Dust

Dust is a general name for minute solid particles with diameters less than 500 micrometers. On Earth, dust occurs in the atmosphere from various sources; soil dust lifted up by wind, volcanic eruptions, and pollution are some examples. Airborne dust is considered an aerosol and can have a strong local radiative forcing on the atmosphere and significant effects on climate. In addition, if enough of the minute particles are dispersed within the air in a given area (such as flour or coal dust), under certain circumstances this can be an explosion hazard.

Coal dust is responsible for the lung disease known as Pneumoconiosis, including black lung disease, which occurs among coal miners. This danger has resulted in a number of laws regulating environmental standards for working conditions.

Dust in outer space
Cosmic dust is widely present in space, where gas and dust clouds are primary precursors for planetary systems. The zodiacal light, seen in the sky on a dark night, is produced by sunlight reflected from particles of dust in orbit around the Sun. The tails of comets are produced by emissions of dust and ionized gas from the body of the comet. Dust also covers solid planetary bodies, and vast dust storms can occur on Mars that can cover almost the entire planet. Interstellar dust is found between the stars, and high concentrations can produce diffuse nebulae and reflection nebulae.

Dust samples returned from outer space could provide information about conditions in the early solar system. Several spacecraft have been launched in an attempt to gather samples of dust and other materials. Among these was Stardust, which flew past Comet Wild 2 in 2004 and returned a capsule of the comet's remains to Earth in January 2006. The Japanese Hayabusa spacecraft is currently on a mission to collect samples of dust from the surface of an asteroid.

Domestic dust
Dust in homes, offices, and other human environments consists of human skin cells, plant pollen, human and animal hairs, textile fibers, paper fibers, minerals from outdoor soil and dust, and many other materials which may be found in the local environment. The precise composition of domestic dust can vary widely: "The quantity and composition of house dust varies greatly with seasonal and environmental factors such as the surroundings, exchange of outside air, age of the house, building materials and their condition, and the quantity of furniture and carpets, as well as their state of preservation. It varies further with ventilation and heating systems, cleaning habits, activities of the occupants or users of a room, etc. House dust consists of inorganic and organic matter, yet the relative proportions of these components may vary considerably. 'House dust' from kindergartens often consists almost completely of inorganic materials such as sand, loam, and clay from sand pits. On the other hand, house dust from residences of animal owners with worn out carpets may consist nearly completely of organic material. The proportion of organic matter in 318 house dust samples was found to vary between <5% and >95% (Butte and Walker, 1994). Fergusson et al. (1986) reported the organic content of house dust from 11 homes in Christchurch, New Zealand, to be within the range from 25.7% to 41.5%. Floor dust from seven Danish offices had a mean organic fraction of 33% (Mølhave et al., 2000)."

According to the German Environmental Survey, approximately 6 mg/m²/day of house dust is formed in private households, depending primarily on the amount of time spent at home. Nearly 1000 dust particles per square centimeter settle on domestic surfaces every hour. Some dust consists of human skin; it is estimated that the entire outer layer of skin is shed every day or two at a rate of 7 million skin flakes per minute, which corresponds to a mass emission rate of about 20 mg/minute.

Insects and other small fauna found in houses have their own subtle interactions with dust that may have adverse impact on the health of its regular occupants. Thus, in many climates it is wise to keep a modicum of airflow going through a house, by keeping doors and windows open or at least slightly ajar. In colder climates, it is essential to manage dust and airflow, since the climate encourages occupants to seal even the smallest air gaps, and thus eliminate any possibility of fresh air entering.

House dust mites are on all surfaces and even suspended in air. Dust mites feed on minute particles of organic matter, the main constituent of house dust. They excrete enzymes to digest dust particles; these enzymes and their feces, in turn, become part of house dust and can provoke allergic reactions in humans. Dust mites flourish in the fibers of bedding, furniture, and carpets.

The particles that make up house dust can easily become airborne, so care must be exercised when removing dust, as the activity intended to sanitize or remove dust may make it airborne. One way to repel dust is with some kind of electrical charge, but house dust can be removed by many methods, including wiping, swiping, or sweeping by hand, or with a dust cloth, sponge, feather duster, or broom, or by suction by a vacuum cleaner or air filter. The device being used traps the dust; however, some may become airborne and come to settle in the cleaner's lungs, thus making the activity somewhat hazardous. "Dust bunnies" are little clumps of fluff that form when sufficient dust accumulates. Dust is known to worsen hay fever.

Dust control
Dust control is the suppression of solid particles with diameters less than 500 micrometers. Because dust in the air is a serious health threat to children, older people, and those with respiratory illnesses, the U. S. Environment Protection Agency (EPA) mandates facilities that generate dust must work to minimize it in their operations.

The most frequent dust control violations occurred at new residential housing developments in urban areas. Federal law requires permits for earth moving at construction sites, include plans to control dust emissions. Control measures include such simple practices as watering down construction and demolition sites, as well as preventing dust from being tracked out onto adjacent roads. In addition, federal laws require dust controls on sources such as vacant lots, unpaved parking lots, and unpaved roads. Control measures for these sources include paving, gravel, or stabilizing the surface with water or other dust suppressants.

Dust in fiction

 * In JM Barrie's children's novel Peter Pan (1911), "pixie dust" is a substance used to help make people fly who can't already.
 * In Clark Ashton Smith's short horror story "The Treader In The Dust" (1935), a scholar unwittingly calls forth a demon that personifies dustiness.
 * In Arthur C. Clarke's A Fall of Moondust (1961), 21st century tourists "cruise" across the Moon's "Seas" that have filled over eons with very fine dust, which is so fine that it almost behaves like water.
 * In Hal Clement's short science fiction story "Dust Rag" (1965), two astronauts struggle with dust that stuck to their helmets, blinding them.
 * In the science fiction series Babylon 5, Dust was a psychoactive illegal drug that enhanced latent telepathic abilities in non-humanoids, that often led to fatalities in both the user and "victim".
 * In the novel by Phillip Pullman, His Dark Materials trilogy referrs to a shadow particle that created angels and is a concious particle. It created the first angel, the Authority, not God, and in the trilogy a young girl named Lyra and a boy name Will try to find out what Dust is in order to save it and destroy the Authority thus building a Republic of Heaven that lets the dead rise again. (1995-2000)
 * In the T.V. series Buffy the Vampire Slayer by Joss Whedon, vampires are reduced to dust when staked- or "dusted"- a reference to earlier mythology in which vampires consist of earth or dust.

Dust in religion
In ancient Sumerian mythology: In the Bible:
 * The afterlife consists of the dreary "House of Dust and Darkness".
 * In Genesis 3:19, God — following The Fall, Adam and Eve's transgression — states to the couple:
 * By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return. [Emphasis added]

This latter clause is used in the Ash Wednesday service in some churches for the administering of ashes, and is adapted in funeral services to the common prayer "Dust to Dust".
 * In Genesis 13:16, God states to Abram (later Abraham):
 * I will make your offspring like the dust of the earth, so that if anyone could count the dust, then your offspring could be counted.

Note however that in both of these Biblical passages, the Hebrew word is עפר (`âfâr), which can also mean earth or dirt.


 * Micah 7:17, "They shall lick dust like a serpent..."


 * John 8:1-11 features Jesus "writing on the ground." Many translators substitute "dust" for "ground". This scripture provides the only witness of any writing by Jesus. The choice of dust as a medium for writing has created speculation as to what Jesus wrote.