How long should emergency lighting operate during a power outage?

Emergency lighting is crucial in ensuring safe egress during a power outage, particularly in facilities where safety is a high priority, such as healthcare and commercial buildings. The National Fire Protection Association (NFPA) standards, particularly NFPA 101, specify that emergency lighting should be capable of providing illumination for a minimum duration.

The correct answer indicates that emergency lighting must operate for 90 minutes. This duration allows occupants enough time to evacuate safely and for emergency personnel to respond in the event of an emergency. The requirement is based on the understanding that power outages can last longer than a few minutes and that egress routes must remain illuminated to avoid confusion and promote safety.

When considering the other options, while 30 minutes and 120 minutes may seem reasonable to some, they do not meet the standard duration specified for emergency lighting. A duration of only until power returns lacks the necessary safety margin, as it may not account for the time it takes to ensure everyone has evacuated or that emergency services can effectively manage the situation.