# Evaluation of the Level of Reliability in Hazardous Technological Processes
## 1 Introduction  
Any technical system has no zero faults, no one makes zero-point errors, and in any part of the software design, it is not possible to predict all the operational possibilities of the error. Therefore, the concept of zero risks in a technical system is not achievable nowadays [1]. However, general risk perception, especially as a result of a larger accident, often contributes to perceiving the notion of ideally zero risks. In general, most people understand that this is not possible [2]. Automated safety-critical systems that are used in different industries are characterized by the fact that any unforeseen situation or failure in functionality can cause significant financial losses, loss of life or environmental pollution [3]. In terms of running modern computer safety-critical systems, most unexpected situations or failures are due to abnormal software work [4; 5]. Enhanced software functionality, the speed of the spread of alarm [6] and the degree of responsibility for safety-critical systems is reflected in the need for a high-quality design and safety of software safety. Therefore, the concept of defining and accepting acceptable risk for some specific activities is predominant [7]. The actual risk level that is considered tolerable will vary depending on many factors such as the degree of human control over the circumstances, the voluntary or involuntary nature of the risk, the number of people at risk in an individual case. This partly explains why the household remains at one of the highest positions inthe daily human risk table because we have control over what we have decided to do, and therefore we are willing to tolerate the risks. Safety technologies have been developed to address the level of target-risk and to assess whether the proposed projects meet these objectives, whether they are technological devices, transport systems, medical equipment or any other application. The development of hazardous industrial process management systems has been conducted in line with international technical standards (mainly IEC 61508 and IEC 61511). These standards describe the life cycle stages of safety-critical systems and also describe the required level of risk. The safety-related systems contain various elements such as devices, hardware or software. They may comprise a separate device or may be part of other devices that perform safety functions. These safety functions need to be applied to achieve the required level of safety. Any failure of safety function significantly affects the possibility of a threat to humans or the environment. Different safety-related system types require different solutions. The correct response to the input signals and fulfillment of the set requirements ensure the proper functioning of the system. Ensuring functional safety requires the engagement of all specified safety functions. An example of a safety system may be an overheat protection device. That device uses a temperature sensor on the motor coil, which disconnects the engine power before it can overheat. However, the presence of special packaging as high-temperature protection is not associated with functional safety (although it is generally related to safety and can prevent the same dangerous situation). The following chapters address the design or analysis of control systems that perform a critical function. This function guarantees the required level of safety, which corresponds to technical standards. In the design algorithm, it is an important task to determine the degree of risk. This level can be assigned to a specific safety level according to the requirements of the standards. Fault tree and event tree analysis allow the determination of critical fault paths. The proposed logic control scheme represents the investigated technological process. The required level of safety must be ensured throughout the life cycle of this process. The possible set of goals should be achieved by implementing elements of safety functions. The elements are divided into a high-demand or low-demand mode operation.