Usability of the revised NIOSH lifting equation

Following the revision of the 1981 National Institute for Occupational Safety and Health (NIOSH) lifting equation, research needs related to the new equation were outlined. Aside from epidemiological studies, the need to evaluate the usability of the 1991 NIOSH equation in realistic work environments was expressed. This paper reports on extensive experiences with training users and application of the equation in varied work settings. Qualitative results from training sessions indicated that frequency, asymmetry and duration were the parameters that required relatively longer instruction periods and resulted in the most questions. Field applications indicated that the variable nature of lifting/lowering demands found in many jobs resulted in difficulty applying the equation. Approximately 35% of 1103 lifting and lowering tasks had at least one parameter outside of acceptable ranges, while a majority of workers (62.8%) reported other manual handling tasks that are counter to assumptions made in the development of the equation. The practical implications of the findings are discussed.     

Usability of the revised NIOSH lifting equation

Following the revision of the 1981 National Institute for Occupational Safety and Health (NIOSH) lifting equation, research needs related to the new equation were outlined. Aside from epidemiological studies, the need to evaluate the usability of the 1991 NIOSH equation in realistic work environments was expressed. This paper reports on extensive experiences with training users and application of the equation in varied work settings. Qualitative results from training sessions indicated that frequency, asymmetry and duration were the parameters that required relatively longer instruction periods and resulted in the most questions. Field applications indicated that the variable nature of lifting/lowering demands found in many jobs resulted in difficulty applying the equation. Approximately 35% of 1103 lifting and lowering tasks had at least one parameter outside of acceptable ranges, while a majority of workers (62.8%) reported other manual handling tasks that are counter to assumptions made in the development of the equation. The practical implications of the findings are discussed.     

Accuracy of measurements for the revised NIOSH lifting equation

Twenty-seven non-ergonomists who participated in a one-day training session on the use of the NIOSH lifting equation (NLE) were subsequently tested on a simulated lifting task eight weeks later to determine their accuracy in measuring the variables. Analysis of the results indicate that (1) inter-observer variability was small, especially for the most important factor (i.e. horizontal distance); (2) individuals can be trained to make measurements with sufficient accuracy to provide consistent recommended weight limit and lifting index values; and (3) measurement of the coupling and asymmetric variables were the least accurate.     

New procedure for assessing sequential manual lifting jobs using the revised NIOSH lifting equation

A sequential manual lifting job is defined as a job where workers rotate between a series of manual lifting rotation slots or elements at specified time intervals during the course of a work shift. The original NIOSH lifting equation lacked a method for assessing the physical demands of these types of jobs. This paper presents the sequential lifting index (SLI), a new conceptual method for assessing the physical demands for sequential manual lifting jobs. The new method is similar to the composite lifting index (CLI) method that was provided by NIOSH for assessing multi-task jobs. The SLI method expands upon the methods originally provided by NIOSH by providing a simple method for estimating the relative magnitude of physical stress for sequential manual lifting jobs. It should also be useful in assisting safety and health specialists to prioritize or rank hazardous jobs within a plant.     

A cross-validation of the NIOSH limits for manual lifting

The psychophysical, biomechanical, and physiological criteria used in establishing the NIOSH limits for manual lifting were cross-validated against the data published by different researchers in the subject literature. Assessment of the 1991 NIOSH lifting equation indicated that: (1) NIOSH-based limits are significantly different from the psychophysical limits in the (i) low and high frequencies of lift, and (ii) small and large horizontal distances; (2) NIOSH limits are highly correlated with the data of Snook and Ciriello (1991) in the low frequency range, with the Recommended Weight Limit (RWL) protecting about 85% of the female population and 95% of the male population; (3) the 3·4 kN limit for compression on the lumbosacral joint cannot protect the majority of the worker population on the basis of damage load concept; and (4) energy expenditure limits used in development of the RWL index can be sustained by 57 to 99% of worker population when compared to the physiological limits based on previous fatigue studies. Results of the cross-validation for psychophysical criterion confirmed the validity of assumptions made in the 1991 NIOSH revised lifting equation. However, the results of cross-validation for the biomechanical and physiological criteria were not in total agreement with the 1991 NIOSH model     

Comparing the revised NIOSH lifting equation to the psychophysical,biomechanical and physiological criteria used in its development

The purpose of this study was to perform a systematic and comprehensive comparison between the recommended weights of lift (RWL) from the revised NIOSH lifting equation, and the specific biomechanical, psychophysical and physiological criteria that were stated to be used in the equation's development. A composite acceptable load (CAL) table was developed for the 216 conditions presented in the female lifting table of Snook and Ciriello (1991). Each CAL value was calculated to correspond to the most conservative load of the three design criteria. The RWLs caused lumbar compression forces close to the biomechanical limit of 3400 N for lifts below knuckle height, but resulted in compression forces that are much lower at higher lifting heights. At moderate lifting frequencies, the average RWL would be acceptable to more than 95% of female workers according to the psychophysical criterion. At the highest frequencies, the RWL was found to be an average of 63% of the CAL values based on the integration of the psychophysical and physiological criteria. It is recommended that ergonomists acknowledge the very conservative nature of the revised NIOSH lifting equation when using it to evaluate occupational lifting tasks.     

Influence of measurement accuracy on the application of the 1991 NIOSH equation

A relatively neglected topic in manual materials handling (MMH) research is the impact of the accuracy of task parameter measurements on the application of various assessment methods. A laboratory experiment was conducted to investigate the accuracy of NIOSH equation parameter measurements made by eight subjects following a 4-h training session. Five individual tasks were measured; two were single tasks and three were part of a multiple-component simulated palletizing operation. Significant differences between reference parameter measurements and average measurements made by subjects were found. The sensitivity analysis showed that frequency and horizontal location are the most important parameters. These parameters also tended to have the highest measurement errors. Recommendations for increasing the effectiveness of training programs for NIOSH equation users based on the results of the study are presented.     

Biomechanical evaluation of lifting tasks: A microcomputer-based model

This paper discusses a static and dynamic biomechanical evaluation of sagittal lifting activities via a microcomputer model. The input to the developed model includes operator's anthropometric data, and sex. The model provides the reactive forces and torques at the various joints of the body expressed in both British and metric systems. Also, the model shows the calculated compressive force on the spine at the fifth lumber/first sacral joint (L5/S1), and both kinematic and kinetic informations are displayed. The model has a menu of five options: (1) to analyze stress imposed on the L5/S1 during a dynamic activity; (2) to determine maximum weight to be allowed during a dynamic motion; (3) to check stress on the spine (L5/S1) for specified static postures; (4) to determine maximum weight to be allowed for a static posture; or (5) to stimulate the lifting action and determine critical postures while performing lifting tasks based on static biochemical analysis.     

一种图像放大的偏微分方程综合模型

针对传统图像放大处理过程中基于线性插值方法通常导致边缘模糊问题,分析了各向同性扩散模型和各向异性扩散模型在图像处理中的优缺点,提出了一种线性扩散和P-M方程自适应结合的图像放大综合模型。该模型对图像非平滑区域采用各向异性扩散模型处理,而平滑区域则采用各向同性扩散模型处理。实验结果表明,该综合模型在保持图像边缘锐度的同时提高了图像的清晰度,能够有效提高放大图像的主观视觉质量和客观SNR及PSNR。     

Use of NIOSH equation inputs to calculate lumbosacral compression forces

The purpose of the current paper was to develop regression-based models that use NIOSH lifting equation H and V values to accurately calculate L₅/S₁ compression forces during symmetrical load-bearing tasks. Results from a linked-segment, biomechanical model were used as the criterion. Twenty-two subjects (11 males, 11 females) performed movements through a wide range of postures in the sagittal plane. Each model was developed with the data from 16 subjects (n = 1704 postures) and validated with 6 subjects (n = 750 postures). Five loads were iterated from 0 to 28 kg (females) or 36 kg (males) or until the strength demand at one joint exceeded the 98th percentile value predicted for that gender. Both models required the input of the NIOSH H and V values, subject body mass, load mass and trunk angle. MODEL1 used regression equations to calculate the moment arm from the load, and the upper body centre of mass, to the L₅/S₁ joint. These lengths were subsequently used in a biomechanical model to calculate the joint compression force (R ² = 0.989, RMS error = 147 N). MODEL2 predicted compression force directly with one equation using the same inputs as MODEL1. (R ² = 0 983, RMS error = 183 N, both models n = 6467). The results were slightly improved for both models when applied to the validation subject data (n = 2303). Regression models were also developed to estimate the maximum and minimum expected trunk angles for all possible H and V combinations so that ‘worst case’ scenarios could be evaluated for given load positions.     

The relationship between isometric strength of Cantonese males and the US NIOSH guide for manual lifting

A laboratory study was undertaken to assess the relationship between the maximal voluntary isometric strength (MVIS) of a group of Hong Kong Cantonese males and recommended limiting values for lifting proposed in the Work Practices Guide for Manual Lifting (NIOSH, 1981). Forty-one male subjects were required to apply a 'free-style' vertical 'lift' force to a horizontal bar located 150 mm from the ground. Forces were applied with the horizontal location of the midpoint of the ankles at 200, 400, 600 and 800 mm from the bar. The results were compared with the Maximal Permissible Limit (MPL) and the Action Limit (AL) values proposed in the NIOSH guide. The results showed that the mean MVIS of the Hong Kong subjects lay between the MPL and AL when the load was 200 mm and 400 mm from the ankles, but was significantly below the AL at 600 mm. At 800 mm more than half of the subjects were unable to apply any measurable positive vertical force. The compressive force at the L5/S1 disc of four subjects was estimated using a static biomechanical model. The relationship between the disc pressure and the force exerted was largely in accordance with NIOSH guide values. The results are discussed in terms of differences in subject population and lifting technique. Comments on the applicability of the NIOSH standards internationally, are also presented.     

A 2-D simulation model for lifting activities

Occupational biomechanics models deal with the evaluation of physical activities such as lifting of loads. This allows the user to determine the stresses imposed on the musculoskeletal system while holding or moving a load. These models are useful tools in estimating these stresses especially those imposed on the lumbar spine. dynamic biomechanical models, as opposed to static models require the displacement-time information to obtain the kinematics needed to estimate the kinetics of the motion. However, the collection of this displacement data is both tedious and can require expensive equipment.

Simulation models on the other hand can provide an indirect means of performing the biomechanical analyses without having to collect the displacement-time data. A typical simulation model for 2-D lifting activities will be presented. The basis for this is the hypothesis that the body will perform the activity in such a manner so as to minimize the work done. Using this assumption an objective function was developed subject to a set of constraints. These constraints relate to the human movement, the physical workplace layout, and maintenance of balance. Using this model, it was possible to generate the lifting motion patterns, as well as the kinematics and kinetics of motion. The paper discusses the model development, the model output and the kinematics and kinetics of the simulation of the lifting action.     

Ergonomic job design in frequent manual lifting tasks: A microcomputer-based model

The main objective of this paper is to generate ergonomic software that can be used in the design and evaluation of manual materials handling tasks so as to minimize the risk of injury. Specifically, this study is aimed at developing a microcomputer-based model for the design of frequent manual lifting tasks based ont he concept of job saverity index. The microcomputer-based software package is intended to be used by non-experts in the field of MMH. Possible engineering and administrative controls are implemented in the software in case if human lifting abilities are exceeded. The software was written in AutoLISP for the IBM personal computer. The knowledge base of the software is built upon a set of two models which were developed in the present study. The models were based on 2,736 observations.     

Trust beyond reputation: A computational trust model based on stereotypes

Models of computational trust support users in taking decisions. They are commonly used to guide users’ judgements in online auction sites; or to determine quality of contributions in Web 2.0 sites. However, most existing systems require historical information about the past behavior of the specific agent being judged. In contrast, in real life, to anticipate and to predict a stranger’s actions in absence of the knowledge of such behavioral history, we often use our “instinct”—essentially stereotypes developed from our past interactions with other “similar” persons. In this paper, we propose StereoTrust, a computational trust model inspired by stereotypes as used in real-life. A stereotype contains certain features of agents and an expected outcome of the transaction. When facing a stranger, an agent derives its trust by aggregating stereotypes matching the stranger’s profile. Since stereotypes are formed locally, recommendations stem from the trustor’s own personal experiences and perspective. Historical behavioral information, when available, can be used to refine the analysis. According to our experiments using Epinions.com dataset, StereoTrust compares favorably with existing trust models that use different kinds of information and more complete historical information.     

A comprehensive model for software rejuvenation

Recently, the phenomenon of software aging, one in which the state of the software system degrades with time, has been reported. This phenomenon, which may eventually lead to system performance degradation and/or crash/hang failure, is the result of exhaustion of operating system resources, data corruption, and numerical error accumulation. To counteract software aging, a technique called software rejuvenation has been proposed, which essentially involves occasionally terminating an application or a system, cleaning its internal state and/or its environment, and restarting it. Since rejuvenation incurs an overhead, an important research issue is to determine optimal times to initiate this action. In this paper, we first describe how to include faults attributed to software aging in the framework of Gray's software fault classification (deterministic and transient), and study the treatment and recovery strategies for each of the fault classes. We then construct a semi-Markov reward model based on workload and resource usage data collected from the UNIX operating system. We identify different workload states using statistical cluster analysis, estimate transition probabilities, and sojourn time distributions from the data. Corresponding to each resource, a reward function is then defined for the model based on the rate of resource depletion in each state. The model is then solved to obtain estimated times to exhaustion for each resource. The result from the semi-Markov reward model are then fed into a higher-level availability model that accounts for failure followed by reactive recovery, as well as proactive recovery. This comprehensive model is then used to derive optimal rejuvenation schedules that maximize availability or minimize downtime cost.     

Determinants of academic use of the Internet: A structural equation model

The last decade of the 20th century brought radical changes in information and communication technology. Internet usage is being widely researched in the business world. However, the use of the Internet in academic settings in general and in vocational and technical establishment in particular is a neglected area. Successful use of the Internet is largely dependent upon the user's behaviour that, in turn, affects their attitudes. Even when remarkable opportunities exist for the deployment of technology, adverse attitude can inhibit use. Keeping this in mind, a survey of 166 academics of four technical and vocational colleges was conducted to study the attitudes of academics toward the use of the Internet. This study develops a model and validates two specific attitudinal variables--perceived usefulness and perceived ease of use--which are hypothesized to be fundamental determinants of use of the Internet. Adding two more variables--such as task characteristics and computer exposure--test the parsimony of the model further. A structural equation modelling technique is used to validate the model. The study confirmed that 79% of academics are using the Internet. Computer experience, perceived usefulness and perceived ease of use remain to be fundamental determinants of attitude formation. No other variables have been found to be significant.     

The SIC botnet lifecycle model: A step beyond traditional epidemiological models

Botnets, overlay networks built by cyber criminals from numerous compromised network-accessible devices, have become a pressing security concern in the Internet world. Availability of accurate mathematical models of population size evolution enables security experts to plan ahead and deploy adequate resources when responding to a growing threat of an emerging botnet. In this paper, we introduce the Susceptible-Infected-Connected (SIC) botnet model. Prior botnet models are largely the same as the models for the spread of malware among computers and disease among humans. The SIC model possesses some key improvements over earlier models: (1) keeping track of only key node stages (Infected and Connected), hence being applicable to a larger set of botnets; and (2) being a Continuous-Time Markov Chain-based model, it takes into account the stochastic nature of population size evolution. The SIC model helps the security experts with the following two key analyses: (1) estimation of the global botnet size during its initial appearance based on local measurements; and (2) comparison of botnet mitigation strategies such as disinfection of nodes and attacks on botnet’s Command and Control (C&C) structure. The analysis of the mitigation strategies has been strengthened by the development of an analytical link between the SIC model and the P2P botnet mitigation strategies. Specifically, one can analyze how a random sybil attack on a botnet can be fine-tuned based on the insight drawn from the use of the SIC model. We also show that derived results may be used to model the sudden growth and size fluctuations of real-world botnets.     

A comprehensive quality model for service-oriented systems

In a service-oriented system, a quality (or Quality of Service) model is used (i) by service requesters to specify the expected quality levels of service delivery; (ii) by service providers to advertise quality levels that their services achieve; and (iii) by service composers when selecting among alternative services those that are to participate in a service composition. Expressive quality models are needed to let requesters specify quality expectations, providers advertise service qualities, and composers finely compare alternative services. Having observed many similarities between various quality models proposed in the literature, we review these and integrate them into a single quality model, called QVDP. We highlight the need for integration of priority and dependency information within any quality model for services and propose precise submodels for doing so. Our intention is for the proposed model to serve as a reference point for further developments in quality models for service-oriented systems. To this aim, we extend the part of the UML metamodel specialized for Quality of Service with QVDP concepts unavailable in UML.

A comprehensive model for the storage structure design of codasyl databases

The performance of a database system depends, to a large extent, on the storage structure selected to represent the logical schema of the database. A comprehensive model for the physical design of network model databases is presented. It evaluates the retrieval time for each user query, database updating cost, storage requirements and total cost of the system in terms of design parameters. A linear 0–1 goal programming model, because of its multicriteria nature, has been selected here as a solution procedure. It finds the optimal location mode of each database record type based on the priority and weights assigned to the conflicting design objectives; short retrieval time for a user query, low database updating cost, small storage requirements and low total cost of the system. The designer can interactively change value of design parameters, priority and weights to perform tradeoff analysis. The model has been tested in the design of a department store database.