The purpose of aprons and smocks is to protect employees from liquids and particles that can cause injury or illness while working with hazardous or non-hazardous substances. An apron is a garment that covers the front of the worker's body up to the knees or lower and is tied at the waist. The bib apron is a garment that is sleeveless and has an open back compared to garments that cover both the front and the back. In terms of length, they range from the knee to the calf.