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OSHA & GHS Safety Glossary

222 essential terms for workplace chemical safety, hazard communication, and OSHA compliance — each with CFR references, cross-linked related terms, and shareable anchor links.

Verified vs OSHA sources · 2026-10-05

This is a free, continuously maintained glossary of 222 OSHA, GHS, SDS, and construction-safety terms — covering hazard communication, chemical classification, permissible exposure limits, respiratory protection, recordkeeping, and enforcement. Every definition is written for working safety professionals and is tied to its governing regulation (29 CFR references) and verified against primary sources such as OSHA.gov, the eCFR, and NIOSH.

Browse all 222 terms below — searchable, filterable by category, and organized A→Z. Each entry links to a full explainer with a plain-English summary, a worked example, the exact CFR text, common misconceptions, FAQs, and related terms and free compliance tools. Use the search box for a quick lookup (try PEL, fit test, or GHS pictogram), or jump to a letter.

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29 CFR 1910: The part of Title 29 of the Code of Federal Regulations that contains OSHA's General Industry standards — the default rulebook for most American workplaces (manufacturing, warehousing, healthcare, etc.) that aren't covered by the construction, maritime, or agriculture standards. It includes core rules like Hazard Communication (1910.1200) and the permissible exposure limits (1910.1000). Several 1910 standards are cross-referenced into construction via Part 1926.
29 CFR 1926: The part of Title 29 of the Code of Federal Regulations that contains OSHA's Construction standards — the “Safety and Health Regulations for Construction.” It governs construction, alteration, and repair work, with construction-specific rules for fall protection (Subpart M), scaffolds (Subpart L), excavations (Subpart P), electrical (Subpart K), and more. Where a task isn't addressed in 1926, some general-industry (1910) standards apply by reference.

A

Abatement: The action an employer takes to fix a cited violation or eliminate a hazard OSHA identified during an inspection. The citation sets an abatement date, the deadline to correct the hazard, and within 10 calendar days after that date the employer must certify to OSHA that the violation was abated. Failure to abate accrues additional penalties of up to $16,550 per day.
Action Level: An airborne concentration of a substance — typically half the PEL — at which certain provisions of an OSHA standard kick in (such as exposure monitoring, training, and medical surveillance), even though it is below the legal exposure limit. For respirable crystalline silica the action level is 25 µg/m³ as an 8-hour TWA, half the 50 µg/m³ PEL.
Acute Toxicity: A GHS health-hazard class for the harmful effects that follow a single dose, several doses within 24 hours, or a 4-hour inhalation exposure. Chemicals are sorted into categories by route (oral, dermal, inhalation) using LD50/LC50 cut-offs — Category 1 is the most toxic. OSHA's HazCom standard uses Categories 1–4.
Administrative Controls: Changes to how and when work is done — job rotation, scheduling, safe work practices, housekeeping, training, and signage — that reduce a worker's exposure without altering the hazard itself. They are the fourth tier of the hierarchy of controls, below engineering controls and above PPE.
Aerial Lift: A vehicle-mounted, boom-supported aerial device used to elevate personnel to jobsites above ground. OSHA (29 CFR 1926.453) lists five types: extensible boom platforms, aerial ladders, articulating boom platforms, vertical towers, and combinations. Workers in an aerial lift must wear a body belt (or harness) with a lanyard attached to the boom or basket. Note: scissor lifts are NOT aerial lifts — OSHA treats them as mobile scaffolds.
Aerosol: As a GHS/HazCom hazard class, an aerosol is a non-refillable pressurized container (an aerosol dispenser) — a can holding a gas compressed, liquefied, or dissolved under pressure, fitted with a release valve that ejects the contents as a spray, foam, paste, powder, liquid, or gas. HazCom classifies aerosols into three categories by their flammable content and heat of combustion: Category 1 (extremely flammable), Category 2 (flammable), and Category 3 (non-flammable).
Affected Employee: In OSHA's Lockout/Tagout standard (29 CFR 1910.147(b)), an affected employee is one whose job requires operating or using a machine that's being serviced under lockout/tagout, or whose job requires working in the area where that servicing is performed. Affected employees do not apply the locks — that's the authorized employee's role — but they must be notified before lockout begins and trained on the purpose and use of the procedures.
Anchor Point: The secure attachment point a personal fall arrest system (PFAS) ties off to — the “A” in the ABC of fall arrest. Under 29 CFR 1926.502(d)(15), a non-engineered anchorage must support at least 5,000 pounds per attached worker; alternatively, it can be an engineered anchorage designed and supervised by a qualified person with a safety factor of at least two.
Arc Flash: An arc flash is the sudden release of thermal energy from an electrical arc fault — a short circuit that jumps through the air between energized parts. The arc can reach temperatures over 35,000°F (nearly four times the surface of the sun), causing severe burns, igniting clothing, and driving an explosive pressure wave known as the arc blast. OSHA sets no single “arc-flash standard”: the analysis method — the arc-flash boundary, incident energy, and arc-rated PPE — comes from the NFPA 70E consensus standard, which OSHA enforces through its electrical-PPE rules (29 CFR 1910.335, 1910.269) and the General Duty Clause.
Area Director: The senior OSHA official in charge of a specific OSHA Area Office — the local unit that runs inspections and enforcement in its geographic territory. The Area Director has the authority to issue citations, propose penalties, hold informal conferences with employers, and approve settlement agreements. When a Compliance Safety and Health Officer (CSHO) completes an inspection, it's the Area Director who ultimately issues the citation.
Asbestos: A group of naturally occurring fibrous silicate minerals once widely used in insulation, fireproofing, flooring, and roofing. When asbestos-containing materials are disturbed, microscopic fibers become airborne and, when inhaled, cause asbestosis (lung scarring), lung cancer, and mesothelioma — a fatal cancer of the lung or abdominal lining. OSHA sets a permissible exposure limit of 0.1 fibers per cubic centimeter (f/cc) as an 8-hour TWA and an excursion limit of 1 f/cc over 30 minutes, under separate standards for construction (29 CFR 1926.1101), general industry (1910.1001), and shipyards (1915.1001). OSHA recognizes no "safe" level of asbestos exposure.
Aspiration Hazard: A GHS health-hazard class for chemicals that can be fatal if swallowed and then enter the airways — directly or by vomiting — causing chemical pneumonia or lung injury. Thin, low-viscosity hydrocarbons (gasoline, kerosene, lamp oil) are the classic example. It is Category 1, with the health-hazard pictogram (GHS08) and signal word “Danger.”
Assigned Protection Factor (APF): The workplace level of respiratory protection that a properly functioning respirator (or class of respirators) is expected to provide to a properly fitted and trained user. OSHA codifies APFs in Table 1 of 29 CFR 1910.134(d)(3)(i). An APF of 10 means the respirator reduces the wearer's exposure to one-tenth of the ambient concentration. Representative values: half-mask air-purifying = 10; full-facepiece air-purifying = 50; loose-fitting PAPR/hood = 25; tight-fitting full-facepiece PAPR = 1000; and full-facepiece pressure-demand SCBA = 10,000. The APF is used to compute the Maximum Use Concentration (MUC = APF × PEL).
Atmospheric Testing: Measuring the air in a confined space (or other hazardous atmosphere) with a calibrated direct-reading instrument before and during entry. OSHA requires testing in a set order — oxygen first, then flammable gases and vapors, then potential toxic contaminants — and defines the acceptable ranges: oxygen 19.5%–23.5%, flammables below 10% of the LEL, toxics below their exposure limits.
Authorized Employee: In OSHA's Lockout/Tagout standard (29 CFR 1910.147(b)), an authorized employee is the person who locks out or tags out machines or equipment to perform servicing or maintenance. They apply and remove the energy-isolating devices, so they must be trained to recognize the hazardous energy sources and know the procedures to control them. The role is task-specific: an employee can be authorized for one machine and merely affected for another.

B

Benching: An excavation cave-in protective system that cuts the sides into a series of horizontal steps (benches), usually with vertical or near-vertical faces between levels. It's one of OSHA's accepted protective systems under Subpart P — but it is NOT permitted in Type C (the least stable) soil.
Benzene: A colorless, sweet-smelling flammable liquid and a confirmed human carcinogen that causes leukemia and other blood disorders (including aplastic anemia). Benzene is found in crude oil, gasoline, and many industrial processes. OSHA regulates it under 29 CFR 1910.1028 with a permissible exposure limit of 1 ppm as an 8-hour TWA, a short-term exposure limit (STEL) of 5 ppm over any 15-minute period, and an action level of 0.5 ppm. Employers must establish regulated areas wherever exposures exceed the PEL or STEL.
Biological Exposure Index (BEI): An ACGIH guidance value for interpreting biological monitoring results — the concentration of a chemical (or its metabolite) measured in a worker's blood, urine, or exhaled breath. A BEI represents the level most likely found in a healthy worker whose inhalation exposure was at the TLV, so it measures the dose the body actually absorbed, not just what's in the air.
Biological Monitoring: Measuring a chemical or its breakdown product (metabolite) in a worker's biological specimen — usually blood, urine, or exhaled breath — to gauge how much of the substance the body has actually absorbed. Unlike air sampling, which measures what's in the breathing zone, biological monitoring captures total uptake across all routes, including skin absorption and ingestion. Results are often compared to ACGIH Biological Exposure Indices (BEIs).
Bloodborne Pathogens: Pathogenic microorganisms present in human blood that can cause disease — primarily Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV), and Hepatitis C Virus (HCV). OSHA's Bloodborne Pathogens Standard (29 CFR 1910.1030) applies to all workers with 'occupational exposure' — reasonably anticipated contact with blood or Other Potentially Infectious Materials (OPIM) — and requires a written Exposure Control Plan, engineering controls, PPE, HBV vaccination at no cost, annual training, and post-exposure follow-up.
Bureau of Labor Statistics (BLS): The federal statistical agency within the U.S. Department of Labor that collects, analyzes, and publishes data on workplace injuries, illnesses, and fatalities. BLS conducts the annual Survey of Occupational Injuries and Illnesses (SOII) — compiled from employer OSHA 300 logs — and the Census of Fatal Occupational Injuries (CFOI). SOII data drives OSHA's Site-Specific Targeting (SST) program: establishments whose DART rates significantly exceed their BLS industry average are placed on the SST inspection list.

C

Cadmium: A soft, toxic heavy metal used in batteries (nickel-cadmium), pigments, coatings/electroplating, and some solders and alloys. Inhaling cadmium fume or dust damages the lungs and kidneys and causes cancer. OSHA regulates it under 29 CFR 1926.1127 (construction) and 1910.1027 (general industry) with a permissible exposure limit of 5 µg/m³ as an 8-hour TWA and an action level of 2.5 µg/m³.
California Proposition 65: California's Safe Drinking Water and Toxic Enforcement Act of 1986. It requires businesses to warn Californians before exposing them to any of the ~900+ listed chemicals known to the state to cause cancer, birth defects, or other reproductive harm, and prohibits discharging those chemicals into drinking-water sources. It's a California law, but it reaches nearly any product sold there.
Carcinogenicity: A GHS health-hazard class for chemicals that cause cancer or increase its incidence. GHS (and OSHA's HazCom standard) sorts carcinogens into Category 1A (known human carcinogen), 1B (presumed, from animal evidence), and Category 2 (suspected). Carcinogens carry the health-hazard pictogram (GHS08) and a hazard statement such as H350 (“May cause cancer”).
CAS Number: A unique numerical identifier assigned by the Chemical Abstracts Service (a division of the American Chemical Society) to every distinct chemical substance. It has the format of up to seven digits, a dash, two digits, a dash, and a final check digit (e.g., 67-64-1 for acetone). Because chemical names vary, the CAS number is the unambiguous global key used on SDSs, inventories, and regulations.
Caught-In/Between Hazard: One of OSHA's construction “Focus Four” hazards. It occurs when a worker is caught, crushed, squeezed, or compressed between two or more objects, or between parts of an object — for example a trench cave-in, being pinned by unguarded machinery, or an equipment rollover. The defining feature is crushing/compression, which distinguishes it from a struck-by injury.
Ceiling Limit: An exposure limit that must not be exceeded at any instant during the workday — the strictest type of OSHA exposure limit. In OSHA's Z-tables it is marked with a “C” before the value. Unlike an 8-hour TWA (an average) or a 15-minute STEL, a ceiling applies to a single moment.
CERCLA: The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 — better known as Superfund. It gives the EPA authority and a fund to clean up hazardous-waste sites and emergency releases, holds responsible parties liable for the cleanup, and sets Reportable Quantities (RQs) — the release amounts that must be reported to the federal government.
Chemical Compatibility: Whether two or more chemicals can be safely stored or used near each other without reacting dangerously — releasing heat, toxic gas, or fire. Incompatible chemicals must be physically separated (segregated) in storage. Each chemical's incompatibilities are listed in Section 10 of its SDS, and compatibility drives storage layout and spill response.
Chemical Inventory: A list of the hazardous chemicals known to be present in a workplace, identified in a way that cross-references each chemical's safety data sheet. It's a required part of OSHA's written HazCom program (29 CFR 1910.1200(e)(1)(i)) and the foundation for SDS management, EPCRA Tier II reporting, and emergency planning.
Chemicals Under Pressure: A physical-hazard class added by OSHA's 2024 HCS update (aligning with GHS Revision 7) for liquids or solids pressurized with a gas, held in pressure receptacles other than aerosol dispensers and not classified as gases under pressure. It is categorized by the flammability of its contents and always carries the gas-cylinder pictogram (GHS04) for the pressure hazard.
Citation: The formal written notice OSHA issues to an employer after an inspection, describing each alleged violation, the standard cited, the proposed penalty, and the date by which the hazard must be corrected (abated). OSHA must issue a citation with reasonable promptness and no later than six months after the violation occurred.
Classification: The process of evaluating the available scientific evidence for a chemical against the GHS criteria to decide whether it is hazardous and, if so, the hazard class and category of each effect. Classification is the first step in HazCom — its result determines every label element (pictogram, signal word, hazard and precautionary statements) and SDS content.
Closing Conference: The meeting at the end of an OSHA inspection where the compliance officer confers with the employer and informally advises them of any apparent violations found. Importantly, the closing conference discusses what was observed and the employer's rights — but it does NOT state final citations or penalties, which come later in the written Citation and Notification of Penalty.
Combustible Dust: Fine particles of a solid material that can catch fire and, when suspended in air at the right concentration, explode (deflagrate). Many everyday materials become combustible dust in finely divided form — wood, flour, sugar, grain, coal, plastics, and metals like aluminum and magnesium. OSHA has no single comprehensive combustible dust standard; it addresses the hazard through the General Duty Clause, the Hazard Communication Standard, and specific standards, alongside NFPA consensus standards.
Combustible Liquid: A liquid that burns, but needs warming first — and a term OSHA no longer defines. The definition lived at 29 CFR 1910.106(a)(18) until the 2012 GHS alignment struck it; that paragraph now reads only “[Reserved]”. What 1910.106(a)(19) defines today is a flammable liquid — “any liquid having a flashpoint at or below 199.4 °F (93 °C)” — divided into four categories, the same four that 1910.1200 Appendix B.6 uses for classification and labels. The familiar 100 °F line and the Class II / IIIA / IIIB scheme come from NFPA 30, not from the current 29 CFR, and they remain in force through fire codes, insurers, and the consensus standards OSHA still incorporates by reference — whose titles still say “Flammable and Combustible Liquids”. So the word is alive on a jobsite; it just no longer points at a federal definition.
Competent Person: Under OSHA's construction standards, a person who is capable of identifying existing and predictable hazards in the surroundings or working conditions, and who has the authorization to take prompt corrective measures to eliminate them. The role requires both knowledge and the authority to act, and is mandated by name in many specific standards — excavations, scaffolds, fall protection, asbestos, and more.
Competent Person (Excavation): The competent person OSHA's excavation standard (Subpart P) requires on every trenching job — someone trained in soil classification and protective systems, who can identify cave-in and other hazards AND has authority to remove workers and correct problems. They must inspect the excavation daily before work starts, throughout the shift, and after any rain or event that could increase the hazard.
Competent Person (Scaffold): The competent person OSHA's scaffold standard (Subpart L) requires — someone able to identify scaffold hazards and authorized to correct them. They must inspect the scaffold and its components for visible defects before each work shift and after any occurrence that could affect its structural integrity, and they oversee safe erection, moving, alteration, and dismantling.
Compliance Officer (CSHO): An OSHA Compliance Safety and Health Officer — the inspector who conducts workplace inspections. A CSHO presents credentials (a photo ID and a serial number), holds the opening conference, performs the walkaround, collects evidence, interviews employees, and recommends citations. CSHOs are either safety specialists or industrial hygienists.
Confined Space: A space that is large enough for a worker to bodily enter, has limited or restricted means of entry or exit, and is not designed for continuous occupancy. If it also contains — or could contain — a serious hazard (a hazardous atmosphere, engulfment material, an entrapping configuration, or any other recognized serious hazard), it becomes a permit-required confined space (PRCS).
Confined Space Entry Permit: A written document that authorizes and documents entry into a permit-required confined space (PRCS) before anyone enters. It records the space, the purpose and authorized duration, the authorized entrants, the attendant(s) and entry supervisor, the space's hazards, the isolation and control measures, the acceptable entry conditions, atmospheric test results, rescue and emergency services, and communication procedures. In construction, permit-required confined spaces are governed by 29 CFR 1926 Subpart AA (permit contents at 1926.1206); general industry uses the parallel 29 CFR 1910.146 standard.
Contest: An employer's formal challenge to an OSHA citation, penalty, or abatement date. To contest, the employer must file a written Notice of Contest with the OSHA Area Director within 15 working days of receiving the Citation and Notification of Penalty. Filing sends the case to the independent Occupational Safety and Health Review Commission (OSHRC); missing the deadline makes the citation a final, un-appealable order.
Controlling Employer: Under OSHA's Multi-Employer Citation Policy (CPL 02-00-124), the controlling employer is an employer with general supervisory authority over a worksite — including the power to correct safety and health violations itself or to require others to correct them. This is typically the general contractor or construction manager. A controlling employer can be cited for a hazard at the site even if none of its own employees are exposed, because it has a duty to exercise reasonable care to prevent and detect violations by the other employers on site.
Corrosive to Metals: A GHS physical-hazard class for chemicals that, by chemical action, will materially damage or even destroy metals. It is a single category (Category 1), determined by corrosion-rate testing on steel and aluminum, and uses the corrosion pictogram (GHS05) with the hazard statement H290. It is a separate hazard from skin corrosion, even though both use GHS05.
Crane Operator Certification: OSHA's requirement (29 CFR 1926.1427) that construction crane operators be certified — by an accredited crane-operator testing organization or an employer's audited program — for the equipment type they run. The certifying body may issue by type, or by type and capacity (1926.1427(d)(1)(ii)(B)); capacity alone is not mandatory. Certification is one part: the employer must also train the operator and separately evaluate their ability to operate the specific equipment safely.

D

DART Rate: Days Away, Restricted, or Transferred rate — an injury-rate metric from OSHA 300-Log data: (number of DART cases × 200,000) ÷ total hours worked. DART cases are those with days away from work (Column H) plus those with job transfer or restriction (Column I). OSHA uses it to target inspections at higher-injury establishments.
De Minimis Violation: A technical deviation from an OSHA standard that has no direct or immediate relationship to safety or health. Because there's no real hazard, a de minimis condition carries no penalty and no abatement requirement, and it isn't included on the citation — the compliance officer simply notes it to the employer.
Decontamination: The process of removing or neutralizing hazardous substances from workers, their PPE, tools, and surfaces so contamination isn't spread or carried home. Under OSHA's HAZWOPER standard (1910.120), decon procedures must be planned and carried out in a dedicated contamination-reduction zone before anyone leaves a contaminated area — critical for spill response, asbestos/lead work, and confined-space entry.
Desensitized Explosives: A physical-hazard class added by OSHA's 2024 HCS update (GHS Revision 7) for solid or liquid explosives that have been phlegmatized — wetted or diluted — to suppress their explosive properties for safe transport and storage. It has four categories based on the corrected burning rate, and uses the flame pictogram (GHS02), not the exploding-bomb.
Dose-Response Relationship: The core principle of toxicology that the effect of a substance depends on the dose — the amount and duration of exposure. As dose rises, the severity or likelihood of the health effect changes in a predictable way. This relationship is the scientific basis for setting occupational exposure limits like PELs and TLVs.

E

Egregious Violations: OSHA's violation-by-violation (per-instance) citation approach, under which each instance of noncompliance is cited as a separate violation with its own penalty rather than being grouped into one. Historically reserved for willful violations, it can turn a single inspection into millions of dollars in penalties. A 2023 policy expanded instance-by-instance citations to certain serious, repeat, and other-than-serious violations too.
Electrical Safety (Construction): The requirements of 29 CFR 1926 Subpart K, which protect construction workers from electrical hazards — shock, electrocution, arc flash, and fire. It covers ground-fault protection (GFCIs or an assured equipment grounding conductor program), proper wiring and grounding, safe distances from overhead power lines, lockout/tagout of energized equipment, and safe work practices. Electrocution is one of construction's “Fatal Four.”
Electrocution: Death caused by exposure to electrical energy — one of OSHA's construction “Focus Four” leading causes of death. It results from contact with energized circuits, overhead or buried power lines, or faulty equipment. (An electrical injury that isn't fatal is an electric shock; electrocution specifically means death.) Prevention centers on de-energizing, GFCIs, clearances from power lines, and grounding.
Emergency Action Plan (EAP): A plan required by 29 CFR 1910.38 that spells out what workers do when an emergency happens — how to report it, how and where to evacuate, and how everyone is accounted for afterward. It must be in writing and available to employees (an employer with 10 or fewer employees may communicate it orally). An EAP is about responding to emergencies; its companion, the Fire Prevention Plan, is about preventing fires in the first place.
Employer: Under the OSH Act (Section 3(5)), an employer is “a person engaged in a business affecting commerce who has employees,” excluding the federal government and states/political subdivisions. The employer is the party that carries OSHA's core duties — complying with all applicable standards and the General Duty Clause, and keeping the workplace free of recognized hazards. Self-employed individuals with no employees are generally not covered.
Engineering Controls: Physical changes to the workplace, process, or equipment that reduce or remove a hazard at its source — ventilation, enclosure, wet methods, machine guarding — without relying on the worker to do anything. They sit in the third tier of the hierarchy of controls, above administrative controls and PPE, and OSHA requires them before PPE whenever feasible.
EPCRA: The Emergency Planning and Community Right-to-Know Act — the 1986 federal law (Title III of SARA) administered by the EPA that gives communities the right to know what hazardous chemicals are near them. It sets four reporting duties: emergency planning (§302), release notification (§304), hazardous-chemical inventory reporting (§§311–312, including Tier II), and toxic release reporting (§313, the TRI).
Ergonomics: The science of fitting the job to the worker — designing tasks, tools, and workstations around human capabilities and limits to prevent strain and injury. Poor ergonomics (repetitive motions, awkward postures, forceful exertions, sustained loads) causes musculoskeletal disorders (MSDs), one of the largest categories of workplace injury. OSHA has no specific ergonomics standard — its 2000 rule was repealed by Congress in 2001 — so it addresses ergonomic hazards through the General Duty Clause and voluntary guidelines.
Excavation: Any man-made cut, cavity, trench, or depression formed by removing earth. Under OSHA's Subpart P, workers in an excavation must be protected from cave-ins by a protective system (sloping, benching, shoring, or shielding) at 5 feet or deeper. There are exactly two exceptions, and they are not interchangeable: an excavation made entirely in stable rock is exempt at any depth, while a competent person's examination can exempt an excavation only if it is less than 5 feet deep. Below 5 feet, that examination must actually have been made and must find no indication of a potential cave-in. Trenching and excavation are among construction's deadliest activities.
Experience Modification Rate (EMR): A workers' compensation insurance multiplier that adjusts an employer's premium to reflect its own claims history versus the average for its industry. An EMR of 1.0 is average; above 1.0 means worse-than-average losses and a higher premium; below 1.0 means better-than-average and a lower premium. It's set by rating bureaus (NCCI or a state bureau), not by OSHA.
Explosive: As a GHS/HazCom physical hazard class, an explosive is a solid or liquid chemical that is itself capable, by chemical reaction, of producing gas at such a temperature, pressure, and speed as to cause damage to the surroundings — as defined in Appendix B.1 of 29 CFR 1910.1200. The class is organized into six divisions (1.1 through 1.6) by the type and severity of the explosion hazard, plus a separate 'unstable explosive' designation for chemicals too thermally unstable or sensitive for normal handling. Explosives carry the exploding-bomb pictogram (GHS01).
Exposing Employer: Under OSHA's Multi-Employer Citation Policy (CPL 02-00-124), the exposing employer is an employer whose own employees are exposed to a hazard — regardless of who created it. If the exposing employer created the hazard, it is citable. If another employer created it, the exposing employer is still citable when it knew (or should have known) of the hazard and failed to take reasonable protective steps: correcting it if within its authority, or otherwise asking the creating/controlling employer to correct it, informing its employees, and taking feasible alternative protective measures.
Exposure Assessment: The industrial-hygiene process of measuring or estimating how much of a hazard a worker is exposed to — its intensity (concentration), frequency, duration, and route — to decide whether it exceeds a limit and what controls are needed. It's the “Evaluate” step of industrial hygiene, and OSHA's health standards (like silica) require employers to perform it.

F

Failure-to-Abate: A violation that exists when an employer does not correct a previously cited hazard by the abatement date on the citation. Because the hazard was already identified and the employer had time to fix it, OSHA can assess a penalty of up to $16,550 per day for each day the violation continues past the deadline, a running penalty that can quickly exceed the original fine. OSHA's Field Operations Manual caps the total at 30 times the daily amount.
Fall Protection: The systems that keep workers from falling off elevated surfaces — guardrail systems, safety net systems, or personal fall arrest systems (PFAS). In construction, OSHA generally requires fall protection whenever a worker is exposed to a fall of 6 feet or more to a lower level (29 CFR 1926.501, Subpart M). It ranked first on OSHA's list of most-cited standards for FY2025.
Filtering Facepiece Respirator (N95): A disposable, tight-fitting air-purifying respirator in which the entire facepiece is the filter — most familiarly the N95. It filters airborne particles but provides NO protection against gases, vapors, or oxygen-deficient atmospheres. NIOSH certifies particulate filters under 42 CFR Part 84 by oil resistance (N = Restricted to workplaces free of oil aerosols, R = Intended for particulates that include oil-based liquids, P = Also intended for oil-based particulates; the usual mnemonic reads P as oil-proof) and efficiency (95 = ≥ 95%, 99 = ≥ 99%, 100 = ≥ 99.97% (HEPA-equivalent, 29 CFR 1910.134(b))), giving nine classes. As a tight-fitting respirator it has an assigned protection factor of 10 and, when used to comply with OSHA requirements, needs fit testing, medical evaluation, and a written program.
Fire Prevention Plan: A plan required by 29 CFR 1910.39 that focuses on preventing fires — by identifying major fire hazards, controlling their fuels and ignition sources, and maintaining fire-related equipment. It must be in writing and available to employees (an employer with 10 or fewer employees may communicate it orally). Where OSHA requires one, it typically accompanies an Emergency Action Plan, which covers what to do once a fire or emergency occurs.
First Aid: For OSHA recordkeeping, “first aid” is a specific closed list of minor treatments in 29 CFR 1904.7(b)(5)(ii) — bandages, non-prescription medications at OTC strength, tetanus shots, wound cleaning, hot/cold therapy, and similar. Any treatment not on that list is “medical treatment beyond first aid,” which makes a work-related case recordable. The list is exhaustive: nothing else counts as first aid.
Flammable Gas: A gas that has a flammable range with air at 20°C (68°F) and standard pressure. Under OSHA's HazCom 2024 update, flammable gases are classified as Category 1A, 1B, or 2. Category 1A is the most hazardous and now includes pyrophoric gases (those igniting spontaneously in air at or below 54°C) and chemically unstable gases (which can react explosively even without air). Examples include hydrogen, methane, propane, and acetylene.
Flammable Liquid: Under OSHA's HazCom standard, a liquid with a flash point at or below 93°C (199.4°F). GHS/HCS sorts flammable liquids into four categories by flash point (FP) and initial boiling point (BP): Category 1 is the most dangerous (very low flash point and boiling point, e.g. gasoline), Category 4 the least. The lower the flash point, the more readily the liquid gives off ignitable vapor at ordinary temperatures.
Flash Point: The lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture with air near its surface. It is the key property GHS uses to sort flammable liquids into categories — the lower the flash point, the more easily the liquid ignites.
Focus Four Hazards: OSHA's name for the four leading causes of death in construction: Falls, Struck-By, Caught-In/Between, and Electrocution. Together they account for the largest share of construction worker deaths — with falls alone the single leading cause — so OSHA concentrates its construction training and enforcement on them. Also called the “Fatal Four.”
Formaldehyde: A colorless, pungent gas (often used in water solution as formalin) that is a confirmed carcinogen and a strong respiratory and skin sensitizer. It is used in resins, adhesives, composite wood products, embalming, and many laboratory and industrial processes. OSHA regulates it under 29 CFR 1910.1048 with a permissible exposure limit of 0.75 ppm as an 8-hour TWA, a short-term exposure limit (STEL) of 2 ppm over any 15-minute period, and an action level of 0.5 ppm.

G

Gas Under Pressure: A GHS/HazCom physical hazard class (Appendix B.5 of 29 CFR 1910.1200) for gases contained in a receptacle at a pressure of 200 kPa (gauge) or more, or that are liquefied or refrigerated liquefied. It is divided into four groups by the physical state of the gas in the container: compressed gas, liquefied gas, refrigerated liquefied gas, and dissolved gas. The hazard is primarily physical — the stored energy of the pressurized (or cryogenic) contents can cause an explosion, projectile, or cold burn. Gases under pressure carry the GHS04 (gas cylinder) pictogram.
General Duty Clause: Section 5(a)(1) of the OSH Act, which requires every employer to provide a workplace free from recognized hazards likely to cause death or serious physical harm — even when no specific OSHA standard covers the hazard. It is OSHA's catch-all enforcement tool for hazards like heat, ergonomics, and workplace violence that have no dedicated rule.
GFCI (Ground-Fault Circuit Interrupter): A protective device that constantly compares the current flowing out to and back from a tool; if it detects even a small imbalance (current leaking to ground — like through a worker's body), it cuts the power in milliseconds. On construction sites, OSHA requires GFCI protection on 120-volt, 15- and 20-amp temporary receptacles to prevent electrocution.
GHS Revision 7: The 7th revision of the UN Globally Harmonized System, which OSHA adopted in its 2024 update to the Hazard Communication Standard (with selected elements of Revision 8). It adds new hazard classes — desensitized explosives and chemicals under pressure — folds pyrophoric and chemically unstable gases into flammable gases, and updates label and SDS provisions. The final rule was effective July 19, 2024, with phased compliance dates.
GHS01 (Exploding Bomb): The GHS hazard pictogram showing an exploding bomb. It's used for explosives (unstable explosives and Divisions 1.1–1.4), self-reactive substances Types A and B, and organic peroxides Types A and B — hazards that can mass-explode or throw fire, blast, or projectiles. On US labels it appears inside the red diamond frame.
GHS02 (Flame): The GHS hazard pictogram showing a flame. It covers the whole family of fire hazards: flammable gases, aerosols, liquids, and solids; pyrophoric (auto-igniting) liquids and solids; self-heating substances; substances that emit flammable gas when wet; the less-reactive self-reactives and organic peroxides (Types C–F); and desensitized explosives.
GHS03 (Flame Over Circle): The GHS hazard pictogram showing a flame over a circle. It marks oxidizers — oxidizing gases, liquids, and solids — which can cause or intensify a fire or explosion by releasing oxygen, even when they don't burn themselves. It's one of OSHA's eight required workplace pictograms.
GHS04 (Gas Cylinder): The GHS hazard pictogram showing a gas cylinder. It marks gases under pressure — compressed, liquefied, refrigerated liquefied, and dissolved gases — which can violently rupture or explode if heated, and, for refrigerated gases, cause cryogenic burns. The new chemicals-under-pressure class also uses it.
GHS05 (Corrosion): The GHS hazard pictogram showing a hand and a surface being eaten away. It covers three “corrosion” hazards: skin corrosion (Category 1), serious eye damage (Category 1), and corrosive to metals (Category 1). It signals a substance that chemically destroys living tissue and/or metals.
GHS06 (Skull and Crossbones): The GHS hazard pictogram showing a skull and crossbones. It marks the more severe acute toxicity — Categories 1, 2, and 3 by oral, dermal, or inhalation route — chemicals that can be fatal or toxic from a small, single exposure. The milder Category 4 (“harmful”) uses the exclamation mark (GHS07) instead.
GHS07 (Exclamation Mark): The GHS hazard pictogram showing an exclamation mark. It flags the less-severe hazards: acute toxicity Category 4 (“harmful”), skin and eye irritation (Category 2), skin sensitization, respiratory tract irritation and narcotic effects (STOT single-exposure Category 3). The international GHS also assigns ozone-layer hazards to this symbol, but OSHA's Appendix C does not carry that class, so it never appears on a US workplace label. It is not used for the serious chronic hazards, which use the health-hazard pictogram (GHS08).
GHS08 (Health Hazard): The GHS hazard pictogram showing a human silhouette with a starburst on the chest. It flags the serious, often long-term health hazards: carcinogenicity, germ cell mutagenicity, reproductive toxicity, respiratory sensitization, specific target organ toxicity (STOT), and aspiration hazard. It's the pictogram for hazards that can cause cancer, organ damage, or lasting harm.
GHS09 (Environment): The GHS hazard pictogram showing a dead tree and a dead fish. It marks substances hazardous to the aquatic environment — acute Category 1 and chronic Categories 1–2. It's the one pictogram OSHA does NOT require on US workplace labels, because environmental hazards are outside OSHA's jurisdiction; it still appears on shipped containers and SDSs.
Globally Harmonized System (GHS): An internationally agreed framework created by the United Nations (first adopted in 2003) that standardizes how chemical hazards are classified and communicated — using common hazard classes, pictograms, signal words (Danger / Warning), and coded hazard (H) and precautionary (P) statements on labels and safety data sheets. The US adopted GHS into law through OSHA's 2012 Hazard Communication Standard update.
Good Faith Reduction: A reduction of up to 25% that OSHA may apply to a proposed penalty when an employer demonstrates a genuine, effective commitment to safety — chiefly a documented, implemented safety and health management program. It's one of three serial penalty reductions (size, good faith, history) OSHA applies to the Gravity-Based Penalty.
Guardrail System: A passive fall-protection barrier — a top rail, a midrail, and (where needed) a toeboard — installed along unprotected edges, holes, and elevated platforms. Under 29 CFR 1926.502(b), the top rail sits 42 inches (±3 inches) above the surface and must withstand a 200-pound force without deflecting below 39 inches; the midrail must withstand 150 pounds.

H

Hazard Category: The division of severity within a GHS hazard class. Within a class, Category 1 is the most severe, with higher numbers less severe; some classes add sub-categories (1A, 1B). Categories compare severity only inside the same class — a Category 1 flammable is not “as bad as” a Category 1 carcinogen.
Hazard Class: The nature of a hazard a chemical presents — for example flammable liquid, oxidizer, acute toxicity, carcinogenicity, or aquatic toxicity. GHS groups hazard classes into physical, health, and environmental hazards (roughly 29 classes in Revision 7). A single chemical can fall into several hazard classes at once.
Hazard Communication Standard (HCS): OSHA's standard (29 CFR 1910.1200) requiring that the hazards of all chemicals produced or imported are classified, and that the information is passed to employers and workers through labels, safety data sheets, and training. It is built on six pillars — a written program, a chemical list, labels, SDSs, training, and access — and is aligned with the GHS.
Hazard Statement (H-code): A standardized phrase, with a fixed H-code, that describes the nature and degree of a chemical's hazard — for example H225, “Highly flammable liquid and vapor.” The wording is set by GHS and assigned to a specific hazard class and category, so the same hazard reads identically on every compliant label and SDS.
Hazardous Energy: Any source of electrical, mechanical, hydraulic, pneumatic, chemical, thermal, or other energy in machines or equipment that can cause injury during servicing or maintenance if released unexpectedly. Under OSHA's Control of Hazardous Energy standard (29 CFR 1910.147, 'Lockout/Tagout'), equipment is 'energized' when connected to an energy source OR when it contains residual or stored energy. The standard requires that all such energy be isolated, locked out or tagged out, and verified as controlled before an authorized employee begins work.
Hazardous to the Aquatic Environment (Aquatic Toxicity): A GHS environmental hazard class describing a chemical's potential to harm aquatic life. It has two forms: ACUTE (short-term) aquatic toxicity, classified into Categories 1–3 from the concentration lethal or immobilizing to test organisms; and CHRONIC (long-term) aquatic toxicity, classified into Categories 1–4 from toxicity combined with environmental fate (degradation and bioaccumulation). Classification uses fish 96-hour LC50, crustacea 48-hour EC50, and algae 72/96-hour ErC50 data. It uses the GHS09 (environment) pictogram — but OSHA does NOT require environmental hazard classification, because it falls outside OSHA's human-health jurisdiction.
Hazardous Waste: A solid waste that is dangerous to human health or the environment and is regulated under the federal Resource Conservation and Recovery Act (RCRA), administered by the EPA (40 CFR Part 261). A waste is hazardous if it either exhibits one of four CHARACTERISTICS — ignitability (D001), corrosivity (D002), reactivity (D003), or toxicity (D004–D043, via the TCLP test) — or appears on one of the LISTED-waste lists: F (non-specific source), K (specific source), or P and U (discarded commercial chemical products, with P being acutely hazardous). Worker protection during hazardous-waste operations and emergency response is governed separately by OSHA's HAZWOPER standard (29 CFR 1910.120).
HazCom Program: The written hazard communication program that 29 CFR 1910.1200(e) requires every employer with hazardous chemicals to develop, implement, and maintain at each workplace. It documents how the employer meets the three pillars of HazCom — labels and warnings, safety data sheets (SDSs), and employee information and training — and includes a list of the hazardous chemicals known to be present, tied to their SDSs by product identifier.
HCS 2024 Compliance Deadlines: The phased dates by which the 2024 update to OSHA's Hazard Communication Standard (aligning with GHS Revision 7) must be met. A January 15, 2026 final rule (FR Doc. 2026-00653 (Jan 15, 2026), +4 months) extended every original deadline by four months — these are the dates now in force under 29 CFR 1910.1200(j): substances — manufacturers, importers, and distributors by May 19, 2026 (j)(2)(i); substances — employers (as necessary: alternative workplace labeling used under (f)(6), written program, and training for newly identified hazards) by November 20, 2026 (j)(2)(ii); mixtures — manufacturers, importers, and distributors by November 19, 2027 (j)(3)(i); mixtures — employers by May 19, 2028 (j)(3)(ii). During the interim, parties may comply with the 2012 HCS, the 2024 HCS, or both.
Hearing Conservation Program: A program 29 CFR 1910.95 requires in general industry whenever a worker's noise exposure equals or exceeds an 85 dBA 8-hour TWA — the "action level." It includes noise monitoring, audiometric (hearing) testing, hearing protectors, training, and recordkeeping, and its goal is to catch and prevent noise-induced hearing loss before it becomes permanent. Note the two thresholds: the program triggers at the 85 dBA action level, which sits below the 90 dBA permissible exposure limit.
Heat Illness Prevention: As of 2026, there is no final federal OSHA heat-illness standard. Heat hazards are enforced through the General Duty Clause (OSH Act Section 5(a)(1)) and OSHA's Heat National Emphasis Program (NEP, Directive CPL 03-00-024). OSHA has issued a proposed rule (NPRM, 89 FR 70698, Aug 30, 2024) that would establish heat-index triggers of 80°F (initial) and 90°F (high heat) for both outdoor and indoor workplaces. Until finalized, the 'Water. Rest. Shade.' campaign and OSHA-NIOSH Heat Safety Tool represent the enforcement-relevant guidance. No final federal OSHA heat standard as of 2026. A proposed rule (89 FR 70698, Aug 30, 2024) would set heat-index triggers of 80°F (initial) and 90°F (high heat). Until finalized, heat hazards are enforced under the General Duty Clause 5(a)(1) and OSHA's Heat NEP.
Hexavalent Chromium: A toxic form of the metal chromium (chromium in the +6 oxidation state, "Cr(VI)") that is a confirmed carcinogen and a potent respiratory and skin irritant. It is produced during welding on stainless steel, chrome electroplating, and the use of chromate pigments and coatings. OSHA regulates Cr(VI) under 29 CFR 1926.1126 (construction) and 1910.1026 (general industry) with a permissible exposure limit of 5 µg/m³ as an 8-hour TWA and an action level of 2.5 µg/m³.
Hierarchy of Controls: NIOSH's framework for choosing hazard controls, ranked from most to least effective: Elimination, Substitution, Engineering controls, Administrative controls, and Personal Protective Equipment (PPE). The top levels are more effective because they reduce the hazard itself without relying on worker behavior; PPE is the last resort, not the first.
Hot Work Permit: A written authorization, issued after a pre-work inspection, to perform welding, cutting, brazing, grinding, or other spark- or flame-producing operations in an area where fire or explosion hazards may exist. Under OSHA's welding and cutting standard (29 CFR 1910.252), the individual responsible for authorizing the work must inspect the area, confirm fire prevention precautions are in place, and designate the precautions — preferably as a written permit. The permit documents the location, the safeguards, the fire watch, and the authorization to proceed.

I

IDLH: Immediately Dangerous to Life or Health — an airborne exposure level that poses an immediate threat to life, would cause irreversible or delayed permanent health effects, or would impair a worker's ability to escape. IDLH values are set by NIOSH using a 30-minute maximum escape time as a safety margin, and they decide where only the most protective respirators may be used.
Imminent Danger: A workplace condition or practice where a danger exists that could reasonably be expected to cause death or serious physical harm immediately — or before it could be eliminated through OSHA's normal enforcement procedures. It's OSHA's highest-priority situation: workers can request an immediate inspection, and OSHA can go to federal court to shut the hazard down.
Industrial Hygiene: The science and practice of protecting worker health by anticipating, recognizing, evaluating, controlling, and confirming protection from workplace hazards (the ARECC framework). Industrial hygienists (IHs/CIHs) assess exposures to chemical, physical, biological, and ergonomic stressors — running air sampling, comparing results to limits like PELs and TLVs, and recommending controls.
Informal Conference: An optional meeting between an employer and the OSHA Area Director, held after a citation is issued, to discuss the citation, penalties, abatement dates, or the facts of the case — and often to reach an informal settlement. It should be requested within the 15-working-day response window, but it does NOT extend the deadline to file a formal Notice of Contest.
Injury Tracking Application (ITA): OSHA's secure online portal for the electronic submission of workplace injury and illness records required under 29 CFR 1904.41. Annual submissions are due by March 2 each year for prior-calendar-year data. As amended by the July 21, 2023 final rule (effective 2024-01-01), there are three tiers: (1) 20–249 employees in an Appendix A (Subpart E) industry — submit Form 300A (summary only); (2) 100+ employees in an Appendix B (Subpart E) high-hazard industry (construction: NAICS 2381 only) — submit Forms 300, 301, and 300A; (3) 250+ employees not in a partially-exempt (Subpart B App A) industry — submit Form 300A (summary only). From construction, the Tier B high-hazard list reaches only NAICS 2381 (Foundation, Structure and Building Exterior Contractors); the rest of NAICS 23 is on Appendix A and submits the summary alone.

J

Job Hazard Analysis (JHA): A systematic technique (OSHA Publication 3071) that breaks a job into its individual steps, identifies the hazards associated with each step, and determines controls to eliminate or reduce them. It focuses on the relationship between the worker, the task, the tools, and the work environment. Also called a Job Safety Analysis (JSA).

L

LC50: Lethal Concentration 50 — the concentration of a substance in air (or in water, for aquatic tests) that kills 50% of a test population over a set exposure time, typically a 4-hour inhalation exposure. It's the inhalation counterpart to the LD50 and is used to classify acute inhalation toxicity. A lower LC50 means a more toxic substance, because it takes less in the air to be lethal.
LD50: Lethal Dose 50 — the single dose of a substance that kills 50% of a test population, expressed in milligrams of substance per kilogram of body weight (mg/kg). It's used to classify acute oral and dermal toxicity. A lower LD50 means a more toxic substance: it takes less to be lethal. Under HazCom, oral LD50 cut-offs define Categories 1 (≤ 5 mg/kg, most toxic) through 4 (≤ 2000 mg/kg).
Lead: A toxic heavy metal that accumulates in the body and damages the nervous system, kidneys, blood, and reproductive system. Occupational lead exposure is common in construction (demolition, renovation of painted surfaces, welding/cutting coated steel, bridge work) and in general industry (battery manufacturing, smelting, radiator repair). OSHA sets a permissible exposure limit of 50 µg/m³ as an 8-hour TWA and an action level of 30 µg/m³, under 29 CFR 1926.62 (construction) and 1910.1025 (general industry). A distinctive feature is Medical Removal Protection (MRP): workers with elevated blood lead levels must be removed from exposure with their earnings and benefits protected.
Leading Edge: The edge of a floor, roof, or formwork that changes location as additional sections are placed, formed, or constructed — for example the advancing edge of a roof deck as sheets are laid. It's a moving, often unprotected drop-off. OSHA requires workers constructing a leading edge 6 feet or more above a lower level to be protected by a guardrail, safety net, or personal fall arrest system.
LEL / LFL: Lower Explosive Limit (LEL), also called Lower Flammable Limit (LFL): the minimum concentration of a gas or vapor in air — by volume — that can ignite. Below the LEL the mixture is too lean to burn; between the LEL and the UEL it is flammable. Gas meters read in “% LEL,” and OSHA's confined-space rule treats 10% of the LEL as a hazardous atmosphere.
LOTO (Lockout/Tagout): Procedures that isolate and de-energize machines during servicing and maintenance so they can't unexpectedly start up or release stored energy. Lockout applies a physical lock to an energy-isolating device; tagout applies a warning tag; lockout is preferred. Important scope note: the general-industry LOTO standard, 29 CFR 1910.147, explicitly excludes construction — construction energy control is enforced under 1926.417, 1926.702(j), Subpart V, and the General Duty Clause.

M

Material Safety Data Sheet (MSDS): The legacy hazard-communication document that preceded today's Safety Data Sheet (SDS). Before OSHA aligned the Hazard Communication Standard with the Globally Harmonized System (GHS) in 2012, MSDSs had no mandated section order or format, so information appeared in inconsistent places from one manufacturer to the next. The 2012 HazCom update replaced the MSDS with the standardized 16-section SDS. Under the transition schedule, compliance with all modified provisions — including GHS-aligned 16-section SDSs — was due June 1, 2015, with the phase-in closing June 1, 2016. The term 'MSDS' is now obsolete, though it persists in older files and everyday speech.
Medical Surveillance: An ongoing program of employer-provided medical exams and tests for workers exposed to specific hazards, required by substance-specific OSHA standards (silica, lead, asbestos, benzene, cadmium, and others). Its purpose is to detect early, often reversible signs of occupational disease — before permanent harm — and to determine fitness for tasks like respirator use. It's provided at no cost, on work time, and performed by or under a licensed health care professional (PLHCP), with results kept confidential.
Multi-Employer Worksite: A worksite where employees of more than one employer are present, the norm on construction projects. Under OSHA's Multi-Employer Citation Policy (CPL 02-00-124), more than one employer can be cited for a single hazard, based on four roles: the creating, exposing, correcting and controlling employer. A general contractor can be cited for a subcontractor's hazard when it failed to use reasonable care to prevent and detect it.
Mutagenicity: A GHS health-hazard class (formally “germ cell mutagenicity”) for chemicals that can cause heritable genetic mutations — changes in the DNA of egg or sperm cells that can be passed to offspring. GHS sorts it into Category 1A (known), 1B (presumed), and Category 2 (suspected). Mutagens carry the health-hazard pictogram (GHS08).

N

National Emphasis Program (NEP): An OSHA enforcement initiative that concentrates inspection resources on a specific high-hazard industry, process, or substance for a set period. NEPs are how OSHA proactively targets known killers — silica, heat, amputations, combustible dust — driving programmed inspections and specific inspection procedures rather than waiting for a complaint.
Near Miss: An unplanned event that did not result in injury, illness, or damage — but had the potential to do so. Near misses (also called “close calls” or “near hits”) are a leading indicator of safety performance: reporting and investigating them lets you fix hazards before they cause harm. They are distinct from lagging indicators like recorded injuries.
NFPA 704 Diamond: The NFPA “fire diamond” — a four-quadrant placard that gives emergency responders an at-a-glance sense of a material's hazards: blue (health), red (flammability), and yellow (instability/reactivity) each rated 0 (minimal) to 4 (severe), plus a white quadrant for special hazards (like OX for oxidizer or W̶ for water-reactive). It's for responders at fixed installations — a different system from GHS labels.
NIOSH: The National Institute for Occupational Safety and Health — the federal research agency, part of the CDC, created by the same 1970 OSH Act that created OSHA. NIOSH conducts research and makes recommendations to prevent work-related injury and illness; it publishes Recommended Exposure Limits (RELs), IDLH values, the Pocket Guide to Chemical Hazards, and approves respirators. It does not write or enforce standards — that is OSHA's role.
Noise Exposure: OSHA's Permissible Exposure Limit (PEL) for occupational noise is 90 dBA as an 8-hour Time-Weighted Average (TWA) in both general industry (29 CFR 1910.95) and construction (29 CFR 1926.52). In general industry, an 85 dBA TWA action level triggers mandatory hearing conservation program requirements — monitoring, baseline and annual audiometric testing, hearing protection, and training. In construction, the 85 dBA action level is a NIOSH-recommended best practice, not a codified construction standard requirement. Both standards use a 5-dB exchange rate: for every 5 dB increase in noise level, the permissible exposure time is halved.

O

Occupational Exposure Limit (OEL): An umbrella term for any limit — regulatory or recommended — on a worker's airborne exposure to a hazardous substance over a defined period. An OEL isn't a single number or a single authority: it covers OSHA's enforceable Permissible Exposure Limits (PELs), NIOSH's Recommended Exposure Limits (RELs), and ACGIH's Threshold Limit Values (TLVs). Most OELs are expressed as an 8- (or 10-) hour time-weighted average, sometimes with short-term or ceiling limits.
Occupational Illness: Any abnormal condition or disorder — other than one caused by a physical injury — that results from exposure to factors associated with employment, whether by inhalation, absorption, ingestion, or direct contact. On the OSHA 300 Log, recordable illnesses are grouped into categories such as skin disorders, respiratory conditions, poisoning, hearing loss, and all other illnesses.
Opening Conference: The meeting that starts an OSHA inspection. The compliance officer presents credentials, explains why the establishment was selected and the scope of the inspection, describes the walkaround procedures and employee-representation rights, and answers questions — before beginning the walkaround. It's the employer's first chance to understand and shape how the inspection will proceed.
Organic Peroxide: A liquid or solid organic chemical containing the unstable bivalent –O–O– (peroxide) structure. Organic peroxides are thermally unstable and can undergo exothermic self-accelerating decomposition — meaning they generate their own heat and can accelerate toward fire or explosion, sometimes without any external ignition. GHS classifies them into seven types (A through G) by how violently they react; many require temperature control during storage.
OSHA 300 Log: The Log of Work-Related Injuries and Illnesses (Form 300) — the running list where an employer records each recordable case during the year, with a one- or two-line description and a classification of the outcome (death, days away, restricted/transfer, or other). It must be kept for 5 years and updated as cases develop.
OSHA 300A: The annual Summary of Work-Related Injuries and Illnesses (Form 300A) — the year-end totals from the 300 Log. A company executive must certify it, and it must be posted in the workplace from February 1 through April 30 of the following year. Covered establishments must also submit it electronically to OSHA by March 2.
OSHA 301: The Injury and Illness Incident Report (Form 301) — the detailed record behind a single recordable case. It captures what happened, the body part affected, the object/substance involved, and the treatment, and must be completed within 7 calendar days of learning of a recordable case. It's the third of OSHA's three recordkeeping forms, alongside the 300 Log and 300A summary.
OSHRC: The Occupational Safety and Health Review Commission — an independent federal agency, separate from OSHA and the Department of Labor, that adjudicates disputes when an employer contests an OSHA citation or proposed penalty. Created by the Occupational Safety and Health Act of 1970, OSHRC provides two levels of review: a case is first heard by an Administrative Law Judge (ALJ), whose decision becomes final after 30 days unless one of the three presidentially-appointed Commissioners directs review by the full Commission. Commission decisions may then be appealed to a U.S. Court of Appeals.
Other-Than-Serious Violation: An OSHA violation that has a direct relationship to job safety and health but is not likely to cause death or serious physical harm. Unlike a serious violation, its penalty is discretionary — OSHA may propose up to $16,550, but often reduces it, sometimes to zero. It sits between a de minimis violation (no penalty) and a serious violation (mandatory penalty).
Oxidizer: A chemical that can cause or intensify a fire — generally by yielding oxygen — even though it may not burn itself. GHS classifies oxidizing gases, liquids, and solids as separate hazard classes, all using the flame-over-circle pictogram (GHS03). Oxidizing gases are Category 1; oxidizing liquids and solids span Categories 1–3.

P

Penalty: The monetary fine OSHA proposes for a violation. In 2026, maximums are $16,550 per serious or other-than-serious violation and $165,514 per willful or repeated violation — unchanged from 2025 (no CPI adjustment). The proposed amount starts from a Gravity-Based Penalty (severity × probability) and is then reduced for employer size, good faith, and inspection history.
Permissible Exposure Limit (PEL): The maximum amount or concentration of a chemical (or other harmful agent) a worker may legally be exposed to under OSHA regulations, almost always expressed as an 8-hour time-weighted average (TWA). Example: the PEL for respirable crystalline silica is 50 µg/m³ as an 8-hour TWA (29 CFR 1926.1153).
PFAS (Personal Fall Arrest System): A fall-arrest system made of an anchorage, a full-body harness, and a connector (lanyard or self-retracting lifeline), plus a deceleration device. Under 29 CFR 1926.502(d) it must limit the maximum arresting force on the worker to 1,800 lbf, allow a free fall of no more than 6 feet (and no contact with a lower level), and limit deceleration distance to 3.5 feet.
pH: A measure of how acidic or alkaline (basic) a water-based solution is, on a scale from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic. The scale is logarithmic — each whole number is a tenfold change in acidity. In chemical safety, extreme pH matters: GHS treats a pH of 2 or lower, or 11.5 or higher, as a signal that a substance may be corrosive to skin. It's reported in Section 9 of a Safety Data Sheet.
Pictogram: A GHS hazard symbol — a black image on a white background inside a red diamond-shaped frame — that conveys a chemical's hazard at a glance on labels and SDSs. The UN GHS system defines 9 pictograms (GHS01–GHS09), but OSHA's HazCom Standard requires only 8 on US workplace labels; GHS09 (Environment) is outside OSHA's jurisdiction and is voluntary. A red frame with no symbol inside is prohibited.
Powered Air-Purifying Respirator (PAPR): An air-purifying respirator that uses a battery-powered blower to draw ambient air through filters or cartridges and deliver it to the wearer. Because the blower supplies air, a PAPR maintains positive pressure inside the facepiece/hood, reducing inward leakage and breathing effort. PAPRs come in tight-fitting (facepiece) and loose-fitting (hood/helmet) forms with different assigned protection factors: a loose-fitting PAPR/hood has an APF of 25, while a tight-fitting full-facepiece PAPR can reach an APF of 1,000. Like all air-purifying respirators, a PAPR does NOT protect against oxygen-deficient or IDLH atmospheres.
PPE (Personal Protective Equipment): Equipment worn to protect a worker from injury or illness when a hazard can't be fully eliminated — gloves, safety glasses and face shields, respirators, hearing protection, hard hats, and protective footwear. In the hierarchy of controls, PPE is the last line of defense: it doesn't remove the hazard, it only reduces the wearer's exposure. OSHA (1910.132) requires employers to assess hazards, select appropriate PPE, and generally provide it at no cost to employees.
Precautionary Statement (P-code): A standardized phrase, with a fixed P-code, that tells the user what to do about a chemical's hazard — how to prevent harm, respond to an incident, store it, and dispose of it. The wording is fixed and must be reproduced in full: P210 is “Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.” — not a shortened paraphrase of it. GHS groups P-codes into five families (general, prevention, response, storage, disposal).
Process Safety Management (PSM): OSHA's standard (29 CFR 1910.119) for preventing catastrophic releases of highly hazardous chemicals — toxic, reactive, flammable, or explosive substances that can cause a major fire, explosion, or toxic cloud. PSM applies when a process involves a listed highly hazardous chemical at or above its threshold quantity (Appendix A), or a Category 1 flammable gas or a flammable liquid (flashpoint below 100°F) present in one location at 10,000 pounds or more. It requires an integrated program of 14 interrelated elements, from process hazard analysis to mechanical integrity to management of change.
Product Identifier: The name or number used to identify a hazardous chemical on its label and in its SDS — a chemical name, trade name, code, or CAS number. Under 29 CFR 1910.1200 it must be identical on the container label and in Section 1 of the SDS, so a worker can cross-reference the two and the chemical inventory.
Programmed Inspection: An OSHA inspection selected in advance using objective criteria — high injury/illness rates, a National or Local Emphasis Program, or neutral scheduling plans — rather than being triggered by a specific event or complaint. Programmed inspections are the lowest of OSHA's four inspection priorities, coming after imminent danger, fatalities/catastrophes, and complaints/referrals.
Pyrophoric: A chemical that ignites spontaneously in air — no spark or flame needed. Under GHS/HazCom, a pyrophoric liquid or solid is one liable to ignite within five minutes after coming into contact with air, even in small quantities. (A pyrophoric gas ignites spontaneously in air at or below 54°C.) Pyrophorics carry the GHS02 flame pictogram and demand inert handling (nitrogen/argon blanketing).

Q

Qualified Person: In OSHA construction terms (29 CFR 1926.32(m)), a qualified person is someone who — by a recognized degree, certificate, or professional standing, or by extensive knowledge, training, and experience — has demonstrated the ability to solve or resolve problems relating to the subject matter, the work, or the project. The defining trait is expertise. It's distinct from a “competent person,” whose defining trait is the authority to identify hazards and take prompt corrective action.

R

Readily Accessible: The OSHA requirement that safety data sheets be readily accessible to employees during each work shift, in their work areas (29 CFR 1910.1200(g)(8); adopted for construction by 1926.59). “Readily accessible” means without barriers or unreasonable delay — electronic access is allowed, but only with reliable backup for power or system failures and no obstacle between the worker and the SDS.
Recognized Hazard: A workplace hazard that is known to be dangerous — recognized by the specific employer, by the industry generally, or by common sense. “Recognition” is the linchpin element of a General Duty Clause citation: OSHA can only cite an uncovered hazard under 5(a)(1) if it can show the hazard was recognized.
Recommended Exposure Limit (REL): An occupational exposure limit recommended by NIOSH to protect workers from a hazardous substance. Unlike an OSHA PEL, a REL is not legally enforceable — NIOSH is a research agency, not an enforcement one — but RELs are often more protective because they reflect newer science. A NIOSH REL is typically a time-weighted average for up to a 10-hour workday during a 40-hour workweek, sometimes with a short-term (STEL) or ceiling limit.
Recordable Injury: A work-related injury or illness an employer must enter on the OSHA 300 Log because it meets one of the general recording criteria in 29 CFR 1904.7: death, days away from work, restricted work or job transfer, medical treatment beyond first aid, loss of consciousness, or a significant injury/illness diagnosed by a physician or licensed health care professional.
Repeat Violation: A violation of any OSHA standard where the employer has already been cited for a substantially similar condition — and that earlier citation has become a final order — within the past 5 years. Because it signals a pattern, it carries penalties up to $165,514 per violation, the same maximum as a willful violation.
Reproductive Toxicity: A GHS health-hazard class for chemicals that harm sexual function and fertility in adults, or the development of offspring. GHS uses Category 1A (known), 1B (presumed), and Category 2 (suspected), plus a separate category for effects on or via lactation. Reproductive toxicants (Cat 1–2) carry the health-hazard pictogram (GHS08).
Respirable Crystalline Silica: The very fine fraction of crystalline silica dust — particles small enough (generally under about 10 microns) to be inhaled deep into the lungs. It's created when workers cut, grind, drill, or crush silica-containing materials like concrete, stone, brick, and mortar. OSHA's construction standard (29 CFR 1926.1153) sets a permissible exposure limit (PEL) of 50 µg/m³ as an 8-hour TWA and an action level of 25 µg/m³.
Respirator Fit Test: A required test that verifies a tight-fitting respirator forms an adequate seal on a specific worker's face. Under 29 CFR 1910.134(f), a fit test must be performed before the first use of a tight-fitting respirator, whenever a different facepiece (make, model, style, or size) is used, when facial changes could affect the seal, and at least every 12 months (annually). Two methods exist: Qualitative (QLFT), a pass/fail test based on the wearer's sense of taste, smell, or irritation, valid only up to a fit factor of 100; and Quantitative (QNFT), which numerically measures leakage (pass criterion: fit factor ≥ 100 for a half mask, ≥ 500 for a full facepiece). A medical evaluation must precede fit testing.
Respiratory Protection Program: The written, worksite-specific program 29 CFR 1910.134(c) requires wherever respirators are necessary to protect worker health (or the employer requires their use). Administered by a trained program administrator, it must cover respirator selection, medical evaluation, fit testing, proper use, maintenance and care, breathing-air quality, training, and program evaluation. Even voluntary respirator use carries requirements — a medical evaluation (for non-filtering-facepiece respirators) and the Appendix D information sheet.
Respiratory Sensitization: A GHS health-hazard class for chemicals that cause hypersensitivity of the airways after inhalation — that is, occupational asthma. Like skin sensitization it has an induction phase, then once a worker is sensitized even very low concentrations can trigger a severe asthmatic reaction. Respiratory sensitizers carry the health-hazard pictogram (GHS08) and the signal word “Danger.”
Right to Know: The foundational principle that workers have a right to know about the hazardous chemicals they may be exposed to on the job — their identities, hazards, and protective measures. In the U.S. workplace, that right is codified in OSHA's Hazard Communication Standard (1910.1200), which requires labels, safety data sheets, and training. A parallel “community right-to-know” (under EPA's EPCRA) extends similar information to the public and emergency responders.
Risk Assessment: A systematic process for identifying hazards and then evaluating the risk each one poses — combining the likelihood that harm occurs with the severity if it does — so controls can be prioritized. Risk assessment goes a step beyond simply spotting hazards: it judges how bad and how likely, which lets an organization focus effort on the biggest risks first. (OSHA standards more often use the narrower “hazard assessment,” e.g., for PPE under 1910.132(d).)
Root Cause Analysis (RCA): A structured investigation method that identifies the fundamental, underlying, system-related reason an incident (or near miss) occurred — not just its immediate symptom. OSHA and EPA both urge employers to perform RCA after incidents, because fixing only the immediate cause treats a symptom while leaving the real problem in place. Common techniques include the “5 Whys” and the Fishbone (Ishikawa) diagram.

S

Safety Culture: The shared values, beliefs, attitudes, and behaviors that determine how an organization actually manages safety — beyond what its written policies say. A strong safety culture shows up in leading indicators such as near-miss reporting rates, worker participation, and prompt hazard correction, rather than only in lagging indicators like injury counts after the fact. OSHA does not enforce a mandatory 'safety culture' standard; instead it promotes safety-and-health programs built on seven core elements, and recognizes strong programs through voluntary initiatives such as the Voluntary Protection Programs (VPP).
Safety Data Sheet (SDS): A standardized 16-section document the chemical manufacturer, importer, or distributor must provide for every hazardous chemical, detailing its hazards, safe handling, storage, exposure controls, first aid, and emergency information. Its content and order are set by 29 CFR 1910.1200(g) and Appendix D; it replaced the unstandardized MSDS under GHS alignment.
Safety Net: A passive fall protection system — a net installed below a walking/working surface to catch workers (and debris) who fall. OSHA's construction criteria (29 CFR 1926.502(c)) require it to be installed as close as practicable under the surface, but no more than 30 feet below, to extend outward a set distance from the edge, and to have mesh openings and a border rope meeting fixed limits, plus drop-test verification.
SARA (Superfund Amendments and Reauthorization Act): The 1986 federal law that amended and expanded CERCLA (Superfund). Its most important piece for chemical safety is Title III — the Emergency Planning and Community Right-to-Know Act (EPCRA) — which created the emergency planning, hazardous-chemical inventory, and Toxic Release Inventory reporting programs. When people say “SARA Title III,” they mean EPCRA.
Scaffold: A temporary elevated platform (and its supporting structure) used to hold workers, materials, and equipment during construction. Under OSHA Subpart L, every scaffold must support its own weight plus at least 4 times the maximum intended load, be inspected by a competent person before each work shift, and provide fall protection for workers more than 10 feet above a lower level.
Secondary Container: A workplace container that a hazardous chemical is transferred into from the original, manufacturer-labeled (primary) container — for example a spray bottle, bucket, or drum you fill on site. Under HazCom (29 CFR 1910.1200(f)(6)), it must be labeled with either the full GHS label information or, at minimum, the product identifier plus words/pictures/symbols conveying the hazards — unless it qualifies for the “immediate use” exemption.
Section 1: Identification: The first section of a Safety Data Sheet. It identifies the chemical and who's responsible for it: the product identifier (matching the label), recommended use and restrictions, the manufacturer/importer's name, address, and phone, and — critically — an emergency phone number. It's the section a responder reads first to confirm they have the right SDS.
Section 10: Stability & Reactivity: The SDS section on the chemistry of danger: whether the chemical is stable, what could make it react hazardously, the conditions to avoid (heat, shock, static, moisture), the materials it's incompatible with, and the hazardous products it can decompose into. It's the technical basis for safe storage and handling decisions.
Section 11: Toxicological Information: The SDS section with the detailed health-effects data behind the hazards: the likely routes of exposure, the symptoms and immediate/delayed/chronic effects, numerical toxicity measures (LD50/LC50 or acute toxicity estimates), and whether the chemical is listed as a carcinogen by NTP, IARC, or OSHA. It's the reference physicians and hygienists rely on.
Section 12: Ecological Information: The SDS section on the chemical's effect on the environment: its ecotoxicity (harm to aquatic and other organisms), how persistent and degradable it is, its potential to bioaccumulate, its mobility in soil, and other adverse effects. It is one of the four sections (12–15) that OSHA does not enforce, because environmental protection is outside OSHA's jurisdiction, and Appendix D makes it optional rather than mandatory — but nearly every SDS includes it.
Section 13: Disposal Considerations: The SDS section on getting rid of the chemical safely: recommended waste-treatment and disposal methods for the product and its contaminated packaging, and any special precautions. It's one of sections 12–15 that OSHA does not enforce (disposal is the EPA's jurisdiction) and that Appendix D makes optional rather than mandatory — though nearly every SDS carries it.
Section 14: Transport Information: The SDS section for shipping the chemical: its classification for transport under DOT, IATA (air), and IMDG (sea) — the UN number, proper shipping name, transport hazard class, packing group, and any environmental hazards (e.g., marine pollutant) or special precautions. Like sections 12–15, OSHA does not enforce its content.
Section 15: Regulatory Information: The SDS section listing the safety, health, and environmental regulations specific to the chemical that aren't covered elsewhere on the sheet — for example SARA Title III (302/311/312/313), CERCLA reportable quantities, TSCA inventory status, and state right-to-know or California Prop 65 listings. It's one of sections 12–15 OSHA doesn't enforce.
Section 16: Other Information: The final SDS section. It holds the housekeeping and traceability information: the date the SDS was prepared or last revised, an indication of what changed from the previous version, a key to any abbreviations and acronyms used, and the references or data sources. Unlike sections 12–15, Section 16 is OSHA-enforced.
Section 2: Hazard Identification: The SDS section that states what's dangerous about the chemical: its GHS hazard classification (each hazard class and category), all the required label elements (pictograms, signal word, hazard statements, precautionary statements), and any hazards not otherwise classified (HNOC). It's the fastest read for “how could this hurt me?”
Section 3: Composition / Information on Ingredients: The SDS section that discloses what the chemical is made of: the chemical name, common names/synonyms, CAS number, and concentration (or concentration range) of the substance or of each hazardous ingredient in a mixture. Any ingredient that contributes to a classified hazard must be listed, subject to limited trade-secret protection.
Section 4: First-Aid Measures: The SDS section that tells you what to do if someone is exposed. It gives first-aid instructions broken out by route of exposure — inhalation, skin, eye, and ingestion — plus the most important symptoms (immediate and delayed) and any indication of the need for immediate medical attention or special treatment. It's the section to open in a medical emergency.
Section 5: Fire-Fighting Measures: The SDS section written for anyone fighting a fire involving the chemical. It lists suitable and unsuitable extinguishing media, the specific hazards the chemical creates in a fire (toxic combustion products, explosion risk, reactivity), and the special protective equipment and precautions firefighters need. It's a key reference for the fire department's pre-planning.
Section 6: Accidental Release Measures: The SDS section that tells you how to handle a spill or leak. It covers personal precautions, protective equipment, and emergency procedures (protecting people first), environmental precautions (keeping it out of drains and waterways), and the methods and materials for containment and cleanup. It's the spill-response playbook for the chemical.
Section 7: Handling & Storage: The SDS section on how to work with and store the chemical safely day to day. It covers precautions for safe handling (hygiene practices, avoiding ignition sources or incompatible conditions) and conditions for safe storage — temperature, ventilation, container type, and, importantly, which materials it must be kept away from (incompatibilities).
Section 8: Exposure Controls / Personal Protection: The SDS section that tells you how to keep exposure safe. It lists the applicable occupational exposure limits (OSHA PELs, ACGIH TLVs, and any manufacturer-recommended limits), the appropriate engineering controls (like ventilation), and the individual protection measures — the specific PPE (gloves, eye/face, respirator) for handling the chemical. It's the section a safety pro uses to build a control plan.
Section 9: Physical & Chemical Properties: The SDS section that lists the chemical's measurable physical and chemical properties — appearance, odor, pH, melting/boiling point, flash point, flammable (explosive) limits, vapor pressure and density, relative density, solubility, auto-ignition and decomposition temperatures, and viscosity. These numbers underpin the hazard classification and tell you how the chemical will behave.
Self-Classification: The approach OSHA's HazCom standard takes to hazard classification: each chemical manufacturer or importer must evaluate the available scientific evidence and classify its own chemicals against the GHS criteria — rather than relying on a government-published list of classifications. Two companies must reach the same result for the same data, but each does its own classifying.
Self-Contained Breathing Apparatus (SCBA): An atmosphere-supplying respirator in which the wearer carries their own breathing-air supply in a cylinder, rather than filtering the surrounding air. Because it does not depend on ambient air quality, an SCBA is the highest level of respiratory protection and is required for the most hazardous atmospheres. A full-facepiece pressure-demand SCBA has the maximum assigned protection factor of 10,000. For IDLH atmospheres, OSHA (29 CFR 1910.134(d)(2)) permits only a full-facepiece pressure-demand SCBA certified for at least a 30-minute service life, or a combination supplied-air respirator with an auxiliary self-contained air supply.
Self-Heating Substance: A solid or liquid chemical — other than a pyrophoric — that reacts with air and, without any energy supply, is liable to self-heat. Unlike a pyrophoric (which ignites within minutes), a self-heating substance ignites only when present in large amounts (kilograms) and after long periods (hours or days), once the rate of internally generated heat outpaces the rate it can escape. GHS assigns Category 1 or 2, with the GHS02 flame pictogram.
Self-Reactive Substance: A GHS/HazCom physical hazard class (Appendix B.8 of 29 CFR 1910.1200) covering thermally unstable liquid or solid chemicals liable to undergo a strongly exothermic decomposition even without the participation of oxygen (air). Self-reactive substances are sorted into seven types, A through G, by how violently they react when heated or confined: Type A can detonate or deflagrate rapidly as packaged, while Type G is thermally stable and shows no hazardous reaction. Types with explosive or fire properties carry the GHS01 (exploding bomb) and/or GHS02 (flame) pictogram.
Serious Eye Damage / Eye Irritation: A GHS/HazCom health hazard class (Appendix A.3 of 29 CFR 1910.1200) covering effects on the eye from a chemical. It is split by reversibility: Category 1 (serious eye damage) is the production of tissue damage or serious physical decay of vision that is NOT fully reversible within about 21 days; Category 2 (eye irritation) is a reversible change that fully resolves within 21 days, with subcategory 2A (irritating) and 2B (mildly irritating, reversible within 7 days). Category 1 uses the corrosion pictogram (GHS05); Category 2 uses the exclamation-mark pictogram (GHS07).
Serious Violation: An OSHA violation where there is a substantial probability that death or serious physical harm could result, and the employer knew or, with reasonable diligence, should have known about the hazard. It carries a mandatory penalty up to $16,550 per violation and is the classification behind most OSHA citations.
Shoring: An excavation protective system that braces the walls in place — with hydraulic, pneumatic, mechanical, or timber supports — to prevent a cave-in. Unlike a trench box (which protects the worker after a collapse), shoring actively holds the soil back so it doesn't move. It's one of OSHA's accepted Subpart P systems.
Signal Word: A single standardized word on a GHS label that signals the relative severity of a chemical's hazard. GHS uses only two — “Danger” for more severe hazards and “Warning” for less severe ones. Only one signal word appears on a label: “Danger” if any hazard class on the product warrants it.
Silicosis: An incurable, irreversible fibrotic lung disease caused by inhaling respirable crystalline silica. Scar tissue forms in the lungs and progressively stiffens them, reducing the ability to breathe. It has three forms — chronic, accelerated, and acute — and can keep progressing even after exposure stops. It is preventable but has no cure.
Simple Asphyxiant: A hazard classification, unique to OSHA's Hazard Communication Standard (29 CFR 1910.1200), for a substance or mixture that displaces oxygen in the ambient atmosphere and can thereby cause oxygen deprivation — leading to unconsciousness and death by suffocation. Simple asphyxiants have no chemical toxicity of their own; the danger is purely that they crowd out breathable oxygen. Any gas that is a simple asphyxiant must be labeled with the signal word 'Warning' and the hazard statement 'May displace oxygen and cause rapid suffocation.'
Site-Specific Targeting (SST): OSHA's primary programmed-inspection plan for non-construction (general industry) establishments with 20 or more employees. SST uses the Form 300A injury and illness data — principally the DART rate — that employers submit through the Injury Tracking Application (ITA) to build inspection lists. Establishments are selected in several categories: those with high injury/illness rates, those with rates trending sharply upward, a sample of low-rate establishments for quality control, and establishments that failed to submit their required 300A data. The program is governed by a periodically reissued CPL directive (most recently updated in 2025).
Skin Corrosion: A GHS health-hazard class for chemicals that cause irreversible damage to the skin — visible necrosis through the epidermis into the dermis — after up to 4 hours of contact. Corrosion is Category 1 (sub-divided 1A/1B/1C by how fast it acts); the milder, reversible effect is skin irritation (Category 2). Corrosives carry the corrosion pictogram (GHS05).
Skin Sensitization: A GHS health-hazard class for chemicals that cause an allergic skin reaction (allergic contact dermatitis) after skin contact. The first exposure “induces” the allergy; later exposures “elicit” the reaction, so once a worker is sensitized even small amounts can trigger it. Skin sensitizers carry the exclamation-mark pictogram (GHS07).
Sloping: An excavation cave-in protective system that cuts the trench walls back at an angle inclined away from the excavation so they can't collapse inward. The maximum allowable slope depends on the soil type — steeper for stable soil, flatter for loose soil: Type A 3/4:1 (53°), Type B 1:1 (45°), Type C 1½:1 (34°).
Soil Classification: The system OSHA uses (29 CFR 1926 Subpart P, Appendix A) to categorize excavation soil by stability, so a competent person can choose the correct protective system. The four categories — Stable Rock, Type A, Type B, and Type C — are keyed mainly to unconfined compressive strength: Type A is the most stable (≥1.5 tsf), Type C the least (≤0.5 tsf). Weaker soil requires flatter sloping or stronger shoring.
STEL (Short-Term Exposure Limit): A 15-minute time-weighted average exposure that should not be exceeded at any time during a workday, even when the 8-hour TWA stays within the PEL. The STEL guards against acute effects (irritation, narcosis, tissue damage) from short, intense exposures that an 8-hour average would mask.
STOT (Specific Target Organ Toxicity): A GHS health-hazard class for chemicals that cause specific, non-lethal damage to particular organs — separate from acute lethality. It splits into STOT — Single Exposure (STOT-SE, Categories 1, 2, 3) and STOT — Repeated Exposure (STOT-RE, Categories 1, 2). Most STOT hazards carry the health-hazard pictogram (GHS08).
Struck-By Hazard: One of OSHA's construction “Focus Four” hazards — injury or death from being hit by a moving object. OSHA groups struck-by into four types: flying (e.g., from a tool or grinder), falling (dropped or wind-blown objects), swinging (loads, booms), and rolling (vehicles, equipment). If the impact alone caused the injury, it's struck-by (not caught-in/between).
Supplemental Label Element: Any non-standardized information a manufacturer adds to a GHS label beyond the six required elements — such as handling directions, fill dates, batch numbers, hazards not otherwise classified, or other regulatory notices (e.g., a California Prop 65 warning). It's allowed, but under OSHA's rules it must not contradict or cast doubt on the required GHS information.

T

Table 1: The chart in OSHA's construction silica standard (29 CFR 1926.1153(c)) titled “Specified Exposure Control Methods When Working With Materials Containing Crystalline Silica.” It pairs 18 common construction tasks with prescribed engineering controls, work practices, and respiratory protection. An employer that fully and properly implements the listed controls for a task is deemed in compliance with the exposure-limit requirement — with no air monitoring needed.
Threshold Limit Value (TLV): An occupational exposure guideline published by the ACGIH (American Conference of Governmental Industrial Hygienists) — the airborne concentration of a substance to which nearly all workers may be repeatedly exposed without adverse effect. TLVs are advisory, not law, and are reviewed yearly, so they are often more current and more protective than OSHA's enforceable PELs.
Tier II Report: The annual hazardous-chemical inventory report required under EPCRA §312 (SARA Title III) for facilities that store hazardous chemicals at or above the reporting thresholds. It lists the chemicals, quantities, and storage locations, and is due by March 1 each year to the State Emergency Response Commission (SERC), the Local Emergency Planning Committee (LEPC), and the local fire department.
Time-Weighted Average (TWA): The average airborne concentration of a substance a worker is exposed to, weighted over a set time — almost always an 8-hour workday. It is how OSHA expresses most PELs (and ACGIH TLVs): brief high exposures and quiet periods are averaged into a single number that is compared to the limit.
Toolbox Talk: A short, informal safety meeting — usually 5 to 15 minutes, held at the jobsite before a shift — focused on one specific hazard or task relevant to that day's work. Also called a tailgate talk or safety briefing. OSHA does not mandate toolbox talks by name, but they're a widely used way to satisfy the employer's duty (29 CFR 1926.21(b)(2)) to instruct workers in recognizing and avoiding hazards.
Trench Box: A prefabricated steel or aluminum structure (also called a shield or trench shield) placed in an excavation to protect workers from a cave-in. Critically, it does NOT prevent a cave-in — it's engineered to withstand the forces of one and keep the workers inside it safe. It's OSHA's “shielding” protective system under Subpart P.
Trenching: Working in a trench — a narrow excavation (narrow relative to its length) made below the ground surface, where the depth is generally greater than the width and the width at the bottom is 15 feet or less. Trenches are the deadliest form of excavation: like all excavations, they require cave-in protection at 5 feet or deeper (unless in stable rock).

U

UEL / UFL: Upper Explosive Limit (UEL), also called Upper Flammable Limit (UFL): the maximum concentration of a gas or vapor in air that will still ignite. Above the UEL, the mixture is too “rich” — too much fuel and not enough oxygen — to burn. Together with the LEL, it defines the flammable range: a mixture only ignites when it falls between the two.
UN Number: A four-digit identification number assigned by the United Nations to hazardous substances and articles for transport (for example, UN1203 for gasoline). It's used worldwide on shipping papers, placards, and packaging to identify what's being transported, and it appears in Section 14 of the SDS alongside the proper shipping name and hazard class.
User Seal Check: A quick check the wearer performs EACH time a tight-fitting respirator is put on, immediately before entering a hazardous area, to confirm the facepiece is seated and sealing properly that day. Under 29 CFR 1910.134(g)(1)(iii) and Appendix B-1, it is done as a negative-pressure check (block the inlet, inhale gently — the facepiece should collapse slightly and hold) and/or a positive-pressure check (block the exhalation valve, exhale gently — the facepiece should bulge slightly and hold without leaking). A user seal check is NOT a substitute for a fit test; it verifies today's donning, not the periodic qualification of the respirator to the wearer.

V

Vapor Pressure: The pressure a substance's vapor exerts when it's in equilibrium with its own liquid (or solid) at a given temperature — a measure of how readily it evaporates. The higher the vapor pressure, the more volatile the chemical, and the more vapor it puts into the air, raising the potential for inhalation exposure and flammable-atmosphere buildup. It's listed in Section 9 of every SDS.
Variance: An official OSHA authorization to deviate from a specific standard's requirements. To get one, an employer must generally show that its alternative conditions, methods, or processes protect workers at least as well as the standard would. OSHA's variance program (29 CFR Part 1905) recognizes four types: temporary, permanent, experimental, and national defense.
Voluntary Protection Programs (VPP): OSHA's programs that recognize employers and worksites with exemplary, effective safety and health management systems. Participants (at the Star, Merit, or Demonstration level) partner with OSHA, must maintain injury and illness rates below their industry's national averages, and are removed from OSHA's programmed inspection list while in good standing.

W

Water-Reactive Substance: Under GHS/HazCom, a solid or liquid chemical that, on contact with water, becomes spontaneously flammable or gives off flammable gases in dangerous quantities. The GHS class is specifically about emitting flammable gas — sodium hitting water releasing hydrogen is the classic case. Three categories rank the hazard by how fast the flammable gas evolves and whether it ignites on its own.
Wet Stacking: A condition in diesel engines — most commonly standby and jobsite generators — in which unburned fuel and carbon soot accumulate in the exhaust system because the engine has run for extended periods at too low a load (typically below about 60% of rated output). At light load, the combustion temperature is too low to burn all the injected fuel, so the excess passes into the exhaust as a wet, oily residue at the exhaust 'stack.' Wet stacking fouls injectors, valves, and the turbocharger, degrades performance and efficiency, and creates a real fire hazard because unburned fuel and soot can ignite in the hot exhaust. It is corrected by running the unit under adequate load — often via a load bank at roughly 75% capacity for several hours.
Whistleblower Protection: Section 11(c) of the OSH Act, which makes it illegal for an employer to fire or otherwise retaliate against a worker for exercising safety and health rights — filing an OSHA complaint, participating in an inspection, reporting an injury, requesting records, or raising a safety concern. A worker who is retaliated against must file an 11(c) complaint with OSHA within 30 days.
Willful Violation: The most serious OSHA classification: a violation the employer commits intentionally and knowingly, or with plain indifference to the law. Penalties range from $11,823 to $165,514 per violation (2026), and a willful violation that causes a worker's death can also trigger criminal prosecution.

Z

Zero Energy State: The verified condition in which all energy sources to a machine or piece of equipment — electrical, mechanical, hydraulic, pneumatic, chemical, thermal, and gravitational — have been isolated, locked out or tagged out, and confirmed to hold no residual or stored energy. Achieving and verifying a zero energy state is the objective of the 29 CFR 1910.147 energy control procedure: the authorized employee must verify isolation and de-energization (1910.147(d)(6)) before any servicing or maintenance begins.

Frequently Asked Questions

What is the difference between GHS and OSHA HazCom?

GHS (Globally Harmonized System) is an international framework for classifying and labeling chemicals. OSHA's Hazard Communication Standard (HCS) is the US regulation that adopted GHS criteria. OSHA HazCom (29 CFR 1910.1200) is the legal requirement; GHS is the classification system it's based on.

How many GHS pictograms does OSHA require?

The UN GHS system defines 9 pictograms — GHS01 (Exploding Bomb), GHS02 (Flame), GHS03 (Flame Over Circle/Oxidizer), GHS04 (Gas Cylinder), GHS05 (Corrosion), GHS06 (Skull and Crossbones), GHS07 (Exclamation Mark), GHS08 (Health Hazard), and GHS09 (Environment) — but OSHA's Hazard Communication Standard requires only 8 on US workplace labels (29 CFR 1910.1200 Appendix C). GHS09 (Environment) covers aquatic/environmental hazards that are outside OSHA's jurisdiction, so it is voluntary on workplace labels, though it commonly appears on shipped containers.

What are the 16 sections of a Safety Data Sheet (SDS)?

The 16 SDS sections are: 1) Identification, 2) Hazard Identification, 3) Composition, 4) First Aid Measures, 5) Firefighting, 6) Accidental Release, 7) Handling & Storage, 8) Exposure Controls/PPE, 9) Physical Properties, 10) Stability & Reactivity, 11) Toxicological Info, 12) Ecological Info, 13) Disposal, 14) Transport, 15) Regulatory Info, 16) Other Information.

What is the OSHA penalty for HazCom violations in 2026?

In 2026, OSHA penalties are up to $16,550 per serious violation and up to $165,514 per willful or repeat violation. HazCom (29 CFR 1910.1200) ranked second on OSHA's FY2025 list of most-cited standards.

What does 'readily accessible' mean for SDS under OSHA?

OSHA requires SDSs to be 'readily accessible during each work shift' per 29 CFR 1910.1200(g)(8) (adopted for construction by 29 CFR 1926.59). This means workers must be able to access SDSs without leaving the work area or experiencing unreasonable delays. Electronic access is acceptable if devices are available and functional at the worksite, with a backup for system or power failures.

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