Struck-by and caught-in hazards field guide for crews

What struck-by and caught-in hazards are

Struck-by is a worker being hit by something with energy in it: a flying object thrown off a tool, a falling object dropped from above, a swinging load on a crane or pump boom, or a rolling vehicle or piece of equipment. Caught-in or caught-between is a worker being crushed, pinned, or pulled into something: an unguarded moving machine part, a collapse, or the closing gap between two objects. The line between them is energy direction. Struck-by, the energy comes at the person. Caught-in, the person ends up inside the energy or the gap.

Both come down to the same root. A person is in a place where stored or moving energy can reach them, and nothing was put between the two. The whole job of controlling these hazards is keeping people out of that place, or shutting the energy off before anyone is in it.

These are jobsite hazards, not concrete-only hazards, but concrete work stacks them up. You have ready-mix trucks backing to the chute, a pump boom swinging overhead, saws throwing chips, rebar standing up out of a mat, and forms that can let go if the bracing is wrong. A pour is a moving-equipment job with people working close to the iron the entire time.

Why these two are part of the Focus Four

OSHA groups the leading construction killers into the Focus Four, also called the Fatal Four: falls, struck-by, caught-in/between, and electrocution. Together these four account for the majority of construction deaths year after year. Falls lead by a wide margin. Struck-by is consistently the next-largest category, driven mostly by vehicles and dropped objects. Caught-in/between is a smaller share of the count but high in severity, because a crush or a cave-in rarely leaves a survivable injury.

Struck-by and caught-in are two of those four. That is the reason they get their own training topic and their own attention on the JHA. They are not freak accidents. They repeat, in the same handful of patterns, on jobs that skipped a known control.

The patterns are short and they are old. No spotter on a backing truck. Someone under a load that let go. A guard removed off a saw or a hand into a machine that was never locked out. A worker standing between equipment and a wall when the equipment moved. Learn the patterns and you can see the hazard before it has a person in it, which is the only point at which any of this is fixable.

What are the four types of struck-by hazards?

OSHA sorts struck-by into four types by where the object's energy comes from: flying, falling, swinging, and rolling. Each has its own control, so naming the type tells you what to do about it.

Flying is an object thrown or projected by a tool or machine: a chip off a grinder, a fragment from a saw blade, a fastener from a nail gun or a powder-actuated tool. The control is a guard on the tool and eye and face protection on anyone in range, the operator and the bystander both. Falling is an object dropped from above: a tool off a deck, material off a load, debris over an edge. The control is keeping objects from leaving the upper level and keeping people from being under them. Swinging is a suspended load moving sideways, a crane pick or a pump boom, or a load that pivots when it is lifted off-center. The control is a tag line, a clear swing radius, and nobody under or in the arc. Rolling is a vehicle or a piece of equipment moving, plus loads that can roll, like pipe or coils. The control is traffic separation, spotters, and staying out of the path.

Rolling is the one that kills the most people, so it gets its own section next. The other three are not far behind on any site with overhead work and powered tools.

Vehicles and mobile equipment: the number-one struck-by

Most struck-by deaths involve a vehicle or a piece of mobile equipment, and a large share of those happen while the equipment is backing up. A backing truck, loader, or excavator has a blind zone directly behind it that the operator cannot see, and a worker on foot in that zone is invisible until it is too late. On a pour, the ready-mix trucks are doing exactly this all day, backing to the chute on ground crowded with people.

The controls stack, and you want more than one. A reverse signal alarm warns people that equipment is backing, and OSHA requires either an audible backup alarm or a spotter for equipment with an obstructed rear view. A spotter gives the operator eyes where the operator has none. High-visibility clothing makes the worker on foot easier to see. And an internal traffic control plan, the jobsite version of a road plan, separates equipment routes from where people work so the two cross in as few places as possible.

The mistake is treating the backup alarm as the whole answer. An alarm that beeps on every machine all day becomes background noise that nobody hears. The alarm warns; the spotter and the traffic plan are what actually keep a person out from behind the wheels. Confirm the specific requirement for the equipment and the jurisdiction with OSHA and the AHJ.

How do you prevent vehicle struck-by injuries?

You separate people from the equipment, and where they have to be close, you put a trained spotter between the operator's blind spot and any worker on foot. The spotter is the control of last resort and it only works if a few rules hold every time.

The spotter and the operator agree on hand signals before anything moves, and the operator stops the instant they lose sight of the spotter. The spotter stays out of the equipment's path and never in the pinch between the machine and a fixed object, which is how spotters themselves get killed. Eye contact is the test: if the operator cannot see the spotter, the equipment does not move. Workers on foot stay out of the blind zones, which on large equipment can run many feet to the rear and the sides.

Above the spotter sits the internal traffic control plan. Lay out where trucks enter, where they back, where they stage, and where people work, and keep those apart by distance and by barricade rather than by reflex. The plan is what makes the spotter the backup instead of the only thing standing between a worker and a moving machine. Treat any task that puts people on foot next to running equipment as a planned operation, not a habit.

Falling objects and working under a load

Falling objects come off the upper level or off a lift, and the two halves of the control are keeping the object up there and keeping people out from under. You attack both. Toeboards and screens on a working deck or scaffold stop tools and debris from sliding off the edge. Tool tethers keep a hand tool from becoming a projectile when it slips at height. A barricade on the ground below keeps people out of the drop zone. Hard hats are the last layer, sized for the energy of a small object, not a heavy one.

The blunt rule is the suspended-load rule: do not work or walk under a suspended load. A crane pick, a pump boom carrying concrete, a loaded fork on a telehandler, all of it has a zone underneath that nobody should be in while the load is up. The rigging can fail, the load can shift, and the object that comes down has the whole height as a head start. This crosses straight into swinging-object struck-by, because a load that drops also swings on its way.

A hard hat is not a license to stand under a load. It buys margin against a dropped bolt, not against a dropped beam or a hose full of concrete. The control that matters is the empty space under the load, kept empty.

Flying debris from saws, grinders, and tools

Flying debris is the struck-by you create with your own tool, and the controls are a guard on the tool and eye and face protection on everyone in range. A grinder throws sparks and can throw a wheel fragment if the wheel comes apart. A saw throws chips and can kick back. The guard is there to redirect that energy away from the operator, and running a tool with the guard removed or pinned back is one of the most common, and most pointless, ways people get hurt.

Eye and face protection is not just for the person on the trigger. The bystander ten feet away catches the same chip with no warning, because they were not the one expecting it. Anyone inside the debris range wears the protection, which is why the protection requirement follows the hazard, not the job title. For cutting and coring specifically, the silica dust, the slurry, the blade selection, and the kickback are their own discipline; see the concrete cutting and coring guide for that work.

The tell that someone has normalized the hazard is a guard that has been modified to make the tool faster or easier to hold. That guard was redirecting the one fragment that was going to find an eye. Confirm tool guarding and PPE requirements against OSHA and the manufacturer's instructions.

Nail guns and powder-actuated tools

Pneumatic nail guns drive struck-by injuries through unintended firing, and the trigger system is the difference between most of them. A contact or bump-fire trigger fires whenever the nose is pushed in while the trigger is held, which is fast and which fires a nail any time the tool bumps something or someone. A sequential trip trigger requires the nose to be pressed first and then the trigger pulled, in that order, for every nail. Near other people, in tight work, or with anyone new on the tool, the sequential trip is the trigger to use.

The injuries are not abstract. A bump-fired nail can pass through a hand holding the work, ricochet off a hard surface, or fire double when the recoil bounces the nose back into the wood. Keep the hand that holds the work clear of the line of the fastener, and treat the tool as live whenever it is connected to air.

Powder-actuated tools are a separate animal with their own hazard. They use an explosive charge to drive a fastener, so a misfire, a fastener that blows through thin material, or a ricochet off steel or hard concrete carries far more energy. They require operator certification, the right fastener and charge for the base material, and face protection. Confirm the training and use requirements with OSHA, the manufacturer, and the AHJ before anyone runs one.

What is the difference between struck-by and caught-in?

Struck-by is being hit by something. Caught-in/between is being caught, crushed, pinned, or pulled into something. The rule of thumb OSHA teaches: if the injury was caused mostly by the impact alone, it is struck-by; if it was caused by being squeezed, pinched, or compressed between objects or inside a machine, it is caught-in/between.

Caught-in/between shows up in four main patterns. Trench and excavation collapse, where soil buries or crushes a worker in the cut, which is its own large topic governed by the excavation rules and an entire trench-safety discipline. Machinery, where an unguarded moving part grabs a hand, a sleeve, or a tool and pulls the worker in. Caught-between, where a person ends up in the closing gap between two objects, such as equipment and a wall, or a load and a fixed structure. And collapse of materials or a structure, where a wall, a stack, or formwork comes down on someone.

The severity is the thing to respect. Caught-in/between is a smaller slice of the fatality count than struck-by, but the outcomes are worse per event, because a body caught in a machine or under a collapse absorbs the full force with nowhere to go. There is rarely a near-miss version. The control has to be in place before the task, because once a person is in the gap there is no reaction time left.

Machine guarding and lockout before you clear a jam

The caught-in hazard on machines is the moving part that can grab and pull: a rebar bender or shear, a masonry or table saw, a concrete mixer's drum and blades, a pump's hopper and agitator. The first control is the guard. OSHA's general tool and machine guarding requirements, in 1926.300 and the related rules, call for guards on rotating parts, points of operation, and pinch points where a person can reach the moving part. A removed or defeated guard is the setup for most machine caught-in injuries.

The second control is the one people skip, and it is the one that kills: lock out the energy before any part of your body goes into the machine. The classic case is clearing a jam. The mixer clogs, the bender binds, the pump hopper packs off, and someone reaches in with the machine still energized because shutting it down and locking it out feels like too much for a twenty-second fix. That is the exact scenario the lockout rules were written to prevent. The machine has to be at a zero-energy state, locked and verified, before a hand crosses the plane of the danger zone, no matter how quick the task looks.

Reaching into a running machine to clear a jam is the line where this hazard turns fatal. Shut it off, lock it out, verify it is dead, then clear it. The lockout details and the limited exceptions are governed by OSHA's hazardous-energy rules and the manufacturer's procedure; confirm them and the AHJ's requirements before you rely on any shortcut.

Caught-between: never get into the pinch

The caught-between hazard is the closing gap, and the single rule that prevents it is to never put your body between a moving object and a fixed one. The fixed object does not move. The moving object does. When the gap closes, whatever is in it is crushed, and a person cannot out-react hydraulics or momentum.

The patterns repeat. A worker between a backing truck and a wall, where the spotter himself is often the one killed. A worker between mobile equipment and a structure, a stockpile, or another machine. The swing of an excavator's counterweight, which rotates into a fixed space behind the cab and pins anyone standing there against a wall or a trench box. A worker between a load and the structure it is being set against, with hands or body in the closing gap as the load lands.

Plan the work so nobody has to stand in the pinch. Keep the swing radius of rotating equipment barricaded so a person cannot walk into the counterweight's path. When a load is being landed, guide it with a tag line from outside the gap, not with hands inside it. Distance from the closing gap is the control. There is no PPE for being crushed.

Concrete pump struck-by and caught hazards

A concrete pump concentrates several of these hazards in one piece of equipment, so it is worth calling out on its own. The pump boom is a long suspended arm carrying a load, which is swinging-object and falling-object struck-by any time the crew is under it or in its arc. Keep people out from under the boom and clear of the swing.

The sharpest pump-specific hazard is hose whip. When the line blocks and pressure builds behind the blockage, then the blockage suddenly clears or blows out, the end hose can whip with enough force to break bones or throw a worker off a deck. The end hose is never clamped to a reducer, and the zone around the end of the hose is kept clear of anyone who is not placing. A blockage is cleared by relieving pressure the right way, not by standing next to a charged line and hoping.

The pump also has a hopper with a moving agitator and a grate, which is a caught-in point if a hand goes in to clear it without shutting the pump down. Lock it out before reaching into the hopper. The full discipline of choosing the pump, the pumpable mix, priming, and clearing blockages safely is covered in the concrete pumping and placement guide; the point here is that the pump is a struck-by and caught-in machine the whole time it runs.

Protruding rebar and impalement

Exposed rebar that sticks up out of a mat, a footing, or a wall dowel is an impalement hazard, a specific and lethal form of struck-by. A worker who trips, slips, or falls onto unprotected vertical bar can be impaled, and the height does not have to be large to be fatal. Concrete work is full of standing bar waiting for the next lift, the next wall, or the next pour, and that bar is exposed for days.

The control is to protect the exposed ends so they cannot impale. OSHA's concrete and masonry rules require that protruding reinforcing steel onto and into which employees could fall be guarded to eliminate the impalement hazard. In practice that means rebar caps rated for impalement protection, not the small plastic mushroom caps meant only to protect against scrapes, or wood troughs laid over a run of horizontal bar where people cross. The rated caps are designed to keep the bar from punching through on a real fall.

The tell is a field full of bare bar with a box of cheap caps that nobody installed, or the wrong caps installed for show. Confirm the impalement-protection requirement and the rated cap specification with OSHA, the cap manufacturer, and the AHJ. Cheap caps that do not stop the bar are worse than none, because they look like the hazard was handled.

Material, wall, and formwork collapse

Collapse is caught-in by a structure or a stack instead of a machine, and on concrete work the high-energy version is formwork and shoring that lets go during a pour. Wet concrete is heavy and it pushes outward and downward with real force, so forms and shores have to be designed and braced for the load before the truck shows up. A blowout buries the crew below in concrete and steel.

Tilt-up panels add their own collapse hazard during lifting and bracing. A panel that is not braced to its design, or braced to a slab that has not reached strength, can come down on the crew. The bracing design, the concrete strength before lifting, and the sequence are engineered decisions, not field judgment calls.

Material stacks and walls collapse too: a poorly stacked pile of block or bagged material, a freestanding masonry wall before it is tied off, a stockpile undercut by equipment. Keep stacks stable and within safe height, keep people from working below an unsupported wall, and let the engineer control formwork, shoring, and tilt-up bracing. Confirm the requirements with OSHA's concrete and masonry rules and the AHJ.

High-visibility clothing and lighting

Being seen is a struck-by control, because the worker the operator cannot see is the worker who gets hit. High-visibility clothing of the right class for the setting makes a person on foot stand out against equipment and against the background, and it is the cheapest control on this list. It does not replace the spotter or the traffic plan; it makes both of them work better.

Lighting is the other half. Night work, enclosed pours, parking-structure decks, and dawn and dusk shifts all cut the operator's ability to see people and the worker's ability to see a moving hazard. Light the work and the equipment routes to a level where a person on foot is visible, and treat low light as a reason to add a spotter, not to lean harder on the alarm. Confirm the high-visibility class and the lighting levels against OSHA and the project requirements.

Separation: put distance between people and the energy

If there is one principle under all of this, it is separation: keep people away from the energy, and where you cannot, put something solid between them. Distance is the most reliable control there is, because it does not depend on a person reacting in time, a guard staying in place, or an alarm being heard over the noise. A worker who is not in the path, not under the load, not in the pinch, and not reaching into the machine cannot be struck or caught by it.

This is the same logic as the hierarchy of controls. Eliminating the exposure beats guarding it, and guarding it beats warning about it, and warning beats relying on PPE. A barricade that keeps people out of the swing radius is better than a sign. A traffic plan that routes equipment away from people is better than a backup alarm. PPE, the hard hat and the safety glasses, is the last layer and the weakest, because it only limits the injury after contact instead of preventing the contact.

When you plan a task, ask first whether anyone has to be in the hazard zone at all. Most of the time the answer is that the task was arranged out of habit, and the person could stand somewhere safe with no loss of work. Move the person out of the zone and you have solved the problem at the level where it stays solved.

How do you plan struck-by and caught-in hazards out of a task?

You run a job hazard analysis before the task and you find the struck-by and caught-in exposures while there is still time to design them out. The JHA, also called a job safety analysis, breaks the task into steps and asks at each step where the moving energy is and who could end up in its path or in a pinch. Done honestly, it turns a vague worry into a specific list of where to put a barricade, a spotter, a guard, or a lockout.

Walk the task the way it will actually run. Where do the trucks back and who is on foot near them. What is overhead and who works under it. Which machines have a part a hand can reach and what is the lockout step before clearing a jam. Where does equipment swing or pin against a fixed object. The JHA is also where the crew gets trained on the Focus Four for this specific job, not in the abstract, so the people doing the work know the patterns to watch for on this site today.

The JHA that lives in a binder and never changes is theater. The one that gets walked, marked up when the site changes, and used to brief the crew is the one that keeps a person out of the line of fire. Tie the standard back to OSHA's requirements and the AHJ, and keep the analysis specific to the conditions in front of you.

Field checklist

What to document

The record is what proves the control existed before the incident, not after. For struck-by and caught-in work that means the JHA, the daily briefing, the spotter assignment, the lockout, the tool and guard inspections, and the rebar-cap and barricade checks. Capture the hazard, the control you put on it, and a note that ties it to the day and the conditions, so a reviewer can see the decision and the person who made it.

Keep it in a system the crew actually uses in the field instead of a binder in the trailer. A field tool like FieldOS lets the foreman log the JHA, the toolbox talk, the spotter and lockout assignments, and the daily inspections with the date, the crew, and a photo, so the record matches what was on the ground. The point is not paperwork for its own sake. It is that the next person, the inspector, or the investigation can reconstruct what control was on the hazard and when.

Common mistakes

• No spotter on backing equipment, or a worker standing in the blind spot.
• Working or walking under a suspended load, trusting the rigging and the hard hat.
• Running a saw or grinder with the guard removed, and no eye or face protection on bystanders.
• Reaching into a mixer, bender, or pump hopper to clear a jam without locking out the energy.
• Standing between equipment and a fixed object, in the path of a swinging counterweight or a backing truck.
• Bump-firing a nail gun near other people, or running a powder-actuated tool without certification.
• Leaving protruding rebar uncapped, or using scrape caps that do not stop impalement.
• Treating the backup alarm as the whole control instead of the traffic plan and the spotter.

Standards and references

OSHA's construction standards, 29 CFR 1926, are the framework. Struck-by and caught-in/between are two of OSHA's Focus Four, and OSHA publishes Focus Four outreach training on exactly these topics. The caught-in/between rules are spread across several subparts: excavations and trench collapse under Subpart P, tools and machine guarding under Subpart I including the general guarding requirements in 1926.300, and concrete and masonry under Subpart Q. Motor vehicles and mechanized equipment, including the backup-alarm-or-spotter requirement for an obstructed rear view, fall under Subpart O.

Specific points have their own rules. Head protection and eye and face protection are covered by OSHA's PPE requirements for construction. Protruding reinforcing steel and impalement protection are addressed in the concrete and masonry rules in Subpart Q. The control of hazardous energy, the lockout that has to happen before a hand goes into a machine, is governed by OSHA's lockout requirements and the manufacturer's procedure. Nail-gun and powder-actuated-tool safety draws on OSHA and NIOSH guidance plus the tool manufacturer's instructions.

Code citations and edition specifics change, and jurisdictions adopt and amend. Cite the standard that governs the point, confirm the exact section against the edition OSHA and the AHJ have in force, and let the project safety plan and the manufacturer's instructions control where they are stricter. The three controls to hold onto are the durable ones: separate people from the energy, spot the equipment and keep people out from under loads, and guard the machines and lock them out before anyone reaches in.

Units and terms

Struck-by and caught-in work carries a vocabulary that shows up across OSHA documents, the JHA, and the daily briefing, and the same idea goes by more than one name.

Knowing the terms keeps the briefing precise, because a control that is named wrong on the JHA is a control that nobody checks.

Focus Four / Fatal Four

OSHA's four leading construction killers: falls, struck-by, caught-in/between, and electrocution

Struck-by

Worker hit by a flying, falling, swinging, or rolling object or vehicle

Caught-in/between

Worker crushed, pinned, or pulled into machinery, a collapse, or between objects

Blind spot / blind zone

The area around equipment the operator cannot see, largest directly behind a backing machine

Spotter

A trained worker who guides an operator and keeps people out of the equipment's path

LOTO (lockout/tagout)

Isolating and locking a machine to a zero-energy state before anyone enters the danger zone

Swing radius

The arc a boom or counterweight sweeps through as equipment rotates, kept barricaded

Hose whip

A concrete pump end hose lashing out when a blockage clears under pressure

Impalement protection

Rated caps or troughs on protruding rebar that stop the bar from penetrating on a fall

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