About Building Exit Signs
Exit signs are devices placed inside commercial buildings to guide occupants in case of an emergency. They are designed to help occupants quickly locate the building’s exits and to evacuate efficiently. The design and placement of building exit signs in the United States is regulated by the Life Safety Code Standard 101, which is produced by the National Fire Protection Association (NFPA). Though this Standard itself is not a law, it has been adopted by most cities and states and incorporated into local building codes. Does this Spark an idea?
Lettering and Display
In most of the world, exit signs display pictorial symbols. It is only in the United States and a handful of other countries that these signs are marked with the word “Exit.” Similarly, most countries use green lettering or pictures on exit signs, based on the understanding that green is linked to “go.” In the United States, exit sign colors vary depending on code requirements in individual states. Most states require red lettering, believing it is easier to see in an emergency, while some states use green lettering to align themselves with international standards. All exit signs in the United States must be continuously illuminated from within, with letters at least 6 inches tall in accordance with NFPA 101.
Placement at Doors
According to NFPA 101, exit signs must be placed at all building exits, including stairways, exterior doors or passageways. They are not required at main entrance doors that are made from glass, as these are easily identifiable as exits. When nonexit doors are close enough to exit doors to cause confusion, the nonexits must be identified as such. NFPA stipulates that “No Exit” signs be placed on these doors with the word “No” displayed twice as large as the word “Exit” to prevent confusion. These doors must also be labeled with their true function (e.g., storage, restroom, copy room).
Placement in Hallways
The intent of NFPA 101 is that building occupants should be able to see an exit sign from any spot in the building. Signs in corridors must be visible from no more than 100 feet away and are generally placed roughly 200 feet apart so that someone standing in the middle of the two signs can see at least one of them at less than 100 feet. Signs placed in hallways must also have directional areas to indicate the location of exits. In addition, signs should be placed within rooms or other areas so that occupants are able to find an escape route from any location. Often, the final placement of exit signs is left up to the local fire marshal or building inspector.
Historically, exit signs were self-contained devices that were lit using a single incandescent bulb. These early devices were susceptible to power outages, however, and manufacturers began to add backup power supplies in the form of battery packs. In the case of a power failure, the battery pack will keep the sign lit normally to help improve evacuation procedures. Because of the inefficiency and short life of incandescent bulbs, exit signs are often equipped with fluorescent or LED bulbs instead.
Tritium Exit Signs
Tritium exit signs are self-luminous models that do not rely on electrical or battery power. They are used in situations where power connections are not available or are impractical. These signs contain a phosphorous-lined glass tube filled with radioactive tritium gas. When tritium reacts with phosphorous, it emits a green glow bright enough to light the exit sign from within. These signs can last up to 20 years with little or no maintenance.