U.S. Sen. John McCain wants the Department of Defense to explain how a 500-pound military bomb wound up in a scrap yard, where it partially exploded and killed an employee trying to cut into it.

Daniel Wright, 46, died in the explosion Wednesday afternoon at the Tucson Iron and Metal yard, which handles recycling materials, Tucson police said.

The ordinance was an MK-82 general purpose bomb, according to police, who said Thursday that detectives still were investigating how it ended up at the scrap yard.

McCain, R-Ariz., said he is “extremely concerned about the tragic death” of the scrap yard worker who was killed as he tried to dismantle and dispose of the bomb.

In a letter sent Thursday to Secretary of Defense Ashton Carter, McCain said it was “imperative for the Department of Defense to explain how this unexploded ordnance made its way into a civilian place of business.

“As a matter of national security, as well for the safety of the American public, this issue demands appropriate attention by the department’s senior leadership,” McCain wrote.

The MK-82 bomb, used by the Air Force and Navy, is about 5 feet long.

The bomb squad at nearby Davis-Monthan Air Force Base was called in to help with the investigation.

Base officials said Davis-Monthan doesn’t take any ordnance to scrap yards.

“Ordnances are not metal to be reused for recycling,” said 1st Lt. Erin Ranaweera, a base spokeswoman.

(AP)