# Evaluation of the Level of Reliability in Hazardous Technological Processes
## 6 Discussion  
The use of safety-critical systems in the industry carries the risk of a dangerous event, which may be caused by an unforeseen situation, as well as the failure of the system with possible economic, environmental consequences, or injuries to loss of life. By defining the concept of safety-critical systems, concepts such as failure, dangerous events, etc., come to the fore. These concepts are relevant throughout the life cycle of safety-critical systems, and their essence is determined by probability theory. The technical standards for the implementation of safety-critical systems contain basic calculation procedures for determining the probability of failure, and the basis for the calculations are statistical parameters obtained from theoretical calculations or the analysis of data from the previous operation of similar systems [21; 22; 23; 24]. The calculation results then form the basis for the design and implementation of a system, which ensures the safety of a technological process throughout its entire life cycle. Methods for the analysis and design of software and hardware systems for the implementation of safety functions widely use various principles of theoretical mathematical calculations, mathematical and simulation modeling [25]. These methods describe the principles of ensuring the required level of safety at all stages of the process life cycle. To assist with the selection of methods and means, tables are available for the various methods according to the four safety integrity levels [10]. Possible modeling methods include:  
* Analysis of the consequences of the causes of failure [10];
* Fault tree analysis [26];  
Figure 10: The timing diagram of system failure. * Markov models [27; 28];
* Block diagrams of reliability [29; 30]. Methods designed for the analysis of hardware and software systems for the implementation of safety functions show the possibilities of using the application for specific technological processes. These methods describe the technologies that can be used to ensure the safe operation of the technological process. The event tree method allows you to graphically display possible scenarios of system operation in terms of the time factor. By building an event tree, it is possible to prove the safety of the entire system even in the event of unwanted basic events. The fault tree method allows a graphical representation of unreliable locations and provides an in-depth analysis of system reliability. By applying the use of the event tree and the fault tree to a specific winder dryer process, it is possible to optimize the failure rate of the entire system. The example given also shows the analysis of the evaluation of the failure of safety-critical functions of a part of the technological process of production of automotive clutches using the most used methods. The above methods allow the development of systems for the implementation of nonchalant-critical functions. However, they do not solve the issue of changing some parameters of reliability during the animal cycle of the technological process. For example, the aging of electrical components. The presented methodology for modeling the dynamics of standard control implementation architectures allows us to optimally decompose their servicing in time. Figures 4 and 5 present the results of the analysis of the safety of the technological process using the methods recommended by the standards IEC 61508-6. This standard contains the formulas that were the basis for the analysis of the safety level of the technological process. In the structure of elements of control systems, there are elements of continuous demand and operation with low demand. For elements with low demand, there is an assumption that maintenance takes place periodically. After the service, this element becomes more reliable. The level of safety decreases with operating time. This fact seriously affects the overall reliability of the system. There is a chance of random occurrence when several elements at the same time have the lowest reliability.