5.4 Precision Landing, Dunnage & Safe Unrigging

5.4 Precision Landing, Dunnage & Safe Unrigging

Operational Directive: The final phase of load handling—precision landing, placement of structural dunnage, controlled rope slackening, and unrigging—demands meticulous execution. Safe landing prevents load damage, eliminates sling pinching, and protects riggers from severe pinch-point and crush hazards.

Controlled Lowering and Precision Touchdown Procedures

Landing a heavy load requires smooth, micro-positioning control to prevent floor structural damage, load tipping, or sudden impact forces.

The Touchdown Sequence

1. Approach Elevation: Lower the load at standard speed until it reaches approximately 12 to 18 inches above the landing surface.
2. Position Verification: Halt downward motion completely. Verify that the landing area is clear of debris, floor clutter, and unauthorized personnel. Confirm with the signalperson that the load alignment matches layout marks.
3. Creep Speed Final Lowering: Engage creeping speed (or low VFD frequency) to lower the load at a rate of a few inches per minute.
4. Touchdown Contact: Observe the bottom of the load as it makes initial contact with the dunnage or blocking. As weight transfers from the hoist wire rope to the floor, engine tone and wire rope tension will noticeably shift.
5. Halt Hoisting Motion: Immediately stop lowering as soon as full load weight rests securely on the landing support.

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Selection and Strategic Placement of Dunnage and Blocking

Dunnage (hardwood timber blocks, composite pads, or steel structural cribbing) serves vital mechanical functions during load landing:

Functions of Dunnage

• Prevents Sling Crushing: Dunnage elevates the load off the floor surface, maintaining a physical gap (typically 3 to 6 inches) so synthetic webbing, wire rope, or chain slings are not pinched under hundreds or thousands of pounds of deadweight.
• Facilitates Safe Unrigging: Without dunnage, removing slings from beneath a landed load requires dangerous prying or dragging, damaging rigging hardware and risking load movement.
• Distributes Weight: Dunnage spreads concentrated point loads over a broader floor area, preventing structural damage to plant concrete slabs or trailer beds.
• Prevents Load Tipping & Rolling: Shaped or contoured blocking prevents cylindrical or asymmetrical loads from rolling or shifting after unrigging.

Dunnage Placement Rules

• Always inspect dunnage for split grain, rot, cracks, or crushing damage before placement.
• Position dunnage directly beneath structural load points (skids, corner blocks, or reinforced frames).
• Never place hands, feet, or body parts beneath a suspended load while adjusting dunnage. Use long handles or push/pull sticks to position blocking!

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Hook Block Control & Preventing Wire Rope Slack

Once the load is safely resting on dunnage, the operator must carefully control the slackening of the hook block and rigging.

Controlled Slackening Protocol

Lower the hook block only far enough to allow the rigging slings to become slack so riggers can detach them from the hook bowl.

Hazards of Over-Lowering Wire Rope

Continuing to lower the hoist block after rigging has gone slack creates severe cable hazards:

• Wire Rope Unspooling: Excess slack causes wire rope on the hoist drum to loosen, jump out of drum grooves, and overlap incorrectly (birdcaging or criss-crossing).
• Kinking and Deformity: Loose wire rope hanging near the hook can loop and kink when tension is re-applied, permanently ruining the rope.
• Contamination and Damage: Allowing wire rope or hook blocks to drag on dirty, oily shop floors introduces abrasive grit into cable strands and causes premature wear.

Operators should maintain tension control, stopping hoist lowering the moment sling eyes can be easily unhooked from the saddle.

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Safe Unrigging Protocols & Pinch-Point Hazard Avoidance

Unrigging—removing slings, shackles, and hardware from the landed load—is one of the highest-risk phases for ground riggers.

Pinch-Point Hazards

A pinch point is any location where a body part can be caught between moving rigging components, between a sling and the load, or between a sling and the hook bowl.

Mandatory Unrigging Rules

1. Never Place Hands Under Slings: Never position fingers or hands between a sling body and the load edge. If a sling shifts or the load settles, severe crushing or amputation will occur.
2. Use Hand Handles or Taglines: Hold slings by external body handles or outer loops away from contact points.
3. Verify Zero Load Tension: Before unhooking sling eyes, verify that all load weight has transferred to the dunnage and wire ropes are slack.
4. Beware of Stored Elastic Energy: Synthetic webbing and wire rope store elastic energy under load. When released, slings can snap back or whip toward riggers. Stand to the side of the sling line of force.
5. Clear Hands Before Signal: Riggers must step clear of the hook footprint and give verbal/visual confirmation before signaling the operator to raise the empty hook block.

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Rigging Gear Inspection, Restoration & Storage

After completing the lift and unrigging:

1. Post-Lift Inspection: Visually inspect all slings, shackles, spreader bars, and softeners for heat damage, cuts, capacity tag legibility, or permanent deformation.
2. Remove Damaged Gear: Any sling exhibiting damaged stitching, broken wires, or distortion must be removed from service immediately and destroyed/tagged out.
3. Proper Storage: Return rigging gear to designated storage racks, trees, or lockers. Never leave slings lying on shop floors where they can be run over by forklifts, exposed to moisture, or contaminated by chemicals.
4. Hook Park Position: Raise the empty crane hook block to a safe parking height (at least 7 feet above floor level) and center the trolley to avoid impeding floor traffic.

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Precision Landing & Unrigging Workflow