UL stands for Underwriters Laboratories, an independent product safety certification organization approved by OSHA to test products and issue certifications. UL 924 is the organization’s standard for the Safety of Emergency Lighting and Power Equipment. It governs the testing and certification of exit signs, emergency lights, and combo emergency exit signs to ensure these meet the standards specific to functionality, reliability, and visibility.
Exit signs are mentioned in the OSHA standard 1910.37 - Maintenance, safeguards, and operational features for exit routes. It requires exits to be clearly visible and marked by a sign that reads "Exit." The standard also requires direction-indicating signs along the exit access where the direction of travel to the exit or exit discharge is not immediately apparent.
Additionally, the standard also specifies the use of signs that say “Not an Exit” or convey a similar message on doorways or passageways along an exit access that could be mistaken for an exit. Alternatively, these may also be marked with signs that communicate their actual use, like closets, stores, etc.
Yes. OSHA requires exit signs to be illuminated to a surface value of at least five foot-candles (54 lux) by a reliable light source. It also permits the use of exit signs that are self-luminous or electroluminescent with a minimum luminance surface value of at least .06 foot-lamberts (0.21 cd/m2).
Other than this, NFPA also requires that all exit signs be suitably illuminated using a reliable source of light. NFPA exit signs must put out at least an average of 1 foot-candle and never less than .1 foot-candle. These must remain lit for a minimum of 90 minutes during a power outage.
The placement requirements regarding exit signs are mentioned in NFPA 101 - Life Safety Code, which is acceptable by OSHA as well. The NFPA code states that any new exit signs must be located such that no point in an exit access corridor is over the sign’s rated viewing distance or 100-feet, whichever is less, from the nearest sign. Additionally, it requires that exit signs with directional indicators be placed in every location where the direction of travel to the nearest exit is not apparent.
The Life Safety Code also talks about the height of exit signs. In section 184.108.40.206, it states, “The bottom of new egress markings shall be located at a vertical distance of not more than 6ft 8 in. (2030 mm) above the top edge of the egress opening intended for designation by that marking.”
The letter height requirement for exit signs is mentioned in OSHA 1910.37(b)(7). It requires exit signs to display the word "Exit" in plainly legible letters at least 6 inches high. The principal strokes of the letters in "Exit" should be at least 3/4 of an inch wide.