What is Functional Safety?
Functional safety is one of the most important parts of industrial automation. It is about finding out the safety hazards and mitigating the risks to ensure safety in a plant. It includes risk analysis, the implementation of safety, and the design of systems that automatically shut down hazardous processes if needed. This helps to reduce risks to personnel, equipment, and the environment to a minimum, ensuring smooth and safe plant operations.
In practice, functional safety entails a systematic approach to safety, starting with a risk analysis. Once hazards are identified, the next step is to evaluate their severity, and finally, determine the necessary safety measures. These measures include creating systems capable of detecting and resolving safety issues before they lead to accidents.
Safety Instrumented System (SIS)
A Safety Instrumented System is an important constituent in industrial automation for safety assurance in operations. It provides an additional layer of protection to control systems in environments that are considered to have a high level of risk. In a normal control system where there are two sensors, the introduction of a third sensor as the master controller may override the first two in case it detects a failure situation.
The SIS usually involves the implementation of safety-specific PLCs, sensors, and actuators to protect processes. These systems will automatically shut down a process in case any unsafe condition is detected to prevent an accident and maintain operational safety.
Safety Integrity Level (SIL)
Safety Integrity Level, or SIL, is one important measure to denote the dependability and robustness of safety systems within an industrial setting. SIL levels run from 1 to 5, with increasing numbers showing increased amounts of safety that need to be implemented. SIL-1 defines basic needs for safety; SIL-5 represents the highest level of safety, generally resorted to in very few critical industries related to oil and gas, where the factor of catastrophe is high in case of failure.
It has a direct impact on the design of safety systems in redundancy; the higher the SIL, the more loops and backup instruments are needed along with improved component quality to minimize any safety risk.
Risk Assessment in Functional Safety
Risk assessment is the process of analysis of the potential risks involved in plant operations and determination of the failure conditions that may arise. It involves the quantification of the likelihood of these failures and understanding their possible consequences. Once identified, the necessary safety measures can be designed and implemented to mitigate these risks.
The essential purpose of risk assessment is to consider the balance between the risk and the safety measures involved in controlling it. Higher potential risks mean that safety standards should be more stringent, with greater use of fail-safes, for example.
IEC 61508: International Safety Standard
IEC 61508 is the international standard that has been laid down for functional safety in industrial automation. It gives a framework that helps in designing systems operating in hazardous environments safely by addressing safety-related operations, detecting hazards, and eliminating them before they cause harm. This standard provides comprehensive guidelines for engineers to design fail-safe systems that meet industry requirements.
By following IEC 61508, automation engineers can ensure that their safety systems are compliant with global standards, reducing risk and enhancing safety across industrial operations.
Safety Functions in Industrial Automation
Safety functions are integral parts of a safety system and include processes such as the use of safety drives, safety remote I/Os, and safety networks. These functions can be customized to meet specific needs, depending on the nature of the operation.
Some of the popular safety functions include STO- Safe Torque Off, SS1-Safe Stop -1 and SOS- Safe Operating Stop, which allows safe controlling of machinery; while specialty safety devices involving safety mats, switches as well as power-switching devices supplement the movement to ensure that correct response in hazardous situations is suitably dealt with.
Safety Circuit Structure
A well-designed safety circuit structure is indispensable in ensuring redundancy and reliability in industrial automation systems. Unlike standard circuits, safety circuits may have two sensors connected in parallel for a single PLC input or a distributed sensor configuration across multiple PLC inputs.
Architectures, like "1oo2" where a single sensor is able to trigger a safety shutdown, introduce redundancy. The concept behind it is that even though one failed sensor cannot detect a hazardous occurrence, the system still must safely shut down the process due to the presence of its redundant counterpart.
Diagnostic Coverage and Safety
Diagnostic coverage is the process of monitoring and analyzing system signals in order to find faults or failures before they become critical. Good diagnostic coverage means designing the systems that provide accurate and actionable diagnostics through either SCADA screens, alarm conditions, or specific controller states.
Good diagnostic coverage ensures that operators promptly recognize any issues and give an effective response to prevent incidents. By limiting superfluous signals and focusing resources on relevant ones, it improves overall system safety.
