The Drill Crew was in the process of slipping and cutting 1-3/8” drill line. Two Floormen were assigned to un-spool wire rope until there was approximately a 40 ft. loop below the storage reel. The rig arrangement necessitates this to facilitate slipping the drill line through the deadline anchor. As the drill line reached the desired slack, the spool continued to rotate due to its momentum. An attempt was made to stop the rotation of the spool using a wooden board as a break lever. When it became evident it was not possible to stop the spool from rotating, all personnel were instructed to vacate the area and stay clear. The drill line eventually became entangled, which stopped the rotation of the spool. Several thousand feet of drill line un-spooled from the storage reel. Fortunately there were no injuries associated with this incident.