Patent ID: 6889798

Claim:
An apparatus for the descent and retrieval of a worker through an opening in a below-the-surface location, comprising: a mobile transport device, a boom assembly, means for pivotally securing the boom assembly to the mobile transport device for pivotal movement of the boom assembly between an inoperative position and a vertical operative position, said boom assembly including an elongate mounting boom member, an extensible and retractable moveable boom structure mounted on said mounting boom member and being variously adjustable between a fully extended position and a fully retracted position, said moveable boom structure comprising a plurality of elongate moveable boom members including a distal boom member and a proximal boom member, said moveable boom members being telescopically disposed within the proximal boom member when in the fully retracted position and being telescopically extended to its maximum length in the fully extended position with the boom positioned such that it telescopes into a below-the-surface location, a support for supporting a worker thereon and having a vertical center line, means securing the support to the distal boom member to dispose the vertical center line of the support in coextensive relation with the longitudinal center line of the moveable boom members, and power means connected to the distal boom member and being operable to vertically retract the boom assembly upwardly from an extended position to a retracted position and to retain said moveable boom assembly in a retracted position, said power means being operable to release the boom members from a retracted position and permit controlled downward extension of the moveable boom members by action gravity.