Transportation
Transportation, the movement of goods and persons from place to place and the various means by which such movement is accomplished. The growth of the ability—and the need—to transport large quantities of goods or numbers of people over long distances at high speeds in comfort and safety has been an index of civilization and in particular of technological progress.
Safety
Safety, those activities that seek either to minimize or to eliminate hazardous conditions that can cause bodily injury. Safety precautions fall under two principal headings, occupational safety and public safety. Occupational safety is concerned with risks encountered in areas where people work: offices, manufacturing plants, farms, construction sites, and commercial and retail facilities. Public safety involves hazards met in the home, in travel and recreation, and other situations not falling within the scope of occupational safety.
Safety was not considered to be a matter of public concern in ancient times, when accidents were regarded as inevitable or as the will of the gods. Modern notions of safety developed only in the 19th century as an outgrowth of the Industrial Revolution, when a terrible toll of factory accidents aroused humanitarian concern for their prevention. Today the concern for safety is worldwide and is the province of numerous governmental and private agencies at the local, national, and international levels.
The frequency and severity rates of accidents vary from country to country and from industry to industry. In the industrialized nations of the world, accidents now cause more deaths than all infectious diseases and more than any single illness except those related to heart disease and cancer. Accidents in the home, in public and private transportation, and on farms and in factories are by far the predominant cause of death in the population under 35 years of age in industrialized nations. In the United States each year, about six times as many persons receive nonfatal injuries in accidents in the home as in motor-vehicle accidents, and about twice as many at home as in industrial accidents. On a worldwide basis, motor-vehicle accidents tend to be the primary cause of accidental deaths, followed by those in industry and in the home.
Industrial accidents can occur because of improper contact with machinery, the lifting or other handling of bulk materials, and contact with electrical, chemical, or radiation hazards. The mining and lumbering industries are among those that have the highest rate of severe accidents. High-technology industries such as electronics have relatively low accident rates.
Industrial accidents can occur because of improper contact with machinery, the lifting or other handling of bulk materials, and contact with electrical, chemical, or radiation hazards. The mining and lumbering industries are among those that have the highest rate of severe accidents. High-technology industries such as electronics have relatively low accident rates.
Several international organizations provide means by which national safety organizations can exchange information and pass on new ideas. Among the bodies serving in this capacity are the International Social Security Association (ISSA) and the International Labour Organisation (ILO). These two bodies have sponsored international safety congresses every three years since 1955. Every four years a congress is held by the Permanent International Association of Road Congresses, a body that is maintained by the transport ministries of its member countries and by groups representing the highway-construction industry. The World Touring and Automobile Organization (OTA) holds a safety congress every other year.
A number of organizations, including the ILO, ISSA, the World Health Organization, and the European Economic Community, maintain a joint information bureau in Geneva. The International Organization for Standardization, which is also based in Geneva, helps establish safety codes and standards for numerous areas of activity (such as nuclear energy) among the many nations that sponsor it.
National-level safety organizations tend to deal with safety questions most closely associated with the economic structure of the country concerned. Nations having limited industrial development tend to concentrate on road safety, for example. At the local level many groups exist that specialize in one aspect or another of safety. Much of their activity is conducted by professionals whose jobs relate closely to questions of safety, among them policemen, firemen, medical officers, and others concerned with health and with accident prevention. These groups seek to enlist the cooperation of educators, local governments and officials, industrial associations, and trade unions and to effect liaison with professional safety groups such as the American Society of Safety Engineers in the United States or the Institution of Occupational Safety and Health in the United Kingdom. In the United States, local safety councils may be accredited to the National Safety Council, the world’s largest safety body. In the United Kingdom the Royal Society for the Prevention of Accidents performs a role comparable to that of the National Safety Council.
Among the chief activities of individuals and organizations concerned with safety are the collection of statistics on accidents and injuries and the publication of analyses of those statistics; the study of hazardous situations and environments and the development of safer designs, procedures, and materials; the development of educational programs for employers, workers, drivers, and other groups at risk; and the design, through safety engineering, of machines, workplaces, and safety equipment that minimize the risk of injury. In recent years much activity has centred on identifying and preventing risks posed by such hazards as ionizing radiation and a wide array of chemicals and hazardous industrial wastes. The greatest challenge in the field of safety is to keep legislation and public awareness in step with the rapid development of technology and with the fresh hazards that it constantly presents.
Mineral deposit
Mineral deposit, aggregate of a mineral in an unusually high concentration.
About half of the known chemical elements possess some metallic properties. The term metal, however, is reserved for those chemical elements that possess two or more of the characteristic physical properties of metals (opacity, ductility, malleability, fusibility) and are also good conductors of heat and electricity. Approximately 40 metals are made available through the mining and smelting of the minerals in which they occur.
Certain kinds of mineral can be smelted more readily than others; these are commonly referred to as ore minerals. Ore minerals tend to be concentrated in small, localized rock masses that form as a result of special geologic processes, and such local concentrations are called mineral deposits. Mineral deposits are what prospectors seek. The terms ore mineral and mineral deposit were originally applied only to minerals and deposits from which metals are recovered, but present usage includes a few nonmetallic minerals, such as barite and fluorite, that are found in the same kinds of deposit as metallic minerals.
No deposit consists entirely of a single ore mineral. There are always admixtures of valueless minerals, collectively called gangue. The more concentrated an ore mineral, the more valuable the mineral deposit. For every mineral deposit there is a set of conditions, such as the level of concentration and the size of the deposit, that must be reached if the deposit is to be worked at a profit. A mineral deposit that is sufficiently rich to be worked at a profit is called an ore deposit, and in an ore deposit the assemblage of ore minerals plus gangue is called the ore.
All ore deposits are mineral deposits, but the reverse is not true. Ore deposit is an economic term, while mineral deposit is a geologic term. Whether a given mineral deposit is also an ore deposit depends on many factors other than the level of concentration and the size of the deposit; all factors that affect the mining, processing, and transporting of the ore must be considered as well. Among such factors are the shape of a deposit, its depth below the surface, its geographic remoteness, access to transportation, the political stability of the region, and market factors such as the price of the metal in world trade and the costs of borrowing the money needed to develop a mine. Because market factors change continually, a given mineral deposit may sometimes be an ore deposit, but at other times it may be uneconomic and hence not an ore deposit.
Mineral deposits have been found both in rocks that lie beneath the oceans and in rocks that form the continents, although the only deposits that actually have been mined are in the continental rocks. (The mining of ocean deposits lies in the future.) The continental crust averages 35–40 kilometres (20–25 miles) in thickness, and below the crust lies the mantle. Mineral deposits may occur in the mantle, but with present technology it is not possible to discover them.
Metals used in industrial and technological applications can be divided into two classes on the basis of their abundance in Earth’s crust. The geochemically abundant metals, of which there are five (aluminum, iron, magnesium, manganese, and titanium), constitute more than 0.1 percent by weight of Earth’s crust, while the geochemically scarce metals, which embrace all other metals (including such familiar ones as copper, lead, zinc, gold, and silver), constitute less than 0.1 percent. In almost every rock, at least tiny amounts of all metals can be detected by sensitive chemical analysis. However, there are important differences in the way the abundant and scarce metals occur in common rocks. Geochemically abundant metals tend to be present as essential constituents in minerals. For example, basalt, a common igneous rock, consists largely of the minerals olivine and pyroxene (both magnesium-iron silicates), feldspar (sodium-calcium-aluminum silicate), and ilmenite (iron-titanium oxide). Careful chemical analysis of a basalt will reveal the presence of most of the geochemically scarce metals too, but no amount of searching will reveal minerals in which one or more of the scarce metals is an essential constituent.
Geochemically scarce metals rarely form minerals in common rocks. Instead, they are carried in the structures of common rock-forming minerals (most of them silicates) through the process of atomic substitution. This process involves the random replacement of an atom in a mineral by a foreign atom of similar ionic radius and valence, without changing the atomic packing of the host mineral. Atoms of copper, zinc, and nickel, for example, can substitute for iron and magnesium atoms in olivine and pyroxene. However, since substitution of foreign atoms produces strains in an atomic packing, there are limits to this process, as determined by temperature, pressure, and various chemical parameters. Indeed, the substitution limits for most scarce metals in common silicate minerals are low—in many cases only a few hundred substituting atoms for every million host atoms—but even these limits are rarely exceeded in common rocks.
One important consequence that derives from the way abundant and scarce metals occur in common rocks is that ore minerals of abundant metals can be found in many common rocks, while ore minerals of scarce metals can be found only where some special, restricted geologic process has formed localized enrichments that exceed the limits of atomic substitution.
Two factors determine whether a given mineral is suitable to be an ore mineral. The first is the ease with which a mineral can be separated from the gangue and concentrated for smelting. Concentrating processes, which are based on the physical properties of the mineral, include magnetic separation, gravity separation, and flotation. The second factor is smelting—that is, releasing the metal from the other elements to which it is chemically bonded in the mineral. Smelting processes are discussed below, but of primary importance in this consideration of the suitability of an ore mineral is the amount of energy needed to break the chemical bonds and release the metal. In general, less energy is needed to smelt sulfide, oxide, or hydroxide minerals than is required to smelt a silicate mineral. For this reason, few silicate minerals are ore minerals. Because the great bulk of Earth’s crust (about 95 percent) is composed of silicate minerals, sulfide, oxide, and hydroxide ore minerals are at best only minor constituents of Earth’s crust—and in many cases they are very rare constituents.
The preferred ore minerals of both geochemically abundant and geochemically scarce metals are native metals, sulfides, oxides, hydroxides, or carbonates. In a few cases, silicate minerals have to be used as ore minerals because the metals either do not form more desirable minerals or form desirable minerals that rarely occur in large deposits.