## 3 Fault Tree Analysis (FTA) Analysis  
The gradual development of civilization brings together, along with many technical facilities, the possibility of significant damage to the natural environment and one of the greatest possible threats to it is chemical failures and disasters [9]. Occupational risk assessment is one of the employer's core duties but there are no practical implementing provisions for the use of hazard identification and risk assessment methods [10; 11; 12; 13]. As mentioned above, leaching in the autoclave is accompanied by the risk of material damage and in the worst case an injury to the health of the operator. This fact is influenced by risk factors such as the aggressive environment due to an alkaline slurry reaction, high temperature, and pressure, electrical installation, the risk of injury from handling by heavy autoclave. They together create an indirect risk of a failure, for example, if the operator is injured, the autoclave will be out of service with great probability. These sources of risk, in view of their indirect action, are not considered in the construction of FTA [14; 15]. Many authors, for example [PERSON] et al., propose to construct a cause-and-effect diagram, also called Ishikawa's diagram by its creator, before constructing a fault tree. It allows for \"clarification\" of the problem and is often serviceable as a basis for the graphic design of a \"tree\". The aim is to identify the sources that contribute to the analysis problem and the relationships between them [16; 17; 18]. The diagram is a visualization tool for categorizing the potential causes of the problem --the top event to identify its basic or root causes. The design of the diagram looks much like a skeleton of a fish. Fishbone diagrams are typically worked right to left, with each large \"bone\", or \"ribs\", of the fish branching out to include smaller bones containing more detail. The head and backbone of the fish list the top event--the problem or issue to be studied. Five \"causes\" that contribute to the problem (Materials, Machines, Manpower, Methods, Measurement, and Environment) create the first bones (ribs) of the fish [19]. Other, more specific levels of bones (horizontal, vertical, horizontal...) can be added to the \"ribs\" until the cause of the problem can be divided into subcategories. The practical number of levels is usually four to five. The lowest level is a basic event. When the diagram is complete, we provide an overview of the possible causes (not symptoms) of the solved problem. It is important to explore more times repeating subcategories to find a link between them or eliminate unnecessary duplication. Correctly designed diagram significantly facilitates the design of fault tree analysis. As can be seen in Figure 1, the ribs have been modified according to actual problems of the leaching process (Material-tested concentrate, Machine--autoclave, Methods, Environment, Measurement methods, and Appraisers). The whole diagram was not used to construct the FTA; it did not address the problem of the appraiser, which is rather a matter of human resources. The influence of the environment was also not considered. It does not have a statistically significant influence on the probability of the process failure in according to the results of the observation (the autoclave is in a heated room, and it is isolated from plants that would negative (for example dustiness) affect its operation. Problems with negligible probability of occurrence have also not been considered. Failure Tree Analysis (FTA) is a qualitative and quantitative analysis of the failure in the shape of a tree [20]. It defines the relationship between a top event--a failure--and basic events (roots), which are the faults of the lowest elements of the system or external influences. Logical links, that is, branch of the tree of failures, are made up of gates using the logical symbols (AND) and (OR). The gate has one output event and several input events. The \"AND\" gate uses a logical sum.