The analysis of human-centered systems (HCS) is complex, involving vagueness, uncertainty and ill-defined data. The subjective nature of human classifications renders classical logics approaches almost useless to deal with HCS. Fuzzy Logics (FL) provides a mathematical framework for the systematic treatment of vagueness and imprecision; facilitates the elicitation and encoding of uncertainty-related knowledge; and a flexible representation mechanism for dealing with vague data. The broad variety of fuzzy operators covers the continuum from union operators to intersection operators, including average operators. This paper presents several application examples of FL in HCS analysis, namely related with Ergonomics and Safety Analysis.