Industrial hygiene is the science of protecting workers from health hazards in their environment. Formally defined as the anticipation, recognition, evaluation, and control of workplace conditions that can cause sickness, impaired health, or significant discomfort, it covers everything from chemical fumes and excessive noise to repetitive motion injuries and biological threats like mold or bacteria.
The Four Core Functions
Industrial hygiene is built around four actions, each building on the last. Anticipation means identifying potential hazards before they cause harm, often during the design phase of a new process or facility. Recognition involves spotting existing hazards through workplace walkthroughs, reviewing injury logs, and talking directly to workers about what they experience on the job. This approach of documenting hazards through observation and worker interviews dates back to the early 1900s, when physician Alice Hamilton pioneered occupational health investigations by visiting factories and interviewing workers in their homes, “where they had courage to speak out what is in their minds.”
Evaluation is the measurement phase: quantifying how much of a hazard workers are actually exposed to. And control is putting solutions in place to reduce or eliminate the exposure. Most of an industrial hygienist’s day-to-day work cycles through these four steps across different parts of a workplace.
Types of Workplace Hazards
The hazards industrial hygienists deal with fall into several broad categories:
- Chemical hazards: solvents, adhesives, paints, toxic dusts, and any airborne substance that can be inhaled, absorbed through skin, or ingested.
- Physical hazards: noise, radiation, extreme heat or cold, and vibration.
- Biological hazards: infectious diseases, mold, bacteria like Legionella (which causes Legionnaires’ disease), and bloodborne pathogens.
- Ergonomic hazards: heavy lifting, repetitive motions, awkward postures, and vibration that can lead to musculoskeletal disorders over time.
A single workplace often has hazards from multiple categories at once. A manufacturing plant might expose workers to chemical fumes, high noise levels, and repetitive assembly tasks simultaneously, each requiring a different evaluation and control strategy.
How Hazards Are Measured
Evaluation is where industrial hygiene gets technical. The goal is to measure a worker’s actual exposure and compare it against established safety limits.
For airborne chemicals, industrial hygienists use personal air sampling pumps clipped to a worker’s clothing near the breathing zone. These pumps draw air through a collection medium over the course of a full shift, and the sample is sent to a lab for analysis. The result tells you exactly how much of a substance the worker breathed in during that period.
For noise, there are two main instruments: sound level meters and dosimeters. A sound level meter captures the intensity of sound at a given moment, which is useful for mapping noise levels across different areas of a facility. A dosimeter clips to the worker’s shoulder and records sound levels continuously throughout the day, then calculates an average exposure for the full shift. Both instruments need to be calibrated before and after each use to ensure accurate results.
For ergonomic hazards, industrial hygienists use structured assessment tools. The NIOSH Lifting Equation calculates a recommended weight limit based on factors like how far the object is from the body, how high it’s lifted, and how often the task is repeated. Tools called RULA (Rapid Upper Limb Assessment) and REBA (Rapid Entire Body Assessment) score the risk of musculoskeletal injury from awkward postures involving the arms, neck, and trunk. Body discomfort maps, where workers mark where they feel pain or strain, help identify which jobs need closer evaluation.
Biological hazards require their own methods. For Legionella, for example, assessment involves checking water system temperatures (water heaters should operate at 140°F or above, with distant faucets reaching at least 122°F) and identifying places where water can stagnate, like storage tanks, dead-end pipes, or infrequently used faucets. When contamination is suspected, water samples are sent to certified labs, where culture-based testing can take up to 14 days to determine the concentration of bacteria.
Exposure Limits and Standards
Industrial hygienists compare their measurements against occupational exposure limits, but not all limits carry the same weight. OSHA sets Permissible Exposure Limits (PELs), which are legally enforceable in the United States. Employers must keep worker exposures at or below these levels. NIOSH, the research arm of the CDC, publishes Recommended Exposure Limits (RELs), which are based on the latest scientific evidence but are not enforceable on their own. NIOSH develops these recommendations and transmits them to OSHA for potential adoption into law.
A third set of limits comes from ACGIH, a professional organization that publishes Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs). These are updated regularly, with 2026 documentation currently available, and represent the consensus of independent scientists. TLVs are often more protective than PELs because OSHA’s legal limits, many of which date back decades, are difficult to update through the regulatory process. Industrial hygienists typically use all three sets of limits when evaluating a workplace, aiming for the most protective standard even when the law only requires the PEL.
How Hazards Are Controlled
Once a hazard is measured and found to exceed safe levels, the next step is control. The standard framework is called the hierarchy of controls, which ranks solutions from most to least effective.
Elimination is the top priority: removing the hazard entirely. This might mean changing a work process so a toxic chemical is no longer needed, or redesigning a task to eliminate heavy lifting. When elimination isn’t possible, substitution uses a safer alternative. Switching from solvent-based printing inks to plant-based inks is a classic example.
Engineering controls come next. These are physical changes to the workspace that reduce exposure without relying on worker behavior. Examples include installing ventilation systems to capture chemical fumes at the source, enclosing noisy equipment, or adding protective barriers between workers and hazards.
Administrative controls change how work is organized rather than the physical environment. Job rotation limits how long any one person is exposed. Scheduling high-exposure operations for periods when fewer workers are present reduces the number of people affected. Training, rest breaks, and restricting access to hazardous areas all fall into this category. OSHA also includes basic work practice controls here: proper housekeeping, regular equipment maintenance, and prohibiting eating, drinking, or smoking in areas where hazardous materials are present.
Personal protective equipment (PPE) sits at the bottom of the hierarchy. Gloves, respirators, hearing protection, hard hats, and safety glasses are the last line of defense when other controls can’t reduce exposure enough. PPE is considered least effective because it depends entirely on workers wearing it correctly and consistently.
What Industrial Hygienists Do Day to Day
Industrial hygienists work in a wide range of settings: manufacturing plants, construction sites, hospitals, office buildings, government agencies, and consulting firms. Their work typically involves conducting workplace assessments, collecting air, noise, or water samples, interpreting lab results, recommending control measures, and ensuring compliance with OSHA standards. Some specialize in a particular hazard type, like chemical exposure or ergonomics, while others are generalists who handle whatever a facility needs.
The field also extends beyond the factory floor. Industrial hygienists assess indoor air quality in office buildings, evaluate mold contamination after water damage, and investigate disease clusters that may be linked to workplace exposures. The original definition of the field explicitly includes protecting not just workers but “citizens of the community,” recognizing that workplace hazards can affect people beyond the facility’s walls.
Becoming a Certified Industrial Hygienist
The professional credential in this field is the Certified Industrial Hygienist (CIH) designation, administered by the Board for Global EHS Credentialing. Earning it requires a combination of education, experience, and examination. Candidates need at least 60 semester hours of science, math, engineering, or science-based technology coursework, plus 180 academic hours (or 240 continuing education contact hours) specifically in industrial hygiene topics like toxicology, exposure measurement, and hazard controls. At least two hours of ethics coursework are also required.
Beyond education, candidates need four years of professional-level industrial hygiene experience documented by references, including at least one from an existing CIH. They must pass a comprehensive exam and agree to follow the BGC Code of Ethics. The CIH is widely recognized as the gold standard credential for the profession and is often required or preferred for senior-level positions.