Industrial hygiene defines five primary categories of workplace hazards: chemical, physical, biological, ergonomic, and psychosocial. A sixth category, air contaminants, is sometimes listed separately but overlaps heavily with chemical hazards. Understanding these categories helps you recognize what you’re actually being exposed to at work and what protections should be in place.
Chemical Hazards
Chemical hazards are harmful compounds that exist as solids, liquids, gases, mists, dusts, fumes, or vapors. They enter your body through four routes: breathing them in, absorbing them through your skin or eyes, swallowing them, or injection through a skin puncture. Inhalation is the most common route in workplace settings.
The physical form of a chemical determines how it travels and how dangerous it is. Dusts are solid particles kicked up by grinding, cutting, or drilling, and they’re generally heavy enough to settle to the ground over time. Fumes are much finer: tiny solid particles that form when heated metal evaporates and then condenses back into solid form, which is why welding generates so much concern. Mists are small liquid droplets created when a liquid is splashed, sprayed, or atomized, such as acid mists from electroplating or oil mists from machining. Gases and vapors behave differently still, dispersing freely through the air and often remaining invisible.
To determine whether chemical exposure is dangerous, industrial hygienists measure airborne concentrations against established limits. OSHA sets legally enforceable Permissible Exposure Limits (PELs), while a separate scientific organization called the ACGIH publishes Threshold Limit Values (TLVs) as health-based guidelines. The two numbers don’t always match. TLVs are based purely on health data without considering whether the limit is economically or technically feasible for employers to achieve, while PELs factor in feasibility as part of the regulatory process. In practice, many industrial hygienists use the more protective TLV as a target even though only the PEL is legally required.
Physical Hazards
Physical hazards are forms of energy that can damage the body. The major types are noise, vibration, radiation (both ionizing and non-ionizing), and extreme temperatures.
Noise is one of the most widespread. Continuous exposure above 85 decibels, roughly the volume of heavy city traffic, can cause permanent hearing loss over time. Industrial hygienists measure personal noise exposure using dosimeters worn throughout a shift. Vibration splits into two categories: whole-body vibration from operating heavy vehicles or standing on vibrating platforms, and hand-arm vibration from tools like jackhammers, grinders, and chainsaws. Prolonged hand-arm vibration can cause a condition called hand-arm vibration syndrome, which damages blood vessels and nerves in the fingers.
Radiation hazards divide into ionizing and non-ionizing types. Ionizing radiation, the kind found in X-ray facilities and nuclear energy work, carries enough energy to damage DNA directly. Non-ionizing radiation includes ultraviolet light, infrared, lasers, and microwaves. While less immediately destructive, prolonged exposure to non-ionizing sources can still cause burns, eye damage, and skin injury. Extreme heat and cold round out the physical hazard category, covering everything from foundry work to outdoor winter construction.
Biological Hazards
Biological hazards are living organisms or their byproducts that cause infection or disease. This includes bacteria, viruses, fungi, and parasites. Healthcare workers face the broadest range of biological hazards, but they also affect agricultural workers, lab technicians, veterinarians, and anyone who handles waste or works with animals.
Transmission routes vary by pathogen. Bloodborne pathogens like hepatitis B, hepatitis C, and HIV spread through contact with infected blood and body fluids. Others spread through the air: tuberculosis transmits via tiny airborne particles, while influenza and COVID-19 can spread through droplets, aerosols, and direct contact. Some infections like MRSA and C. difficile spread primarily through surface contact, making hand hygiene and surface decontamination critical controls. Mold and fungi present their own hazard category, particularly in buildings with water damage or in agricultural settings where workers handle decaying organic material.
Ergonomic Hazards
Ergonomic hazards come from the physical demands of how work is performed. The three core risk factors are force, repetition, and posture. When these overlap, the risk of developing a work-related musculoskeletal disorder rises sharply.
Awkward or sustained postures are a major driver of injury. Holding your arms overhead, twisting while carrying loads, or maintaining the same position for extended periods all force muscles and tendons to work harder while restricting blood flow. Repetitive motions compound the problem. Assembly line workers performing the same hand movement thousands of times per shift face elevated risk for carpal tunnel syndrome and tendinitis, especially when the motion also requires force. Carpal tunnel syndrome specifically is linked to combinations of forceful gripping with repetitive wrist movements or awkward hand positions.
Low-back disorders remain among the most common ergonomic injuries and are associated with heavy lifting, bending and twisting, whole-body vibration, and static postures held for long periods. Many ergonomic problems have worsened with technological changes: faster assembly lines, more specialized and repetitive tasks, and workstation designs that don’t account for the range of body sizes using them.
Psychosocial Hazards
Psychosocial hazards are the newest addition to the industrial hygiene framework and cover factors in the work environment that cause stress, strain, or interpersonal harm. These include work organization issues, shift work, fatigue, workplace violence, and bullying.
Shift work, defined as any schedule outside the 7 a.m. to 6 p.m. window, carries measurable health consequences. Shift workers face higher rates of cardiovascular disease, gastrointestinal disorders, diabetes, certain cancers, and difficulty managing chronic health conditions. Fatigue compounds these risks, and it’s not simply tiredness. Occupational fatigue is a persistent lack of physical and mental energy that isn’t resolved by sleep, often driven by long hours, mandatory overtime, or insufficient recovery time between shifts.
Workplace violence is formally categorized into four types. Type I is criminal intent, where someone with no connection to the business commits violence during a robbery or trespass. Type II is client-on-worker violence, the most common form in healthcare, involving patients, family members, or visitors. Type III is worker-on-worker conflict, often manifesting as bullying, verbal abuse, or emotional intimidation. Type IV involves personal relationships that spill into the workplace. Bullying specifically involves repeated actions intended to humiliate or undermine a person, and it can become so normalized that it’s treated as just part of the culture.
How Hazards Are Measured
Industrial hygienists don’t just categorize hazards. They quantify them. For airborne chemical hazards, the standard method is personal air sampling, where a small pump clipped to a worker’s clothing draws air through a collection device positioned within about six to nine inches of the nose and mouth. The sample is then sent to a lab for analysis. For gases and vapors, passive diffusive samplers can be used instead, which absorb contaminants without needing a pump. Direct-reading instruments and detector tubes provide faster, on-the-spot readings useful for initial screening.
Dust sampling gets more specific. Total dust sampling captures all airborne particles using a filter at a flow rate of 2 liters per minute over up to eight hours. Respirable dust sampling uses a size-selective device that captures only particles small enough to reach the deepest parts of the lungs, with a 50% collection efficiency at 4 micrometers. This distinction matters because larger particles get filtered out by your nose and throat, while the smallest ones penetrate to the gas-exchange region where oxygen enters your blood.
The Hierarchy of Controls
Once a hazard is identified and measured, industrial hygiene follows a ranked system for controlling it, moving from most effective to least effective: elimination, substitution, engineering controls, administrative controls, and personal protective equipment (PPE).
Elimination removes the hazard entirely. If a process uses a toxic solvent, you stop using it. If work at height creates a fall hazard, you redesign the task to happen at ground level. Substitution replaces something dangerous with something less so. Engineering controls are physical changes to the workspace that reduce exposure without relying on worker behavior: local exhaust ventilation to capture fumes at the source, noise enclosures around loud machinery, machine guards, and mechanical lift equipment to reduce manual handling.
Administrative controls change how work is organized. Rotating workers through tasks to limit any one person’s exposure time, adjusting shift schedules, and providing training all fall here. PPE, items like respirators, gloves, earplugs, and safety glasses, sits at the bottom because it depends entirely on the worker using it correctly every time. It’s the last line of defense, not the first, and it’s the least reliable precisely because human compliance is never perfect.