This article introduces the idea of applying the aviation concept of performance envelopes — testing and defining the outer limits of safety — in health care. The author proposes that there are two health care safety envelopes to be considered: 1) the boundaries of caregivers (human factors) that are defined by their skills, knowledge, and human capabilities, and often impacted by fatigue, the work environment, and distractions; and 2) the system or systems that the caregiver is operating within.