Hazards in the workplace can be identified through sight, smell, or hearing. Employers identify hazards through inspections of the physical workplace, task analyses, and investigations of past accidents. Hazards can be intrinsic to operations or transitory due to human error. When assessing risk, the consequences, exposure, and probability of a hazard are considered to determine if the risk is high, medium, or low. Standard procedures aim to eliminate or control risks through substitution, engineering controls, administrative controls, or personal protective equipment based on a hierarchy of risk controls.