What category corresponds to activities or systems capable of causing major injury or death?

The category that corresponds to activities or systems capable of causing major injury or death is indeed Category 1. This classification is crucial within the context of NFPA 99, which outlines the performance criteria for medical gas systems to ensure patient safety and minimize risk. Category 1 systems are typically associated with applications where a failure could lead to severe consequences, including significant injury or death, primarily because these systems are essential for patient care and life support.

In contrast, the other categories represent lower risks. Category 2 systems may involve some level of risk but are not associated with immediate life-threatening outcomes. Category 3 and Category 4 systems are further removed from critical impact, dealing with less than significant issues relative to patient safety. Therefore, understanding the critical nature of Category 1 helps in recognizing the importance of stringent regulations and maintenance requirements tied to these systems.