Struck-by hazards cause a wide range of injuries, from surface bruising to fatal internal damage, depending on the size, speed, and weight of the object that hits you. In 2024, 757 workers in the United States died from contact with objects or equipment on the job, with 357 of those deaths caused specifically by propelled, falling, or suspended objects. Understanding what these impacts actually do inside your body helps explain why even seemingly minor incidents can cause serious harm.
The Four Types of Struck-By Hazards
OSHA classifies struck-by hazards into four categories, and each one delivers force to the body in a different way.
- Flying objects are propelled through the air, either thrown, hurled, or ejected by a tool or machine. A nail from a pneumatic nail gun or a fragment breaking off a grinding wheel are common examples. These tend to concentrate force on a very small area, which allows them to penetrate skin and even bone.
- Falling objects drop from an elevation. Tools slipping off scaffolding, materials tipping from a shelf, or loads released from a crane all fall into this category. The higher the drop, the more energy the object carries when it lands.
- Swinging objects are attached at some point and move in an arc. A crane load that twists as it’s lifted, a door slamming in wind, or a beam pivoting on a hinge can all catch a worker off guard. The whipping motion generates surprising force.
- Rolling objects move along the same surface where you’re standing. Vehicles, pipes rolling off a stack, or heavy equipment sliding on a slope are typical sources. These hazards can pin or run over a person, applying prolonged crushing pressure.
What Happens at the Moment of Impact
When a moving object strikes your body, it transfers kinetic energy into your tissues. The severity of the resulting injury depends on the force, speed, duration of contact, the surface area involved, and how elastic the tissue is at the point of impact. A small, fast object like a metal fragment concentrates energy into a tiny area and can pierce through layers of tissue. A large, slow-moving object spreads force across a wider zone, crushing rather than cutting.
At the surface level, a moderate blow ruptures capillaries beneath the skin without breaking it, producing a bruise (contusion). A harder impact tears the skin open in a laceration, which looks different from a clean cut because strands of tissue bridge the wound edges. Both types of damage can also occur on internal organs if the force travels deep enough. Blunt trauma frequently causes internal or external hemorrhaging depending on the location and mechanism of the strike.
Head Injuries and Brain Damage
The skull can withstand a surprising amount of force, but it has limits. Research on head impact biomechanics estimates that a force of roughly 7,500 newtons (about 1,700 pounds of force) or greater can fracture the skull. A wrench falling 20 feet or a swinging steel beam can easily reach that threshold.
Even without a fracture, a struck-by impact to the head can cause traumatic brain injury. When your head accelerates and then suddenly stops, the brain moves inside the skull. It can slam against the front of the skull at the point of impact and then rebound against the back, a pattern called coup-contrecoup injury. This causes bruising on two sides of the brain simultaneously.
Rotational forces are particularly dangerous. Studies on head impact biomechanics show that angular acceleration of the head, the kind of twisting or rotating motion that occurs when a swinging object clips the side of your head, creates shearing forces deep inside brain tissue. These forces can stretch and tear the long fibers that connect different brain regions, a condition called diffuse axonal injury. This type of damage doesn’t always show up on a standard CT scan, but it can cause lasting cognitive problems, personality changes, and impaired coordination. Even with a helmet, angular acceleration often exceeds the thresholds associated with concussion and more severe brain injuries.
Chest and Abdominal Injuries
A blow to the torso can fracture ribs, but the more dangerous consequences happen underneath. Broken ribs can puncture the lungs, causing air to leak into the chest cavity and making it progressively harder to breathe. A direct hit to the chest wall can also bruise the lung tissue itself (pulmonary contusion), which causes swelling that reduces oxygen exchange for days.
In the abdomen, the spleen is the organ most commonly damaged by blunt force, followed by the liver and the small intestine. A falling object landing on your midsection or a rolling vehicle pinning your torso can rupture the spleen or create blood-filled pockets (hematomas) inside these organs. Splenic and liver hematomas sometimes appear stable at first, then rupture hours or even months later, causing significant delayed bleeding that requires emergency treatment.
Intestinal wall injuries follow a different pattern. Rather than bleeding heavily, a bruised intestinal wall can slowly perforate, releasing gut contents into the abdominal cavity and triggering a severe infection called peritonitis. This is one reason abdominal struck-by injuries need monitoring even when the initial pain seems manageable.
Eye Injuries From Flying Debris
Small flying particles pose an outsized risk to your eyes. When a foreign body contacts the cornea (the clear front surface of the eye), it causes direct trauma to the outer layer. Superficial injuries affect only that outer layer and typically heal within a few days, though they’re intensely painful. High-speed or sharp fragments can penetrate deeper into the structural layers of the cornea, causing lasting damage to vision.
At the extreme end, a fast-moving fragment can puncture the eye entirely. Signs of this include bleeding inside the front chamber of the eye and leaking of the fluid that maintains the eye’s shape. Full-thickness penetration carries a high risk of infection inside the eyeball, which can result in permanent vision loss even with treatment. This is why safety glasses or goggles are considered non-negotiable around grinding, cutting, or nail-driving operations.
Crush Syndrome From Prolonged Compression
Rolling and falling hazards can pin a person under heavy weight for an extended period. When large muscle groups are compressed for more than a short time, the muscle cells begin to die and release their contents into the bloodstream. This triggers a cascade of systemic problems collectively known as crush syndrome.
The most dangerous substance released is myoglobin, a protein normally contained inside muscle cells. The kidneys filter myoglobin from the blood, but beyond a certain volume it overwhelms and physically damages the kidney’s filtering structures, leading to acute kidney injury. At the same time, dying muscle cells dump potassium into the bloodstream. Elevated potassium disrupts the heart’s electrical rhythm and can cause fatal cardiac arrhythmias. The muscle breakdown also releases lactic acid and uric acid, creating a state of metabolic acidosis that compounds kidney damage.
What makes crush syndrome particularly treacherous is that a trapped person may initially feel and appear relatively stable. The most dangerous moment often comes after the weight is removed, when the accumulated toxins from the crushed tissue flood into general circulation all at once. Severe cases require dialysis because the kidney damage doesn’t respond to fluids alone.
Long-Term Health Effects After Recovery
Surviving a serious struck-by injury is only the beginning. Research framing traumatic injury as a chronic condition has found that survivors face substantially elevated rates of post-traumatic stress disorder, chronic pain, and lasting functional limitations. Many experience poor quality of life and social functioning years after the initial event, along with delayed return to work.
Head injuries carry some of the longest tails. Post-concussion symptoms, including headaches, difficulty concentrating, irritability, and sleep disruption, can persist for months or years. Musculoskeletal injuries often lead to chronic pain cycles, especially when fractures heal improperly or nerve damage occurs at the impact site. Abdominal injuries that required surgical repair can cause adhesions (internal scar tissue) that produce intermittent pain and bowel issues long after the wound has closed.
Survivors of crush injuries face ongoing monitoring for kidney function, since the initial damage may leave the kidneys permanently less resilient. There’s also an increased risk of developing other medical conditions in the years following a major traumatic injury, likely driven by a combination of reduced physical activity during recovery, chronic pain, and the physiological stress the body endured.