Failure modes human

Process Hazards Analysis. Analysis of processes for unrecogni2ed or inadequately controUed ha2ards (see Hazard analysis and risk assessment) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects ha2ard and operabiHty (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify ha2ards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

Frequency Phase 1 Perform Qualitative Study, Typically Using HAZOP, FMEA, or What-if Analysis. To perform a qualitative study you should first (1) define the consequences of interest, (2) identify the initiating events and accident scenarios that could lead to the consequences of interest, and (3) identify the equipment failure modes and human errors that could contribute to the accident... 

Human operator errors are not usually examined in a FMEA, but the effects of human error are indicated by the equipment failure mode. FMEAs rarely investigate damage or injury that could arise if the system or process operated successfully. Because FMEAs focus on single event failures, they are not efficient for identifying an exhaustive list of combinations of equipment failures iliat iead to accidents. 

Core damage and containment performance was assessed for accident sequences, component failure, human error, and containment failure modes relative to the design and operational characteristics of the various reactor and containment types. The IPEs were compared to standards for quality probabilistic risk assessment. Methods, data, boundary conditions, and assumptions are considered to understand the differences and similarities observed. 

The use of a model of human error allows a systematic approach to be adopted to the prediction of human failures in CPI operations. Although there are difficulties associated with predicting the precise forms of mistakes, as opposed to slips, the cognitive approach provides a framework which can be used as part of a comprehensive qualitative assessment of failure modes. This can be used during design to eliminate potential error inducing conditions. It also has applications in the context of CPQRA methods, where a comprehensive qualitative analysis is an essential precursor of quantification. The links between these approaches and CPQRA will be discussed in Chapter 5. 

Task Analysis and Error Analysis of the Blowdown Operation Task analysis was carried out in order to organize all the performance data about the way that workers process information, the nature of the emergency and the way that decisions are made. Figure 7.20 shows a tabular task analysis of the workers response to a significant unignited gas leak in MSM. The analysis was a combination of a tabular HTA and a CADET analysis (see Chapter 4). Human error analysis identified the major human failure modes which could affect time to blowdown (see Table 7.2). 

Appendix III contains failure rate estimates for various genetic types of mechanical and electrical equipment. Included ate listings of failure rates with range estimates for specified component failure modes, demand probabilities, and times to maintain repair. It also contains some discussion on such special topics as human errors, aircraft crash probabilities, loss of electric power, and pipe breaks. Appendix III contains a great deal of general information of use to analysts on the methodology of data assessment for PRA. 

It should be noted tliat FMECA identifies single failure modes tliat eitlier directly result in or contribute significantly to important accidents. Human/operator errors are generally not examined in a FMECA however, tlie effects of a misoperation are usually described by an equipment failure mode. It should also be noted that FMECA is not efficient for identifying combinations of equipment failures tliat lead to accidents. 

Aleatory uncertainty —the roll of the die—describes risks that cannot practicably be predicted within the research process, for example, new failure modes, or modes that can only be detected in late stages of work, for example, humans. An example of aleatory uncertainty is the withdrawal in the UK of Bextra on the basis of two serious adverse events out of 40,000 patients this could only be discovered after launch [2]. This, without hindsight, was an uncontrollable risk. ... 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

Pressure-time histories caused by explosions may be nonuniform and subject to amplification because of secondary shocks and shock reflections. Current models can provide only one- or two-dimensional histories. Failure modes are typically permanent deformation (plastic deformation/buckling), stable cracking (leaking), and brittle failure. Table 2.3 (Theodore et al., 1989) describes expected damage estimates for humans, structural elements, and process equipment for particular overpressures. 

The risk assessment process can be conducted by examining record types to see if they are GxP or non-GxP, and then applying severity checks, likelihood, and probability of detection criteria, as illustrated in Figure 15.2. The most severe scenarios shonld be linked to direct patient/consnmer impact. GxP noncompliance and broken license conditions are severe in their own right bnt not as critical as patient/consumer health in this analysis." Its likelihood will be influenced by the degree of human error in how the record is input and used. The probability of detection needs to take into account the probability of the impacted record being used. Once failure modes are understood, then the appropriate design controls can be introduced. These should be documented and validated as part of the computer system life cycle discussed earher in this book. 

Process step definition Functional performance criteria Functional failure mode analysis Failure mode recovery requirements Informational requirements Information structures Legacy system interfaces Data entry range Data retention requirements Human/machine interface requirements Screen specifications Data entry modes Refresh rates Data migration... 

There are various types of analyses that are used for a process hazard analysis (PHA) of the equipment design and test procedures, including the effects of human error. Qualitative methods include checklists, What-If, and Hazard and Operability (HAZOP) studies. Quantitative methods include Event Trees, Fault Trees, and Failure Modes and Effect Analysis (FMEA). All of these methods require rigorous documentation and implementation to ensure that all potential safety problems are identified and the associated recommendations are addressed. The review should also consider what personal protective equipment (PPE) is needed to protect workers from injuries. 

All elaborations made cannot and shall not claim to be exhaustive in any form. There are numerous other methods, such as the failure mode and effect analysis, which is preferably applied to the investigation of signal processing devices, or the human error analysis. 

The human factors literature is rich in task analysis techniques for situations and jobs requiring rule-based behavior (e.g., Kirwan and Ainsworth 1992). Some of these techniques can also be used for the analysis of cognitive tasks where weU-practiced work methods must be adapted to task variations and new circumstances. This can be achieved provided that task analysis goes beyond the recommended work methods and explores task variations that can cause failures of human performance. Hierarchical task analysis (Shepherd 1989), for instance, can be used to describe how operators set goals and plan their activities in terms of work methods, antecedent conditions, and expected feedback. When the analysis is expanded to cover not only normal situations but also task variations or changes in circumstances, it would be possible to record possible ways in which humans may fail and how they could recover from errors. Table 2 shows an analysis of a process control task where operators start up an oil refinery furnace. This is a safety-critical task because many safety systems are on manual mode, radio communications between control room and on-site personnel are intensive, side effects are not visible (e.g., accumulation of fuel in the fire box), and errors can lead to furnace explosions. 

Operation and System Safety Group. It will cover topics such as criticality control, administrative controls to prevent accidents, radiation protection, normal emission, system failure mode, and human error. 

It should be emphasized that a FMEDA provides failure rates, failure modes and diagnostic coverage effectiveness for random hardware failures. If done properly, it does not include failure rates due to "systematic" causes including incorrect installation, inadvertent damage, incorrect calibration or any other human error. 

Column 4 describes the failure modes of the component. One row is typically used for each component failure mode. Examples of component failure modes include fail short, fail open, drift, stuck at one, stuck at zero, etc., for electronic components. Mechanical switch failure modes might include stuck open, stuck closed, contact weld, ground short, etc. Column 5 describes the cause of the failure mode of column four. Generally this is used to list the primary "stress" causing the failure. For example, heat, chemical corrosion, dust, electrical overload, RFI, human operational error, etc. 

Overview of potential failure modes of technical components and conceivable human errors. 

Kazan has two significant difficulties. One is that for some failure modes, including those involving human error, data is lacking or uncertain. The other problem is that it is hard to estimate the effectiveness of mitigatory measures, particularly those taken by the process operator. Lees has collected information on the failure rates of various types of valves, thermocouples, pressure switches and other instruments. The same author and his associates - have reviewed and analysed data from incidents in batch reactors and constructed fault trees from the data on incident frequency. 

For the most part, the objectives associated with identifying behaviours of the S/W most related to safety are included from Level C (the objective where it is first acknowledged that the SAV failure modes may be adverse to human safety). At Level C, testing should already be addressing the complete suite of ... 

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