Error-tolerant system

The final element in management s communication of a desire to reduce human error is the identification and elimination of error-likely situations. Every task is an opportunity for a human error, but some situahons represent greater risks than others. Identifying these high-risk situations is not easy and an expertise in applying human factors principles to the workplace is an essential prerequisite for this identification. Eliminating these hazardous situations is often relatively simple once they have been identified. In some cases it may be appropriate to provide error-tolerant systems, which are those that facilitate identification of and recovery from the errors. 

Design for error tolerance Rasmussen notes that people make errors all the time, but we are able to detect and correct them before adverse consequences occur [165]. System design can limit people s ability to detect and recover from their errors. He defined a system design goal of error tolerant systems. In these systems, errors are observable (within an appropriate time limit) and they are reversible before unacceptable consequences occur. The same applies to computer errors they should be observable and reversible. 

Error-tolerant system— A system with corrective actions to recover from errors. 

Evaluation level create a system, in accordance with ergonomic criteria, that is error tolerant and supports error recovery redesign charging manifold (see Figure 7.7) using functional grouping corresponding to the actual layout of system. 

Root cause 6. The system was not error tolerant. The error made was not detectable. 

If the above condition is fulfilled, the selection advantage of the error-free system is so large that a number of errors in the total population can be tolerated. 

Simplify (simplification and error tolerance) Keep piping systems neat and visually easy to follow Design control panels that are easy to comprehend Design plants for easy and safe maintenance Pick equipment that requires less maintenance Pick equipment with low failure rates Add fire- and explosion-resistant barricades Separate systems and controls into blocks that are easy to comprehend and understand Label pipes for easy walking the line Label vessels and controls to enhance understanding... 

The independence approach allows for a good encapsulation of the APS issue but requires major changes in business processes. It requires the creation and maintenance of an independent data model with its own data structure and the definition of new business processes. Introduction of the APS system must be done in a big bang. Integration is not fully guaranteed, its quality depends on the throughput and the error tolerance of the integration interface. 

Develop new less-energetic chemical reaction systems for product manufacture, including alternate catalytic and biological routes where appropriate Emphasize need to develop economically viable inherently safer systems at the research and development stages of new process development Develop new process equipment and strategies for product manufacture using lower inventories of reactive chemicals, error tolerant approaches, and process conditions further from limits of control where appropriate... 

Exceeding these known limits will result in unpredictable actions usually resulting in significantly reduced performance, and a resulting increase in human error. Investigators and designers should be constantly on the alert for opportunities to make a system more reliable by considering the worker-machine interface and search for every opportunity to make the system less error-prone and more error-tolerant. 

The standard required a site review, and a head-office level review of all reported occurrences. There was good cooperation between head-office and the plant to get the system underway. Apparent inconsistencies between the definition of the class, and the examples were fairly quickly resolved, with the help of head-office. A data-base of events was established, with an extensive sort facility. The system became very well respected and well used, and much improvement of performance was achieved through experience feedback. Near-misscs were reported freely, from which much information was gained in order to facilitate performance improvement and the development of error tolerant. and error recovery systems. 

A system is called error tolerant if the intended task result can be achieved without or with minimum effort of correction by the user despite incorrect input. The dialogue system should support the user in finding and avoiding input mistakes, and it should secure that under no circumstances an incorrect user input leads to data loss or even a system break down. 

The residues (Nb-kNp at each node) are reduced to zero (a small positive number fixed by specifying an error tolerance at input) iteratively by computing corrections to current values of the unknowns using the Newton-Raphson method (14). Elements of the Jacobian matrix required by this method are computed from analytical expressions. The system of equations to be solved for the corrections has block tridiagonal form and is solved by use of a published software routine (1.5b... 

An important part of simplification concerns making systems error tolerant in one or more of... 

The system should also be designed to be error tolerant such that, if a person does make a mistake, the system fails into a safe condition. For example, different types of hose nozzles are used for different chemicals. Therefore, if an operator tries to connect the wrong hose to a truck or rail car, the nozzle type will prevent him from doing so. 

The design of fault tolerant systems consists in preventing a fault to cause an error and consequently a failure in the implemented system. Therefore, there is a cause-effect relationship from the particle hit (fault) to the erroneous result (system failure), as demonstrated in Fig. 2.2. In this work, we will use the definition presented inAvizienis (2004). 

Redundancy or Backup Systems, Monitors Isolation of Systems, Components and Elements Designed Failure Effect Limits Designed Failure Path Fault and Error Tolerance... 

Reduce the severity of the error. The focus here is to acknowledge that an error is possible and therefore the aim is to (1) reduce the consequence of such error (i.e. make the system error tolerant), (2) to provide systems or instructions on how to recover from that error in a timely fashion and (3) to consider improving system degradation rates (i.e. offering the crew more time to assess the problem and respond accordingly). 

---