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-        Protect your mother earth     jatinder pal singh  assistant prof. physics

There are several reasons why it is instructive to begin an overview of the global environmental crisis with a detailed study of the problem of the infamous s” ozone hole.”

First many people are very frightened and puzzled by it, and we might all be glad to understand it a little better.

Second it is indeed very serious; some especially among those living in the  (Southern Hemisphere) would insist that it is the most immediately. Pressing environmental problem we ace today.

Third, it is in certain respects relatively conceptually simple and the philosophical and policy imperatives that it raises are relatively clear cut although no less painful to conform than those arising out of many other issues we will consider. Most people, although certainly not all agree about that should be done about it. There is surprisingly little scientific disagreement about the basic nature and seriousness of the hole as compared to many other highly contentious issues such as the greenhouse effect, deforestation and nuclear safety. From the scientific and historical point of view, we know pretty well what went wrong. This makes the ozone hole quite rare among ecological problems, where disputes about the facts of the mater get inextricably entangled with disputes about values. The consensus on the ozone hole is very recent. Ten years ago the debates about the ozone hole is very recent. Ten years ago the debates about the ozone hole sounded much like the debates about the ozone hole sounded much like the debates about the greenhouse effect today.

Hence the ozone surprises are almost a “textbook” case, if there could be such a thing, of an environmental disaster. It defines a basic pattern that we will see repeated again and again in other contexts. It is also, as we shall see, replete with terrible ironies and devastating surprises.

IN THE BEGINNING ………….

Very early in the Earth’s history (more than 3 billion years ago), our planer possessed what is technically known as a “reducing” atmosphere – a mixture of compounds such as water vapour, carbon dioxide, and probably methane and ammonia, with little or no free oxygen. There was a high flux of UV (ultraviolet radiation) from the sun, at levels which would be lethal to most forms of life today. Somehow, simple life-forms appeared on the Earth that used anaerobic processes ( processes not requiring oxygen) to get their energy. There are many such bacteria still present on the Earth – the so-called chemoautotrophic bacteria that make iron plumbing smell of sulfur, for example.

About 3.5 billion years ago, photosynthetic forms evolved. Photosynthesis is the complex process by which organisms containing chlorophyll or similar compounds can utilize solar energy to create carbohydrates from water and carbon dioxide, releasing free oxygen in the process. Photosynthesis was the most sophisticated strategy that had yet been fund for extracting energy from the environment, and these early photosynthesizes (such as the blue-green algae) eventually came to dominate the biosphere.

With the evolution of photosynthesis, the planet experienced its first pollution crisis, for oxygen is very toxic to most anaerobic organisms. As oxygen released by photosynthesis built up, the anaerobes declined, and now survive only in places where there is very little free oxygen, such as the bottom of the sea and our intestines. Aerobic organisms, which could use the oxygen, for respiration, evolved. Respiration (which is really a highly controlled combustion process) makes much more energy available to the organism than any anaerobic process; this in turn allows respiring organisms a much higher level of activity than anaerobic organisms or photosynthesizes, and these organisms quickly took over as dominant life-forms on the planet.

As oxygen accumulated in the atmosphere, an ozone layer begin to form. Ozone is a form of oxygen created by the action of high energy ultraviolet light (UV) son oxygen. Ozone observes ultraviolet light ( or more precisely, UV is observed by the  creation and destruction of ozone). This protected the surface of planet from the high energy ultraviolet light from the Sun, which allowed  more complex and delicate life-forms ( like us) to evolve. Hence we could summarize this whole process by  saying that life itself help to create the very atmospheric conditions that made its own continuance and further evolution possible, The ozone layer is one among many important examples of components of the earth’s physical environment that are are  bioorgenic (meaning, created and maintained by life itself).

The ozone layer also helps to maintain the very structure of the atmosphere. The ultraviolet energies observed by the ozone layer are re-radiated to the upper atmosphere ( the stratospheres) as heat, warming it and  thereby causing the temperature inversion that defines the boundary between the stratosphere and the lower atmosphere ( or troposphere). The total or near total disappearance of the ozone layer might result in atmospheric instabilities of a type never before  experienced, quite apart from the destruction of most life on Earth by irradiation.

Ozone and the Ozonosphere

Ozone itself is a bluish, irritating gas with a pungent odour. It is a powerful oxidant and can be used as bleach and sterilizing agent; in large enough concentration it is quite toxic.

Ninety present of the ozone in the atmosphere is normally in the stratosphere, concentrated at an altitude of around 12 to 25 kilometers.( This layer is sometimes called the ozonosphere.) However, in a heavy smog, ozone concentration at ground level can be as much as ten times higher than normal, causing respiratory irritation and damage to plants. One of the many ironies of the ozone story is that while we  have to little where it is needed, we are often getting too much where it is not, both effects being due to different kinds of pollution.

If all the ozone that is normally present in the atmosphere were to be separated out from the air in which it is mixed, and were concentrated into a single  layer at ground- level temperature and pressure, it would only be about 3 millimeters thick. The existence of all life on Earth more complex than bacteria depends on this evanescent wisp of gas.

The  UV  radiation that can reach the earth ‘s  surface can be divided into two bands , usually called UV—B ( the far ultraviolet )  and UV—A  ( or the near ultra – violet). The UV that gives us a sunburn sis mostly UV – A, a little bit of which can actually be good for us. The effect of ozone is to filter most out of the UV-B, the most energetic (and hence the most potentially damaging) radiation that would otherwise reach the Earth’s  surface. Hence the depletion f the ozone layer not only increases the intensity of the UV radiation reaching the surface, but it tends to shirt the peak energy into the UV-B range. This is the kind of UV that does the most harm to sensitive biomolecules such as proteins and nucleic acids.

Ozone is constantly being created and destroyed by the action of UV on oxygen  in the stratosphere. There are other natural processes that destroy ozone as well, but until recently the processes of creation and destruction were usually in balance, so that the net amount of ozone created was equal to the amount being destroyed. ( This is an example of as dynamic equilibrium.) This happy sate of affairs went on for a few billion years until about the year A.D. 1928, when a brilliant industrial chemist named Thomas Midgley, Jr., invented CFCs(chlorofluorocarbons). These compounds, which are rare or non-existent in the Earth’s normal chemistry, break down ozone, leaving the planet’s surface again at risk from ultraviolet radiation from the Sun. and this is where our story really begins.

What Are CFCs?

Midgley ( who was also the creator of tetraethyl lead) was really just trying to solved what seemed to be straight  forward problem of product safety. By1928, the refrigeration industry was expanding rapidly, but the only working fluids available for refrigerators were compound like ammonia, methylene chloride, or sulfur dioxide, all toxic flammable, or corrosive. Some accidental deaths from leaky refrigerators had actually occurred. It was essential to find a refrigerant that was safe, sand CFCs fit the bill perfectly.

Chlorofluorocarbons are chemically very similar to methane and other simple hydrocarbons, but with the hydrogens replaced by fluorines and chlorines. They have great chemicals stability, which makes them almost entirely nontoxic and nonflammable. Midgley demonstrated these desirable properties by inhaling some CFCs and then blowing out a candle flame. They also turned out to have many other useful properties – as solvents, propulsion agents for spray cans, and forming agents in plastic manufacture. But it is precisely their stability that allows them to survive the rip to the stratosphere; most other chlorine – containing compounds break down long before then. Before CFCs, there was no mechanism that could transport significant amounts of chlorine to the stratosphere. Hence there is a considerable irony in this story: the very property of CFCs that makes them so useful is also the property that makes them so deadly. Sit was many years, however, before anyone became aware of this.

First Warnings

The first intimations that CFCs could be endangering the ozone layer came by an indirect route. In the late 1960s, there was considerable controversy in the United States over weather the government should support major project to develop a fleet  of commercial SSTs,  These  would have that could fly high in the stratosphere at supersonic speeds , cutting international  travel times to a fraction of the time required by standard subsonic commercial aircraft . jet aircraft release nitric oxide as a combustion  by product,  and it was known that nitric oxide  can attack ozone. Hence a worry was born that fleets of  SSTs  might damage the ozone  layer,  and this fear may have had something to do with the eventual abandonment of the project. ( cost was likely at least  as important a factor in the decision. See roan 1989.)It is now believed that he nitric  oxide from jet exhaust would pose a minimal threat to the ozone layer. But the debate led scientists to ask if there were other industrial pollutants that might damage ozone. The first measurements  of CFC  concentrations  in the atmosphere  had been made in the early 1970s by  James lovelock .  Because the amount revealed by his measurements were so low  (  a few parts per trillion at that  time —–  they are now much higher )  Lovelock remarked  that they posed  no danger, a position he later  reversed.  In 1973 , chemist  Sherwood  Rowland  set his  postdoctoral  fellow  Mario Molina the problem of investigating  whether CFCs  could be  having any effect  on the ozone layer.  Rowland  and Molina  soon  discovered to their consternation  that ozone  can  be broken down by chlorine  via a catalytic reaction cycle —–  that is a reaction in which a substance (  in this case chlorine )  promotes a reaction but is not used up by it .

The  important point to not is that because  the  reaction is  catalytic, a very  small amount of the catalyst ( chlorine )  can  break down a great deal of ozone , even thought the concentration of CFCs  in the atmosphere is at trace levels.  In fact , one chlorine atom  will  break  down  between 10,000 and 100, 000 ozone molecules before it finally precipitates  out of the atmosphere (  usually as a form of acid rain , to add environment insult to injury). This is a good illustration of general rule that we are gradually learning to respect: the danger posed by a pollutant may not be in simple proportion to its amount or concentration in the environment.

A check of CFC production figures convinced Rowland sand Molina that CFCs could eventually (but not for several decades, they first estimated ) do significant damage to the ozonosphere. It is reported that Rowland came home from the lab one day and reported to his wife, ” It looks like the end of the world!”4

Rowland and Molina, and then many other scientists and concerned citizens, began to argue that CFCs should be restricted. Sin the late 1970s a number of countries (Canada, the United States, Norway and Sweden) introduced bans on CFCs usage for aerosol sprays, and overall consumption of CFCs briefly decreased before beginning its inexorable climb again in the 1980s. However, there was, up until the mid 1980s, still no absolutely convincing evidence either that    CFCs actually were breaking down ozone in the stratosphere, sor that ozone was becoming depleted. In other swords it was not known  with certainly that CFCs do harm the ozone layer, only that they could. The CFC industry fraught back vigorously, using all the public relations powers at its disposal, and played on the scientific uncertainties to argue that the case against CFCs had not been established. The debate became at times very bitter and personal?

Bit by bit, further scientific evidence accumulated that CFCs might indeed be doing exactly what Rowland and Molina had predicted they would do. But many uncertainties remained.

The Ozone Hole Appears

Since 1957 ( the international Geophysical Year), a team of scientists led by James Farman had been measuring ozone levels, among other geophysical data, at the British research station in Antarctica. This was just for the sake of “pure” science, and they were close to being   shut down by budget cuts on at least one occasion.

In 1984, Far man and colleagues noticed that ozone reading over the polar region had been dropping markedly since the late 1970s, with a more dramatic drop each year. It seemed that a large hole was appearing over Antarctica in the ozone layer each Antarctic spring. Farman publishes his results in 1985.Sshortly afterward, it was discovered that an American NIMBUS weather satellite had been showing the same thing since the late 1970s,but the data from the satellite had been rejected because it was assumed that any readings that were so low must be due to  instrumental error!

In the southern spring ( September to November) there is nearly 100 percent depletion of ozone in some areas of Antarctica and over the Southern Sea. There is a loss of zero to 10 percent ( and occasionally higher) in other areas of  the world, even as far as the Equator. These differences are definitely greater than the normal variations in the long – run average levels. And there is a similar deflection in the Arctic each northern spring , but less severe.

Intense debate sprang up on the cause of the ozone hole, and the call was renewed to ban CFCs. Several theories were proposed to account for the hole; sat the time of its discovery there still was no proof (although certainly a strong suspicion) that it was due to CFCS. In 1986 and 1987, teams of scientist went to Antarctica and under conditions of some hardship studied the ozone hole intensively. Aircraft were flown through the hole to take direct samples of the air. ( It was no travel matter to fly a treatmental  ER-2 at altitudes above 60,000 ft over Antarctica in the winter time. If a plane had gone down, the pilots would have had little hope of being rescued. Considerable personal courage, both physical amoral may be needed to answer the question that need to be answered). By early 1988, scientist were finally convinced that they had found unmistakable evidence that  CFCs were guilty : ” The extensive new data leave no doubt that man made CFCs are primarily responsible for the ozone could be broken down so quality. The situation is much worse than they had predicted.

The explanation for this lies partially in an important fact about catalytic chemistry that ha not been noticed, and partially in the very unusual  meteorological condition in the Antarctic winter. I will most of the fascinating but very technical details. Here is the essence of the matter: CFCs are broken down by energetic ultraviolet in the stratosphere, releasing chlorine which quickly is taken up in harmless ” reservoir compounds.” In the Antarctic winter, a stratospheric vortex forms, a great whirlpool of air as big ass the continent itself. Within the vortex, polar stratospheric clouds (PSCs) form, clouds of tiny ice crystals. This was some what unexpected since the stratosphere is usually too dry to form cloud. The reservoir compounds can breakdown into highly reactive chlorine and chlorine monoxide at very high rate on  the ice crystals; this is the “heterogeneous” chemistry that surprised the experts . When sunlight hits the PSCs in the Antarctic spring, it stimulates the breakdown  of ozone by the accumulated chlorine and chlorine monoxide, and a huge forms in the ozone layer. Eventually as the polar vortex breaks up un late spring, the depleted air mixes with air at lower latitudes, causing patches of low ozone world wide. A similar process occurs in the Northern Hemisphere, although the hole formed is less deep because the northern polar vortex is much less intense. And there is strong evidence, as well that this process can occur anywhere in the stratosphere where dust or ice particles are available. The eruption of the volcano Pinatubo, for instance, is suspected to have provided enough stratospheric dust to contribute significantly to recent ozone deplection.9

The key factor that no one had originally anticipated was the ability of tiny ice crystals and dust particles to promote and accelerate the catalytic breakdown reactions. Sin fact, it is well known that catalytic reactions of many kinds go faster on surfaces; perhaps this possibility had not occurred even to the most vigilant of experts because of a belief in the stratosphere as a volume of pristine clean air.

The ozone story is therefore a history of surprises: first, that CFCs can decompose ozone catalytically, sand second that the decomposition can be further accelerated by the freakish ” heterogeneous chemistry” that occurs on the surface of ice crystals in the Antarctic winter vortex.

One often hears of “worst case scenarios”; it is as if for CFCs every worst case scenario has, so far, come true.

BIOLOGICAL EFFECTS OF OZONE DEPLETION

For simplicity, we can divide the biological effects of ozone depletion into two sorts: effects on humans, and effects on life in general.

The effects on humans naturally get the most press. The most dramatic dangers are skin cancer and retinal burn. A 2 percent increase in UN-B reaching the ground is predicated to lead to a 6 to 8 percent increase in skin cancer in people with light skin. People in the Southern Hemisphere are especially at risk. It is estimated, for instance, that two-thirds of all Australians now loving will eventually need treatment for skin cancer, while in Canada skin cancer rates have been going up 5 to 7 percent per year. There will also be an increase in sunburn and retinal burn. Three is also a poorly understood effect upon the human immune system; UV-B seems to suppress the activity of certain types of immune system cells. It is suspected that neither pigmentation nr sunscreen protects against this effect. For that matter, there is no epidemiological evidence that sunscreen actually protects against skin cancer either, only a presumption that it must do because it blocks UV-B.11

The deepest concern, from the viewpoint of understanding the consequences of the ozone hole for the integrity of the ecosystem as a whole, is the possible effects upon animals, plants, and marine organisms. Recently, sheep near Punta Arenas in southern Chile, an area that occasionally finds itself directly under the ozone hole,12 have been suffering unusual tumours, cataracts, and retinal burns. While locals are convinced, there is no “scientific” sroof that this is due to increased UV exposure.13

Much investigative work has ready been done on the biological effects of UV. There is much reason to fear that ozone depletion could lead to greatly diminished growth and vitality of forests and agricultural crops. For instance, some recent studies indicate that land plant biomass can be reduced by as much as 10 to 20 percent; even a short burst of UV early in the growing season can irreversibly stunt plant growth.14 Even more serious could be its effects son the krill ( near –microscopic crustaceans, which serve as staple food for many marine mammals and birds) and marine micro-organisms such as plankton and algae. UV can  penetrate sea water to a considerable depth ( sunburn is a hazard for scuba shivers). The plankton and algae are the very base of the marine food chain and, furthermore, provide much more the planets oxygen. Of course, marine organism must already be adapted to a fair amount of UV, but they clearly have their limits. There is already evidence that UV levels 10 to 20 percent higher than normal can damage marine micro-organisms, as well as small fish. A recent detailed survey of Antarctic waters found evidence that photosynthesis by those phytoplankton regularly exposed to the ozone hole is reduced by 6 to 12 perecent.15

No one yet knows exactly how serious the situation could become, although it appears probable that the base of the planetary food chain will, from now on, suffer some and possibly significant extra stress from UV – B, above and beyond  all other stresses being imposed upon it by human action, for decades to come.

Where Thing stand Now

By 1988, it was clear that there is a worldwide ozone depletion of a few percent, and between 50 percent sand nearly 100 percent depletion in the Antarctic hole. This implies a significant increase in ultraviolet exposure for many parts of the world, especially in the Southern Hemisphere. Governments at last began ponderously to address fact that this is an international emergency. In 1987, a treaty was signed in Montreal by 51 nations and the European community, under the auspices of UNEP ( United Nations Environmental Program) to limit the release of CFCs, and halos. In March 1988, Dupont Corporation, a major producer ( and defender) of CFCs, finally conceded the danger and said that it will phase out production of CFCs. The Montreal Protocol was strengthened in 1990 and again in 1992, with phase out deadlines moved up, but some countries have not yet signed.

CFCs had already been band as aerosol propellants by the late 1970s by Canada, the United States, Norway, and Sweden. This resulted in a brief drop in production of CFCs, but production rose quickly again to a peak of over a million tones per year in the late1980s. Finally, production has begun to fall sharply in the mid-1990s as a consequence of the Montreal Protocol.16 On the face of it, therefore, the worst of the crisis may have passed. Unfortunately, matters are not so simple.

The Antarctic ozone hole continues to appear every Antarctic spring and is, if anything, deepening and becoming more stable and long lived. CFCs remain in the atmosphere  for a hundred years or more, and are still being added to the atmosphere a significant rate. All over the world, there are old refrigerators rusting in dumps, just waiting to release their loads of Freon into the atmosphere. Even given full compliance with the Montreal Protocol, the concentration of CFCs in the stratosphere is expected to double or triple over the next few years. Even if we entirely stop producing CFCs this very day, the stratospheric concentration will continue to increase for some years because it takes some time for CFCs to diffuse to the stratosphere. According to Environment Canada (19994b). ” he period of maximum stratospheric ozone depletion will be around the turn of the century.”

There is a little recent good news: the rate of increase of CFCs sin the atmosphere is slowing from 6 percent per year to a mere 3 percent per year.17 It is difficult to tell how much is due to the slowdown of industrial activity coming from the economic recession of the early 1990s.

The Outlook

For  decades  the biosphere will be subjected  to more UV- B  than normal –  some areas  such as the southern sea, dangerously  more at some times of the years. There is no question that will this have some deleterious effect on the  ecosystem , as well as putting human beings themselves at higher risk in a number of ways. Exactly how much harm will be done is very difficult to say , expect that is very likely that it will get worse than it is now .  It is within the bounds of possibility that  UV levels over some parts of the earth will become near—lethal , particularly in the southern latitudes.

Best case scenario; CFCs  are phased out or replaced by about the turn of he century, and life on earth succeeds in enduring marginal UV—B  stress for 100 years or so, although with a hard to predict overall  reduction  in vitality  the global  ecosystem and possibly some species extinctions or at least realignment of marine ecosystem .

The worst case ;  use of CFCs  does not stop,  due to a failure to uphold  effective international agreement.  It is impossible to predict the result of this, but the experiment should not be tried – especially given the possibility that there could be further ‘’ surprises”

Ozone is still being created at a constant rate by sunlight, and eventually, s the CFCs finally settle out of the atmosphere, the ozone layer  will “self heal.” But it will take at least a hundred for it to return to its pre-1970s condition.

“Lifestyle” Changes

Many parents now accept the necessity of leathering their small children with sunscreen before sending them out to play, much as sexually active adults in the 1990s nows accept the grim necessity of ” safe” sex. In 1987, the regain administration briefly dared to suggest that such ” personal protection” would do in place of regulation to control CFCs. It was not made clear how sunglass and floppy hats  were expected to protect krill or field crops from UV-B. This proposal was greeted with howls of derision, sand the embarrassment may have helped to persuade the United States to eventually support the Montreal Protocol.18 It seems painfully clear that while lifestyle changes ( such as wearing sunglass regularly) are a reasonable, personal response to the UV – B threat, they are hardly going to solve the problem.

Structure of the Problem

The ozone problem has the following structure, which with minor variations one sees repeated in the case of many of the technologies that human ingenuity has provided:

Ingenious invention of very useful product or method, done with the best of intentions. However, no one asks if product could do long term damage ;  there is a  complete lack of foresight.
we  come to depend on this product.  It becomes so useful, at least to some, that almost nothing else will do quite as well; society evolves a kind of dependency on the product, which makes it very difficult to drop it or switch a substitute. There is a real reason why the market supports the vast trade in CFCs; it is not just corporate greed is a factor in the response to the problem.
Experts warn of danger, but  are mostly disbelieved.
Evidence (often indirect) mounts, but disbelief continues.
Strongest denial of warnings from those who benefit most from the product or process. It becomes a political issue, decided in part by advertisement and lobbying.
Conflict between short-term economic and long-term environmental interest.
Finally there is undeniable evidence that experts were right; indeed, it is worse than they predicted, because there is a completely unexpected mechanism that enhances the effect.
Some still can’t be convinced.

Battery Operated Lights.

Battery operated lights have come a long way. Many people believe batteries are a fairly new invention. Did you know the first battery was invented in 1800? Or that the first flashlight was made in 1898? Now, those batteries were not the kind you and I think of today. They were actually quite unstable and not very reliable. Lets take a look at how battery lights came to be.

History of Lights.

Light has been used by man for a long time. Light gives our plants energy, which in turn feeds us. We also get vitamin D from light. Before modern scientific times, light was something that was thought just to be seen by our eyes. By the 1500’s and 1600’s though, telescopes, microscopes and new lenses were being invented. We could then see things on a smaller scope. Isaac Newton discovered the color spectrum in 1666. Soon the electric light bulb was invented by Thomas Edison. Light is useful in many aspects of our life. It helps us to see at night, directs traffic, helps us see while we read and gives us light for photography. It’s also useful in areas of health such as giving our food vitamin A, helping plants to grow and fights disease. We use light for everything now a days.

History of Batteries.

Batteries came on the scene around 1800. Batteries were invented by an Italian, Volta. They were rather unstable because they were wet cell batteries. For that reason, wet cell batteries were used to power stationary devices. In 1859, the first rechargeable battery was invented by Gaston Plante. Finally a dry cell battery was invented in 1887 by Carl Gassner that was much safer to use and portable. It changed the liquid material into a paste to make it more stable. In 1955, alkaline batteries were introduced to the public. Up until then, batteries had a short life and were very expensive.

Battery Lights, Together.

Batteries and lights came together. The first battery operated lights were flashlights. Today though, we have battery operated lights. Many Christmas tree lights are battery powered. It allows for mobility of your tree. Also, many people use battery lights for weddings. Battery operated lights are popular for outdoor weddings where electrical outlets are unavailable. You can also string the battery lights through the bouquets to make them shine at an evening ceremony. Actually, battery lights are popular for almost any occasion. The flexibility of battery operated lights allows them to be used almost anywhere.

LED Lights.

LED lights are becoming very popular. LED stands for light emitting diode. They use very little energy and put out much less heat. This attracts many people trying to save on their electric bill, especially with rising energy costs. LED lights are more expensive, right now, but the total cost of ownership is far less then the average incandescent light. LED lights produce more light than the average bulb, per watt. LED lights are the way of the future.

It is said that a picture is worth a thousand words.  That may be understating the case.  Political cartoonists continually have a field day with ever-changing subjects – persons seeking political office, the state of the economy, the debacle in the housing market, unpopular wars, invasions of weak countries by powerful neighbors champing at the bit to exert brute power that had been lost but which is now in full flower again.

Other pictures are more benign and less personal in their impact, but which nevertheless have the inherent power to impel the viewer to strong thoughts and incitements to action – but of a financial nature, free of personal dislikes and of bombs and artillery in action.  I’m speaking now of Candlestick patterns in stock and commodity price reporting, a Japanese invention of many centuries ago which was used initially in the rice trade.  This system of price display has come into increased use in this country over the past 20 years or so, and with good reason: when correctly understood, they can put money in your pocket.

Why is this so?  The Candles begin with the old “bar chart” form of price reporting and add to it.  Nothing is lost or cast aside; the net result is an improvement upon an old system.  Specifically, what the Candles do is show the underlying psychology of the market traders, in a way that the eye instantly recognizes and the brain computes.

The Candles “inflate” or “fatten out” the old bar chart formation by creating a cylinder out of a bar line, whereby that part of the total price action of the day (or week, or month, or minute) which lies between the opening price and the closing price is shown as a cylinder.  If the closing price is higher than the opening price, then the closing price will be at the top of the cylinder and the opening price will be at the bottom of the cylinder; and the cylinder will be left uncolored, or “white.”  Conversely, if the closing price is lower than the opening price, the cylinder which comprises the space between them will be colored black.  Simple!  And those parts of the total price action for that particular time period which lie above and below the cylinders are shown as “tails,” or “shadows,” or “wicks.”

This produces a picture which is easier to understand, and reveals in a flash the traders’ intention and mood during that time period.  It is fascinating to watch the picture move and evolve when the data feed is provided in real time, in “streaming” fashion.

The real value of the Candles lies in their ability to spot reversals of trend.  There are only about a dozen major patterns which need to be remembered.  Some of them have been given titles which quite clearly reflect their namesakes – such as the “Shooting Star,” the “Evening Star,” the “Spinning Top,” and the “Dark Cloud Cover.”  Even the “Hammer” – which takes a little imagination to see – reflects that the bears attempted to “hammer” prices lower, but failed.  All of these, and more, are warnings of the possibility of a trend change in the making.

The proof is in the pudding.  These reversal patterns do have predictive power.  They have been extremely valuable to me in my investing and trading over the years.  I would never go back to the “old way.”  In my estimation, everyone who is active in the financial markets owes it to himself or herself to become knowledgeable about the Candlesticks, because in so doing you will come to a more complete understanding of the human emotional forces which drive prices one way or the other.

Absolute, gauge and differential pressures – zero reference

Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used:

Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.

Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted.

Differential pressure is the difference in pressure between two points.

The zero reference in use is usually implied by context, and these words are only added when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute. Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings. Moderate vacuum pressures are often ambiguous, as they may represent absolute pressure or gauge pressure without a negative sign. Thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg (typical atmospheric pressure) 26 inHg = 4 inHg.

Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude and weather. If the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes. For example, when a car drives up a mountain, the tire pressure goes up. Some standard values of atmospheric pressure such as 101.325 kPa or 100 kPa have been defined, and some instruments use one of these standard values as a constant zero reference instead of the actual variable ambient air pressure. This impairs the accuracy of these instruments, especially when used at high altitudes.

Use of the atmosphere as reference is usually signified by a (g) after the pressure unit e.g. 30 psi g, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg).

A vented gauge pressure transmitter for example allows the outside air pressure to be exposed to the negative side of the pressure sensing diaphragm, via a vented cable or a hole on the side of the device, so that it always measures the pressure referred to ambient barometric pressure. Thus a vented gauge reference pressure sensor should always read zero pressure when the process pressure connection is held open to the air.

A sealed gauge reference is very similar except that atmospheric pressure is sealed on the negative side of the diaphragm. This is usually adopted on high pressure ranges such as hydraulics where atmospheric pressure changes will have a negligible effect on the accuracy of the reading, so venting is not necessary. This also allows some manufacturers to provide secondary pressure containment as an extra precaution for pressure equipment safety if the burst pressure of the primary pressure sensing diaphragm is exceeded.

There is another way of creating a sealed gauge reference and this is to seal a high vacuum on the reverse side of the sensing diaphragm. Then the output signal is offset so the pressure sensor reads close to zero when measuring atmospheric pressure.

A sealed gauge reference pressure transducer will never read exactly zero because atmospheric pressure is always changing and the reference in this case is fixed at 1 bar.

An absolute pressure measurement is one that is referred to absolute vacuum. The best example of an absolute referenced pressure is atmospheric or barometric pressure.

To produce an absolute pressure sensor the manufacturer will seal a high vacuum behind the sensing diaphragm. If the process pressure connection of an absolute pressure transmitter is open to the air, it will read the actual barometric pressure.

Units

Pressure Units

 

pascal

(Pa)

bar

(bar)

technical atmosphere

(at)

atmosphere

(atm)

torr

(Torr)

pound-force per

square inch

(psi)

1 Pa

1 N/m2

105

1.0197105

9.8692106

7.5006103

145.04106

1 bar

100,000

106 dyn/cm2

1.0197

0.98692

750.06

14.5037744

1 at

98,066.5

0.980665

1 kgf/cm2

0.96784

735.56

14.223

1 atm

101,325

1.01325

1.0332

1 atm

760

14.696

1 torr

133.322

1.3332103

1.3595103

1.3158103

1 Torr;  1 mmHg

19.337103

1 psi

6.894103

68.948103

70.307103

68.046103

51.715

1 lbf/in2

Example reading:  1 Pa = 1 N/m2  = 105 bar  = 10.197106 at  = 9.8692106 atm, etc.

The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (Nm2 or kgm1s2). This special name for the unit was added in 1971; before that, pressure in SI was expressed in units such as N/m. When indicated, the zero reference is stated in parenthesis following the unit, for example 101 kPa (abs). The pound per square inch (psi) is still in widespread use in the US and Canada, notably for cars. A letter is often appended to the psi unit to indicate the measurement’s zero reference; psia for absolute, psig for gauge, psid for differential, although this practice is discouraged by the NIST .

Because pressure was once commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g. inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury’s density allows for a shorter column (and so a smaller manometer) to measure a given pressure.

Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. When ‘millimetres of mercury’ or ‘inches of mercury’ are quoted today, these units are not based on a physical column of mercury; rather, they have been given precise definitions that can be expressed in terms of SI units. The water-based units usually assume one of the older definitions of the kilogram as the weight of a litre of water.

Although no longer favoured by measurement experts, these manometric units are still encountered in many fields. Blood pressure is measured in millimetres of mercury in most of the world, and lung pressures in centimeters of water are still common. Natural gas pipeline pressures are measured in inches of water, expressed as ‘”WC’ (‘Water Column’). Scuba divers often use a manometric rule of thumb: the pressure exerted by ten metres depth of water is approximately equal to one atmosphere. In vacuum systems, the units torr, micrometre of mercury (micron), and inch of mercury (inHg) are most commonly used. Torr and micron usually indicates an absolute pressure, while inHg usually indicates a gauge pressure.

Atmospheric pressures are usually stated using kilopascal (kPa), or atmospheres (atm), except in American meteorology where the hectopascal (hPa) and millibar (mbar) are preferred. In American and Canadian engineering, stress is often measured in kip. Note that stress is not a true pressure since it is not scalar. In the cgs system the unit of pressure was the barye (ba), equal to 1 dyncm2. In the mts system, the unit of pressure was the pieze, equal to 1 sthene per square metre.

Many other hybrid units are used such as mmHg/cm or grams-force/cm (sometimes as kg/cm and g/mol2 without properly identifying the force units). Using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force is forbidden in SI; the unit of force in SI is the newton (N).

Static and Dynamic pressure

Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure.

While static gauge pressure is of primary importance to determining net loads on pipe walls, dynamic pressure is used to measure flow rates and airspeed. Dynamic pressure can be measured by taking the differential pressure between instruments parallel and perpendicular to the flow. Pitot-static tubes, for example perform this measurement on airplanes to determine airspeed. The presence of the measuring instrument inevitably acts to divert flow and create turbulence, so its shape is critical to accuracy and the calibration curves are often non-linear.

Applications

Altimeter

Barometer

MAP sensor

Pitot tube

Sphygmomanometer

Instruments

Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column (a vertical tube filled with mercury) manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christian Huygens in 1661.

Hydrostatic

Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration. They have poor dynamic response.

Piston

Piston-type gauges counterbalance the pressure of a fluid with a solid weight or a spring. Another name for piston gauge is deadweight tester. For example, dead-weight testers used for calibration or tire-pressure gauges.

Liquid column

The difference in fluid height in a liquid column manometer is proportional to the pressure difference.
Liquid column gauges consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which might be the atmospheric pressure or a vacuum) is applied to the other. The difference in liquid level represents the applied pressure. The pressure exerted by a column of fluid of height h and density is given by the hydrostatic pressure equation, P = hg. Therefore the pressure difference between the applied pressure Pa and the reference pressure P0 in a U-tube manometer can be found by solving Pa P0 = hg. If the fluid being measured is significantly dense, hydrostatic corrections may have to be made for the height between the moving surface of the manometer working fluid and the location where the pressure measurement is desired.

Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm3) and low vapour pressure. For low pressure differences well above the vapour pressure of water, water is commonly used (and “inches of water” is a common pressure unit). Liquid-column pressure gauges are independent of the type of gas being measured and have a highly linear calibration. They have poor dynamic response. When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a loop filled with gas or a light fluid must isolate the liquids to prevent them from mixing. Simple hydrostatic gauges can measure pressures ranging from a few Torr (a few 100 Pa) to a few atmospheres. (Approximately 1,000,000 Pa)

A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Based on the use and structure following type of manometers are used

Simple Manometer

Micromanometer

Differential manometer

Inverted differential manometer

A McLeod gauge, drained of mercury

McLeod gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and unsuited to continual monitoring, but is capable of good accuracy.

Useful range: above 10-4 torr (roughly 10-2 Pa) as high as 106 Torr (0.1 mPa),

0.1 mPa is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated to SI units via a direct measurement, most commonly a McLeod gauge.

Aneroid

Aneroid gauges are based on a metallic pressure sensing element which flexes elastically under the effect of a pressure difference across the element. “Aneroid” means “without fluid,” and the term originally distinguished these gauges from the hydrostatic gauges described above. However, aneroid gauges can be used to measure the pressure of a liquid as well as a gas, and they are not the only type of gauge that can operate without fluid. For this reason, they are often called mechanical gauges in modern language. Aneroid gauges are not dependent on the type of gas being measured, unlike thermal and ionization gauges, and are less likely to contaminate the system than hydrostatic gauges. The pressure sensing element may be a Bourdon tube, a diaphragm, a capsule, or a set of bellows, which will change shape in response to the pressure of the region in question. The deflection of the pressure sensing element may be read by a linkage connected to a needle, or it may be read by a secondary transducer. The most common secondary transducers in modern vacuum gauges measure a change in capacitance due to the mechanical deflection. Gauges that rely on a change in capacitances are often referred to as Baratron gauges.

Bourdon

Membrane-type manometer

A Bourdon gauge uses a coiled tube, which, as it expands due to pressure increase causes a rotation of an arm connected to the tube. In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.

The pressure sensing element is a closed coiled tube connected to the chamber or pipe in which pressure is to be sensed. As the gauge pressure increases the tube will tend to uncoil, while a reduced gauge pressure will cause the tube to coil more tightly. This motion is transferred through a linkage to a gear train connected to an indicating needle. The needle is presented in front of a card face inscribed with the pressure indications associated with particular needle deflections. In a barometer, the Bourdon tube is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed. Differential Bourdon gauges use two Bourdon tubes and a mechanical linkage that compares the readings.

In the following illustrations the transparent cover face of the pictured combination pressure and vacuum gauge has been removed and the mechanism removed from the case. This particular gauge is a combination vacuum and pressure gauge used for automotive diagnosis:

Indicator side with card and dial

Mechanical side with Bourdon tube

the left side of the face, used for measuring manifold vacuum, is calibrated in centimetres of mercury on its inner scale and inches of mercury on its outer scale.

the right portion of the face is used to measure fuel pump pressure and is calibrated in fractions of 1 kgf/cm on its inner scale and pounds per square inch on its outer scale.

Mechanical details

Mechanical details

Stationary parts:

A: Receiver block. This joins the inlet pipe to the fixed end of the Bourdon tube (1) and secures the chassis plate (B). The two holes receive screws that secure the case.

B: Chassis plate. The face card is attached to this. It contains bearing holes for the axles.

C: Secondary chassis plate. It supports the outer ends of the axles.

D: Posts to join and space the two chassis plates.

Moving Parts:

Stationary end of Bourdon tube. This communicates with the inlet pipe through the receiver block.

Moving end of Bourdon tube. This end is sealed.

Pivot and pivot pin.

Link joining pivot pin to lever (5) with pins to allow joint rotation.

Lever. This an extension of the sector gear (7).

Sector gear axle pin.

Sector gear.

Indicator needle axle. This has a spur gear that engages the sector gear (7) and extends through the face to drive the indicator needle. Due to the short distance between the lever arm link boss and the pivot pin and the difference between the effective radius of the sector gear and that of the spur gear, any motion of the Bourdon tube is greatly amplified. A small motion of the tube results in a large motion of the indicator needle.

Hair spring to preload the gear train to eliminate gear lash and hysteresis.

Diaphragm

A pile of pressure capsules with corrugated diaphragms in an aneroid barograph.

A second type of aneroid gauge uses the deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used.

Useful range: above 10-2 Torr (roughly 1 Pa)

For absolute measurements, welded pressure capsules with diaphragms on either side are often used.

Shape:

Flat

corrugated

flattened tube

capsule

Bellows

In gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid, which means “without liquid”. (Early barometers used a column of liquid such as water or the liquid metal mercury suspended by a vacuum.) This bellows configuration is used in aneroid barometers (barometers with an indicating needle and dial card), altimeters, altitude recording barographs, and the altitude telemetry instruments used in weather balloon radiosondes. These devices use the sealed chamber as a reference pressure and are driven by the external pressure. Other sensitive aircraft instruments such as air speed indicators and rate of climb indicators (variometers) have connections both to the internal part of the aneroid chamber and to an external enclosing chamber.

Electronic pressure sensors

Main article: Pressure sensor

Piezoresistive Strain Gage

Uses the piezoresistive effect of bonded or formed strain gauges to detect strain due to applied pressure.

Capacitive

Uses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure.

Magnetic

Measures the displacement of a diaphragm by means of changes in inductance (reluctance), LVDT, Hall Effect, or by eddy current principal.

Piezoelectric

Uses the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure.

Optical

Uses the physical change of an optical fiber to detect strain due applied pressure.

Potentiometric

Uses the motion of a wiper along a resistive mechanism to detect the strain caused by applied pressure.

Resonant

Uses the changes in resonant frequency in a sensing mechanism to measure stress, or changes in gas density, caused by applied pressure.

Thermal conductivity

Generally, as a real gas increases in density -which may indicate an increase in pressure- its ability to conduct heat increases. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 Torr to 103 Torr, but they are sensitive to the chemical composition of the gases being measured.

Two wire

One wire coil is used as a heater, and the other is used to measure nearby temperature due to convection.

Pirani (one wire)

A Pirani gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined. This type of gauge was invented by Marcello Pirani.

Thermocouple gauges and thermistor gauges work in a similar manner, except a thermocouple or thermistor is used to measure the temperature of the wire.

Useful range: 10-3 – 10 Torr (roughly 10-1 – 1000 Pa)

Ionization gauge

Ionization gauges are the most sensitive gauges for very low pressures (also referred to as hard or high vacuum). They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. The calibration of an ion gauge is unstable and dependent on the nature of the gases being measured, which is not always known. They can be calibrated against a McLeod gauge which is much more stable and independent of gas chemistry.

Thermionic emission generate electrons, which collide with gas atoms and generate positive ions. The ions are attracted to a suitably biased electrode known as the collector. The current in the collector is proportional to the rate of ionization, which is a function of the pressure in the system. Hence, measuring the collector current gives the gas pressure. There are several sub-types of ionization gauge.

Useful range: 10-10 – 10-3 torr (roughly 10-8 – 10-1 Pa)

Most ion gauges come in two types: hot cathode and cold cathode, a third type exists which is more sensitive and expensive known as a spinning rotor gauge, but is not discussed here. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 103 Torr to 1010 Torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold Cathode gauges are accurate from 102 Torr to 109 Torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.

Hot cathode

Bayard-Alpert hot cathode ionization gauge

A hot cathode ionization gauge is mainly composed of three electrodes all acting as a triode, where the cathode is the filament. The three electrodes are a collector or plate, a filament, and a grid. The collector current is measured in picoamps by an electrometer. The filament voltage to ground is usually at a potential of 30 volts while the grid voltage at 180210 volts DC, unless there is an optional electron bombardment feature, by heating the grid which may have a high potential of approximately 565 volts. The most common ion gauge is the hot cathode Bayard-Alpert gauge, with a small ion collector inside the grid. A glass envelope with an opening to the vacuum can surround the electrodes, but usually the Nude Gauge is inserted in the vacuum chamber directly, the pins being fed through a ceramic plate in the wall of the chamber. Hot cathode gauges can be damaged or lose their calibration if they are exposed to atmospheric pressure or even low vacuum while hot. The measurements of a hot cathode ionization gauge are always logarithmic.

Electrons emitted from the filament move several times in back and forth movements around the grid before finally entering the grid. During these movements, some electrons collide with a gaseous molecule to form a pair of an ion and an electron (Electron ionization). The number of these ions is proportional to the gaseous molecule density multiplied by the electron current emitted from the filament, and these ions pour into the collector to form an ion current. Since the gaseous molecule density is proportional to the pressure, the pressure is estimated by measuring the ion current.

The low pressure sensitivity of hot cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce x-rays that produce photoelectric noise in the ion collector. This limits the range of older hot cathode gauges to 108 Torr and the Bayard-Alpert to about 1010 Torr. Additional wires at cathode potential in the line of sight between the ion collector and the grid prevent this effect. In the extraction type the ions are not attracted by a wire, but by an open cone. As the ions cannot decide which part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be passed on to a

Faraday cup

Microchannel plate detector with Faraday cup

Quadrupole mass analyzer with Faraday cup

Quadrupole mass analyzer with Microchannel plate detector Faraday cup

ion lens and acceleration voltage and directed at a target to form a sputter gun. In this case a valve lets gas into the grid-cage.

See also: Electron ionization

Cold cathode

There are two subtypes of cold cathode ionization gauges: the Penning gauge (invented by Frans Michel Penning), and the Inverted magnetron, also called a Redhead gauge. The major difference between the two is the position of the anode with respect to the cathode. Neither has a filament, and each may require a DC potential of about 4 kV for operation. Inverted magnetrons can measure down to 1×1012 Torr.

Such gauges cannot operate if the ions generated by the cathode recombine before reaching the anodes. If the mean-free path of the gas within the gauge is smaller than the gauge’s dimensions, then the electrode current will essentially vanish. A practical upper-bound to the detectable pressure is, for a Penning gauge, of the order of 103 Torr.

Similarly, cold cathode gauges may be reluctant to start at very low pressures, in that the near-absence of a gas makes it difficult to establish an electrode current – particularly in Penning gauges which use an axially symmetric magnetic field to create path lengths for ions which are of the order of metres. In ambient air suitable ion-pairs are ubiquitously formed by cosmic radiation; in a Penning gauge design features are used to ease the set-up of a discharge path. For example, the electrode of a Penning gauge is usually finely tapered to facilitate the field emission of electrons.

Maintenance cycles of cold cathode gauges is generally measured in years, depending on the gas type and pressure that they are operated in. Using a cold cathode gauge in gases with substantial organic components, such as pump oil fractions, can result in the growth of delicate carbon films and shards within the gauge which eventually either short-circuit the electrodes of the gauge, or impede the generation of a discharge path.

Calibration

Pressure gauges are either direct- or indirect-reading. Hydrostatic and elastic gauges measure pressure are directly influenced by force exerted on the surface by incident particle flux, and are called direct reading gauges. Thermal and ionization gauges read pressure indirectly by measuring a gas property that changes in a predictable manner with gas density. Indirect measurements are susceptible to more errors than direct measurements.

Dead weight tester

McLeod

mass spec + ionization

Dynamic transients

When fluid flows are not in equilibrium, local pressures may be higher or lower than the average pressure in a medium. These disturbances propagate from their source as longitudinal pressure variations along the path of propagation. This is also called sound. Sound pressure is the instantaneous local pressure deviation from the average pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The effective sound pressure is the root mean square of the instantaneous sound pressure over a given interval of time. Sound pressures are normally small and are often expressed in units of microbar.

frequency response of pressure sensors

resonance

History

Further information: Timeline of temperature and pressure measurement technology

European (CEN) Standard

EN 472 : Pressure gauge – Vocabulary.

EN 837-1 : Pressure gauges. Bourdon tube pressure gauges. Dimensions, metrology, requirements and testing.

EN 837-2 : Pressure gauges. Selection and installation recommendations for pressure gauges.

EN 837-3 : Pressure gauges. Diaphragm and capsule pressure gauges. Dimensions, metrology, requirements and testing..

See also

Force gauge

Piezometer

Vacuum engineering

External links

Home Made Manometer

Manometer

References

^ NIST

^ [Was: "fluidengineering.co.nr/Manometer.htm". At 1/2010 that took me to bad link. Types of fluid Manometers]

^ Techniques of high vacuum

^ Beckwith, Thomas G.; Roy D. Marangoni and John H. Lienhard V (1993). “Measurement of Low Pressures”. Mechanical Measurements (Fifth ed.). Reading, MA: Addison-Wesley. pp. 591595. ISBN 0-201-56947-7. 

^ Product brochure from Schoonover, Inc

^ VG Scienta

^ Robert M. Besanon, ed (1990). “Vacuum Techniques” (3rd edition ed.). Van Nostrand Reinhold, New York. pp. 12781284. ISBN 0-442-00522-9. 

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Categories: Underwater diving | Vacuum | Pressure gauges | Measuring instruments

by: Geoff Ficke

The first commercially successful mouthwash product is still one of the most famous: Listerine. First marketed in the late 19th century as a surgical antiseptic, the product enjoyed modest success. Listerine was created by Dr. Joseph Lawrence and Jordan Lambert and named in honor of Dr. Joseph Lister, the pioneer of antiseptic surgery. 

In distilled form, Listerine was sold in the early years of the 20th century as a floor cleaner and gonorrhea treatment. However, it was only in the 1920’s that the product started to sell in great volume, and only because of a clever marketing strategy. The Listerine advertising group invented a faux medical term to describe bad breath. At that time, bad breath was considered the norm, not a malodorous condition to be treated with over the counter medicinal-like products.  

The term, “chronic halitosis”, while sounding clinical, was an early example of verbally engineering a malady that could be cured only by using an existing product, in this case Listerine. The Listerine marketing team created halitosis as a way to apply a cure through gargling Listerine. The Company’s early advertising campaign depicted forlorn young lovers put off by the “bad breath” of their partners. Sales soared. 

This is a classic case of creating a novel, fresh Unique Selling Proposition for an existing consumer product. Listerine had enjoyed modest success when sold as a surgical antiseptic, floor polish and venereal disease treatment. However, by creating and driving a negative connotation for bad breath, and labeling the new hygiene “chronic halitosis”, a new superstar product was born. 

Use of mouthwash in oral hygiene is simply reflexive in modern industrial societies. We do not think twice about finishing our daily personal care ritual by gargling with a rinse. And yet, less than 100 years ago, no one gave oral halitosis a second thought. Like many advances, until the product was marketed to meet the need, the consumer did not know that Listerine was essential.

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The countenance faced miss / the strong-jawed man

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A new 12-year cycle started at Feb 7, 2008 with the Year of the Rat according to the Chinese calendar. This important cycle (or era) ends at Feb 5, 2019. It is a 12-year period generally ruled by the universal element of Earth. There are also other elements which rule over each of the 12 years. For example Earth rules over the first and the second year of the cycle (2008, 2009) while Metal rules over the third and the fourth year of the cycle (2010, 2011). The year 2008 is also ruled by the sign of the Rat and has a Yang (male) nature. So 2008 is the Yang year of the Earth Rat. What are the predictions for the sign of the Monkey for 2008? This is what this article is all about.

Monkey rules over 2016 in this 12-year cycle. Monkey is a sign from which most of the innovative and important creations will derive. These creations will affect the entire world. Monkey people have already started thinking and working on their inventions. They can’t wait for their favorable year to come. After all, they were always so impatient.

During 2008 they will use their genius minds to visualize the things that will happen the next years. Monkey people will know that they will play a significant part on this 12-year era. They will use their flexibility to take control of situations and resolve difficult problems. They will be aware of the obstacles on their way and they will find clever ways to bypass them.

This is a good year for Monkey people to deal with their friends and associates. The Rat, which rules over 2008, will increase their communicating skills and help them become very persuasive. Others will perceive Monkey people as a very reliable source of information.

The element of Earth, which rules over 2008, will give Monkey people common sense and will make them agreeable, sometimes more than necessary. The Yang (male) nature of 2008 might cause some frustration to them by discouraging them and making them leave their projects. They should use their strong will to avoid such bad outcomes.

Here are my predictions using the five star system. This has to do with the overall positive energy that the Monkey will receive during 2008. One star (*) means less energy than expected, while five stars (*****) mean more energy than expected. Three stars (***) mean equal amount of positive and negative energy which is a balanced situation:

Monkey energy prediction for 2008
Work issues:****
Love issues:***
Social issues:*****
Spiritual issues:*****
Body issues:**

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Make sure to use an ‘Online-Guide’ as many of these guides are auto-updated with new and important information.

Conclusions

There is no question – Do It Yourself Solar Energy Kit truly provides an outstanding opportunity for any household to ‘cut’ their elec. expenses to almost zero. There are so many other advantages provided by this remarkable idea, simply because it is innovative. By the end of this quick article the best advice would be to evaluate it so you could explore the various advantages that it provides.

Christmas Day is coming. What is amazing and romantic Christmas Gift for your boyfriend?

Just like boys invent ideas to please girls at the time of Christmas, girls also run their imagination riot to dish out one of the most exclusive Christmas gifts to their boyfriends. And below is a host of tips to that are sure to help you do the same.

Christmas gifts to their boyfriends. And below is a host of tips to that are sure to help you do the same.

Tips and Ideas for Christmas Gifts for Boyfriend

Personalized Christmas gift would be an ideal Christmas gift for boyfriend. Get a beautiful romantic book for your beloved.

Leather wallet looks quite trendy and elegant. These wallets are available in varied range and styles. For instance, you may go for multi color buckle wallet, rusty oilpullup, Trifold Ocean etc. This would be a perfect Christmas gift for boyfriend.

Home made Christmas gifts reflect your love and affection. So, start knitting a mobile pouch. This would be a cool Christmas gift for boyfriend.

If your boyfriend often comes late then a wristwatch would be perfect Christmas gift for him. This timepiece will keep reminding him about the time. So, buy a wristwatch for him. It would be advisable not to exceed the budget.

The joyous occasion of Christmas will be considered incomplete without Christmas cakes. Christmas cakes are perfect Christmas gifts for the boyfriend. In order to make the occasion a little romantic, you can gift the Christmas cake in varied ways. You can gift Christmas cake with beautiful fresh flowers. To personalize the Christmas gift, you may also attach a note for him.

Real fresh flowers are ideal Christmas gifts for the boyfriend. They symbolize beauty and fragrance.

If your boyfriend loves to wear cool dresses then funky T-shirts with cool messages would be a great Christmas gift for him.

If your boyfriend have well-toned body and loves to exercise then simply get a treadmill or stationery bike for him. This would be the best Christmas gift for boyfriend.

For example, If he love golf, you could buy golf clubs for him, such as Callaway X-22 Iron Set. only 9

Time is limited, hurry up, and you can not miss it.

 More details at  http://www.wowgolfclubs.com/activity.php  

Rail breakages

There are many reasons why rail tracks break. In bygone days, it was common for a rail break to start near the joint between discrete rail segments. Manufacturing defects in rail can cause fissures. Wheelburns can also contribute to rail breaks by changing the metallurgy of a rail. Rails are also more likely to break when the weather is cold, when the ballast and ties/sleepers aren’t providing as much support as they should, and when ground or drainage condition is such that ‘pumping’ occurs under heavy load. All of these conditions can contribute to a broken rail, and in turn a possible derailment. Recently, the ‘gauge corner cracking’ phenomenon has come under the spotlight after a GNER high-speed train derailed in 2000 near Hatfield, England.

Rail breaks at rail joints

Fishplate bolted joint

Each rail segment is 39 feet long, and fishplates must be used to join them together. Rail joined with fish plates is known as jointed-rail or jointed track. The method to join two pieces of rail together is to drill two or three holes on the web of the rail at each segment-end, and bolt the two rail segments together using two fishplates, one on either side. The bolts and the area of rail around the drilled holes endure huge stresses as train wheels pass over the joint. If the rail joint is not properly supported by railroad tie and ballast underneath, the stresses may be even greater. Over time, the cumulative action of many wheel passages can cause a crack to appear. It is quite common for the crack to begin at the bolt holes. Cracks can also begin internally within the rail. Once began, the crack can travel within the rail, eventually finding its way to a surface, causing a piece of rail to break off.

Manufacturing defects in rail

The quality of rail steel has improved dramatically since the early days of railroading. The trend toward using continuously welded rail (CWR) requires a higher quality rail, due to the cyclic thermal expansion and contraction stresses that a CWR would be required to endure. In addition, rail operations in general have been trending toward higher speed and higher axle-load operation. Under these operating conditions, rail pieces rolled in the 19th century would likely break at an unacceptable rate. Despite the improved rail quality and rail metallugry, if impurities find their way into rail steel and are not detected by the quality assurance process, they can cause rail breaks under certain conditions.

Recent rail-making processes have also been trending toward a harder rail, requiring less frequent replacements under heavy loads. This has the side-effect of making the rail more brittle, and thus more susceptible to brittle fracture rather than plastic deformation. It is therefore imperative that unintentional impurities in rail be minimized. Corus of Holland and England, and U.S. Steel of Pittsburgh, are two current rail manufacturers.

Wheelburn-related rail breaks

When a locomotive wheel spins without moving the train forward (also known as slipping), the small section of rail directly under the wheel is heated by the forces of friction between the wheel and itself. The wheel rests on an area of rail no larger than a dime in size, so the heating effect is very localized and occurs very quickly. While wheelburn typically does not cause the entire rail section to melt, it does heat the steel to red-hot temperatures. As the locomotive stops slipping and starts movingr worse still, slips forward by a matter of inches and heats a different piece of railhe heated spot cools down very quickly to normal temperature, especially when the weather is cold.

This heat-quench process results in annealing of the rail steel and causes substantial changes to its physical property. It can also cause internal stresses to form within the steel structure. As the rail surface cools, it may also become oxidized, or undergo other chemical changes by reacting with impurities that are on the surface of the rail. The net result of this process is that an area of the rail that is more susceptible to breakage is created.

Wheelflat-related rail breaks

If the brakes are dragging or the axle ceases to move on a rail vehicle while the train is in motion, the wheel will be dragged along the head of the rail, causing a ‘flat spot’ to develop on the wheel surface where it contacts the rail. When the brakes are subsequently released, the wheel will continue to roll around with the flat spot, causing a banging noise with each rotation. This condition is known as wheel out of round.

The banging of flat wheels on the rail causes a hammering action that produces higher dynamic forces than a simple passage of a round wheel. These dynamic forces can exacerbate a weak rail condition and cause a rail break.

Cold weather-related rail breaks

In continuously welded rail (CWR), the ribbons of rail are designed to survive under compression during the summer heat, and under tension during the winter. The welded rail cannot expand or contract lengthwise, thus must deal with temperature-related physical expansion and contraction by changing cross-sectional area. During cold weather, this results in substantial tension along the direction of travel.

This tension, if sufficiently large, will cause a crack to develop at the weakest point in the rail. As previously discussed, the weak point could be caused by a manufacturing defect, a wheelburn, a poor weld, or some other irregularity in the rail. During exceptionally cold weather, the rail may break cleanly across, and a large gap may open up between two sections of formerly welded rail. This condition can easily cause a derailment under load.

The tension in the rail is amplified if a train rolls over the rail and brakes. A decelerating train has a tendency to pull the rails forward, resulting in increased tension in the part of the rail that follows directly beneath the rail-wheel interface. Part of this problem is mitigated by the use of rail anchors, which grips the rail at the bottom and anchors it to a railroad tie. The rail anchors prevent the rail from slipping longitudinally (along the direction of travel) and also serve to ensure the thermal stresses are evenly distributed along the CWR sections.

Methods to detect rail breaks

If a rail breaks cleanly, it is relatively easy to detect. A track occupancy light will light up in the signal tower indicating that a track circuit has been interrupted. If there is no train in the section, the signaler must investigate. One possible reason is a clean rail break. For detecting the rail break this way, one has to use signal bonds that are welded or pinbrazed on the head of the rail. If one uses signal bonds that are on the web of the rail, one will have a continued track circuit.

If a rail is merely cracked or has an internal fissure, the track circuit will not detect it, because a partially-broken rail will continue to conduct electricity. Partial breaks are particularly dangerous because they create the worst kind of weak point in the rail. The rail may then easily break under loadhile a train is passing over itt the point of prior fissure.

Typically, these type of rail breaks are detected by the visual inspection of a track engineer walking the line, or ultrasonic testing. Ultrasonic testing is accomplished by running a detector car over the tracks. Invented by Elmer Ambrose Sperry in the early 1900s, the detector car initially used induction to detect cracks within the steel. Later, ultrasonics were introduced and have remained the industry standard for detecting defects within rail. It works by sending an ultrasonic signal into the rail, which detects characteristic patterns in the reflected ultrasound since anomalies within the steel reflect ultrasonic energy. In effect, the testing device works like a Sonar that could ’see’ internal crack and defects within the rail.

Misaligned railroad tracks

Death on the Rail, a fanciful washout derailment depicted in Harper’s Weekly, May 10, 1873

Several different types of misaligned plain line tracks can cause or contribute to a derailment:

Wide-to-gauge

CWR buckling

Incorrect crosslevel

Incorrent cant/superelevation

Incorrect alignment

Washout

Track-caused derailments are often caused by wide gauge. Proper gauge, the distance between rails, is 56.5 inches (four feet, eight-and-a-half inches) on standard gauge track. As tracks wear from train traffic, the rails can develop a wear pattern that is somewhat uneven. Uneven wear in the tracks can result in periodic oscillations in the truck, called ‘truck hunting.’ Truck hunting can be a contributing cause of derailments.

In addition to rail wear, wooden ties can weaken and crack from the stress of bearing train load tonnage. As ties weaken, they lose a solid tight grip on the spikes, which hold the rails in position. Over time, the rail gauge can drift substantially from the proper specification, hence the need for regular track maintenance and tamping. More usually, a rail that isn’t properly held in position tends to roll when a train passes over it at excessive speeds. In that case, poorly maintained track and excessive speeds are both contributing causes for the derailment.

Train tracks most often lose gauge in curves, where the outside wheels tend to push the gauge rail outward. If the gauge between the rails are sufficiently wide, the train wheels can drop between the rails. This, however, is not a common cause of derailments.

Many rail operators in the United States are replacing wood ties with concrete ties on lines with high tonnage or high speed trains. Amtrak’s Acela New Haven to Boston Electrification Project replaced practically all wooden ties between New Haven and Boston with concrete ties. However, converting existing tracks to concrete ties is a costly and time-consuming method to reduce out-of-gauge derailments.

Concrete ties have been standard on mainline railroads in Europe since the 1960s. Concrete ties have also been the renewal standard on rapid transit applications in North America. For subway tunnels, ’slab track’ is the preferred option, where support structures for rails are directly poured into the tunnel floor using readymix concrete.

Excessive speed derailments

Two different mechanisms cause excessive speed derailments:

Wheel climb, in which the wheel is lifted off the track because the friction between the flange and the gauge face of the rail is too great, causing the wheel flange to climb outwards over the head of the rail.

Rail roll, in which the horizontal forces applied by the flange to the gauge face of the rail is too great, overcoming the anchoring forces of rail spikes and clips.

These are two extreme conditions that result from excessive vehicle speed. The “L/V ratio,” which is the ratio of the lateral to vertical forces on the rail, is a critical factor in maintaining a safe speed.

In the United States, the maximum permissible speed for set degree of curvature and superelevation is defined in 49 CFR, Part 213. In the UK, the Rail Group Standards defines maximum permissible speeds.

Slow speed derailments

There are some derailments because of slow speed in tight curves, especially in freight trains with high center of gravity.

The main reason for this phenomena is unloading in the outer wheel, which goes to a critical situation because of the larger superelevation that creates an inward acceleration, resulting in an unloading.

Because of the action of outer wheel as the steering force, this can lead to the climbing of wheel according to the Nadal formula, which expresses the relation between the lateral forces on the wheel and the vertical downforce of the wheel on the rail.

In-train forces

Several types of derailments can be caused by in-train forces.

Uneven loading

Train “stringlining” on sharp reverse curves

Poor train handling techniques

Rolling stock design issues

Uneven loading

This type of derailment can occur in freight trains if empties (unloaded railcars) are marshalled in train between the locomotive and heavy loaded cars. For example, if the consist contains locomotives, empty trailer racks, followed by a large block of loaded coal hoppers. When the train is braking, brakes on the head end of the train will apply first causing the locomotive to slow down and the slack to run in. The heavy coal cars towards the end of the train would shove the lighter cars forward with considerable force. This can cause the lighter cars to arch upwards and jump the tracks, especially if the in train forces causes couplers to overload.

Stringlining

This type of derailment occurs when a string of light cars travel over reverse curve (S-curve) while locomotives are attempting to accelerate with all slacks pulled out. The reverse curve offers considerable resistance to the locomotive. The cars would tend to prefer to travel in a straight line, the line of least resistance. This causes in-train forces towards the inside of the curve in the middle of the train. If the middle cars are too light, wheels may climb the inside of the curve and travel along a chord to the arc.

Poor train handling

Obviously, anyone can derail a train with poor train handling techniques, regardless of the load. Usually, allowing the slack to run in too fast (while braking or at the bottom of a valley) is the cause of derailment in cases relating to poor train handling. Over hill terrain, experienced train engineers will run the train with dynamic brakes while keeping the slack under control. Air brakes are usually only used to bring the train to a complete stop at low speeds.

Rolling stock design

Some strange failure modes have been recorded in the history of railroading. Amtrak’s first long distance diesel locomotive, the EMD SDP40F, was implicated in certain crossover-related derailments. Investigations revealed that the location of a water tank within the locomotive may have caused excessive swaying while the locomotive traversed crossovers at high speeds, shifting the locomotive’s center of gravity and forcing it to overturn onto its side.

A similar issue arises in unevenly loaded timber cars. Timber spine cars are to be loaded with equal amount of timber on both sides. However, unloading only takes place on one side of the car at a time, which requires the half-loaded car to be run around a wye track to allow the shipper to gain access to the other side of the car. While the car is being run around, the center of gravity of the car is on one side. If crossovers or curves are traversed at too high a speed, the car can easily topple over onto its heavy side.

Wheel and truck failures

Wheel fracture derailments are quite rare. This is partly due to the Federal Railroad Administration’s requirement for 1,000-mile (1,600 km) undercarriage inspections for trains operating in the U.S. Also, a variety of defect detectors en route would highlight most wheel and truck failure precursor conditions. Some reasons for wheel and truck failures are:

Hot axlebox. This has been almost eliminated as freight car (goods wagon) trucks are transitioned from a simple bearing to a roller bearing design.

Fracture of axle. Some freight train derailments have been caused by axle fractures, but these are relatively rare events.

Fracture of wheel. This is also a rare event. However, the failure mode received a great deal of attention due to the InterCity Express (ICE) train’s wreck in Eschede, Germany. The composite wheel then used on the ICE, which includes a rubber inner tire, failed catastrophically, resulting in a 100 mph (160 km/h)+ derailment that sent a train into a support pillar for a highway overpass. The overpass crashed down on top of the train, causing many fatalities.

At present, several technologies are available to detect abnormal wheel and truck conditions:

Hot axlebox detector

Dragging equipment detector

Wheel impact load detector

Derailment detector
Obstacles

Trains can, but do not always, derail if they hit obstacles on the tracks, like animals, fallen branches, vehicles and bikes on level crossings, and so on.

Once one locomotive or wagon derails, it becomes an obstacle for following wagons, leading to a pileup.

The shape of the front of the train is important. If it is curved like a “cowcatcher”, then obstacles may be thrown safely off to one side.

Earthquakes

Trains can be derailed or tipped over by earthquakes. In Japan, JR East actively conducts research to prevent earthquake related derailments, especially of Shinkansen trains, by developing emergency communications systems that send a “train stop” signals to all trains when a heavy earthquake is detected. This permits the train to come to a safe stop if it is not already derailed, rather than allowing trains to continue running and potentially hitting a deformed structure or track segment.

Rerailing

Since engines and wagons are quite heavy, up to 300 tons, even a slight derailment can be difficult to rectify. In the U.S., minor low speed derailments are sometimes rerailed by the engine crew. Wooden blocks, planks, metal bars can be used for this purpose. More serious derailments where the cars are completely removed from the normal track alignment will likely incur track damage, and vehicles may have to be removed by rail mounted cranes.

In some cases, cars are simply left in the field after the derailment, because the cost of retrival exceeds the economic value of the car. However, this can be done only if the abutter does not object.

Contracting companies specializing in derailment recovery exists in both UK and the U.S., smaller railroads often rely on external contractors for disaster recovery.

If rolling stock rolls down an embankment as a result of a derailment, a locomotive and cable can sometimes be used to haul those vehicles back to the top again.

Inventions

George Westinghouse, amongst others, invented devices that helped rerail derailed vehicles.

Example accidents

Most railway accidents involve derailment. See list of rail accidents: pre-1950; 19501999; 2000resent.

19th Century

November 11, 1833 Hightstown, New Jersey, United States: Carriages of a Camden & Amboy train derail at 25 miles per hour in the New Jersey meadows between Spotswood and Hightstown when an axle breaks on a car due to an overheated journal. One car overturns, killing two and injuring 15. Among the survivors is Cornelius Vanderbilt, who will later head the New York Central Railroad. He suffers two cracked ribs and a punctured lung, and spends a month recovering from the injuries. Uninjured in the coach ahead is former U.S. President John Quincy Adams, who continues on to Washington, D.C. the next day.

January 6, 1853 Andover, Massachusetts, United States: The Boston & Maine noon express, traveling from Boston to Lawrence, Massachusetts, derails at 40 miles per hour when an axle breaks at Andover, and the only coach goes down an embankment and breaks in two. Only one person is killed, the 12-year-old son of President-elect Franklin Pierce, but it is initially reported that General Pierce is also a fatality. He is on board, but is only badly bruised. The baggage car and the locomotive remain on the track.

April 16, 1853 Cheat River, West Virginia, United States: Two Baltimore & Ohio passenger cars tumble down a 100-foot ravine above the Cheat River in West Virginia, west of Cumberland, Maryland, after they are derailed by a loose rail.

20th Century

December 12, 1917 Saint Michel de Maurienne, France: A military train derails at the entrance of the Frjus Rail Tunnel after running away down a steep gradient; brake power was insufficient for the weight of the train. Around 800 deaths were estimated, with 540 officially confirmed. This was the world’s worst-ever derailment, and worst rail disaster up to the end of the 20th century.

July 2, 1922 Winslow, Camden County, New Jersey, United States: The Owl, a Reading Railroad train derailment, at Winslow Junction on the West Jersey and Seashore Line tracks near the Winslow Tower. Shortly before midnight, train 33 derails when the seashore-bound locomotive going more than 90 miles per hour speeds through an open switch. Four passengers, the engineer, fireman and conductor were killed.

 Jamaica July 30, 1938 near Balaclava Station, Jamaica: five overcrowded cars derail; 32 killed, 70 injured.

February 18, 1947 Blair County, Pennsylvania, United States: The Red Arrow, a Pennsylvania Railroad express passenger train, jumps off the track on the Bennington Curve near Altoona, Pennsylvania and tumbles down a large hill, resulting in 24 deaths and 131 injuries.

Stein-Saeckingen 1991 – 8 tank cars derailed

Zuerich-Affoltern 1994 – 5 tank cars derailed
Lausanne 1994 – 15 tank cars derailed

21st Century

2000 Hatfield rail crash.

May 10, 2002 Potters Bar rail crash, Potters Bar, England, United Kingdom: A points failure causes a British Rail Class 365 to derail on the approach to Potters Bar railway station. As a result, the train slides sideways across the station platform, killing six on the train and one under the road bridge.

January 31, 2003 Waterfall train disaster, Waterfall, New South Wales, Australia: A train derails as it rounds a sharp curve rated for 60 km/h at a speed of 117 km/h, after the train driver has a heart attack. The two safety mechanismshe driver’s deadman’s brake, which remains depressed because of the driver’s weight, and the guard who could have applied the emergency brake, but is in a microsleep at the timere found to be the direct causes of the incident.

February 23, 2007 Grayrigg derailment, Grayrigg, England, United Kingdom: The 17:15 Virgin West Coast Pendolino service from London Euston to Glasgow Central, travelling on the West Coast Main Line, derails due to stretcher bar disconnection.

April 28, 2008 Jiao-Ji line derailment, Shandong, China: The T195 Express service from Beijing to Qingdao derails at Shandong due to excessive speed, and collides moments later with another passenger train traveling in the opposite direction, killing over 70 passengers and railroad maintenance workers, and injuring more than 400.

April, 2008 – Larissa, Greece – passenger train derails; 28 of 174 passengers injured
February 13, 2009 – Orissa train derailment a passenger train derailment that occurred at 19:45 local time (14:15 UTC) in the dark in the eastern state of Orissa, India, on 13 February 2009. Nine people were killed and 150 people were injured in the incident.

23 February, 2009 – Limpopo
This locomotive was derailed by the 1906 San Francisco earthquake. The locomotive had three link and pin coupler pockets for moving standard and narrow gauge cars.

See also

List of rail accidents:

Rail accidents pre-1950

Rail accidents 19501999

Rail accidents 2000resent

Classification of railway accidents

Tram accident

Kenya Railways Corporation – accidents

References

^ http://www.bahnindustrie.info/uploads/media/04_Knorr.pdf

^ http://www.eawag.ch/publications/eawagnews/www_en53/en53e_screen/en53e_schmidt_s.pdf

^ http://www.safetynews.co.uk/March 2008.htm

^ http://railwaysafrica.com/index.php?option=com_content&task=view&id=3883&Itemid=38

v  d  e

Rail accidents

Main topics

Classification Boiler explosion Bridge failure Derailment Fire Level crossing accident Signal passed at danger Stop and examine Telescoping Train wreck Tram accident

Chronology

Pre-1950 19501999 20002009 20102019

Related lists

Main list By death toll By country (Category) By year Investigators Victims

Categories: Railway accidents | Rail transportHidden categories: Articles needing additional references from January 2010 | All articles needing additional references