Under standards for the Occupational Safety and Health Administration, red indicates fire protection equipment, danger or stop; and yellow indicates caution and marks physical hazards, according to the U.S. Department of Labor. Red is used to mark emergency stop bars on equipment machinery and electrical switches.
Red also indicates danger and is used on danger signs and containers that hold flammable liquid, explains the U.S. Department of Labor. Red lights are used at barricades and obstructions. Some hazards indicated by yellow include falling, tripping, striking against and getting caught in between something.
Since OSHA regulations are vague with limited requirements for color, symbols and size of warning signs, the American National Standards Institute created a more detailed safety color code, states Grainger. Red and yellow have the same indications assigned by OSHA. Fluorescent orange or orange-red indicates biosafety hazards and orange provides machinery safety warnings. For example, it might warn a worker of machine parts that could crush him.
Green means safety and indicates things such as first aid and safety equipment, advises Grainger. Blue signs provide information such as on bulletin boards. Black, white and yellow indicate boundaries for housekeeping or traffic passages such as stairways. A yellow sign with magenta or purple markings warns of radioactive hazards such as X-rays or proton radiation.