Abnormal situations

Alarms should be restricted to abnormal situations for which the process operator is responsible. A high alarm on the temperature in one of the control system cabinets should not be issued to the process operator. Correc ting this situation is the responsibility of maintenance, not the process operator. 

As microprocessor-based controls displaced hardwired electronic and pneumatic controls, the impac t on plant safety has definitely been positive. When automated procedures replace manual procedures for routine operations, the probability of human errors leading to hazardous situations is lowered. The enhanced capability for presenting information to the process operators in a timely manner and in the most meaningful form increases the operator s awareness of the current conditions in the process. Process operators are expected to exercise due diligence in the supervision of the process, and timely recognition of an abnormal situation reduces the likelihood that the situation will progress to the hazardous state. Figure 8-88 depicts the layers of safety protection in a typical chemical jdant. 

Nimmo, I. 1996. Abnormal Situation Management. Process and Control Engineering, 49(5), 8, 1996. 

Emergency operations Process changes initiated by the operations staff to place the process into a safe condition (back to normal operations or shutdown) in response to any abnormal situation that could cause a release, explosion, or other significant event. 

From a broader perspective, the Abnormal Situation Management Consortium is working to apply human factors theory and expert system technology to improve personnel and equipment performance during abnormal conditions. In addition to reduced risk, economic improvements in equipment reliability and capacity are expected (Rothenberg and Nimmo, 1996). 

Rothenberg, D. H., and I. Nimmo (1996). The Concept of Abnormal Situation Management and Mechanical ReUability. 1996 Process Plant Safety Symposium, April 1-2, 1996, Houston, Texas. Volume 2, ed. H. Cullingford, pages 193-208. Houston, TX South Texas Section of the American Institute of Chemical Engineers. 

Process control philosophy (e.g., computerization that removes supervisory control from the operator and may lead to inability of the operator to respond effectively to an abnormal situation)... 

Embrey, D. E. (1986). Approaches to aiding and training operators diagnoses in abnormal situations. Chemistry and Industry 7 July, 454-459. 

Peaking and Non-isothermal Polymerizations. Biesenberger a (3) have studied the theory of "thermal ignition" applied to chain addition polymerization and worked out computational and experimental cases for batch styrene polymerization with various catalysts. They define thermal ignition as the condition where the reaction temperature increases rapidly with time and the rate of increase in temperature also increases with time (concave upward curve). Their theory, computations, and experiments were for well stirred batch reactors with constant heat transfer coefficients. Their work is of interest for understanding the boundaries of stability for abnormal situations like catalyst mischarge or control malfunctions. In practice, however, the criterion for stability in low conversion... 

Postma and Stock [81] showed that HPr or E-I mutants were unable to grow on PTS carbohydrates suggesting that transport without phosphorylation did not take place in apparent contradiction with the studies presented above. The explanation may be that facilitated diffusion via PTS carriers is observed only in abnormal situations, carbohydrate being transported by the incorrect PTS carrier (galactose via the mannose carrier) or transport via a mutated carrier. Efflux, which also reflects facilitated diffusion, is more common for PTS carriers. 

Several significant challenges exist in applying data analysis and interpretation techniques to industrial situations. These challenges include (1) the scale (amount of input data) and scope (number of interpretations) of the problem, (2) the scarcity of abnormal situation exemplars, (3) uncertainty in process measurements, (4) uncertainty in process discriminants, and (5) the dynamic nature of process conditions. 

By now, I hope that I have convinced you that much of what has passed for common wisdom about depression and antidepressants is simply wrong. Depression is not caused by a chemical imbalance in the brain, and it is not cured by medication. Depression may not even be an illness at all. Often, it can be a normal reaction to abnormal situations. Poverty, unemployment, and the loss of loved ones can make people depressed, and these social and situational causes of depression cannot be changed by drugs. 

As the level of automation increases, the operators assigned must be carefully considered and selected operators should neither be left the simple tasks that cannot be automated, nor should their tasks become annoying ones thus, the control system must provide the operators with sufficient information about the condition of the process, and they should have adequate facilities to interact with abnormal situations. 

Many possible abnormal situations can initiate a runaway reaction. These include... 

Note The previous formulations for both normal and abnormal situations are very general and include inputs to the process as well as different types of perturbations (jumps) in normal process behavior. Later on in this chapter we will consider a reduced version of this formulation, since we will be mainly interested in the measurement bias detection and identification problem. 4k... 

During the standard Kalman filter calculations, the matrix M has been evaluated from Eq. (8.38). When the test gives an alarm of malfunction, one or more elements of the innovation sequence vector is supposed to be at fault. In order to satisfy the abnormal situation, if one element is assumed to be at fault, the corresponding term in the matrix M would be greater than under normal circumstances. Thus,... 

The coil heat transfer coefficient had a value of 0.1159 and a x2 statistic of 27.8. This value suggests that a gross error is present. Some clues can be found from examination of the residuals of the balances. They are presented in Table 7. There appears to be a problem with the balances for coils 2 and 3 their residuals are different from the others (especially coil 2). The reconciled value for the coil 2 cracking temperature is also significantly different from the measured value, thus suggesting an abnormal situation associated with both coils 2 and 3. 

Abnormal situations can occur such that too much heat is generated (or too little cooling occurs) and a substance or mixture gets hotter than... 

Deviations are abnormal situations, outside the bounds of intended design and operation. (The example shown in Table 4.10 does not indicate the possible causes for each deviation.) Examples of other deviations that are typically encountered in reactive systems involving intentional chemistry include ... 

The team must be able to systematically identify abnormal situations involving chemical reactivity, estimate the likelihood of each abnormal situation occurring, and assess the consequences of each situation if it continues uncontrolled. The team must also be able to come to a consensus on where existing safeguards are inadequate and where risk control actions are needed. 

Reporting procedures for abnormal situations, near misses, incidents, leaks and spills... 

Can incompatible materials coming into contact cause undesired consequences NO No scenarios identified beyond those for intentional chemistry abnormal situations... 

Employ plant simulators for better operator training in learning how to detect, diagnose and respond to abnormal situations... 

To decide if we handle reactive materials, we want to identify those materials that can cause a dangerous release, such as of heat, blast energy, toxic vapors, or gases that could rupture a container, when exposed to conditions that may reasonably occur in normal or abnormal situations. This step is sometimes called an intrinsic evaluation, as the information we are seeking relates to a property of the material itself. 

When performing chemical reactions it is necessary to consider conceivable deviations (e.g., upsets, abnormal situations, failures) from the normal operation of a process and equipment and their possible effects on the reaction enthalpy AHr, the gas volume M produced and the rate of gas production (dM/dt), the heat flow balance (dQR/dt) - (dQ /dt) and the maximum permissible temperature TeXo for thermal stability under the applicable process conditions. Upsets (abnormal situations, failures) can be divided into two categories, and their consequences can be assessed using the following tables3 ... 

T. Kourti, Abnormal situation detection, three-way data and projection methods robust data archiving and modeling for industrial applications, Ann. Rev. Control, 27, 131-139 (2003). 

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