A containment seal seals a cable or tube to an opening accessing a containment vessel. The containment seal includes a lower body that attaches over the opening into the containment vessel. The cable or tube is inserted through a hole that extends axially through an upper body of the containment seal. Compression fittings are attached to the top and bottom ends of the upper body sealing the cable inside of the upper body. The cable sealed inside of the upper body in inserted through the lower body and into the opening accessing the containment vessel and a lower portion of the upper body is seated into the opening formed in the lower body. A retaining device compresses the upper body down against the lower body forming a seal between the upper body and lower body.