The OSHA regulations do not mention any particular frequency for inspecting emergency lighting systems. However, the agency has incorporated by reference NFPA 101® Life Safety Code® which does address the issue. Section 7.9.3 of that code recommends a monthly test of emergency lighting for at least 30 seconds, as well as an annual test for at least 90 minutes to verify that the lights would remain on for an extended period of time. While employees might evacuate during some emergencies (such as fire), other events such as a tornado may require employees to shelter in place but could knock out electrical power. The NPFA code also recommends keeping records of these tests; a local fire or building inspector may ask to see them.