V . 1 • . ,ci°* \**^ ' ■%..^'' * .-/ .MC4'-. %<** .'»fe-- \/ .'^". \,** .* •y% \w° /\ ■• ^r* (4.V "^ e.^*^ «? '^i) '>i^ t^ v^ »!:^'* <^ ■?• -^o. ^^..^^ ^••, "^o 0,0 ,v, .o* . « • • ' ' o ^» ^-^^ '^ .\ m cN^' ^u^.i'^^ t~ .n %i^ °-°'' / ... V^-\y ,.. V*^\^«' \.;^^^\/ V'"^-'.o^' ^'^^^ •- 4* .: "-^0 .^^ '^_ <. ^'T:.* .0^ "^^ 'o.»- A ^ *?^T*' 6*- ' •0* v^ ..r^'*^ o^ > .A^ /^'- %. .^ * V^ .** VI'* "C^ . / n • .-^.^ ^. .^ ^^mD%\ 'V /^' .'k^f/h.^^ ^e.. A^ -^^^^^ ^^^^ "o ^Ovv >; o-.o'- 0^ ^^/*i^.^\/ V"^%°' \*^-'\/ ^''^^-^c^ V'^f r^ -■ -.J- "^-"^ i^' ^--^^ -^"t %/ A'-^ \/ -m- %.** .<^ >«^-^ . « * . G^ ^ ^^•n^^ .♦^'^^ -.^IK.- «,^^'^^.. \['^f^^\^ .-lOx. ^""^t^ 0> ^•^' •A . I ' « ^ -^ IC 8983 Bureau of Mines Information Circular/1984 Improved Personnel Access for Surface Mining Equipment By Dennis A. Long UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 8983 Improved Personnel Access for Surface Mining Equipment By Dennis A. Long UNITED STATES DEPARTMENT OF THE INTERIOR William P. Clark, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Long, Dennis A Improved personnel access for surface mining equipment. (Information circular / U.S. Dept, of the Interior, Bureau of Mines ; 8983) Bibliography: p. 19. Supt. of Docs, no.: I 28. 27:8985. 1. Strip mining— Equipment and supplies— Safety measures. 2. Ladders— Safety measures. 3. Stairs— Safety measures. I. Title. II. Series: Information circular (United States. Bureau of Mines) ; 8983. TN295,U4 [TN291] 622s [622'.8] 84=600089 \J CONTENTS <^ Page k 1^ Abstract 1 N. Introduction 2 (>^ Safety hazard assessment 2 "^ Haulage trucks and front-end loaders 3 Access design problems 3 Improved ladders 7 Development 7 Description and use 12 Track dozers and shovels 13 Access design problems 13 Powered safety steps 14 Development 14 Description and use 16 Summary and economic considerations 18 References 19 Appendix 20 ILLUSTRATIONS 1. Typical ladder on off -highway haulage truck 3 2. Ladder located at right front of truck 4 3 . Truck bumper as part of ladder system 5 4. Damaged truck ladder 6 5 . Cable ladder showing height of first step 8 6. Cable ladder showing lack of rigidity when stepped on 9 7 . Pre-tensioned spring step design 10 8. Spring step retrofitted to truck ladder 11 9 . Spring step during collision 12 10. Track dozer 14 11. Loading shovel 15 12. Powered safety step on loading shovel 16 13. Powered safety step on track dozer 17 TABLES 1. Recommended design dimensions for ladder systems on large haulage trucks and front-end loaders 7 2 . Pre-tensioned spring specifications 10 A-1 . Field test locations for pre-tensioned spring step 20 A-2. Equipment used for evaluating pre-tensioned spring step 20 v^ A-3. Field test locations for powered safety step 20 1 A-4. Equipment used for evaluating powered safety step 20 ^-a '^ UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT deg degree lb pound ft foot pet percent in inch yr year IMPROVED PERSONNEL ACCESS FOR SURFACE MINING EQUIPMENT By Dennis A. Long ABSTRACT Slip and fall accidents are a major cause of lost-time injuries asso- ciated with large mobile equipment in surface mines. An evaluation of the safety hazards associated with getting on and off large surface mining vehicles showed that most of the accidents occur at the point where personnel attempt to mount or dismount the machine at ground lev- el. The major hazardous design conditions were identified as exces- sively flexible supports for lower steps or rungs, inappropriate ground-level-to-first-step distances, poor step designs, access designs that use vehicle components as steps or walkways, and inadequate hand- rail and guardrail designs. Additional hazards are introduced by the lack of proper maintenance of ladder hardware and the work practices of operators in carrying articles while mounting and dismounting the vehi- cle. This Bureau of Mines report describes the design and in-mine testing of improved access systems for large mobile mining equipment. ^Mining engineer. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN, INTRODUCTION Mobile equipment manufacturers and min- ing companies recognize the difficulty of getting on and off the large mining equipment. Overall, there is a lack of effective guidance and design standards, and access systems appear to have been added as an afterthought in mobile equip- ment design. Thus, the stringent system design concepts employed for most of the machine features are not generally ap- plied in ladder access designs. On-site reviews were conducted to iden- tify design deficiencies of access lad- ders being used in surface mines. These reviews focused on handrail specifi- cations, step and ladder design, step and ladder placement, ground clearance, environment-induced problems , and human factors. General design problems were identified along with numerous specific safety problems. Design diversity and lack, of good safe- ty analysis may be a direct cause of the high slip and fall rates associated with mobile mining equipment. For example, drivers and maintenance personnel must usually work with various types of vehi- cles, creating a "transfer of training" problem associated with ladders of dif- ferent designs. In moments of inatten- tion or carelessness, or in emergencies, people react according to how they "ex- pect" to find access hardware. When de- signs deviate from these expectations (e.g., a step is only half as wide as the one above or below it), the potential for accidents increases. A review of a large number of mine mo- bile equipment (J^)^ identified the fol- lowing significant design deficiencies: • Inadequate handrail and guard- rail designs, which increase the difficulty of mounting and dismounting the vehicle. • Excessively flexible lower section supports for lower steps or rungs on lad- ders, making ascent or descent difficult. • Inappropriate ground-level-to-first- step distances, which create hazards. • Poor step designs that permit accu- mulations of mud, snow, ice, grease, and oil and create hazardous footing. • Access paths that require use of equipment components as primary steps , such as the tracks on dozers and shovels. • Work practices of operators in car- rying personal articles on and off the equipment introduce additional hazards. The access problem involves two types of mobile equipment. The first category includes haulage trucks and front-end loaders. These vehicles have vertical or near vertical ladders in the vicinity of the cab. Analysis has shown that the chief hazards are found in the first few steps of the ladder where the operator mounts or dismounts the machine (2^) . The second category includes tracked vehi- cles, such as dozers, shovels, and drag- lines. These vehicles have one common hazard: the primary access path usually involves using the track as a step, walk- way, or both. The Bureau conducted this investigation to determine and reduce the hazards asso- ciated with mounting and dismounting large mine mobile equipment. This report summarizes the research results for each of the two types of equipment , and in- cludes recommendations for alleviating the access problem. SAFETY HAZARD ASSESSMENT Evaluation of the safety hazards asso- ciated with mobile equipment in surface ^Underlined numbers in parentheses re- fer to items in the list of references preceding the appendix. mines confirmed that slip and fall acci- dents account for a substantial propor- tion of vehicle related accidents. Ac- cording to 1978-79 data from the Mine Safety and Health Administration (MSHA) , U.S. Department of Labor, slips and falls while mounting and dismounting machines constitute over one-third of all lost- time accidents associated with the opera- tion of haulage trucks, front-end load- ers, track dozers, shovels, and draglines (2^) . These five types of equipment ac- count for 80 pet of the mobile equipment operating in U.S. surface mines. An average slip and fall results in 15.3 lost worker days and the characteristic injuries resulting from getting on and off mobile equipment are cuts, lacera- tions, contusions, fractures, sprains, and strains. The hands, fingers, back, legs, and feet are most frequently in- jured in these accidents (2). The slip and fall accident reports were further analyzed to determine where in the process of mounting or dismounting the machine people are getting hurt. The analysis revealed that 40 pet of all sur- face mine equipment slip and fall acci- dents occurred at the first step on the vehicle; that is, during the operator's initial attempt to mount or dismount the vehicle, with the accident occurring at the zone between the equipment and the ground (2^) . Nearly 60 pet of all slip and fall accidents involving track dozers occur at this point. HAULAGE TRUCKS AND FRONT-END LOADERS ACCESS DESIGN PROBLEMS Off -highway haulage trucks usually have ladders mounted on the front of the truck adjacent to the left side of the engine compartment (figs. 1-2), with the angle of inclination between 75° to 90° (verti- cal) . On some model trucks, the bumper FIGURE 1. - Typical ladder on off-highway haulage truck. FIGURE 2. - Ladder located at right front of truck. is used as part of the ladder structure (fig. 3). Most of the designs have lower ^ steps supported by flexible material such as wire rope, chain, or a rubber belting material. The ladders used on almost all front- end loaders are located directly along- side the cab. This design forces the operator to change direction in the mid- dle of the ladder in order to open the door. He must also negotiate a difficult transition from the ladder into the cab. Some front-end loaders have a movable or retractable ladder that the operator must pull down to mount the vehicle. Ladders provided as original equipment are often easily damaged once the vehicle operates in the mine environment, and even slight damage can render them in- operable. A damaged ladder represents a safety hazard (fig. 4). In many cases, after making numerous repairs, the mine maintenance shop personnel will construct a ladder from available scrap steel, ca- ble, and grip-strut material. Conse- quently, a wide range of ladder designs exists throughout the mining industry. Ladder reliability is directly related to the complexity, placement, and quality of installation. The most significant problem or defi- ciency of the primary ladder system is the lower steps. Within the open pit mine environment , the problem of vehicle ground clearance is critical; the truck FIGURE 3. - Truck bumper as part of ladder syste m. FIGURE 4. - Damaged truck ladder. is designed to ensure the maximum possi- ble ground clearance. The lower portion of the primary ladder assembly must be below this level for the operator to reach the first step, placing the first two steps in a vulnerable position. As a result, the ladders are subjected to con- tinual impacts from the objects in the roadway. To minimize damage, lower ladder sup- ports are usually constructed from a very flexible material. Usually this means suspending the lower one or two steps on a cable which is then mounted to the bumper or the ladder. These wire rope or cable ladders are invariably knocked out of position, and do not return to their initial configuration (figs. 5-6). The height of the lower rung is usually about 36 to 42 in above the ground. Drivers and other personnel ascending or de- scending the vehicle using these damaged lower steps are subject to knee and shin bruises, scrapes, or worse. The flexi- bility of the ladder supports for the lower steps and the fact that the steps are too high for the operator to mount and dismount the machine safely contrib- utes to the slip and fall accidents. IMPROVED LADDERS Development In 1978, the Bureau of Mines began to design and develop improved ladder de- signs for haulage trucks and loaders. Several alternative designs were sub- jected to human-factor field evaluation and structural testing demonstrations in various surface mines. The effort was first focused on off-highway haulage trucks, and design recommendations were developed for improved total access sys- tems. Table 1 summarizes the recommended ladder dimension systems for large haul- age trucks and loaders (_3) . Field inves- tigations showed that the most serious design deficiencies were at the lower end of the ladders; further Bureau of Mines research focused on solving the problem of the lower ladder design. Several primary lower ladder designs were subjected to use by mine personnel and field evaluation, and structural- testing demonstrations. As a result of the initial field demonstrations, it was concluded that the four-spring design (figs. 7-8) could appreciably reduce slip TABLE 1. - Recommended design dimensions for ladder systems on large haulage trucks and front-end loaders (3) Parameter Specification Minimum Maximum Angle of inclination deg. . Step dimensions, in: First-step height above ground Distance between steps ^ Distance from top step to platform Ladder depth^ Step width Step depth^ Handrail dimensions, in: Diameter Height above ground Width between at ground level Hand clearance Height above landing 76 90 None 28 10 12 10 12 8 10 12 16 4-3/4 7-1/2 3/4 1-1/2 28 56 18 21 3 None 33 36 'Measured vertically from top of step to top of step. ^To provide a minimum of 3 in from back of step to pan for toe clearance and a passage for debris to drop through. ^Standard dimensions for grip-strut step material. FIGURE 5. - Cable ladder showing height of first step. FIGURE 6. - Cable ladder showing lack of rigidity when stepped on. and fall accidents on haulage trucks and loaders. The first-generation spring steps were evaluated for operator accept- ability and structural performance at the Cyprus Pima Mine, south of Tucson, AZ, in 1978, and at the Bingham Canyon Mine, near Salt Lake City, UT, in 1979 ( 4_) . The prototype lower steps substantially reduced the height of the first step and were much more rigid when stepped on, or off. Because of their high stiffness co- efficient and the pre- tensioning of the springs, the prototype lower steps close- ly maintained the step distance and the angular inclination of the ladder. How- ever, the pre-tensioned springs used in the first step proved to be too brittle to withstand the rugged mine environment. placement of the spring step on the mine vehicle. For example, a step mounted either directly on the bumper or on the side of the vehicle is likely to have limited survivability. As a result of the in-mine test- ing, a second-generation pre-tensioned spring step was developed. The second- generation design parameters are listed in table 2. The most significant change was to adopt a modular design; rather than a one-piece welded unit, the grip- strut steps and each two-spring set are replaceable as individual parts. Further development has made the pre-tensioned springs more durable, using more rigid spring steel and different welding techniques. The test program demonstrated that proper installation techniques were im- portant for the survivability of the spring step. These techniques include good welding practices and proper A followup testing program was con- ducted at seven surface mines , where various types of haulage trucks larger than 100-ton capacity were fitted with ladders of the new design (2). The 10 TABLE 2. - Pre-tensioned spring specifications Material , Rockwell hardness Spring, OD in, Wire size in. Type of ends , Direction of helix , Pre-tension lb. Free length in, Chrome-nickel steel, 17-7 pH (ASTM 3-313 or AMS 5678) 47-52, C-scale 1.75+0.030 0.312 Ground, plain LH, optional 150±10 11-1/8 NOTE. — Tensile test coupons 8 in long should be taken of wire before winding each spring lot and also of each heat lot and shipped with springs for quality control. ladders were subjected to normal operat- ing use for at least 1 yr, during which evaluations were made of the safety, maintenance, and driver acceptance of the spring step. Further field testing of the pre-tensioned spring step is being conducted at six additional mines using a variety of mobile equipment. The mines and equipment are listed in the appendix tables. Table A-1 identifies the mines where the spring step has been field tested, and table A-2 lists the surface mining equipment on which spring steps have been installed. FOUfi SFRINe-SDPPORTED LOWER STEPS RIGID LADDER ASSEMBLY GRIP-STRUT STEP MATERIAL PRE-TENSION SPRING ASSEMBLY FIGURE 7. - Pre-tensioned spring step design. 11 FIGURE 8. - Spring step retrofitted to truck ladder. Since 1978, about 30 spring steps were field tested at 13 mines on 27 vehicles. The results of the field testing indicate that the pre-tensioned spring step can help prevent first-step accidents. How- ever, the testing also shows that proper installation techniques, correct vehicle applications , and management support for proper maintenance are important for long life of the spring step. Spring-step failure occurred for a variety of rea- sons, and the damage inflicted on the spring ladders varied greatly from mine to mine. At some mines, the ladders sus- tained damage after 3 or 4 weeks; at oth- ers, ladders remained on the trucks with little or no damage for more than a year. The most common reasons for failure included shear at the point where the step is welded to the ladder, spring failure resulting from low ground clear- ance, and lack of operator or supervisory acceptance. Some damage seemed to be a result of a misconception that the Bureau of Mines spring step is indestructible. In several cases , the vehicle operator may have been experimenting to see how much punishment the spring step could withstand. In summary, the following include the results from the long-term field tests. These points should be considered in all future spring step applications: 1 . The ladders should be mounted higher than they were in most of the test installations. The spring failures oc- curred mostly at the connection of the upper supporting springs and the collar. By mounting it higher, this connection would be more protected. Although Soci- ety of Automotive Engineers (SAE) stan- dards advise a 28-in minimum ground clearance, best results will occur at heights greater than 30 in. In mines 12 that have parking ditches or extraordi- nary ground clearance problems (soft, muddy haulroads or special guide berms), the operator should ensure that the bot- tom of the step will not undergo continu- ous ground impact. 2. Never install the spring step di- rectly on the bumper. This causes large shear forces to develop at the top of the step. 3. Proper welding and installation techniques are important. Normally, in- stallation will take around 2 worker hours, and should be supervised. 4. The spring step should only be in- stalled perpendicular to primary vehicle movement; e.g., never install the spring step on the side of a haulage truck. 5. Vfliere possible, the complete three- step unit (as shown in figure 7) should be used, even if part of the existing ladder must be cut off to maintain suffi- cient ground clearance. 6. Keep the step weight as low as pos- sible by using lighter gauge metal. 7. Spring step width should correspond to the overall ladder width; and a 15-in step width for front-end loaders and rubber-tired dozers. Description and Use The spring ladder concept is shown in figure 9. The design is to provide the operator with basic human-factor de- sign and to minimize damage to the lower steps on the primary ladder system. The FIGURE 9. = Spring step during collision. 13 ladders are designed to deflect with min- imal damage when impacting an object, but support the weight of the operator with minimal deflection (less than 2 in). The steps are highly resistent to col- lision damage because they yield on im- pact if rammed into obstructions such as rocks or berms. The ground clearance re- quired for rigid ladders mounted on large mining equipment is commonly 36 to 42 in. The flexibility of the durable spring- mounted supports allows the new ladders to be mounted with the bottom step be- tween 24 and 36 in above the ground, de- pending on the application. The spring step is a totally passive system; i.e., it needs no activation by the operator. The unit consists of two steps constructed with grip-strut mate- rial to minimize the acciimulation of de- bris and provide an antiskid surface for good footing. The steps are joined with two pairs of spring assemblies and mount- ing brackets. The mounting brackets con- sist of a flat plate and a collar to sup- port the spring, which is welded to the flat plate. The springs are fabricated from stainless steel and pre-tensioned to 150 lb. The best results will be ob- tained by following the specifications developed in Bureau of Mines contract (2^). The entire primary ladder assembly, including the spring ladder, should con- form to the SAE requirements (3) . These SAE recommendations cover access sys- tems for large construction and mining machines, and specify ladder inclination, handrail dimensions and clearance, rung spacing, rung width, and other features. There are other options available for using the spring step. On some trucks, a single-step spring ladder was installed in place of the standard oil check step. These ladders underwent no damage dur- ing the course of the program, but these steps were in a more protected area mounted under the engine compartment. On certain front-end loaders and smaller haluage trucks, a single-step ladder (one-half of ladder shown in figure 7) was installed at the bottom of the lad- der. However, wherever possible, the double spring step should be used for op- timum survivability. TRACK DOZERS AND SHOVELS ACCESS DESIGN PROBLEMS Over the past decade, the size of track dozers in surface mines has increased substantially. Today the operator must climb 4 ft or more to mount the dozer, usually stepping onto or climbing over the track assembly. Because of the harsh working environment encountered by the dozer, the tracks are usually covered by mud, snow, or ice, making them an unsat- isfactory accessway. On some dozers, the track assembly is the only way to mount the vehicle (fig. 10). In this situation, the operator must use the track grips to mount the dozer at the rear of the machine, then walk on the track to reach the cab. On certain large dozers, the person must mount the machine at the front by step- ping onto the blade arm and then walking along the track to enter the cab. On some machines , the person uses a toe-hole in the side track frame, then steps up to the track. In any event, the distance from the ground to the track usually ex- ceeds 48 in, presenting a challange under any environmental condition. The ladders and stair systems used on mining shovels and draglines vary in quality of design and safety. Many of the larger excavators use electricity or hydraulically operated stairways for access to the main decking or cab. Small to medium machines often utilize sev- eral variations of the pull-down and counterbalanced-stair systems (fig. 11). The Bureau's work determined that the design area requiring the most work was the zone where the operator mounts or dismounts the piece of equipment. Almost all models require the operator to climb over the track assembly. An improved 14 FIGURE 10. - Track dozer. system would result in a safer method of transporting operators and materials up and over the track assembly. There have been several efforts to de- vise alternative entry systems for track dozers and shovels. One method used a* ladder extending out over the tracks. A second method entailed the use of a load- ing berm that the dozer pulled up next to, permitting the operator to exit via the berm, rather than having to climb down the tracks. A third method, spon- sored by the Bureau of Mines on a cost- sharing basis , uses a hydraulic lift "power step" to transport the person from the ground level to the cab. This devel- opment has proved to be a practicable solution to the access problem on track dozers and shovels. POWERED SAFETY STEP Development The powered safety step was designed in 1975. A prototype unit was installed on a Caterpillar 16G grader at Consolidation Coal Co.'s Glenharold Mine, near Stanton, ND, This unit is still in operation after 7 yr of continuous service. In view of its potential to reduce the num- ber of accidents caused by slips and falls from large mining equipment, in 1978 the Bureau of Mines began working with the powered step on a cost-sharing basis to make the technology more mine- worthy. This work included developing and fabricating step-design alternatives, and conducting in-mine tests to determine 15 FIGURE 11. - Loading shovel. survivability of the mine environment. step in the rugged Since 1978, the powered step has been field tested at different mines in North Dakota, Indiana, Illinois, Wyoming, and Tennessee. Thirty of the test units are still in operation and many more have been sold commercially during the past 2 yr. Current installations of the powered step include loading shovels, track doz- ers , draglines , haulage trucks , and graders. Table A-3 lists the field test locations, and table A-4 lists the mining equipment on which the powered steps have been installed. The results of the field testing have proved conclusively that the powered safety step can solve the problem of mounting and dismounting tracked mining vehicles. Almost 90 pet of the powered step units are still in use today on the original machines; several step units have been in continual use for more than 5 yr. The mines have reported that main- tenance is surprisingly low and survival is high. Almost without fail, installations on shovels , draglines , and dozers have proved successful over the long-term. More recently, installations on haulage trucks , graders , and scrapers have shown promising results. The following com- ments were made by the mine personnel in- volved with the field testing of the pow- ered steps: • "The safety steps that we have on our equipment are well accepted by em- ployees and management . " • "We feel that slip and fall acci- dents have been virtually zero since we installed these steps. They have been 16 accepted by the mining crews , and they would not be without them," • "It is the best method for getting on and off large shovels that I have ever seen. We plan to install similar appara- tus on all our shovels. We have not had any accidents with the powered steps. Very well accepted by all employees." • "I have been associated with these powered steps from the very beginning. We have had very few maintenance problems with the step." Description and Use The powered safety step is a hydrauli- cally powered device to lift personnel and materials from the ground to working levels on large equipment (figs. 12-13). The primary application of the powered step is for the large track dozers, shovels, and draglines. It eliminates hazardous blind steps, and makes it un- necessary for the operator to climb on irregular surfaces such as the track or push arm (_5) . The step is activated by a self- contained electric-hydraulic unit. Power comes either from the vehicle's auxiliary power supply or from its own battery source, depending on the application. When the step is in the "down" position, it rests approximately 15 in from ground level. When the machine is operating, the step automatically locks in the "up" position, protecting it against damaging obstructions. Visual alarms and machine interlocks are provided where necessary to prevent machine operation when the step is in the "down" position. On ro- tating machines, such as draglines and shovels, an electrical interlock is pro- vided to prevent operation of the swing motors when the step is down (5). 4r '■w^l! FIGURE 12. - Powered safety step on loading shovel 17 FIGURE 13. - Powered safety step on track dozer. 18 During step operation, when the power unit is activated with an electrical switch located on the step, a single cy- linder attached between two lifting arms smoothly lifts the step. The step is lowered by activating a pressure-release solenoid, bypassing the hydraulic pump. The hydraulic fluid is released through an in-line orifice, controlling the downward speed and preventing free fall. On most machines, additional control switches are located at ground level and in the cab. There are two basic designs of the pow- ered safety step. One operates only in the "up" and "down" directions. The sec- ond design, using a linkage and bearing arrangement on the mounting end of the lift arms, rotates the step toward the machine in conjunction with the lifting motion. Thus, the step moves in an arc from ground level to platform level. Each design is suited for specific appli- cations. With minor modifications, a powered step can be adapted to any type or model of large machinery. SUMMARY AND ECONOMIC CONSIDERATIONS Evaluation of the safety hazards asso- ciated with large mobile mining equipment has confirmed that slip and fall acci- dents account for a substantial propor- tion of vehicle-related accidents. Slips and falls while ascending or descending equipment constitute over one-third of all lost-time accidents associated with the operation of haulage trucks, front- end loaders , track dozers , shovels , and draglines. As a result, the Bureau of Mines initiated a program to develop and in-mine test improved access systems to reduce the hazards associated with mount- ing and dismounting large equipment. For haulage trucks and front-end load- ers , the Bureau of Mines developed a pre- tensioned step. The spring steps are de- signed to rigidly support the weight of the operator as he or she steps up onto the equipment, and are highly resistent to collision damage because they yield on impact if rammed into obstructions such as rocks or berms. Because the spring- mounted supports are flexible and dur- able, the improved ladders can be mounted with the bottom step 30 in above the ground. The improved spring steps can be in- stalled on existing haulage trucks or new ones at reasonable cost; they cost more than the current cable steps, but main- tenance and repair costs are substan- tially less, with individual replace- able parts. The complete step would cost around $400 under large-scale production and marketing. Although the spring-step units are commercially available, the Bureau recommends that individual mines operators construct their own spring steps using the design concepts devel- oped in this project. The pre-tensioned springs can be purchased in bulk quan- tity, and the step unit could be con- structed by mine personnel and using locally available material. In order to reach the cab of track dozers , shovels , and draglines , the oper- ator must climb up and over the tracks; the tracks are usually a part of the pri- mary access system. Because of the envi- ronment in which the equipment must oper- ate, those tracks are usually covered by mud, snow, or ice, making them an unsat- isfactory accessway. The most hazardous area is the zone where the operator mounts or dismounts the dozer or shovel. The height of the first step is most sig- nificant in all cases where the track as- sembly must be climbed over. Through a cost-sharing agreement, the Bureau has helped to develop and test a hydraulic lift safety step to transport people and supplies from the ground to working levels on large surface mining equipment. The powered step has proved to be a safe, effective method of trans- porting operators and material over the track assembly. The primary application of the powered step is for the large track dozers, shovels, and draglines. It eliminates hazardous blind steps and 19 makes it unnecessary to climb on irregu- lar surfaces, such as the track or push arm. The cost of the powered step ranges from $2,000 to $5,000, depending on the equipment application. The low- maintenance record should justify the in- stallation of the powered step, especial- ly when compared to the overall cost of shovels, draglines, or dozers. Installa- tions are recommended for most large doz- ers except at mines where the dozer must work in close, confining conditions. The powered step has proved to be a reliable, maintenace-free safety improvement in mobile surface mining equipment, and mine operators are encouraged to investigate the application of this new technology. REFERENCES 1. Gavan, G. A., D. P. Strassel, and D. A, Johnson, The Development of Im- proved Ingress/Egress Systems for Large Haulage Trucks, Pres, at SAE Earthmoving Industry Conf. (Peoria, IL, Apr. 14-16, 1980). SAE Tech. Paper 800680, 1980, 7 pp. 2. Gavan, G, A., P, Mote, D. P. Stras- sel, and K, Conway. Development and Dem- onstration of Improved Truck Ladders (contract H0282001, Woodward Associates, Inc.). BuMines OFR 87-81, 1979, 332 pp.; NTIS PB 81-223406. 3. Society of Automotive Engineers. Access Systems for Off-Road Machines. SAE J185, June 1981, 6 pp. 4, Johnson, D, A. Improved Ingress/ Egress Systems For Large Haulage Trucks: Development and In-Mine Testing. Paper in Surface Mine Truck Safety. Proceed- ings: Bureau of Mines Technology Trans- fer Seminars, Minneapolis, MN, June 25, 1980; Birmingham, AL, July 9, 1980; and Tucson, AZ, July 24, 1980, Comp. by Staff, Bureau of Mines. BuMines IC 8828, 1980, pp. 40-51. 5. Winters, K. Analysis of the Pow- ered Safety Step Ingress/Egress System for the Caterpillar DIG Crawler Tractor (contract P3391232, Woodward Associates, Inc.). BuMines Final Report, 1979, 65 pp.; available upon request from D. A. Long, BuMines, Minneapolis, MN. 20 APPENDIX TABLE A-1. - Field test locations for pre-tensioned spring step Mine Operator State Bingham Canyon Bonner Springs Quarry Cyprus Pima Detroit Salt Erie Georgetown Ribbing Taconite Indianhead Leahy Martiki Minntac Minorca Pinto Valley Tilden White Pine Kennecott Lone Star AMOCO Minerals.... International Salt Pickands Mather... CONSOL Pickands Mather... North American. . . . AMAX MAPCO U.S. Steel Inland Steel Newmont Cleveland-Cliffs . . Copper Range Utah. Kansas. Arizona. Michigan. Minnesota. Ohio. Minnesota. North Dakota. Illinois. Kentucky . Minnesota. Do. Arizona. Michigan. Do. TABLE A-2. - Equipment used for evaluating pre-tensioned spring step Equipment Manufacturer and model Bottom dump coal hauler. ...................... Dart 4120, 4150. Loader ...•...•.•...............*......•....... Caterpillar 988B. Michigan 27 5B. Caterpillar 777. Dart 2085. Euclid R-85, R-170. Terex 170. Unit Rig M36. Wabco 120 C, 120 D, 170. Caterpillar 657 B. Rear dump truck ............................... Scraper TABLE A-3. - ] Field test locations for pow( Bred safety step Mine Operator State Mine Operator State Ayshire. . . . Belle Ayr.. Beulah AMAX Indiana. Wyoming . » North Dakota. Wyoming . North Dakota. Indiana. Wyoming. Delta Falkirk.... Glenharold. Hooker Indianhead. Minnehaha . . Seminoe. . . . AMAX Illinois. • ••ClO*«««*»*««* Knife River. . . . Black Butte.... Baukol Noonan. . AMAX North American. CONSOL North Dakota. Do. Black Butte Center Chinook. ... Hooker Chemical North American. AMAX Tennessee. North Dakota. Indiana. Cordero. . . . Sunoco Arch Mineral. . . Wyoming . TABLE A-4. - Equipment used for evaluating powered safety step Equipment Manufacture and model Equipment Manufacture and model Haulage truck Unit Rig BD-180. Scraper Caterpillar 657. Dozer Caterpillar D7-G, D9-L, Shovel Bucyrus Erie 155 B, 190 B, DIO. 195 B, 290 B, 295 B. Fiat-Allis HD41 B. Marion 151 M, 182 M, Komatsu D455A-1. 192 M, 201 M. 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