Safety life cycle and HAZOP method for risk assessment
The safety management of the electrical and electronic systems is entrusted to the IEC 61508 standard from design to decommissioning .
For the process industry, its implementation is defined by the IEC 61511 standard. Let’s see together an introduction to the functional safety!
In the past we have already talked about this topic, but let’s do a little review of the definition of functional safety: “Functional safety is the part of the overall process safety and BPCS (basic process control system) safety which depends on the correct operation of the SIS system (Safety Instrumented Systems) and other levels of protection”. In other words, we can define it as the reduction of risks provided by the functions implemented to ensure the safe operation of the entire process.
How can we comply with the standard? The main factors concern:
- The nature of the risks
- The severity of the consequences
- The necessary risk reduction
- The applicable life cycle stage
- The technology involved
- The novelty of the project
It is really important to make your own decisions based on the risks, maybe cooperating with an external subject for a more accurate assessment. Functional safety can only be applied to full functions and not to parts of equipment. Let’s take an example: if a manufacturer certifies that his product is a SIL 2 pressure sensor, this means that the pressure sensor can be used in a SIL2 safety function. At this point the manufacturer must qualify the attestation with warnings or restrictions to use it or functional tests to obtain the indicated SIL degree.
LIFE CYCLE OF SECURITY
The safety life cycle includes all necessary activities, from specification to system maintenance. Your company may be involved only in some parts of the functional safety lifecycle, but we present you all of them.
- Danger and risk assessment: in this part you need to define the field of application taking into account the physical, social and political context and considering the safety implications in terms of dangers and perception of the risk.
- Assignment of safety functions to protection levels: you need to define the instruments to achieve risk reduction.
- Safety requirements and SIS (Safety Instrumented Systems) specification: you need to specify the safety requirements necessary for the next phase in order to minimize the problems of the safety function.
- SIS development: you realize the process by programming and planning the installation and commissioning activities.
- Installation, commissioning and validation: the SIS is fully installed and it works at full capacity.
- Operation and maintenance: in order to ensure functional safety during this phase, the implementation of maintenance and repair procedures is necessary.
- Modification: the modifies can only place after the authorization of the request. It must contain three indications (dangers that may be affected, proposed changes and reasons for changes with the impact analysis document).
- Decommissioning: it is a modify that occurs at the end of the life cycle. It is managed in the same way described in the previous phase.
HOW ARE THE RISKS ASSESSED? THE HAZOP METHOD
In order to assess the risks, first of all it is necessary to identify the hazards. There are many methods to do this, but the best known is the HAZOP analysis.
This method is based on a system for predicting deviations from the main design objective. These deviations can occur due to various conditions or process problems, such as malfunction of the equipment or human error.
The HAZOP team first focuses its attention on some keywords in order to discover all the possible deviations of the system (it starts from a particular aspect or some parameters and then combines them with possible deviations). From here we begin the study of the dangers and operability. How can we do that? Considering each operating mode separately.
An expert of Rockwell Automation gives us an advise: when we are evaluating the consequences, we don’t need to consider the action of protection tools that are already included in the system, so that we can better evaluate the risks of our system.
Keep following us to read the next articles on the Rockwell Automation functional safety guide!
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