Layer of protection analysis as a multifunctional team problem solving tool

Safety analysis is extremely important to avoid and prevent industrial accidents.Process safety system must act on failures so that they are prevented in the protection layers designated by the chemical process and its respective control system.The growing complexity of industrial processes creates a demand for more efficient methods to measure and prevent accidents.Conventional safety methods, such as Hazard and Operability Study (HAZOP) and Layer of Protection Analysis (LOPA), often have limitations, highlighting their qualitative aspects.In this context, the present work explores the integration of process safety into advanced control system, more specifically, with Model Predictive Control (MPC) framework to enhance the safety performance of chemical process.The advancements in this framework focus on enhancing inner layers of LOPA, specifically the control and process design layers.This improvement enables a thorough evaluation of the performance of the closed-loop control structure, particularly in the presence of disturbances and hazardous situations.The first strategy consists in the change of the basic process control layer in the LOPA to an advanced process control.It occurs implementing two different MPC formulations: a conventional infinite horizon model predictive control (IHMPC), and IHMPC with zone control.Both structures are integrated with safety index constraint based on the process state, that is a safety function that defines the safe region of operation.The safety function is developed based on fundamental process operating knowledge, first-principles models, industrial hazard analysis tools, and process operating data.When possible, IHMPC with zone control integrated with safety index constraint resulted in the better option for the control layer in LOPA, since the zone control also may work as an additional safety barrier, being safely and economically attractive.The second strategy for LOPA in this work combines the control and process design layers to improve process safety in these stages simultaneously.This approach is called simultaneous safety process design and control (SSPDC), and is established as an optimization problem that computes, at the same moment, the optimal equipment sizing, operating points, and the tuning parameters for the control system, under safety constraints.Two explicit safety constraints are adopted in this approach: the safety index based on process state for the control system, and the Safety Weighted Hazard Index (SWeHI) for the process design.SWeHI quantitatively evaluates risks associated with fire, explosion, and toxic substance release.By integrating SWeHI within the process design phase, the methodology enables the identification and mitigation of potential hazards before they manifest in operations.In SSPDC methodology, the process design has the goal of maximizing the economic return of the process in the steady-state.At the same time, the control system aims to achieve the optimal dynamic process operation ensuring safety.In this context, IHMPC with zone control is adopted, which is divided into three optimization levels: the first level is real time optimization (RTO), that defines the optimal operating points; the second level is the target calculation (TC) that estimates feasible targets for the controller by means of the optimal operating points from the RTO; and the third level is the controller model that has the goal to maintain the process operating in a safe region.This problem was addressed for a styrene polymerization reactor, as case study.Simulation results illustrate the efficacy of the proposed methodology to compute the safety, economic, and dynamic aspects with changes in the product marketing conditions and disturbances representing hazard situations.Besides, the results indicate that incorporating safety constraints enhances the process's operational safety.

Off-site hydrogen refueling stations (HRS) handle large volumes of high-pressure hydrogen, requiring precise and systematic risk-reduction strategies. In this study, a Hazard and Operability (HAZOP) analysis was performed for an off-site HRS, and Layer of Protection Analysis (LOPA) was conducted for four risk-level-4 events using two different approaches. The Functional Safety only LOPA, based on IEC 61511, and the All Safeguards LOPA, developed according to the Center for Chemical Process Safety (CCPS) guideline, were both applied. The Functional Safety only approach, which considers only automated protection layers, required Safety Integrity Level (SIL) ratings of 1 and 2, whereas the All Safeguards approach, accounting for mechanical and procedural protection layers, achieved the Target Mitigated Event Likelihood (TMEL) in all scenarios without additional SIL requirements. Consequently, it was confirmed that the definition of protection layer scope significantly influences the required SIL, design cost, and system complexity. This study proposes a hybrid approach in which all safeguards are considered during the early design stage, while in the final design stage, protection measures are evaluated from a functional safety perspective in accordance with IEC 61511 to ensure both design efficiency and safety integrity.

The overall performance of a system that shares inputs and outputs between the BPCS and SIS can be better than the performance of a BPCS system and SIS system with dedicated inputs and outputs. Layer of Protection Analysis (LOPA) assumes that independent protection layers (IPLs) are independent of the initiating event (IE) components and any components of any other IPL in the LOPA scenario. This paper first focuses on those situations where protection layers all have separate components but are not independent solely because they: share common utilities such as plant air, electricity, or cooling water, share components in instrumented loops with other instrumented IPLs or the IE, be in the same location and share vulnerability to a common failure such as a fire, or extreme weather Second, this paper demonstrates each of these situations using simple examples and a fault tree model of the LOPA scenarios to address the impact of sharing components or subsystems. Third, this paper, shows the difference between analyzing sharing at the order of magnitude LOPA level and using the best estimate component reliability data with fault tree models.Fourth, this paper provides examples showing the overall performance of a system that shares inputs and outputs between the IPLs or between the BPCS and SIS can be better than the performance of a BPCS system and SIS system with dedicated inputs and outputs. The maintenance and operational management issues involved with linking formerly “independent” systems can be managed to maintain the shared system performance advantage.Fifth, this paper suggests some general guidelines addressing sharing issues in LOPA. Finally, this paper discusses the potential benefits of selected sharing and the costs associated with assuring that the related complexities are controlled. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009

Layer of Protection Analysis – Quantifying human performance in initiating events and independent protection layers

ExSys-LOPA for the chemical process industry

Background: Fire safety is one of the most important issues in high-rise buildings. The purpose of this study is to assess maximum possible loss in the fire in Central Insurance Building of Islamic Republic of Iran using the layer of protection analysis (LOPA) method.
 Method: In 2017, this analytical study was conducted on the 21-floor building of the Central Insurance in Iran. To identify the hazard sources and assess the maximum possible loss, the authors used the preliminary hazard list (PHL) and layer of protection analysis (LOPA) respectively. In addition, the analysis of the study data was performed based on the 10×10 risk assessment matrix.
 Results: The results of the PHL showed that 26 hazardous conditions and four major sources including structural engineering, fire alarm systems and fire extinguishers, design and maintenance of building safety, and behavioral habits were identified as main hazards of fire in the studied building. The application of the LOPA method showed that highest risk level was associated with the fire caused by the exhaust heat from the engine room (RL=48) and the emergency power generator diesel (RL=40), respectively.
 Conclusion: The findings of this study indicated that calculating the maximum possible loss in the fire of high-rise buildings can help to increase the safety factor. Moreover, the use of the two methods, PHL and LOPA, can be useful in these types of risk assessments.

Layers of protection analysis in the framework of possibility theory

For the purpose of solving problems in water treatment system of the power station boiler from perspective of chemical process safety, a new method which uses the LOPA method in risk assessment for anticorrosion and scale inhibition properties of boiler system is proposed. First of all, a new annotation on the basic principle and calculation steps of LOPA is made in this paper. And then the consequence of the hazard scenario is determined by calculating the probability of accidents, such as putting poor quality water treated by the water treatment agents as initial event. Finally, specific implementable recommendations are provided by comparing the risk levels of independent protective layers system and ordinary system. The results show that the method that LOPA used in risk assessment for anticorrosion and scale inhibition properties of boiler is feasible, measures that recommended can reduce the risk; LOPA can further enrich HAZOP analysis results when introduced into boiler capacity link; layers of protection analysis, risk assessment together with humanistic management could be a new and effective security management model used by energy enterprise.

The commercialization of eco-friendly hydrogen vehicles has elicited attempts to expand hydrogen refueling stations in urban areas; however, safety measures to reduce the risk of jet fires have not been established. The RISKCURVES software was used to evaluate the individual and societal risks of hydrogen refueling stations in urban areas, and the F–N (Frequency–Number of fatalities) curve was used to compare whether the safety measures satisfied international standards. From the results of the analysis, it was found that there is a risk of explosion in the expansion of hydrogen refueling stations in urban areas, and safety measures should be considered. To lower the risk of hydrogen refueling stations, this study applied the passive and active independent protection layers (IPLs) of LOPA (Layer of Protection Analysis) and confirmed that these measures significantly reduced societal risk as well as individual risk and met international standards. In particular, such measures could effectively reduce the impact of jet fire in dispensers and tube trailers that had a high risk. Measures employing both IPL types were efficient in meeting international standard criteria; however, passive IPLs were found to have a greater risk reduction effect than active IPLs. The combination of RISKCURVES and LOPA is an appropriate risk assessment method that can reduce work time and mitigate risks through protective measures compared to existing risk assessment methods. This method can be applied to risk assessment and risk mitigation not only for hydrogen facilities, but also for hazardous materials with high fire or explosion risk.

Introduction to layers of protection analysis

The paper indicates advantages (and disadvantages) of layer of protection analysis (LOPA) over other methods to support its paramount position among different process safety analysis (PSA) methods in use today. Its simplicity (using order-of-magnitude estimates for all elements that constitute an accident scenario), universality (easy adaptation to particular needs), directness to indicate the effect of risk reduction measures as well as to assess the total level of risk to be compared with the company risk tolerance criteria are strong arguments for wider application of LOPA. However, the method may have some limitations (disadvantages) in comparison to other methods and therefore different extended approaches of LOPA have been developed to overcome the problem. Those approaches include an inclusion of an expert system into accident scenario identification (ExSysLOPA), new approach to deal with uncertainty connected with input data (fuzzy LOPA) as well as for explosion at workplace risk assessment (ExLOPA). Some of these combined techniques will be presented here and they support and extend the applications of layer of protection analysis, especially for safety assurance assessment of risk-based determination that is used in oil and gas process industries.

Chapter 21 - Understanding Layers of Protection Analysis

Risk analysis and self-healing approach for resilient interconnect micro energy grids

Chapter 2 - Hazan (Quantified risk assessment)

Study on the risk analysis and system safety integrity of enclosed ground flare