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IC 
 
 9097 
 
 Bureau of Mines Information Circular/1986 
 
 Bureau of Mines Research Into Reducing 
 Materials-Handling Injuries 
 
 By Richard L linger and Thomas G. Bobick 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 

 , ^ 
 
 Information Circular 9097 
 
 n / 
 
 Bureau of Mines Research Into Reducing 
 Materials-Handling Injuries 
 
 By Richard L Linger and Thomas G. Bobick 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
Library of Congress Cataloging in Publication Data: 
 
 
 c6 
 
 V 7 
 
 n 
 
 7 
 
 Unger, Richard L 
 
 Bureau of Mines research into reducing materials-handling injuries. 
 
 (Information circular; 9097) 
 
 Bibliography: p. 22. 
 
 Supt. of Docs, no.: I 28.27:9097. 
 
 1. Mine haulage - Safety measures. 2. Mine haulage- Accidents. 3. Coal mines and min- 
 ing-Safety measures. 4. Coal mines and mining- Accidents. 5. Spine -Wounds and injuries. 
 I. Bobick, T. G. II. United States. Bureau of Mines. III. Title. IV. Series: Information cir- 
 cular (United States. Bureau of Mines); 9097. 
 
 TN295.U4 [TN331] 622 s [622'.8] 86-600129 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduct ion 2 
 
 Acknowledgments 2 
 
 Past research to reduce underground materials-handling injuries 3 
 
 Program 1 3 
 
 Program 2 3 
 
 Program 3 4 
 
 Present areas of cooperation 5 
 
 Present research project 5 
 
 General description of the supply-handling system 6 
 
 Organization problems 6 
 
 Storage areas 6 
 
 Supply packaging 7 
 
 Excessive manual materials handling 7 
 
 Lack of mechanical assists 8 
 
 Other hazards 8 
 
 Accident analysis 8 
 
 Proposed solutions 8 
 
 Systems approach — unitized-load supply system 9 
 
 Unitizing supply loads 12 
 
 Modular packaging 13 
 
 Job redesign 13 
 
 Mechanical-assist devices 13 
 
 Task or load redesign 14 
 
 Task elimination 17 
 
 Laboratory simulation 18 
 
 Summary 21 
 
 References 22 
 
 ILLUSTRATIONS 
 
 1. Materials-handling flowcharts 7 
 
 2. Scoop-mounted forks and adapter plate 10 
 
 3. Forks attached to low-seam scoop 11 
 
 4. Experimental underground supply-handling forklift 11 
 
 5. Summary flowcharts of materials paths using palletization 12 
 
 6. Prototype mine jack and wheel changer during testing 14 
 
 7. Pivot boom mounted on maintenance vehicle 15 
 
 8. Scoop beam at an eastern Kentucky coal mine 15 
 
 9. Acceptable levels of lifting, vertical reference planes 16 
 
 10. Acceptable levels of lifting, transverse reference planes 17 
 
 11. Hanging miner cable: laboratory simulation 18 
 
 12. Building a stopping: laboratory simulation 19 
 
 13. Handling rock dust: laboratory simulation 19 
 
 14. Controlled studies related to lifting in the stooped posture 21 
 
11 
 
 TABLES 
 
 Page 
 
 1. Materials handling and back injuries for an eastern Kentucky coal company, 
 
 1983 9 
 
 2. Accident frequency and average cost for nonfatal accidents reported to 
 
 MSHA, 1983 9 
 
 3. Energy expenditure requirements for performing specific simulated low-coal 
 
 mining activities 20 
 
 4. Energy expenditure and grades of work 20 
 
 
 
 UNIT OF MEASURE ABBREVIATIONS USED IN THIS 
 
 REPORT 
 
 ft 
 
 
 foot L/min 
 
 liter per minute 
 
 h 
 
 
 hour lb 
 
 pound 
 
 in 
 
 
 inch min 
 
 minute 
 
 kca 
 
 1/min 
 
 kilocalorie per minute pet 
 
 percent 
 
 kg 
 
 
 kilogram yr 
 
 year 
 
BUREAU OF MINES RESEARCH 
 INTO REDUCING MATERIALS-HANDLING INJURIES 
 
 By Richard L. linger 1 and Thomas G. Bobick 2 
 
 ABSTRACT 
 
 The Bureau of Mines entered into a cooperative agreement with an east- 
 ern Kentucky coal mining company to comprehensively redesign the flow of 
 equipment and supplies throughout its underground mines. Items were 
 tracked from delivery to the warehouse and from surface storage areas to 
 their final usage locations underground. Three underground mines were 
 visited, and a great variety of tasks were videotaped for subsequent 
 laboratory analysis. Of particular interest were tasks that required 
 manual handling of the supplies or equipment components. Activities 
 such as handling daily supplies (concrete blocks, rock dust, and cross- 
 beams) and handling or lifting the continuous miner power cable were de- 
 termined to be the most hazardous. 
 
 Recommendations to the company included redesigned surface storage 
 areas to facilitate the use of forklift vehicles to load the underground 
 supply cars. Designs were also developed for different mechanical- 
 assist devices to help in unloading the supply cars underground and 
 to handle equipment maintenance tasks underground. Additionally, the 
 videotapes of the underground manual handling tasks became the basis for 
 simulating those activities in controlled laboratory conditions. This 
 testing will contribute to developing guidelines for proper lifting 
 techniques for low-seam coal mines. 
 
 'Civil engineer. 
 ^Mining engineer. 
 Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA, 
 
INTRODUCTION 
 
 Underground coal mining has justifiably 
 developed a reputation for being an ex- 
 tremely hazardous occupation. The condi- 
 tions encountered in the underground 
 environment (possibility for fires, ex- 
 plosions, and roof falls) pose a high 
 potential for fatalities and injuries. 
 Extensive research by the Bureau of Mines 
 and the coal mining industry, together 
 with enforcement of Federal regulations, 
 has substantially reduced the catastroph- 
 ic disasters associated with mine explo- 
 sions and fires that were commonly en- 
 countered in the earlier years of this 
 century. During the 1930' s and 1940' s, 
 more than 1,000 miners were killed yearly 
 in underground coal mines (JO . •* Injuries 
 and deaths now typically occur as single 
 incidents, and the number of fatalities 
 each year currently ranges from 100 to 
 150. 
 
 As mining technology has improved and 
 work conditions have become somewhat 
 safer, the major disasters have de- 
 creased. The problems that remain are 
 the kinds of accidents and injuries that 
 occur in any industrial setting, although 
 they may well happen more frequently in 
 mining. Specifically, back injuries con- 
 stitute the largest single category of 
 lost-time accidents in the mining in- 
 dustry. The mining environment, by its 
 very nature, presents extremely difficult 
 
 working conditions not normally encoun- 
 tered in general industry. Lack of ade- 
 quate illumination and uneven footing 
 contribute to tripping hazards; wet con- 
 ditions can cause slippage accidents; and 
 low seam height forces the miners to work 
 on their knees or in a stooped, bent-over 
 posture. All of these hazards contribute 
 to the back injury problem. 
 
 The Mine Safety and Health Administra- 
 tion (MSHA) Health and Safety Analysis 
 Center, located in Denver, CO, indicated 
 that in 1978-79 approximately 34 pet of 
 the accidents that occurred while han- 
 dling materials in underground coal mines 
 resulted in back injuries (2^). In 1981, 
 approximately 25 pet of the more than 
 37,000 accidents in the mining industries 
 involved the back ( _3_) . Additionally, 
 back injuries account for more lost work- 
 days than any other type of injury; for 
 example, 40 pet of the lost-time back 
 injuries incurred by underground coal 
 miners during 1981 resulted in the em- 
 ployee's missing more than 4 weeks of 
 work (_3) . 
 
 Statistics compiled by MSHA for 15 
 mines in the central Pennsylvania area 
 indicated that, during the years 1981 
 to 1984, accidents related to manual han- 
 dling of supplies and materials ranged 
 from 28 to 50 pet of all the accidents in 
 those mines. 
 
 ACKNOWLEDGMENTS 
 
 The authors want to extend their sin- 
 cere appreciation to the following em- 
 ployees of the Bureau's Pittsburgh Re- 
 search Center: William Doyak and George 
 Fischer, mechanical engineering techni- 
 cians, for fabricating the mechanical- 
 assist devices and delivering them to the 
 test mines for field evaluation; Sean 
 Gallagher, research physiologist, for 
 assisting with the simulation studies at 
 the University of Kentucky and for his 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this report. 
 
 input to the writing of the "Laboratory 
 Simulation" section of this report; and 
 Henry Kellner, industrial engineering 
 technician, for his suggestions and modi- 
 fications to the underground task analy- 
 sis procedure, for designing and con- 
 structing the low-seam mine simulator, 
 and for his assistance in conducting the 
 simulation studies at the University of 
 Kentucky. 
 
 Additionally, the authors want to thank 
 the management and workers of the eastern 
 Kentucky coal company that cooperated 
 with this research program. 
 
PAST RESEARCH TO REDUCE UNDERGROUND MATERIALS-HANDLING INJURIES 
 
 During the mid-1970' s, the Bureau began 
 to research the possibility of developing 
 a systems approach to mechanical handling 
 of the daily supplies and equipment used 
 in the underground environment in order 
 to reduce the number of accidents and in- 
 juries from manual handling activities. 
 The three research programs discussed be- 
 low included design of hardware intended 
 to reduce such accidents and injuries. 
 
 PROGRAM 1 
 
 The first program resulted in a de- 
 tailed study (4) that defined the physi- 
 cal characteristics of the supplies that 
 are manually handled, the typical envi- 
 ronmental conditions under which the sup- 
 plies are handled (including distances 
 moved) , injury data associated with the 
 manual handling tasks, and an estimate of 
 the daily supply-maintenance-production 
 tasks that had the best possibilities for 
 replacement by mechanical handling de- 
 vices. This study defined, in great de- 
 tail, the supply flow in typical under- 
 ground mines and identified the items 
 that were (and still are) handled under- 
 ground, including the range of sizes and 
 weights. 
 
 This work resulted in classifying the 
 supply-handling functions of the various 
 items used underground into five general 
 categories: 
 
 1. Production end use . — The handling 
 of items during their end use at the 
 working face, such as rock dusting, roof 
 bolting, and erecting temporary ventila- 
 tion curtains (this activity represented 
 11.2 pet of the total accidents studied 
 in this 22-mine research project). 
 
 2. Production supply . — The handling of 
 materials from the surface storage areas 
 to locations near the working face (but 
 excluding the actual end use handling) , 
 such as transportation of the rock dust, 
 roof bolts, support timbers, or ven- 
 tilation curtains (49.5 pet of the 
 accidents) . 
 
 3. Section move . — The handling of ma- 
 terials as mining proceeds from one 
 
 production section to another, such as 
 moving haulage belts, tearing up or re- 
 laying rails, or moving airlines, com- 
 pressors, or longwall face supports (13.0 
 pet of the accidents) . 
 
 4. Equipment maintenance . — The han- 
 dling of items involving the maintenance 
 of mine equipment, such as removing mo- 
 tors from face equipment, replenishing 
 hydraulic oil or transmission fluid, or 
 replacing extinguisher canisters (16.3 
 pet of the accidents). 
 
 5. Mine maintenance . — The handling of 
 supplies for maintenance of the mine it- 
 self, such as erecting permanent venti- 
 lation stoppings, setting crossbars and 
 cribbings for roof support, and install- 
 ing or upgrading of rail (10.0 pet of the 
 accidents) . 
 
 These designations were utilized by sub- 
 sequent researchers (_5 - _7) • 
 
 Essentially, this early study provided 
 valuable information on the materials- 
 handling practices in underground mining. 
 This program identified the importance 
 of mechanical-assist devices for manual 
 lifting-lowering-maneuvering tasks, based 
 on the injury frequencies for the equip- 
 ment maintenance and mine maintenance 
 handling modes. Although the program was 
 very thorough, logical, and well planned, 
 the prototype vehicle developed (a three- 
 wheeled, battery-powered vehicle, with a 
 6-degrees-of-f reedom manipulator) was far 
 too complex for easy maintenance and us- 
 age in underground coal mines. 
 
 PROGRAM 2 
 
 The second program (_5_) followed di- 
 rectly from the first one and made use 
 of the extensive materials-handling data 
 generated by the previous research. The 
 objective of this second project was to 
 design, construct, implement, and eval- 
 uate a system for the mechanical han- 
 dling of production supplies in under- 
 ground coal mines; the end result was a 
 battery-powered, skid-steer forklift that 
 was equipped with ancillary handling 
 attachments. 
 
The report contains an excellent de- 
 scription of the current supply-handling 
 methods, various materials-handling vehi- 
 cles commercially available to the mining 
 industry, and the supply-handling prob- 
 lems that are the most hazardous, have 
 high labor costs, or interrupt produc- 
 tion. The study identified the need for 
 mechanization of the loading-unloading 
 tasks at the working section. Research- 
 ers also looked at the typical supply- 
 handling systems in underground coal 
 mines and investigated the possibilities 
 of unitizing (palletizing) the supply 
 loads. Additionally, specifications of 
 a mechanical handling system that could 
 handle palletized loads were discussed 
 and design concepts for such a system 
 generated. Finally, researchers evalu- 
 ated the potential and cost effectiveness 
 of the concepts, selected the most appro- 
 priate concept to develop a workable de- 
 sign, and then constructed the prototype 
 piece of equipment. 
 
 The prototype vehicle was a battery- 
 powered forklift, which was permissible 
 for use in underground coal mines; it was 
 fairly successful in its initial testing. 
 A few design deficiencies were identi- 
 fied, which are being improved upon in a 
 second-generation, diesel-powered fork- 
 lift now being designed and tested by the 
 Bureau in-house. The permissible fork- 
 lift method of handling palletized daily 
 supplies in underground coal mines has 
 great potential for reducing manual han- 
 dling of materials. The results should 
 be a reduction in materials-handling in- 
 juries and more efficient of supplies, as 
 well as savings in daily supply-handling 
 labor. 
 
 PROGRAM 3 
 
 Data from the two earlier studies indi- 
 cated that production supply, mine main- 
 tenance, and equipment maintenance ac- 
 count for approximately 76 pet of all 
 materials-handling accidents. The third 
 research program (6^) was initiated in 
 1981 to investigate and design equipment 
 to reduce the manual effort (and hence 
 the accidents and injuries) associated 
 with mine and equipment maintenance 
 
 activities. This program began with a 
 literature review with the manual mate- 
 rials-handling problem, which indicated 
 that except for the Bureau-funded re- 
 search, no maintenance-related programs 
 for the mining industry had been con- 
 ducted. A number of mines were then vis- 
 ited to observe maintenance activities 
 and to discuss the problems with the 
 miners and safety personnel. The two 
 prior Bureau research programs (4-5) were 
 used to identify the items handled dur- 
 ing all types of supply activities. Ac- 
 cident data were analyzed to identify 
 possible trends and any hazardous tasks 
 that could be addressed during this spe- 
 cific project. 
 
 Thus, specifications were compiled to 
 help devise a mine-equipment maintenance 
 vehicle. A series of vehicle concepts 
 was developed by the contractor. Howev- 
 er, because of the resultant complexity 
 and high cost of the proposed machines, 
 the contractor was requested to devise a 
 series of materials-handling devices or 
 tools (instead of a vehicle) that could 
 be fabricated by a typical mine mainte- 
 nance shop. Based on the accident sta- 
 tistics, the personnel interviews, and 
 the mine visits, eight device-tool con- 
 cepts were developed (_8) . Of these, the 
 three most useful devices were fabricated 
 and provided to an eastern Kentucky coal 
 company for evaluation and testing. The 
 three devices, which have been undergoing 
 testing since early in 1984, are de- 
 scribed in the section "Job Redesign." 
 
 In late 1983, the coal company cooper- 
 ating in the testing of the materials- 
 handling devices developed an outline of 
 the Preventive Back Injury Program to re- 
 duce back injuries for its employees. 
 Specific program goals were a reduction 
 of injuries by 80 pet within an 18-month 
 period after implementation. The preven- 
 tive program included a discussion of 
 workplace modification and job redesign, 
 and a training program that emphasized 
 proper lifting techniques and the impor- 
 tance of exercise and correct diet. This 
 proposed program became the basis for 
 further cooperation between the mining 
 company and the Bureau. 
 
PRESENT AREAS OF COOPERATION 
 
 Two categories mentioned in the Cooper- 
 ator' s Preventive Back Injury Program — 
 lifting techniques and workplace modi- 
 fication and/or job redesign — are areas 
 where the Bureau is presently doing re- 
 search and where in-mine cooperation be- 
 gins. During discussions regarding the 
 in-mine testing of the materials-handling 
 devices, the cooperating company inquired 
 whether the Bureau could assist in devel- 
 oping its comprehensive program for pre- 
 venting back injuries. The Bureau agreed 
 to help in this venture, since it was re- 
 lated to on-going Bureau research that 
 included a detailed analysis of the man- 
 ual handling activities in underground 
 coal mines and their relationship to back 
 injuries for certain work groups. The 
 cooperator agreed to allow the Bureau to 
 gather data at its mines and to use vol- 
 unteers for laboratory simulations of 
 certain materials-handling tasks. 
 
 The cooperator runs three low-seam 
 mines (defined as having seam thicknesses 
 less than 48 in). Compared with working 
 in high-seam (greater than 72 in) under- 
 ground operations, working in low coal 
 prevents the miners from standing erect, 
 thus forcing them to perform heavy work 
 while in stooped or kneeling positions. 
 This imposes significantly more stress on 
 their backs than experienced by other in- 
 dustrial workers, who can lift supplies 
 and move about in an erect posture. 
 
 The traditional approach to reducing 
 back injuries has been to train the 
 miners to be more aware of the restric- 
 tions caused by the existing environmen- 
 tal conditions. Although regular train- 
 ing is important, ideally the task should 
 be redesigned or modified to reduce the 
 potential of injury. 
 
 The best way to evaluate a manual han- 
 dling task is in terms of the percent- 
 age of the worker population who can be 
 
 expected to perform the task without 
 overexertion or excessive fatigue. The 
 higher the percentage of workers who can 
 perform the task, the lower the risk of 
 injury or illness; the lower the percent- 
 age, the higher the risk of injury (9^). 
 If a task can be safely performed by only 
 a small percentage of workers, it should 
 be redesigned or modified so that more 
 of the workers can do it. The ideal 
 task will fit 90 pet or more of the work 
 population. 
 
 When redesign of a heavy lifting task 
 is infeasible, workers must be carefully 
 selected who can perform that particular 
 task safely. The lower the percentage of 
 workers who can safely do the task, the 
 more carefully the workers should be se- 
 lected to avoid an injury ( jO . Detailed 
 tables that list the maximum weights ac- 
 ceptable to various percentages of the 
 male and female industrial population for 
 various manual handling tasks, and the 
 methodology used to determine these 
 weights, are provided in Snook and Cir- 
 iello (9) and Snook U0 ) . 
 
 Redesigning the task to fit the average 
 worker is the preferred approach, rather 
 than trying to select the most suitable 
 workers, because it eliminates problems 
 that can develop when replacement workers 
 have to fill in for absent employees. 
 
 Bureau research studies to be conducted 
 with selected coal companies will em- 
 phasize the concepts of supply system 
 organization and job redesign. In job 
 redesign, there will be three primary 
 approaches investigated: (1_) utilizing 
 mechanical-assist devices, (2) task or 
 load redesign, and (3) task elimination. 
 Some work has been initiated in all three 
 areas, and further plans will be devel- 
 oped in the near future. These are dis- 
 cussed in more detail in the "Job Rede- 
 sign" section of this report. 
 
 PRESENT RESEARCH PROJECT 
 
 Before solutions 
 implemented on 
 handling problems, 
 
 can be developed and 
 specific materials- 
 the existing supply 
 
 system has to be thoroughly studied and 
 evaluated. A detailed task analysis must 
 be conducted to identify problem areas 
 
that are unique to each particular system 
 being investigated. Such a task analysis 
 was conducted at three underground mines 
 of the cooperating eastern Kentucky coal 
 company. 
 
 The techniques used to gather the in- 
 formation on manual materials handling at 
 these mines involved interviews, on-site 
 observations, and accident analysis. All 
 facets of the materials-handling system 
 were studied, from the purchasing depart- 
 ment to the actual end-use handling of 
 the supplies. Interviews were conducted 
 with purchasing agents, section super- 
 visors, warehouse employees, and under- 
 ground supply workers to determine how 
 they performed their jobs and to document 
 any suggestions they had for improving 
 the supply distribution system. 
 
 Once the general procedures of the 
 supply-handling system were determined, 
 the various supplies were traced from 
 their arrival at the mine site to their 
 final use underground. Videotaping and 
 still photography were used to document 
 the materials-handling activities. When- 
 ever possible, miners and warehouse work- 
 ers were interviewed immediately after 
 they had completed a task to record their 
 impressions of the work and any problems 
 they might be having. The videotapes 
 were studied to uncover hazardous manual 
 handling tasks and to serve as a basis 
 for future work in futher task analyses 
 and laboratory simulations. 
 
 GENERAL DESCRIPTION OF THE 
 SUPPLY-HANDLING SYSTEM 
 
 taken underground on a pallet and then 
 dragged off the flatcar with a chain that 
 was attached to a face vehicle (scoop or 
 shuttle car). 
 
 Supplies were taken to their end-use 
 area by whatever means was convenient. 
 Usually they were loaded by hand onto a 
 face vehicle, whether the unloading was 
 done by hand or mechanically depended on 
 the vehicle used. 
 
 In addition, there were no established 
 procedures for handling infrequently 
 used items such as replacement motors or 
 tires. Presumably they were loaded onto 
 whatever vehicle was convenient to carry 
 them, and all subsequent handling was 
 done manually. 
 
 A variety of problems were uncovered in 
 the supply-handling systems of the mines 
 studied. Most were common to all three 
 mines visited. These problems can be 
 categorized into two general areas: lack 
 of an organized method (systems approach) 
 to supply handling, and not using mechan- 
 ical-assist devices where feasible. 
 
 ORGANIZATIONAL PROBLEMS 
 
 The problems associated with the lack 
 of a systems approach mean that the pre- 
 planning and organization vital to run- 
 ning an efficient and safe supply-han- 
 dling operation are not present. The 
 following problems, identified at these 
 mines, could be eliminated by utilizing a 
 systems approach. 
 
 Storage Areas 
 
 The equipment used to handle supplies 
 at mines included battery locomotives and 
 tractors, scoops and jeeps, rail-mounted 
 and rubber-tired flatcars and trailers, 
 and shuttle cars. Generally, supplies 
 were loaded by hand onto the supply trip. 
 A forklift was available on the surface 
 of one mine and used when convenient; 
 however, the rough terrain and close con- 
 fines of the supply yard usually made its 
 use impractical. 
 
 On arriving in the underground sec- 
 tion, supplies were generally unloaded 
 one piece at a time, by hand. The only 
 exception was the roof plates, which were 
 
 Both the surface and underground stor- 
 age areas were, to some extent, unorga- 
 nized and mismanaged. Supplies were not 
 always placed where they could be loaded 
 or unloaded most efficiently. For exam- 
 ple, the concrete blocks used to con- 
 struct ventilation stoppings were stacked 
 where a forklift could not conveniently 
 reach them; the supply workers frequently 
 had to handle them twice before they were 
 loaded onto the supplly car for the 
 trip underground. Many of the smaller 
 items, such as wedges and cap blocks, 
 were piled randomly, with little apparent 
 concern for breakage or loss. This lack 
 
of organization can easily contribute to 
 strain and sprain injuries by causing 
 supplies to be handled many times. 
 
 Supply Packaging 
 
 Many times supplies were packaged in 
 such a way as to magnify the problems of 
 handling once they were underground. 
 Roof bolts are a good example. During 
 this study, roof bolts were delivered in 
 wire-wrapped bundles of 500 bolts, which 
 were loaded onto the supply car by a 
 forklift. The wire straps were then cut 
 to allow the bolts to spread out so they 
 could clear a low roof area of the mine 
 along the main haulageway. However, this 
 meant that the bolts had to be manually 
 unloaded underground, three to six at a 
 time. What would have been a 1-min task 
 using mechanical means (a chain attached 
 to the scoop bucket) was turned into a 
 20- or 25-min task that involved poten- 
 tial pinching, twisting, and lifting haz- 
 ards. The Bureau recommendation was to 
 contact the vendor to request that the 
 bolts be delivered in bundles of 250. 
 The smaller bundles could clear the low 
 area along the haulageway. Thus, the 
 bolts could remain strapped together, 
 which would permit workers to use the 
 scoop to pull the bundles off the supply 
 car to the section storage area, saving 
 time and eliminating manual handling. 
 
 Excessive Manual Materials Handling 
 
 This problem is closely related to poor 
 materials packaging and storage. Some 
 supplies, most notably rock dust bags and 
 concrete blocks, were handled as many as 
 five times before reaching their end use. 
 This means that each block or bag was 
 probably lifted and lowered manually four 
 or five times before being handled the 
 final time to complete the task. This 
 unnecessary excessive handling increases 
 the risk of strains to the workers and, 
 of course, materials breakage. 
 
 Figure 1 shows the flowcharts, devel- 
 oped from the task analysis that was 
 conducted at each underground mine, of 
 the paths that some of the most commonly 
 used supplies take through the mine(s). 
 
 ROOF PLATES 
 
 Palletized plates Pallet dragged off 
 looded on supply supply cor with chain 
 car with forklift 
 
 Loaded manually 
 onto face vehicle 
 
 CROSSBEAMS 
 
 KEY 
 
 Q Manual transfer 
 O Manual transport 
 /\ Mechomcal transfer 
 
 V ) 
 
 n — y use 
 
 Lifted to roof Loaded monually 
 "on'" onto face vehicle 
 monually 
 (end use) 
 
 Unloaded with 
 forklift 
 
 ROCK DUST 
 
 Stacked in rear of 
 rock dust trailer 
 
 Loaded manually 
 onto face vehicle 
 
 CONCRETE BLOCKS 
 
 Transported from 
 
 surface storage 
 
 to supply car 
 
 Looded monually 
 onto face vehicle 
 
 FIGURE 1.— Materials-handling flowcharts. 
 
 Three modes of transportation are shown. 
 Manual transfer occurs when the materials 
 are moved manually with support, such as 
 sliding a rock dust bag across a supply 
 car. Manual transport refers to unsup- 
 ported transportation of materials; an 
 example would be carrying a rock dust bag 
 to the face area. Mechanical transfer- 
 transport covers any handling of sup- 
 plies or materials conducted entirely by 
 mechanical means. An example of a mech- 
 anical transfer would be using a winch to 
 drag equipment or supplies to another 
 area; an example of a mechanical trans- 
 port would be using a forklift to pick up 
 and move supplies and equipment. 
 
 The flowcharts show that all supplies 
 required some degree of manual handling. 
 The supply-handling technique for the 
 roof bolt plates, however, eliminated all 
 but the most necessary manual handling. 
 The other three charts indicate that the 
 supplies were being handled unnecessarily 
 many times before reaching the end-use 
 area. 
 
LACK OF MECHANICAL ASSISTS 
 
 The following example illustrates the 
 problem of not using mechanical-assist 
 devices when feasible. On the surface, 
 crossbeams were lifted manually onto the 
 forklift forks, driven to the supply car, 
 and then unloaded manually from the 
 forks. These wooden crossbeams, which 
 are usually 8 by 8 in or 10 by 10 in, 
 with lengths ranging from 10 to 16 ft, 
 are installed in haulageways that need 
 extensive roof support. They weigh 200 
 to 300 lb and were typically lifted and 
 supported manually by two workers (and in 
 extraordinary cases, a single worker) on 
 each end. When the Bureau observed the 
 installation of the beams, a hydraulic 
 jack that could have assisted in lifting 
 the beam was actually moved aside to make 
 room for an extra worker to help lift. 
 
 The hazards associated with manual han- 
 dling of some of the more common items in 
 the mines observed are discussed below: 
 
 1. Crossbeams (timbers) . — Attempting 
 to pull heavy timbers to the edge of the 
 supply car for unloading is highly haz- 
 ardous. Pinched fingers, strains and 
 sprains to the trunk and upper and lower 
 extremities, and crushed or fractured 
 feet are potential injuries. 
 
 2. Posts . — Injuries are similar to 
 those for timbers. Back strains occur 
 easily from lifting and twisting with the 
 posts during installation. 
 
 3. Concrete blocks . — The blocks lo- 
 cated in the middle of the supply car 
 have to be lifted an extra time and 
 placed at the edge of the car for unload- 
 ing. Crushing injuries can occur to the 
 hands and feet of the supply workers; 
 back injuries can occur quite easily be- 
 cause of the lifting and twisting move- 
 ment during loading and unloading the 
 supply car. Additionally, eye injuries 
 
 can occur from pieces of the block chip- 
 ping off during loading or unloading. 
 
 4. Rock dust bags . — Loading and un- 
 loading 50-lb rock dust bags can cause 
 strains or sprains to both the upper and 
 lower extremities, as well as to the 
 back, from the constant, repetitive 
 twisting. Additionally, eye injuries can 
 result if the rock dust bag tears and the 
 dust gets into the worker's eyes. 
 
 OTHER HAZARDS 
 
 The section floor also presents hazard- 
 ous conditions. Blocks and other loose 
 materials can lie scattered about. The 
 floor is often wet and slippery. Workers 
 carrying supplies can trip over the loose 
 items or the haulage tracks and can slip 
 in the muddy conditions. In addition, 
 little is known about the cumulative ef- 
 fect that repeated lifting and twisting 
 with heavy loads in restricted workspaces 
 has on injury rates. The laboratory work 
 discussed later in this report begins to 
 address this question. 
 
 ACCIDENT ANALYSIS 
 
 The materials-handling accident records 
 of the cooperating company for 1983 were 
 examined to uncover any trends in acci- 
 dent types or parts of the body injured. 
 A summary of the materials handling and 
 back injuries is given in table 1. 
 
 Given the limited number of accidents, 
 little can be said except that, based on 
 Bureau experience, the types and causes 
 of these materials-handling accidents 
 closely parallel those in the coal indus- 
 try as a whole. 
 
 A cost analysis was also done on the 
 cooperator's accidents reported to MSHA. 
 The results of this analysis are given in 
 table 2. 
 
 PROPOSED SOLUTIONS 
 
 The following are proposed solutions to 
 excessive and hazardous manual materials 
 handling in the mines visited: 
 
 1. Implement a systems approach to 
 daily supply handling by developing a 
 unitized-load supply-handling system for 
 each mine. 
 
 2. Develop the concept of job rede- 
 sign — this includes developing and uti- 
 lizing mechanical materials-handling de- 
 vices for some of the more hazardous 
 handling tasks, and, where possible, re- 
 structuring or eliminating other tasks. 
 
TABLE 1. - Materials handling and back injuries for 
 an eastern Kentucky coal company, 1983 
 
 Activity 
 
 Handling and/or pulling cable.... 
 
 Moving rock , 
 
 Maintenance: 
 
 Tightening or loosening bolts.. 
 
 Changing motor or transmission. 
 
 Other 
 
 Lifting: 
 
 Guard rail on miner , 
 
 Cross ties 
 
 Belt roller , 
 
 Pipe 
 
 Parts 
 
 Hydraulic jack , 
 
 Being struck by or against: 
 
 Back of deck rail , 
 
 Loose coal 
 
 Rerailing mantrip , 
 
 Shoveling 
 
 Unloading rock dust , 
 
 Loading belt structure , 
 
 Welding overhead , 
 
 Washing out dryer , 
 
 Total , 
 
 Number of 
 injuries 
 
 Total days 
 lost 
 
 1 175 
 
 
 
 2 
 
 3 
 
 4 
 10 
 5 
 1 
 
 
 
 13 
 
 
 11 
 5 
 
 
 
 
 
 229 
 
 1 specific accident accounted for a total of 156 days lost. 
 
 TABLE 2. - Accident frequency and average cost for nonfatal accidents 
 reported to MSHA, 1983 
 
 
 Frequency 
 
 Average cost 
 
 Accident type 
 
 United 
 States 
 
 Ken- 
 tucky 
 
 Coop- 
 erator 
 
 United 
 States 
 
 Ken- 
 tucky 
 
 Coop- 
 erator 
 
 
 8,085 
 5,337 
 2,748 
 
 1,099 
 1,649 
 
 1,077 
 698 
 379 
 
 178 
 
 201 
 
 28 
 18 
 
 10 
 
 5 
 5 
 
 $7,312 
 
 5,708 
 
 10,427 
 
 4,421 
 14,430 
 
 $8,281 
 
 7,287 
 
 10,111 
 
 4,536 
 15,049 
 
 $2,613 
 
 
 2,824 
 
 Materials-handling: 
 
 Back 
 
 2,233 
 3,366 
 
 
 1,101 
 
 SYSTEMS APPROACH— UNITIZED-LOAD 
 SUPPLY SYSTEM 
 
 The general structure of the unitized- 
 load or palletized supply-handling system 
 is — 
 
 1. On the surface, unit loads or pal- 
 lets of supplies will be loaded onto 
 low-profile flatcars or trailers by a 
 forklift. 
 
 2. Once underground, the loads will be 
 handled with some form of a forklift de- 
 vice. One possibility that the Bureau is 
 testing is a scoop equipped with a spe- 
 cial fork attachment. The attachment 
 will allow the scoop to switch from the 
 bucket to the forks in just a few minutes 
 for supply handling and then back to the 
 bucket for coal and/or rock clean-up 
 (figs. 2-3). A dedicated supply-handling 
 
10 
 
 FIGURE 2.— Scoop-mounted forks and adapter plate. 
 
 forklift is also an option the Bureau is 
 working on for higher seams (fig. 4). 
 The supplies will be kept in section 
 storage until needed. 
 
 3. As supplies are needed at the face, 
 the forklift will be used to transport 
 them in unit loads. 
 
 Figure 5 illustrates the paths that 
 most supplies would take if this system 
 were implemented. The Bureau estimates 
 that a unitized-load system could reduce 
 manual handling of supplies by up to 60 
 pet. 
 
 Implementation of this system would not 
 be without problems, some of which are 
 described below: 
 
 1. Unit-load handling equipment. — 
 There are no fork trucks commercially 
 available that are permissible for under- 
 ground coal mines. A proposed cost- 
 effective solution is to install forks on 
 a proven vehicle to perform the required 
 pallet handling. The Bureau is currently 
 working on design of a quick-attach fork 
 
 system for low-seam scoops, as mentioned 
 previously, as well as a diesel-powered 
 permissible fork truck for supply han- 
 dling and general mine maintenance. 
 
 2. Unit-load design. — Every inch is 
 critical in the thinner seams; most cur- 
 rent pallet designs are too high and thus 
 not applicable for usage in low-seam 
 mines. A pallet would have to be found 
 or developed to meet an underground low- 
 seam coal mine's height restrictions and 
 durability requirements. This is dis- 
 cussed further in the next section. 
 
 3. Supply car and trailer design. — To 
 minimize the height of the supply trips, 
 the supply cars and trailers would have 
 to be designed to be as low as possible. 
 Several manufacturers have indicated that 
 they will build their supply cars to 
 whatever specifications are required by 
 their customers, which would provide a 
 feasible solution to this problem. 
 
 4. Supply vendors. — To have an effec- 
 tive supply-handling system, supplies 
 
11 
 
 FIGURE 3.— Forks attached to low-seam scoop. 
 
 FIGURE 4.— Experimental underground supply-handling forkllft. 
 
12 
 
 ROOF PLATES 
 
 Pallets loaded on Pallets unloaded 
 supply car with at section storage 
 (orklift 
 
 Plates loaded manually 
 onto face vehicle 
 
 KEY 
 O Manual transport 
 /^Mechanical transfer 
 or transport 
 
 V 
 
 End use 
 Pallet taken to face 
 
 CROSSBEAMS 
 
 End 
 use 
 
 Picked up 
 with forklift 
 
 Unloaded by 
 
 forklift 
 
 onto timber car 
 
 Unloaded with Put into place Taken to end 
 forklift by timber car use area with 
 
 in section forklift 
 
 ROCK DUST AND CONCRETE BLOCKS 
 
 Pallets loaded on 
 
 supply car with 
 
 forklift 
 
 Pallets unloaded Taken to end- 
 with forklift use area with 
 
 forklift 
 
 FIGURE 5.— Summary flowcharts of materials paths using 
 palletization. 
 
 must be delivered to the mine in unit 
 loads or stacked so they can be easily 
 palletized manually. Most vendors will 
 deliver their products however the cus- 
 tomer wants them, sometimes at no extra 
 cost, but the customer must make a pref- 
 erence known. 
 
 5. Supply trip planning. — For the sup- 
 ply system to operate most effectively, 
 the needs of each underground section 
 must be discussed with the supply person- 
 nel before the trip is loaded. An accu- 
 rate projection of supply needs must be 
 made daily with the intent to optimize 
 unit-load design, minimize underground 
 storage, and minimize the number of sup- 
 ply trips. This will allow better inven- 
 tory and cost control. 
 
 Unitizing Supply Loads 
 
 The purpose of unitizing supply loads 
 is to reduce the handling frequency and 
 to facilitate mechanical handling. Gen- 
 erally, two types of unit loads are sug- 
 gested for underground coal mine sup- 
 plies. The first type, end-use units, 
 consists of the package that would be de- 
 livered to the face or underground end- 
 use area. One example of these loads 
 would be a pallet or container loaded 
 with a small bundle of roof bolts and 
 plates, a bag of rock dust, and a small 
 
 bundle of wedges. The second type, stor- 
 age units, consists of the larger unit 
 loads that would be carried to and stored 
 at the section. Examples of this type of 
 load are several bundles of roof bolts 
 and plates strapped together, a cube 
 formed out of bundles of wedges, or sev- 
 eral dozen rock dust bags stacked on a 
 pallet. The makeup of each type of unit 
 should be based on the following 
 criteria: 
 
 1. The end-use unit load must not con- 
 tain more than the number of pieces used 
 in one end-use operation, including an 
 allowance for scrap during the operation. 
 An end-use operation is the final han- 
 dling of the materials. Larger unit 
 loads would involve rehandling of loose 
 pieces. The number of pieces used in one 
 end-use operation depends on the standard 
 work practice and equipment in the par- 
 ticular mine or section. 
 
 2. The storage unit load must not con- 
 tain more than the number of units re- 
 quired in the end-use operations for the 
 period that the unit load is stored at 
 the section. Larger storage unit loads 
 would require rehandling of the remaining 
 end-use units when the section storage 
 area is moved periodically during advance 
 or retreat of the section. 
 
 3. Both end-use and storage unit loads 
 must be accommodated in the space avail- 
 able at the face or the section storage 
 area. 
 
 4. The unit loads must be transported 
 as individual units on underground trans- 
 port vehicles such as the supply car or 
 the face trip vehicle. They must be able 
 to be unloaded as individual units. 
 
 5. If unit loads are supplied already 
 palletized by the supplier, it must be at 
 a cost acceptable to the mine operator. 
 
 6. The unit loads, after being pack- 
 aged in a container, on a pallet, or in 
 a self-wrap, must be within the han- 
 dling capacity of the mechanical-handling 
 device. 
 
 The final makeup of both types of unit 
 loads can be determined only after imple- 
 mentation of the supply-handling system. 
 Periodic refinements, which will be based 
 on input from the mine's suppliers and 
 the miners, will be required. 
 
13 
 
 The choice of suitable pallets or con- 
 tainers to carry unit loads will depend 
 on the availability of space on the sup- 
 ply car, on the section floor conditions, 
 and most significantly on whether mate- 
 rials arrive on pallets or slipsheets 
 from the suppliers. Four basic types of 
 pallets that may be needed are — 
 
 1. Timber and post pallets, which have 
 removable vertical side bars. 
 
 2. Flat boards for blocks and bags. 
 
 3. Tub pallets for items such as 
 grease pails, wedge bundles, etc. 
 
 4. Self-wrapping as a method of pack- 
 aging so the unit load can be handled as 
 a pallet. 
 
 The flat pallets can be used for stor- 
 age and handling at the yard and for some 
 unloading at the section. The unit loads 
 should be wrapped so they can be mechan- 
 ically handled as a single item. This 
 way the supply car pallets will be imme- 
 diately returned with the empties, avoid- 
 ing pallet rehandling at the section. 
 
 In most cases, the width of pallets 
 should be limited to a standard 36 in. 
 Larger pallets will be too wide to be 
 easily unloaded in the narrow space 
 available on either side of the supply 
 car. However, the exact determination of 
 pallet size should be made during the de- 
 sign of the supply-handling system. 
 
 An alternative to pallets or contain- 
 ers for some loads would be slipsheets. 
 Loads such as rock dust would arrive at 
 the mine stacked on a strong sheet of 
 cardboard or synthetic material that 
 would be handled by a specialized fork- 
 lift attachment. This would save the 
 cost of a pallet and further reduce the 
 height of the load. 
 
 face. The empty car can be returned to 
 the surface supply yard and replaced by 
 another modular car on a single-shift or 
 daily basis. Modular packaging, however, 
 does have the following limitations: 
 
 1. The unit consisting of sufficient 
 rock dust bags, timbers, roof bolts, 
 blocks, and the like for a shift or one- 
 day operation may be too large to be car- 
 ried on one supply car. 
 
 2. The large supply module, if left 
 close to the face (in some mine configur- 
 ations), could hinder vehicle traffic and 
 movement of personnel during the face 
 operations. 
 
 3. The supplies required at a section 
 will vary during the course of mining. 
 Thus, a standard modular package will 
 realistically match only the average 
 daily needs. Additional nonmodular sup- 
 plies would have to be handled daily. 
 
 4. Since so many supplies are stored 
 in' a single unit, the pickup of individ- 
 ual items may be difficult because of 
 overlapping. This mixing may also damage 
 some supplies such as rock dust, oil 
 cans, and grease pails. 
 
 5. The operations at a section are 
 carried out at several locations. For 
 example, two rock dust bags may be used 
 for dusting the face, while several dozen 
 bags may be used for the rock duster or 
 the trickle dusters located at crosscuts. 
 Similarly, concrete blocks are needed at 
 the crosscut that is to be blocked and 
 not at the face. The supplies will still 
 have to be distributed from the modular 
 unit, and rehandling may not necessarily 
 be reduced. 
 
 JOB REDESIGN 
 
 Modular Packaging 
 
 Another possible method of unitization 
 is based on a modular packaging concept. 
 All the supplies needed at the section 
 may be bound together in one package and 
 supplied to the section as a unit for one 
 shift or one day. This method of unit- 
 ization can reduce the handling at the 
 section. The daily needs of a section 
 can be transported on a single supply car 
 that can be left close to the working 
 
 There are three primary approaches in 
 the concept of job redesign: (1) utiliz- 
 ing mechanical-assist devices, (2) task 
 or load redesign, and (3) task 
 elimination. 
 
 Mechanical-Assist Devices 
 
 Many of the most hazardous manual han- 
 dling tasks occur during mine and equip- 
 ment maintenance. To address these prob- 
 lems, the Bureau has designed specialized 
 
14 
 
 mechanical-assist devices to handle the 
 more difficult jobs. Each device is in- 
 expensive and can be built in any reason- 
 ably equipped mine shop, which will allow 
 the mine to fabricate enough of the de- 
 vices to be generally useful. Three of 
 the devices developed thus far and their 
 intended uses are — 
 
 1. Mine jack-wheel changer. — This de- 
 vice (fig. 6) is the underground version 
 of the floor jack found in most surface 
 maintenance shops. High-flotation tires 
 provide quick transport and positioning 
 in wet or rocky bottom, and the fore-and- 
 aft saddle adjustment permits easy align- 
 ment of bolt holes. With a jack of this 
 type, a shuttle car tire can be replaced 
 or a motor removed from under the machine 
 frame without any manual lifting. 
 
 2. Pivot boom. — This device (fig. 7) 
 is an adaption of a common device found 
 
 on pickup trucks. It can be used to lift 
 and position loads up to 500 lb that are 
 adjacent to any machine. 
 
 3. Scoop boom. — This is a hydrauli- 
 cally driven boom mounted on the front of 
 a scoop for heavy lifting and transport- 
 ing (fig. 8). It incorporates a hydrau- 
 lic winch and 100 ft of cable for pull- 
 ing objects and for general lifting 
 activities. 
 
 When the detailed engineering drawings of 
 these and other mechanical-assist devices 
 are finalized, they will be supplied to 
 all interested mining companies. 
 
 Task or Load Redesign 
 
 In this second category, the standard 
 rock dust bag may provide an example of 
 the advantages of redesigning packaging. 
 Rock dust is packaged in heavy paper bags 
 
 FIGURE 6.— Prototype mine jack and wheel changer during testing. 
 
15 
 
 FIGURE 7.— Pivot boom mounted on maintenance vehicle. 
 
 
 
 FIGURE 8.— Scoop boom at an eastern Kentucky coal mine. 
 
16 
 
 that are fairly unstable and can break 
 open rather easily. Although the weight 
 of the package, 50 lb, seems reasonable, 
 it may be excessive in the unique situa- 
 tion of lifting in low-seam mines. 
 
 The unloading of the rock dust supply 
 car at the underground storage area was 
 observed as part of the task analysis. 
 The supply car had a normal load of 216 
 rock dust bags. These were unloaded by 
 the two supply workers in two 10-min work 
 periods separated by a 5- or 10-min rest 
 period. Thus each worker unloaded an 
 average of 54 bags per 10-min work peri- 
 od. Working in low coal, these employees 
 generally alternated among working on 
 both knees, working on one knee (the oth- 
 er one being used as a brace or support) , 
 and working in a stooped-over position. 
 This task involved fully extending the 
 arms and picking up the 50-lb bag (or, if 
 possible, sliding the bag across the sup- 
 ply car closer to the body and then lift- 
 ing it with arms bent) , twisting with the 
 load, and then fully extending the arms 
 again to place the rock dust bag onto the 
 storage pile that is lined up along the 
 haulage track. Of course, because of the 
 restricted height (42 in) , only about 
 eight bags could be stacked on top of one 
 another; placing the last two bags on the 
 pile involved a great deal of lateral 
 twisting and swinging the arms higher 
 than the worker's shoulder to put the bag 
 at the top of the pile before starting a 
 new pile along the track. This slide, 
 lift, twist, extend, and place activity 
 occurred every 11 seconds for a constant 
 10 min before they took a rest. 
 
 Reference 11, "Force Limits in Manual 
 Work," gives some idea of the strenuous- 
 ness of this particular task. This ref- 
 erence was developed in 1980 by the Mate- 
 rials Handling Research Unit in the 
 Institute of Industrial and Environmental 
 Health and Safety of the University of 
 Surrey (England) primarily to prevent in- 
 juries in the European coal and steel in- 
 juries. Figure 9, which is from refer- 
 ence 11, presents the acceptable weights 
 that can be lifted at various distances 
 from the acromion (the prominence) of the 
 worker's shoulder; this point is marked 
 in the figure by the black dot. 
 
 KEY 
 
 The vertical reference planes 
 used in the guide 
 / Hand(s) in front of the trunk 
 (sagittal plane) 
 
 2 Hand (s) in a plane at 45° 
 
 3 Hand(s) in line with shoulders 
 (coronal plane) 
 
 
 Age groups 
 
 -40 yr 
 
 4l"50yr 
 
 5l-60yr 
 
 
 male 
 
 male 
 
 male 
 
 A 
 
 14 kg 
 
 14 kg 
 
 10 kg 
 
 B 
 
 15 kg 
 
 15 kg 
 
 1 1 kg 
 
 C 
 
 20 kg 
 
 20 kg 
 
 14 kg 
 
 D 
 
 22 kg 
 
 22 kg 
 
 16 kg 
 
 E 
 
 25 kg 
 
 25 kg 
 
 18 kg 
 
 F 
 
 28 kg 
 
 28 kg 
 
 20 kg 
 
 G 
 
 30 kg 
 
 30 kg 
 
 2 1 kg 
 
 H 
 
 35 kg 
 
 35 kg 
 
 25 kg 
 
 K 
 
 40 kg 
 
 40 kg 
 
 28 kg 
 
 L 
 
 45 kg 
 
 45 kg 
 
 3 2 kg 
 
 M 
 
 50 kg 
 
 50 kg 
 
 36 kg 
 
 Two-handed upward, vertical forces 
 (including lifting) when kneeling on 
 one knee with the thigh of the other 
 leg approximately parallel to the 
 floor. The trunk should be main- 
 tained in a reasonably upright 
 position, with the weight divided 
 equally between the two hands, 
 which should be in similar positions 
 on either side of the body. 
 
 FIGURE 9.— Acceptable levels of lifting, vertical reference 
 planes. (By permission of Butterworth Scientific Ltd., P.O. Box 
 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH, 
 UK) 
 
 Assigning acceptable levels of force 
 application for a particular activity 
 "assumes that the worker [s] can perform 
 the particular maneuver in free space, 
 and that [they are] not required to carry 
 out the activity more than once a minute. 
 The effects of space limitation are un- 
 known. If the activity has to be per- 
 formed more than once per minute, then 
 the acceptable levels given in the tables 
 should be reduced by 30 pet. . . . Diagram 
 1 in each set gives the force levels with 
 the hand(s) directly in front of the 
 trunk, diagram 2 with the hand(s) in a 
 plane at 45° to the left or right, and 
 diagram 3 with the hand(s) in a plane in 
 
17 
 
 line with the shoulders" (11). (Emphasis 
 is in the original.) 
 
 Since the workers unloading rock dust 
 bags are positioned between the supply 
 car (on one side) and the stacks of rock 
 dust bags (on the other side) , their 
 movements are approximately from a 45° 
 plane on the right to a 45° plane on the 
 left and then back again. Thus, diagram 
 2 in figure 9 is applicable in deter- 
 mining what acceptable weight could be 
 lifted. Since the workers have to extend 
 their arms fully to grasp a rock dust bag 
 and then start to lift it, value C or E 
 in the table— 20 or 25 kg (44 or 55 lb) — 
 would be acceptable for 95 pet of the 
 male work force (similar acceptable lim- 
 its for female workers have not yet been 
 developed). However, since the activity 
 is performed more than once per minute, 
 the values have to be reduced by 30 pet; 
 thus, the acceptable values would really 
 be in the range of 14 to 17.5 kg (31 to 
 38.5 lb). This is when the workers are 
 kneeling; when they are lifting from a 
 stooped (standing, but bent over) posi- 
 tion, the situation is much more criti- 
 cal. The guide (_1J_) "does not consider 
 acceptable force levels for workers in 
 stooping positions. Stooping is known to 
 be dangerous, and should be avoided." 
 
 Figure 10 presents the acceptable lev- 
 els of lifting when the hand(s) are in 
 the horizontal plane directly in front of 
 the body (diagram 2) and when the hand(s) 
 are in a plane 45° above (diagram S) and 
 45° below (diagram 1) the horizontal 
 plane. These positions would correspond 
 to the movements of the workers when they 
 are placing the rock dust bag at the be- 
 ginning of a stack, and at the end (near 
 the roof). The critical values, as ex- 
 pected, are when the workers have to 
 raise the load into the 45° plane above 
 the horizontal; these values are again C 
 and E— 20 and 25 kg (44 and 55 lb). At 
 the same 30-pct reduction factor de- 
 scribed previously, the acceptable values 
 range from 31 to 38.5 lb. 
 
 As a result of these findings, the Bu- 
 reau recommended that the cooperator ini- 
 tiate a program to find a supplier who 
 will assist in developing a 25- or 30-lb- 
 capacity paper tube with a twist-gathered 
 
 2 <■ 
 
 KEY 
 The transverse planes used in 
 the guide 
 
 2 Hand(s) in the horizontal plane 
 level with the shoulders 
 
 3 Hand(s) in a plane 45° above 
 the horizontal plane 
 
 / Hand(s) in a plane 45° below 
 the horizontal plone 
 
 
 Age groups 
 
 = 40 yr 
 
 41-50 yr 
 
 51-60 yr 
 
 
 male 
 
 male 
 
 male 
 
 A 
 
 14 kg 
 
 14 kg 
 
 10 kg 
 
 B 
 
 15 kg 
 
 15 kg 
 
 1 1 kg 
 
 C 
 
 20 kg 
 
 20 kg 
 
 14 kg 
 
 D 
 
 22 kg 
 
 22 kg 
 
 16 kg 
 
 E 
 
 25 kg 
 
 25 kg 
 
 18 kg 
 
 F 
 
 2 8 kg 
 
 28 kg 
 
 20 kg 
 
 G 
 
 30 kg 
 
 30 kg 
 
 2 1 kg 
 
 H 
 
 35 kg 
 
 35 kg 
 
 25 kg 
 
 K 
 
 40 kg 
 
 40 kg 
 
 28 kg 
 
 L 
 
 45 kg 
 
 45 kg 
 
 32 kg 
 
 M 
 
 50 kg 
 
 50 kg 
 
 36 kg 
 
 Two-handed upward, vertical forces 
 (including lifting) when kneeling on 
 one knee with the thigh of the other 
 leg approximately parallel to the 
 floor. The trunk should be main- 
 tained in a reasonably upright 
 position, with the weight divided 
 equally between the two hands, 
 which should be in similar positions 
 on either side of the body. 
 
 FIGURE 10.— Acceptable levels of lifting, transverse 
 reference planes. (By permission of Butterworth Scientific 
 Ltd., P.O. Box 63, Westbury House, Bury Street, Guildford, Sur- 
 rey GU2 5BH, UK) 
 
 end. The tube would be easier to handle 
 because of the lighter weight, and the 
 twisted end would provide a more positive 
 means of grabbing and handling the pack- 
 age. Modifications to other supplies 
 may also be considered based on future 
 research. 
 
 Task Elimination 
 
 Task elimination is the best way to 
 avoid possible injuries, but it presents 
 the most difficult change to accomplish. 
 One of the most common tasks in under- 
 ground coal mining is lifting and secur- 
 ing the continuous miner power cable to 
 the roof bolt plates so the continuous 
 miner and other mobile equipment can 
 travel freely without running over and 
 
18 
 
 damaging the cable. An alternative that 
 is being tested is a lightweight cable 
 ramp. This device will eliminate the 
 
 hazardous task of lifting the power cable 
 by enabling mobile equipment to drive 
 safely over the (protected) cable. 
 
 LABORATORY SIMULATION 
 
 A previous Bureau research project (12) 
 evaluated the job demands associated with 
 working in low-coal mines. The physio- 
 logical data were collected as the coal 
 miners performed their normal activities 
 underground. Ventilation volumes were 
 used to estimate the energy requirements 
 of the tasks performed. Other, more sen- 
 sitive instrumentation that could have 
 measured the oxygen consumption could not 
 be used since it was not approved for use 
 in underground mines. 
 
 In the current study, the Bureau col- 
 lected metabolic data while the coopera- 
 tor's miners performed several manual 
 tasks in a simulated low-seam environ- 
 ment. The mine simulator was located in 
 a laboratory setting where sophisticated 
 instrumentation could be used to collect 
 the pertinent data. The objective of the 
 laboratory research was to determine how 
 
 closely data from the simulated tasks, 
 which were conducted under controlled 
 conditions, compared with data collected 
 in the underground environemt. 
 
 The initial laboratory simulation test- 
 ing was conducted at the University of 
 Kentucky during January 1985, using nine 
 test subjects regularly employed in un- 
 derground coal mines owned by the cooper- 
 ator. Each test subject performed four 
 specific tasks: lifting the continuous 
 miner power cable and securing it to a 
 standard roof bolt plate; constructing a 
 roof support cribbing and installing 
 tightening wedges; lifting and position- 
 ing concrete blocks to build a ventila- 
 tion stopping; and moving 50-lb rock dust 
 bags from one side of the simulator to 
 the other. Some of these tasks are shown 
 in figures 11 through 13. 
 
 FIGURE 11.— Hanging miner cable: laboratory simulation. 
 
19 
 
 FIGURE 12.— Building a stopping: laboratory simulation. 
 
 FIGURE 13.— Handling rock dust: laboratory simulation. 
 
20 
 
 The mine simulator was designed and 
 constructed by Bureau employees; it con- 
 sisted of standard 2- by 4-in studding 
 for the sides, 3/16-in plywood for the 
 floor, and chicken wire for the roof. 
 The roof design allowed overhead photos 
 to be taken is desired, but prevented the 
 test subjects from standing upright. The 
 roof was variable from 32 to 48 in, in 
 increments of 2 in; most tasks were 
 conducted with a roof height of 42 in. 
 Rock and coal were scattered about on 
 the floor, so the test subjects had a 
 sense of kneeling in a typical mine 
 environment. 
 
 As each task was conducted, high-speed 
 films were taken of the subject simulta- 
 neously from locations that were perpen- 
 dicular to the front and one side of the 
 simulator. The analysis of these films 
 will determine the range of motion that 
 the various body segments of the workers 
 moved through as the tasks were con- 
 ducted. This type of information, cou- 
 pled with anthropometric measurements of 
 each miner, will be used to determine the 
 amount of torsional loading experienced 
 by a miner's lower back during these work 
 activities. 
 
 In addition to this biomechanical eval- 
 uation, metabolic measurements were col- 
 lected for three of the four tasks. 
 
 Metabolic data were not collected for the 
 cable lift because this activity occurs 
 so quickly that the data would be mean- 
 ingless. The other tasks, however, were 
 ideal since they were conducted long 
 enough so that a measure of the worker's 
 energy expenditure (V02> which is the 
 volume of oxygen used) was obtainable for 
 each activity. Analysis of these data 
 will provide an indication of the physio- 
 logical cost of the job in terms of the 
 volume of oxygen utilized per minute of 
 activity performed. Thus, the absolute 
 oxygen requirements for the three differ- 
 ent tasks will be determined; these data 
 will be published in the future. 
 
 Table 3 presents the mean and standard 
 deviation of the metabolic data collected 
 from the nine test subjects for the three 
 simulated tasks. The data indicate that 
 building a roof support cribbing and mov- 
 ing concrete blocks to build a ventila- 
 tion stopping are equally strenuous. 
 Moving rock dust bags, however, is quite 
 a bit more demanding. Another Bureau- 
 funded research study (13) utilized oxy- 
 gen-consumption information to catego- 
 rize the grade of manual work (table 4). 
 Based on these categories, handling 
 concrete block and building a cribbing 
 are considered heavy work and moving 
 
 TABLE 3. - Energy expenditure requirements for performing 
 specific simulated low-coal mining activities 
 
 Task' 
 
 V0 2 , L/min 
 
 Mean Std dev 
 
 Energy, kcal/min 
 
 Mean Std dev 
 
 Building cribbing 
 
 Moving concrete block 
 
 Moving 50-lb rock dust bags, 
 
 1.68 
 1.69 
 2.06 
 
 0.26 
 .32 
 .34 
 
 8.4 
 8.45 
 10.3 
 
 1.3 
 1.6 
 1.7 
 
 Bureau of Mines-University of Kentucky laboratory simulation 
 data. 
 
 *9 replications for each task. 
 
 TABLE 4. - Energy expenditure and grades of work 
 
 Grade of work 
 
 Energy expenditure, kcal 
 
 Approx O2 con- 
 
 
 Per minute 
 
 Per 8-h shift 
 
 sumption, L/min 
 
 
 >12.5 
 
 10.5- 12.5 
 
 7.5- 10.0 
 
 5.0- 7.5 
 
 2.5- 5.0 
 
 <2.5 
 
 >6,000 
 4,800- 6,000 
 3,600- 4,800 
 2,400- 3,600 
 1,200- 2,400 
 
 <1,200 
 
 >2.5 
 2.0- 2.5 
 
 
 1.5- 2.0 
 
 
 1.0- 1.5 
 
 
 .5- 1.0 
 <.5 
 
21 
 
 FIGURE 14.— Controlled studies related to lifting In the stooped posture (while the test subject's expired air is collected and 
 analyzed), conducted at the Bureau's Ergonomics Laboratory at the Pittsburgh Research Center. 
 
 rock dust bags is considered very heavy 
 work. 
 
 The biomechanical data analysis was 
 completed by February 1986. It is impor- 
 tant to note that only nine workers have 
 been tested under these controlled con- 
 ditions; a much larger sample popula- 
 tion has to be tested before any meaning- 
 ful conclusions can be drawn from this 
 testing. 
 
 As a continuation of this research, 
 biomechanical and physiological testing 
 has been initiated at the Bureau's Pitts- 
 burgh Research Center Ergonomics Lab 
 (fig. 14). Future plans include conduct- 
 ing the same type of underground task 
 
 analysis with selected coal companies in 
 central and western Pennsylvania. As the 
 task analysis is conducted in the under- 
 ground workplace, volunteers will be 
 selected from the job categories that 
 normally involve a great deal of manual 
 handling of supplies and equipment (la- 
 borer, supply worker, mechanic, shuttle 
 car or scoop operator, continuous miner 
 helper, etc.) to participate in labora- 
 tory studies under closely controlled 
 test conditions. This laboratory testing 
 will increase the data base to enable the 
 Bureau to develop guidelines for handling 
 and lifting supplies and equipment in un- 
 derground low-seam coal mines. 
 
 SUMMARY 
 
 Working in underground mines involves 
 a great deal of manual handling of mate- 
 rials. Accidents from manually han- 
 dling supplies and equipment typically 
 
 represent 30 to 40 pet of all lost-time 
 accidents in underground coal mining. 
 
 A task analysis conducted at three un- 
 derground coal mines in eastern Kentucky 
 
22 
 
 identified a need for organization in 
 both the surface and underground storage 
 areas. Additionally, it indicated that 
 commercially available materials-handling 
 devices should be utilized. Other types 
 of mechanical-assist devices were de- 
 signed and tested underground in an at- 
 tempt to modify several lifting tasks. A 
 few tasks were identified that could be 
 eliminated by utilizing materials-han- 
 dling devices or through modifications to 
 the work procedure. 
 
 Another possibility for reducing in- 
 juries from manually handling supplies 
 depends on communication between the cus- 
 tomer and vendor. For example, the ven- 
 dor may be able to supply smaller sized 
 loads or palletized loads, which can be 
 handled more easily at the mine. This 
 type of communication is critical. 
 
 The task analysis identified that only 
 9 of a total of 48 tasks observed (less 
 than 20 pet) were conducted by mechanical 
 means; a total of 39 (more than 80 pet) 
 were handled manually. The Bureau esti- 
 mates that approximately two-thirds of 
 the manual handling tasks that were ob- 
 served could be modified by existing or 
 easily designed mechanical-assist de- 
 vices. Finally, the analysis indicated 
 that some of the manual activities ex- 
 ceeded acceptable lifting limits. 
 
 Laboratory simulation of several lift- 
 ing tasks, which tested coal miners under 
 controlled conditions, permitted a bio- 
 mechanical and physiological analysis of 
 those activities. This type of testing 
 will be the basis for developing lifting 
 guidelines for the underground low-seam 
 coal mining industry. 
 
 REFERENCES 
 
 1. National Academy of Sciences. To- 
 ward Safer Underground Coal Mines. 1982, 
 190 pp. 
 
 2. Mine Safety and Health Administra- 
 tion (U.S. Dep. Labor). Back Injuries in 
 Coal Mining, 1978-1979. MSHA Yellow- 
 jacket, 1980, 10 pp. 
 
 3. Peay, J. M. (comp.). Back Injur- 
 ies. Proceedings: Bureau of Mines Tech- 
 nology Transfer Symposia, Pittsburgh, PA, 
 August 9, 1983, and Reno, NV, August 15, 
 1983. BuMines IC 8948, 1983, 110 pp. 
 
 4. Foote, A. L. , and J. S. Schaefer. 
 Mine Materials Handling Vehicle (MMHV) 
 (contract H0242015, MBAssociates) . Bu- 
 Mines OFR 59-80, 1978, 308 pp.; NTIS PB 
 80-178890. 
 
 5. Booz Allen and Hamilton Inc. Sys- 
 tem for Handling Supplies in Underground 
 Coal Mines, Executive Summary. Ongoing 
 BuMines contract HO 188049; available upon 
 request from R. Unger, BuMines, Pitts- 
 burgh, PA. 
 
 6. Canyon Research Group, Inc. /Essex 
 Corp. Mine Maintenance Material Handling 
 Vehicle: Investigative Study and Concept 
 Development. Ongoing BuMines contract 
 H0113018; for inf., contact R. Unger, 
 BuMines, Pittsburgh, PA. 
 
 7. Unger, R. L. , and D. J. Connelly. 
 Materials Handling Methods and Problems 
 in Underground Coal Mines. Paper in Back 
 Injuries. Proceedings: Bureau of Mines 
 
 Technology Transfer Symposia, Pittsburgh, 
 PA, August 9, 1983, and Reno, NV, August 
 15, 1983, comp. by J. M. Peay. BuMines 
 IC 8948, 1983, pp. 3-13. 
 
 8. Unger, R. L. Mechanization of Ma- 
 terials Handling Tasks. Paper in Back 
 Injuries. Proceedings: Bureau of Mines 
 Technology Transfer Symposia, Pittsburgh, 
 PA, August 9, 1983, and Reno, NV, August 
 
 15, 1983, comp. by J. M. Peay. BuMines 
 IC 8948, 1983, pp. 102-110. 
 
 9. Snook, S. H., and V. M. Ciriello. 
 Maximum Weights and Work Loads Acceptable 
 to Female Workers. J. Occup. Med., v. 
 
 16, No. 8, 1974, pp. 527-534. 
 
 10. Snook, S. H. The Design of Manual 
 Handling Tasks. Ergonomics J. (London), 
 v. 21, No. 12, 1978, pp. 963-985. 
 
 11. Materials Handling Research Unit, 
 University of Surrey (England). Force 
 Limits in Manual Work. IPC Sci. and 
 Technol. Press Ltd., 1980, 25 pp. 
 
 12. Texas Tech University. Mining in 
 Low Coal. Volume 1: Biomechanics and 
 Work Physiology (contract H0387022) . Bu- 
 Mines OFR 162(l)-83, 1981, 175 pp.; NTIS 
 PB 83-258160. 
 
 13. . Biomechanical and Work 
 
 Physiology Study in Underground Mining 
 Excluding Low Coal (contract J0308058) . 
 BuMines OFR 90-85, 1984, 211 pp.; NTIS PB 
 85-243566. 
 
 6 U.S. GOVERNMENT PRINTING OFFICE: 1986—605-017/40,071 
 
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