Participant list 2. Focus group Programme 3. Summary 4. Action list Germany master notes. Attendee 2 1. Very complex standard Not ease of understand Not ease of use Status in Germany Not well know in the process industry Attendee 3 1.
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In other words, the cycle is intended to be a risk evaluation guide during the entire system life, since the project conception to the daily maintenance. Why the Safety Life Cycle?
Accidents may happen and, therefore, it is necessary to minimize them in frequency and severity. Figure 1 - Typical example of a Safety Life Cycle The Safety Life Cycle involves the probability analysis so as to ensure the safety project integrity. In addition, it allows, by the calculations, reducing the risk at an effective cost.
Keeping a SIS integrity during the plant life cycle is extremely important for the safety management. An effective management program should include strict controls and procedures ensuring that: The identification of critical points, concepts and choice of sensors, technology, logic solver and final equipment and elements and the redundancy need comply with the safety levels and calculated risks reduction.
Once the technology and the architecture are chosen, there is an analysis plan and periodic review of them, reassessing the overall safety.
The SIS goes back to its normal operation after a maintenance. The system integrity is not compromised by non-authorized access to set up, trip or bypasses points. Procedures of change management are always followed to any system change.
The changes quality is verified and the system is revalidated before returning to operation. In this way, it will be conveniently adopted and applied in a conscious way and involving employees in all its stages and company levels.
Risk Analysis The more risks a system has, the more difficult is to meet the requirements of a safe system. Basically, the risk is the sum of the probability of something undesirable happening as a consequence of such occurrence.
The risk of a process may be defined as the product of the frequency of occurrence of a specific event F and the consequence resulting from the event occurrence C. Figure 2 - Risk considerations according to IEC In the safety systems, the search is for minimizing the risks at acceptable levels and the SIL level for control may be determined by the analysis and identification of process risks.
The IEC defines requirements for a system operation and integrity. The requirements for operation are based on the process and for integrity; they are based on reliability, which is defined as the Safety Integrity Level SIL.
There are 4 discreet levels which have 3 important properties: Applicable to the overall safety function; The highest the SIL level, the stricter are requirements; Applicable to technical and non-technical requirements Table 1 - SIL Levels How to interpret the SIL levels?
Possible damages to employees. In terms of SIL levels, the higher the required level, the higher the cost due to more complex and stricter specifications for hardware and software.
Usually, the SIL choice of each safety function is associated with the staff experience, but one may chose the HAZOP matrix analysis or the Layers of Protection Analysis LOP , where the policy, procedures, safety strategies and instrumentation are included.
Follows below some stages and details of Risk Analysis: 1. Identification of potential risks a. The company should have a group of experts in the process and in its risks c. The standards suggest methodologies for the SIL identification e. The available methods are qualitative, quantitative or semiquantitative f. Determine the SIL appropriate for the SIS, where the risk inherent to the process should be equal to or lower to the acceptable risk, ensuring the necessary safety for the plant operation.
Evaluate the probability of a potential risk related to a. Equipment failure 3. Evaluate the potential risks and consequences of the event impacts Table 3 - Example of Risk Matrix Table 4 - Frequency Range - Qualitative Criteria Table 5 - Consequence Range - Qualitative Criteria Some terms and concepts involved in safety systems Demand: Every condition or event generating requiring a safety system to operate PFD Probability of Failure on Demand : Indicator of reliability appropriate for the safety systems.
The MTBF is a basic measure of the reliability in repairable items of a piece of equipment. It may be expressed in hours or years. It is commonly used in systems reliability and sustainability analysis. If such safety tolerance is used as a project parameter, such type of failure may be ignored.
The random failures may be permanent they exist until they are eliminated or intermittent occur under some circumstances and disappear in the following moment. Systemic failures: A failure hidden within a project or assembling hardware or typically software or failures due to errors including mistakes and omissions in the safety activities cycle which cause the SIS to fail in some circumstances, under specific combinations of input or under a specific environmental condition.
Failure in a common mode: The result of a defect in common mode. Defect in a common mode: A single cause may cause failures in several elements of the system.
May be internal or external to the system.
BMS (Boiler \ Burner Management System) and BPS (Boiler \ Burner Protection System)
Liquiphant S FDL61
DIN V 19250:1994-05