The history of fireworks goes back thousands of years to China during the Han dynasty (~200 B.C.), even long before gunpowder was invented.  It is believed that the first "firecrackers" were likely chunks of green bamboo, which someone may have thrown onto a fire when dry fuel ran short.  The rods sizzled and blackened, and after a while, unexpectedly exploded.  Bamboo grows so fast that pockets of air and sap get trapped inside of the plant's segments.  When heated, the air inside of the hollow reeds expands, and eventually bursts through the side with a long bam!

The strange sound, which had never been heard before, frightened people and animals terribly.  The Chinese figured that if it scared living creatures so much, it would probably scare away spirits – particularly an evil spirit called Nian, who they believed to eat crops and people.  After that, it became customary for them to throw green bamboo onto a fire during the Lunar New Year in order to scare Nian and other spirits far way, thus ensuring happiness and prosperity to their people for the remainder of the year.  Soon, the Chinese were using bursting bamboo for other special occasions, such as weddings, coronations, and births.  The "bursting bamboo", or pao chuk as the Chinese called it, continued to be used for the next thousand or so years.

History of Fireworks :: PyroUniverse.com.