Search Documents

By R. S. Conti, M. R. Krump, C. P. Lazzara Ph. D., R. L. Derick, L. L. Chasko

A mine fire is one of the most challenging safety issues facing a mine operator and can occur at any location underground. The National Institute for Occupational Safety and Health (NIOSH) and the Twentymile Coal Mine, CO, conducted in-mine experiments to determine the capability of high-expansion foam for addressing underground fires. The tests were conducted in sloping entries with high-capacity diesel-powered foam generators. The following results were observed: a well-designed, maintained and properly operated high-expansion foam generator can propagate a foam plug hundreds of feet in steep upward-sloping (20%) multiple entries against a ventilation pressure; stoppings and partitions designed to contain the foam plug in upward-sloping entries must be substantially constructed; and the predicted quantity of foam concentrate can be significantly less than the actual amount used, due to foam losses, such as bubble breakage on dry surfaces. This paper describes the production of high-expansion firefighting foam and discusses the in-mine experimental tests and results.

Jan 1, 2010

By R Bertuzzi

This paper presents a three-dimensional analysis of a trapezoidal-shaped segmental tunnel lining for a recent tunnelling project in Sydney. Two- dimensional analyses, hand calculations and equipment selection defined the lining geometry and loads. The analysis, which was undertaken using 3DEC (Itasca), included a complete ring of six segments bolted together to assess the impact of imperfectly built rings. Asymmetry was induced in the analysis by unfavourable positioning of segments within construction tolerances. Model output includes displacement and stress within the entire ring and normal, shear and bending moments at the joints. For the case analysed, the results suggest a 10 mm construction tolerance increases normal and shear stresses along the radial joints by approximately 25 per cent and 15 per cent, respectively and up to a doubling of the induced moments.

Jan 1, 2008

By Syd S. Peng

Introduction The most commonly used ground control design in coal mining is the determination of pillar size by various pillar strength formulae for mine layout (Bieniawski, 1983; Holland, 1973; Hustrulid, 1976; Obert and Duvall 1967; Wilson and Ashwin, 1972). However, there have been few documented case histories concerning the validity of those strength formulae. Recently there are indications that those strength formulae tend to overdesign considerably. From a safety point of view, there is nothing wrong with overdesign. But an overdesign with large chain pillars reduces the flexibility of machine movement and decreases production. It also reduces coal recovery and, thus, shortens the reserve's life. This is especially true for small operators who own a limited reserve. Those small mines, through past practices or out of necessity, experiment with smaller pillars than those predicted by the strength formulae. Conclusive ev¬idence has been collected that points to the need of a new concept of coal pillar design. Two case studies will be cited to illustrate this point. 3-D US pillar strength formulae Figure 1 shows a sectional layout of a one-unit mine. The seam was about 1.3 m (50 in.) thick with a uniform cover of 64 m (210 ft). A house was located near the center of the section. The homeowner demanded that no surface subsidence and domestic well dewatering should ever be allowed as a result of underground room-and-pillar mining. Physical properties - strength and Young's modulus - of the rock strata including coal were obtained by testing small samples in the laboratory. The uniaxial compressive strength of the coal was 3660 kPa (823 psi). Using various pillar strength formulae, the homeowner recommended that square chain pillars be at least 11 m (35 ft) wide. The coal company, however, desired to pursue optimum coal recovery in the safest and most economical manner. They engaged in three-dimensional finite element analysis of the section taking into account the complete stratigraphic sequence of the overburden. Results indicated that the section can be developed by 5.5 m (18 ft) wide entries at 21 m (70 ft) center-to-center. In retreat, the pillars can be splitted along both centerlines leaving a stump pillar of 5.5 m (18 ft) square at each of the four corners. The 5.5 m (18 ft) square stump pillars still maintained a safety factor of 1.5, although the safety factors calculated by various pillar strength

Jan 11, 1986

By Jorge Meza

El presente texto señala la aplicación del sistema de gestión de demanda y consumo de energía eléctrica en la fundición de Southern Perú. El sistema está compuesto por un módulo predictor de demanda eléctrica y un módulo de simulación del sistema eléctrico de la planta. El primero, se construyó utilizando redes neuronales con algoritmos de aprendizaje backpropagation, capaz de pronosticar la evolución horaria de la demanda eléctrica con un porcentaje de error cercano. Mientras que el segundo está basado en técnicas de estimación paramétrica, redes neuronales y ecuaciones matemáticas obtenidas por regresión estadística, que simula el comportamiento del sistema de energía eléctrica de la fundición. En ese sentido, los módulos facilitan una adecuada planificación, ya que permiten conocer el comportamiento de la demanda horaria y los patrones de consumo de la planta, incluyendo los componentes de la facturación. Así como las deficiencias energéticas y oportunidades de mejora, sobre la base del análisis de la información acerca de los equipos, procesos y planes de producción, así como programas de mantenimiento.

Sep 24, 2008

By James M. Riddle

A discussion of frequently asked questions may help individuals trying to interpret subsidence regulations or prepare permit applications. The subsidence permitting process involves just one part of the mass of Surface Mining Control and Reclamation Act regulations. But of the 18 main SMCRA sections, subsidence is critical to the permitting process for coal operators. It's an area in which applicants have had problems interpreting regulations and preparing permit applications. Of 22 western states, only Wyoming, Montana, Colorado, and Utah heave thus far received approval for their mining and reclamation plans. The other states are now involved in the permit application process and will be dealing with SMCRA regulations for the next year or so. Some state programs, when approved, may differ substantially from the federal SMCRA program. But, to be approved, the state programs must be deemed equal to or more stringent than the federal regulations. SMCRA regulations apply to any coal operation "that exhibits surface effects." Thus they apply to surface strip mines as well as underground coal operations. The regulations do not apply to hardrock mining operations. Since August 3, 1977, the government, industry, and the public have wrestled with SMCRA. They have struggled through an initial program with the US Geological Survey; a new agency, the Office of Surface Mining Reclamation and Enforcement (OSM); an interim program; and a "final" permanent regulatory program. Even now, OSM is reluctant to publish formal program guidelines because: •The regulations are still in the process of judicial review. • Some approvable state programs will supersede the federal regula¬tions. • The flexible regulations are open to interpretation, which is desir¬able to maintain. •Guidelines could be misleading until regulations and interpretations are revised and finalized.

Jan 12, 1980

By H. P. Hermance

Preliminary examinations of the Parker and Webb deposits were made by E. E. Maillott, Bureau of Mines engineer in July 1942. The chemical and spectrographic analyses included in this report wore made at the Eastern Experiment Station of the Bureau of Mines at College Park, Md., under the general supervision successively of S. M. Shelton and of Paul M. Tyler, formerly regional engineer, Eastern Region. Beneficiation tests were conducted under the supervision of Frank D. Lamb. The mineral exploration was under the general supervision of J. D. Bardill, formerly district engineer. Acknowledgment is gratefully made to the St. Joseph Lead Co., in particular to John S. Brown and P. J. Mechin for their assistance. Special acknowledgment is made to the American Metal Co., Ltd., ,Ind to T. C. Moore for furnishing core-drill and assay data; to the Universal Exploration Co. and P. B. Jennings; and to the Northern New York Mining Corp. and C. H. Sprague for their permission to publish the core-drill dta. Excellent cooperation was given by Dr. W; M. Agar and C, L. Rogers of the Geological Survey.

Jan 1, 1949

By Peter White

The Hemlo Gold District, located on the north shore of Lake Superior, was discovered in 1981 and will become one of the largest gold mining camps in Canada. Three major Canadian mining companies are presently developing large orebodies and are scheduled to commence production at various times through 1985 and 1986. This paper describes the types of shaft sinking equipment and technology being used by contractors in constructing the required shafts to depths below 1000 metres. The principal shaft design criteria, types of shaft sinking machinery and relevant manpower allocations are discussed.

Jan 1, 1985

By P. L. M. Wong, N. W. Johnson

Surface analysis by X-Ray Photoelectron Spectroscopy (XPS) of samples taken from the galena flotation section of the Hilton Concentrator of Mount Isa Mines Limited are presented. Flotation rate and pulp chemical data taken during the sampling period are also presented and discussed. Surface analysis suggested that, under normal operating conditions, an overlayer of precipitated calcium sulfate existed at the surface of the sulfide minerals. In particular, there was a decrease in the surface concentration of calcium sulfate for the concentrate samples relative to that occurring on the tailing samples. This suggests that the flotation process was selective against minerals which have calcium sulfate predominating at the surface. Heterocoagulation of hydrophilic calcium sulfate on to the galena surface considerably reduced galena flotation rate. Methods to control calcium sulfate precipitation, which include sodium carbonate treatment of the pulp, are also discussed. Sur- face analysis results of samples taken from the Hilton Concentrator during sodium carbonate addition to the grinding circuit are also presented. This shows clear evidence for the removal of calcium sulfate from the mineral surfaces without concomitant surface precipitation of calcium carbonate. Reasons for the apparent dispersion of precipitated calcium carbonate are discussed. Galena flotation rate was increased by the addition of sodium carbonate apparently due to the removal of interfering calcium sulfate.

Jan 1, 1995

By Robert F. Chaiken

An absorption-desorption model of particle reactivity was employed to describe the observed relationship between two apparently diverse phenomena which have been the subject of considerable study at the U.S. Bureau of Mines: (1) coal-rock dust reflectance and (2) coal-rock dust explosibility. The model accounts for heterogeneities in particle-size and material properties; however, in the present report, only particle-size distribution is considered. A mean particle-size parameter, appropriate to the explosion extinction process, is derived, and then taken as appropriate to describing optical reflectance. The derived form-to-function relationships for the two processes, when compared with experimental data, suggest that a problem exists with previously derived theory relating optical reflectance to rock dust concentration. A reexamination of that theory leads to a new theoretical expression, changed by a factor of 2, for the variation of rock dust concentration with reflectance which is in quite good agreement with experimental results. The current work offers justification for measuring and establishing rock dust requirements for specific coal dust size distribution(s) found in the mine-distributions that undoubtedly depend on the mining method and the type of coalbed.

Jan 1, 2010

An understanding of the origin of mineral deposits and their relationship to local and global geotectonics is essential if regional targets for mineral exploration are to be chosen. Volcanism, metamorphism and tectonism are especially significant for the origin and emplacement of mineral deposits, which, far from being fortuitous oddities of nature, occupy well defined positions within distinctive lithofacies. Thus, suggestions for mineral exploration targets can be made taking into consideration the position of 'fossil' convergent and divergent plate tectonic boundaries to indicate areas of specific types of mineralisation. To be borne in mind, though, that level of exposure, time and location of magma generation are all additional and important controlling factors. To further understand the importance of the above parameters, one must refer to the concept of paired metamorphic belts (Miyashiro 1973) which develop during an orognic cycle. These belts are generally constructed in such a way that an ophiolite type complex with metamorphic grades related to high pressure and moderate temperature regimes is flanked by an area of calc-alkaline volcanism and granitic activity with metamorphic grades within a region of high temperature and low pressure. The former situation is usually the seat of primary magmatic mineralisation, whereas the latter contains base metal. Deposits of acid plutonic and volcanic association. As will be seen later, this particular metamorphic-volcano-orogenic situation is well developed in some parts of New Zealand. For the present purpose a distribution of potential ores as related to plate tectonic processes is given below:a) Divergent plate boundaries: primary magmatic Ni-Cu, Pt,Cr, PeS2 and Cu, Pb,Zn in hot brines-hydrothermal environments Mn deposits.b) Convergent plate boundaries: stratabound Cu-Fb-Zn-Ag of felsic volcanogenic association. Porphyry eu-Au of island arc type, porphyry Cu-Mo of continental type. Cu, Au, Y, Sn, Hg, Sb of vein type and replacement lode related to granitic activity.c) Au of hydrothermal vein association, related to late dynamo-metamorphic events. By virtue of ocean floor spreading, regions of divergent plate boundaries are eventually juxtaposed or welded n to areas where plate collisions occur. This is then followed by partial melting due to various causes, just above the descending plate; thus creating a zone of acid to intermediate magmatism. The final picture is that of an orogenic zone with the paired metamorphic belts outlined above.

Jan 1, 1976

By Daniel Su

Approximately 90% of the primary roof bolts used in CONSOL?s Pittsburgh seam coal mines is 2-piece, 8-foot long, 7/8? (or ¾?), high-strength, resin assisted, mechanical shell tensioned bolt. The remaining 10% is the 2-piece, 8-foot long, 7/8? combination bolt, which employs 4 feet of fast resin to anchor the deformed rebar at the top of the hole. In either system, a 1-3/8? hole is required to accommodate the mechanical shell and the coupler. The cheaper torque-tension rebar system, which is typically fully-grouted with 2-speed resin and which typically provides low bolt tension, is not used in CONSOL?s Pittsburgh seam mines. Rather, it is used in CONSOL?s Central Appalachia mines, where the roof rocks have CMRR rating of 50 or higher. Fully-grouted headed rebars, on the other hand, are used in CONSOL?s room-and-pillar mines. The selection of tensioned versus non-tensioned, fully-grouted bolts for coal mine primary roof support has been debated for the past thirty years. Many researches have been conducted to understand the theoretical bases behind the two systems. This paper describes CONSOL?s experience of using a new fully-grouted, mechanical shell tensioned bolt in the Pittsburgh seam with the development of low insertion force resin.

Jan 1, 2007

The quantity, quality and detail of project information increases as project development moves from initial scoping level studies, to pre-feasibility and option studies, then definitive feasibility study and basic engineering stages. Data accumulates from metallurgical and vendor testing from various ore types and composites carried out to assess physical characteristics and processing responses of the ore. Over-simplification or assumptions about the orebody for flow sheet development can result in using æaverageÆ information for design. Use of averages of data can have adverse implications on sizing of plant and equipment and consequently on definitive study cost estimates and detailed engineering. In practice, the treatment plant workforce is faced with managing a non-homogeneous or non-average orebody in a variable operating environment that is not always predictable. This paper presents views on how to use the data generated from testwork in project development and for process and plant design. Examples of process design risk or operating risk are presented. Although this topic is applicable to the broad range of process design decision making in the minerals industry, this discussion references comminution, flotation and extraction processes for gold and base metal ores.

Jan 1, 2004

By W. M. Bangert, F. S. Boericke

"INTRODUCTION Determination of the thermodynamic properties of metallurgically important compounds of chromium has been one of the activities of the Pacific Experiment Station of the Bureau of Mines. Earlier reports have dealt with the entropies 4/ 5/ of chromium, chromic oxide, and chromous and chromic chlorides, with the thermodynamic properties of the chlorides of chromium, 6/ and wits the thermodynamic properties of the carbides and oxide of chromium. 7/ Evaluation of the thermodynamic properties of chromite, FeO.Cr2O3, is desirable, as this material in impure form constitutes the only natural source of chromium of any consequence.Two general methods are available for directly determining heats of formation - (1) measurement of heats of combustion and (2) measurement of heats of solution. Neither of these methods is directly applicable at present to ferrous chromite, which accounts for the lack of previous data. Combustion of a stoichiometrical mixture of iron and chromium under conditions prevailing in a calorimetric bomb yields a mixture of iron and chromium oxides rather than chromite. None of the usual calorimetric solution media dissolve chromite at temperatures low enough for solution calorimetry. Sulfuric acid and an oxidizing agent, such as MnO2 or CrO3, are known to dissolve chromite, but the possible calorimetric use of t is medium would require long preliminary investigation. Consequently, recourse must be taken to some indirect method. At the start of the present work, the most promising method appeared to be the determination of equilibria in the selective, reduction of the iron in chromite by hydrogen;"

Jun 1, 1945

By K. A. Grace

K.A. Grace's article advocates usage of the terms describing resources as defined by the US Bureau of Mines (USBM) and the US Geological Survey (USGS). Originally recommended in 1943, the terms were revised in 1976 and again in 1980. Mr. Grace further recommends that the term reserves should be severely restricted and that it should encompass mining and processing factors. The list of references quoted in the article does not, however, mention the study concerning reserves that was made over a period of almost four years by a joint Committee on Definitions. This committee was sponsored by three societies - the American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME), the Society of Economic Geologists (SEG), and the American Institute of Professional Geologists (AIPG). Most of the detailed work was done by a working party appointed by the Society of Mining Engineers (SME) of AIME. After studying previous definitions in the US as well as in the United Kingdom, Canada, Australia, France, and other European countries, the following definitions were proposed and accepted in 1974 by the SME board of directors. (Ore reserve definitions in Rhodesia, South Africa, or New Zealand were not mentioned as having been reviewed.) Table 1 lists definitions from MINING ENGINEERING, July 1975. Notice in Table 1 it was mentioned, under Resources, that the definitions of reserves were recommended for the purposes of commercial evaluation. It was further stated that the terminology adopted by the USBM and the USGS, as released to the public, covering resources, was recognized as such. Mr. Grace also recommends that reserve calculations should allow for future losses in ore tonnage, ore grade, milling, and smelting. Unfortunately, it might take years to develop a prospect after it has been discovered. Mining methods have to be tested before being finalized in order to know what tonnage of ore is going to be lost, or how much dilution is likely to occur. The same problems are present in concentrating or in smelting. Operating mines usually know how mined grade compares with ore reserve grade. They can usually predict fairly closely what their final metal recoveries are probably going to be. It is, however, expecting too much to have to delay quoting reserves from say a recently drilled prospect. Any responsible mining geologist or mining engineer (or company for that matter) should state several things about an ore reserve calculation: that it is or is not a preliminary estimate only; that estimated grades have not been diluted to allow for a future, as yet unknown, mining method; that metal recoveries are or are not only tentative, based perhaps on drill hole samples only or on no metallurgical testing at all. Reserves of a partially explored prospect are always quoted when it becomes necessary to raise capital. If they are described as preliminary only (really just tonnage and grade estimates and not true "reserves") in addition to being accompanied by some of the items just mentioned, nobody is going to be misled. If, on the other hand, a report by a member of the SME or SEG is intentionally misleading, the individual must be reported and eventually disbarred from his or her society. To summarize, let us stay with the definitions of ore, ore reserves, and related terms as recommended and accepted by SME. I might add that on occasion I have used a fourth category in my ore reserve calculations, namely Geologically Possible Ore. This category is more or less the same as Inferred ore defined by the USBM and USGS. I have never given a grade to this category, which may be based only on geological mapping, geochemical sampling, or geophysical traversing.

Jan 8, 1985

By T. T. Read, F. C. Houghten

"The bad effects upon the health and output of miners that result when the ventilating current in a mine lacks sufficient cooling power have been described by Harrington and Sayers in a previous report (1)*** The normal temperature of the human body is about 98.5°F. and whenever work is done by the muscles, indeed even when sitting still, the normal bodily processes generate heat which must be given off, otherwise the body will become overheated and a number of bad effects will be produced. If it were possible to so enclose a man that he could continue to breathe and no heat could escape from his body he would die within a short time. In a series of experiments made at the Pittsburgh Station of the Bureau of McConnell and Houghton (2) found that a dry-bulb and a wet-bulb temperature of 112.5°F could he borne for only 35 minutes, even when the subject was at rest. A wet-bulb temperature of 100.4°F (dry-bulb 157°F) could only be tolerated for 45°F minute. Under such conditions the bodily temperature rises as much as 45°F above normal and the pulse is accelerated. Very uncomfortable sensations are felt when the pulse rate exceeds 135. The human body, like any other internal combustion engine, must be cooled in order to function properly.Under ordinary circumstances the air surroundings people is enough coder than themselves to permit this heat generated within the boiy to be river off with¬out difficulty. At higher temperatures, or when the rate of work, with its corresponding generation of heat is high, the body can not throw off heat fast enough, so it begins to sweat and the evaporation of the sweat cools the body. But the results of the experiments cited above indicate that in still air, even with the body at rent, it can not adjust its temperature when the air is above 90° wet- bulb. J. S. Haldane (4) says ""at a wet-bulb temperature of 60°F the actual amount of work done by the miner begins to fall off; as the wet bulb temperature rinse farther the work Bona gradually diminishes to the vanishing point. Then the temperatures indicated by the wet-bulb exceeds 85°F hard work in a mine seems hardly or the commercial working of a mine the wet-bulb thermometer should not in generaI, be allowed to rise above 80°F, unless perhaps where there it a good current."

Dec 1, 1923

By Ron Board

"Probably the only thing that can he said about conveyor belt scales without fear of contradiction is that they have been responsible for as much or more puzzlement, argument and frustration than almost any other piece of equipment commonly found in ore processing facilities. To be sure, there are certainly a good number of satisfactory installations, some of these having been achieved through forethought and careful consideration in the early stages of plant design, while others seem to owl their success to what seems to be little more than good luck or white witchcraft; and it might also appear that black witchcraft or other gremlins are solely responsible for the poor performance of many belt scales that enjoy well-designed installations with apparently good operating conditions.This paper is intended to acquaint users with the major operational reasons why belt scales seem so fickle (and downright ornery too), and establish some reasonably simple test standards against which the performance of scale hardware can be measured. Then it shall be shown how the design flexibility of electronic scale systems can offer particular advantages in overcoming some of these everyday problems in a practical way, and without undue inconvenience to plant operations."

Jan 1, 1975

By L. C. IlsLey

Many accidents rightly classifiable as electrically caused are not so classified for the reason that in numerous accidents the part that electricity played in causing the fatality is only suspected. For instance, a workman might receive a shock that would cause him to lose his balance and fall beneath a trip of cars; if no one saw the first part of the accident, the cause undoubtedly would be charged to "haulage." This paper covers a brief study of fatal and nonfatal electrical accidents. The first usually result from direct contact with the electrical circuit or electrical apparatus; the second more often are the result of arcing or flashing due to handling defective apparatus or making repairs on "live" equipment or circuits. It is hoped that helpful suggestions may be offered for minimizing accidents of these two classes.

Jan 1, 1938

By A. U. Miller

Protection against fire is a greater problem at a coal mine, than at an ordinary industrial plant. Generally mines are located in isolated districts and do not have the protection of city fire departments; consequently fire fighting aquipment must be installed by the mining company. Fire protection around a mine is just as essential as it is in the city.. and undoubtedly is more important if the fire should be underground where many lives would be endangered and all means of escape cut off. A surface fire can generally be attacked from any angle, but an underground fire can be attacked only as conditions will permit.. U. S. Bureau of Mines engineers have investigated many serious mine fires that undoubtedly could have been extinguished in incipiency if a fire extinguisher or fire hose and water had been readily available. In past years very little attention was given..to fire fighting equipment and organization around mines, but in recent years three gen a derde hange of opinion among many of those engaged in mining, and nearly all up-to-date mining companies now have some kind of fire protection about their mine Probably the first company in Illinois to install regular fire fighting equipment and effect a fire fighting organization at its mines, was the Madison Coal Corporation, which operates several mines in Illinois. The main office of this company is in Chicago and the general field office is at Glen Carbon, Ill.

Jul 1, 1930

By Roberto Folchi, Hans Wallin

Having so many norms and technical content of legislation to deal with is a problem that an explo-sives engineer has to face, especially when working at an international level. Each country has its own norms and legislation, sometimes even each other region or state, as if the physics of explo-sions, rock, concrete, and masonry characteristics would change across the borders. Both norms and laws are frequently out of date, being mainly developed at the beginning of the previous century and adjusted, piece by piece, to a technical and political context that is constantly changing, with adjustment being frequently adopted in a hurry, due to a problem arising such as that of internation-al terrorism. Sometime also, norms are not harmonized with those they intend to amend, so required explanations and new adjustments lead to a vicious circle that increases confusion, complexity and depresses the explosive industry.

Jan 1, 2015

By M. King Hubbert

"The present large-scale use of energy and power by the human species represents a unique event in the billions of years of geologic history. Furthermore, in magnitude, most of the development has occurred during the present century. In the United States, the peak in the rate of petroleum production occurred in 1970 and that for natural gas is imminent. The peak in the world production of crude oil is expected to occur at about the year 2000 and that for coal production at about 2150 or 2200. For other sources of energy and power, water power, geothermal power and tidal power are inadequate to replace power from fossil fuels. Nuclear power, based on the breeder reactor and utilizing lowgrade deposits of uranium and thorium, has a larger potential than the fossil fuels, but it also constitutes a large perpetual hazard. The largest source of energy available to the earth is solar radiation. This source has a life-expectancy of a geologic time scale, is nonpolluting and is larger in magnitude than any likely requirements by the human s pecies. In consequence of the large supplies of available energy, the period since 1800 has been one of an unprecedented exponential industrial growth. This also has been accompanied by a world-wide ecological disturbance, including that of the human population. It can easily be seen that such a period of growth must be ephemeral in character and, in fact, is now almost over. One aspect of this transition from a state of exponential growth to a state of nongrowth is the present alarm over an ""energy crisis."" Actually, the world's present problems are by no means unmanageable in terms of present biological and technological knowledge. The real crisis confronting us is, therefore, not an energy crisis but a cultural crisis. During the last two centuries, we have evalved what amounts to an exponential- growth culture, with institutions based on the premise of an indefinite continuation of exponential growth. One of the principal consequences of the cessation of exponential growth will be an inevitable revision of some of the tenets of that culture."

Jan 1, 1973