The PTO driveline hazard (sometimes identified as a machinery wrapping point hazard) is one of the oldest and most common farm machinery hazards, and refers specifically to the part of the implement (machine) drive shaft that connects to the tractor. This drive shaft is known as the implement input driveline (IID). The entire IID shaft is a wrapping point hazard if the IID is completely unshielded. If the IID shaft is partly guarded, the shielding is usually over the straight part of the shaft, leaving the universal joints, the PTO connection (the front connector), and the Implement Input Connection (IIC, the rear connector) as the wrapping point hazards. Protruding pins and bolts used as connection locking devices are particularly adept at snagging clothing. If clothing doesn’t tear or rip away, as it sometimes does for the fortunate, a persons limb or body may begin to wrap with the clothing. Even when wrapping doesn’t occur, the affected part may become compressed so tightly by the clothing and shaft that the person is trapped against the shaft.
The machines IID shaft is coupled to the tractors PTO stub. Therefore, it too rotates at either 540 rpm (9 times/sec.) or 1,000 rpm (16.6 times/sec.) when at full recommended speed. At these speeds, clothing is pulled around the IID shaft much quicker than a person can pull back or take evasive action. Many IID shaft entanglements happen while the shaft is turning at one-half or one-quarter of recommended operating speed. This may be the situation on occasions when the tractor has been stopped but not turned off, and the PTO is left engaged. Why an operator might do this is discussed in the paragraph below. The point here is that even at slower speeds, once caught by a IID shaft, a person may not have time for evasive action. A 540 rpm shaft makes over two complete revolutions per second when operating at one-quarter speed. Even with a relatively quick reaction time of five-tenths of a second, the wrapping action has begun. Once wrapping begins, the person instinctively tries to pull away. This action simply results in a tighter, more binding wrap. The 1,000 rpm shaft roughly cuts in half the opportunity for evasive action.