Domain 1 · Safety Principles · 7 min read
Hazard Classification and Prevention Through Design
What a Hazard Is and How Hazards Are Classified
A hazard is any source, situation, or act with the potential to cause harm in terms of human injury, illness, damage to property, damage to the environment, or a combination of these. Risk is the combination of the likelihood of that harm and the severity of its consequences. A hazard exists whether or not anyone is exposed; risk exists only when exposure is possible.
Hazards are grouped by their nature and the type of harm they cause. The six primary classes are physical, chemical, biological, ergonomic, psychosocial, and safety hazards. Each class calls for its own recognition methods, measurement tools, and controls. Health-oriented classes (chemical, physical agents, biological, ergonomic) are developed in the Occupational Health and Applied Science domain; Domain 1 concentrates on safety hazards and on designing them out.
| Class | Nature of harm | Typical examples | Typical evaluation tools |
|---|---|---|---|
| Physical | Energy transferred to the body without direct contact with a substance | Noise, vibration, ionizing and non-ionizing radiation, heat and cold, pressure changes | Sound level meter, dosimeter, WBGT, radiation survey meter |
| Chemical | Toxic, corrosive, or reactive action of solids, liquids, gases, mists, vapors, fumes | Solvents, acids, metal fumes, silica, flammable liquids | SDS review, air sampling, GHS classification |
| Biological | Infection, allergy, or toxicity from living organisms or their products | Bloodborne pathogens, TB, Legionella, mold, zoonoses | Exposure determination, surveillance, water and surface sampling |
| Ergonomic | Mismatch between worker and task, tool, or workstation | Repetition, force, awkward or static posture, contact stress | NIOSH Lifting Equation, RULA, Strain Index |
| Psychosocial | Psychological or physical harm from work organization and relationships | Workload, lack of control, shift work, violence, bullying | Surveys, workload and staffing analysis |
| Safety | Acute traumatic injury or death from an uncontrolled release of energy | Machinery, electricity, falls, struck-by, caught-in/between | JHA, inspections, PHA, design review |
Safety Hazards: Acute Energy Release
Safety hazards are conditions or practices that increase the likelihood of incidents causing injury or death. They are best understood as uncontrolled energy: kinetic, potential (gravitational), electrical, mechanical, pressure, thermal, or chemical. Controls aim to eliminate the energy source, reduce the quantity of energy, prevent its release, or separate people from it in time and space.
Prevention Through Design
Prevention through Design (PtD) addresses occupational hazards and risks at the earliest possible point: in the design and redesign of facilities, work premises, tools, equipment, machinery, substances, and work processes. The consensus standard ANSI/ASSP Z590.3 sets out PtD concepts so that hazards are anticipated and risks reduced to an acceptable level before exposure occurs, rather than retrofitted after an incident.
PtD applies across the entire life cycle: concept and preliminary design, detailed design, procurement, construction or installation, commissioning, operation and maintenance, modification, and decommissioning and disposal. The ability to influence safety is greatest and cheapest at concept and design; once equipment is built, every change is more expensive and usually less effective.
| Level | Design intent | Design example |
|---|---|---|
| 1. Risk avoidance | Prevent the hazard from entering the workplace at all | Select a process that never uses a toxic intermediate; site the facility outside a flood plain |
| 2. Elimination | Remove an existing hazard through design or redesign | Lower a valve to grade so no elevated work is needed; design parapets at least 42 in high on roofs |
| 3. Substitution | Replace with a less hazardous material, process, or equipment | Water-based coating for solvent-based; lower-voltage control circuits; smaller inventory |
| 4. Engineering controls | Isolate people from the hazard or reduce it at the source | Fixed guards, interlocks, local exhaust ventilation, permanent anchorages, enclosures |
| 5. Warnings | Alert people to remaining hazards | Signs, labels, alarms, beacons, floor markings |
| 6. Administrative controls | Change how people work | Procedures, permits, training, scheduling, job rotation, inspections |
| 7. PPE | Protect the individual when other controls are insufficient | Respirators, arc-rated clothing, personal fall arrest systems |
Z590.3 places risk avoidance above elimination: the best hazard is the one that is never designed in. Warnings are separated from administrative controls because they are a distinct, weaker layer that depends on perception and compliance. Controls higher in the hierarchy are more reliable because they do not depend on human behavior; PPE is the last line of defense, not the first.
Design Criteria and the PtD Process
Effective PtD converts hazard knowledge into design criteria: measurable requirements written into specifications, such as clearances, guarding requirements, anchorage loads, isolation points, ventilation rates, and maximum inventories. Criteria come from regulations (the minimum), consensus standards, company standards, lessons learned from incidents, and risk assessments performed during design reviews.
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