Struck-By and Caught-In Hazards: Construction Fatal Four Explained and How to Prevent Them

Construction kills about 1,000 workers every year in the United States. OSHA data consistently shows that four hazard categories account for roughly 60% of those deaths. OSHA calls them the Fatal Four: falls, struck-by objects, electrocution, and caught-in/between hazards. Falls are the top killer. Struck-by is second. And the combination of struck-by and caught-in incidents makes up a substantial share of the remaining deaths.

Understanding how these incidents happen, and what the regulations actually require, is the starting point for preventing them.

What the Fatal Four Actually Are

OSHA began tracking and publicizing the Fatal Four as a focused enforcement and outreach strategy in the early 2000s. The goal was to give employers a concrete target: if you eliminate the Fatal Four from your site, you cut your fatality risk by more than half.

Falls remain the single biggest category, but struck-by hazards account for roughly 8-9% of construction fatalities annually based on BLS data. Caught-in/between adds another 1-2%. Combined, they represent dozens of preventable deaths every year.

The four categories aren’t equally preventable with the same tools. Falls require fall protection systems and planning. Struck-by hazards require physical barriers, PPE, and work zone controls. Electrocution requires lockout/tagout and grounding protocols. Caught-in/between requires machine guarding, trench protection, and equipment exclusion zones. Treating them as one undifferentiated problem doesn’t work.

Struck-By Hazards: The Four Categories

OSHA breaks struck-by hazards into four types. Each has different causes and different controls.

Flying Objects

Flying object struck-by incidents happen when a tool, fastener, or fragment becomes a projectile. Nail guns are a major source. A nail driven through thin material, a misfire, or a ricochet can travel at lethal speed. Angle grinders throw sparks and fragments. Power-actuated fastening tools can send a pin through drywall and into the next space.

The controls for flying objects center on eye and face protection, keeping bystanders out of the line of work, and using guards on tools that generate projectiles. OSHA 1926.102 covers eye and face protection requirements for construction. The PPE guide covers selection and fit for eye protection.

Falling Objects

Falling object incidents happen when materials, tools, or debris drop from overhead. A dropped hammer from 20 feet doesn’t need to be traveling fast to kill someone. Toeboards, debris nets, catch platforms, and hard hat requirements all address this category.

OSHA 1926.502(j) requires protection from falling objects whenever workers are below elevated work. That includes using toeboards on scaffold platforms, solid barriers at open edges, and catch nets where overhead work is ongoing. Workers below should never be in a position where falling tools are a routine hazard they’re expected to accept.

Crane and rigging operations get specific attention because suspended loads can swing, slip, or drop. Workers should never stand under a suspended load. That’s not a guideline. It’s a prohibition under 1926.550 and the general crane standards.

Swinging and Sliding Objects

Swinging loads from cranes and hoists can hit workers who are too close to the load path. Truck doors can swing open and hit workers. Concrete forms can shift during placement. Pipes being set can swing before they’re secured.

Controls here are physical: barricading the swing radius of equipment, setting up exclusion zones during crane picks, and positioning workers clear of the load path before lifts begin. Communication between riggers and operators matters a lot in this category.

Vehicles and Mobile Equipment

Vehicle-related struck-by incidents are the deadliest category within struck-by hazards. CPWR data on construction fatalities shows that most of these deaths involve workers on foot being struck by trucks, cranes, or heavy equipment during backing and turning. The leading factors are workers entering blind spots, no spotter assigned during backing, and no separation between pedestrian paths and equipment travel areas.

Backup alarms are required under 1926.602(a)(9)(ii) for earthmoving and material handling equipment. But backup alarms alone aren’t enough. A worker wearing hearing protection near a loud saw may not hear the alarm. The real fix is physical separation: exclusion zones that keep workers on foot away from equipment travel paths at all times.

Your construction safety plan should define pedestrian exclusion zones, spotter requirements, and high-visibility vest rules by work zone type. High-visibility vests meeting ANSI/ISEA 107 Class 2 or Class 3 are required wherever workers are exposed to vehicle or equipment traffic.

Forklifts get their own set of requirements because of how frequently they’re involved in struck-by incidents. The forklift safety guide covers operator certification, speed limits, pedestrian traffic zones, and the OSHA 1910.178 requirements specific to powered industrial trucks.

Caught-In/Between Hazards

Caught-in/between is a broader category than it sounds. OSHA defines it as any incident where a worker is caught, compressed, crushed, or pinched by equipment, objects, or materials. It splits into a few main scenarios.

Rotating Machinery

Getting caught in rotating machinery is the classic caught-in scenario. Augers, conveyors, mixing drums, power take-off shafts on compactors, unguarded pulleys and belts on equipment. Loose clothing, hair, or a glove gets pulled in. The machine doesn’t stop.

OSHA’s machine guarding standards under 1910.212 (general industry) and 1926.300 (construction) require guards on all rotating parts that workers can contact. There’s no exception for “we’ve always done it this way” or “the guard slows us down.” If a rotating part can contact a body part and cause injury, it needs a guard.

Lockout/tagout, covered under 1910.147, applies when workers perform maintenance or service on machines with stored energy. Caught-in incidents during maintenance happen when energy sources aren’t properly de-energized and locked out before work starts.

Excavations and Trenches

Trench collapses are caught-between incidents in the most fatal sense. An unsupported trench wall can collapse and bury a worker in seconds. A worker trapped in a trench collapse typically can’t be reached in time to survive.

OSHA’s excavation standards under 1926.652 require protective systems for trenches and excavations over 5 feet deep in most soil conditions. The options are sloping, benching, shoring, or trench boxes. The choice depends on soil type, depth, and surrounding conditions. For more on trench-specific requirements, the excavation and trenching guide covers the soil classification system and protective system requirements in detail.

Equipment Pinch Points

Pinch points around equipment are common on construction sites and in manufacturing. The gap between the rear of a backing concrete truck and a fixed wall. The space between a scissor lift platform and an overhead beam. The area alongside an excavator as it swings. A worker gets into a space that closes while equipment moves.

These incidents are largely preventable with exclusion zones, designated work areas with physical barriers, and pre-task planning that identifies where pinch points will exist during specific operations. The risk changes moment to moment on a busy site, which is why pre-task briefings matter.

What Your Safety Plan Must Address

A written construction safety plan isn’t optional on sites covered by OSHA 29 CFR 1926. For struck-by and caught-in hazards specifically, the plan should cover:

Hard hat requirements by zone. Not just “hard hats required on site” but which ANSI/ISEA Z89.1 class is required where. Class E for areas with electrical exposure, Type II where overhead impact from multiple directions is possible.

High-visibility vest requirements. Class 2 for most pedestrian-vehicle exposure situations, Class 3 for higher-speed or lower-visibility environments. Who makes the call on which class applies.

Equipment travel paths and pedestrian exclusion zones. Specific designated paths for heavy equipment that workers on foot don’t cross without authorization. Physical barriers where possible, cones or flags where physical barriers aren’t feasible.

Spotter and flagging requirements. When spotters are required during backing operations. Who fills that role. What authority the spotter has to stop equipment movement.

Machine guarding inspection procedures. Who checks that guards are in place before equipment is used. What happens when a guard is missing.

Overhead work controls. When toeboards, netting, or catch platforms are required. How materials are stored and secured on elevated surfaces.

The fall protection guide addresses the overlap between fall hazards and the overhead work controls that also protect workers below from falling objects.

Controls That Actually Work

The hierarchy of controls applies here the same way it does everywhere. Elimination is best. If the work design can remove a struck-by or caught-in hazard entirely, that’s the right answer. Crane lifts over occupied areas can sometimes be rescheduled for non-working hours. Equipment travel through pedestrian areas can be rerouted.

When elimination isn’t practical, engineering controls come next. Physical barriers, machine guards, trench protection systems. These work whether or not workers remember to follow a procedure.

Administrative controls, like spotter requirements and exclusion zone policies, rely on humans following them correctly every time. They’re less reliable than physical controls. They’re still required, but they’re not a substitute for engineering.

PPE is the last layer. Hard hats and high-visibility vests are required and they matter. But a hard hat doesn’t stop a construction vehicle, and a high-visibility vest doesn’t prevent a trench collapse. Plan for the controls above the PPE layer first.

The data shows that most struck-by and caught-in incidents aren’t freak accidents. They’re predictable patterns, backing operations without spotters, workers in swing radii of equipment, unguarded machinery during maintenance. The patterns repeat because the controls weren’t in place. That’s the piece that’s fixable.