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OPERATOR PROTECTION SYSTEMS AFETY ENHANCEMENT OF OPERATOR PROTECTION SYSTEMS ON SELF-PROPELLED MINING EQUIPMENT In the long term, with development of skill, knowledge, exposure and confidence within the engineering profession, rigorous analysis techniques have the potential to become a reliable and far more comprehensive method for design and verification of the structural adequacy of OPS, write Nimal J Perera, David P Thambiratnam and Brian Clark. This paper explores the potential to enhance operator safety of self-propelled mechanical plant subjected to roll over and impact of falling objects using the non-linear and dynamic response simulation capabilities of analytical processes to supplement quasi-static testing methods prescribed in International and Australian Codes of Practice for bolt on Operator Protection Systems (OPS) that are post fitted. The paper is based on research work carried out by the authors at the Queensland University of Technology (QUT) over a period of three years by instrumentation of prototype tests, scale model tests in the laboratory and rigorous analysis using validated Finite Element (FE) Models. The FE codes used were ABAQUS for implicit analysis and LSDYNA for explicit analysis. The rigorous analysis and dynamic simulation technique described in the paper can be used to investigate the structural response due to accident scenarios such as multiple roll over, impact of multiple objects and combinations of such events and thereby enhance the safety and performance of Roll Over and Falling Object Protection Systems (ROPS and FOPS). The analytical techniques are based on sound engineering principles and well established practice for investigation of dynamic impact on all self-propelled vehicles. They are used for many other similar applications where experimental techniques are not feasible. Heavy vehicles that are commonly used in mining, forestry and construction are susceptible to rollovers and impact from falling objects. Vehicle rollovers are due to their high centre of gravity and operation within close proximity of steep and unstable embankments and hill sides. Machinery operating close to unstable or newly excavated steep embankments and in forestry are susceptible to falling objects. There can be multiple causes such as unstable terrain and embankments and weather induced deterioration that can initiate accidents. The result could be either a single impact and rollover over or 68 AUSTRALASIAN MINE SAFETY JOURNAL multiple impacts and rollovers. There is also the potential for falling object impact and roll over to occur simultaneously in rare situations. The primary protection against such events is operational safety practiced by industry and well trained operators with a very high degree of care and diligence. Therefore despite the potential risks, extreme accidental events do not occur frequently. The purpose of the Operator Protection System (OPS) is to prevent the machine operator from being crushed or directly impacted by such a rare accident. Designers of OPS have the capability to investigate various scenarios of accidents using computer aided simulation techniques. They can include multiple impacts and rollovers on OPS. Galloway (1995) who targeted accidents associated with rollovers of tractors on farms suggested that ‘nearly nine out of every ten people killed on farms died as a result of accidents involving tractors. Of these, rollovers, where drivers or passengers are crushed beneath the tractor, are the most common type of accident.’ OPS are able to maintain the survival zone technically known as the Deflection Limiting Volume (DLV) for the safety of the occupant by absorbing the energy of the impact and rollover as it undergoes a combination of elastic and plastic deformation. Design and analysis are carried out to determine that they are flexible enough to absorb energy and rigid enough to limit deformation and maintain the DLV. Computer-aided techniques are used by the designers to simulate multiple accident scenarios and investigate the structural integrity of an operator protection system during the design phase. When large numbers of such units are produced by manufacturers of the heavy vehicles and earthmoving equipment it is feasible to carry out prototype testing to validate the design for different accident scenarios. However, similar testing processes are rarely if ever practiced for retrofitted and repaired OPS that are not mass produced and therefore are “one-off” products. They are very often designed using non-rigorous static analysis methods and subjected to test procedures prescribed in governing codes such as AS 2294.1 (1997) and Supplement 1 of 2003 and the previous and more recent ISO publications: ISO 3471(1994), ISO 10262 (1998), ISO 8084 (2003), ISO 8082 (2003), ISO 3449 (2005), ISO 8083 (2006) and ISO 12117 (2008). All these standards require physical testing for verification of the adequacy of OPS and do not permit the use of analytical techniques as the sole means of verification. There are many reasons for this requirement such as simplicity and convenience of a quasi-static test method, common and well established knowledge of such testing procedures, the ability to visually inspect and capture impact of manufacturing defects and geometric variances, repeatability of test until compliance requirements are met and capability and availability of competent testing facilities. The testing standards are performance based, with force and energy absorption criteria derived from empirical formulae related to the type of machine and operating mass. Deflection restrictions are defined to enable the DLV to be maintained to protect the vehicle operator under the test load conditions. The method has been correlated to actual performance with extensive studies to compensate for the dynamic influence of the loads for the recommended test loads imposed under quasi-static conditions. It is unlikely that the quasi static procedures in the current standards can adequately demonstrate dynamic elasto-plastic response, deformation and resistance that are essential to dissipate the energy of multiple impacts and rollovers although they substantially improve the operator’s chances of survival within the limitations of the testing regime. The testing requirements for very large machines can be onerous, expensive and time consuming especially if they have to be repeated several times for compliance with the specified criteria. The test criteria are sometimes satisfied by increasing the fabricated strength of frame components of the OPS without carrying out rigorous design procedures. That may not be the most desirable solution for the operator’s chances of survival, as the OPSs are in principle energy absorption and dissipation devices that require a balance between