(Steven King AP/Casa Grande Dispatch)

Authorities are investigating a small explosion that occurred Friday morning at the back door of a Social Security Administration office in Casa Grande, Ariz., about 50 miles outside of Phoenix, according to a CBS report

The Casa Grande fire marshall said no one was injured in the blast, which occurred just before 8:30 a.m., the CBS report said.  

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives has reportedly sent investigators to the scene.