Science and Technology | John Clarke Online

Of Mussels and Whales

Wal_Cuviera — Cuvier’s Beaked Whale. Image from Wikimedia Commons.

It was a coincidence forty years in the making. I was recently at the Scripps Institute of Oceanography, talking to Scripps professor and physician Paul Ponganis about deep diving whales. He told me about the recent discovery that Cuvier’s Beaked Whale, an elusive whale species, had been found to be the deepest diving of all whales.

How deep I asked? One whale dived to 9,816 feet, about 3000 meters. At that depth, water pressure exerts a force of about 4400 pounds per square inch (psi), equal to the weight of a Mercedes E63 sedan pressing on each square inch of the whale’s ample body surface. That is a seriously high pressure, a fact that I knew well since I had once created that much pressure, and more, in a small volume of seawater in a pressure vessel at the Florida State University.

Early in my science career, I published my work on the effect of deep ocean pressure on intertidal bivalves, a mussel (Modiolus demissus) being among them. I found that if you removed the hearts of such molluscs (or mollusks) and suspended them in seawater, they would continue to beat. Furthermore, those excised hearts would beat when subjected to 5000 psi of hydrostatic pressure. As if that wasn’t surprising enough, the slight genetic differences between Atlantic subspecies and Gulf Coast subspecies of mussels resulted in the isolated hearts responding slightly differently to high pressure.

oyster-anatomy — If you’ve eaten live raw oysters, a cousin to mussels, you’ve eaten beating hearts like the one in this photo. (Click to enlarge. Photo credit: rzottoli, Salt Marshes in Maine, at HTTP:// wordpress.Com )

120-modiolus-demissus-excellent-mb-oct-19-20041 — The mussel Modiolus demissus in their natural habitat at low tide (Photo credit: rzottoli, Salt Marshes in Maine, at HTTP:// wordpress.Com )

That was a remarkable finding I thought since none of those mussels had ever been exposed to high pressure; ever as in for millions of years. (This study occurred long before the discovery of deep sea vents and the almost miraculous growths of deep sea clams.)

Eventually, my research transitioned from invertebrates to humans. Humans, like intertidal mussels and clams, are not normally exposed to high pressure. But like my unwilling invertebrate test subjects, sometimes humans do get exposed to high pressure, willingly. But not so much of it. Deep sea divers do quite well at 1000 feet seawater (fsw), manage fairly well at 1500 fsw, but don’t fare well at all at 2000 fsw. That depth seems to be the human pressure tolerance limit due to the high pressure nervous syndrome, or HPNS. At those pressures, cell membranes seem to change their physical state, becoming less fluid or “oily” and more solid like wax. Cells don’t work normally when the very membranes surrounding them are altered by pressure.

The Beaked Whale is genetically much more similar to man than are mussels. Therefore, man is far more likely to benefit by learning how Cetaceans like whales tolerate huge pressure changes than we are to benefit from the study of deep diving (albeit forced diving) clams and mussels.

As I talked to Dr. Ponganis it was obvious to him, I suspect, that I was excited about learning more about how these animals function so beautifully at extreme depths. But to do that, you have to collect tissue samples for study and analysis in a laboratory. The only problem is, collecting useful tissue samples from living whales without hurting them may be a bridge too far. Humans rarely even see Beaked Whales, and if the Cetaceans wash up on shore, dead, their tissues have already been degraded by post-mortem decomposition, and are no longer useful for scientific study.

RoboTuna,_1994,_view_2_-_MIT_Museum_-_DSC03730 — MIT’s RoboTuna; ca. 1994. Photo from Wikimedia Commons.

Potentially, here is a job for underwater Cetacean-like robots that when released in a likely Beaked Whale environment, can locate them, dive with them, and perhaps even earn their trust. And when the whale beasts least expect it, those robotic Judases could snatch a little biopsy material.

If only it were that easy.

Considering how difficult it would be to acquire living tissue samples, would it be worth the effort? Well, if man is ever to dive deeper than 1500 to 2000 feet without the protection of submarines, we must learn how from either the mussels or the whales. My bet is on the whales. Unlike mussels, the whales dive deep for a living, to catch their preferred prey, squid and deep sea fish.

What are arguably the first studies of the effects of high pressure on intertidal bivalves (mussels and clams) can be found here and here. Moving up the phylogenetic scale, Yoram Grossman and Joan Kendig published high pressure work on lobster neurons in 1990, and rat brain slices in 1991. I made the leap from mussels to humans by conducting a respiratory study on Navy divers at pressures of 46 atmospheres (1500 feet sea water), published in 1982. For a more recent review of high pressure biology applied to animals and man, see the 2010 book entitled Comparative High Pressure Biology. My theoretical musings about the mathematics of high pressure effects on living cells can be found here.

With time, these studies, and more, will add to our understanding of mammalian pressure tolerance. However, it may well take another generation or two of such scientific effort before we understand how the Beaked Whales make their record-breaking dives, and survive.

How to Read an e-Book

In days not too long past, proper lighting and posture were the keys to enjoyable and prolonged reading comfort. Now, things have changed.

Fotothek_df_ps_0000370_002_Kinder_^_Kinderbeschäftigungen_^_lesend — Child reading by candle light. Deutsche Fotothek‎ [CC-BY-SA-3.0-de (http://creativecommons.org/licenses/by-sa/3.0/de/deed.en)], via Wikimedia Commons

When reading by candle light, you placed your reading material in close proximity to the candle, and placed your chair in as comfortable a position as could be managed.

Electric lighting, by nature of its enhanced luminosity, gives the reader greater flexibility. I well remember the days when studying required the reading of physical books, not electronic displays, and so students were routinely counseled to set up a study environment with a flat desk and a study lamp off to the left side to avoid casting shadows on the reading material.

Body posture was a critical complement to this system. Slouching was as strongly discouraged then as it is today.

A__L__Leroy_-_Interior_with_a_Man_Reading_at_His_Desk_-_Google_Art_Project — Man reading at his desk. By A. L. Leroy (Details of artist on Google Art Project) [Public domain], via Wikimedia Commons.

However, with self-lit electronic displays, all the former concerns about lighting and posture have become irrelevant. Or so it seems.

In many ways children make ideal subjects for scientific observation. If caught young enough, they have not yet learned the “proper” ways of acting, or sitting. Therefore I am convinced that if left to their own innocent, non-self-aware devices they will instinctively find the most energy efficient and bodily pleasing ways to read, as long as lighting is not a concern. For popular devices such as iPad, Kindle Fire and Nabi, lighting is never an issue. The screen glows with light, sharply contrasting with the dark words of print on electronic books, those so-called “e-books.”

The subject in this photo essay was approximately six years old, freshly out of a bath, in her PJs and pushing her bed time by some very determined reading. In these photos she was reading about dinosaurs, using Booksy on an iPad.

As the following photos demonstrate, gravity itself seems not to impede elementary school reading.

SnapShot(5) — The subject first assumed a standard kid reading posture, possible only for pint-sized kids. Neck support is important.

SnapShot(7) — The inverted standard kid position. Apparently forehead support is important too.

Since kids are ever inventive, sometimes they spice things up with variations on a theme.

SnapShot(18) crop — 90° rotated, inverted kid reading position.

SnapShot(17) — Reach Out and Touch Someone

When engaged in challenging reading, increasing blood flow to the brain is important. Apparently the easiest way to do that is to raise the body’s center of gravity above the heart, as the following photo shows.

SnapShot(14) — The Rabbit Ears reading position.

This observation demonstrates that lighted reading displays have freed us from the unnatural constraints imposed by archaic reading and writing instruments. Our work devices have become smaller, lighter, and brighter, enabling a renaissance in body awareness and endless possibilities for comfortable and stimulating postures, never before thought possible.

TheFaulknerPortable — Faulkner’s portable work space

SnapShot(12) Sepia 75 — Kindergartner’s work space.

Admittedly, it helps if you’re six-years old and weigh 40 pounds. I do not guarantee that similar gyrations during reading are entirely safe for adults.

Reader beware.

Don’t Dive Cold When You Don’t Have To

San Diego Center of Excellence in Diving

Clarke JR¹, Moon RE², Chimiak JM³, Stinton R⁴, Van Hoesen KB⁵, and Lang MA^5,6.

¹ US Navy Experimental Diving Unit, Panama City, Florida
² Duke University, Durham, North Carolina
³ Divers Alert Network, Durham, North Carolina
⁴ Diving Unlimited International, Inc., San Diego, California
⁵ UC San Diego – Emergency Medicine, San Diego, California
⁶ OxyHeal Health Group, National City, California

Introduction

The San Diego Center of Excellence in Diving at UC San Diego aims to help divers be effective consumers of scientific information through its “Healthy Divers in Healthy Oceans” mission. In this monograph we explore a research report from the Navy Experimental Diving Unit (NEDU) that is leading some divers to think they should be cold if they want to reduce decompression risk. That is a misinterpretation of the report, and may be causing divers to miss some of the joy of diving. There is no substitute for comfort and safety on a dive.

Background

In 2007 NEDU published their often-cited report “The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness” (Gerth et al., 2007). The authors, Drs. Wayne Gerth, Victor Ruterbusch, and Ed Long were questioning the conventional wisdom that cold at depth increases the risk of decompression illness. After conducting a very carefully designed experiment, they were shocked to find that exactly the opposite was true. Some degree of cooling was beneficial, as long as the diver was warm during ascent.

Discussion and Implications

There are some important caveats for the non-Navy diver to consider. First of all, it was anticipated that a diver would have a system for carefully controlling their temperature during the separate phases of bottom time and decompression. Most non-Navy divers do not have that sort of surface support.

Secondly, the “cold” water in the NEDU study was 80 °F (27 °C). For most of us, 80 °F (27 °C) is an ideal swimming pool temperature, not exactly what you are going to find in non-tropical oceans and lakes. The warm water was 97 °F (36 °C), also a temperature not likely to be available to recreational and technical divers.

When testing the effect of anything on decompression results, the Navy uses their extensive mathematical expertise to select the one dive profile that is, in their estimation, the most likely to identify a difference in decompression risk, if that difference in risk exists. In this case the profile selected was a 120 fsw (37 msw) dive with 25 to 70 min bottom time, decompressed on a US Navy Standard Air table for 120 fsw (37 msw) and 70 min bottom time. That table prescribes 91 minutes of decompression divided thusly: 30 fsw/9 min (9msw/9 min), 20 fsw/23 min (6 msw/23 min), 10 fsw/55 min (3 msw/55 min).

A total of 400 carefully controlled dives were conducted yielding 21 diagnosed cases of decompression sickness. Overwhelmingly, the lowest risk of decompression was found when divers were kept warm during decompression. The effects of a 9 °C increase in water temperature during decompression was comparable to the effects of halving bottom time.

That is of course a remarkable result, apparently remarkable enough to cause civilian divers to alter their behavior when performing decompression dives. However, before you decide to chill yourself on the bottom or increase your risk of becoming hypothermic, consider these facts.

Do you have a way of keeping yourself warm, for instance with a hot water suit, during decompression? If not, the study results do not apply to you.
Of the many possible decompression schedules, the Navy tested only one schedule, the one considered to be the best for demonstrating a thermal influence on decompression risk. Although it seems reasonable that this result could be extrapolated to other dive profiles, such extrapolation is always risky. It may simply not hold for the particular dive you plan to make, especially if that dive is deeper and longer than tested.
Most commercial decompression computers do not adhere to the U.S. Navy Air Tables; few recreational dives are square profiles. Furthermore, additional conservatism is usually added to commercial algorithms. NEDU is not able to test the effects of diver skin temperature on all proprietary decompression tables, nor should they. That is not their mission.
The scientific method requires research to be replicated before test results can be proven or generalized. However, due to the labor and expense involved in the NEDU dive series, it seems unlikely that any experiments that would determine the relevance of these results to recreational or technical diving will ever be performed. As such, it may raise as many questions as it answers. For instance, the original question remains; if you become chilled on a dive, how does that affect your overall risk of decompression illness compared to remaining comfortably warm? Unfortunately, that question may never be answered fully.
Thermoneutral temperatures for swim suited divers are reported to be 93 °F to 97 °F (34 to 36 °C) for divers at rest and 90 °F (32 °C) during light to moderate work (Sterba, 1993). So a skin temperature of 80 °F (27 °C) is indeed cold for long duration dives. If your skin temperature is less than 80 °F (27 °C), then you are venturing into the unknown; NEDU’s results may not apply.In summary, beer and some types of wine are best chilled. Arguably, divers are not.

Acknowledgments

Support for the San Diego Center of Excellence in Diving is provided by founding partners UC San Diego Health Sciences, UC San Diego Scripps Institution of Oceanography, OxyHeal Health Group, Divers Alert Network, Diving Unlimited International, Inc. and Scubapro.

References

Gerth WA, Ruterbusch VL, Long ET. The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness. NEDU Technical Report 06-07, November 2007.

Sterba JA. Thermal Problems: Prevention and Treatment, in P.B. Bennett and D.H. Elliot, eds., The Physiology and Medicine of Diving, 4^th ed. (London: Saunders, 1993), pp. 301-341.

Redundancy – a Life Saver in Diving and Aviation

Photo taken from the author’s aircraft one stormy Florida Panhandle morning. (click to enlarge)

I was recently flying a private aircraft down the Florida Peninsula to Ft. Lauderdale to give a presentation on diving safety. As I continually checked the cockpit instruments, radios and navigation devices, it occurred to me that the redundancy that I insist upon in my aircraft could benefit divers as well.

In technical and saturation diving, making a free ascent to the surface is just as dangerous as making a free descent to the ground in an airplane, at night, in the clouds. In both aviation and diving, adequate redundancy in equipment and procedures just might make life-threatening emergencies a thing of the past.

Aviation

As I took inventory of the redundancy in my simple single engine, retractable gear Piper, I found the following power plant redundancies: dual ignitions systems, including dual magnetos each feeding their own set of spark plug wires and redundant spark plugs (two per cylinder). There are two sources of air for the fuel-injected 200 hp engine.

There are two ways to lower the landing gear, and both alarms and automatic systems for minimizing the odds of pilot error — landing with wheels up instead of down. (I’ve already posted about how concerning that prospect can be.)

I also counted three independent sources of weather information, including lightning detection, and two powerful communication radios and one handheld backup radio. For navigation there is a compass and four electronic navigation devices: one instrument approach (in the clouds) approved panel mount GPS with separate panel-mounted indicator, an independent panel mounted approach certified navigation radio, plus two portable GPS with moving map displays and superimposed weather. Even the portable radio has the ability to perform simple navigation.

photo (17) - no Exif — There’s two of just about everything in this Arrow panel.

The primary aircraft control gyro, the artificial horizon or attitude indicator, also has a fully independent backup. One gyro operates off the engine-powered vacuum pump, and the second gyro horizon is electrically driven. Although by no means ideal, the portable GPS devices also provide attitude indicators based upon GPS signals. In a pinch in the clouds, it’s far better than nothing. Of course, even if all else fails, the plane can still be flown by primary instruments like rate of climb, altimeter, and compass.

There is only one sensitive altimeter, but two GPS devices also provide approximate altitude based on GPS satellite information.

Diving

But what about divers? How are we set for redundancy?

Starting with scuba (self-contained underwater breathing apparatus), gas supplies are like the fuel tanks in an aircraft. I typically dive with one gas bottle, but diving with two or more bottles is common, especially in technical diving. In a similar fashion, most small general aviation aircraft have at least two independent fuel tanks, one in each wing.

The scuba’s engine is the first stage regulator, the machine that converts high pressure air into lower pressure air. Most scuba operations depend on one of those “engines”, but in extreme diving, such as low temperature diving, redundant engines can be a life saver. While most divers carry dual second stage regulators attached to a single first stage, for better redundancy polar divers carry two independent first stages and second stages. Two first stage regulators can be placed on a single tank.

tv9200rhlg[1] — An H-valve for a single scuba bottle. Two independent regulators can be attached.

Two Regs — A Y-valve for Antarctic diving with two independent scuba regulators attached.

Even then, I’ve witnessed dual regulator failures under thick Antarctic ice. The only thing saving that very experienced diver was a nearby buddy diver with his own redundant system.

There is a lot to be gained by protecting the face in cold water by using a full face mask. But should the primary first or second stage regulator freeze or free flow, the diver would normally have to remove the full face mask to place the second regulator in his mouth.

Two regulators, one full face mask. Photo courtesy of Michael Lang and Scuba Pro.

Reportedly, sudden exposure of the face to cold water can cause abnormal heart rhythms, an exceedingly rare but potentially dangerous event in diving. If the backup or bail out regulator could be incorporated into the full face mask, that problem would be eliminated. The photo on the right shows one such implementation of that idea.

Inner Space 2014_Divetech _Nikki Smith_Rosemary E Lunn__Roz Lunn_The Underwater Marketing Company_Nancy Easterbrook_rebreather diving_2014-05-27 22.30.47 — Nikki Smith, rebreather diver with open circuit bailout in her right hand. Photo courtesy of Rosemary E Lunn (Roz), The Underwater Marketing Company.

Rebreathers are a different matter. Most rebreather divers carry a bailout system in case their primary rebreather fails or floods. For most technical divers, that redundancy is an open circuit regulator and bailout bottle. However, there are options for the bail-out to be an independent, and perhaps small rebreather. (One option for a bail-out semiclosed rebreather is found here.) Such a bail-out plan should provide greater duration than open-circuit bailout, especially if the divers are deep when they go “off the loop”.

SPECWAR1 — U.S. Navy photo by Bernie Campoli.

For some military rebreather divers, there is at least one complete closed-circuit rebreather available where a diver can reach it in case of a rebreather flood-out.

SLS-Diver-Side-View — A commercial saturation diver with semi-closed rebreather backpack as emergency bail-out gas.

For deep sea helmet diving, the bail-out rebreather is on their back and a simple valve twist will remove the diver from umbilical-supplied helmet gas to fresh rebreather gas.

The most common worry for electronically controlled rebreather divers is failure of the rig’s oxygen sensors. For that reason it is common for rebreathers to carry three oxygen sensors. Unfortunately, as the Navy and others have noted, triple redundancy really isn’t. Electronic rebreathers are largely computer controlled, and computer algorithms can allow the oxygen controller to become confused, resulting in oxygen control using bad sensors, and ignoring a correctly functioning oxygen sensor.

The U.S. Navy has performed more than one diving accident investigation where that occurred. Safety in this case can be improved by adding an independent, redundant sensor, by improving sensor voting algorithms, by better maintenance, or by methods for testing all oxygen sensors throughout a dive.

In summary, safe divers and safe pilots are always asking themselves, “What would I do if something bad happens right now?” Unfortunately, private pilots and divers quickly discover that redundancy is not cheap. However, long ago I decided that if something unexpected happened during a flight or a dive, I wouldn’t want my last thoughts to be, “If only I’d spent a little more money on redundant systems, I wouldn’t be running out of time.”

Time, like fuel and breathing air, is a commodity you can only buy before you run out of it.

Disclaimer: This blog post is not an endorsement of any diving product. Diving products shown or mentioned merely serve as examples of redundancy, and are mentioned only to further diver safety. A search of the internet by interested readers will reveal a panoply of alternative and equally capable products to enhance diver safety.

When Cars Can Tweet

I was quite surprised when I learned that the U.S. government is mandating, and U.S. engineers are devising, ways for cars to share messages about their status, speed, and location. That is, they will be talking to each other.

What will that talking sound like? Well, I don’t think its going to be like Mater in Disney’s Car series.

I suspect it will probably resemble something like minimalistic messaging —to save bandwidth.

Here’s an example of what it might sound like:

RedHondaCivic564: “OMG, my peeps is a lunatic.”

BlackAccuraJ76: “How so?”

RedHondaCivic564: “He’s straddling the center line!”

BlackAccuraJ76: “LMAO. What a twit.”

RedCherokeeH65: “Watch out, I’m swerving, coming up fast on your six.”

OrangeSonata97B: “What’s the prob?”

RedCherokeeH65: “My peeps is a stoner. Smoking weed in the car. ”

BlackAccuraJ76: “Is that bad?”

RedCherokeeH65: “It’s filling my passenger compartment. Cough, cough.”

BlackAccuraJ76: “I should be so lucky.”

RedCherokeeH65: “Uh _ why are pink bunnies dancing on my hood?”

OrangeSonata97B: “Seriously? Turn your AC to outside air.”

RedCherokeeH65: “Ah, much better. No more bunnies.”

Maserati I’m a Doc: “Out of my way! Move over!”

RedHondaCivic564: ‘What’s ur rush pretty grl?”

Maserati I’m a Doc: “I’m a go-fast car.”

Ford: “Sucks for you since ur stuck in a 45 zone.”

Maserati I’m a Doc: “Tell me ’bout it. So frustrated.”

Ferrari SiliconeDoc: “Me too. I never get my pipes cleaned.”

PinkMercedes: “SiliconeDoc, like the sound of that. Talk to me.”

BlackAccuraJ76: “Watch out for that poo…”

RedCherokeeH65: “Oh crap.”

BlackAccuraJ76: “…dle!”

FordKJ7: “Cute the crap folks. We’re s’posed to be talking safety.”

RedHondaCivic564: “Yeah right. Boring!”

UnknownCaddy: “Get over, make way!”

RedHondaCivic564: “Another fast mover? What’s your hurry?”

UnknownCaddy: “Getaway car.”

RedHondaCivic564: “What are you getting away from?”

UnknownCaddy: “Cops.”

Copper1: “Thanks for that.”

UnknownCaddy: “What you mean?”

Copper1: “I’ve gotta a BOLO out for you.”

UnknownCaddy: “Did you just hit my kill switch?”

Copper1: “Do the crime, do the time.”

Does Your Rebreather Scrubber Operate in Its Goldilocks Zone?

gliese581d — Exoplanet Gliese 581d, orbiting the red-dwarf star Gliese 581, only 20 light-years away. (The existence of this planet is currently in dispute.)

In space, there is a so-called Goldilocks zone for exoplanet habitability. Too close to a star, and the planet is too hot for life. Too far from its star, and the planet is too cold for life, at least as we understand biological life, life dependent on water remaining in a liquid state. Earth is clearly in the Goldilocks zone, and so is a purported planet Gleise 581d, from another solar system.

Carbon dioxide absorbing “scrubber” canisters in rebreathers have similar requirements for sustaining their absorption reactions. If it’s too hot, the water necessary for the absorption reaction is driven off. Too cold and the water cannot fully participate in the absorption reactions.

Those with some knowledge of chemistry recognize that cold retards chemical reactions and heat accelerates them. But that does not necessarily apply to reactions where a critical amount of water is required. Water thus becomes the critical link to the reaction process, and so maintaining scrubber temperature within a relatively narrow “Goldilocks” zone is important, just as it is for life on distant planets.

Temperature within a scrubber canister is a balance of competing factors. Heat is produced by the absorption of CO2 and it’s conversion from gas to solid phase, specifically calcium carbonate. A canister is roughly 20°C or more warmer than the surrounding inlet gas temperature due to the heat-generating (exothermic) chemical reactions occurring within it.

Heat is lost from a warm canister through two heat transfer processes; conduction and convection. Conduction is the flow of heat through materials, from hot to cold. Hot sodalime granules have their heat conducted to adjacent cooler granules, and when encountering the warm walls of the canister, heat passes through the canister walls, and on to the surrounding cold water.

You can think of this conduction as water flowing downhill, down a gravity gradient. But in this case, the downhill is a temperature gradient, from hot to cold. If the outside of the canister was hotter than the inside, heat would flow in the opposite direction, into the canister.

Copper is a better conductor of heat than iron (it has a higher thermal conductivity), explaining why copper skillets are popular for cooking on stoves. Air is a poor conductor of heat, explaining why neoprene rubber wet suits, filled with air bubbles, are good insulators. Air-filled dry suits are an even better insulator.

Capturecan1 — Chemical absorption reactions heat an otherwise cold canister (yellow is hot, red is warm, black is cold.) (Copyright John R. Clarke, 2014).

Convection is the transfer of heat to a flowing medium, in this case gas. You experience convective cooling when you’re working hard, generating body heat, and a cool dry breeze passes over your skin. Convective cooling can, under those circumstances, be delightful.

When you walk outside on a cold, windy day, convective cooling can be your worst enemy. Meteorologists call it wind chill.

There is wind chill within a canister, caused by the flow of a diver’s exhaled breath through the canister. In cold water the diver’s exhaled breath leaves the body quite warm, but is chilled to water temperature by the time it reaches the canister. Heat is lost through uninsulated breathing hoses exposed to the surrounding water.

As you might expect, if the canister is hot, that convective wind chill can help cool it. If the canister is cold, then the so-called wind chill will chill it even more.

Capturecan2 — Copyright John R. Clarke, 2014.

The amount of heat transferred from a solid object to gas is determined by three primary variables; the flow rate of the gas, the density of the gas, and the gas’s heat capacity. Heat capacity is a measure of the amount of heat required to raise the temperature of a set mass of gas by 1° Celsius.

Both the heat capacity and density of the gas circulating through a rebreather changes not only with depth (gas density), but with the gas mixture (oxygen plus an inert diluent such as nitrogen or helium). The heat capacity of nitrogen, helium and oxygen differ, and the ratio of oxygen and inert gas varies with depth to prevent oxygen toxicity. Nitrogen and helium concentrations vary as well, as the diver attempts to avoid nitrogen narcosis.

Q is heat transferred by convection, and the terms on the right are, in sequence, diver ventilation rate, gas density, heat capacity of the inspired gas mixture at constant pressure, and the difference in temperature between the absorbent and environmental temperature.

The interaction of all these variables can be complex, but I’ve worked a few examples relevant to rebreather diving. The assumptions are a low work rate: ventilation is 22 liters per minute, water temperature is 50°F (10°C), oxygen partial pressure is 1.3 atmospheres, and dive depths of 100, 200 and 300 feet sea water. The average canister temperature is assumed to be 20°C (68°F) above water temperature, a realistic value found in tests of scrubber canister temperatures by the U.S. Navy.

The heat capacities for mixtures of diving gases come from mixture equations, and for the conditions we’re examining are given in the U.S. Navy Diving Gas Manual. (This seems to be a hard document to obtain.)

At 100 fsw, the heat transfer (Q) for a nitrogen-oxygen (nitrox) gas mixture is 34.2 Watts (W). For a helium-oxygen mixture (heliox), Q is 27.4 W. At 200 fsw, Q for nitrox is 59.9 W, and for heliox Q is 50.3 W. At 300 fsw, Q for nitrox gas mixture is 85.5 W, and for heliox, is 59.9 W.

Interestingly, the heat transferred from the absorbent bed to the circulating gas is the same at 300 fsw with heliox as it is at 200 fsw with nitrox.

Photo courtesy of David L. Conlin, Ph.D., Chief – National Parks Service Submerged Resources Center. Photo by Brett Seymour, NPS.

Dr. Jolie Bookspan briefly mentioned the fact that helium removes less heat from a diver’s airways than does air in her short article on “The 36 Most Common Myths of Diving Physiology” (see myth no. 20). Conveniently, heat exchange equations apply just as well to inanimate objects like scrubber canisters as they do to the human respiratory system.

From these types of heat transfer calculations it is easy to see that for a given depth, work rate and oxygen set point, it is better to use a heliox mixture than a nitrox mixture if you’re in cold water. That may sound counterintuitive considering helium’s high thermal conductivity, but the simple fact is, the helium background gas with its low density carries away less heat from the canister, and thereby keeps the canister warmer, than a nitrox mixture does. The result is that canister durations are longer in cold water if less heat is carried away.

In warm water, the opposite would be true. Enhanced canister cooling with nitrox would benefit the canister.

An earlier post on the effect of depth on canister durations raised the question of whether depth impedes canister performance. The notion that increased numbers of inert gas molecules block CO2 from reaching granule absorption sites has little chemical kinetic credence. However, changing thermal effects on canisters with depth or changing gas mixtures does indeed affect canister durations.

I’ve just given you yet another reason why helium is a good gas for rebreather diving, at least in cold water. Unfortunately, these general principles have to be reconciled with the specific cooling properties of all the rebreather canisters in current use. In other words, your canister mileage may vary. But it does look like the current simple notions of depth effects are a bit too simplistic.

My Medicines Saved my iPhone

I’ve heard about all sorts of disasters with smartphones, and other small, portable electronic devices. Being small and portable makes them easy to drop — something I’ve personally witnessed. Phones are tough by design, but they really don’t like water. Drop one in a toilet while you’re relaxing, and it’s gone — for all practical purposes.

So I had my phone outside with me one evening while I was safety diver for my granddaughter who was practicing scuba skills in our pool. She was enthusiastic and stayed in the pool until it became completely dark outside.

Well, out of sight, out of mind. I helped her out of her dive gear, and then went inside. The phone stayed outside in the dark, quite forlorn and forgotten.

Next morning I noticed it had rained in the early morning hours. Great, I thought, the lawn needs water. But when I went outside I discovered my phone sitting face up on a glass table with beads of water everywhere, including on the phone. A few expletives followed, as you might imagine.

My phone had been somewhat protected by an almost all enclosing Otter box, so I was hopeful not all was lost. Indeed, when I brought the phone in, removed the Otter box sheaving and dried off the phone with paper towels, the phone came back on. Immediate disaster avoided. Thank-you Mr. Otter.

But it took a little while before the potential damage became apparent. When my phone would ring, I’d hear nothing on the ear speaker. I had to switch to speaker phone mode to hear anything. Well, that was annoying.

And then I tried to take a phone photo of the scuba gear, and I could barely see through the camera view finder for the obscuring droplets of water. Rats! Clearly, water had gotten inside the phone. It was merely a matter of time before more damage was done.

With nothing to lose, I plundered through my medicine cabinet and found a potential solution, pictured below.

In fact, I found four of them. I placed those small cylinders of silica gel in a quart-size zip-lock style bag, and placed the dampish phone inside and sealed the bag after squeezing out excess air. If the silica gel canisters didn’t hurt the medicine, it probably wouldn’t hurt my ailing phone.

And there the phone sat, with the small vials of desiccant.

I don’t pray for the healing of phones, but I did have some thoughts somewhat resembling prayer.

I let the phone-in-a bag sit overnight, and in the morning I found I could hear the voices on the other end of the phone connection, and my camera lens no longer had droplets of water on it. As you can see from these photos, the camera worked just fine, and all functions have worked fine ever sense.

Even Siri didn’t seem to mind getting rained on.

I am Neanderthal, Pt. 3

image_1734-Neanderthal-DNA — Neanderthal. Image credit: Trustees of the Natural History Museum, London.

I feel like a seeded watermelon.

Ever since I was created by the curiosity of government and university scientists, I have lived through no efforts of my own. I have the largesse of the U.S. government to thank for that. You see, they paid for the research that created me.

And now, I contribute nothing to society. I pay no taxes, work no jobs. The only decisions I’m allowed to make are restricted to which television program to watch, or which book I want to read. (In case you wondered, I’m not a slow reader. I read quite well, thank-you.)

I live basically in a zoo, except I am the only specimen there, and the zoo keepers all wear lab coats. I suppose the lab coats are designed to protect them were I to spit on them or throw excrement.

I admit, as a child I used to act out with what you consider primitive behavior, throwing feces to vent my anger. I do have tough skin, but no child wants to be continuously poked and needled and questioned. Would you?

But I’ve outgrown that. I’ve learned that when it suits me I can produce a terrifying stare or a teeth-bared snarl that scares the crap out of the more timid researchers. Ah yes, I do enjoy having fun at their expense. It’s about the only thing they can’t control in my otherwise manufactured and manipulated world.

And of course they don’t dare punish or threaten me, because I am, after all, the rarest person in the universe, the only living Neanderthal.

But about that watermelon?

Having nothing to do of any real value gives me time to think … lots of time. Now, since a part of me is a part of you (genetically that is), I’ve been inclined to wonder why my kind is gone, and you Homo sapiens have become the overlords of the planet, at least for the time being.

And I’ve decided that I am truly a seeded watermelon, and you’re seedless.

The seedless watermelon is very much like the older, and almost extinct seeded variety, but with one subtle difference; it’s infertile. (If this analogy becomes too Freudian for you, just keep your mind on watermelons.) Watermelon is, I sincerely believe, one of God’s gifts to man.

But of course you Homo sapiens weren’t content with that. No, you decided to take advantage of a genetic flaw, a freak watermelon with few if any seeds, that is quite incapable of sustaining itself in the gene pool.

Since spitting out melon seeds is apparently such a difficult proposition for your kind, the seedless variety is overwhelmingly popular. It has crowded out the natural watermelon from grocery stores, so I hear.

Photo Credit: Steve Evans (Watermelons) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

I’ve been reading about how, based partially on my IQ test results and other research, scientists have decided we weren’t mentally inferior to you. And for sure, as my own testing by the Army has confirmed, we were far stronger.

So what’s not to love?

OK, we are a little shorter, squattier than Homo saps, and from what I hear tall men have a selective breeding advantage over shorter men. So could it be simply a matter of Neanderthal women preferring to breed with you guys, the new kids on the block, and not with us more vertically-challenged guys? Could that be why my kin disappeared, and why many of you have Neanderthal genes?

I mean, really, could it be that simple; a matter of sexual attraction? Did short-sighted Neanderthal women breed our unique species out of existence?

Well, who would have thought an infertile and obviously biologically deficient watermelon would have replaced the real thing in popularity?

But it has.

Where Have All the Letters Gone?

SONY DSC — By Petar Milošević (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

When is the last time you wrote a letter to a family member or loved one?

I’m not talking about email or text messages; digital communications do not count. I mean a letter on a piece of paper, placed in an envelope with a stamp, and mailed at a mailbox or post office; or in a very private way, lovingly slipped underneath someone’s door.

In the hurry-up, speak sparingly Twitter generation, there seems to be little value in penning an honest-to-goodness letter. Compared to instant communication, letter writing with an ink-filled pen seems agonizingly slow, sloppy and so twentieth century.

I recently opened a grey metal box that had lain dormant, ignored, for up to 50 years. It was a time capsule, holding remnants of this young man’s life in 1964 and before. In it were letters, letters my Dad had written to me during my college years.

My parents have been gone for many decades now and reading those letters after such a long time was a joy. Unlike emails and tweets, those letters told a story, a story of how my parents were reacting to and appreciating my newfound freedom and expressions of individuality.

My father, a physician who practiced medicine for 50 years, wrote words that are even deeper in meaning now than they seemed at the time. “We are glad that you seek the places that are apart, such as the mountains and the sea,” he wrote. “It is so easy to rush past the beauty and truth of life, especially in this age. An older and wiser one once said, ‘Let us not hurry, not worry, and let us take a moment now and then to smell the flowers along the way.’ “

And then there were the words I puzzled over briefly before realizing what it meant. “Their being and meaning will never know the obsolescence of most of that which is taught.”

Frankly, that was a lesson that takes a lifetime to understand, for in time we come to know that many things we are taught while young will eventually be found wrong, or at least inaccurate. In other words, so-called truths change.

In 2064, fifty years from now, how will you or your descendants be reminded of things you said or things your parents and other loved ones thought way back in 2014? How will memories of 2014 be renewed?

Even now, the concept of writing love letters seems sweet but archaic to those in their twenties. So I wonder, will there be such a thing as love letters in the future?

Facebook posts certainly won’t be preserved for fifty years. In fact, both Facebook and Twitter will be long forgotten, replaced by more culturally relevant trends. And let’s face it, have you ever said anything on Facebook that deserves to be preserved for fifty years?

I suppose that as my father saw his time on earth becoming increasingly limited, he realized that time, the time to enjoy life, was a precious commodity, yet one not well appreciated until the sand in the clock is half run out. That is an important lesson that I, with my own sand ebbing away, have at last come to appreciate. But if I did not have my Father’s letter to read now, fifty years later, it would be a lesson long forgotten.

In a tweeting, Facebook society, how will we hold pages and memories in our hands when our parents and other loved ones are gone?

Sad to say, I don’t think we will.

The Patients, the Pilot, and the Politicians

Beechcraft_Baron_58TC — A Beechcraft Baron similar to the one used by Quest Diagnostics. (From Wikimedia Commons).

Every night a pilot from Atlanta makes a round-robin cargo flight to Albany GA and Dothan AL, then continues down to the coast to load cargo from Panama City FL, Pensacola, and Mobile AL before returning home. He used to fly a single engine Beech Bonanza, but now pilots a Baron, a twin-engine, 190 kt fast mover.

On really rough weather nights I’ve watched vicariously through FlightAware.com as he scurries away from lethal skies and diverts to any safe harbor. His cargo is your lifeblood, literally, but it’s not worth dying for.

He makes that flight each night because during the day in each of those cities patients had blood drawn at their doctor’s office. The samples that will tell the doctor the life and death stories of the day’s patients are whisked away to a large laboratory near Atlanta for processing overnight.

After taking off from Gwinnett County Airport near Lawrenceville, GA at 6 PM or so, the solitary pilot returns to his home base about midnight.

Centurion C210 — A Centurion 210; not your ordinary Cessna.

I was alerted one night that a plane I’d flown to Houston and back, a Cessna Centurion 210, had a gear collapse at the local Panama City Airport. I knew the plane well.

Unfortunately, shortly after the only runway was closed the Quest Diagnostics Baron approached the area, attempting to land. I turned on my aviation radio and heard the “850”, as it’s called, being told to hold, circling, while airfield crews attempted to move the damaged Centurion off the runway.

PFN 2007 — The original two-runway Panama City Airport, circa 2007. (Click to enlarge)

And that’s where the politicians come in.

Local Panama City politicians felt obliged to close down the Panama City airport with two runways (formerly known as PFN) and relocate to a larger facility, again with two runways. The new two runway airport, KECP, looked great in an artist’s rendition.

But artists don’t build airports. The reason why the second runway was not built is not a subject for this blog posting. What is the subject, is that promises made to the citizens of Panama City were not promises kept. And on that night as “850” circled overhead, there would be real consequences for the political decisions which had been made.

Once construction began on the main 10,000 ft long runway at the donated site, all mention of the second runway was forgotten; not by the local pilots, but by the local politicians and the land company.

Second runways serve important purposes. They are usually called “cross-wind” runways. I’ve landed many times on the cross-wind runway at PFN, and I’ve also been on Delta flights that used that runway when the wind across the main runway was dangerously high.

Cross-wind runways are not only a safety factor for overbearing wind conditions, but also provide an alternate landing site in case the main-runway is closed due to an aircraft being stuck on the runway.

That night as “850” was trying to land to pick up the day’s tissue samples from the Panama City area, the main runway was closed by the broken Centurion, and there was no backup runway. The pilot circled Panama City until his fuel became critical, and then he flew on to his next stop in Pensacola.

So all the blood drawn from patients in the Panama City area that day missed the trip to the Quest Diagnostics laboratory, due to a promise made but not kept.

But I suppose that is hardly news. Rather, it appears to be deeply woven into the very fabric of politics.