Coffee Break Training: Inspection Techniques: Understanding Emergency and Standby Power Levels [open pdf - 549KB]
"When emergency or standby power systems are required by the model fire codes, they refer to National Fire Protection Association (NFPA) 110, 'Standard for Emergency and Standby Power Systems' for design and installation guides for emergency power supply systems (EPSS).1 NFPA 110 recognizes two levels of classification: critical to life and safety (Level 1) or less critical (Level 2). Level 1 systems generally are employed where critical life safety systems are employed, such as for emergency lighting. Level 2 systems are intended to supply power to so-called selected loads, where interruptions of the primary electrical supply could create hazards or hamper rescue or firefighting operations."
Coffee Break Training - Fire Protection Series No. FP-2014-19
United States Fire Administration: http://www.usfa.fema.gov/