Оценка уровня тяжести последствий сценариев аварий при проведении анализа слоев защиты (LOPA)

The semi-quantitative risk assessment method «Layer of Protection Analysis» (LOPA) is used, as a rule, to assess the risk acceptability of increased hazard scenarios identified during the qualitative hazard analysis (HAZOP) and to make the respective risk management decisions. The adopted risk management measures can include the introduction of additional protection layers to prevent or mitigate the consequences of potential scenarios or increasing the safety integrity level for safety instrumented functions of safety instrumented systems. When using the LOPA method for risk assessment, as well as other methods, the risk management decisions are made based on the comparison of the design risk value with the established criterion of acceptability. The absence of a unified approach to establishing scenario risk acceptability criteria can cause significant discrepancies in risk assessment results: in some cases, the existing hazard can be underestimated, and in other cases, overestimated. The divergence of opinions creates preconditions to establish the diversity of approaches to acceptability criteria. The study discusses various approaches in order to determine the scenario risk acceptability criterion when performing LOPA, such as ALARP, determining acceptable risk using the risk reduction matrix, and the concept of acceptable individual risk. The choice of approach based on the risk reduction matrix represented in IEC 61511-3 is substantiated. The limitations associated with the approach and potential ways to overcome them have been discussed. An example of the use of LOPA, where the risk acceptability is determined using the ALARP principle, and the risk reduction matrix has been provided.

HAZOP analysis as a qualitative method can better identify the potential risks in the early design stage and in-service stage of the device. However, it is greatly influenced by the subjective factors of the appraisers during the assessment, which has a great impact on the accuracy and effectiveness of the risk assessment results. A semi quantitative compound risk assessment method (HALOPA method) is used to study the possible problems in the process flow and safety protection system of typical domestic diesel hydrogenation units. Taking the failure scenario of deoxygenated water pump as an example, the protective layer analysis method (HALOPA analysis) is adopted. On the basis of calculating the frequency of failure scenario and considering the acceptable risk standards of enterprises, the suggestions for improving the current independent safety protection layer and its safety integrity level (SIL) are put forward. The analysis results show that there are some shortcomings in existing process control, interlock protection, alarm setting and other protection measures of diesel hydro fining unit. The composite risk assessment method (HALOPA method) is of positive significance for effectively discovering and eliminating potential safety hazards in the operation process of the unit and ensuring safety in production.

The assignment of performance targets, or target Safety Integrity Levels (SILs), is a critical step in the application of the Safety Instrumented System (SIS) standards, i.e., ANSI/ISA S84.0.01-1996, IEC 61508 and IEC61511. Although the SIL is a key concept in the implementation of the standards, the development and application of a method for determining the target SIL has been left to the owner/operator. The standards do, however, provide guidance on this topic and present a number of techniques that can be considered, including risk matrix, risk graph, and Layers of Protection Analysis (LOPA). Generally, the methods for SIL assignment are qualitative or semi-quantitative risk assessment methods that are based upon the judgments of an assignment team. In most cases the methods based on expert opinion and limited historical data are adequate. However, in the case of overpressure protection for reactive systems, the number and complexity of the scenarios often overwhelms these simplified approaches. There are warning signs that can aid in the identification of cases where the simplified methods may break down and provide non-conservative results. In cases such as this, a quantitative assessment should be conducted to evaluate the likelihood of SIF demands, the risk reduction supplied by the other protection layers, with the aim of determining the risk reduction required from the instrumented overpressure protection system.

Traditional hazard and operability analysis (HAZOP) is one of the most widely applied methods for process safety management in process enterprises. Due to its principles based on the conservative and qualitative judgment, it often leads to too conservative risk identification results for the fluorine chemical industry usually with high-risk processes to keep the continuity of production. Most of improved quantitative and semi-quantitative methods are based on the layer of protection analysis (LOPA) to resolve the over-conservative problem of traditional HAZOP with the database of LOPA. However, the improved model, taking LOPA as the main line and HAZOP only as the provider of scenarios and influencing factors, is limited to the fact that LOPA can only analyze complete and independent protection layers (IPLs). Therefore, in order to realize the quantitative or semi-quantitative analysis of disaster causes and consequences, a new semi-quantitative HAZOP method takes HAZOP as the main line to integrate LOPA, F&EI (fire and explosion index) for quantitatively calculating the reduction factors, probability on failure demand (PFD) of general protection layers (GPLs) and PFD of IPLs. With the case comparison of fluorine chemical industry, it is proved that this new method can effectively improve the problem that traditional HAZOP are too conservative in complex scenarios.

Objective: To explore the applicability of semi-quantitative risk assessment methods in wood furniture manufacturing companies. Methods: Two medium-sized wooden furniture manufactures were randomly selected as research objects, namely A company and B company. Used the Semi-Quantitative risk assessment method (the ratio method, the index method and the comprehensive method) in the "Guidelines for occupational health risk assessment of chemicals in the workplace" (GBZ/T 298-2017) to conduct occupational hygiene survey, occupational hazard factor testing and occupational health risk assessments for two wood furniture manufacturers from January to October 2018, and compared and analyzed the applicability of these three semi-quantitative risk assessment methods in wooden furniture manufacturing enterprises. Results: The occupational health status of A enterprises was worse than that of B enterprises, and the occupational health risk level was higher than that of B enterprises, and the risk level of A enterprise is 3~4, and the risk level of B enterprise is 2~3. The occupational health risk level obtained by the index method was consistent with the comprehensive method, while the risk level of some occupational disease hazards used the ratio method was inconsistent with the results of the index method and the comprehensive method. Compared with the index method and the comprehensive method, when E/OEL<0.5 or E/OEL≥2, there might be a certain fluctuation in the occupational health risk level obtained by the ratio method. Conclusion: The semi-quantitative risk assessment is more objective, comprehensive and flexible in the application of occupational health risk assessment, and can assess the occupational health risk level of chemical poisons in wood furniture manufacturing enterprises.

Objective: To apply the semi-quantitative risk assessment model in the Technical Guidelines for Occupational Health Risk Assessment of Chemical Hazardous Factors in the Workplace to assess the occupational health risk of electroplating enterprises and explore its applicable conditions and characteristics. Methods: Three electroplating enterprises were selected as the research objects. Occupational hygiene survey and hazard factor detection were conducted on the spot. Three semi-quantitative risk assessment methods were used to assess the risk, and the evaluation results were compared. Results: The consistency between the contact index method and the comprehensive index method was strong. The weighted Kappa value was 0.946 and the P value was less than 0.001, but the consistency between the contact ratio method, the contact index method and the comprehensive index method was poor. The weighted Kappa value was 0.345 and 0.391, and the P value was 0.009 and 0.004, respectively. When the contact concentration is less than 50% OELs, the evaluation results of the contact ratio method are lower than those of the exponential method and the comprehensive exponential method. The consistency of the three methods was the highest when the contact concentration (>50%) and (<OELs). When the contact concentration >OELs, the results of the contact ratio method are higher than those of the index method and the comprehensive index method. Conclusion: Contact ratio method is suitable for occupational health risk assessment under the condition of incomplete occupational health information and for enterprise managers to identify key control points of health risk through self-assessment; Contact index method is suitable for hazard risk assessment of occupational hazards without sampling test conditions or OELs, and pre-assessment of occupational hazards of construction projects without access to analogical test data. The index method is suitable for occupational health risk assessment with available testing data and complete occupational health information.

Both Hazard and operability study (HAZOP) and Layer of Protection Analysis (LOPA) are two recognised techniques (or ‘tools') in the Process safety toolkit. Application of these techniques however has historically been restricted to a limited range of operations within upstream. This paper will describe how these tools can, and have been, successfully applied in broader applications. HAZOP was first applied in the heavy organic chemicals division of Imperial Chemical Industries in 1963. The technique was subsequently developed and matured over the following years. Today in the upstream industry HAZOP is typically applied to both existing process operations and new projects. LOPA generally follows after a HAZOP to perform a semi-quantitative assessment of the event likelihood. Application of these techniques however has historically been restricted to a limited number of operations within upstream. The objectives of the paper are to i) describe examples where HAZOP has been successfully applied to novel operations and activities ii) show how LOPA can be applied, not just for determination of Safety Integrity Level (SIL) but to hazards not associated with an instrumented function and iii) demonstrate that broader application of these tools can lead to and improved understanding of risk and, through effective risk reduction, create value for operating companies. An overview of potential challenges associated with implementing this adapted approach towards HAZOP is described, but also possible solutions. Following this the links between HAZOP and LOPA, including the information flows from one study to another are re-capped. This includes highlighting the difference between safeguards and layers of protection and qualitative risk assessment (HAZOP) versus semi-quantitative (LOPA). Current triggers for applying LOPA are compared to other approaches that result in a broader perspective and applicability. The key here is to demonstrate that there are a number of additional hazards that may be identified through HAZOP study, but for which an instrumented function may not be provided. As a result these are currently not always taken forward for further, semi-quantitative assessment. This current approach therefore limits our understanding of the associated risk. In summary, through the use of example scenarios, the paper reveals some of the limitations resulting from restricted application of HAZOP and LOPA. The intent is to raise awareness of how companies are applying these tools to analyse additional operations or activities and, as a result, reduce the frequency of high severity events. The key conclusion is that these existing tools i) with some effort can be readily applied to new / novel areas and ii) can help management understanding of risk and provide assurance that these risks are being adequately managed. In short to fully understand the Process Safety risks associated with our projects and operations we must look to broaden the application of both HAZOP and LOPA tools.

A rapid semi-quantitative ecological risk assessment method (productivity and susceptibility analysis) indicated that, despite its low biological productivity, the Port Jackson shark Heterodontus portusjacksoni is at low risk to all fishing methods in far-eastern Victoria, Australia, under the present fishing practices, because of its low catch susceptibility. The risk to this population, however, would increase if the shark gillnet fishery operating in the region were to retain the species as a by-product. Demographic analysis indicated that the species has medium intrinsic population growth rate and potential rebound in comparison with other chondrichthyan species, juveniles have higher elasticity than mature females and both juvenile and mature females have higher elasticities than hatchlings. Because of its low biological productivity and moderate resilience to the effects of fishing, cautious management measures will be necessary to ensure the sustainable use of H. portusjacksoni if its marketing increases in the future. Information on the dynamics of a population that is valuable to provide management advice can be obtained through demographic methods, but rapid assessment methods can also provide complementary information on the effects of fishing by considering the catch susceptibility of the population to each fishing method.

This paper focuses on an advanced layers of protection analysis (LOPA) method to assess the risk of a chemical process. Based on the chemical accident statistics between 2001 and 2014 in China, an acceptable risk function was built for chemical processes to confirm the acceptable risk value for an accident scenario. The assessment index for an emergency system was developed to assess the protective function of emergency protection based on analytic hierarchy process (AHP), and the probability of failure on demand (PFD) of emergency protection was obtained by fuzzy comprehensive assessment method and fuzzy set theory. The proposed method was applied to a methanol distillation installation. The result showed that the protections, including emergency protection, were sufficient because the probability of mitigation protection (1×10−8) was less than the acceptable risk value (3.04×10−7). The advanced LOPA method was proven to be able to improve the integrity and accuracy of traditional LOPA.

BP-Risk is a semi-quantitative approach for railway risk assessments, which has been published and validated. Semiquantitative methods are a combination of qualitative and quantitative approaches. They can be defined as qualitative, model-based' risk assessment methods. This means, that for semi-quantitative risk assessment methods, numerical (quantitative) values are assigned to qualitative scales. This article shows how a semi-quantitative risk assessment method can be applied for the estimation of safety requirements for wayside derailment detectors. Wayside derailment detectors were recently developed as a part of modern wayside train monitoring systems to guarantee operational safety in centralised and remote controlled railway operation. (5 pages)

An improved layer of protection analysis based on a cloud model: Methodology and case study

ExSys-LOPA for the chemical process industry

“Bow-tie” model in layer of protection analysis

The Layers of Protection Analysis (LOPA) method is a semi-quantitative risk assessment tool that is used to determine the ability of safeguards to protect against unplanned hazardous scenarios. One possible outcome of a LOPA is that existing and proposed safeguards are deemed sufficient to reduce the risk associated with the hazardous scenario to a level that can be deemed as acceptable. Alternatively, the LOPA may also show that the safeguards are insufficient and therefore additional Safety Instrumented Function(s) (SIF) would be required to reduce risk to an acceptable level. In the latter case, the LOPA method will inform the end user as to the reliability requirements of the safety function in question. The LOPA method has been used extensively in the process industries (e.g., oil and gas) as a useful tool to manage and understand risk and to demonstrate if the facility is ‘safe’ to operate, but much less so in the biosafety sector. This paper describes the LOPA method and provides some practical examples of how it may be applied in microbiological high Containment Level (CL) facilities.

Semi-quantitative risk assessment methods become more popular. However, to the knowledge of the author there are no standards about their construction so far. In this paper the requirements from a new German pre-standard DIN V VDV V 0831-101 [3] called Elektrische Bahn-Signalanlagen: Semi-quantitative Verfahren zur Risikoanalyse technischer Funktionen (Semi-quantitative methods for risk analysis of technical functions in railway signalling) are introduced. The requirements as given in the pre-standard are used to assess a new semi-quantitative approach for a risk assessment method for safety functions of vehicles as presented in [4]. The analysis focuses mainly on the requirements for the construction of the method. The major findings from this assessment will be explained and discussed relating them to the general procedure of constructing semi-quantitative risk assessment methods in Germany and other European countries. (8 pages)