Many celebrations including birthdays, graduations, and Father’s Day, are happening and Mylar balloons are common decorations.  But Eversource cautioned that Mylar balloons can cause power outages and even pose a significant safety risk. 

The silver metallic coating is a conductor of electricity.  If the balloon makes contact with power lines, it can damage electric wires and equipment, and cause power outages.  In some cases, Eversource says they could cause an electrical surge impacting nearby homes if the silver coating comes in contact with utility lines. 

They suggest making sure the balloons are secured, not released outside and that metallic ribbons aren't used.  People should never attempt to retrieve a balloon that is tangled in electric lines; instead, call Eversource.