9.6 Crane Assembly & Disassembly: Lattice Boom, Counterweights & the A/D Director
Key Takeaways
- Crane assembling and disassembly is an explicit Crane Knowledge topic on the NCCER Advanced Rigger written assessment and is taught in module 21306, Lattice Boom Assembly and Disassembly.
- OSHA 29 CFR 1926.1404 requires assembly/disassembly to be directed by an A/D director who both understands the procedures and meets the criteria for a competent person and a qualified person (or works with one).
- The A/D director must address a defined list of hazards including ground bearing conditions, blocking material and placement, verified assist-crane loads, boom and jib pick points, center of gravity, stability upon pin removal, snagging, counterweight movement, boom hoist brake failure, and loss of backward stability.
- Rigging for assembly/disassembly must be performed by a qualified rigger under 1926.1404(r)(1) — this is one of only two places OSHA names the qualified rigger by title.
- Lattice sections are non-symmetrical: the center of gravity is rarely at the geometric middle, so pick points, blocking placement, and pin-removal sequence all follow the manufacturer procedure, not judgment.
9.6 Crane Assembly & Disassembly: Lattice Boom, Counterweights & the A/D Director
The Advanced Rigger written assessment lists "crane assembling and disassembly" under Crane Knowledge, and NCCER module 21306, Lattice Boom Assembly and Disassembly, teaches it. Assembly/disassembly (A/D) is also one of exactly two places in OSHA Subpart CC where a qualified rigger is named by title — which is why it belongs in a rigger study guide rather than only an operator one.
A/D deserves that attention. The crane is at its least stable while it is being built or taken apart: sections are supported by blocking rather than by the machine, counterweights are being moved, and pins are being pulled from members that are still carrying load.
The A/D Director
Under 29 CFR 1926.1404, assembly and disassembly must be directed by a person who meets the criteria for both a competent person and a qualified person, or by a competent person who is assisted by a qualified person. That person is the A/D director, and the standard gives them concrete duties:
- Understand the applicable assembly/disassembly procedures before the work starts.
- Review the procedures immediately prior to beginning work, unless they have already applied them to the same type and configuration of equipment.
- Ensure crew members understand their tasks, the hazards, and the hazardous positions or locations they must avoid.
- Verify that any crew member who moves out of the operator's view has a means of signaling or an agreed protocol before re-entering a hazardous area.
The employer must use either the manufacturer procedures or employer procedures that meet the standard's requirements — improvised sequences are not an option.
The Hazards OSHA Requires the Director to Address
29 CFR 1926.1404(h) names them explicitly. Learn this list; it is the skeleton of any A/D exam question.
| 1926.1404(h) | Hazard | What it means on the ground |
|---|---|---|
| (h)(1) | Site and ground bearing conditions | The ground must support the equipment during A/D, not just during the lift (cross-reference 1926.1402) |
| (h)(2) | Blocking material | Size, amount, condition, and stacking method sufficient to sustain the loads and maintain stability |
| (h)(3) | Proper location of blocking | Placed to protect structural integrity and prevent dangerous movement and collapse |
| (h)(4) | Verifying assist crane loads | Loads imposed on the assist crane at each phase must be verified before work begins |
| (h)(5) | Boom and jib pick points | Rigging attachment points must prevent structural damage and allow safe handling |
| (h)(6) | Center of gravity | CG must be identified where the stability method depends on it; where information is insufficient, use measures that prevent unintended dangerous movement |
| (h)(7) | Stability upon pin removal | Sections, suspension systems (gantry A-frames, jib struts), and components must be rigged or supported to stay stable when the pins come out |
| (h)(8) | Snagging | Suspension ropes and pendants must not catch on connection pins, cotter pins, keepers, or locking pins |
| (h)(9) | Struck by counterweights | Unintended movement from inadequately supported counterweights and from hoisting counterweights |
| (h)(10) | Boom hoist brake failure | The brake must be tested before each time reliance is placed on it to hold the boom during A/D |
| (h)(11)+ | Loss of backward stability | Backward stability before swinging the upperworks, travelling, and during A/D |
Lattice Boom Handling: Why the Middle Is Not the Middle
A lattice section looks symmetrical and almost never is. Chord sizes taper along the boom, splice plates and lugs sit on one end, and inserts differ from butt and tip sections. That has three consequences:
- Pick points are designated, not chosen. The manufacturer specifies where to rig a section. Rigging at the geometric center of a section whose CG is offset will make it swing the instant it leaves the blocking.
- Blocking supports the chords, not the lacing. Lattice lacing members are slender compression/tension web members. Blocking placed under lacing crushes the section. Blocking goes under the chords, at the locations the procedure specifies, on material sized for the load.
- Pin removal order is fixed. Pins are pulled in a sequence that keeps the section supported at every step. A section that becomes a cantilever mid-sequence will bind the last pin so hard it cannot be driven — and when it finally releases, it releases violently.
Pin-driving discipline: never align a pin bore with fingers, never stand in the swing path of a suspended section, and never assume a pin is free because it is loose in the bore — a boom section under residual load can pinch a pin that has already been backed out.
Counterweights
Counterweight handling causes a disproportionate share of A/D fatalities. The controls are simple and non-negotiable:
- Install and remove counterweights strictly in the manufacturer sequence and quantity. Partial or mismatched counterweight configurations produce a crane that matches no load chart at all.
- Support slabs so they cannot tip or slide when the lifting force is released — a leaning slab on a trailer deck is a crush hazard the moment the rigging goes slack.
- Keep the crew out of the swing path of the counterweight and out of the pinch between the counterweight and the carrier or superstructure.
- Backward stability is a live hazard during A/D: an upperworks carrying full counterweight with no boom, or with the boom at a high angle, can tip rearward. That is why the standard treats loss of backward stability as its own listed hazard.
The Rigger's Specific Duties
Under 1926.1404(r), when rigging is used for assembly/disassembly:
- (r)(1) the rigging work must be done by a qualified rigger;
- (r)(2) synthetic slings must be protected from abrasive, sharp, or acute edges and from configurations that reduce rated capacity, such as distortion or localized compression;
- (r)(3) the synthetic sling manufacturer's instructions must be followed.
Combined with 1926.1425(c) — qualified rigger required whenever employees are in the fall zone hooking, unhooking, or guiding a load — these are the two places where OSHA converts "qualified rigger" from a general expectation into a specific legal requirement.
Under OSHA 29 CFR 1926.1404, who must direct crane assembly and disassembly operations?
While disassembling a lattice boom, a crew places timber blocking under the diagonal lacing members of a boom section. Why is this wrong?
Which of these is specifically listed in 1926.1404(h) as a hazard the A/D director must address?
A crane superstructure is fitted with its full counterweight package but the boom has not yet been installed. What specific hazard does this configuration present?