Eric Smith, 36, of Islip Terrace was hospitalized in serous condition, the Long Island Press reported.
Smith was using a 3-foot-long metal tube to set off the illegal fireworks about 5:45 p.m. when one round hit his arm, Suffolk County Police Department detectives said.
Friends placed his severed limb on ice and transported it with him to the hospital. Doctors were expected to try to reattach the arm to Smith's body, the newspaper said.
2014: The Year in Music [PHOTOS]