As the globe warms, use of electric fans can help people stay cool if they can remain hydrated and if temperatures are low enough. Yet, there are limits to how hot it can be to safely use a fan—when temperatures are too high, a fan will increase the amount of heat traveling over the skin. We use data based on historical meteorological observations to study the number of hours in the continental US that exceed recommended temperature thresholds for safe fan use. We also examine where climate conditions considered unsafe for fan use overlap with socially vulnerable communities.
We find that the geographic extent of temperatures too high for safe fan use is expanding and the number of safe hours is decreasing. In the last two decades, people have experienced double the number of hours with outdoor temperatures that are too hot for safe fan use compared to 50–70 years ago. Additionally, communities in socially vulnerable areas are experiencing higher rates of increases in unsafe hours than the overall population. Locations of particular concern include the southern and western US, highlighting the need to direct resources to invest in alternative forms of cooling in these regions.