calcium carbonate, gets deposited inside the canister.

To the right is calcite, a form of calcium carbonate. Divers never see crystals of calcite in the scrubber canister because sodalime granules are never completely converted to calcite. Typically, no more than 50% of the granules react completely with exhaled CO2.

The following images show the interior of a a scrubber canister as the sodalime granules begin reacting with exhaled CO2. When sodalime granules first begin to absorb CO2 the image becomes purple. With more CO2 the color turns reddish, and when all binding sites are filled with reacted CO2, the granule color becomes yellow.  

The more carbonate in a particular location in the granule bed, the more yellow the image.

The probability that an exothermic absorption reaction would occur is dependent on the granule temperature, the granule size, the number of granules and the number of sites available for reaction in each granule.

In the second image, CO2 absorption sites in the inlet to the canister were completely filled (thus showing yellow), and small pockets of absorption were extending up the canister walls.

When I saw the third computer-generated image, I was surprised. It showed that in the central portion of the absorbent bed, the moving thermal front seen in the previous post was leaving behind a calcited bed. However, sheets of calcium carbonate were forming on the outer surface of the canister, the coldest portion of the canister.

Initially that result was counter-intuitive. Then I realized that low temperature makes the odds very low that the first granule encountered would absorb CO2. All chemical reaction rates are temperature dependent, therefore exhaled CO2 would be very likely to proceed downstream to the next granule. There again the odds of being absorbed would be low so the CO2 molecule would continue downstream.

However, given enough opportunities, even low probability events eventually occur. That means that along the cold canister walls, carbonate begins to be deposited much further downstream than in the warmest, and most highly reactive portion of the bed.

Unfortunately, the low probability of CO2 absorption in cold granules means that CO2 hugging the cold canister walls is likely to pass completely through the canister, unabsorbed. Chances are also high that the same molecule would be shunted to a different portion of the canister on its second pass through the canister, and therefore would eventually be reabsorbed.

The following link is to a high definition video showing carbonate deposition in a cylindrical scrubber canister as the simulated diver plunges into icy water. For best effect go to full screen and 1080p mode.

 

 

Further details about the computer simulation involved in the production of these images and video can be found in the paper “Computer Modeling of the Kinetics of CO2 Absorption in Rebreather Scrubber Canisters”, in MTS/IEEE OCEANS 2001 Conference Proceedings, published by the Marine Technology Society; Institute of Electrical and Electronics Engineers; Oceanic Engineering Society (U.S.); IEEE Xplore (Online service).

A Look Inside Rebreather Scrubber Canisters, Part 1

If you’re diving a rebreather (closed-circuit breathing apparatus to be exact), then you know the scrubber removes carbon dioxide from your recirculated breath. Without the scrubber working, you’d go unconscious from carbon dioxide intoxication within a very few minutes of starting the dive.

But do you really know what’s going on inside that scrubber canister?

A stochastic computer simulation developed by the author gives as realistic a glimpse inside as we can get.

Loose granular and rolled sodalime. Click to enlarge.

Carbon dioxide scrubber canisters usually contain a chemical mixture called sodalime that chemically reacts with carbon dioxide in a diver’s expired breath. That material may be in granular form, or in a preformed roll. Sodalime is a mixture of calcium hydroxide and sodium hydroxide, which when it reacts by absorbing carbon dioxide is converted into calcium carbonate (CaCO3, calcite), a major constituent of limestone.

The overall chemical reaction can be simplified to:

CO2 + Ca(OH)2 → CaCO3 + H2O + heat

In the following sequence of images we see a rectangular prism shaped scrubber canister arranged axially such that the diver’s expired breath enters the section from the left, passing completely through the canister section before exiting to the right. A portion of the canister was cut away digitally after the simulation was run to allow visualization of temperatures within the canister interior.

Beginning of the simulation. Click to enlarge.

Initially, the canister is at room temperature, and then is immersed in cold water as the diver begins his dive. Temperature is color coded: the coldest temperature is black, and increasing warmth is portrayed in an intuitive fashion from purple to red to yellow, and finally white, being the highest temperature.

In the first image, CO2 has just started reacting with the sodalime at the entrance to the canister section, with a slight heating resulting. Thermal conduction is cooling the exterior surface of the canister, but most of the inside still remains at room temperature.

In the second image, the reaction front has clearly formed, and the hottest portion of the canister has begun moving downstream. Convection carries heat rapidly downstream to heat the diver’s inspired breath, and is seen to offset canister cooling due to conduction from the surrounding cold water.

Click to enlarge

In the image to the left, the heating front is fully developed, and residual heat has spread almost completely throughout the downstream portion of the canister.

In the next image, to the right, the front is beginning to weaken in intensity.

 

 

 

Finally (lower left figure), the thermal heating in the reaction front, indicative of CO2 absorption effectiveness, is fading out, and the cooling of the canister from the surrounding cold water is beginning to win the tug of war between heat generation and conductive cooling.

At that point in time, the canister is spent, and essentially all of the exhaled CO2 is passing right through the canister without being absorbed. If the diver had not ended his dive before his canister reached this point, he would be at great risk of passing out due to CO2 accumulation.

The last figure (lower right) shows temperature readings at various locations, and at various times (reps) throughout the simulation run. The orange and brown traces marked “temp” are measured temperatures from locations near the entrance to the canister. They rise abruptly as the absorption reactions start, and fall quickly as the reaction front moves past them, downstream.

Click to enlarge

The curves that remain elevated longer represent the average exhaled gas temperature, and the average temperature within the absorbent bed. After reaching a peak, the average bed temperature steadily drops as cold gas from the inlet (exhaled) gas chills the portion of the bed behind the reaction front. Exhaled gas temperature, on the other hand, climbs more slowly, but remains more stable until the bed becomes depleted of absorbent activity.

The monitoring of absorbent canister temperature changes is what makes the rebreather scrubber canister monitors used in the Inspiration and Sentinel rebreathers possible. The Sentinel technology is licensed from the U.S. Navy Experimental Diving Unit.

In the next posting, we’ll see the surprising way that cold canisters fill up with calcium carbonate.

 

 

 

 

 

 

 

 

 

The following is a high definition video of the computer simulation of heat generation and loss in a short cylindrical canister. For best effect go to full screen and 1080p mode.

 

 

Further details about the computer simulation involved in the production of these images and video can be found in the paper “Computer Modeling of the Kinetics of CO2 Absorption in Rebreather Scrubber Canisters”, in MTS/IEEE OCEANS 2001 Conference Proceedings, published by the Marine Technology Society; Institute of Electrical and Electronics Engineers; Oceanic Engineering Society (U.S.); IEEE Xplore (Online service).

Diving Accident Investigation

Diving helmets waiting for accident investigations. Click for a larger image.

Compared to aircraft accident investigations, diving accident investigations are often ad hoc in nature, poorly conceived and poorly funded. Nevertheless, these investigations are just as important for the safety of the diving public as are similar investigations for the flying public. Unfortunately, no national regulations presently address how investigations of diving accidents should be conducted: volunteer investigators have no legal status for extracting information about an accident, and they have no legally binding protection from litigation based on the conduct of their investigation or on its results. That is, no business case can be made for conducting diving accident investigations, in spite of the moral authority for conducting them.

With the conviction that this untenable situation must eventually change, this presentation will describe one approach to diving accident investigations with particular emphasis on rebreathers and will draw some comparisons to aviation accident investigations by the National Transportation Safety Board (NTSB).

Aircraft accident investigations

The "black box" containing data recorded just prior to, and during, a commercial aircraft accident.

Pilots know that if they are involved in a fatal crash, the NTSB will investigate the accident by examining in excruciating detail everything those pilots did for hours, perhaps even days or weeks, leading up to that accident. It will investigate how often they called flight service to check on the weather. The NTSB will go through those pilots’ personal logbooks to check on their currency and proficiency, and it will check Federal Aviation Administration (FAA) records for a history of violations. NTSB investigators will also examine an aircraft’s logbooks to scrutinize its maintenance records. They will play back voice and radar data, and if a data recorder is available, they will analyze its contents.

Then they get personal. The NTSB and its FAA counterparts will talk to mechanics, surviving passengers, and friends to ask questions such as, “What were the aviators’ attitudes toward flying? Were they cavalier? Did they take unnecessary risks, or were they careful and methodical?”

Accidents happen.

Due to the detailed, scripted nature of NTSB procedures, the investigation may take up to a year to complete.

A few years ago a pilot’s engine failed and he was forced to make a water landing just off a beach. The ditching should have been survivable, but he lost consciousness on impact and sank with the airplane as it settled to the bottom in relatively shallow water. He drowned.

If he had been a diver, that would have been the end of the story. The public judgment would have been, “A diver drowned. He tried to breathe underwater; this is what happens.” But this victim happened to drown inside an airplane. So instead of the medical examiner simply saying that he drowned, the NTSB started its very thorough investigation procedures.

Fortunately, the pilot also had a surviving passenger. From the survivor’s statement, the aircraft’s maintenance records, and the mechanic’s testimony, an ugly story of reckless disregard for the most basic safety rules of flying began to emerge.

Do divers ever show a reckless disregard for basic safety rules? You bet. It’s unfortunate that the pilot died, but the events leading to his death were a useful reminder that the media in which we work and play, high-altitude air and water, are not forgiving. Humans are not designed for flying or diving, and nature only begrudgingly lets us trespass — on its terms.

The U.S. Navy and Coast Guard are chartered to investigate diving accidents. Unfortunately, there is a huge discrepancy in the number of personnel and the amount of funding for aviation accident investigations compared to diving accident investigations. The NTSB has hundreds of personnel and tens of millions in funding available, whereas the entire U.S. Navy has at most a handful of investigators with no investigation-specific funding.

Investigation team requirements

In the best of all worlds, an investigation team should have access to both a manned and an unmanned test facility, access to experts in all diving equipment (scuba, rebreathers, helmets), and the ability to conduct and interpret gas analyses — sometimes from minuscule amounts of remaining gas. At a minimum, such a team needs the ability to download and interpret dive computer/recorder data. Some investigations may require the simulation of UBA-human interactions for “re-enactment” purposes. An investigation team should also have diving medical expertise available to review medical examiner reports for consistency with known or discovered facts regarding the accident. Last, it should have in-depth knowledge of police investigative procedures, particularly of the procedures and documentation for maintaining “chain of custody”.

Do rebreather investigations have a future?

Considering the resources and time-frames required for laboratories such as the Navy Experimental Diving Unit (NEDU) to conduct diving equipment evaluations on a limited set of accident cases, and the unfunded costs associated with those investigations, it is difficult to imagine a resolution to an ever-increasing need for rebreather investigations. Almost certainly, no independent federal agency similar to the NTSB will ever be responsible for investigating diving accidents, simply because diving accidents lack national attention: the public at large is not being placed in jeopardy.

It is also unlikely that diving equipment manufacturers would welcome federal agency oversight and regulations comparable to those engendered by the FAA and NTSB. Diving might become exorbitantly expensive. For instance, if a $5 part available for purchase in an automotive store were to be used in an aircraft, it would become a $50–$500 part because of FAA required  documentation that it meets airworthiness standards.

The U.S. Coast Guard initiates diving accident investigations and in some cases conducts hearings into those accidents; however, with its enhanced role in Homeland Security, the Coast Guard is unlikely to welcome any efforts to diversify its mission. The cost/benefit ratio would appear to be too great.

For the future, as Dick Vann of DAN has suggested, the resolution may ultimately depend on rebreather users funding a team of dedicated, professional accident investigators. The cost of conducting worthwhile investigations has yet to be determined, and therefore the amount of funding needed to support it is unknown. I suggest that obtaining those estimates should be a priority as we, rebreather users and the industry, decide the next steps in investigating rebreather accidents.

 

The above are highlights from this author’s publication of the same name, found in: Vann RD, Mitchell SJ, Denoble PJ, Anthony TG, eds. Technical Diving Conference, Proceedings. Durham, NC: Divers Alert Network; 2009; 394 pages. ISBN# 978-1-930536-53-1.

This book is available for download at no cost as a PDF file from the Divers Alert Network website (http://www.DiversAlertNetwork.org/or from http://archive.rubicon-foundation.org/8300

On the Odds of Being Struck by Falling Satellites

UARS satellite before deployment. Photo credit: NASA Johnson Space Center.

NASA says the odds that someone will be struck by falling space debris when the bus-sized NASA Upper Atmosphere Research Satellite comes down this week is 1 in 3200. Which got me to thinking … if I was struck while out walking Friday night, would I be unusually lucky because I beat the odds, or unlucky because I beat the odds?

Would my life insurance company pay off? Arguably it would not be an act of God, or an act of war, so I think the insurance company should pay. But I really don’t know if they would; admittedly, I don’t have a falling space debris clause in my policy. (As the space around our planet becomes increasingly crowded, perhaps space debris insurance would be a good investment.)

Now if the odds were 1 in 3200 for each of us, can you imagine the chaos? That would be a mass casualty event in the making. Those odds would be much higher than the odds of being killed by almost anything else I can think of.

From Dr. Strangelove. Click to activate the video.

I suspect there would be anti-NASA marches on the capitols of all the nations affected, which would be most of the world’s nations, by people demanding we nuke the satellite before it poses a hazard. Or maybe they’d demand we send space cowboys up to guide the careening space bus to a safer impact. (I’m not sure how those heroic bronco busters would get back; maybe they’d ride it down a la Dr. Strangelove.)

Fortunately, the odds are mighty small (1 in 21 trillion) that you or I would be hit by this particular satellite. There are much greater chances of winning a state lottery.

But assuming a piece did actually hit me without putting a hole through my head or chest, maybe simply winging me, could I profit from it? Would I become an instant celebrity? Would there be book deals? Can you imagine the television talk show questions, like “How did you feel about your impending death when you saw the fire ball heading your way?”

Let’s face it, with burning metal hurtling to Earth at 18,000 miles per hour I likely wouldn’t see it in time to react, and if I did see it, I undoubtedly wouldn’t have time to mentally compute its trajectory. Should I stand still or run? In fact, I think that calculation would be impossible. An incoming missile simply gets larger and larger in your field of view, giving you perhaps just enough time to say “Oh…” but not enough time to finish the four letter expletive you had intended.

But frankly, I’m not at all concerned. If it happens at all, it wouldn’t happen to me. It always happens to the other guy. Which I’m sure is what the insurance companies are hoping – it will be the other guy, and the other guy will be uninsured.

If pressed, I suppose I could see the insurance company’s point; If I did get squashed by supersonic satellite debris it probably would be an act of God.

Now, I’m trying to think, have I done anything to tick Him off lately?

 

 

 

 

 

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