When an internal combustion engine is used for the emergency system, how long should the onsite fuel supply last?

The onsite fuel supply for an internal combustion engine used in an emergency system is required to last a duration of 6 hours. This requirement is outlined in the National Fire Protection Association (NFPA) standards, specifically NFPA 70, which governs electrical installations, as well as NFPA 110, which addresses emergency and standby power systems. The rationale behind the 6-hour duration is to ensure that the emergency system can sufficiently support critical operations and provide electrical power during a power outage or emergency situation.

This duration is designed with the intent of covering a reasonable window for response during emergencies, allowing for initial response actions to take place and potentially allowing for restoration of external power sources or effective transfer of load to alternative systems without compromising safety or functionality. Consequently, ensuring that the emergency power supply can last for this period is a crucial component of a facility's safety and resilience strategy.