The attached proposed Recommended Practice represents the accumulative effort of Working Group E, SAE ORMTC Sub-Committee 17.
The proposed Recommended Practice establishes minimum performance criteria for devices which signal or prevent two-blocking of hoist mechanisms on cranes being used in lifting service.
Damage to the crane boom or wire rope or wire rope failure due to the raising of the load block into the boom point or upper load block has resulted in the need for defining and establishing performance requirements of two-block systems.
This document was balloted by ORMTC in March, 1980 under the title "Two-Block Prevention Systems in Lifting Crane Service" with 3 disapproval votes among the ballot results. Subsequent revision to accommodate these disapprovals become significant enough in both editorial and technical areas that it was deemed appropriate to recirculate the revised document through SC 17 members.
The next balloting among SC17 members resulted in three disapprovals, all of which questioned certain technical descriptions of the system's occurring functions. These three disapprovals were subsequently fully satisfied and the document sent on for ORMTC approval.
Resulting ORMTC ballotting resulted in no disapprovals, however, several suggestions and comments accompanying the ballot approvals were considered and implemented, if possible, by the Working Group evolving the document into the form as represented here.