Common cause problems

Unless the user specifies otherwise, each simulator block is mapped to a default Icarus project component. The mapping defaults need to be understood properly, as large errors can be introduced if unit operations are mapped incorrectly. The default mapping specifications are given in Section 3 of the user s guide (AspenTech, 2002a). Some mappings that commonly cause problems include... 

It is interesting to note that Mg ions have been present in cells from the very beginning whereas Ca + has only become essential in the later, more sophisticated species, for example those which require signal transmission along nerves and, perhaps, also a bony skeleton or a hard shell Ca, therefore, like the beneficial elements mentioned earlier, is one of the newer elements. Despite being essential for human life. Homo sapiens has not yet adapted or evolved to handle completely all the chemical problems raised by the presence of Ca in the body, and its precipitates, as phosphates, oxalates, etc., all too commonly cause problems such as atherosclerosis, kidney or gall stones, and cataracts. 

As described in Section 8.4, only those proteins which interact actively with the spot surfaces are analyzed in the Pro-teinChip Reader, since all other components are washed off in advance. Such washing provides one of the most obvious advantages of the SELDI process - that certain components (e.g., salts or detergents) which commonly cause problems with other analytical tools are removed. 

A more feasible solution may be to utilize a non-redundant second system using components as diverse as possible (in order to minimize potential common cause problems). 

Human error is frequently die source of common cause problems. It is also very difficult to quantify. On one chemical plant, for example, the material balance around a large reactor did not balance. The instruments showed that more material was going in than coming out, yet all other indicators showed that there were no problems. The follow-up investigation showed that an instrument technician had installed all the orifice plates the wrong way round. As soon as that error was corrected, the flows balanced perfectly. The technician s lack of training (or lack of attention to detail, or errors in the instrument data sheets) was the common cause error in this example. 

The general effect of common cause problems is to place an upper limit on the MTBF of any protective system. SIL 3 level systems require diversity as well as redundancy to be considered in order to overcome the limits due to common cause failures. 

There is no requirement for additional actuators for example at the flare because the cause of the problem was not expected to be anything to do with the existing actuators, hence no risk of a common cause problem. 

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Identification and quantitative estimation of common-cause failures are general problems in fault tree analysis. Boolean approaches are generally better smted to mathematically handle common-cause failures. 

The nature of the conditions of intensive production, however, can increase the risk of diseases and infections which can spread very rapidly and devastate large numbers of animals." Thus it is common practice for producers of poultry to add coccidiostats to their diets and vaccines to their drinking water in order to prevent coccidiosis and other infectious diseases such as bronchitis and Newcastle disease. A similar problem exists for intensively reared fish, where it is necessary to add antibiotics to their diets. A problem with intensively reared fish is that their diet is added directly into the water in which they live thus drugs and other additives in the diet are relatively easily dispersed into the local environment of fish farms, where they can increase bacterial resistance and also cause problems such as algal blooms. 

Inlet Line. Unstable circulation can result if the inlet line to a vertical theimosyphon reboiler is too large. The tubes of a vertical thermosyphon reboiler fire individually. The tubes can backfire excessively if the liquid inlet line is too large. They don t have to backfire all the way into the tower to cause problems, just to the inlet tubesheet. It is common to put flanges in the inlet liquid line so an orifice can be added later, if required, to provide proper dampening effect. 

High or low fuel gas pressure ean have a dramatic effect on the operation of a firetube heater. Burners are typically rated as heat output at a specified fuel pressure. A significantly lower pressure means inadequate heat release. Significantly higher pressure causes overfiring and over heating. The most common causes of a fuel gas pressure problem are the failure of a pressure regulator or an unacceptably low supply pressure. 

The grounds represent the bottom branch of the current loops discussed earlier. Grounds, though, serve a very important function as the common point of reference for the circuitry. Therefore, grounds must be carefully placed in the layout. Intermingling these grounds will cause problems with the stability of the power supply. 

Health hazards now associated with what was one of the most common vulcanising agents for the rubber (ethylenethiourea) have caused problems because of the difficulties of finding an acceptable alternative. 

Internal surfactants, i.e., surfactants that are incorporated into the backbone of the polymer, are commonly used in PUD s. These surfactants can be augmented by external surfactants, especially anionic and nonionic surfactants, which are commonly used in emulsion polymerization. Great attention should be paid to the amount and type of surfactant used to stabilize urethane dispersions. Internal or external surfactants for one-component PUD s are usually added at the minimum levels needed to get good stability of the dispersion. Additional amounts beyond this minimum can cause problems with the end use of the PUD adhesive. At best, additional surfactant can cause moisture sensitivity problems with the PUD adhesive, due to the hydrophilic nature of the surfactant. Problems can be caused by excess (or the wrong type of) surfactants in the interphase region of the adhesive, affecting the ability to bond. 

The threshold for toxic injury is not the same for everyone because sensitivity varies greatly among individuals. Most chemicals in consumer products remain untested for health effects, such as cancer, reproductive problems, and the impacts of long-term, low level exposure. How these substances affect women, children, and people with existing conditions is also little studied. Once a person s defenses have been broken down and he or she has become hypersensitive, a wide variety of common chemical exposures can trigger a reaction. Just what products and other chemicals which cause problems varies greatly among affected individuals. 

USC may be modeled as a power-series expansion of non-CCF component failure nates. No a priori physical information is introduced, so the methods are ultimately dependent on the accuracy of data to support such an expansion. A fundamental problem with this method is that if the system failure rate were known such as is required for the fitting process then it would not be neces.sary to construct a model. In practice information on common cause coupling in systems cannot be determined directly. NUREG/CR-2300 calls this "Type 3" CCF. 

Do classify the problems into groups that have a common cause and special cause. 

Arctic Drilling. Corrosion problems encountered in arctic area drilling are no different from problems faced in other areas of the world. It is a general misconception that during arctic drilling corrosion-related problems are either not very severe or totally absent due to low temperatures. Cool temperatures may slow down the corrosion process. However, they also increase the solubility of oxygen, carbon dioxide and hydrogen sulfide. Therefore, the net result can be an increase in the rate of corrosion. While cold temperatures may cause problems, the temperature fluctuation common in arctic environments can be a more severe source of corrosion-related problems [215]. 

Many industrial buildings, and industrial projects in the broader sense, are completed entirely to the owner s satisfaction in terms of the key criteria of time, cost and quality. It is also true that many are not. There can be various reasons for this some related to the nature of the construction industry in general, some to the performance of professional teams and others related to the manner in which the project was initially set up. The most common cause of problems with the finished product is the way in which the owner s requirements were specified, and this extends to include the selection of the project team. 

Inadequate FW deaeration is a common cause of serious corrosion problems that affect many hundreds (if not thousands) of boiler plants of all sizes around the world. Despite the abundance of available literature advising the need to eliminate oxygen from boiler FW, inadequate deaeration continues to cause permanent waterside damage. 

Myositis may also have an infective basis. Viral myositis has been recorded in association with influenza and picomavirus infections, particularly those due to viruses of the Coxsackie group, and HIV infection is an increasingly common cause of myositis seen in routine practice. Fungal, bacterial, and parasitic myositis is seen much more rarely in North America and Europe than in tropical parts of the world, but in these regions these forms of infective myositis constitute a significant problem. In any survey of inflammatory muscle disorders, it is also necessary to consider other inflammatory conditions which affect muscle indirectly, but do not cause myositis in the strict sense of the word. In this group are to be found various forms of arteritis and fascitis and granulomatous conditions such as sarcoidosis. 

Often overlooked but of no less importance, information access breakdowns often occur even when there is no underlying technical reason. Common causes are that it is not clear what system should be used to find a particular piece of information or that its absence on one system incorrectly implies that it is not available elsewhere. Even if a scientist knows which system to use to look for a piece of information, if the interface is not contextualized for her particular domain or project the information may be missed because it is presented in a fashion that is not familiar to the user. A problem that is harder to correct occurs when a person requires a piece of information but is unsure whether that information even exists at all. 

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