The Occupational Safety and Health Administration (OSHA) Occupational Safety and Health standards include a section on Exit Routes and Emergency Planning incorporating Design and construction requirements for exit routes.
This defines an exit route as “a continuous and unobstructed path of exit travel from any point within a workplace to a place of safety,” and states that there must be exit access and exit discharge as well as the exit itself that is generally separated from parts of the building to ensure there is a protected path to the exit discharge.
Exit routes are permanent and the exit from an exit route must be separated by fire-resistant materials to make it safe. A one-hour fire resistance rating is required if the exit connects three or fewer stories and a two-hour fire resistance rating if it connects more than four stories.
There must be an adequate number of exit routes in buildings, ideally with at least two in a workplace to allow the immediate evacuation of employees and any other occupants in an emergency. It stands to reason that exit routes should be located as far away from each other as possible so that if one route is blocked because of smoke or flames the second exit can be used.
In smaller buildings, where fewer people work, a single exit route may be permitted. Safety of employees is the primary deciding factor.
Limited exits (and therefore doorways) are allowed in an exit route and doors must have compliant fire doors that stay closed or close automatically if a fire alarm or employee alarm system is sounded in an emergency.
OSHA requires all fire doors, their frames, and their hardware to be approved by, or listed by, nationally recognized laboratories.
Generally, exit routes discharge to some sort of open space in a public area or street, or to a predefined refuge area. This area needs to be big enough to accommodate the likely number of people who would be evacuated if there was a fire. Sometimes, exit stairs continue from here, in which case the remaining route must also be uninterrupted.
Key to safety is the requirement in all codes and regulations that regulate exit doors, which is why they mandate that doors must remain UNLOCKED at all times. Employees need to be able to open exit doors at any time without using keys or any kind of tools, and without any special skills or knowledge. Also, doors may not be equipped with any form of alarm or device that might restrict the use of the exit route in an emergency if the alarm or device fails.
Panic or crash bars that lock from the outside only are allowed on exit discharge doors so that firefighters can access through them.
Like the areas they discharge to, exit routes must have the capacity to cater for the number of people likely to use them. The NFPA Fire Code, NFPA 1, has a detailed table that covers the occupant load factor for the full range of buildings.
The OSHA standard requires ceilings to be at least 7 feet 6 inches high and at least 2 feet 4 inches wide. If there is only one exit route, it must be at least as wide of the exit access point. Again, NFPA 1 has detailed measurement specifications.