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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.
Domestic dust
Dust in homes, offices, and other human environments is mainly generated by humans from their skin cells that slough off:
An average skin flake has an equivalent diameter of 14µm. 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. Tests of indoor environmental dust in homes and offices have shown it to be primarily (70-90%) composed of skin flakes. Assuming a density of 1 g/cm³, 7 million skin flakes per minute corresponds to a mass emission rate of about 20 mg/minute.
Some comes from domesticated pets such as dogs, cats and birds. Some atmospheric dust from the outdoors is also present. On average, approximately 6 mg/m³/day of house dust is formed in private households, depending primarily on the amount of time spent at home. "Dust bunnies" are little clumps of fluff that form when sufficient dust accumulates. Dust is known to worsen hayfever.
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 Control (Suppression)
Dust control is the suppression of solid particles with diameters less than 500 micrometers. Because dust in the air is a serious health threat, especially 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 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. Giant Razengan
Dust in fiction
- In JM Barrie's children's novel Peter Pan (1911), "pixie dust" is a substance used to help make people who can't already, fly.
- 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 the Peanuts comic strip, the character Pig-Pen (1954) is constantly surrounded by a cloud of dust.
- 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 Philip Pullman's best-selling series His Dark Materials (1995), dust (or "Dust", as it is spelled in the books) plays an important part by creating a connection between different worlds and is drawn to conscious beings.
- In the TV comedy Little Britain (2003), Fat Fighters group leader Marjorie Dawes distinctively instructs the dieters to eat dust as it is "low in fat."
- In "The Dust Has Landed", an episode of Graham Duff's science-fiction radio comedy Nebulous, sentient dust declares war against humanity, forcing the reinvention of the vacuum cleaner.
- In Arthur Slade's Dust (2001), a stranger comes to the small town of Horshoe, promising rain. Children begin to disappear. Young adult fiction.
- 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".
Dust in religion
In ancient Sumerian mythology:
- The afterlife consists of the dreary "House of Dust and Darkness".
In the Bible:
- 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.
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".
- 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.
See Also
References
- Holmes, Hannah; (2001)The Secret Life of Dust. Wiley. ISBN 0-471-37743-0
- Steedman, Carolyn; (2002) Dust. Manchester University Press. ISBN-13: 978-0719060151
- Heinsohn, R., Cimbala, J., (2003) Indoor Air Quality Engineering: Environmental Health and Control of Indoor Pollutants. page 146. CRC Press.
- House dust formation rate (in German)