Human factors control design

Generally the easiest concepts to place are controls. Any characteristic of the system or its operation designed to reduce risk should be expressed as a control. In this case the need for staff to check they are administering medication to the correct patient is clearly a control, indeed a human factor control. This control will need a parent cause and/or hazard to belong to and, as yet, there are no obvious candidates. We should put this to one side for now. 

Figure 33-4. Examples of controls. (Reprinted with permission from R. Dale Huchingson, New Horizons for Human Factors in Design, McGraw-Hill book Company, New York, 1981.)...

Close attention to detail is essential in the design of all safety-related control systems, whether they are simple hard-wired systems, or complex systems implemented by software. It is important that safety analysis techniques are used to ensure that the requirements in the specification are met, and that the foreseeable failure modes of the control system do not compromise that specification. Issues of concern, which have been identified, include an over-optimistic dependence on the safety integrity of single channel systems, failure to adequately verify software, and poor consideration of human factors. Good design can also eliminate, or at least reduce, the chance of error on the part of the operator or maintenance technician. ... 

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... 

The case study described here concerns a human factors audit of a computer controlled process system which was being introduced in a distillation imit of a chemical plant. The unit was in transition from replacing its pneumatic panel instrumentation with the new system. However, control had not yet been transferred and the staff were still using the panel instrumentation. The role of the project was to evaluate a preliminary design of the computer-based display system and provide recommendations for future development. 

The human factors audit was part of a hazard analysis which was used to recommend the degree of automation required in blowdown situations. The results of the human factors audit were mainly in terms of major errors which could affect blowdown success likelihood, and causal factors such as procedures, training, control room design, team communications, and aspects of hardware equipment. The major emphasis of the study was on improving the human interaction with the blowdown system, whether manual or automatic. Two specific platform scenarios were investigated. One was a significant gas release in the molecular sieve module (MSM) on a relatively new platform, and the other a release in the separator module (SM) on an older generation platform. 

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. 

Take human factors into account in the design and implementation of the control system and the facility procedures (Human Error, Key Procedures). 

Whatever method is used, there should be a clear design philosophy for the basic process control system (BPCS) employed at a facility that is consistent throughout each process and throughout the facility. Consistency in application will avoid human factor errors by operators. The philosophy should cover measurements, displays, alarms, control loops, protective systems, interlocks, special valves (e.g., PSV,... 

Where loss of control could lead to severe consequences, the integrity of the basic process control system and the protective safeguards must be designed, operated and maintained to a high standard. Industry standards such as ANSI/ISA-S84.01 (1996) and IEC 61508 (2000) address the issues of how to design, operate and maintain safety instrumented systems such as high temperature interlocks to achieve the necessary level of functional safety. The scope of these standards includes hardware, software, human factors and management (HSE 2000). 

MS Carey, "Safety Management of Process Faults A Position Paper on Human Factors Approaches for the Design of Operator Interfaces to Computer Based Control Systems", HSE Contract Research Report No 60/1993, HSE Books, 1993... 

Plant designers must strive to develop user-friendly piping, layout, and control schemes, as well as clear, unambiguous labeling on equipment safety systems to reduce opportunities for human factor failings. 

In this chapter we will emphasize system upsets or abnormal situations where the loss or degradation of components or controls could allow process parameters to exceed the design intent or limit of the process or equipment, resulting in an accidental chemical release. The time factor involved in an operator s ability to assess and correct an operating deviation is discussed in more detail in CCPS Guidelines for Integrating Human Factors into Process Safety Management Systems ... 

Contents indude techniques for evaluating basic process control system and safety interlock system Integrity, human factors, and safety considerations In the selection and design of basic process control systems and safety Interlock systems. 

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