A perfect process would have no hazards, but perfection is impossible in the real world. Nearly all process units have inherent risk associated with their design and operation. Safe operation is maintained with a risk reduction strategy relying on a wide variety of safety systems. This article focuses on the most common safety systems for managing process deviations during planned operating modes—instrumented safety systems (ISSs), such as safety alarms, safety controls, and safety instrumented systems. Rigorous quality assurance is necessary to achieve real‐world risk reduction, so this article follows the Plan, Do, Check, and Act process to discuss quality assurance and its application to ISS. © 2008 American Institute of Chemical Engineers Process Saf Prog 2008
Risk analysis assesses the likelihood and consequence of events. The acceptability of the identified risk is determined by comparing it to a specified risk tolerance. The criteria applied depend on the analysis boundary, which may be the hazardous event or extend to the harm posed by the hazardous event. Risk analyses generally begin with a determination of the likelihood that the hazardous event occurs. This is where the process deviation exceeds the safe operating limit of the process resulting in loss of containment, release of hazardous materials, or other undesirable consequence. These analyses require estimation of the likelihood that the initiating event occurs and the probability that the proactive protection layers do not operate as required, allowing the hazardous event to occur. Reactive protection layers and conditional modifiers are considered when the analysis is evaluating the likelihood that harm is caused by the hazardous event. Various methods for performing risk analyses are discussed in several CCPS publications including Chemical Process Quantitative Risk Analysis [CCPS/AIChE, Guidelines for Chemical Process Quantitative Risk Analysis, 2000], Hazard Evaluation Procedures [CCPS/AIChE, Guidelines for Hazard Evaluation Procedures, 2008], and Layers of Protection Analysis [CCPS/AIChE, Layer of Protection Analysis: Simplified Process Risk Assessment, 2001]. However, the link between the selected risk criteria as described in Guidelines for Developing Quantitative Safety Risk Criteria [CCPS/AIChE, Guidelines for Developing Quantitative Safety Risk Criteria, 2009] and the factors considered in the analysis is not clearly described in these texts. Recognizing this opportunity, this article begins with a brief introduction to risk analysis concepts to provide a foundation for a discussion of the typical analysis boundaries and associated risk criteria. Then, it discusses how the analysis boundary and risk criteria affect the consideration of protection layers, enabling conditions, and conditional modifiers. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011
Overfills have resulted in significant process safety incidents. Longford (Australia, 1998), Texas City (United States, 2005), and Buncefield (United Kingdom, 2005) can be traced to loss of level control leading to high level and ultimately to loss of containment. A tower at Longford and a fractionating column at Texas City were overfilled, allowing liquid to pass to downstream equipment that was not designed to receive it. The Buncefield incident occurred when a terminal tank was overfilled releasing hydrocarbons through its conservation vents. The causes of overfill are easy to identify; however, the risk analysis is complicated by the combination of manual and automated actions often necessary to control level and to respond to abnormal level events. This article provides a brief summary of the Longford, Texas City, and Buncefield incidents from an overfill perspective, and highlights five common factors that contributed to making these incidents possible. Fortunately, although overfill can be a complex problem, the risk reduction strategy is surprisingly simple. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2010
A roundleaf mutant in ‘Bighart’ pimiento pepper readily classified in segregating F2 and backcross progenies, is determined by a recessive gene, rl. The rl gene reduces the length of the leaves but not the width, changing the length/width ratio from 1.50 to 1.24. The rl gene does not produce obvious pleiotropic deleterious effects on the plant and could prove useful as a marker gene in producing F1 hybrids or for characterizing new pepper cultivars.
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