Safe Operation Margins

The safe operation window (=water window) for iridium oxide (IrOx) is —0.6 V +0.8 V versus Ag AgCl [28,32]. Outside this range electrode damage and solution pH change are possible. For cathodic excursions below —0.6 V versus Ag AgCl delamination of AIROF may occur which is not reversible and deteriorates the electrode properties considerably (Fig. 6.9). This delamination can be identified by a sharp anodic discontinuity of the cyclic voltammetry plot as shown in Fig. 6.10 [28]. 

It is better to consider the —0.6 and +0.8 V versus Ag AgCl potential boundaries for the electrode potential without subtracting the / - / drop on the electrode access resistance (= access voltage). It was observed that when the electrode potential subtracted by the access voltage is used as the variable to be limited inside the water window, electrodes were damaged. This is because of the non-uniformity of the current distribution on the electrode surface and because the maximum potential excursions are not constant over the electrode geometry [28]. 

The charge injection capacity of iridium oxide was evaluated as 4mC/cm in [32]. Troyk et al. have developed a simple but effective current cutback method to retain the electrode potential inside the water window. In this method, the supply voltages of the electrode driver current sources are set to the water window voltage boundaries. In this way, with only a modest decrease in charge injection, the 

Xenia Beebe et al. evaluated the maximum charge injection capacity of activated iridium wire electrodes in bicarbonate buffered saline as 2.1 m C/cm and l.OmC/cm for anodic-first and cathodic-first, 0.2ms charge balanced biphasic current pulses, respectively [1]. Bicarbonate buffered saline has a pH between 7.35 and 7.45 (similar to the human blood plasma) and is comparable to PBS with a pH value of 7.4. The counter electrode was an iridium foil. The reference electrode was a saturated calomel electrode. Cyclic voltammetry at lOOmV/s revealed a water window of -0.6 V +0.8 V, the same as versus Ag AgCl. 

As in the subretinal stimulation structure no reference electrode is available, the above ranges are not applicable, because the solution potential is not controlled by a reference electrode. Furthermore, if any faradaic reactions occur, the solution 

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To minimize flue losses it is important to keep excess air to a minimum, but the practicalities of the burner must be considered and a safe operating margin incorporated. 

Zio, E. Sansavini, G. 2011b. Modeling Interdependent Network Systems for Identifying Cascade-Safe Operating Margins. Reliability, IEEE Transactions on, Vol.60,p.94-101. 

Whereas the transport of water to major centers allowed civilizations to flourish, the measurement and control of fluid flow has been a critical aspect of the development of industrial processes. Not only is metering flow important to maintaining stable and safe operating conditions, it is the prime means to account for the raw materials consumed and the finished products manufactured. While pressure and temperature are critical operating parameters for plant safety, the measurement of flow rate has a direct impact on process economics. For basic chemicals (as opposed to specialty chemicals or pharmaceuticals) like ethylene, propylene, methanol, sulfuric acid, etc. profit margins are relatively low and volumes are large, so high precision instruments are required to ensure the economic viability of the process. 

Limits and conditions for normal operation are intended to ensure safe operation that is, to ensure that the assumptions of the safety analysis report are valid and that established safety limits are not exceeded in the operation of the plant. In addition, acceptable margins should be ensured between the normal operating values and the established safety system settings to avoid undesirably frequent actuation of safety systems. Figme A-1 in the Annex demonstrates a correlation between safety limits, safety system settings and limits for normal operatioa... 

In addition to the weaknesses in the RBMK design described above, the detailed implementation of the design also allowed greater freedom of action for the operators than would be normal in a reactor design elsewhere. For example, the operators could override reactor trip systems at the flick of a switch in Western designs, key interlock systems would have prevented this. Also it was essential for the safe operation of the plant that the control rods should never be withdrawn beyond the point at which the control rod reactivity margin became dangerously low, yet this vital aspect was left entirely to the operators, with no automatic trip system. 

Employee knowledge and experience are key prerequisites for the safe operation of nuclear power stations. However, knowledge and experience are not fixed quantities but constantly collected, expanded and updated in the course of plant operation and familiarity with the plant. At the same time, plant complexity requires highly specialized knowledge which might leave some gaps in the interfaces with other disciplines or as far as the consideration of marginal conditions is concerned. 

Table 6.1 lists the mentioned safe margins. The safe operation limits are typically smaller for cathodic polarity. Cathodic voltages are more harmful to TiN than the anodic ones [2],... 

Most aircraft are designed and certified with a significant amount of equipment redundancy, such that the airworthiness requirements are satisfied by a substantial margin. In addition, aircraft are generally fitted with equipment that is not required for safe operation under all operating conditions, e.g., instrument lighting in day... 

Following the defence-in-depth concept, it also supervises data related to the safety systems, in order to check Limiting Conditions for safe Operation (LCOs), which are established to provide acceptable margins between the normal operating values and the safety system settings during all operational states of the reactor. Therefore, data used or generated by the trip units are read by the SCS from its three redundant one-way TLIUs, which are updated periodically by their appropriate trip units. 

Plate-Column Capacity The maximum allowable capacity of a plate for handling gas and liquid flow is of primaiy importance because it fixes the minimum possible diameter of the column. For a constant hquid rate, increasing the gas rate results eventually in excessive entrainment and flooding. At the flood point it is difficult to obtain net downward flow of hquid, and any liquid fed to the column is carried out with the overheaa gas. Furthermore, the column inven-toiy of hquid increases, pressure drop across the column becomes quite large, and control becomes difficult. Rational design caUs for operation at a safe margin below this maximum aUowable condition. 

The side depth of the thickener is determined as the sum of the depths needea for the compression zone and for the clear zone. Normally, 1.5 to 2 m of clear liquid depth above the expected pulp level in a thickener will be sufficient for stable, effective operation. When the location of the pulp level cannot be predicted in advance or it is expected to be relatively low, a thickener sidewall depth of 2 to 3 m is usually safe. Greater depth may be used in order to provide better clarity, although in most thickener applications the improvement obtained by this means will be marginal. 

Protection with internal fuses is easier, as fuses are provided for each element which can contain the severity of the fault well within the safe zone in all probability. Some users even recommend capacitor units 250/300 kVAr and above with internal fuses only. Figure 26.1 shows a typical operating band of (he internal fuses for an internally protected unit. It demonstrates a sufficient margin between the operation of (he fuses and (he shell s safe zone. The fuse characteristics are almost the same for all manufacturers. 

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