Triggering Conditions

An improved CHF model for low-quality flow The Weisman-Pei model was later improved by employing a mechanistic CHF model developed by Lee and Mu-dawwar (1988) based on the Helmholtz instability at the microlayer-vapor interface as a trigger condition for microlayer dryout (Fig. 5.21). The CHF can be expressed by the following equation due to the energy conservation of the microlayer (Lin et al. 1989) ... 

Avoid exposure to cues that might trigger conditioned craving. 

Before the incident, neither the reaction and decomposition energy potentials nor the triggering conditions of the decomposition were known. Thus, a potentially severe process was entirely under manual control, without provision for an alarm system and emergency measures. A correct assessment of the energies and triggering conditions of the decomposition predicts such an incident, giving the opportunity to design a process that will avoid such incidents. 

The thermal risk linked to a chemical reaction is the risk of loss of control of the reaction and associated consequences (e.g. triggering a runaway reaction). Therefore, it is necessary to understand how a reaction can switch from its normal course to a runaway condition. In order to make this assessment, the theory of thermal explosion (see Chapter 2) needs to be understood, along with the concepts of risk assessment. This implies that an incident scenario was identified and described, with its triggering conditions and the resulting consequences, in order to assess the severity and probability of occurrence. For thermal risks, the worst case will be to lose the cooling of a reactor or in general to consider that the reaction mass or the substance to be assessed is submitted to adiabatic conditions. Hence, we consider a cooling failure scenario. 

Secondary decomposition reactions may have serious consequences when they get out of control. In this case history, the thermal stability of the reaction mass was not known before the incident. If only the energy released by this decomposition had been known, the production staff would not have decided to maintain this reaction mass without active temperature control and monitoring. Thus, assessing the consequences and the triggering conditions of secondary decomposition reactions and predicting their behavior requires a specific knowledge and a systematic approach. 

This chapter describes a runaway scenario. The first section presents a general review of the decomposition reaction characteristics. The second section is devoted to the energy release that defines the consequences of a runaway. The third section deals with triggering conditions of undesired reactions, based on the concept of TMRld. The next section reviews some important aspects for the experimental characterization of decomposition reactions. Finally, the last section gives some examples stemming from industrial practice. 

A major difference with desired reactions is that the stoichiometry is often unknown, that is, the decomposition products are unknown. The reason is that decomposition reactions are often affected by the triggering conditions and thus often run along different reaction paths. This is a major difference compared to a total combustion, for example. The consequence is that the decomposition enthalpy cannot be predicted using standard enthalpies of formation AHjj taken from, for example, tables or estimated by group increment methods, such as Benson groups [3, 4] ... 

The hemispheric magnetic delivery device produced can release macromolecular drugs, like bovine serum albumin, at a low basal rate, by diffusion process, and under a non-triggering condition, or it can release the same drug at a much higher rate, when the magnet is activated, to vibrate by an external electromagnetic field. 

Schafer is concerned with refuting the idea of a lawlike connection between triggering conditions and emotions. "Should this apparently... 

In each case the results Indicated a reduced time of flight for all signals associated with the shoulder bolts. Two possible causes for this are firstly, Incorrect machining of the flat surface on viilch the probe seats compounded by some alterations In the triggering conditions of the displays between the test well and reactor. Alternatively, the reduced time of flight may Indicate the charge pan bolts being 5mm shorter than anticipated. 

Monitor the performance of the system and match monitored performance against that expected. "Trigger" conditions may be developed (e.g. level of leachate mounding and concentration of contaminants in the leachate concentrations at volume of fluid collected from secondary collection systems) such that back-up measures can be implemented once a failure of part of the system has been detected, and before conditions have been established which will ultimately cause contamination of groundwater. 

Tang, C., Rengers, N., van Asch, Th.W.J., Yang, YH. Wang, G.F. 2011. Triggering conditions and deposi-tional characteristics of a disastrous debris flow event in Zhouqu dty, Gansu Province northwestern China. Natural Hazards and Earth System Sciences (11) 2903-2912. 

Comprehensiveness of the procedures relates to the extent to which it contains all of the information that the literature suggests procedures should include, such as purpose and scope of the procedure, hazards and precautions, related documents, tools and equipment, triggering conditions, and procedural steps. 

The entire sequence of events is exposed, including triggering conditions, outcome, and the various twists and turns involved (Dekker, 2002). 

A safety trigger condition (STC) is a condition that, when asserted, triggers a safety intervention. The intervention is applied when the STC is true. The STC is chosen such that it becomes true before the safety invariant is violated. Example the robot speed is greater than 2 m/s (i.e., less than the safety invariant threshold of 3m/s) . 

Safety rule = if [safety trigger condition] then [safety intervention]. 

Mekki-Mokhtar, A., Blanquart, J.P., Guiochet, J., Powell, D., Roy, M. Safety trigger conditions for critical autonomous systems. In 18th Pacific Rim Int l Symp. on Dependable Computing (PRDC), pp. 61-69. IEEE (2012)... 

Is it possible to define trigger conditions that automatically cause the execution of predefined procedures This permits the user to define conditions (such as concentration, time, conjunctions of observations, etc.) that will automatically create reports, flag the user s terminal, or create warning messages. 

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