A safety barrier is a component which prevents access to a dangerous area. In an industrial system, it is a guard such as a fence or window, designed to keep the operator away from moving parts or other hazards. It is commonly used to mitigate risk in the Hazard-Barrier-Target model, as studied in safety science.
Hard barriers are be fixed or removable guards which prevent entry. Soft barriers are devices such as light curtains which detect the presence of a foreign body and are tied into the control circuit to stop the machine.