Firefighting is commonly regarded as one of the most stressful jobs in America. But just how physically and mentally stressful is firefighting? Historically, the stressful assertion has been supported with little more thanpe anecdotal evidence. In recent years, however, FDNY performance leaders have embarked on an important mission to comprehensively quantify the physical, mental, and physiological demands of firefighting. This class will highlight what FDNY has learned about tactical and operational rigors at fires and emergencies with scientifically backed biometric data and cognitive instruments. The sizable data set from hundreds of fires and emergencies of consequence certainly raise questions about a number of tactical, operational, and logistical practices as well as theoretical concepts (i.e., "situational awareness") that the American fire service has long subscribed to absent of an understanding of the human factor at real-world fires.