Science and Technology | John Clarke Online

The Dinosaur in the Window

Child-Looking-at-Dinosaur-Through-Window--61512 — Result of a FreakingNews Photoshop contest. Image credit: Matro1. Click for original link.

Even a child can appreciate the strangeness of watching the broad, glistening side of a dinosaur lumbering past the bedroom window. Fortunately the creature paid me no heed; it didn’t pause to look in the window, just kept moving on, quickly disappearing from view.

I lay there, frightened I suppose, but all I remember in detail very many years later is the remarkable sight of that moving mass of ponderous flesh. I didn’t see its head or its tail, just its massive hulk of a body sliding along the side of the house as close as could be without touching the house wall, or ripping off the roof. I sensed somehow that the dinosaur was not carnivorous; likely a plant eater, perhaps a brontosaurus, and thus no immediate threat to me.

I frankly cannot tell if that image was a flash of a dream, or a waking hallucination.

I was maybe seven and much more interested in cowboys and Indians than dinosaurs. I was not a toy dinosaur collector, and neither were my friends. In fact, I think this was long before kids, or adults, knew enough about dinosaurs to be fascinated with them. And yet there it was, gliding quietly and smoothly past my bedroom window.

That image lasted maybe four seconds, and yet those four seconds have lasted a lifetime — literally.

If my brain is at all typical, then it seems to me that visual images occurring spontaneously and transiently in six and seven year olds are perhaps associated with a growing and rewiring brain. However, as an adult my most remarkable memories are of similar dreamlets, extremely vivid dreams lasting but a few seconds, just as did the imagery of the dinosaur walking past the window.

Due to my being an adult I can’t explain them by remodeling of my brain. So perhaps there is something unique about them that has nothing at all to do with age.

They are certainly varied, and seem to have nothing whatsoever in common with my actual life. For instance, one dreamlet was of launching off a tall spire in a crystal city, and gliding on wings in an obviously nonhuman form, in a non-Earthlike place. That was probably the strangest, and yet most interesting five seconds of my life.

Another dreamlet, hypnagogic in that I was falling asleep, lasted maybe only a second. In it I clearly saw a white car veer directly into the path of my car, and what had to be an unavoidable head-on collision.

For some time I was on the lookout for white cars (Do you have any idea how many white cars there are?), but years have passed since then and I am still very much alive.

I’m well aware that no one wants to hear about someone else’s dreams, unless they’re being paid to do so. But that is not what this writing is about. Instead it’s about the strange events called dreamlets, moving images that pop into our heads when we are not concentrating on anything in particular.

I suspect we all have them, but due to their brevity few people talk about them. They really aren’t open to interpretation, at least in the same manner as more prolonged dreams which have been interpreted by psychoanalysts like Jung and Freud, and a host of modern day analysts.

Arguably, the most modern discussion of these dreamlets is by Professor Charles Tart who has built a world-wide reputation on such matters. And yet he, like me, is reduced to only asking questions. In a recent blog posting he mentions a few potential explanations for dreamlets, some of which would be considered bizarre by most readers, but admits that none of them seem to match his experiences completely.

What interests me about his writing, however, is the fact that what he experiences during meditation and what I’ve experienced spontaneously share points in common. That leads me to believe these events are generalized throughout the human population. In other words, you may remember events similar to the dinosaur passing by your window, and may wonder what that was about. This posting, then, is to tell you that you are not alone. Unfortunately no one has authoritative answers for you.

If you have an interest in learning more about these brief events, then you may find Dr. Tart’s blog stimulating.

http://blog.paradigm-sys.com/where-do-all-those-images-and-dreamlets-come-from/

The Google Generation and College Life

I was recently reminded that almost everyone who is literate and has access to a computer and Internet connection has used Google to find something of interest to them.

The way I was reminded of that was from Google Analytics which gives me feedback on this blog. Over a period of a few days I witnessed a curious rise in the number of hits on a tongue-in-cheek description of a faux energy company (Cosmic Capacity Corporation) that purportedly sells personal black holes.

https://johnclarkeonline.com/2012/09/23/frequently-asked-questions-about-personal-black-holes/

Typically, the draw of a sample of my dry humor is low. So why should there be a rapid uptick in interest?

Well, I’m just as mindful of national security as the next person, so as I witnessed the first wave of unexpected interest my thoughts were that bad people were trying to expand their knowledge of potentially dangerous devices. After all, anything that could make most anything disappear, and if detected, evaporate itself beyond all trace of detectability must be of interest to criminals.

But whoever they were, they weren’t stupid: they caught on quickly that the posting was a ruse. Stay time was approximately 30 sec.

However, over the period of a week, the numbers continued rising, and then fell just as quickly back to their normal near-dormancy levels. Something strange was going on.

Capture2 — A Gaussian curve-fit to the Google Analytics data, January 20 – 28, 2013.

The limited data I have points to a total of 333 hits occurring with an approximately Gaussian (normal, Bell-shaped curve) frequency between January 21 and 27.

With that realization, I may have now solved the mystery. When I looked at the timing and shape of the rise and fall, a memory was triggered of college student life.

0909_TheatreL_005a — From strangethoughtsbyjohn.blogspot.com. Click to go to the link.

I have no way of knowing if this is true, but let’s assume that on Monday the 21st, over 300 students attended the first of the week’s Monday, Wednesday, Friday classes on introductory science in a large University. The lecture hall was packed when the professor announced that a paper on Personal Black Holes was due on Monday week.

On that day (Monday) ten students hit Google and immediately found my blog posting on Personal Black Holes. The next day 25 students hit the site followed on Wednesday (perhaps encouraged by a reminder in class) and Thursday by a much larger group of students. On Friday, 35 procrastinators did the same thing.

I don’t think I would be wrong to suggest that after a Friday night spent in college recreation, Saturday was a day of hangovers and recovery. (Yes, I am speaking from personal experience.) No one hit my site on Saturday, and I imagine the majority were resting, or perhaps writing.

On Sunday, it appears that three late-bloomers hit the site, and the rest were preparing their paper for Monday.

Early Monday morning, one desperate procrastinator hit the site. I can just imagine the student screaming, “You have got to be kidding! This is a joke?”

Yes, it was a joke, a fact the average student figured out in 39 seconds before moving on.

Government and industry is constantly pressing for metrics, ways to measure business success other than from sales. The problem with metrics is that figuring out what to do with the numbers is not always obvious . What do they represent?

Since my site is not a business, and does not earn me a cent, I normally pay no attention to its metrics. However, this time, after moving beyond my initial alarm, I felt that I might be gaining insight into the hidden “research” trends of young college students. As a scientist, that intrigues me.

It would be more intriguing if someone discovered that A students were the first to turn to Google for answers. I’m sure Google would find that satisfying.

It could of course be just the opposite. Perhaps top students hit the library first and then follow up with Google search as a last check. Actually, that result would surprise me, but arguably it cannot be ruled out.

Lastly, it could be that my college class hypothesis is completely wrong. It could be that Chechen rebels were exploring ways to solve their political/military problem, but somehow I doubt it.

As we scientists are trained to say, more research is needed.

GoPro, YouTube, and the Need for Speed

Have you ever watched a local sailboat race from the shore?

It’s not exactly an adrenaline-pumping spectator sport. On the boats of course there is plenty of excitement — shouting, sometimes cursing. But from shore, all the on-boat drama is missing.

GoPro cameras have ushered in a new era of taking the viewer into the action. And based on the action that I commonly see on the Internet, that action is not of local sailboat races. It is instead full of speed and thrills. The penultimate example of testosterone-driven thrill-seeking, in my opinion, is the dangerous sport of wingsuit flying, always perilously close to terrain.

The visual rush is not subtle. You are left with the impression that any second you’ll witness a fatal crash. You leave the video thinking that the flyer is one very brave, very skilled, and very lucky person. Or else you just think they’re CRAZY!

But honestly, I’d love to be that crazy— just once anyway.

When I watch such videos on YouTube I get the sense that I am a spectator at a blood sport event. There is beauty and grace which I admire, but ultimately I know there is a risk to the participant, as evidenced occasionally by the literally rib-splitting, pink mist endings to some of those flights. We enter into the action, but comfortably in front of our TV or computer screens with no personal risk to ourselves.

Arguably we are really not so different from the crowds at the Gladiator games, or for a more modern though fictional example, the Hunger Games.

What I like about the new class of miniature, high-definition video cameras is that they allow us to video what we love doing and then share it with the world. That’s nice, but unless what you do is high speed, endearingly cute, or down-right funny, it may be difficult to attract viewers.

I’ve uploaded flying videos, including the high-definition video below, but they are not exciting. Instead, they appeal, I think, to those who simply love flight: the visual sensations of landing, of entering clouds or skimming cloud tops. That type of flight is the way the FAA expects pilots to fly — safely. Yet safe flight is also capable of generating visual sensations that secretly thrill even highly experienced pilots, and keep them in love with their profession.

On the other hand, the adrenalin-packed videos that high-definition cameras provide can entice some pilots to fly unsafely, simply to titillate the cameraman and the viewer. I suspect the pilot in the following video got a high viewer count but I also suspect his wings are about to be clipped by the FAA.

I am very unlikely to engage in risky flying simply because it looks thrilling when posted on the Internet. I want to keep my license; it is a treasured privilege to be able to fly. But also because I’ve lived long enough to know it is quite a different thing to watch a Miss Universe pageant, and quite another to entertain a pageant contestant when she shows up unexpectedly at your door. The thrill may be more intense in the latter case, but the personal risk may be far greater; especially if your significant other meets her at the door.

Sailboat race photo by Lewis Westwood Flood on Unsplash

My Respiratory System is So Embarrassed

stk85284cor — Royalty free image from Punchstock.com

“Respiratory embarrassment” is an uncommon phrase most likely spoken by physicians and physiologists.

This week I found myself telling an engineer that “respiratory embarrassment can lead to an untoward event”. It quickly became apparent from the puzzled stare I received that I was not communicating.

Scientists and some medical personnel tend to do that; fail to communicate. In fact, they do it a lot.

What I was really saying is that in the right circumstances a person could have difficulty breathing, and that difficulty could cause something bad to happen; an “untoward” event. That bad thing would not necessarily be an aircraft crash, or in the case of a diver, a drowning, but it would mean that the pilot’s or diver’s performance would be impaired.

Why didn’t I just say so?

Laziness I suppose. I was using the language clinicians and physiologists are taught in graduate or medical school, and it flows out of our mouths naturally, without effort. Translating those same words into laymen’s terms takes time and effort.

I next started talking about respiratory impedance, a term understood by some but not all engineers, and rarely if ever by laymen. So once again I was not communicating well with all of my audience which was composed mostly of engineers, but not entirely.

That was the case until I used pictures to explain the otherwise difficult concepts of respiratory impedance and physiological embarrassment. The images below seemed to work, so I thought it worthwhile to share those images with you.

For you engineers, respiratory impedance is proportional to the sum of respiratory flow resistance and pulmonary and chest wall elastance.

pb-110104-buried-shulman_photoblog900 — From Shulman photoblog.

So what is that?

Well, for elastance, at least chest wall elastance, think of being buried to your neck in sand. Breathing difficulty comes from the difficulty of moving your chest wall in and out with the weight of sand pressing in on all sides. The pressure of sand impedes your breathing, hence elasticity (the inverse of compliance) is a major component of respiratory impedance.

Based on the photo of the young man pictured on the right, being partly buried for supposedly therapeutic reasons is not a pleasant experience.

Some might disagree. The man on the left is an actor in the 2008 French short film Le Tonneau des Danaïdes by David Guiraud, who seems quite at ease impeding his breathing for the sake of art. I’m guessing he’s either very dedicated, or very well paid.

In diving, respiratory elastance can be elevated by tight fitting wet suits; in aviators by tight fitting chest pressure garments, and in patients, by pulmonary fibrosis brought about by, for example, asbestos exposure.

Another key component of respiratory impedance, that thing that causes respiratory embarrassment, is flow resistance. Sticking your head in the sand would certainly be one way of generating

head-in-sand — *This image is found randomly throughout the web without attribution. The original source is unknown.*

severe respiratory resistance, with its attendant embarrassment.

out-of-breath-286x300 — From news.menshealth.com

Clinically, there are far more common sources of respiratory resistance, for example the narrowing of air passages in the lung caused by asthma. (Sticking your head in sand is probably a reasonable analogy to the sensations experienced during an asthma attack.) Chronic obstructive pulmonary disease (COPD) can also lead to a significant increase in respiratory resistance.

When you focus on the human respiratory system, the body parts shown in pink below, keep in mind that breathing can be impaired by things occurring inside the body (like asthma, COPD, fibrosis) or outside the body. Any life support system used for aviation, diving, mining, or firefighting imposes an impedance on breathing. That impedance in turn can lead to breathing difficulty, which can result in a failure to complete assigned duties.

Perhaps that’s where the “embarrassment” part comes in.

Created on www.biodigitalhuman.com ©2012.

The Siren’s Call of Rebreather Oxygen Sensors

In Greek mythology irresistibly seductive female creatures were believed to use enchanted singing to beckon sailors to a watery grave.

Why this myth endured through the centuries is difficult to say. However, my theory is that it helped explain to grieving widows and mothers why ships sometimes inexplicably disappeared, taking their crew with them, never to be seen again. By the reasoning of the time, there must have been some sort of feminine magic involved.

The oxygen sensors in closed-circuit, electronically or computer-controlled rebreathers are a magic device of sorts. They enable a diver to stay underwater for hours, consuming the bare minimum of oxygen required. The only thing better than a rebreather using oxygen sensors would be gills. And in case you wondered, gills for humans are quite impractical, at least for the foreseeable future.

I have written, or helped write three diving accident reports where the final causal event in a rebreather accident chain proved to be faulty oxygen sensors. So for me, the Siren call of this almost magical sensor can, and has, lured divers to their seemingly blissful and quite unexpected death.

Those who use oxygen sensors know that if the sensor fails leading to a hypoxic (low oxygen) state, loss of consciousness comes without warning. If sensor failure results in a hyperoxic state (too high oxygen), seizures can occur, again leading to loss of consciousness, usually without warning. Unless a diver is using a full facemask, loss of consciousness for either reason quickly leads to drowning.

EX19 — EX 19 rebreather (U.S. Navy photo)

Due to the life-critical nature of oxygen control with sensors, three sensors are typically used, and various “voting” algorithms are used to determine if all the sensors are reliable, or not. Unfortunately, this voting approach is not fail-proof, and the presence of three sensors does not guarantee “triple” redundancy.

In one rebreather accident occurring during the dawn of computer-controlled rebreathers, a Navy developed rebreather cut off the oxygen supply to a diver at the Navy Experimental Diving Unit, and all rebreather alarms failed. The diver went into full cardiopulmonary arrest caused by hypoxia. Fortunately, the NEDU medical staff saved the diver’s life, aided in part by the fact that he was in only 15 feet of water, in a pool.

In two more recent accidents the rebreathers kept feeding oxygen to the diver without his knowledge. One case was fatal, and the other should have been but was not. Why it did not prove fatal can only be explained by the Grace of God.

The two cases were quite different. In one the diver broke a number of safety rules and began a dive with known defective equipment. He chose to assume that his oxygen sensors were in better shape than the rest of his rebreather. If he had been honest with himself, he would have realized they weren’t. If he had been honest with himself, he would still be alive.

The other dive was being run by an organization with a reputation for being extremely safety conscious. Nevertheless, errors of omission were made regarding oxygen sensors which almost cost the experienced diver his life.

In the well-documented Navy case, water from condensation formed over the oxygen sensors, causing them to malfunction. The water barrier shielded the sensors from oxygen in the breathing loop, and as the trapped oxygen on the sensor face was consumed electrochemically the sensor would indicate a declining oxygen level in the rig, regardless of what was actually happening. Depending on how the sensor voting logic operated, and the number of sensors failing, various bad things could happen.

During its accident investigation, when NEDU used a computer simulation to analyze the alarm and sensor logic, it found that if two of the three sensors were to be blocked (locked) by condensed water, the rig could lose oxygen control in either a hypoxic or hyperoxic condition. Based on a random (Monte Carlo) sensor failure simulation, low diver work loads were more often associated with hypoxia than higher work rates, even with one sensor working normally.

We deduce from this result that “triple redundancy” really isn’t.

The white circles at the top left of this scrubber canister housing are the three oxygen sensors used in an experimental U.S. Navy rebreather.

When the accident rig was tested in the prone (swimming) position at shallow depth, after 2 to 3 hours sensors started locking out, and the rig began adding oxygen continuously. The computer simulation showed that the odds of an alarm being signaled to the diver was only 50%. The diver therefore could not count on being alerted to a sensor problem.

Unfortunately in this near fatal case the rig stopped adding oxygen, the diver became hypoxic and the diver received no alarms at all.

After NEDU’s investigation, the alarm logic was rewritten with a vast improvement in reliability. The orientation of the sensors was also changed to minimize problems with condensation.

Today what is being seen are divers who extend the use of their sensors beyond the recommended replacement date. Like batteries, oxygen sensors have a shelf-life, but they also have a life dependent on use. Heavily used sensors may well be expended long before their shelf-life has expired.

the-siren — The Siren, by John Williams Waterhouse.

Presumably, the birthing pains of the relatively new underwater technology based on oxygen sensors have now passed. Nevertheless, those who use rebreathers should be intimately familiar with the many ways sensors, and their electronic circuitry, can lead divers ever so gently to their grave.

Like sailors of old, there are ways for divers to resist being lulled to their death by oxygen sensors. First among them is suspicion. When you expect to have a great day of diving, you should be suspicious that your rebreather may have different plans for you. Your responsibility to yourself, your dive buddies and your family is to make sure that the rebreather, like a Siren, does not succeed in ruining your day.

The best way to ward off sensor trouble is through education. To that end, Internet sites like the following are useful. Check with your rebreather manufacturer or instructor for additional reading material.

http://rebreathers.es/celulas%20o2/celulas%20o2.htm

http://www.rf30.org/

http://www.deeplife.co.uk/or_files/DV_O2_cell_study_E4_160415.pdf

In Search of Glories

Recently my inner child took notice of a circle of light racing across the cloud tops as I cruised at 7000 feet and 180 mph with the prevailing westerlies at my back. I was headed east above the Gulf Coast between New Orleans and the Florida Panhandle, and the late afternoon sun crept ever lower behind my right wing. Like a fighter in loose formation, the ring of colored light was keeping pace with the aircraft, just in front of my left wing.

My adult self realized that the spot contained a shadow of the airplane, but the bright halos around the dark shadow puzzled me. When my inner child asked me what it was, I had no ready answer.

I’d seen those halos before without really understanding them, but now I had a chance to photograph them. I grabbed cameras and recorded the beautiful phenomenon while the autopilot kept the aircraft on course.

One of the advantages of general aviation aircraft is that we often fly at the altitudes of the DC3s, the early airliners. Which meant that at 7000 feet I could open a small window beside me without depressurizing the cabin and give the camera a clear view of what I was experiencing.

An understanding of what I was seeing would have to wait.

[youtube id=”sV90o44sCE8″ w=”700″ h=”600″]

With few exceptions, Glories remain in the realm of pilots and Angels. By association, many pilots feel privileged to see a glory. I know I do.

Without knowing the science behind glories, pilots may even interpret them as signs of the divine. After all, they do look suspiciously like halos seen in medieval religious art. Indeed, “glory” is another name for those iconic halos.

Science is only able to partly demystify the subject of glories. The best technical explanation is that glories are the result of reflections (back-scattering) of sunlight coming from directly behind the observer. The tiny spherical water drops in clouds are the objects that scatter the sun light. Oddly enough, the size of the water droplets determines the size of the glory, which by the way may contain multiple rings as seen on the videos in this posting.

Laven-Fig13 — MiePlot simulation of scattering of sunlight from r = 4.8 µm water drops superimposed on a digital image of a glory taken from a commercial aircraft. From philiplaven.com.

This process of ring formation from water droplets is called Mie Scattering, and is described mathematically by Mie Theory. Phillip Laven’s website, http://www.philiplaven.com/index1.html, provides an ample resource for the curious.

Glories have proven to be such an elusive quarry, that I, like many pilots, have developed a fascination with them. Therefore I could not resist making a brief video, with music, of the glories encountered on that one eastward flight. In it you see a classical glory, followed by a fleeting and hard to photograph glory on the side of a cloud, followed by apparent flight into an ever moving cloudbow.

[youtube id=”CKtkzOpmSUM” w=”700″ h=”600″]

Would You Rather Face a Cunning or Relentless Foe?

Suppose you find yourself on an alien planet, battling with indigenous species. On your side, you have smarts, both natural and technological. The alien defenders have nothing; no technology. Well, they do have slime, but that’s all.

Brains against the brainless: Who do you think will win?

Before the Ticks — Blithely headed into tick-infested woods.

I spent a summer weekend with my family in a cabin in the Virginia mountains a few years ago. It was nature at its finest, until we discovered after a short walk in the woods that ticks seemingly rained down upon us and were invading our bodies as fast as their little legs could move. We were food, and they were hungry. Human-sized meals didn’t come around those woods very often, apparently.

The entire family, adults and children, stripped down to our underwear on the porch of the cabin, trying to rid ourselves of the invaders. Modesty took second place to the fear of miniature arachnids.

Once the imagined itching had abated and the baby was asleep, we soothed our nerves with puzzles and games, or reading from a well-stocked bookshelf. I picked a book with an interesting cover; it was John Scalzi’s Old Man’s War.

I cannot say enough good things about Scalzi’s debut novel, a futuristic science fiction, other worlds story. Suffice it to say, it features combat between Earthling soldiers and all sorts of bizarre and ruthless alien life forms. Although Scalzi didn’t write about invading armies of ticks, per se, I could easily envision such a terrifying encounter.

Cabin 1 crop — This author devouring Scalzi’s “Old Man’s War”.

I also think and write about extraterrestrial aliens. Like most writers, I assume ETs are sentient, and calculating. Depending upon the writer, those ETs may have either high morals, or no morals at all, but they always have a brain.

Lately, I’ve had to rethink potential plot elements dealing with intelligent life forms. The reason is, scientists now claim that a single celled animal, a slime mold, acts with a shocking degree of intelligence. The kicker is, being a single celled organism, slime mold does not have a brain.

800px-Slime_mold_grows_on_anything_001 — Slime mold knows a good thing when it finds it. (Photo credit: SB_Johnny)

Intelligence without a brain?

Compared to slime mold, ticks are geniuses if we count the gray matter cells contained in their single-minded heads. However, according to a Japanese researcher the brainless slime mold can solve problems even scores of engineers could not easily solve.

Sounds like science fiction to me.

So now imagine the following storyline. Your spaceship lands on a verdant planet that has no higher, brain-possessing life forms, at all. However, what it does have in abundance is slime mold. And of course the threat from slime mold is easy to ignore — until it is too late. The mindless protoplasm senses all sources of food, and fans out in all directions, following the scent.

The ship’s science officer tries to warn the mission commander, but the arrogant and miscalculating commander responds with a volley of lead rounds into the nearest slime; which of course is not in the least bit deterred from its food-finding task.

And when the crew sleeps, as of course they must, the brainless mold finds the food sources, one by one, absorbing the human nutrients.

Human-sized meals don’t come around those woods very often, apparently.

Being brainless, slime mold cannot be considered cunning. But, one could argue, it’s not stupid either: it can’t be tricked. It is, if anything, relentless.

From a cinematic perspective this is not an entirely new theme. The 1958 movie The Blob starring Steve McQueen popularized the idea of mindless organisms devouring humans. But at that time there was no real science behind it. Now there is.

Some interesting science facts about slime mold are found in this link and the following Scientific American – NOVA video.

[youtube id=”lls27hu03yw” w=”700″ h=”600″]

In Diving, What is Best is Not Always Good

In technical or recreational rebreather diving, safety is a matter of personal choice. Wrong choices can turn deadly.

Some poor choices are made for expediency, while others are made with the best of intentions but based on faulty or incomplete information. As a diving professional, it is those latter choices that concern me the most.

A poignant and well documented diving fatality involved a record setting Australian diver, David Shaw. David was an Air Bus pilot for Cathay Pacific.

Professional pilots are immersed in a culture of safety, a culture that makes airline travel the surest means of long distance transport. David applied that same sort of attention to his diving, recording on his personal web site his detailed plans for a record setting dive to recover the body of a diver who died in the 890 feet (271 meter) deep Boemansgat Cave of South Africa 10-years prior to David’s ill-fated dive.

Despite his extensive preparations, David Shaw made a fatal mistake. Like those who fail to appreciate the threat of an approaching hurricane, David failed to recognize the risk of really deep diving with a rebreather.

Unlike other types of underwater breathing equipment, a rebreather is entirely breath powered. That means you must force gas entirely through the “breathing loop” with the power of your respiratory muscles. On a dive to 890 feet, you are exposed to 28 times normal pressure, and breathing gas more than five times denser than normal. The effort involved is enough to dismay some U.S. Navy divers at depths far less than David Shaw intended to dive. Yet in David’s own words, he had previously never had a problem with the effort of breathing.

“The Mk15.5 (rebreather) breathes beautifully at any depth. WOB (work of breathing) has never been an issue for me. Remember that when at extreme depth I am breathing a very high helium mixture though, which will reduce the gas density problem to a certain extent.”

He goes on to say, “I always use the best quality, fine-grained absorbent on major dives. The extra expense is worth it.”

“I have had 9:40 (9 hrs, 40 min duration) out of the canister and felt it still had more time available, but one needs to qualify that statement with a few other facts. Most of the time on a big dive I am laying quietly on deco (decompression), producing minimal CO₂ (carbon dioxide).

In those words lie a prescription for disaster.

Scrubber canister — A rebreather scrubber canister containing granular absorbent through which a diver has to breathe.

David wanted to use a single rebreather that would accomplish two tasks — provide a long duration gas supply and CO₂ absorbing capability for a dive lasting over nine hours, and provide a low work of breathing so he could ventilate adequately at the deepest depth. To ensure the “scrubber canister” would last as long as possible, he chose the finest grain size, most expensive sodalime available. His thought was, that was the best available.

Arguably, the two aims are incompatible. He could not have both a long duration sodalime fill and low breathing resistance.

BALLPIT schematic — Cartoon of breathing through a scrubber canister.

As illustrated in a previous blog posting, the smaller the size of granules you’re breathing through, the harder it is to breathe. Think of breathing through a child’s ball pit versus breathing through sand.

Perhaps if David had maintained a resting work rate throughout the deepest portion of his fatal dive, he might have had a chance of survival. After all, he had done it before.

But the unexpected happens. He became fouled and was working far harder to maintain control of the situation than he had anticipated. That meant his need to ventilate, to blow off carbon dioxide from his body, increased precipitously.

A sure sign of high breathing effort is that you cannot ventilate as much as is necessary to keep a safe level of carbon dioxide in your blood stream. CO_2, which is highly toxic, can build rapidly in your blood, soon leading to unconsciousness. From the videotaped record, that is exactly what happened.

Purer A, Deason GA, Hammonds BH, Nuckols ML. The effects of pressure and particle size on CO2 absorption characteristics of High-Performance Sodasorb. Naval Coastal Systems Center Tech. Manual 349-82, 1982. (Click for larger image.)

Had David been fully aware of the insidious nature of carbon dioxide intoxication from under breathing (hypoventilating), he probably would have chosen an alternative method to conduct the dive.

One alternative would be to use a larger granule size absorbent in a rebreather at considerable depth (say, 100 meters and deeper), and reserve the fine-grain absorbent for use in a separate rebreather shallower than 100 meters.

David chose the fine-grain absorbent because of the longer dive duration it made possible. Although fine grains are more difficult to breathe through than large grain absorbent, fine grain absorbent lasts longer than large grain absorbent.

But that long duration is only needed during decompression which is accomplished far shallower than the deep portions of the dive. The time spent deep where work of breathing is a threat is quite short. He did not need the capabilities of a long duration, fine grain absorbent.

From the U.S. Navy experience, there are other problems with this dive which might have hastened the end result. A rapid and deep descent causes the oxygen pressure within the rebreather to climb to potentially dangerous levels; a phenomenon called oxygen overshoot. Thus he might have been affected somewhat by oxygen toxicity. A rapid descent might also have induced the High Pressure Nervous Syndrome which would affect manual dexterity.

While those contributing factors are speculative and not evident on the tape, the certainty of the physics of dense gas flow through granular chemical absorbent beds is an unavoidable fact.

No doubt, many have offered opinions on what caused David’s accident. I certainly do not claim to be intimately involved in all the details, nor familiar with all the theories offered to date. Nevertheless, David’s mistaken belief that using the “best absorbent” was the best thing for his dive, is a mistake that needs to be explained and communicated before this accident is repeated with a different diver in some other deep and dark place.

tim051wc14_61083a — Click to go to the source document.

Is Your Local Ball Pit Safe for Children?

http://nl.wikipedia.org/wiki/Bestand:Ballpit.jpg

I sat on the edge of a ball pit at Chuck E. Cheeses, calipers in hand, measuring the diameters of a random sampling of plastic balls within the pit.

I suppose I stood out, an officious-looking adult wielding a precision instrument in a place designed for fun. So much so that a father attending his child asked me what I was doing.

I was measuring the ball sizes. I explained that if the balls were too small, and a child became covered with them, then the void space around the balls, the contorted empty volumes that represented places where air can be exchanged, would be too small, making breathing difficult. That made sense to the father, and he seemed pleased that I was looking after his child’s safety.

A child is almost completely covered by balls. A single hand is sticking out, and part of a face can be seen.

Contrary to the way it seemed, I was not a corporate inspector for Chuck E. Cheeses. I was also not a government inspector. But I was curious, gaining information for ideas I was developing about the breathing resistance imposed by particles of various sizes. I was acting, as it were, as a freelance scientist investigating flow through porous beds.

Consider the circumstance where a person is forced to breathe through a mass of balls, as in the illustration below. You can see, better than in the case of the ball pit, that if the balls become too small, or smaller balls fill in the void spaces between larger balls, then the person would be at risk for suffocation.

Advertisements for balls sold for ball pits point out the safety advantage of larger balls for children under age 3. The smaller children are obviously more susceptible to tunneling deeper into a pit of balls, some of which may be piled to two feet or deeper depths.

Balls of 3.1 in. diameter are touted as being ideal for three-year-olds, whereas other popular sizes [2.5 in. (65 mm), 2.75 in. (70 mm)] are not. The 3.1 in. ball is almost twice as large, in terms of actual volume, as the 2.5 in. balls.

A problem awaits a child if the ball pit has poorly sorted ball sizes, especially a mixture of larger and small balls. As shown in the figure to the right, well-sorted balls provide a porosity (airspace for breathing) of over 32%, whereas a mixture with balls fitting into the void spaces between larger balls can reduce void space down to about 12%. That would not be a good plan for a ball pit.

It also is not a good plan for the Namib mole.

The Namib Golden Mole is found in one region of Namibia because of the peculiar characteristics of the sand in that area. The sand grains are surprisingly homogeneous in size, and as the illustration to the right shows, similarly sized particles have a relatively large porosity. For the mole that means that when they burrow deep into the sand to escape blistering noonday heat, they will not suffocate. They can breathe through the sand.

If the sand were of mixed grain sizes, which is more typical of sand dunes, then porosity would be low and the mole would not be able to burrow deep enough to avoid the African heat without suffocating.

So, quite unexpectedly there is a connection between the uniform size of plastic balls in a ball pit and the survival of a mole in a faraway African desert.

You never know where scientific curiosity will lead you.

As will be shown in an upcoming blog post, the topic of breathing through porosities in packed beds is relevant to diving with rebreathers or breathing through chemical absorbent cartridges in gas masks.

Making Fuel

avo-small — Buffalo Airways C-46 Commando.

While watching an “Ice Pilots” episode on the Weather Channel I heard a pilot of a Curtiss C-46 Commando talking to his inexperienced copilot during a flight. At one point he said they were “making fuel.”

I have enough common sense and experience as a pilot to know that could not be literally true. But I had no idea what the Ice Pilot’s comment really meant until recently returning home during a non-stop flight from Dallas, Texas to the Florida Panhandle.

I had purposefully climbed to 11,000 feet to catch good tailwinds heading east. The winds were even stronger at higher altitudes, but if I’d climbed to the next allowed altitude, 13,000 feet, my passenger and I would have needed to wear an oxygen mask. And I’d left the oxygen system at home.

During flight planning before departure, it looked as if going high would give us enough of a tailwind that we would be able to make the trip without a time consuming fuel stop.

Modern aircraft often have fuel computers communicating with the aircraft GPS navigation system. Fuel computers track every ounce of fuel burned during taxi and flight. The pilot programs the total fuel available and then the fuel computer checks with the GPS to see how many miles remain to the destination, and the ground speed. Every few seconds the pilot sees an update of the fuel burned, gallons remaining, predicted flight time available, the fuel required to reach the destination, and the bottom line, the predicted fuel reserve at the destination.

Typically, I want to land with no less than 10 usable gallons remaining, which is enough to remain aloft for an additional hour at the normal fuel consumption rate. If the weather is bad at the destination, then the required fuel reserve is considerably larger.

On the first phase of my flight to Dallas, once I had reached cruising altitude the fuel computer calculated that if the current ground speed and fuel burn were to continue to the end of the trip, I would have five gallons of fuel left at the destination. That is not enough for safe flight, so a refueling stop was looking inevitable. As the flight continued, the estimation of reserve fuel barely budged from its first estimate. In other words, nothing was changing, and the decision to refuel was firmly made.

East Texas from 11,000 ft. Click to enlarge.

On the return flight, however, flying relatively high where the prevailing westerlies were strong, the computed reserves (RES) were changing. They were growing. As the flight progressed I watched the estimated fuel reserve rise slowly from 8 gallons to 9, then 10, and finally 11.4 gallons. By the time we landed we had 12 gallons of fuel remaining in the two fuel tanks.

It truly looked like we were making fuel.

We weren’t, of course. The reality of it was that the tailwind was increasing in our favor for the east-bound trip. But the fuel computer gave every impression that for every gallon of fuel we burned, we were getting a little bit back.

I finally understand what the Ice Pilot meant; I think. If I ever meet him, I’ll ask.