Power for emergency fire/life safety systems

Emergency and standby systems are used to provide backup power for building systems to provide assurance that fire/life safety systems and critical equipment can maintain their operation during a power outage. The use of these systems almost comes as second nature when designing large, complex facilities.
Yet, how well do you know the specific requirements for these systems? Questions we must consider include:
When is emergency and standby power required?
What are the requirements for the design of an emergency and standby power system?
What building fire safety systems need to be provided with emergency and standby power?
What are the primary challenges with small emergency systems versus large emergency systems?