This insight brief from Rocky Mountain Institute is intended to address this knowledge gap by outlining the concept of hours of safety. The concept attempts to define the duration of time that homes can be expected to provide safe temperatures when the power goes out based on key building characteristics (e.g., insulation levels). This metric can be used to quantify the amount of time people are exposed to extremely hot or cold temperatures indoors, information that can be used to effectively guide weatherization efforts, emergency response measures, and more.