Process Safety Management is the identification, prevention, control and mitigation of unintentional releases of hazardous materials or energy from primary containment that have the potential to become serious incidents (fires, explosions, mass injuries, fatality, etc.).
One of the key components to achieve a successful PSM is to create and maintain safeguards or barriers to prevent the release of hazardous materials and mitigate the effect/ consequence of those releases to personnel, asset and environment. This approach is often represented in a Bowtie diagram and Bowtie method is also the most typical and popular technique to identify Safety Critical Elements which prevent and mitigate the impact of Major Accident Hazards (MAHs).
Figure 1 Illustration of a Bowtie technique used identifying barriers and SCE
SCEs management only deal with facility hardware and equipment related software or logic system and do not include HSE processes and procedures.
Why should you identify SCEs for your system?
It is necessary to identify SCEs to ensure that there is a clear understanding of what systems and structures are important in managing the risks associated with Major Accidents and Major Hazards and to establish systems which allow the performance of SCEs to be established throughout their lifecycle.
How to identify SCEs?
Different companies or organizations would have various degree of rigorous to determine SCEs, based on the maturity of their process safety management systems, the type of risk assessments they have available, or on the relative risk of their facilities.
A general approach will be as follow:
Step 1: Identify the Major Accident Events on the installation.
This is carried out using a series of hazard identification techniques, involving both qualitative and quantitative methods.
Qualitative techniques include studies like:
- Hazard Identification Studies (HAZID)
- Hazard and Operability Studies (HAZOP)
- Simultaneous Operation studies (SIMOPS)
Semi-quantitative techniques include studies like:
- Layer of Protection Analysis (LOPA)
Quantitative techniques include studies like:
- Quantitative Risk Analysis (QRA)
The results from this process are generally recorded in a Hazard Register or Risk Register which documents all the potential major accident event scenarios on an installation and should be documented in the Safety Case for the installation.
Step 2: Identification of equipment and systems that can prevent or help recover from a major accidents
Approach in this step is various, but SCEs need to be defined at an appropriate level, such that they have a direct linkage to MAHs, and it is also clear whether or not an equipment item forms part of one or more SCEs.
SCEs identification task is usually proceeded under the form of Bowtie Workshop (usually utilized by using a Bowtie Software) comprises a team of experts because it is unlikely that a single person would have enough technical appreciation of the major accident analyses and detailed knowledge of the installation. Starting from the complete list of equipment the team should assess each item in turn and form a view as to whether it could prevent or help recover from a major accident.
The outcome of these deliberations should be recorded giving the reasons why an item has or has not been identified as safety critical and with reference to the relevant major accident hazard.
Once the SCE has been identified it is necessary to define its critical function in terms of a Performance Standard which contain the following key information:
- Overall SCE Goal;
- SCE boundary/ Equipment components within the SCE system;
- Requirements in terms of Functionality (what to do?), Reliability/ Availability (required successful operate on demand probability) and Dependencies/ Interactions in order to ensure the performance goals of the SCE are met; and
- References as design documentation or codes/ standards.
Based on the Performance Standard, assurance tasks can be defined in the maintenance system to ensure that the required performance is confirmed. By analyzing the data in the maintenance system confidence can be gained that all the SCEs required to manage Major Accidents are functioning correctly. Alternatively, corrective actions can be taken to restore the integrity of the systems if deficiencies are identified.