Construction Hazards and the Focus Four
Construction is among the most dangerous industries, and most deaths trace back to four hazard categories known as the Focus Four: falls, struck-by, caught-in/between, and electrocution. This chapter explains how to recognize these hazards, along with excavation and confined-space dangers, and how the hierarchy of controls guides the safest response. Recognizing hazards early and controlling them at the source saves lives.
The Focus Four
Construction consistently accounts for about one in five worker deaths in the United States, and Bureau of Labor Statistics data show that most of those deaths fall into four categories OSHA calls the Focus Four: falls, struck-by, caught-in/between, and electrocutions. Falls are by far the largest, causing roughly a third to 40 percent of construction fatalities each year, including falls from roofs, leading edges, scaffolds, ladders, and through floor or skylight openings. Struck-by hazards are the next leading cause and involve a worker being hit by a moving object such as a vehicle, a falling tool or load, a swinging crane load, or a flying particle. Caught-in/between hazards involve a worker being squeezed, caught, crushed, pinched, or compressed between two objects, or trapped in a collapsing structure; a trench cave-in is the deadliest example, along with unguarded machinery and being pinned between equipment and a wall. Electrocutions round out the four, resulting from contact with overhead or buried power lines, energized equipment, damaged tools and cords, or improper use of flexible cords. Together these four causes account for well over half of all construction deaths, which is why the OSHA outreach curriculum devotes so much time to them and why they anchor this course. The corresponding standards live in 29 CFR Part 1926 by subpart: fall protection in Subpart M (1926.500-503), electrical in Subpart K (1926.400-449), excavation and cave-in protection in Subpart P (1926.650-652), and scaffolds, cranes, and motor vehicles in Subparts L, CC, and O. Recognizing which Focus Four category a task's hazards fall into is the first step in choosing the right controls. A worker cutting on a roof faces both fall and struck-by risk; a worker in a trench near a road faces caught-in and struck-by risk. Naming the hazard is not academic; it points directly to the standard and the control that will keep the worker alive.
Hierarchy of Controls
Once a hazard is recognized, the hierarchy of controls tells you how to respond in the most effective way. Developed by NIOSH and reflected throughout OSHA's approach, the hierarchy ranks control methods from most to least effective: elimination, substitution, engineering controls, administrative controls, and personal protective equipment. The ranking exists because the higher methods remove or reduce the hazard itself, while the lower methods depend on human behavior that can fail. Elimination, physically removing the hazard, is the most effective; for example, prefabricating components on the ground so no one works at height, or scheduling a task before a system is energized. Substitution replaces the hazard with something less dangerous, such as a less toxic solvent or a quieter tool. Engineering controls isolate people from the hazard through physical changes to the work: a trench shield that stops soil from reaching a worker, machine guarding, local exhaust ventilation that captures silica dust, or a guardrail at a leading edge. Administrative controls change the way people work through safe-work procedures, warning signs, training, job rotation to limit exposure time, and permits. Personal protective equipment (PPE), such as hard hats, safety glasses, respirators, harnesses, and gloves, sits at the bottom because it does nothing to reduce the hazard itself; it only creates a barrier at the worker's body, and it fails the moment it is worn wrong, damaged, or removed. This ranking is exactly why OSHA and this course repeatedly stress that PPE is the last line of defense, not the first answer. In practice, controls are often combined: a worker cutting concrete might use a wet saw (engineering control) plus a rotated schedule (administrative) plus a fit-tested respirator (PPE). But a plan that jumps straight to PPE while ignoring feasible engineering controls is both less safe and, for hazards like silica and noise, a violation of the standard, which requires feasible engineering and work-practice controls first.
Struck-By and Caught-In/Between
Struck-by and caught-in/between are two of the Focus Four, and although they sound similar, OSHA distinguishes them by the direction of the force. In a struck-by injury the impact comes from a moving object hitting the worker; in a caught-in/between injury the worker is caught, crushed, or pinned. OSHA groups struck-by hazards into four types: struck by flying objects (a nail from a nail gun, a particle from a grinder), falling objects (tools or materials dropped from above), swinging objects (a crane load or backhoe bucket), and rolling objects (vehicles and mobile equipment). Vehicle and mobile-equipment incidents are the single most common struck-by killer, so 29 CFR 1926.601 and 1926.602 require backup alarms or a signal person for equipment with an obstructed rear view, and workers on foot must wear high-visibility apparel and stay out of blind spots and the swing radius of rotating equipment such as excavators and cranes. Falling-object protection includes toeboards, screens, guardrails, hard hats (29 CFR 1926.100), and barricading the area below overhead work. Caught-in/between hazards include trench and excavation cave-ins (the deadliest, covered under Subpart P), being caught in unguarded rotating machinery or between a swinging load and a fixed object, and being pulled into equipment by loose clothing. The key controls are keeping workers clear of the swing radius and pinch points, guarding machinery, and following lockout/tagout so equipment cannot move or energize while someone is exposed. A concrete example: an excavator rotating to dump spoil creates a crush zone between its counterweight and a nearby wall or truck, and a worker standing there can be killed instantly, which is why that area must be barricaded. Suspended loads are another; never work or walk under a load, and inspect rigging before every lift. Because these hazards involve moving energy and heavy objects, the winning strategy is separation: putting distance, barriers, and guarding between the worker and the moving thing.
Excavation and Trenching
Trenching and excavation produce some of the most sudden and lethal caught-in incidents in construction, and they are governed by 29 CFR Part 1926 Subpart P (1926.650-652). A cubic yard of soil weighs roughly 3,000 pounds, about the weight of a small car, so a worker buried in a cave-in can be crushed or suffocated in seconds, often before rescue is possible. Subpart P requires a protective system for any excavation 5 feet or more deep unless it is made entirely of stable rock; shallower excavations may still need protection if a competent person finds signs of potential collapse. There are three basic protective systems: sloping or benching the walls back to a safe angle based on soil type, shoring that supports the walls with hydraulic or timber members, and shielding with a trench box that protects workers even if the wall fails. Soil is classified as stable rock, Type A, Type B, or Type C, with Type C the least stable and requiring the flattest slope; the allowable slopes appear in Subpart P Appendix B. A competent person, defined in 29 CFR 1926.32(f) as someone able to identify hazards and authorized to correct them, must inspect the excavation daily before entry, after rain, and after any condition that increases the hazard, per 29 CFR 1926.651(k). Several specific rules protect workers: spoil piles and equipment must be kept at least 2 feet back from the edge (1926.651(j)(2)); in trenches 4 feet or deeper, a ladder, ramp, or stairway for egress must be within 25 feet of lateral travel of every worker (1926.651(c)(2)); and atmospheres must be tested where a hazardous atmosphere could exist, such as deep trenches near landfills or sewers (1926.651(g)). Underground utilities must be located before digging, and workers must be protected from water accumulation and from surface traffic. The single lesson is simple: never enter an unprotected trench, no matter how quick the job seems.
Confined Spaces and Hazard Recognition
A confined space is large enough to enter and work in, has limited means of entry or exit, and is not designed for continuous occupancy; think tanks, vaults, manholes, sewers, pits, and silos. When such a space also contains or could contain a serious hazard, it becomes a permit-required confined space. Construction work in these spaces is governed by 29 CFR Part 1926 Subpart AA (1926.1200-1213), which took effect in 2015 and closely mirrors the general-industry rule. A permit-required space is one with a hazardous atmosphere, a potential for engulfment (such as loose soil or grain), an internal configuration that could trap or asphyxiate, or any other recognized serious hazard. Atmospheric hazards are the biggest killer, and they often kill would-be rescuers too. Before entry, the air must be tested from outside in this order: oxygen content first (a safe range is 19.5 to 23.5 percent), then flammable gases and vapors, then toxic contaminants, with continuous monitoring during the work. Entry into a permit space requires a written entry permit, continuous ventilation where needed, an attendant stationed outside who maintains contact and never enters to attempt a rescue alone, and trained entrants plus a rescue plan. The broader skill this chapter builds is hazard recognition. A Job Hazard Analysis (JHA), sometimes called a Job Safety Analysis, breaks a task into steps, identifies the hazard at each step, and specifies the control before work begins, a practice supported by the general training duty in 29 CFR 1926.21(b)(2). Workers should walk the site with fresh eyes, ask what could go wrong, and check that controls are in place before starting. When a worker finds a hazard they cannot fix themselves, the correct action is to stop and report it immediately to a supervisor or competent person. Recognizing hazards early, whether in a trench, a confined space, or an ordinary work area, is the thread that ties every Focus Four topic together and is the whole point of OSHA outreach training.
Last updated: September 2026
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