Business owners are responsible for the safety of everyone in their property, whether they are employees or visitors. Part of their responsibility is ensuring that exit aisles are wide enough and unobstructed so that people can quickly evacuate in an emergency. In addition to regulations governing the width of exit routes, businesses must designate a certain number of routes depending on the number of employees and layout of the building.
TL;DR (Too Long; Didn't Read)
The aisle of an indoor or outdoor exit route must be at least 28 inches wide at all points.
Emergency Exit Routes Defined
The Occupational Safety and Health Administration (OSHA) defines an exit route as a "continuous and unobstructed path of exit travel from any point within a workplace to a place of safety." It comprises three sections: an "exit access" which leads to the exit route, the "exit" aisle or walkway, and an "exit discharge" which leads directly outside to a refuge area such as a parking lot or a street. The basic rule is that an office must have enough exits, and of sufficient capacity, to ensure the safe and timely evacuation of the building's occupants in an emergency.
Minimum Aisle Width
Generally, the aisle of an indoor or outdoor exit route must be at least 28 inches wide at all points. This is the minimum permitted width for an emergency exit door – the door that leads to the exit aisle – and the aisle must be at least as wide as the door. However, the test is one of capacity. An exit route must be wide enough to accommodate the maximum number of workers who are permitted to work on the floor served by the exit route. For large offices with many employees, the required width may be significantly larger than 28 inches.
Minimum Aisle Height
Ceilings of exit routes must be at least 7 feet, 6 inches high. If there's anything attached to the ceiling, it cannot hang down to a point less than six feet eight inches from the floor. This is to allow sufficient headroom for people who are traveling along the aisle. It is a violation of fire codes to allow objects to project into the aisle that reduce the minimum height or width standards.
Number of Exit Routes
Generally, a workplace must have at least two exit routes of the required size to allow building occupants to evacuate safely during an emergency. Very small workplaces can get away with only one exit route if everyone in the building can evacuate expeditiously. Conversely, large offices with many employees or an unusual layout may need to have more exit routes. The onus is on the building owner to carry out their own risk assessment and determine whether the building meets OSHA's design and construction standards for exit routes.