The Fire Department of the City of New York (FDNY) began using a four-level categorization system for Mass Casualty Incidents (MCI) on August 1, 2016. Use of these levels informs EMS patient transportation decisions and provides hospitals with additional situational awareness. Each level is associated with predetermined numbers of patients that hospitals should be prepared to receive during the MCI. This document is designed to help New York City 911-receiving hospitals consider adjustments to any internal procedures that may be warranted by these changes.