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All the TECHNICAL PUBLICATIONS and CONTRIBUTIONS published in 1938 are available at Institute headquarters, unless otherwise noted. They are also on file in many public, university and technical libraries and, when so indicated in the list, may be found in the TRANSACTIONS. TECHNICAL PUBLICATIONS in Classes A-Metal A-Lining, B-Milling and Concen-tration, H-Industrial Minerals, and I-Mining Geology are distributed in MINING TECHNOLOGY, which is issued every other month. Technical Publications in Classes C-Iron and Steel Division, D-Nonferrous Metallurgy and E-Institute of Metals Division are distributed in METALS TECHNOLOGY, which is issued twice quarterly. TECHNICAL PUBLICATIONS ill Class G-Petroleum Division are distributed in PETRO-LEUM TECHNOLOGY, which is issued quarterly. TECHNICAL PUBLICATIONS in Classes F-Coal Division, .l-Mineral Industry Education Division, K-Mining Administra-tion, and L-Geophysical Methods of Exploration are issued as separate pamphlets. All Institute member is entitled to one copy of any TECHNICAL PUBLICATION or CON-TRIBUTION. Copies of TECHNICAL PUBLICATIONS listed have been mailed to members of the Institute according to their registration by classes. CONTRIBUTIONS and other TECHNICAL PUBLICATIONS will he sent upon request. A member may purchase an additional copy of a TECHNICAL PUBLICATION or a CONTRIBUTION at one cent. a page; in minimum charge, 256. If the TECHNICAL PUBLICATION has been published in METALS TECHNOLOGY, MINING TECHNOLOGY or PETROLEUM TECHNOLOGY, the number of either magazine containing it will be supplied at the sae cent a page (minimum charge, 25¢) rate for the particular TECHNICAL PUBLICATION requested. Nonmembers may purchase any CONTRIBUTION or a TECHNICAL PUBLICATION Of the F, J, K, or L classes at the same rate, butt the nonmember price per copy for METALS TECHNOLOGY, MINING TECHNOLOGY or PETROLEUM TECHNOLOGY is $1. TECHNICAL PUBLICATIONS (Separate pamphlet form), $2 per annum; Canadian and foreign postage 50 cents extra. METALS TECHNOLOGY, $7 per annum; Canadian and foreign postage 50 cents extra (Iron and Steel Division and Institute of Metals Division ferrous and nonferrous papers). MINING TECHNOLOGY, $6 per annum; Canadian and foreign postage 50 cents extra (metal mining, milling and concentration, Industrial Minerals Division, and mining geology papers). PETROLEUM TECHNOLOGY, $4 per annum; Canadian and foreign postage 50 cents extra.

Jan 1, 1938

By Alan R. Holt

"This paper provides an overview of the use of uranium and coal in Ontario Hydro's generation program. The dynamics of available supply sources including mining and transportation infrastructures and regional considerations are described. Included is a discussion of needed procurement strategies, both in place and planned, to meet fluctuating fuel requirements while ensuring adequate supply security and cost effectiveness. IntroductionDuring the first half of this century, Ontario Hydro or the Hydro Electric Power Commission of Ontario, as it was then known substantially supplied all of the province's electricity needs from a large number of hydraulic generating stations. Although hydraulic power still provides a very significant part of Ontario energy requirements, this paper will concentrate on the role of uranium and coal in their generation program. To provide a perspective on the importance of these two fuels, Figure I shows the approximate value of each for the past few years in relation to Hydro's total operating costs. The trend toward increasing nuclear output and a corresponding decline in coal use is also clearly illustrated.Figure 2 shows the currently installed capacity of their three main energy sources, hydraulic, nuclear and coal and the 1986 production totals for each, followed by Table I which compares the average operating or running cost on the basis of dollars per megawatt hour for each type of plant. It demonstrates dramatically why Ontario Hydro base load s its hydraulic and nuclear plants, and why coal has become the swing fuel on the system. Although they have a 1200 megawatt plant in Toronto with natural gas-burning capability, and a 2000 megawatt oil-fired station near Kingston, both are presently mothballed and have not been considered in this paper.This paper starts with a user's perspective of the nuclear fuel supply situation which will be discussed in relation to the usual considerations of security, flexibility and cost."

Jan 1, 1988

By Robert J. Hundhausen

The Young America lead-silver-zinc mine in Stevens County, Wash., was investigated by the Bureau of Mines during parts of 1946, 1947, and 1948. Results of the investigation are described herein. The mine is 1/4 mile northeast of Bossburg, Wash., the nearest railway station. An excellent paved highway (No. 22) connects Bossburg with Colville, Wash., 23 miles to the south. The property was located in October 1885. It is credited with a production of 2,178 tons of shipping ore since 1901. The shipping ore averaged 7 percent lead, 7.7 percent zinc, and 16.1 ounces silver per ton. The property is under lease and option to Walter E. Morris and Perry Leighton of Colville, Wash. The deposit crops out on a steep limestone bluff overlooking the Columbia River. The country rock is a highly metamorphosed, brecciated, marbleized limestone (Northport formation).

Jan 1, 1949

By Yongping Wu

Taking the longwall mining face area in a steeply dipping seam as the research object, the stability of an asymmetrical rock mass structure is analyzed using shell theory and masonry beam theory. The results show that an asymmetrical shell structure is formed at the top strata of the mining stope and its magnitude is mainly determined by the mechanical characteristic of the overburden strata of working face, mining space size and so on. Localized instability of the shell structure is the main factor that leads to the overall structural instability in the stope. The instability modes includes: the shell roof instability dominated by tensile failure, the shell shoulder instability initialized by compression-shear failure, and shell bases composite instability occurs in tensile and compression-shear modes. The shell structure stability dedicates rational strata control measures to choose, and the caving height of overburden strata is the key for shell structure instability.

Jan 1, 2013

By Alicia Esther Ares

The family of Zn-Al (ZA), Zn-Ag and Zn-Al-Ag (ZINAG) alloys offers high mechanical properties, ease of finishing, the advantage of low energy and pollution-free melting. Also, present alternatives to the well developed alloy systems, such as brasses, bronzes, cast irons and aluminum alloys. The main objective of this paper is to measure thermal parameters in ZA, Zn-Ag and ZINAG hypoeutectic and hypereutectic alloys directionally solidified which present columnar, equiaxed and columnar to equiaxed transition structures (CET). Also, estimate the mechanical properties, such as microhardness and tensile parameters and correlate these with the thermal (cooling rate) and structural parameters (grain size and dendritic spacing). The different types of structures were analyzed with optical and scanning electron microscopy. The results showed the influence of concentration, microstructural arrangement and thermal conditions during solidification on the mechanical properties. The results of the present investigation are compared with previous experiments.

Jan 1, 2010

By J. A. Finch

"Gas dispersion in flotation defines the efficiency of the process once the chemistry has been established. There are three measurements, superficial gas velocity, gas holdup, and bubble size, which along with the derived quantity bubble surface area flux, are used to define “gas dispersion.” Sensors for measuring gas dispersion in industrial machines have been developed. This communication describes the working principle of the techniques and illustrates their potential to detect problems and to improve the operation of individual cells, banks and circuits. IntroductionFlotation is the most widely used process to separate minerals and is finding increasing application in other chemical and environmental fields. The process exploits natural and induced hydrophobicity to collect selected particles on the surface of a bubble. Once the process chemistry to control hydrophobicity has been established, the efficiency depends on dispersion of air to generate the necessary bubble surface area. Bubble surface area flux, Sb, the interfacial area generated per unit time and unit area of the machine, is emerging as one of the most useful variables to quantify gas dispersion (Gorain et al., 1997, 1998) although not without its critics (Heiskenan et al., 2001).For a bubble population of mean size db at a superficial gas velocity (or rate) Jg, the bubble surface area flux can be derived from geometric considerations (Finch et al., 1999):"

Jan 1, 2002

By S F. Wang, J J. Yin

Dust pollution poses a persistent challenge within mining processes, giving rise to a spectrum of concerns, including occupational diseases, mechanical degradation, diminished visibility, and the potential for dust explosion incidents. Existing dust detection and monitoring methodologies face limitations, including insufficient measurement accuracy and intricate processing procedures. Consequently, a comprehensive identification and evaluation system rooted in image processing technology is proposed to facilitate real-time measurements of dust pollution in mining worksites. The study primarily employs grey scale average and fractal dimensions to characterise particle features evident in collected dust images. As a result, the data processing platform can dynamically process data and present dust pollution conditions. Notably, this research integrates the monitoring and assessment of dust pollution with the systematic adjustment of mining parameters, ventilation parameters, and strategies for dust reduction. Through statistical analysis of dust concentration and particle size during mining processes, rock properties such as components and cuttability can inform mining parameters. This information, in turn, guides detailed excavation strategies, including cutterhead speeds, torque, and excavation speed. Similarly, analysing dust characteristics derived from images is a valuable resource for gaining deeper insights into the efficacy of implemented ventilation strategies. By harnessing vision-based information detailing dust concentration and distribution, a wealth of direct guidance becomes available for refining ventilation parameters. This encompasses crucial aspects such as the selection of appropriate ventilation systems tailored to the specific mining environment and the optimisation of operational conditions for ventilation fans. Additionally, the detailed information derived from the visual data allows for strategic decisions on factors like the spatial arrangement of ventilation outlets and the calibration of airflow rates. Moreover, precise choices for dust reduction measures and parameters can be made based on the prevailing dust conditions. Upon real-time monitoring of dust pollution using the proposed method, corresponding measures such as spraying and foaming can be promptly implemented. Crucial parameters, such as spray angles and volume, are integral to these application processes. In essence, the proposed method assumes a pivotal role in not only dust monitoring but also the formulation of preventative and control measures within mining processes.

Sep 1, 2024

By T. R. Bieler

"Hot forming and superplasticity in powder metallurgy aluminum alloys and composites is reviewed. The effects of alloy composition, particulate composition, size, and size distribution is summarized. The role of climb distance for recovery is described in connection with the size of strengthening phases. In materials with fine strengthening phases on the order of one micron or less, high strain rate superplastic deformation processes are likely. However, the quality of superplastic deformation depends on the prior processing history, and these effects are reviewed. Very few data describing the effects of hot forming history on post-forming properties exist, but some results emerging in the literature are compared.IntroductionHot deformation in aluminum based materials is done for several technological purposes, such as thermomechanical processing to alter mechanical properties of simple forms, and/or final shaping operations to produce a complex shaped part by means of extrusion, forging, or superplastic forming. In the interest of improving the mechanical properties of aluminum based materials, two microstructural design strategies are commonly used, dispersion strengthening, and composite strengthening. The introduction of fine, stable dispersions is commonly done for high temperature strength, and the dispersions are typically ceramic particles in the range of 10 nm to 1000 nm in volume fractions around 5 vol.% (Higashi et al., 1990; 1991a; 1991b; 1992; Bieler and Mukherjee, 1990; Otsuka et al., 1987; Bieler et al., 1991; Oliver and Nix, 1982). Alternatively, composite strengthening strategies using 10-40 v% of 3 µm to 40 µm ceramic particles provide high modulus and high strength aluminum based materials (Midling and Grong, 1995; Lloyd, 1994; Subramanian et al., 1995)."

Jan 1, 1997

By Joseph T. Duncan, Syd Peng, Larry G. Stolarczyk

The mining business has numerous risks: equipment availability, labor disruptions, foreign exchange rate, etc., but one of the more important risks is assessing the geology. Improving the “intelligence” of geology can and will have significant positive effect on reducing mining risk and thus enhancing operational and financial performance. The use of the advanced Radio Imaging Method (RIM-IV) on coal seams and ore bodies can create useful two-dimensional (2-D) and three-dimensional (3-D) high-resolution images that provide mining engineers with additional intelligence to better plan and improve operations. Improved operational performance will reduce costs and enable mining companies to meet market and financial commitments. For the past decade the underground coal mining industry has been moving toward “super panels” in long-wall mining, and “super sections” for room-and-pillar mining. These mining conventions employ wider faces, longer gate roads, greater room-and-pillar density, and an increased scale in the amount and complexity of mining equipment. An obvious economy of scale exists: amortization of setup investments over greater volume of coal enables mine management to reduce fixed cost per ton. Restricted by equipment considerations, face widths have currently reached about 1,100 ft. Wider longwall panels are planned, with 1,400-ft widths, but this requires an incremental step in hardware that the original equipment manufacturers will soon bring to market. However, longwall panel length has not yet reached its limits, with some panels planned up to 25,000 ft. While longwall panel length is generally dictated by reserve size and extent, practical restrictions in mine planning also include seam thickness, ventilation requirements, or restrictions involving methane drainage. Super panels have certainly enabled the industry to keep pushing the limits of productivity improvement. However, important considerations in mine planning, now and especially in the future, will be driven in large part by geological factors. While larger developments improve productivity and capture economies of scale, the fact that super panels can contain at least four times the area or coal volume means that the probability of encountering serious anomalies is at least four times greater than with the “conventional” panels. Given the increased probability of encountering anomalies, improved assessment of geology is important for super panels and super sections. Proper due diligence requires a thorough and competent evaluation of a mining property and its ore reserve. Using improved geostatistical techniques is most important, and improving the base data for the analysis is equally important. The old cliché “garbage in, garbage out” certainly applies. Also, the quality of coal reserves is (or has been) declining, so, in the future, mining will be in deeper and most likely thinner seams—and these seams appear to contain greater anomalies that threaten efficient operations. To counter the impact of reserve deterioration, the industry is moving toward greater use of geophysical tools and services. Fortunately, tools such as the Radio Imaging Method™ (RIM-IV) system have been improved and can provide the industry with enhanced 2-D and 3-D images of coal seams and ore bodies. To identify and profile the best areas of a coal reserve, geologists, engineers, and mine managers need greater intelligence in the form of RIM-IV tomographic maps of longwall panels and room-and-pillar sections. These images have enhanced the understanding of in-seam features, which in turn has improved operational plans and performance.

Jan 1, 2005

By Rolando Fuentes

El artículo discute la importancia de cada uno de estos 5 elementos, que son: (1) control y aseguramiento de la calidad, (2) distribución de la carga explosiva en la columna; (3) técnicas de múltiples iniciaciones de carga; (4) energía explosiva y (5) Secuencia de iniciación. Finalmente, aplicando técnicas de modelamiento numérico, se pone a prueba un par de elementos de esta técnica, al comparar un diseño estándar de carga explosiva para voladuras de mineral, en rocas de alta competencia con un diseño de VAD. Las curvas de DTP se comparan para cuantificar el impacto que una mejor distribución de tamaños, con mayores contenidos de tamaños finos, genera en el tratamiento de minerales y, por lo tanto, en una mejora sustantiva del negocio minero.

Sep 29, 2023

By Paul M. Linebarger

This paper is one of a series of digests of foreign mining legislation and court decisions prepared in advance of a general report relative to the rights of American citizens to explore for minerals and to own and operate mines in various foreign countries. This interpretation of the laws of Mexico has been pro oared from the best information available in Washington but is released subject to correction and amplification, if necessary, by the proper American diplomatic and consular officers, to whom it has been referred through the courtesy of the Department of State. INTRODUCTION Present-day Mexican mining legislation involves, not only the latest minim enactment (August 1, 1026), but many other enactments and regulations, principal among which are the Constitution, the Civil Code, the Code of Commerce, the Foreign Law, the Mining Tax Law, and. the Civil Jurisprudence of Mexico--the last-mentioned being based in Dart on Supreme Court decisions. Ere Mexican Federal Government is supreme in mining legislation because, among other reasons, a large part of the revenue of the Government must come from the fiscal control of the mines. All circulars, decrees, and rulings that affect the mines not only have their origin in the Central Government but are administered thereby. The Department of Industry, Commerce, and Labor is in control of all mines. Attention may here be called, however,

Jan 1, 1929

By Thomas Cox

The following compilations are made from a series of investigations and are used to present the subject in an unbiased manner, as the writer does not represent any company or financial interest. The present situation is complex. The producers are hard pressed by reason of the low price of crude, while the independent refiner is little better off, because of the corresponding cut in price of refined products, except on occasional contracts. If the real costs are analyzed, it will be seen that the land speculators and the lessors—royalty owners—make the larger profits and not the struggling legitimate operator or independent refiner. The present-day (October, 1922) posted prices per barrel for crudes are Kansas, Oklahoma, Mexia, Gulf Coast, and Louisiana..... $1.25 Healdton............................................. 0.75 Northern Texas and Central Texas...................... 1 . 50 Pennsylvania......................................... 3.00 Wyoming, Elk Basin.................................. 1.25 Wyoming, Salt Creek................................ 0.70 California Base..................................... 0.60 These prices are at the well. In addition, crudes must be gathered and transported to refinery (by pipe line or tank cars), refined, and the refined products marketed. These crudes are of various gravities, ranging within a narrow margin for each field or district, so that averages are not difficult to deduce, and it is these averages that really determine the average operating conditions. In order to show the present realizations, the prices and costs now obtaining are listed against the average yields; the figures are also adjusted VOL. urn.----71

Jan 1, 1923

By Thomas Cox

The following compilations are made from a series of investigations and are used to present the subject in an unbiased manner, as the writer does not represent any company or financial interest. The present situation is complex. The producers are hard pressed by reason of the low price of crude, while the independent refiner is little better off, because of the corresponding cut in price of refined products, except on occasional contracts. If the real costs are analyzed, it will be seen that the land speculators and the lessors—royalty owners—make the larger profits and not the struggling legitimate operator or independent refiner. The present-day (October, 1922) posted prices per barrel for crudes are Kansas, Oklahoma, Mexia, Gulf Coast, and Louisiana..... $1.25 Healdton............................................. 0.75 Northern Texas and Central Texas...................... 1 . 50 Pennsylvania......................................... 3.00 Wyoming, Elk Basin.................................. 1.25 Wyoming, Salt Creek................................ 0.70 California Base..................................... 0.60 These prices are at the well. In addition, crudes must be gathered and transported to refinery (by pipe line or tank cars), refined, and the refined products marketed. These crudes are of various gravities, ranging within a narrow margin for each field or district, so that averages are not difficult to deduce, and it is these averages that really determine the average operating conditions. In order to show the present realizations, the prices and costs now obtaining are listed against the average yields; the figures are also adjusted VOL. urn.----71

Jan 1, 1923

By Richard L. Bullock

The hard rock mining industry has long envied its counterparts in underground mining of evaporites, coal and soft iron ore, who have made great strides in productivity using mechanical excavators. Continuous mining machines produce large tonnages in Canadian potash mines and in modern longwall coal mines. Hard rock is defined here as having an unconfined compressive strength (UCS) of more than 124 MPa (18,000 psi). Silica content, rock quality designation (RQD) and fractures affect the ability of mechanical tools to excavate rock, but the UCS is the main factor. Much research and development work has been devoted to continuous mechanical mining of hard rock, and the technology continues to improve. A few commercial applications have been reported. The development process has been slow and costly, but the outlook for the technology has never been more promising. The current state-of-the-art of continuous, mechanized underground mining technology is reviewed here, with examples of commercial applications that have been tried in recent years.

Jan 1, 1994

By R. K. Hopkins

For a great many years fusion welding has been used in and around petroleum refineries, but it is only within six or seven years that the more important pressure vessels have been constructed by this process, because before that time the properties of fusion welds would not with-stand such rigorous service. Since the adoption of fusion welding for the construction of this equipment, the refiner has required pressure vessels suitable for operation over a very wide range of conditions. On the one hand, vessels must operate at extremely high temperatures, in the range of 950° to 1000° F., and on the other vessels must be suitable for operation at sub-zero temperatures down as low as -75° F. Also, vessels are required suitable for operation at pressures upwards of 1000 lb. per sq. in., and as low as a 29-in. vacuum. In addition, vessels are required to withstand the attack of very corrosive mediums. It has been a rather difficult task for the fabricator to meet all of these require-ments, but as a result of the extensive research carried on by steel manu-facturers and several fabricators of class I vessels, practically all of these demands have been met. In order to meet the refiners' requirements for this wide range of conditions, the fabricator has worked closely with the metallurgist. This has enabled him to choose the proper base metal for each service condition, but it has been the fabricator's problem to develop a welding rod and welding technique, as well as a heat-treatment, that would produce in the welded vessel characteristics in and around the weld comparable to those in the base metal. Where corrosion is not a serious problem, and where the operating temperatures are not too high, ordinary carbon steel has served very well. But when corrosion is serious, and/or when the temperatures are either very high or very low, it is necessary to use some form of alloy steel to give satisfactory service.

Jan 1, 1935

By A. E. Harnsberger

IT is obvious that details such as the physical and chemical properties and methods of heat-treating of the materials mentioned must be omitted in a paper on the subject of materials used in oil-refinery pumps1. Only sufficient identification is given to enable the reader to find additional information from already published data. Also, the subject covers many operating conditions, but only the most important services can be discussed here. To the oil refiner, the pumping equipment is of vital interest. Practically every refinery operation, from the charging of crude oil to a distillation unit to the shipping of refined products, involves some form of pumping machinery. Intermediate refining stages involve a great variety of pumping machinery to carry out successfully the aims of the refinery technologist. Temperatures at which oils are handled vary from -50° F. to 900° F. Pressure may vary from subatmospheric to 2000 lb. per sq. inch. The selection of the proper materials involves a careful consideration of the conditions under which the particular pump must operate. The four, most important considerations are temperature, pressure, corrosion, and abrasion or wear. Consideration of temperature may be divided into three parts: (1) extremely low temperatures of the order of -50° F.; (2) temperatures at atmospheric or slightly above; .(3) temperatures from 200° to 900° F. Pressures fall into two groups: (1) pressures reached by ordinary trade pumps of the order of. 200 lb. per sq. in., (2) extreme pressure conditions involving pressures as high as 2000 lb. Noncorrosive and corrosive oils can be treated differently. Under the latter falls corrosion in the presence of water, which will occur up to 250° F. The second type of corrosion occurs in high-temperature pumping equipment, with temperatures from 450° to 900° F., largely caused by sulfur compounds. There are also other corrosive conditions met with

Jan 1, 1935

By D. M. Loring

Radon progeny have been a health and safety concern for miners since the mining of radioactive minerals began. Through the ?nuclear age?, it has become better understood and the regulations have become more robust. Ventilation and control practices have improved, thus reducing miners? exposures. This paper provides an overview of radon in mining, the progress of the regulations, and discusses some of the uranium miner studies that contributed to the knowledge of the pathology of radon.

Jan 1, 2009

By David Scott

THE MOGOLLON mining district, New Mexico, has received little public attention, although for 15 years it has been the leading silver producer of the state; it is situated in a region remote from the principal lines of travel, and its activities have usually been limited to the operations of two or three companies. The value of the total production of the district in the 44 years of its history has been estimated at $15,000,000. For the years 1904 to 1917, inclusive, the output was: gold, $4,370,000; silver, 10,042,000 oz.; copper, 874,862 lb.; total value, approximately. $10,500,000. In 1913 the district contributed 80 per cent. of the total silver production of New Mexico, but in 1917 only 41 per cent., due to serious interruption in the operations of the leading producer. Since 1914 the silver output has diminished one-half, and the present high value of silver is nearly offset by the increase in cost of production. The output of gold has rarely exceeded 35 per cent, of the total for New Mexico. The ratio of silver to gold, by weight, has averaged 46:1 based on the whole output of the district. LOCATION AND TOPOGRAPHY The town of Mogollon is 75 mi. (121 km.) by a poorly located highway from the nearest railroad terminals, at Silver City and Tyrone. All supplies are transported by motor trucks and teams. The area, sometimes called the Cooney Mining District, lies on the western flank of the Mogollon Mountains, which occupy the western part of Socorro County. The elevations drop steeply on the west to the valley of the San Francisco River, adjacent to the Arizona boundary. The topography is very rugged, the whole area being sharply dissected; deep canyons with steep gradients and rugged walls are characteristic of the whole western-slope of the Mogollon Range. The main canyons run east and west, and usually maintain a flow of water during the entire year. As would be expected in a region of such deep dissection, the

Jan 2, 1920

ADDRESS BY THE PRESIDENT OF THE INSTITUTE (MR. J. G. SYMONS) IN PRESENTING THE CERTIFICATE TO ROBERT COLVILLE BRADSHAW, O.B.E.Today it is my privilege and pleasure to introduce to you, Robert Colville Bradshaw. O.B.E., the third New Zealander to be honoured with Honorary Membership of The Institute. Sir William Hudson and Mr. C. H. Benney were the others.Mr. Bradshaw has been an Affiliate Member of The Institute since the formation of the New Zealand Branch in 1966. Like his friend Matt Benney. Bob Bradshaw is an accountant by training. Last June he retired as senior partner of the firm of chartered accountants, now known as Wilkinson Wilberfoss, with which he served from January 1929.Mr. Bradshaw grew up in New Zealand attending the Terrace School in Wellington, the New Plymouth Boys' High School where he was a boarder, and completing a Bachelor of Commerce at the university now known as the Victoria University of Wellington. He is an elected Fellow of the New Zealand Society of Accountants and an Associate of the United Kingdom Institute of Cost and Works Accountants.

Jan 1, 1977

By H. H. Schrenk

Much has been written and said concerning tables of permissible or maximum allowable concentrations of various toxic substances in air, but not enough attention has been given to their limitations and how to use them intelligently . There is a tendency to place too much reliance on figures , with little or no consideration of their real meaning . The repeated publication of a figure often adds significance to it far beyond that intended by the original author or publisher . How are these figures referred to as "maximum allowable concentrations " established? What is their real meaning? To answer these questions it is necessary first to define maximum allowable concentration . The usual definition is somewhat as follows : "The average concentration to which an industrial worker can be exposed for 8- hours daily for an indefinite period without injury or occupational disease . This definition is made up of the following items : ( 1 ) Average concentration, ( 2 ) 8 - hour day , ( 3 ) indefinite exposure period , and ( 4 ) lack of injury or occupational disease . There is some controversy regarding item ( 1 ) , items ( 2 ) and ( 3 ) are usually though not invariably accepted , and there is definite disagreement regarding the interpretation of item ( 4 ) . . To reach a more satisfactory interpretation of maximum allowable concentration , attention is directed to ( 1 ) the development of tables of maximum allowable concentrations , ( 2 ) criteria on which limits are based , and (3 ) methods used to obtain data on which limits are based .

May 1, 1948