Friction variation has been related to employees' perception of slipperiness in a field study conducted in fast-food restaurants. However, details of friction variation in actual workplaces have not been reported in the literature. This field study investigated friction variations in 10 fast-food restaurants in the USA. The results indicated that friction reductions in a step exceeding 10% were proportional to the ages of the floor tiles in most restaurants. There were more friction reductions exceeding 10% in the sink areas than the other five areas measured, but all the areas had more than 10% friction reductions in at least one of the restaurants. As expected, significant relative friction reductions are common on older floors. A small portion of the newer tiles had significant relative friction reductions, despite their overall higher friction levels. Therefore, slip and fall preventions should not be overlooked in restaurants with newer floors. Friction variation is speculated to be a significant contributor to slip and fall incidents. However, friction variation has not been quantified in the literature. Understanding of potential friction variations in field environments helps identify potential issues for interventions. This field study investigated friction variations in fast-food restaurants in the USA.