What are the five categories of safety?

Five categories of safety can be classified in different ways depending on framework, but commonly in machinery safety standard EN 954-1 there are five categories B, 1, 2, 3, 4 for safety-related control systems. Category B is basic safety with basic components and no special safety considerations. Category 1 uses well-tried safety components and principles like robust relays. Category 2 includes periodic testing where safety function is checked at machine start-up. Category 3 uses redundant dual-channel architecture where single fault does not cause loss of safety function with some fault detection, suitable for serious injury risk. Category 4 provides highest safety with continuous monitoring and fault tolerance where accumulation of faults does not cause loss of safety, used where failure could cause death. In workplace safety, five categories often taught are physical safety protecting from falls and machinery, chemical safety protecting from hazardous substances like bleach and disinfectants requiring ventilation and PPE and HEPA filtration, biological safety protecting from pathogens like tuberculosis requiring negative pressure rooms and BSL levels, ergonomic safety protecting from musculoskeletal injuries, and psychological safety protecting mental health. In construction, five categories include personal safety, equipment safety, environmental safety, public safety, and fire safety. Understanding categories helps design appropriate controls for each risk type, ensuring comprehensive safety management covering people, equipment, and environment.