RULE #1: If you are an acute care facility NFPA 99, Health Care Facilities Code©, states your Emergency System (Life Safety and Critical Branches) will be online within 10 seconds (Type 10) of a power outage and will be able to operate without refueling for a period established by the AHJ (Class X).
The Life Safety Branch supplies power to those circuits used for egress lighting, alarms and alerting systems, emergency communication, generator set lighting, and elevator control.
The Critical Branch supplies power to those areas and receptacles associated with maintaining medical treatment. Transfer switches of the Life Safety and Critical Branch operate automatically to restore power to equipment and receptacles within 10 seconds of a power outage.
Transfer switches of the Equipment System are set to operate either automatically (but delayed) or manually. For the former, the delay time for transferring power to loads is determined by design engineers in coordination with facility needs and the manufacturer of the alternate power source.