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By Ernest B. Snyder

The word "line" has been used loosely for many forms of the common steel plant flux. For example, many people use the word "lime" for nigh calcium and dolomitic limestone, for high calcium and dolomitic quicklime (also called caustic lime, calcined lime; burnt lime, pulverized and pebble lime) and ;van for clinkered dolomite. Calcium hydroxide, also called slaked lime and hydrated lime, is called "lime" but is seldom used as a flux except when the quicklime air slakes in open boxes or bins. All of the above forms of "lime" are used in the steel plant. Calcium hydroxide is used for water treatment, acid neutralizing, and as a lubricant for wire drawing. All the other limes are used as fluxes in the sintering plant, blast furnace or steel producing furnaces. In the production of self-flux or super-flux sinter, high calcium and dolomitic limestone fines are used. Where quicklime fines are available, they may be added to the sinter mix also. The blast furnace uses both high calcium and/or dolomitic limestone. A few trials have been made using iron oxide stabilized dolomitic lime in an attempt to reduce coke consumption and to increase the production rate. The trials were very successful but would' not be economical, except in periods of coke shortages, with resulting extremely high coke cost and exceptionally high hot metal demand.

Jan 1, 1979

By B. D. Hong

The Coal supply and demand review arrived too late to appear in the May issue. In 1991, the US coal industry produced 902 Mt (994 million st) of coal, according to preliminary data compiled by the Energy Information Administration (EIA) (Table 1). This amount was 32 Mt (35 million st) less than the record 933.5 Mt (1 billion st) produced in 1990. Most of the decrease in coal production occurred east of the Mississippi River. The substantial stock buildup that stimulated production in 1990 was not repeated in 1991. In addition, coal consumption by electric utilities and coke plants dropped by about 1.8 Mt and 4.5 Mt (2 million and 5 million st), respectively. Moreover, a higher level of coal exports failed to bolster the 1991 production. Production Surface mines accounted for about 59% of the 902 Mt (994 million st) of coal produced in 1991. Underground mines produced for 41%. More than one-fourth of the total coal output was from federal and Indian coal leases. Production of all ranks of coal, except subbituminous, declined in 1991. Bituminous coal is produced mainly in the East. It totaled an estimated 590 Mt (651 million st), a 6% decrease. Production of subbituminous coal, mostly in the West, rose 3% to a record 228 Mt (252 million st). Lignite output was from Texas and North Dakota. It decreased by 1 % to 79 Mt (87 million st). Anthracite production, all from eastern Pennsylvania, fell by 17% to 2.7 Mt (3 million st).

Jan 1, 1992

By V. F. Swanson

A mathematical model is presented which allows the free or hindered settling velocity to he calculated for any size or- shape particle in any fluid, and at any percent solids up to the maximum. The validity of the model is supported by comparing calculated velocities (or viscosities) with measured values for 1073 data points contained in 80 sets of data encompassing a range of Reynolds’ numbers, from 0.002 to 770.000. The average error was 0.69%, with an average standard deviation of 6.65%. The derivation of the model is too lengthy to include in this paper, which will specifically present the application of the model to the free settling of minerals and spheres, prediction of the friction factor in wind tunnel tests, the viscosity of suspensions of spheres, the hindered settling of mono-sized spheres and closely sized minerals, and the settling of large spheres in suspensions of small spheres.

Jan 1, 1990

By B. J. K. Sullivan, Brian Hornsby

INTRODUCTION Mount Isa Mines Ltd. operates a copper and silver- lead-zinc property at Mount Isa in northwest Queens- land, Australia. Mount Isa is located in the tropics at latitude 20°43'S and longitude 139°30’E (Fig. 1). It is on the upper watershed of the Leichhardt River and at an elevation of 365 m above sea level. The average rain- fall is 360 mm/y, the greater part of which falls in January to March (the hot summer months). The mean summer temperature for these months is 30°C (dry bulb), with a maximum temperature of 43°C; the mean wet bulb temperature is 25°C with a maximum of 28°C. Mount Isa is located geologically towards the western edge of the Precambrian Shield of northwestern Queensland. This complex forms a north-tilting dissected peneplain which extends in the north-south direction for 640 km, with widths varying from 32 km to 190 km. The combination of differential erosion, regional strike, and steep dips has produced a corrugated topography of low north-south orientated hills and valleys. The field was first discovered in 1923 as a silver- lead-zinc field. Mount Isa Mines Ltd. was formed the following year and subsequently became the sole operating company on the field. Lead and copper ore have been mined and treated separately and simultaneously at Mount Isa since 1953. Intensive exploration commenced in 1954 and an active exploration program provided the justification for a series of production expansion programs in both silver- lead-zinc and copper (see Table 1 ). The most recent and largest production expansion program at Mount Isa commenced when a decision was reached in December 1969 calling for an increase in copper production from 100 000 to 150 000 t/y of blister copper. A major factor which influenced this decision was the substantial additions to the ore reserves in the so-called 1100 ore body which is a massive copper sulfide ore body with a known strike length of approximately 2500 m, a height which is variable up to 300 m, and a width of generally 300 m up to a maximum of 370 m (see Figs. 2 and 3). Host to the copper mineralization is a complex and variable rock generally called "silica dolomite." The ore body strikes 6.02 to 6.1 rad (345° to 350°), dips west between 0.78 and 1.13 rad (45° and 65°), and is truncated at depth by fault implaced basement rocks. It first occurs some 600 m below the surface and bottoms at about 1000 m below the surface. The unconfined compressive strength of the silica dolomite ore varies from 150 to 250 MPa, whereas the basement rocks, carbonaceous mylonite, slaty shale, buck quartz, and greenstone (a chloritic schist) are considerably weaker, varying in strength from 20 to 80 MPa. The distribution of mineralization within the ore body is variable, but can be considered as generally high grade at or just above the basement contact and diminishing towards the upper reaches of the ore body. The current

Jan 1, 1982

By B. Cavender

Mining managers trying to rapidly reduce production costs tend to implement a traditional set of topdown managerial practices: reductions in production volume, employee layoffs, renegotiation of supplier contracts, cancellation of employee training, restrictions on travel, reductions in office supplies, and so forth. While these practices do reduce costs, the benefits are often limited in both magnitude and duration, and the workforce is usually left demoralized. Successful cost-cutters take a different approach. They make the continuous reduction of costs a priority for all members of the organization, whether managers or workers. The culture of these firms emphasizes the commitment, voluntarily given, of individuals and work groups to this goal. Cost-cutting practices often reject all of the traditional methods mentioned above, but are far more numerous, innovative and successful. This culture of cost reduction is the result of a set of leadership competencies that establish direction for the organization, align the organization's various constituencies with this direction, and motivate and inspire the organization. Cost reduction then becomes a routine task rather than a heroic achievement.

Jan 1, 2002

By Ali Ekrem Aritan

Exposure to hand-arm vibration (HAV) among the labor force in the mining industry can result in permanent vibration diseases such as behavioral disorders, visual impairment, osteoporosis, pain (mostly in the hands, wrists, and shoulders), circulatory system disorders, and malnutrition. In this study, the vibration exposure of excavator operators working regularly in 25 different natural stone quarries was measured. In addition, the relationship between vibration exposure and rock properties was investigated. Gloved and ungloved vibration measurements were performed and revealed that antivibration gloves reduce excavator operators’ vibration exposure by 7.10–25.95%. Samples from each quarry were characterized with rock mechanics tests. The correlations between the hand-arm vibration measurements and the natural stone physical–mechanical properties (uniaxial compressive strength, Shore hardness, Knoop hardness, apparent density and total porosity) were determined to be over 70%. One finding of the study was that the health risk in excavators cannot be reduced sufficiently by the sole use of antivibration gloves. Furthermore, the excavation of any rock with a Knoop hardness above 121 is associated with an 81% risk of HAV. To increase awareness of the danger of vibration exposure for natural stone miners, training programs should be provided, and technical and operational changes should be implemented.

By T. N. Moore, E. M. De Souza

Vibratory hand-tools can produce Hand Arm Vibration (HAV) Syndrome in their operators. This disease, often called Vibration White Finger, can cause varying levels of hand-arm discomfort and, in severe cases, impairment. In addition to the human suffering, there are also significant economic repercussions for industry. These include reduced operator efficiency, lost time through increased absenteeism and increasing compensation awards. In the mining industry, jackleg rock drills are a particularly troublesome source of hand vibration exposure. As a result, a significant amount of work has focused on redesigning rock drill handles to minimize hand-transmitted vibration. This paper details the results of a study undertaken to determine the effectiveness of using elastomer covered ("cushioned") handles in place of the standard steel design. The results indicate that, for a particular cushioned design, the overall acceleration level experienced at the hand-handle interface can be reduced by as much as a factor of three, relative to the steel handle. It is also shown that this reduction takes place predominantly in the frequency range above 500 Hz, with performance improving with increasing frequency. Qualitative evaluation of the cushioned handles by the drill operator indicates a significant increase in comfort over the standard steel handle.

Jan 1, 1992

By Joe Komadina

DOUG HALBE: Our next topic is one that I would think everyone might want to contribute to. I'm sure everyone here has had some experience in this area. If you haven't, I'd suspect you've never really run a mill. This is what we call "Horrible Spill Areas We Had When We Started Up the Plant and How We Fixed Them." Our next speaker has had a really great operating career. He had many years with Newmont in the Carlin area, and now he's executive vice president and chief operating officer of Independence Mining Company: Jim Komadina. I don't have to be nice to the speakers anymore, do I? [laughter] You may wonder why we picked Jim Komadina to give this talk. I was involved many years ago in the start-up of Newmont7s Gold Quarry plant. Jim held quite a responsible position there. I'm not going to say anymore, but I have in the back of my mind this picture of the pump floor and a rowboat and a guy rowing around on the pump floor. [laughter] Jim, was that you? [laughter] JIM KOMADINA: Probably. I wasn't responsible for the design. [laughter] Actually it's amazing. I've seen a lot of these plants and actually had the opportunity to walk around them, so when I say this, "Horrible spills I have seen and done," it's because I've been responsible for more than my fair share of them. But having seen a lot of spills, I will present a little bit of wisdom about how to prevent them.

Jan 1, 1998

By John Brouwer

Through the use of good preventive maintenance procedures in which the work of both production and maintenance personnel is well-coordinated, production downtime can be drastically minimized, and costly repairs and interruptions in planned maintenance and production schedules can be eliminated. There had been some conflict in the past between production and maintenance people over the proper method of achieving maximum machine performance. The usual practice was to operate production equipment at maximum capacity for the longest possible time until breakdown occurred, and then make hurried repairs to get back into production. In most cases, these repairs involved unscheduled work and were thus performed inefficiently. Both production and maintenance have the same objective: to produce a quality product at maximum efficiency and at minimum cost. Preventive maintenance is a common tool available for both production and maintenance personnel to achieve this objective. Actually, one of the main objectives of preventive maintenance is to find any abnormal machine condition that may cause machine failure before a breakdown occurs. This makes it possible to plan and schedule maintenance work with the least amount of interruption and plan production volume with a higher rate of accuracy. Maintenance people prefer to perform this work on a scheduled basis and get away from the "crash" situation that accompanies breakdowns. They thereby increase the utilization of available manpower and machine time, prolong equipment life, and improve maintenance costs.

Jan 1, 1979

By William R. Groseclose, Cecil E. Tackett

Since 1965 when the first mole was used on Bureau work, the Bureau of Reclamation has completed 17 tunnels of over 5,000 feet in length. The longest was 12.8 miles. Total length of the 17 tunnels was 376,207 feet, or over 71 miles. The finished diameter varied from 7 feet 0 inch to 18 feet 0 inch with 82 percent (58 miles) being less than 12 feet 0 inch in diameter when lined. All of these tunnels except one are gravity flow, water conveyance tunnels with relatively flat gradient. One is a low-head pressure tunnel. All were constructed by contracts resulting from fixed-price bids. Starting in 1964 the Bureau of Reclamation initiated the practice of giving several options in the specifications on methods of tunnel excavation. Since that time, construction work has been completed on 17 tunnels. Of this number, 11 were mole excavated and 6 were excavated by conventional drill and blast methods. In general, there has been 2 feet of mole excavation for every 1 foot of drill and blast. Cost comparisons are based on only 13 tunnels because the Bureau has 4 recently completed tunnels that have pending claims; therefore, final cost data are not available. Some definite trends show from the data available; however, the number of completed tunnels in some categories is so small the results cannot really be considered a trend. As more data become available, the indications will become more reliable. The information is presented to indicate general trends and comparisons and cannot be meaningfully used for a one-on-one comparison because of individual tunnel differences not considered.

Jan 1, 1974

By M. K. Boateng, K. Awuah-Offei

"Language barrier in a workplace affects workers’ productivity and safety. The objectives of this paper are to: (1) review the various approaches for breaking language barriers among miners; and (2) analyze the costs and benefits of these approaches, and make recommendations on the way forward. The authors achieve these objectives by reviewing the current approaches in breaking language barriers among miners. The review reveals that some of these approaches can be expensive with less benefits. Thus, it is concluded that mining companies should carefully select the optimal approach to break language barrier. INTRODUCTION Multi-national mining companies have expanded their operations into non-traditional mining destinations to grow and meet market expectations. For instance, Newmont Mining Corporation has about 14 operations and projects located in Africa, Asia, Australia and America (Newmont Mining Corporation Operations and Projects, 2015). Similarly, Freeport-McMoRan operates about 14 mines in North America, South America, Southern Asia, and Africa (Freeport-McMoRan Inc., 2015). Some mining companies have also attracted expatriate workers into their workforce. For example, Ma’aden, the Saudi Arabian mining company, in its 2013 annual report states that 34% of its total employees are expatriates (Ma'aden, 2013). Expatriates constitute a key source of skilled labor and facilitate skill transfer. The success of many international operations relies greatly on expatriate performance (Erbacher, D'Netto & Espana, 2006). Even companies that do not expand their operations into other foreign countries still have to deal with language barriers due to changing language demography of the country and the areas from which labor is sourced. For example, the language composition of the workforce and languages used in South African mines is diverse with miners proficient in Afrikaans, English, Zulu, Xhosa and others to varying degrees (Research Focus (Pty) Ltd, 2011). As a result of these trends, most mines today operate with a multinational workforce. This means cultural differences, including language barriers, exist among the miners. Marschan-Piekkari, Welch and Welch (1999) emphasize the fact that language problems become prominent as companies internationalize and grow their operations into more countries. According to a survey by Forbes, language barrier affects operations. For example, business owners acknowledge that language proficiency may promote a safer work environment (Rubin, 2011). A research has shown that language and cultural barriers in a workplace contributes to reducing workers’ productivity, increasing accidents, and hurts employers’ ability to recruit, hire and retain workers (Morris, 2002). Hence, mines are making efforts to break language barriers in their operating environments. Ma’aden, for instance reported in 2013 that 1,506 of its employees received training in English as a second language (Ma'aden, 2013)."

Jan 1, 2016

By J. F. Brune

This paper analyzes the explosion hazard resulting from the formation of methane-air mixtures in the mined-out gobs of underground longwall coal mines. Although direct examinations of the gob atmosphere are difficult due to the inaccessibility of these gobs, evidence from methane drainage practices and investigations of numerous mine explosions suggests that explosive methane zones can form within longwall gobs. Explosions and fires resulting from these methane accumulations have led to severe and fatal injuries to the miners. Most recently, this was demonstrated in the explosion of the Upper Big Branch Mine in West Virginia, where 29 miners lost their lives.The paper also reviews current research on numerical modeling of gas flows in longwall gobs and outlines how targeted injection of nitrogen into gobs can effectively reduce the volume of such explosive methane zones. The paper concludes that comprehensive monitoring of gas compositions, along the accessible fringes of the gobs along with inertization, improved ventilation schemes and further research are necessary to control this explosion hazard and make mining operations safe.

Jan 1, 2013

By D. W. Agers

This paper is an extension of previous work evaluating a new extractant, LIX®-64, for recovery of copper from dilute acidic solutions. Large scale pilot plant operations have confirmed the technical and economic feasibility of the process and, with minor exceptions, scale up parameters obtained by previous laboratory work. Operating problems encountered in the pilot plants are discussed. Design parameters for-scale-up to commercial plants are presented and discussed along with a revised capital cost estimate. The future pilot program is discussed, including minor design changes and the effect of entrained organic on dump leaching efficiency.

Jan 1, 1967

By Manuel Bernales, Aldo Leon, Alexandra Carlier, Bern Klein, Andre Xavier

Mining companies and governments at both the local and national levels recognize that Participatory Environmental Monitoring and Surveillance Committees (PEMSC) are necessary mechanisms for meaningful engagement at the community level. In many cases, PEMSCs are established as volunteer initiatives by mining companies or by the mining communities themselves. In Peru however, they can also be recommended by the government as way to address social conflict. Most PEMSCs are launched while a mine is in operation and have the objective of monitoring both water quality and quantity. Many established committees are currently evolving and adopting a more comprehensive approach, as well as expanding their initial scope from a river or micro-basin focus and watchdog agenda, to a broader regional integrated resources management view. This paper examines the origins of Participatory Environmental Monitoring and Surveillance Committees in Peru. It also discusses the typology of these committees, and the scope of their work. Furthermore, it looks at the challenges faced by these committees, as well as existing opportunities for mining companies, governments, and civil society. Finally, this study presents a governance model that could contribute to the long-term existence of these committees. This discussion is further informed by the results of a national workshop that took place in October 2016 in Peru, in which over 200 representatives from 22 monitoring committees, government and mining companies participated.

Jan 1, 2017

By S. Rezaei

Moving ground in the mining industry is almost inevitable; however comprehensive awareness of these movements is necessary to mitigate risk. Monitoring of displacements caused by mining is a key tool for geomechanical risk management. Good monitoring may prevent unexpected failures and protect personnel and equipment. Many displacement monitoring techniques are available, however not all are reliable, accurate, and cost effective. Close range photogrammetry (CRP) is a monitoring method with high accuracy, reliability, and cost effectiveness; and has the ability to measure places that are inaccessible. In CRP, some series of photos are taken in different positions with different angles at different time intervals depending on the displacement rates. These photos are processed using PhotoModeler software and 3D models are made. By comparing 3D models, displacements can be measured. This method has been demonstrated at the Freeport-McMoRan Safford Mine in Arizona. A fault related instability in part of the pit is reactive to mining, and provided an opportunity to compare results between traditional monitoring methods and CRP. In this project, multiple series of photos were taken at different times using a Canon 5D Mark III digital camera, then PhotoModeler software used to make 3D models for each specific measurement event. Movement rates were determined by comparing different 3D models. These results are then compared to results of other monitoring methods to validate the CRP displacement method.

Feb 27, 2013

By Hiroyuki Tamaru, Futoshi Kusumoto, Kosuke Tanimura, Atsuyuki Kimura

"SUMMARY The Hachinoshiri tunnel is a 2,469 m long two-lane road tunnel on the Chubu-Odan Expressway. Since more than 70% of the total tunnel length consists of low strength rock masses the competence factor of which is less than 1.0, it is expected that a self standing span cannot be achievable because of no ground arch to be established. The tunnel was thus designed with tunnel support patterns forming multi-arc early ring closure that can develop the load-carrying capacity estimated from the exerted earth pressure, Po, which can result from the competence factor, cf. The tunnel support pattern was selected based on the competence factor at tunnel face, then the subsequent tunnel support patterns were determined with reference to the monitoring data. The tunnel construction adopted full-face excavation accompanied by early ring closure using a 330 kW road header. The proposed construction methods at this tunnel site have turned out ensuring tunnelling in massive squeezing rock, so that they can be verified as reasonable tunnelling technologies, clarifying the relationship between the characteristics of the mechanical behaviour of the tunnel and its design parameters. INTRODUCTION The presence of highly weathered mudstone having the competence factor less than 1.0 where the tunnel became unstable with the early ring closure having the distance to early ring closure, Lf, of 6 meters, resulting in difficulty in maintaining the inner section of the tunnel, prompted a substantial amount of high strength double support and replacing of the tunnel support (Sato et al., 2015). Based on the mechanical characteristics learned from the construction, the mechanical stability of multi-arc tunnels was investigated using 3D FDM analyses with respect to the ratio of the radius for early ring closure, r3/r1, and the distance to early ring closure, Lf, so that tunnel support patterns for early ring closure can be established in terms of the competence factor, of, which was employed for a 725 m long section. Consequently the tunnel support patterns for early ring closure which can be determined from the competence factor became applicable to tunnel construction. The relationship between the characteristics of the mechanical behaviour of the tunnel and its mechanical parameters was also clarified. The early ring closure method adopted ensured tunnelling in massive squeezing rock, verifying its effectiveness in stabilizing the tunnel."

Jan 1, 2016

By M. Hardy, K. Nielsen, M. Ramey

American Soda, LLP has commissioned the first solution mine for recovery of naturally formed sodium bicarbonate (nahcolite) from low-grade deposits using high-pressure, high-temperature injection fluid. This project, known as the Yankee Gulch Project, was commissioned33 years after discovery of the deposit and followed an intensive four-year feasibility study that included a full-scale pilot test. The nahcoliteis co-mingled with oil shale and is impermeable. Solution mining is achieved by a combination of thermo-mechanical cracking and dissolution. Elevated temperatures are required to initiate the thermally induced cracking and to enhance solubility of the nahcolite, which is highly temperature dependent. This paper will provide an overview of the development of the project from discovery, characterization, pilot testing, permitting and commissioning, with emphasis on the solution mining aspects.

Jan 1, 2003

What is your assessment of the current state of the minerals industry? It is no understatement that domestic mining is facing a severe crisis at this time. The sharp decline in commodity prices and demand is putting a great strain on domestic and worldwide mining, causing major declines in profits and market capital of mining companies. This, in turn, has lead to major production cuts, layoffs, shut-downs of operating properties, and the deferral of new and expansion projects. These changes in the minerals industry have played a major role in the health of the economy. Operationally, the industry continues to develop new technologies that are making our work more efficient, more cost effective and more environmentally acceptable and safe. During downturns like this, companies generally pay closer attention to operational efficiencies and process optimization. Historically, new technologies and processes tend to be developed during down markets, and I believe we will see the same thing as companies strive to preserve liquidity and maintain or improve their margins. On the positive side, the drop in commodity prices has resulted in a reduction in operational costs, as the costs for fuel supplies and construction materials have decreased.

Jan 1, 2009

By J. B. Zachwieja, P. E. Richardson, G. W. Walker

The electrochemical nature of mineral-collector interactions and their relationship to flotation have been investigated to develop a better understanding of the factors controlling sulfide mineral beneficiation. Spectrophotometric and electrochemical techniques have been used to examine the reactions occurring on electrodes composed of a bed of bornite particles in the presence and absence of potassium ethylxanthate (KEtX) at a pH of 9.2. The combined techniques showed that KEtX sequentially reacts with bornite by (1) a chemisorption reaction forming ca hydrophobic species between --0.4 and -0.2 V (SCE), (2) an electrochemical oxidation reaction forming cuprous xanthate between -- 0.2 V and the xanthate/ dixanthogen redox potential, and (3) oxidation to dixanthogen when the potential exceeds the reversible value for the xanthate/dixanthogen couple. The flotation response of bornite closely parallels spectrophotometric and electrochemical evidence for adsorption of KEtX by the reactions listed above. The degree of surface oxidation resulting from the formation of iron oxides on the surface dictates the flotation response as evidenced by the fact that oxidized bornite floats at more anodic potentials than unoxidized bornite. The strong correlations between the flotation response, degree of oxidation, and potential indicate that chemisorbed xanthate produces a hydrophobic layer sufficient to float unoxidized bornite, but cuprous xanthate and dixanthogen arc required to float oxidized bornite.

Jan 1, 1988

By D. E. Ranta, Stephen W. Thomas, Clancy J. Wendt

One of the most difficult tasks associated with placer mining is the sampling of the deposit. More placer projects have failed due to inaccurate assessment of the reserves than to any other reason. Within the realm of placers, those containing valuable minerals with a high unit value are more difficult to sample than those with larger bulk, lower unit value minerals. Some items to consider when sampling a placer deposit are as follows: A. A relatively large sample is needed for accurate valuation of the ground being tested. Placers are composed of many sizes of gravel which makes a representative sample difficult to obtain. B. When sampling placers for high unit value minerals such as gold, any error in mineral content of the sample will be magnified in the calculation of reserves. C. Values are usually erratically distributed within the gravel mass. Therefore, some placers with a more uniform value distribution may be adequately assessed with a minimum number of samples whereas a deposit with a highly erratic distribution of values may not be adequately sampled regardless of how many samples are taken. D. The investigation of a placer deposit should be made by, or be under the direction of, a person experienced in the art of placer sampling. F) During a sampling program, items that must be observed and noted in addition to the sample size and valuable mineral content should include boulder size and number, clay content, bedrock conditions, water, frozen ground, false bedrock, and any other physical characteristics that would affect mining of the deposit.

Jan 1, 1992