Layers of Protection Analysis (LOPA) is a risk assessment method that is used to evaluate the likelihood and severity of hazardous events. It is a semi-quantitative method, meaning that it uses both qualitative and quantitative factors to assess risk.
LOPA is a popular risk assessment method in the process industries, such as the chemical, oil and gas, and power generation industries to improve Chemical Process Safety. It is also used in other industries, such as the nuclear power industry and the healthcare industry.
Steps involved in Layers of Protection Analysis (LOPA)
- Identify the hazardous event. The first step is to identify the hazardous event that you want to assess. This can be done by brainstorming with a team of experts or by using a hazard identification tool such as HAZOP.
- Identify the layers of protection. Once you have identified the hazardous event, you need to identify the layers of protection that are in place to prevent or mitigate the event. These layers can include physical barriers, procedural controls, and safety systems.
- Assess the effectiveness of the layers of protection. The next step is to assess the effectiveness of the layers of protection. This is done by assigning a risk reduction factor (RRF) to each layer. The RRF is a qualitative or quantitative measure of the effectiveness of the layer in preventing or mitigating the hazardous event.
- Calculate the risk level. The final step is to calculate the risk level. The risk level is calculated by multiplying the likelihood of the event by the severity of the event. The risk level is then used to make decisions about risk mitigation.
Four Basic Aspects of LOPA
Prevention, control, protection, and mitigation are all important aspects of LOPA (Layer of Protection Analysis).
Prevention is the act of stopping a hazardous event from occurring in the first place. This can be done by implementing safety procedures, designing safe processes, and using safe equipment.
Control is the act of reducing the likelihood or severity of a hazardous event if it does occur. This can be done by implementing safety systems, such as safety instrumented systems (SISs), and by training personnel on how to respond to hazardous events.
Protection is the act of shielding people and property from the consequences of a hazardous event. This can be done by using personal protective equipment (PPE), such as safety glasses and gloves, and by installing physical barriers, such as blast walls and dikes.
Mitigation is the act of reducing the consequences of a hazardous event that has already occurred. This can be done by providing emergency medical care, evacuating people from the area, and cleaning up hazardous materials.
By implementing a comprehensive LOPA program that includes prevention, control, protection, and mitigation, companies can help to reduce the risk of accidents and injuries.
LOPA is a valuable tool for managing risk. It can be used to identify and assess risks, and to make decisions about risk mitigation. LOPA is a flexible tool that can be tailored to the specific needs of an organization.
Independent Protection Layers (IPL) in LOPA
The Basic Process Control Layer (BPCL) is the first layer of protection in a Layer of Protection Analysis (LOPA) study. It is typically composed of the following elements:
- Process design: The process design should be inherently safe, meaning that it should be designed to minimize the risk of hazardous events.
- Basic process control system (BPCS): The BPCS is a system of instruments and controllers that is used to monitor and control the process.
- Operators: Operators are responsible for monitoring the process and taking corrective action when necessary.
The BPCL is designed to prevent hazardous events from occurring. If a hazardous event does occur, the BPCL should be able to mitigate the consequences of the event.
SIS layer in LOPA is a safety instrumented system (SIS) that is designed to prevent or mitigate a hazardous event. SISs are typically composed of sensors, logic solvers, and actuators, and they are designed to operate independently of the process control system.
An active protection layer (APL) in LOPA is a safety control that actively prevents or mitigates a hazardous event. APLs are typically designed to operate independently of the process control system and can include things like safety instrumented systems (SISs), interlocks, and relief valves.
- APLs are typically the first line of defense against a hazardous event.
- The effectiveness of APLs is assessed based on the probability of the APL detecting the hazardous event, the probability of the APL correctly identifying the event, and the probability of the APL successfully taking the required action.
- If the APL is not effective in preventing or mitigating the hazardous event, then additional protection layers (IPLs) may be required.
- The goal of LOPA is to identify and implement the necessary safety controls to reduce the risk of a hazardous event to an acceptable level.
- Here are some examples of active protection layers:
- Safety instrumented systems (SISs)
- Interlocks
- Relief valves
- Emergency shutdown systems
- Fire suppression systems
- Personal protective equipment (PPE)
A passive protection layer (PPL) in LOPA is a safety control that does not require any action to be taken to prevent or mitigate a hazardous event. PPLs are typically designed to operate independently of the process control system. Some examples of passive protection layers:
- Dikes
- Blast walls
- Containment vessels
- Fireproofing
- Emergency venting systems
An emergency response layer (ERL) in LOPA is a safety control that is designed to mitigate the consequences of a hazardous event that has already occurred. ERLs are typically implemented after the other protection layers have failed or been overwhelmed. If the ERL is not effective in mitigating the consequences of the hazardous event, then the consequences could be severe or even fatal.
- ERLs are typically the last line of defense against a hazardous event.
- The effectiveness of ERLs is assessed based on the probability of the hazardous event occurring and the effectiveness of the ERL in mitigating the consequences of the event.
- If the ERL is not effective in mitigating the consequences of the hazardous event, then the consequences could be severe or even fatal.
- The goal of LOPA is to identify and implement the necessary safety controls to reduce the risk of a hazardous event to an acceptable level.
Here are some examples of emergency response layers:
- Fire departments
- Hazmat teams
- Emergency medical services (EMS)
- Police departments
- Public works departments
- Emergency management agencies
It is important to note that not all safety controls are considered to be emergency response layers. For example, active protection layers, such as safety instrumented systems (SISs), are designed to prevent or mitigate the consequences of a hazardous event, but they require action to be taken to operate.
By understanding the different types of protection layers and their effectiveness, LOPA can be used to identify and implement the necessary safety controls to reduce the risk of hazardous events.
Here are some additional considerations when assessing the effectiveness of an ERL:
- The availability of resources
- The training and experience of personnel
- The effectiveness of communication and coordination
- The reliability of equipment
- The ability to respond in a timely manner
Guidelines & Standards
- CCPS LOPA – Simplified Risk Assessment
- OSHA 29 CFR 1910.119
- IEC 61508 & ANSI/ISA 84.01 (IEC 61511)
Benefits of using LOPA
- LOPA is a systematic approach to risk assessment.
- LOPA is a semi-quantitative method, which means that it is more accurate than qualitative methods, but less expensive than quantitative methods. LOPA is More quantitative than Process Hazards
Analysis (PHA) and Less quantitative than a Quantitative Risk Assessment (QRA).
LOPA can be used to identify and assess risks in a variety of industries. - LOPA can be used to make decisions about risk mitigation.
Limitations of LOPA
- LOPA is a complex method, and it can be time-consuming to implement.
- LOPA is a semi-quantitative method, which means that it is not as accurate as quantitative methods.
- LOPA is not a perfect method, and it can be subjective. It provide good results in conjunction with Process Hazard Analysis (PHA) for Eg, HAZOP.
Software’s for Layer of Protection Analysis (LOPA)
- LOPAWorks is a comprehensive LOPA software program that offers a wide range of features and benefits. It is a popular choice for organizations of all sizes, and it is used by a variety of industries, including chemical, oil and gas, and manufacturing.
- BowTieXP is another popular LOPA software program that offers a variety of features and benefits. It is particularly well-suited for organizations that need to comply with safety standards such as IEC 61511 and ISA 84. Learn more about Bow Tie Analysis.
- exida exSILentia is a powerful LOPA software program that is designed for use by safety professionals. It offers a wide range of features and benefits, including the ability to automate the LOPA process and generate reports and documentation.
- Sphera Process Hazard Analysis (PHA) & HAZOP Software is a comprehensive software program that can be used for a variety of safety management tasks, including LOPA. It offers a wide range of features and benefits, including the ability to automate the LOPA process and generate reports and documentation.
- Open-PHA™ is a cloud-based LOPA software program that is designed for use by small and medium-sized organizations. It offers a variety of features and benefits, including the ability to automate the LOPA process and generate reports and documentation.
Overall, LOPA is a valuable tool for managing risk. It is a systematic, semi-quantitative method that can be used to identify and assess risks in a variety of industries. LOPA can be used to make decisions about risk mitigation.