Struck-By, Caught-Between, and Line-of-Fire Controls

Struck-By, Caught-Between, and Line-of-Fire Controls

Struck-by and caught-between (caught-in-or-between) are two of OSHA's construction Focus Four hazards, alongside falls and electrocution. Together the Focus Four cause roughly 60 percent of construction deaths each year; struck-by alone is consistently the second-leading cause after falls. On the Construction Health and Safety Technician (CHST) exam these scenarios appear across both the Knowledge and Skills question categories, and the tested answer almost always applies the hierarchy of controls rather than PPE or a verbal warning.

Define the Exposure Precisely

The distinction matters for picking the right control. A struck-by injury occurs when a worker is hit by a moving object that retains its energy on impact (a swinging load, a rolling pipe, a flying nail). A caught-between injury occurs when the worker is squeezed, pinned, or crushed between two objects, or between a moving object and a fixed one. OSHA draws a useful test: if the impact alone caused the injury it is struck-by; if the crushing/squeezing caused it, it is caught-between.

Line of fire is the path an object, load, tool, vehicle, or released force will travel if control is lost. Ask not only what is moving now, but what could move if a sling slips, a chain breaks, a trench wall shifts, a tire rolls, a form panel kicks out, or a hydraulic line releases stored pressure.

A Field Scan in Four Energy Categories

• Moving equipment — trucks, forklifts, loaders, excavators, compactors, telehandlers, skid steers; backing and swing radius are the top killers.
• Moving loads — suspended picks, pushed material, rolling pipe, stacked bundles, buckets, forks, crane blocks.
• Stored (released) energy — compressed air, hydraulic pressure, springs, gravity, tensioned cable, unstable soil; control through lockout/tagout (LOTO) under 29 CFR 1910.147 and blocking before opening a system.
• Dropped objects — hand tools, deck materials, formwork, scaffold parts, loose hardware; controlled with toeboards, debris nets, tool tethers, and barricaded drop zones.

Match the Barrier to the Force

Separation is the preferred control. A soft cone line may suffice for pedestrian routing around low-risk storage, but it is never adequate where a worker could be hit by a swinging concrete bucket or a 4,000-pound counterweight — those require hard barricades or a controlled-access zone.

Positive Communication and Stop-Work Triggers

Vague phrases like "watch out" or "be careful" do not create control. Use positive communication: who is moving, where, who signals, what channel or hand signals are used, and what single command stops the work. For mobile equipment the spotter and operator agree on a stop signal before movement; if visual contact is lost, the equipment stops. This mirrors the crane rule that any worker may give an emergency stop signal.

Stop work immediately when: an exclusion zone is missing, a spotter is distracted or doing a second job, a worker walks under a suspended load, material is not secured against rolling or falling, a reversing path is shared with pedestrians, or two crews create crossing lines of fire.

CHST Field Decisions and the Exam

Challenge any plan that puts a worker in the pinch point to save time — guiding a load by its bottom edge, standing between a truck and a dock, reaching into a nip point to clear debris. The better decision is to redesign the task with push poles, tag lines (used from a clear position, never wrapped), remote-release devices, blocking, equipment repositioning, or sequencing changes.

On the CHST exam several options will sound reasonable. The best answer controls the hazard at the source or separates the worker before relying on PPE or attention. Hard hats, high-visibility garments, and safety glasses are required, but they never justify standing under a load, walking through a backing zone, or working inside a crush point. Inspection is your early-warning system: loose guardrails, damaged barricades, dead backup alarms, broken mirrors, or weak stack cribbing all signal that the struck-by system is failing.

Common Exam Traps

Watch three recurring distractors. First, options that add a second PPE layer (thicker gloves, another hard hat) when the worker is still in the line of fire — PPE sits at the bottom of the hierarchy of controls and never substitutes for elimination or separation. Second, options that slow the equipment instead of removing the exposure; a slower crush is still a crush. Third, options that add a verbal reminder or a sign where a physical barrier is required. A reliable rule: if a single failure — a slipped sling, a missed mirror, one distracted second — can still kill the worker, the control is too weak.

Pick the answer that removes the worker from the path or eliminates the released-energy source first.