12.1 Struck-By Hazards: Flying, Falling, Swinging & Rolling Objects
Key Takeaways
- Struck-by is one of the four OSHA Focus Four hazards, which together carry a 6-hour minimum in the 30-hour Construction Outreach curriculum, with falls alone requiring at least 1 hour and 30 minutes.
- Struck-by incidents are classified into four categories — flying, falling, swinging, and rolling objects — and the correct control differs for each.
- Toeboards under 29 CFR 1926.502(j) must be at least 3.5 inches tall, allow no more than a 0.25-inch clearance above the walking surface, and withstand a 50-pound force.
- The dividing line between struck-by and caught-in/between is the injury mechanism: harm from the impact itself is struck-by, while harm from crushing between two objects is caught-in/between.
- Under 29 CFR 1926.759(a) in steel erection, all materials, equipment, and tools not in use while aloft must be secured against accidental displacement.
12.1 Struck-By Hazards: Flying, Falling, Swinging & Rolling Objects
The OSHA Focus Four is a Required topic carrying a 6-hour minimum in the 30-hour Construction Outreach course. Within that six hours, falls must be covered for at least 1 hour and 30 minutes, and the remaining three hazards — electrocution, struck-by, and caught-in or between — each carry a 30-minute minimum. Chapter 2 covered falls. Chapter 3 covered electrocution. This chapter closes the remaining two.
Struck-by is consistently the second-leading cause of construction fatalities after falls. It is also the hazard most often mislabeled, because "something hit me" describes an enormous range of events with entirely different controls.
1. The Four Struck-By Categories
STRUCK-BY: FOUR MECHANISMS, FOUR CONTROL SETS
FLYING ───► Object propelled by a force (tool, wheel fragment, nail,
chip, pressurized debris). Control: guarding + eye/face PPE.
FALLING ──► Object under gravity from an elevation (tool, brick, load).
Control: toeboards, screens, canopies, nets, tool tethers,
exclusion zones below.
SWINGING ─► Suspended or mechanically driven object traversing a path
(crane load, backhoe bucket, unsecured wall panel).
Control: tag lines, exclusion zones, never under the load.
ROLLING ──► Vehicle or equipment moving at grade (haul truck, skid steer,
rolling pipe, loose material). Control: traffic plan, spotters,
backup alarms, high-visibility apparel, chocking.
[!NOTE] The classification decides the answer. A scenario in which a worker is hit by a bundle of conduit sliding off a flatbed is a rolling hazard controlled by chocking and blocking. The same conduit dropped from the third floor is a falling hazard controlled by toeboards and an exclusion zone. Read the mechanism before selecting the control.
2. Falling-Object Protection
Toeboards — 29 CFR 1926.502(j)
When guardrails are used as falling-object protection, the toeboard requirements are precise and heavily tested:
| Requirement | Value |
|---|---|
| Minimum vertical height from top edge to walking/working level | 3.5 inches |
| Maximum clearance above the walking/working surface | 0.25 inch |
| Force the toeboard must withstand (any downward or outward point) | 50 pounds |
| Construction | Solid, or with openings no greater than 1 inch in greatest dimension |
When material is piled higher than the toeboard, paneling or screening must extend from the walking surface to the top rail (or higher) for the full opening length.
The full menu of falling-object protection
| System | Where It Applies |
|---|---|
| Toeboards | Guardrailed edges, scaffold platforms (1926.451(h)(1)) |
| Screens / paneling | Where material is stacked above the toeboard |
| Debris nets / catch platforms | Scaffolds and building perimeters where material could fall past the edge |
| Canopies / sidewalk sheds | Over entrances and pedestrian routes. In demolition, 1926.850(k) requires canopies extending 8 feet from the building, capable of sustaining 150 pounds per square foot |
| Barricaded exclusion zones | The most reliable control: nobody below the work |
| Tool tethers / lanyards | Dropped-object prevention at height — increasingly standard on steel and MEP work |
| Hard hats | Last line only. A hard hat is rated for a defined impact energy; a dropped wrench from ten floors exceeds it |
Steel erection — 1926.759(a)
"All materials, equipment, and tools, which are not in use while aloft, shall be secured against accidental displacement."
This is the cleanest dropped-object rule in Part 1926 and it is absolute — bolts in an open bucket on a beam, a spud wrench balanced on a flange, or a level leaned against a column all violate it.
3. Flying-Object Hazards
Flying objects come from stored or applied energy, not gravity.
| Source | Failure Mode | Control |
|---|---|---|
| Abrasive wheels | Wheel bursts at speed; fragments leave at tangential velocity | Ring test before mounting; never exceed the wheel RPM rating; guards in place (see Section 12.2) |
| Powder-actuated tools | Fastener ricochet or spall through the base material | Correct load level; never fire into soft/brittle base material or near an edge; see Section 10.3 |
| Pneumatic nailers | Blowback and ricochet, especially in sequential-to-contact trip conversions | Sequential trip triggers; safety clips; 1926.302(b)(3) requires a safety clip or retainer on pneumatic tools over 100 psi |
| Compressed air cleaning | Chips propelled at the operator and bystanders | 1926.302(b)(4) — pressure reduced to less than 30 psi, with effective chip guarding and PPE |
| Masonry and concrete saws | Blade fragments, spall | Blade guards; correct blade for material; never remove the guard |
4. Swinging-Object Hazards
Every crane pick, every excavator swing, and every wall panel being set creates a moving mass with momentum. The controls are behavioral and spatial:
- Tag lines — control the load's rotation and pendulum from outside the swing path. Never wrap a tag line around a hand or body.
- Never under the load. 29 CFR 1926.1425 restricts work under a suspended load to specific, narrow conditions (the load is fully supported by blocking or cribbing, or the employees are engaged in hooking/unhooking or initial connection, with the operator at the controls and the load stabilized).
- Exclusion zones — barricade the radius, not just the pick point.
- Load control on windy days. A tilt-up panel or a curtain-wall unit is a sail; wind speed limits come from the manufacturer and the lift plan (Sections 6.2 and 6.4).
- Masonry walls under construction are swinging/falling hazards until braced — the limited access zone of 1926.706 exists precisely for this (Section 13.2).
5. Rolling-Object and Vehicle Hazards
Section 10.5 covers highway work zones, backing operations, and heavy-equipment traffic control in detail. Add three storage-and-material controls specific to struck-by:
- Chock and block anything round. Pipe, conduit bundles, drums, and cable reels must be chocked or racked. 1926.250(b)(9) requires structural steel, pipe, bar stock, and conduit to be racked or blocked to prevent rolling or spreading.
- Secure loads for transport. Material shifting off a flatbed or a buggy is a rolling struck-by.
- Trench and excavation edges. Spoil piles and equipment must be set back at least 2 feet from the edge (1926.651(j)(2)); material rolling into an open trench strikes the crew below.
6. Struck-By or Caught-In/Between? The Deciding Test
OSHA draws the line at the injury mechanism, not the object:
If the injury is produced by the force of the impact alone, it is STRUCK-BY. If the injury is produced by crushing, pinching, or compression between two objects — or by being buried, engulfed, or squeezed — it is CAUGHT-IN/BETWEEN.
| Scenario | Classification | Reasoning |
|---|---|---|
| Brick falls from the 4th floor and strikes a laborer's shoulder | Struck-by | Impact force alone |
| Excavator counterweight pins a worker against a trench wall | Caught-in/between | Compression between two objects |
| Trench wall collapses and buries a pipelayer | Caught-in/between | Engulfment |
| Crane load swings and knocks a rigger off a platform | Struck-by | Impact; the fall is a secondary event |
| Skid steer backs into a laborer standing against a wall | Caught-in/between | Crushed between machine and fixed object |
| Skid steer backs into a laborer in open ground, knocking them down | Struck-by | Impact alone, no compression point |
[!CAUTION] Exam Trap: the same machine produces both classifications depending on whether a fixed second surface is present. "Backed into in open ground" and "pinned against a wall" are different Focus Four categories.
Under 29 CFR 1926.502(j), a toeboard used as falling-object protection along a guardrailed leading edge must meet which combination of specifications?
A skid steer operator backs up and pins a laborer between the machine's rear frame and a concrete masonry wall, producing crush injuries. In a separate incident on the same site, a different skid steer backs into a laborer standing in open ground, knocking him down and fracturing his arm on impact. How should each event be classified within the OSHA Focus Four?
An ironworker aloft on a structural steel frame sets his spud wrench on the top flange of a beam and leans a 4-foot level against a column while he repositions. Which requirement does this violate?