Safety performance hazards” defined

Figure 19 Processing limits for performance and for safety. Processing limits define the perimeter of the operating envelope that results in the range of desired process performance, whereas the safety limits define the safe processing envelope perimeter given the identified hazards that lie heyond. For example, a distillation is to be carried out at 90—100° C, whereas the high-temperature interlock that shuts off the steam is set at 125° C because a significant exotherm initiates at 160°C.

There are four main uses of injury statistics (1) to identify high-risk jobs or work areas, (2) to evaluate company health and safety performance, (3) to evaluate the effectiveness of hazard-abatement approaches, and (4) to identify factors related to illness and injiuy causation. An illness and injuryreporting and analysis system requires that detailed information must be collected about the characteristics of illness and injuries and their frequency and severity. The Occupational Safety and Health Act (1970) established iUness and injury reporting and recording requirements that are mandatory for aU employers, with certain exclusions such as small establishments and government agencies. Regulations have been developed to define how employers are to adhere to these requirements (BLS 1978). 

To achieve this, the sum of the diagnostic test interval and the reaction time to achieve a safe state should be less than the process safety time . The process safety time is defined as the time period between a failure occurring in the process or the basic process control system (with the potential to give rise to a hazardous event) and the occurrence of the hazardous event if the safety instrumented function is not performed. 

The enterprise analyzes and prioritizes potential functional failure modes to define failure effects and identify the need for fault detection and recovery fimctions. Functional reliability models are established to support the analysis of system effectiveness for each operational scenario. Failures, which represent significant safety, performance, or environmental hazards, are modeled to completely understand system impacts. 

The assessment and analysis of the inherent safety performance in the hydrogen system requires sound and appropriate metrics. Several valuable proposals for inherent safety metrics (Cozzani et al. 2007, Tugnoli et al. 2007) as well as the main issues needed for such assessment are well summarized in the literature (Roller ef a/. 2001, Khan eta/. 2003). Recently, a novel consequence-based approach for inherent safety key performance indicators (KPI) assessment was proposed (Tugnoli et al. 2007). The approach bases the calculation of safety indicators on the evaluation of the expected outcomes of the hazard present in the system, by runs of specific physical consequence models. The KPI method was preferred in the current assessment framework, since, unlike other approaches, it allows easily fitting the peculiarities of the analysed systems and does not require subjective judgment. Furthermore, the KPI method was newly reviewed to describe some particular features of the hydrogen chain. In particular the assessment of transport units was added and new index aggregation rules were defined. 

A quantitative target for measuring the level of performance needed for safety function to achieve a tolerable risk for a process hazard. It is a measure of safety system performance, in terms of the probability of failure on demand. There are four discreet integrity levels, SIL 1-4. The higher the SIL level, the higher the associated safety level and the lower the probability that a system will fail to perform properly. Defining a target SIL level for a process should be based on the assessment of the likelihood that an incident will occur and the consequences of the incident. Table S.2 describes SIL for different modes of operation. 

Quantitative Risk Assessment. Previous sections in this chapter dealt with the identification, measurement, and mitigation of hazards in a chlor-alkali plant. Plant safety and Responsible Care programs define the objectives of continuous improvement in safety performance. The discussion of mitigation immediately above naturally leads on to the larger question of the most direct and cost-effective approach to this improvement. 

Safety functions are defined by lEC 61508-4 as operating in the high demand or continuous mode of operation if the demand rate is greater than one per year or greater than twice the proof test frequency. In this case, as discussed below, the measure of the safety performance of the safety function is the limit of hazard rate, h, that achieves tolerable risk. The relationship between the quantified safety performance and the SIL is given in lEC 61508-1 table 3, see Figure 2. 

Therefore, it was necessary to identify all the dependencies between the Core Hazards. Some of the models where in fact, feeding into other models, defining the failure rates of higher level base events, or barriers as represented in Figure 4-3 below. Once all of the dependences were identified, the individual core hazard models were integrated into a system safety performance model (Lucic, 2005d). 

Different sets of attributes define different objeets that make up each hazard, as well as the relationships between each individual hazard and all of the different hazards that are parts of the entirety of safety performance as an emergent property of any system under observation. 

Both of these will be analysed separately and a unified, holistic relational data stracture depicting the hazard universe will be proposed. Analysing the hazard, from a systems safety point of view, it is possible to define the hazard universe as a hierarchical net, consisting of a number of different objects, all of which interact to define the Safety Performance as an emerging property. If we analyse the hazard from a systems point of view, it is possible to distinguish between three sets of attributes related to each hazard ... 

In order to complete the inpact assessment, the effect should be assessed on the safety performance of the system and/or effect of changes to safety analysis already conpleted. For each change, affected interfaces shonld be identified, and then snbjected to ICSA and if necessary CSA. The output of this analysis feeds into a hazard log providing the base for further analysis and snpporting constmetion of safety arguments i.e. the amount of rework to die ICSA and CSA mnst be defined and then completed. 

FMEA is used to assist analysts to perform hazard analyses and it is regarded as a supplement rather than a replacement for hazard analyses. Safety analysts can use FMEA to verify that all safety critical hardware has been addressed in the hazard analyses. The FMEA for hardware systems is an important technique for evaluating the design and documenting the review process. All credible failure modes and their resultant effects at the component and system levels are identified and documented. Items that meet defined criteria are identified as critical items and are placed on the Critical Item List (CEL). Each entry of the CIL is then evaluated to see if design changes can be implemented so that the item can be deleted from the CIL. Items that cannot be deleted from the CIL must be accepted by the programme/project, based on the rationale for acceptance of the risk. The analysis follows a well-deflned sequence of steps that encompass (1) failure mode, (2) failure effects, (3) causes, (4) detectability, (S) corrective or preventive actions, and (6) rationale for acceptance. 

The management system shall address the potential hazards associated with spent fuel storage ilities, identify the safety issues and define and control operator interaction to ensure good safety performance. The Regulatory Body may review and approve the management system and monitor its ongoing performance. 

In 1993, the Center for Chemical Process Safety (CCPS) published Guidelines for Safe Automation of Chemical Processes (referred to henceforth as Safe Automation). Safe Automation provides guidelines for the application of automation systems used to control and shut down chemical and petrochemical processes. The popularity of one of the hazard and risk analysis methods presented in Safe Automation led to the publication of the 2001 Concept Series book from CCPS, Layer of Protection Analysis A Simplified Risk Assessment Approach. This method builds upon traditional process hazards analysis techniques. It uses a semiquantitative approach to define the required performance for each identified protective system. 

Process safety improvement efforts will include performance goals that define the desired future state for the various elements of the process safety system. Examples may include 100-percent reporting of process safety incidents and near misses, 100-percent on-time completion of process safety training, and timely resolution for all hazards analysis recommendations. 

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