Operability, human factors

Smith, Michael J., Barbara G. F. Cohen, Lambert W. Stammegohn, and Alan Happ. 1981. An Investigation of Health Complaints and Job Stress in Video Display Operations. Human Factors 23(4) 387—400. 

Several nontechnical factors can significantly affect the results of a nondestmctive inspection. Many of these are classified as human factors (1,2,17). Operator experience affects the probabiUty of detection of most flaws. Typically, an inexperienced operator has more false rejects, known as Type II errors, than an experienced operator. A poor operator has few false rejects but is more likely to miss a defect in the inspection, known as a Type I error. Operator fatigue, boredom, or an unfavorable environment such as lighting, cold, or rain may further affect performance. Thus it usually is a good investment for the inspection company to assure that the operator environment is most amenable to inspection, that the equipment is suitable for the task, and that the operator is alert and well rested. 

Visual Inspection. Visual inspection should always be regarded as the first defense against failure (1). Without scientific proof, it is estimated that 80% of defects are found by visual inspection. A pilot walking around an aircraft, or a mechanic observing a machine in operation often finds defects very quickly. The cost of this inspection is minimal. Human factor considerations are particularly important for the visual inspection process. Although the visual inspection is perhaps the most inexpensive and finds the most defects, the 20% of the defects remaining after the visual inspection must also be found thus the more costly and technically elaborate NDE methods are needed. 

Human Factors A diseipline eoneerned with designing maehines, operations, and work environments so that they mateh human eapabilities, limitations, and needs. Ineludes any teehnieal work (engineering, proeedure writing, worker training, worker seleetion, ete.) related to the human faetor in oper-ator-maehine systems. 

Test runs also allow the primary steps of operating procedures to be validated and checked for logic or human factors aspects. 

The tools in CCPS (1994a) can be used in each stage of the chemical process life cycle to help evaluate the tradeoffs involving human factors between various options. In many cases, low cost options in design can make the operations inherently safer from a human factors perspective. 

There may be well-run facilities in which the operators are doing their best to be careful with facilities or systems that could be redesigned to be inherently safer. These facilities will be inherently safer if designed for operability. Note that inherently safer human factors features can reduce risk of injury to employees (improved personnel safety) and can reduce risk to the process from the worker (improved process safety). 

For inherently safer interactions of designs and procedures, include an operator trained in human factors on the design team. 

Operations and human factors specialist involvement is important to find optimum solutions to human factors/ergonomics issues. Applying inherent safety principles to ergonomics/human factors issues can reduce risks associated with ... 

Human errors may be dependent on the specific accident sequence displayed in the event tree, and, for that reason, may be included in the event tree. This requires the human-factors specialist to consider the context of the error in terms of stress, operator training in response to the accident, di.tgnosiic paiierns, environmental, and other performance-shaping factors. 

Systems analyses are like formulas, they have little usefulness until the variables are assigned probabilistic numbers from nuclear or chemical data bases. These data concern the probability of failing vessels, pipes, valves, instruments and controls. The primary difference between chemical and nuclear data is that the former may operate in a more chemically active environment, while the later operate in radiation. This chapter addresses both, but most of the data were gathered for nuclear systems. It covers 1) failure rate databases, 2) incident databases, 3) how to prepare failure rates from incidents, and 4) human factors for nuclear and chemical analyses. 

Mill, R. C. (Ed.), 1992, Human Factors in Process Operations, Institute of Chemical Engineers, Rugby, U.K. 

Williams, J. C., 1989, A Data-Based Method for Assessing and Reducing Human Error to Improve Operational Performance, Proceedings of the 1988 IEEE Fourth Conference on Human Factors and Power Plants, Monterey, CA, June 5-9, pp 436-450, IEEE. 

The application of the science of human factors to eliminating error in all aspects of process design, management, operation, and maintenance is the focus of this work. Human error has been a major cause of almost all of the catastrophic accidents that have occurred in the chemical process industries (CPI). If one adopts the broad view of human error as being the result of a mismatch between human capabilities and process demands, then clearly management s role is critical in the following areas ... 

The book begins with a discussion of the theories of error causation and then goes on to describe the various ways in which data can be collected, analyzed, and used to reduce the potential for error. Case studies are used to teach the methodology of error reduction in specific industry operations. Finally, the book concludes with a plan for a plant error reduction program and a discussion of how human factors principles impact on the process safety management system. 

The major benefits that arise from the application of human factors principles to process operations are improved safety and reduced down time. In addition, the elimination of error has substantial potential benefits for both quality and productivity. There is now a considerable interest in applying quality management approaches in the CPI. Many of the major quality experts em-... 

Human Factors Engineering/Ergonomics approach (control of error by design, audit, and feedback of operational experience) Occupational/process safety Manual/control operations Routine operation Task analysis Job design Workplace design Interface design Physical environment evaluation Workload analysis Infrequent... 

Process workers often complain that valves are inaccessible. Emergency valves should always be readily accessible but other valves, if they are operated, say, once a year or less often, can be out of reach. It is reasonable to expect workers to get a ladder or scramble into a pipe trench at this frequency. Designers should remember that if a valve is just within reach of an average person then half of the population cannot reach it. Equipment should be placed such that at least 95% of the population can reach it. Guidance on specific measurements to achieve this objective is available in a number of standard human factors textbooks (see Bibliography). 

Although the issue of PIF interactions has long been recognized by human factors researchers, little has been done to develop practical recommendations. This is partially a result of the large number of possible PIF combinations and the complexity of their interactions. One of the most effective ways of studying this interaction is through an in-company human factors study which will use operational feedback to evaluate the results of design and human factors innovations. 

The term Task Analysis (TA) can be applied very broadly to encompass a wide variety of human factors techniques. Nearly all task analysis techniques provide, as a minimum, a description of the observable aspects of operator behavior at various levels of detail, together with some indications of the structure of the task. These will be referred to as action oriented approaches. Other techniques focus on the mental processes that imderlie observable behavior, for example, decision making and problem solving. These will be referred to as cognitive approaches. 

Management must modify the culture and develop human factors awareness in the hazard identification teams so that they will be capable of identifying the potential for human error. A good practice is to involve operators in the hazard identification team. 

Bellamy, L. J., Geyer, T. A. W. (1988). Addressing Human Factors Issues in the Safe Design and Operation of Computer Controlled Process Systems. In B. A. Sayers (Ed.), Proceedings ofSARSS 88. Human Factors and Decision Making Their Influence on Safety and Reliability. 19-20 October, Altrincham, Manchester, U.K. London Elsevier Applied Science. 

Fitts, P. M., Jones, R. E. (1947). Analysis of Factors Contributing to 460 "Pilot Error" Experiences in Operating Aircraft Controls. Reprinted in H. W. Sinaiko (Ed.) (1961), Selected Papers on Human Factors in the Design and Use of Control Systems. New York Dover. 

---