explosion occurred in the Packing House. The 1818 explosion killed 34 people, the 1890 explosion killed 12 people, and the 1915 explosion killed 30 people. Another explosion in 1857 fatally injured five employees, including company partner Alexis Irénée du Pont. Transformation to a museum and historic site After the introduction of smokeless powder, the mills were to be closed in the 1910s but were kept open at the request of the federal government until after the end of World War I. It closed permanently as a business in 1921. In 1952, family members donated of land and the DuPont company established a $6,000,000 endowment for the Eleutherian Mill-Hagley Foundation for a museum of industrial history. The Hagley Museum and Library formed in 1957. The site was declared a National Historic Landmark in 1966. The site The mill buildings used in the manufacture of gunpowder were built with strong stone-walled structures on three sides but were only covered by light wood structures on the fourth side, which faced out onto the Brandywine Creek. When an accident occurred, the explosion was directed away from the other mills and storage areas and over the creek. Water power was provided from a mill race behind the mills, thus further isolating the mills in case of accident. One water wheel was often used to provide power to two mills. Water turbines were introduced in the 1840s. Alfred Victor du Pont acquired additional property downstream from the Eleutherian Mills to add to the manufacturing site. One of these properties was called Hagley, and it became known as the Hagley Yard. Most of the industrial remains are located in the Hagley Yard. The mills were used in the purification, crushing, and mixing of charcoal, sulfur, and saltpeter. Other mills in the complex were used for glazing and corning, making metal powder kegs, and in cotton and woolen manufacturing. Stables, offices, a machine shop, and a steam powerhouse from the late 19th century also were located in the complex, as was a narrow gauge railway. See also Gunpowder History of gunpowder Gunpowder United States Brandywine Battlefield Hagley Museum and Library Elsewhere Ballincollig Royal Gunpowder Mills Faversham explosives industry Waltham Abbey Royal Gunpowder Mills References External links The DuPont Company on the Brandywine (digital exhibit produced by the Hagley Library that covers the early history of Eleutherian Mills) The Collection of DuPont Company powder yards on the Brandywine Creek