Crane swing radius control lines and crush zones

Find the area where the upperworks can strike or trap someone

A crane or derrick’s rotating superstructure can swing into workers, vehicles, materials, or fixed structures. The hazard is not limited to the counterweight. Employees can be struck by moving parts or pinched between the equipment and a truck, wall, stored material, or another object. OSHA’s work-area-control rule applies where accessible areas present a reasonably foreseeable risk of striking or pinching/crushing an employee. Assess the actual machine, its working radius, nearby objects, and where workers can enter.

The swing radius changes with boom position and machine configuration. Identify the full hazard envelope for the planned operation, including the rear counterweight area, rotating frame, and any temporary projections. A location high above grade may not be a foreseeable hazard if no worker can reach it; placing a truck bed or material stack inside that same radius can create a crush point. Reassess when the crane is repositioned, the boom configuration changes, or site logistics introduce new objects.

Use physical boundaries and train workers

Where swing-radius hazards exist, OSHA requires the employer to train each employee assigned to work on or near the equipment to recognize the struck-by and pinch/crush areas. The employer must also erect and maintain control lines, warning lines, railings, or similar barriers to mark the boundaries. A sign alone is not the default if a barrier can feasibly be installed. Barriers need to remain visible and positioned outside the hazard area so a worker is not already exposed when reaching them.

The training should be specific to the crane setup and task. Explain where the counterweight travels, where pinch points form, how to communicate with the operator, and what to do before entering a marked area. Orient new workers and delivery personnel before they approach. If several contractors share the area, coordinate who maintains the barriers and who authorizes access. A control line removed for a delivery must be restored before normal crane operation resumes.

When barriers are infeasible

OSHA allows an alternative only when the employer can demonstrate that it is not feasible to erect barriers on the ground or equipment. In that case, the hazard areas must be clearly marked using a combination of warning signs, such as “Danger—Swing/Crush Zone,” and high-visibility markings on the equipment that identify the hazard areas. Employees must be trained to understand what the markings mean. This exception is not a convenience option for a crowded or busy site; document why barriers cannot reasonably be used.

Markings should remain visible in the equipment’s working configuration and should not be hidden by dirt, lighting, or attachments. Warning signs need to be positioned where authorized personnel will see them before entering. If the arrangement changes and barriers become feasible, install them. The purpose is to create a recognizable boundary that workers can follow, not just to satisfy a paperwork item.

Control entry for work inside the hazard area

Sometimes workers must enter a swing-radius hazard area to rig a load, inspect equipment, or perform other assigned work. Before an employee enters a location in the hazard area that is out of the operator’s view, the employee or someone instructed by that employee must ensure the operator is informed. When the operator knows a worker has entered a location covered by the rule, the operator must not rotate the superstructure until a prearranged communication system confirms the worker is in a safe position.

Agree on the communication method before the task: radio call, designated signal, or another reliable procedure. The operator should acknowledge the message, and the worker should not assume the crane is stopped because it appears idle. If radios fail or visual contact is lost, stop movement until communication is restored. A signal person helps with crane movement but does not replace the specific communication required before workers enter an area hidden from the operator.

Coordinate multiple cranes and changing site traffic

Where any part of one crane is within another crane’s working radius, the controlling entity must institute a system to coordinate operations. If there is no controlling entity, the relevant employer or employers must coordinate. The system should define operating zones, priority, communications, and steps to avoid collisions. Include swing-radius barriers in the lift plan and daily coordination meeting, especially where mobile cranes, delivery vehicles, and pedestrian paths overlap.

Barriers can be undermined by construction phasing. A new scaffold, concrete truck, storage stack, or temporary fence may create a pinch point where none existed before. Inspect the area after setup and whenever the crane’s position or nearby layout changes. Keep unauthorized workers out and route foot traffic away from the operating envelope. If the hazard boundary cannot be maintained, pause the lift until a safe method is in place.

Example: counterweight near a delivery truck

A mobile crane is set beside a material delivery lane. Its counterweight swings close to a parked flatbed, leaving a crush space between them. The supervisor recognizes that the truck creates a pinch point, installs a control-line boundary, trains the crew, and moves deliveries outside the hazard zone. A worker must enter briefly to attach rigging; the worker contacts the operator using the agreed radio call and waits for acknowledgment. The operator does not rotate the superstructure until the worker confirms a safe position.

Inspect the boundary as part of the lift

Before operation, document the crane configuration, hazard area, barrier type, access points, worker training, communication plan, and adjacent cranes or traffic. Assign someone to check that barriers remain upright and clear. Reposition them only after coordination and restore them before the work continues. If the crane or surrounding arrangement changes, repeat the hazard review rather than assuming the original boundary still fits.