[Dictionary] Hierarchy of Controls (NIOSH)

The hierarchy of controls is a five-level framework, developed and maintained by NIOSH (the National Institute for Occupational Safety and Health), for selecting and ranking measures to reduce or eliminate a workplace hazard, ordered from most to least reliably effective: (1) elimination -- physically removing the hazard entirely; (2) substitution -- replacing the hazard with a less hazardous alternative; (3) engineering controls -- isolating people from the hazard through the design of equipment or the workspace, without depending on a worker's behavior; (4) administrative controls -- changing how people work through policies, training, signage, or scheduling; and (5) personal protective equipment (PPE) -- protecting the individual worker as a last line of defense. A control measure's position in the hierarchy reflects reliability, not preference: the top levels remove or reduce the hazard at its source and do not depend on correct human behavior to work, while the lower levels (administrative controls and PPE) depend on people consistently following a procedure or wearing equipment correctly, and therefore fail more often in practice even when correctly specified on paper.