In 1919, when Edward W. Bullard had just returned to the United States after serving in the cavalry in France, he saw skyscrapers going up all across the country, and dams and bridges were growing ever larger.

These projects brought new life to cities after World War I, but they also presented new dangers for the construction workers who placed girders, poured concrete and pounded nails.

Mr. Bullard, whose father had a business making carbide lamps and other supplies for miners, had an idea: What if the company built a helmet for miners and other laborers, modeled on the metal helmet he and the other soldiers known as doughboys had worn overseas?

The Bullards cobbled one together, and that was the birth of the hard hat, which celebrates its 100th anniversary this year.