Hazard evaluation operation

The SIMULAR, developed by Hazard Evaluation Laboratory Ltd., is a chemical reactor control and data acquisition system. It can also perform calorimetry measurements and be employed to investigate chemical reaction and unit operations such as mixing, blending, crystallization, and distillation. Ligure 12-24 shows a schematic detail of the SIMULAR, and Ligure 12-25 illustrates the SIMULAR reaction calorimeter with computer controlled solids addition. 

After tlie system has been defined, a hazard evaluation technique can be used to identify different types of hazards within tlie system components and to propose possible solutions to eliminate the hazards. This topic is treated in more detail in the next t o chapters. These procedures are e.xtremely useful in identifying system modes and failures that can contribute to the occurrence of accidents diey should be an integral part of different phases of process development from conceptual design to installation, operation, and maintenance. The hazard evaluation tecliniques tliat are useful in tlie preliminary and detailed stages of tlie design process include ... 

In addition to the extra hardware required for these experimental runs, the ARC was operated differently than under standard hazard evaluation conditions. Instead of heating, searching and waiting, the samples were heated to a specified temperature and were then maintained isothermally at that temperature for extended periods of time. Pressure and temperature data were then monitored and stored in the microcomputer at a rate of 1 Hz. It should be noted that the apparatus reverts back to normal operation (i.e., tracking an exotherm), if a heat rise rate greater than 0.02 °C/min is detected. 

In the hazard evaluation of the process, it was found that exotherms occurred with MNB-H2SO4 mixtures at temperatures above 150°C. The initiation temperature and extent of the exotherm depend on the acid concentration. During normal operation, the temperatures in die continuous stirred tank reactors and in the continuously operated separator are between 135 and 148°C. However, operating simulation showed that for certain feed rates well out of the normal operating range, the temperature could reach 180°C and a runaway is thus possible. 

Nine commonly used hazard evaluation procedures are highlighted in the short summary statements that follow. These procedures can be applied not only to the design of a new plant but also can be used to review safety conditions of existing plants, particularly regarding an update of current standards and operations. 

As the project progresses, more information is available therefore, the review technique used can be different at each stage of the project. The use of various hazard evaluation techniques, such as checklist analyses, relative rankings, what-if analyses, and hazard and operability studies, is documented in Guidelines for Hazard Evaluation Procedures Second Edition with Worked Examples (CCPS, 1992). The need to use more quantitative techniques for hazard evaluation may be identified during these reviews, and become an action item for the project team. 

Many different loss event scenarios are possible with intentional chemistry. All of them relate to losing containment or control of the intended reaction, starting another reaction, side reaction or series of reactions that are not intended or expected. A process hazard analysis, using a hazard and operability (HAZOP) study or other appropriate method, should be used to systematically identify and evaluate a full set of loss event scenarios. General causes of uncontrolled reactions include, but are not confined to, the following list ... 

Hazard evaluation-system for investigating reactive hazards, assessing the potential consequences of uncontrolled reactions, and establishing a safe design and operating basis. 

Five of the seven respondents who use a matrix also use chemical testing results as a data source. A similar number review the matrix during qualitative hazard evaluation studies (i.e., hazard and operability [HAZOP] studies, what-if, checklist, etc.). 

Hazard evaluation Systematic process to investigate hazards, assess potential consequences, and establish a design and operating basis for safety. 

Hazard evaluations are conducted in a team environment that typically includes a process engineer, EHS staff, a chemist, maintenance, a production operator, and the customer. 

The rates of reaction (energy release in the form of heat or pressure) which depend on the temperature, pressure, and concentrations. In any hazard evaluation process, the rates of reaction during normal and abnormal operations (including the worst credible case) must be considered in order to design an inherently safe process. 

Fault tree analysis is based on a graphical, logical description of the failure mechanisms of a system. Before construction of a fault tree can begin, a specific definition of the top event is required for example the release of propylene from a refrigeration system. A detailed understanding of the operation of the system, its component parts, and the role of operators and possible human errors is required. Refer to Guidelines for Hazard Evaluation (CCPS, 1992) and Guidelines for Chemical Process Quantitative Risk Assessment (CCPS, 2000). 

Hazard evaluation— The analysis of hazardous situations associated with a process or activity, using qualitative techniques to identify weaknesses in design and operation. 

Other examples of inductive tools that have limited application in incident investigation include failure mode and effects analysis (FMEA), hazard and operability study (HAZOP), and event tree analysis (ETA). These are detailed in the CCPS book, Guidelines for Hazard Evaluation Procedures... 

Hazard and Operability Study (HAZOP)— A systematic qualitative technique to identify and evaluate process hazards and potential operating problems, using a series of guidewords to examine deviations from normal process conditions.ti)... 

Process Hazard Analysis (PHA) can be defined as the application of a systematic method to a process design in order to identify potential hazards and operating problems. It determines the causes and consequences of abnormal process conditions that arise from equipment failure, human error or other events. The goal is to determine whether opportunities exist to reduce the risks of the toll s hazards and then to implement warranted action items. The AJChE CCPS guideline Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples is a good resource for fully detailed approaches to process hazard analysis. It provides an introduction to hazard evaluation as well as guidance on ... 

Hazard and risk analysis is a vast subject by itself and is extensively covered in the literature [22]. In order to plan to avoid accidental hazards, the hazard potential must be evaluated. Many new methods and techniques have been developed to assess and evaluate potential hazards, employing chemical technology and reliability engineering. These can be deduced from Fault Tree Analysis or Failure Mode Analysis [23], In these techniques, the plant and process hazard potentials are foreseen and rectified as far as possible. Some techniques such as Hazards and operability (HAZOP) studies and Hazard Analysis (HAZAN) have recently been developed to deal with the assessment of hazard potentials [24]. It must be borne in mind that HAZOP and HAZAN studies should be properly viewed not as ends in themselves but as valuable contributors to the overall task of risk management... 

Cohen, S.R. Vanden ort, R. (1972) North American Rockwell, Reinforced Plastic Operation, Ashtabula, OH (Health Hazard Evaluation Report No. 72-68-25), Cincimrati, OH, National Institute for Occupational Safety and Health... 

Chlorine Institute. Members of the Chlorine Institute are required to reaffirm their commitment to the Institute s safety pledge, including prevention of chlorine releases. The safety pledge also includes annual safety audits, annual emission and hazard evaluations of chlorine operations, periodic emergency-response test drills, and coordination with local officials for protection of the community (32) (see Alkaliand chlorine products). 

Process Hazards Analysis. Analysis of processes for unrecognized or inadequately controlled hazards (see Hazard analysis and risk ASSESSMENT) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects hazard and operability (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify hazards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

Recommendation 6-1. Quantitative risk assessments and hazard evaluations for both the Newport and Aberdeen facilities should be carried out as early as possible during facility design, and the findings from these assessments should be used in both the design and future operation of the facilities to minimize risk and maximize safety. 

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