# Principles of Occupational Health: Hazard Recognition and Risk Assessment

## Overview

Occupational health focuses on the prevention of work-related disease, injury, and disability. Approximately 5,000 workers die annually from occupational injuries in the United States, with tens of thousands more dying from occupational diseases. The hierarchy of controls is the foundational framework for workplace hazard mitigation. Preventive medicine physicians in occupational settings perform hazard recognition, risk assessment, medical surveillance, and fitness-for-duty evaluations. OSHA (the Occupational Safety and Health Administration) serves as the primary federal regulatory agency, while NIOSH (the National Institute for Occupational Safety and Health) conducts research and develops recommendations.

## Categories of Workplace Hazards

### Chemical Hazards

Chemical hazards encompass dusts, fumes, vapors, gases, liquids, and mists encountered in the workplace. The most common route of exposure is inhalation, followed by dermal absorption and ingestion. Classic examples include silica dust causing silicosis, asbestos causing mesothelioma and asbestosis, benzene causing leukemia, lead causing neurotoxicity, and formaldehyde causing nasopharyngeal cancer. Safety Data Sheets (SDS) are standardized documents that provide hazard, exposure, and handling information for every chemical present in the workplace.

### Physical Hazards

Noise-induced hearing loss is the most common occupational disease, making noise the most prevalent physical hazard. Vibration hazards include hand-arm vibration syndrome and whole-body vibration effects. Radiation exposure affects healthcare workers and those in the nuclear industry (ionizing) as well as workers exposed to ultraviolet light, lasers, and radiofrequency energy (non-ionizing). Extreme temperatures cause heat stress (progressing from heat exhaustion to heat stroke) and cold stress (hypothermia and frostbite). Changes in atmospheric pressure affect divers and compressed air workers.

### Biological Hazards

Biological hazards include bloodborne pathogens (HBV, HCV, HIV), tuberculosis, and respiratory viruses. Healthcare workers, laboratory workers, agricultural workers, and veterinarians face the highest risk. The OSHA Bloodborne Pathogens Standard requires exposure control plans, engineering controls such as sharps disposal containers, personal protective equipment, hepatitis B vaccination for at-risk workers, and post-exposure management protocols. Emerging biohazards from novel pathogens and potential bioterrorism agents represent ongoing concerns.

### Ergonomic Hazards

Repetitive motion injuries such as carpal tunnel syndrome and tendinitis are common ergonomic hazards. Manual lifting and handling is the leading cause of low back pain, which itself is the leading cause of lost workdays. Prolonged static postures — both sedentary desk work and prolonged standing — contribute to musculoskeletal disorders. Vibration-associated musculoskeletal disorders affect workers using power tools. Ergonomic assessment involves job analysis, workstation design evaluation, and task modification recommendations.

### Psychosocial Hazards

Work-related stress, burnout, workplace violence, shift work, and excessive hours constitute psychosocial hazards. These are associated with cardiovascular disease, depression, anxiety, and substance use. The job demand-control model (Karasek) identifies high demands combined with low control as the highest-risk combination. The effort-reward imbalance model (Siegrist) predicts adverse health outcomes when a discrepancy exists between effort expended and reward received. Recognition of psychosocial hazards as legitimate occupational health priorities is growing.

## Hazard Recognition Methods

### Workplace Walk-Through

The workplace walk-through is a systematic physical inspection of the work environment. Observers note work processes, chemical use, equipment condition, ventilation adequacy, and housekeeping practices. Speaking directly with workers about their tasks, concerns, and symptoms provides critical information that inspection alone may miss. Documentation review includes injury and illness logs (the OSHA 300 log), the SDS library, and available exposure monitoring data.

### Job Hazard Analysis (JHA)

Job hazard analysis systematically evaluates each job task to identify potential hazards. The approach breaks each job into individual steps, identifies hazards at each step, and determines appropriate controls. Hazards are prioritized by severity of potential consequences and likelihood of occurrence.

### Industrial Hygiene Monitoring

Industrial hygiene monitoring provides quantitative measurement of workplace exposures. Personal air sampling in the worker's breathing zone, area sampling of the general environment, and noise dosimetry are common techniques. Results are compared to Permissible Exposure Limits (PELs) set by OSHA, Recommended Exposure Limits (RELs) developed by NIOSH, and Threshold Limit Values (TLVs) published by ACGIH. Exposure standards are expressed as time-weighted averages (TWA) over an 8-hour day, short-term exposure limits (STEL) for 15-minute periods, and ceiling values that should never be exceeded.

## Risk Assessment Framework

### Hazard Identification

The first step asks: what agents or conditions in this workplace could cause harm? Sources include the toxicology literature, NIOSH criteria documents, and epidemiologic studies of exposed worker populations.

### Dose-Response Assessment

Dose-response assessment characterizes the relationship between exposure level and health effect. Some agents demonstrate threshold effects (harm occurs only above a certain dose), while carcinogens are often assumed to follow a non-threshold model (any exposure carries some risk). Reference doses (RfD) and reference concentrations (RfC) provide quantitative benchmarks.

### Exposure Assessment

Exposure assessment determines who is exposed, by what route, at what level, and for how long. It combines quantitative monitoring data with detailed work histories. Cumulative exposure is calculated as dose multiplied by duration — for example, fiber-years for asbestos or pack-years for smoking.

### Risk Characterization

Risk characterization integrates hazard, dose-response, and exposure data to express risk quantitatively — for example, an excess lifetime cancer risk of 1 in 10,000. Uncertainty and limitations are communicated alongside risk estimates. Results inform regulatory standard-setting and guide decisions about which controls to implement.

## Hierarchy of Controls

### Elimination

Elimination removes the hazard entirely and is the most effective control. Examples include discontinuing use of a toxic chemical or fully automating a hazardous process so that workers are no longer exposed.

### Substitution

Substitution replaces a hazardous agent with a less hazardous one. Examples include substituting toluene for benzene as a solvent, or using water-based paints instead of solvent-based formulations.

### Engineering Controls

Engineering controls isolate workers from the hazard through physical changes to the workplace. Examples include local exhaust ventilation systems, machine guarding, noise enclosures, and biological safety cabinets. Engineering controls are preferred over administrative controls and PPE because they do not depend on worker behavior.

### Administrative Controls

Administrative controls change work practices, policies, or schedules to reduce exposure. Examples include job rotation, work-rest cycles during heat stress conditions, training programs, warning signage, and reducing shift length. These controls are less reliable because they depend on consistent human behavior and management enforcement.

### Personal Protective Equipment (PPE)

PPE represents the last line of defense and is the least effective level in the hierarchy. Examples include respirators, gloves, hearing protection, safety glasses, and hard hats. PPE requires proper selection, fit testing (particularly for respirators), worker training, and ongoing compliance monitoring. OSHA requires PPE use when engineering and administrative controls are insufficient to reduce exposures to acceptable levels.

## Medical Surveillance

Medical surveillance involves periodic health monitoring of workers exposed to specific hazards. Its purpose is to detect early health effects before clinical disease develops, enabling intervention at a reversible stage. OSHA mandates medical surveillance for specific exposures including lead, asbestos, benzene, noise, silica, and cadmium. Components typically include health questionnaires, physical examinations, biological monitoring (such as blood lead levels or urine cadmium), pulmonary function testing, and audiometry. Results serve both aggregate purposes (population-level trends) and individual purposes (clinical management of affected workers). Sentinel health events — specific diagnoses that signal occupational exposure, such as mesothelioma indicating asbestos exposure — trigger investigation of workplace conditions.

| Exposure Limit | Agency | Legal Status | Currency of Evidence |
|---|---|---|---|
| PEL (Permissible Exposure Limit) | OSHA | Legally enforceable | Often outdated (many from 1971) |
| REL (Recommended Exposure Limit) | NIOSH | Not legally binding (research-based) | More current, generally more protective |
| TLV (Threshold Limit Value) | ACGIH | Not legally binding (professional guidelines) | Most current, frequently updated |

| Hierarchy Level | Effectiveness | Dependence on Worker Behavior | Example |
|---|---|---|---|
| Elimination | Highest | None | Remove toxic chemical from process |
| Substitution | Very High | None | Replace benzene with toluene |
| Engineering Controls | High | Minimal | Local exhaust ventilation, machine guards |
| Administrative Controls | Moderate | High | Job rotation, work-rest schedules, training |
| PPE | Lowest | Very High | Respirators, gloves, hearing protection |

## Regulatory Framework

OSHA sets and enforces Permissible Exposure Limits, conducts workplace inspections, and issues citations and fines for violations. NIOSH is the research agency that develops Recommended Exposure Limits, conducts Health Hazard Evaluations at employer or worker request, and publishes criteria documents. ACGIH is a professional organization that publishes Threshold Limit Values, which are not legally binding but are widely referenced as the most current evidence-based guidelines. The OSHA General Duty Clause (Section 5(a)(1)) requires employers to provide a workplace free from recognized hazards likely to cause death or serious harm — this applies even when no specific exposure standard exists. Critically, many OSHA PELs are outdated, having been last comprehensively updated in 1971. NIOSH RELs and ACGIH TLVs are generally more protective and reflect current scientific evidence.

<image>A pyramid diagram illustrating the hierarchy of controls in occupational health, from most effective at the top to least effective at the bottom: Elimination, Substitution, Engineering Controls, Administrative Controls, and Personal Protective Equipment (PPE). Each level includes a brief example. The pyramid is color-coded from green (most effective) to red (least effective). Annotations emphasize that controls higher in the hierarchy are preferred. Standard NIOSH hierarchy of controls illustration for occupational health education.</image>

<image>A diagram showing the four steps of occupational risk assessment arranged in a circular workflow: Hazard Identification (what agents could cause harm?), Dose-Response Assessment (what is the exposure-effect relationship?), Exposure Assessment (who is exposed, how much, how long?), and Risk Characterization (what is the magnitude and probability of harm?). Arrows connect each step sequentially, with "Risk Management Decisions" as the output leading to the hierarchy of controls. Clean occupational health education illustration.</image>

## Clinical Pearls

The hierarchy of controls should always be applied from the top down — PPE is a last resort, not a first response to workplace hazards. Many OSHA PELs are decades out of date and do not reflect current scientific evidence; NIOSH RELs and ACGIH TLVs are typically more protective and should inform clinical decision-making about exposure safety. Noise-induced hearing loss is the most common occupational disease and is entirely preventable with proper engineering controls and hearing conservation programs. The OSHA General Duty Clause is a powerful regulatory tool for addressing hazards not covered by specific standards. Every clinical encounter should include a thorough occupational history, starting with "What do you do for work?" followed by specific questions about exposures, duration, and protective measures in place. For board preparation, know the hierarchy of controls, the difference between OSHA PELs and NIOSH RELs, and the key components of medical surveillance programs.

## References
- Levy BS, Wegman DH, Baron SL, Sokas RK, eds. Occupational and Environmental Health. 7th ed. Oxford University Press; 2017.
- NIOSH. Hierarchy of Controls. cdc.gov/niosh; 2023.
- OSHA. Permissible Exposure Limits. osha.gov; 2024.
- Rosenstock L, Cullen MR, Brodkin CA, Redlich CA, eds. Textbook of Clinical Occupational and Environmental Medicine. 2nd ed. Elsevier; 2005.
- LaDou J, Harrison RJ, eds. Current Diagnosis and Treatment: Occupational and Environmental Medicine. 6th ed. McGraw-Hill; 2021.