Woodpeckers are part of the family Picidae, a group of near-passerine birds that consist of piculets and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand and the extreme polar regions. Most species live in forests or woodland habitats, although a few species are known that live in treeless areas, such as rocky hillsides and deserts, the Gila woodpecker specialises in exploiting cacti. Members of this family are chiefly known for their characteristic behaviour, they forage for insect prey on the trunks and branches of trees, communicate by drumming with their beak, producing a reverberatory sound that can be heard at some distance. Some species vary their diet with fruits, birds' eggs, small animals, tree sap, they nest and roost in holes that they excavate in tree trunks, their abandoned holes are of importance to other cavity-nesting birds. They sometimes come into conflict with humans when they make holes in buildings or feed on fruit crops, but perform a useful service by their removal of insect pests on trees.
The Picidae are one of nine living families in the order Piciformes, the others being barbets, toucan-barbets, honeyguides which comprise the clade Pici, the jacamars and puffbirds in the clade Galbuli. DNA sequencing has confirmed the sister relationships of these two groups; the family Picidae includes about 240 species arranged in 35 genera. 20 species are threatened with extinction due to loss of habitat or habitat fragmentation, with one, the Bermuda flicker, being extinct and a further two being so. Woodpeckers range from tiny piculets measuring no more than 7 cm in length and weighing 7 g to large woodpeckers which can be more than 50 cm in length; the largest surviving species is the great slaty woodpecker, which weighs 360–563 g, but the extinct imperial woodpecker and ivory-billed woodpecker were both larger. The plumage of woodpeckers varies from drab to conspicuous; the colours of many species are based on olive and brown and some are pied, suggesting a need for camouflage. Woodpeckers tend to be sexually dimorphic, but differences between the sexes are small.
The plumage is moulted once a year apart from the wrynecks, which have an additional partial moult before breeding. Woodpeckers and wrynecks all possess characteristic zygodactyl feet, consisting of four toes, the first and the fourth facing backward and the second and third facing forward; this foot arrangement is good for grasping the trunks of trees. Members of this family can walk vertically up tree trunks, beneficial for activities such as foraging for food or nest excavation. In addition to their strong claws and feet, woodpeckers have strong legs; this is typical of birds that forage on trunks. Exceptions are the black-backed woodpecker and the American and Eurasian three-toed woodpeckers, which have only three toes on each foot; the tails of all woodpeckers, except the piculets and wrynecks, are stiffened, when the bird perches on a vertical surface, the tail and feet work together to support it. Woodpeckers have strong bills for drilling and drumming on trees, long sticky tongues for extracting food.
Woodpecker bills are longer and stronger than the bills of piculets and wrynecks. The bill's chisel-like tip is kept sharp by the pecking action in birds that use it on wood; the beak consists of three layers. Furthermore, woodpeckers' tongues are long, wind around the skull through a special cavity, thereby cushioning the brain. Combined, this anatomy helps the beak absorb mechanical stress. Species of woodpecker and flicker that use their bills in soil or for probing as opposed to regular hammering tend to have longer and more decurved bills. Due to their smaller bill size, many piculets and wrynecks will forage in decaying wood more than woodpeckers, their long sticky tongues, which possess bristles, aid these birds in grabbing and extracting insects from deep within a hole in a tree. It has been reported that the tongue was used to spear grubs, but more detailed studies published in 2004 have shown that the tongue instead wraps around the prey before being pulled out. Many of the foraging and signaling behaviors of woodpeckers involve drumming and hammering using the bill.
To prevent brain damage from the rapid and repeated powerful impacts, woodpeckers have a number of physical features which protect the brain. These include a small and smooth brain, narrow subdural space, little cerebrospinal fluid surrounding it to prevent it from moving back and forth inside the skull during pecking, the orientation of the brain within the skull and the short duration of contact; the skull consists of strong but compressible sponge-like bone, most concentrated in the forehead and the back of the skull. Another anatomical adaptation of woodpeckers is the enormously elongated hyoid bone which subdivides, passes on either side of the spinal column and wraps around the brain case, before ending in the right nostril cavity, it plays the role of sa
Art is a diverse range of human activities in creating visual, auditory or performing artifacts, expressing the author's imaginative, conceptual ideas, or technical skill, intended to be appreciated for their beauty or emotional power. In their most general form these activities include the production of works of art, the criticism of art, the study of the history of art, the aesthetic dissemination of art; the three classical branches of art are painting and architecture. Music, film and other performing arts, as well as literature and other media such as interactive media, are included in a broader definition of the arts; until the 17th century, art referred to any skill or mastery and was not differentiated from crafts or sciences. In modern usage after the 17th century, where aesthetic considerations are paramount, the fine arts are separated and distinguished from acquired skills in general, such as the decorative or applied arts. Though the definition of what constitutes art is disputed and has changed over time, general descriptions mention an idea of imaginative or technical skill stemming from human agency and creation.
The nature of art and related concepts, such as creativity and interpretation, are explored in a branch of philosophy known as aesthetics. In the perspective of the history of art, artistic works have existed for as long as humankind: from early pre-historic art to contemporary art. One early sense of the definition of art is related to the older Latin meaning, which translates to "skill" or "craft," as associated with words such as "artisan." English words derived from this meaning include artifact, artifice, medical arts, military arts. However, there are many other colloquial uses of all with some relation to its etymology. Over time, philosophers like Plato, Aristotle and Kant, among others, questioned the meaning of art. Several dialogues in Plato tackle questions about art: Socrates says that poetry is inspired by the muses, is not rational, he speaks approvingly of this, other forms of divine madness in the Phaedrus, yet in the Republic wants to outlaw Homer's great poetic art, laughter as well.
In Ion, Socrates gives no hint of the disapproval of Homer. The dialogue Ion suggests that Homer's Iliad functioned in the ancient Greek world as the Bible does today in the modern Christian world: as divinely inspired literary art that can provide moral guidance, if only it can be properly interpreted. With regards to the literary art and the musical arts, Aristotle considered epic poetry, comedy, dithyrambic poetry and music to be mimetic or imitative art, each varying in imitation by medium and manner. For example, music imitates with the media of rhythm and harmony, whereas dance imitates with rhythm alone, poetry with language; the forms differ in their object of imitation. Comedy, for instance, is a dramatic imitation of men worse than average. Lastly, the forms differ in their manner of imitation—through narrative or character, through change or no change, through drama or no drama. Aristotle believed that imitation is natural to mankind and constitutes one of mankind's advantages over animals.
The more recent and specific sense of the word art as an abbreviation for creative art or fine art emerged in the early 17th century. Fine art refers to a skill used to express the artist's creativity, or to engage the audience's aesthetic sensibilities, or to draw the audience towards consideration of more refined or finer work of art. Within this latter sense, the word art may refer to several things: a study of a creative skill, a process of using the creative skill, a product of the creative skill, or the audience's experience with the creative skill; the creative arts are a collection of disciplines which produce artworks that are compelled by a personal drive and convey a message, mood, or symbolism for the perceiver to interpret. Art is something that stimulates an individual's thoughts, beliefs, or ideas through the senses. Works of art can be explicitly made for this purpose or interpreted on the basis of images or objects. For some scholars, such as Kant, the sciences and the arts could be distinguished by taking science as representing the domain of knowledge and the arts as representing the domain of the freedom of artistic expression.
If the skill is being used in a common or practical way, people will consider it a craft instead of art. If the skill is being used in a commercial or industrial way, it may be considered commercial art instead of fine art. On the other hand and design are sometimes considered applied art; some art followers have argued that the difference between fine art and applied art has more to do with value judgments made about the art than any clear definitional difference. However fine art has goals beyond pure creativity and self-expression; the purpose of works of art may be to communicate ideas, such as in politically, spiritually, or philosophically motivated art. The purpose may be nonexistent; the nature of art has been described by philosopher Richard Wollheim as "one of the most elusive of the traditional problems of human culture". Art has been defined as a vehicle for the expression or communication of emotions and ideas, a means for exp
A fuel is any material that can be made to react with other substances so that it releases energy as heat energy or to be used for work. The concept was applied to those materials capable of releasing chemical energy but has since been applied to other sources of heat energy such as nuclear energy; the heat energy released by reactions of fuels is converted into mechanical energy via a heat engine. Other times the heat itself is valued for warmth, cooking, or industrial processes, as well as the illumination that comes with combustion. Fuels are used in the cells of organisms in a process known as cellular respiration, where organic molecules are oxidized to release usable energy. Hydrocarbons and related oxygen-containing molecules are by far the most common source of fuel used by humans, but other substances, including radioactive metals, are utilized. Fuels are contrasted with other substances or devices storing potential energy, such as those that directly release electrical energy or mechanical energy.
The first known use of fuel was the combustion of wood or sticks by Homo erectus nearly two million years ago. Throughout most of human history fuels derived from plants or animal fat were only used by humans. Charcoal, a wood derivative, has been used since at least 6,000 BCE for melting metals, it was only supplanted by coke, derived from coal, as European forests started to become depleted around the 18th century. Charcoal briquettes are now used as a fuel for barbecue cooking. Coal was first used as a fuel around 1000 BCE in China. With the energy in the form of chemical energy that could be released through combustion, but the concept development of the steam engine in the United Kingdom in 1769, coal came into more common use as a power source. Coal was used to drive ships and locomotives. By the 19th century, gas extracted from coal was being used for street lighting in London. In the 20th and 21st centuries, the primary use of coal is to generate electricity, providing 40% of the world's electrical power supply in 2005.
Fossil fuels were adopted during the Industrial Revolution, because they were more concentrated and flexible than traditional energy sources, such as water power. They have become a pivotal part of our contemporary society, with most countries in the world burning fossil fuels in order to produce power; the trend has been towards renewable fuels, such as biofuels like alcohols. Chemical fuels are substances that release energy by reacting with substances around them, most notably by the process of combustion. Most of the chemical energy released in combustion was not stored in the chemical bonds of the fuel, but in the weak double bond of molecular oxygen. Chemical fuels are divided in two ways. First, by their physical properties, as a solid, liquid or gas. Secondly, on the basis of their occurrence: primary and secondary. Thus, a general classification of chemical fuels is: Solid fuel refers to various types of solid material that are used as fuel to produce energy and provide heating released through combustion.
Solid fuels include wood, peat, hexamine fuel tablets, pellets made from wood, wheat and other grains. Solid-fuel rocket technology uses solid fuel. Solid fuels have been used by humanity for many years to create fire. Coal was the fuel source which enabled the industrial revolution, from firing furnaces, to running steam engines. Wood was extensively used to run steam locomotives. Both peat and coal are still used in electricity generation today; the use of some solid fuels is restricted or prohibited in some urban areas, due to unsafe levels of toxic emissions. The use of other solid fuels as wood is decreasing as heating technology and the availability of good quality fuel improves. In some areas, smokeless coal is the only solid fuel used. In Ireland, peat briquettes are used as smokeless fuel, they are used to start a coal fire. Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy producing kinetic energy, it is the fumes of liquid fuels.
Most liquid fuels in widespread use are derived from the fossilized remains of dead plants and animals by exposure to heat and pressure inside the Earth's crust. However, there are several types, such as hydrogen fuel, jet fuel and bio-diesel which are all categorized as a liquid fuel. Emulsified fuels of oil-in-water such as orimulsion have been developed a way to make heavy oil fractions usable as liquid fuels. Many liquid fuels play a primary role in the economy; some common properties of liquid fuels are that they are easy to transport, that can be handled easily. They are easy to use for all engineering applications, home use. Fuels like kerosene are rationed in some countries, for example available in government subsidized shops in India for home use. Conventional diesel is similar to gasoline in that it is a mixture of aliphatic hydrocarbons extracted from petroleum. Kerosene is used in kerosene lamps and as a fuel for cooking and small engines. Natural gas, composed chiefly of methane, can only exist as a liquid at low temperatures, which limits its direct use as a liquid fuel in most applications.
LP gas is a mixture of propane and butane, both of which are compressible gases under standard atmospheric conditions. It offers many of the advantages of compressed natural gas (CN
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fiber crops, waste paper, or rags. Many kinds of paper are made from wood with nothing else mixed into them; this includes newspapers and toilet paper. Pulp is one of the most abundant raw materials. Pulp for papermaking was produced by macerating mulberry bark as early as the 2nd century in Han dynasty China, where the invention of paper is traditionally attributed to Cai Lun. Lu Ji, in his 3rd century commentary on the Classic of Poetry, mentions that people residing south of the Yangtze River would traditionally pound mulberry bark to make paper or clothing. By the 6th century, the mulberry tree was domesticated by farmers in China for the purpose of producing pulp to be used in the papermaking process. In addition to mulberry, pulp was made from bamboo, hibiscus bark, blue sandalwood and cotton. Papermaking using pulp made from hemp and linen fibers from tattered clothing, fishing nets and fabric bags spread to Europe in the 13th century, with an ever-increasing use of rags being central to the manufacture and affordability of rag paper, a factor in the development of printing.
By the 1800s, demand exceeding the available supply of rags, the manual labor of papermaking resulted in paper being still a pricey product. Using wood pulp to make paper is a recent innovation, concurrent to the invention of automatic papermaking machines, both together resulting in paper and cardboard becoming an inexpensive commodity in modern times. Although the first use of paper made from wood pulp dates from 1800, as seen in some pages of a book published by Matthias Koops that year in London, large-scale wood paper production began with the development of mechanical pulping in Germany by Friedrich Gottlob Keller in the 1840s, by the Canadian inventor Charles Fenerty in Nova Scotia, Chemical processes followed, first with J. Roth's use of sulfurous acid to treat wood by Benjamin Tilghman's U. S. patent on the use of calcium bisulfite, Ca2, to pulp wood in 1867. A decade the first commercial sulfite pulp mill was built, in Sweden, it was based on work by Carl Daniel Ekman. By 1900, sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods.
The competing chemical pulping process, the sulfate, or kraft, was developed by Carl F. Dahl in 1879; the invention of the recovery boiler, by G. H. Tomlinson in the early 1930s, allowed kraft mills to recycle all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and to produce stronger fibres, made the kraft process the dominant pulping process, starting in the 1940s. Global production of wood pulp in 2006 was 175 million tons. In the previous year, 63 million tons of market pulp was sold, with Canada being the largest source at 21 percent of the total, followed by the United States at 16 percent; the wood fiber sources required for pulping are "45% sawmill residue, 21% logs and chips, 34% recycled paper". Chemical pulp made up 93 percent of market pulp; the timber resources used to make wood pulp are referred to as pulpwood. While in theory, any tree can be used for pulp-making, coniferous trees are preferred because the cellulose fibers in the pulp of these species are longer, therefore make stronger paper.
Some of the most used softwood trees for paper making include spruce, fir and hemlock, hardwoods such as eucalyptus and birch. There is increasing interest in genetically modified tree species, because of several major benefits these can provide, such as increased ease of breaking down lignin and increased growth rate. A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fiberboard which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or chemical methods; the finished product may be either non-bleached, depending on the customer requirements. Wood and other plant materials used to make pulp contain three main components: cellulose fibers and hemicelluloses; the aim of pulping is to break down the bulk structure of the fibre source, be it chips, stems or other plant parts, into the constituent fibres. Chemical pulping achieves this by degrading the lignin and hemicellulose into small, water-soluble molecules which can be washed away from the cellulose fibres without depolymerizing the cellulose fibres.
The various mechanical pulping methods, such as groundwood and refiner mechanical pulping, physically tear the cellulose fibres one from another. Much of the lignin remains adhering to the fibres. Strength is impaired. There are a number of related hybrid pulping methods that use a combination of chemical and thermal treatment to begin an abbreviated chemical pulping process, followed by a mechanical treatment to separate the fibres; these hybrid methods include thermomechanical pulping known as TMP, chemithermomechanical pulping known as CTMP. The chemical and thermal treatments reduce the amount of energy subsequently required by the mechanical treatment, al
Auschwitz concentration camp
The Auschwitz concentration camp was a complex of more than 40 Nazi concentration camps and extermination camps built and operated by Nazi Germany in occupied Poland during World War II and the Holocaust. It consisted of the main camp and administrative headquarters in Oświęcim. Germany invaded Poland in September 1939, sparking World War II, they converted Auschwitz I from an army barracks to a prison camp for Polish political prisoners; the first prisoners were German criminals who were brought to the camp as functionaries in May 1940, the first gassing of prisoners took place in block 11 of Auschwitz I in September 1941. Auschwitz II–Birkenau became a major site of the Nazis' Final Solution to the Jewish Question. Transport trains delivered Jews from all over German-occupied Europe to the camp's gas chambers from early 1942 until late 1944. At least 1.1 million people died at Auschwitz of the estimated 1.3 million sent there, some 90 percent of them were Jews. One in six Jews killed in the Holocaust died at the camp.
Others deported to Auschwitz included 150,000 non-Jewish Poles, 23,000 Roma, 15,000 Soviet prisoners of war, 400 Jehovah's Witnesses, tens of thousands of diverse nationalities, an unknown number of homosexual men. Many of those not killed in the gas chambers died because of starvation, forced labor, infectious diseases, individual executions, medical experiments. In the course of the war, the camp was staffed by 7,000 members of the German Schutzstaffel 12 percent of whom were convicted of war crimes. Several were executed, including camp commandant Rudolf Höss; the Allies did not act on early reports of atrocities, their failure to bomb it or its railways remains controversial. At least 802 prisoners tried to escape, 144 and two Sonderkommando units launched a brief, unsuccessful uprising on 7 October 1944, consisting of prisoners assigned to staff the gas chambers. Soviet troops approached Auschwitz in January 1945, most of the prisoners were sent west on a death march; the remaining prisoners were liberated on 27 January 1945, a day commemorated as International Holocaust Remembrance Day.
In the following decades, survivors wrote memoirs of their experiences in Auschwitz, such as Primo Levi, Viktor Frankl, Elie Wiesel, the camp became a dominant symbol of the Holocaust. In 1947, Poland founded the Auschwitz-Birkenau Memorial and Museum on the site of Auschwitz I and II, it was named a World Heritage Site by UNESCO in 1979; the ideology of Nazism brought together elements of antisemitism, racial hygiene and eugenics, combined them with pan-Germanism and territorial expansionism with the goal of obtaining more Lebensraum for the Germanic people. After the Nazi seizure of power in Germany, boycotts of German Jews and acts of violence against them became ubiquitous, legislation was passed excluding them from the civil service and certain professions, including the law. Harassment and economic pressure were used to encourage them to leave Germany. On 15 September 1935, the Reichstag passed the Nuremberg Laws, prohibiting marriages between Jews and people of Germanic extraction, extramarital relations between Jews and Germans, the employment of German women under the age of 45 as domestic servants in Jewish households.
The Reich Citizenship Law defined as citizens those of "German or kindred blood". Thus Jews and other minorities were stripped of their citizenship. By the start of World War II in 1939, around 250,000 of Germany's 437,000 Jews had emigrated to the United States, the United Kingdom, other countries; when Germany invaded Poland in September 1939, triggering World War II, Adolf Hitler ordered that the Polish leadership and intelligentsia be destroyed. 65,000 civilians, viewed as inferior to the Aryan master race, had been killed by the end of 1939. In addition to leaders of Polish society, the Nazis killed Jews, the Roma, the mentally ill. SS-Obergruppenführer Reinhard Heydrich head of the Gestapo, ordered on 21 September 1939 that Polish Jews be rounded up and concentrated into cities with good rail links; the intention was to deport them to points further east, or to Madagascar. Two years in June 1941, in an attempt to obtain new territory, Hitler invaded the Soviet Union. Auschwitz I, a former Polish army barracks, was the main camp and administrative headquarters of the camp complex.
Intending to use it to house political prisoners, Reichsführer-SS Heinrich Himmler, head of the Schutzstaffel, approved the site in April 1940 on the recommendation of SS-Obersturmbannführer Rudolf Höss of the Concentration Camps Inspectorate. Höss oversaw the development of the camp and served as its first commandant, with SS-Obersturmführer Josef Kramer as his deputy. Around 1,000 m long and 400 m wide, Auschwitz I consisted of 20 brick buildings, six of them two-story; the camp housed the SS by 1943 held 30,000 inmates. The first 30 prisoners arrived on 20 May 1940 after being transported from the Sachsenhausen concentration camp in Oranienburg, Germany. Convicted German criminals, the men were known as "greens" after the green triangles they were required to w
A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen. In cases when fuel plays the role of a combustible material, the explosion is known as a fuel-air explosion. Dust explosions are a frequent hazard in underground coal mines, grain elevators, other industrial environments, they are commonly used by special effects artists and pyrotechnicians, given their spectacular appearance and ability to be safely contained under certain controlled conditions. Thermobaric weapons utilize this principle by saturating area with an combustible material and igniting it to produce explosive force; these weapons are the most powerful non-nuclear weapons in the world. If rapid combustion occurs in a confined space, enormous overpressures can build up, causing major structural damage and flying debris.
The sudden release of energy from a "detonation" can produce a shockwave, either in open air or in a confined space. If the spread of flame is at subsonic speed, the phenomenon is sometimes called a "deflagration", although looser usage calls both phenomena "explosions". Dust explosions may be classified as being either "primary" or "secondary" in nature. Primary dust explosions may occur inside process equipment or similar enclosures, are controlled by pressure relief through purpose-built ducting to the external atmosphere. Secondary dust explosions are the result of dust accumulation inside a building being disturbed and ignited by the primary explosion, resulting in a much more dangerous uncontrolled explosion that can affect the entire structure. Fatalities from dust explosions have been the result of secondary dust explosions. There are five necessary conditions for a dust explosion: A combustible dust The dust is suspended in the air at a sufficiently high concentration There is an oxidant There is an ignition source The area is confined—a building can be considered an enclosure Many common materials which are known to burn can generate a dust explosion, such as coal and sawdust.
In addition, many otherwise mundane organic materials can be dispersed into a dangerous dust cloud, such as grain, starch, powdered milk, cocoa and pollen. Powdered metals can form explosive suspensions in air. Explosive dust can arise from activities such as transporting grain, grain silos have been demolished violently. Mining of coal leads to coal dust, flour mills have large amounts of flour dust as a result of milling. A gigantic explosion of flour dust destroyed a mill in Minnesota on May 2, 1878, killing 14 workers at the Washburn A Mill and another four in adjacent buildings. A similar problem occurs in other places dedicated to woodworking. Since the advent of industrial production–scale metal powder–based additive manufacturing in the 2010s, there is growing need for more information and experience with preventing dust explosions and fires from the traces of excess metal powder sometimes left over after laser sintering or other fusion methods. For example, in machining operations downstream of the AM build, excess powder liberated from porosities in the support structures can be exposed to sparks from the cutting interface.
Efforts are underway not only to build this knowledgebase within the industry but to share it with local fire departments, who do periodic fire-safety inspections of businesses in their districts and who can expect to answer alarms at shops or plants where AM is now part of the production mix. Although not a dust, paper particles emitted during processing - rolling, calendaring/slitting, sheet-cutting - are known to pose an explosion hazard. Enclosed paper mill areas subject to such dangers maintain high air humidities to reduce the chance of airborne paper dust explosions. In special effects pyrotechnics, lycopodium powder and non-dairy creamer are two common means of producing safe, controlled fire effects. To support rapid combustion, the dust must consist of small particles with a high surface area to volume ratio, thereby making the collective or combined surface area of all the particles large in comparison to a dust of larger particles. Dust is defined as powders with particles less than about 500 micrometres in diameter, but finer dust will present a much greater hazard than coarse particles by virtue of the larger total surface area of all the particles.
Below a certain value, the lower explosive limit, there is insufficient dust to support the combustion at the rate required for an explosion. A combustible concentration at or below 25% of the LEL is considered safe. If the fuel to air ratio increases above the upper explosive limit, there is insufficient oxidant to permit combustion to continue at the necessary rate. Determining the minimum explosive concentration or maximum explosive concentration of dusts in air is difficult, consulting different sources can lead to quite different results. Typical explosive ranges in air are from few dozens grams/m3 for the minimum limit, to few kg/m3 for the maximum limit. For example, the LEL for sawdust has been determined to be between 40 and 50 grams/m3, it depends on many factors including the type of material used. Normal atmospheric oxygen can be sufficient to support a dust explosion if the other necessary conditions are present. High-oxygen or pure oxygen environments are considered to be hazardous, as are strong oxidizing gases suc
Pykrete is a frozen composite material made of 14 percent sawdust or some other form of wood pulp and 86 percent ice by weight. During World War II, Geoffrey Pyke proposed it as a candidate material for a supersized aircraft carrier for the British Royal Navy. Pykrete features unusual properties, including a slow melting rate due to its low thermal conductivity, as well as a vastly improved strength and toughness compared to ordinary ice; these physical properties can make the material comparable to concrete, as long as the material is kept frozen. Pykrete is more difficult to form than concrete, as it expands during the freezing process. However, it can be maintained using seawater as a raw material; the mixture can be moulded into any shape and frozen, it will be tough and durable, as long as it is kept at or below freezing temperature. Resistance to gradual creep or sagging is improved by lowering the temperature further, to −15 °C Geoffrey Pyke managed to convince Lord Mountbatten of the potential of his proposal sometime around 1942, trials were made at two locations in Alberta, Canada.
The idea for a ship made of ice impressed the United States and Canada enough that a 60-foot -long, 1,000-ton ship was built in one month on Patricia Lake in the Canadian Rockies. However, it was constructed using plain ice, it took more than an entire summer to melt, but plain ice proved to be too weak. Pyke learned from a report by Herman Mark and his assistant that ice made from water mixed with wood fibres formed a strong solid mass—much stronger than pure water ice. Max Perutz recalled: Then, one day, Pyke handed me a report that he said he found hard to understand, it was by Herman Mark, my former professor of physical chemistry in Vienna, who had lost his post there when the Nazis overran Austria and found a haven at the Polytechnic Institute of Brooklyn. As an expert on plastics, he knew that many of them were brittle when pure, but could be toughened by embedding fibres such as cellulose in them, just as concrete can be reinforced with steel wires. Mark and his assistant, Walter P. Hohenstein, stirred a little cotton wool or wood pulp—the raw material of newsprint—into water before they froze it, found that these additions strengthened the ice dramatically.
When I had read their report, I advised my superiors to scrap our experiments with pure ice and set up a laboratory for the manufacture and testing of reinforced ice. Combined Operations requisitioned a large meat store five floors underground beneath Smithfield Market, which lies within sight of St. Paul's Cathedral, ordered some electrically heated suits, of the type issued to airmen, to keep us warm at less than 0 °C temperatures, they detailed some young commandos to work as my technicians, I invited Kenneth Pascoe, a physics student and became a lecturer in engineering at Cambridge, to come and help me. We built a big wind tunnel to freeze the mush of wet wood pulp and sawed the reinforced ice into blocks. Our tests soon confirmed Hohenstein's results. Blocks of ice containing as little as four percent wood pulp were weight for weight as strong as concrete; when we fired a rifle bullet into an upright block of pure ice two feet square and one foot thick, the block shattered. My stock rose, but no one would tell me what pykrete was needed for, except that it was for Project Habakkuk.
Perutz would learn that Project Habakkuk was the plan to build an enormous aircraft carrier more of a floating island than a ship in the traditional sense. The experiments of Perutz and his collaborators in Smithfield Meat Market in the City of London took place in great secrecy behind a screen of animal carcasses; the tests confirmed that pykrete is much stronger than pure ice and does not shatter, but that it sags under its own weight at temperatures higher than −15 °C. Mountbatten’s reaction to the breakthrough is recorded by Pyke's biographer David Lampe: What happened next was explained several years after the war by Lord Mountbatten in a widely-quoted after-dinner speech. "I was told he was in his bath. I said,'Good, that's where I want him to be.' I nipped up the stairs and called out to him,'I have a block of a new material which I would like to put in your bath.' After that, he suggested that I should take it to the Quebec Conference." The demonstration in Churchill's steaming bath had been most dramatic.
After the outer film of ice on the small pykrete cube had melted, the freshly exposed wood pulp kept the remainder of the block from thawing. Another tale is that at the Quebec Conference of 1943 Mountbatten brought a block of pykrete along to demonstrate its potential to the entourage of admirals and generals who had come along with Winston Churchill and Franklin D. Roosevelt. Mountbatten placed them on the ground. One was a normal ice block and the other was pykrete, he drew his service pistol and shot at the first block. It splintered. Next, he fired at the pykrete to give an idea of the resistance of that kind of ice to projectiles; the bullet ricocheted off the block, grazing the trouser leg of Admiral Ernest King and ending up in the wall. According to Perutz's own account, the incident of a ricochetting bullet hitting an Admiral happened much earlier in London and the gun was fired by someone on the project—not Mountbatten. Despite th