On Saturday, as the skies above Washington host what President Donald Trump has called "the largest fireworks show in history," dogs will be sedated, the elephants at the National Zoo may retreat to an indoor escape, and many residents will abandon the city entirely. Pyrotechnics have brought bombs-bursting-in-air spectacle, joy and national pride to Americans since 1777, though they also come with something else: a lot of smoke and a lot of booms.