OSHA’s permissible exposure limits are the legally enforceable caps on how much of an airborne chemical or dust a worker can breathe during a shift, set out in 29 CFR 1910.1000 and covering roughly 400 substances across three reference tables.1Occupational Safety and Health Administration. 29 CFR 1910.1000 – Air Contaminants Exceed a PEL and the employer can be cited. The catch, and it is a serious one: most of these limits have not changed since 1971, and OSHA itself says complying with them does not guarantee that workers are safe.
The Three Kinds of Limits
A PEL is not one number. Depending on the substance, the enforceable limit takes one of three forms, each covering a different slice of time.
8-Hour Time-Weighted Average
The most common form. A TWA averages exposure across a full shift, so a higher-concentration hour in the morning can be balanced by cleaner air later, provided the shift-long average stays under the limit.2Occupational Safety and Health Administration. Standard Interpretation – OSHA’s PELs and the 8-Hour TWA For any Table Z-1 substance not marked with a “C,” the TWA is the controlling limit for an 8-hour shift within a 40-hour week.3eCFR. 29 CFR 1910.1000 – Air Contaminants The purpose is to prevent toxic material from accumulating in the body over years of employment.
Short-Term Exposure Limit
Some chemicals cause acute harm at levels that would still average out safely over a shift. A STEL caps the 15-minute average concentration on its own, independent of the daily TWA.4Centers for Disease Control and Prevention. NIOSH Pocket Guide to Chemical Hazards Introduction A workplace can be well under the TWA and still in violation if any quarter-hour stretch exceeds the STEL.
Ceiling Limit
The strictest category. A substance marked “C” in Table Z-1 has a concentration that may never be exceeded at any instant during the workday. Where instantaneous monitoring isn’t practical, the ceiling is assessed as a 15-minute TWA that still cannot be breached.1Occupational Safety and Health Administration. 29 CFR 1910.1000 – Air Contaminants Ceilings are used for materials so acutely dangerous that a single high inhalation can cause serious injury.
Where to Find the Limit for Your Substance
The regulation organizes contaminants into three tables. Table Z-1 is the primary reference and lists PELs for the widest range of industrial chemicals, with limits in parts per million for gases and vapors and in milligrams per cubic meter for particulates. Carbon monoxide, chlorine, and toluene sit here, each entry flagged as a TWA or a ceiling.1Occupational Safety and Health Administration. 29 CFR 1910.1000 – Air Contaminants
Table Z-2 covers a smaller group with more complex profiles, often combining a TWA, an acceptable ceiling, and a maximum peak concentration over a specified window. Benzene and formaldehyde appear here. Table Z-3 covers mineral dusts such as crystalline silica, coal dust, and talc, and its limits are often calculated by a formula tied to the percentage of hazardous mineral present in the sample.3eCFR. 29 CFR 1910.1000 – Air Contaminants
Roughly two dozen chemicals bypass the tables entirely and have their own standalone standards in Subpart Z, including asbestos, lead, cadmium, chromium (VI), benzene, formaldehyde, beryllium, vinyl chloride, and respirable crystalline silica.5eCFR. 29 CFR Part 1910 Subpart Z – Toxic and Hazardous Substances These substance-specific standards each run many pages and impose their own PEL (usually stricter than any Z-table number), mandatory medical surveillance, monitoring protocols, engineering control requirements, and recordkeeping obligations. When a substance has a standalone standard, it governs. The Z-table entry is effectively superseded.
Why the Legal Limit May Not Be a Safe Limit
Most PELs are based on Threshold Limit Values published by the American Conference of Governmental Industrial Hygienists in 1968. OSHA adopted them wholesale when the agency stood up in 1971, and the majority have never been updated. Since then, OSHA has successfully established or revised PELs for only about 30 chemicals.
The agency did try. In 1989, OSHA issued a sweeping update covering hundreds of substances. The Eleventh Circuit vacated the entire rule in 1992, holding that OSHA had not built a sufficient scientific case for each individual chemical. OSHA chose not to appeal, and the affected PELs reverted to the 1971 numbers or were removed. That decision is the main reason the tables read the way they do today.
OSHA now publishes annotated PEL tables placing the legally enforceable limit side by side with alternative values from NIOSH, ACGIH, and California’s OSHA program, and the agency recommends that employers consider using the alternatives, warning that exposures above them “may be hazardous to workers, even when the exposure levels are in compliance with the relevant PELs.”6Occupational Safety and Health Administration. Permissible Exposure Limits – Annotated Tables
NIOSH publishes Recommended Exposure Limits based on current research. They are not legally enforceable, since NIOSH is a research agency rather than a regulator, but they often reflect more protective thresholds and are frequently a fraction of the corresponding OSHA PEL.7Occupational Safety and Health Administration. Standard Interpretation – OSHA’s Formaldehyde PEL Compared to NIOSH’s Formaldehyde REL ACGIH’s TLVs are professional guidelines, described by ACGIH itself as “intended for use only as guidelines or recommendations.”8ACGIH. TLV Chemical Substances Introduction Because ACGIH updates them regularly, many safety professionals treat TLVs as the working standard of care even though they carry no legal weight on their own.
What Employers Must Do When Exposure Approaches a PEL
When exposures approach or exceed a limit, 29 CFR 1910.1000(e) prescribes a specific order of response. Engineering or administrative controls must be implemented first whenever feasible. Only when those controls cannot fully achieve compliance may an employer rely on respirators.9eCFR. 29 CFR 1910.1000 – Air Contaminants
Engineering controls attack the contaminant at the source: local exhaust ventilation, enclosing a fume-generating process, substituting a less hazardous chemical. Administrative controls change how work is organized, such as rotating employees through contaminated areas to cap any individual’s exposure time or scheduling high-emission tasks when fewer workers are present. Both must be explored before the employer defaults to respirators.
Respirators come last, and using them triggers 29 CFR 1910.134, which requires a written respiratory protection program, medical evaluations confirming each employee can safely wear the equipment, and fit testing for tight-fitting facepieces.10eCFR. 29 CFR 1910.134 – Respiratory Protection Handing out respirators without running that program is itself a citable violation.
Feasibility is a real test, not a talking point. A control has to be technologically achievable, cost-effective over the short and long term, and recognized as appropriate practice in the industry. It doesn’t have to be cheap; it has to be possible without threatening the business’s viability.
How Compliance Gets Measured
You cannot know whether you comply without measuring. Compliance is determined through personal air monitoring, using a calibrated sampling pump worn by the employee that collects air from the breathing zone throughout the shift. OSHA defines the breathing zone as a roughly hemispherical area in front of the shoulders, within a six-to-nine-inch radius of the worker’s nose and mouth.11Occupational Safety and Health Administration. OSHA Technical Manual – Section II Chapter 1 – Personal Sampling for Air Contaminants The sample then goes to a laboratory for analysis.
Action Levels
Many substance-specific standards set an action level, commonly at half the PEL. Reaching it is not a violation, but it triggers mandatory obligations: more frequent monitoring, medical surveillance of exposed employees, and documented follow-up to keep concentrations from climbing higher. It functions as an early warning built into the regulation.
Mixtures of Chemicals
Workplaces rarely involve just one contaminant. When employees are exposed to several at once, the regulation requires a combined exposure calculation: divide each substance’s measured concentration by its own PEL and add the fractions. If the total is greater than one, the workplace is in violation even if no single chemical exceeds its own limit.3eCFR. 29 CFR 1910.1000 – Air Contaminants The formula exists because different toxins can produce combined effects worse than any one alone.
Construction, Shipyards, and State Plans
The PELs in 29 CFR 1910.1000 apply to general industry. Construction employers work under 29 CFR 1926.55, which uses the same framework of ceilings, TWAs, and a controls hierarchy.12Occupational Safety and Health Administration. 29 CFR 1926.55 – Gases, Vapors, Fumes, Dusts, and Mists Shipyard employment has its own parallel standard at 29 CFR 1915.1000.13eCFR. Occupational Safety and Health Standards for Shipyard Employment
State plans are a separate wrinkle. Under Section 18 of the OSH Act, a state can run its own program as long as it is “at least as effective” as the federal one.14Occupational Safety and Health Administration. State Plan – Frequently Asked Questions That standard allows states to adopt stricter PELs, and several have. Cal/OSHA is the most prominent example and maintains its own set of limits that are frequently lower than the federal numbers, which OSHA’s annotated tables display alongside the federal PELs.6Occupational Safety and Health Administration. Permissible Exposure Limits – Annotated Tables If you operate in a state-plan state, the federal PEL may not be the number you are actually required to meet.
Records Workers Can Request
Under 29 CFR 1910.1020, exposure monitoring records must be preserved for at least 30 years, and employee medical records must be kept for the length of employment plus 30 years.15Occupational Safety and Health Administration. Access to Employee Exposure and Medical Records Those windows exist because occupational diseases, particularly cancers and chronic lung conditions, can take decades to appear.
Employees and their designated representatives have the right to access these records. If you’ve been exposed to air contaminants at work, you can ask to see both the monitoring data and your own medical file. Background material like laboratory worksheets need only be retained for one year, but the sampling results, methodology, and analytical summaries must be kept for the full 30 years.15Occupational Safety and Health Administration. Access to Employee Exposure and Medical Records
Penalties and the General Duty Clause
Failing to keep exposures within a PEL, skipping required monitoring, or ignoring the hierarchy of controls can all draw citations. Under the January 2025 penalty adjustment, a serious violation carries a maximum of $16,550 and a minimum of $1,221; willful or repeated violations can reach $165,514.16Occupational Safety and Health Administration. OSHA Penalties17Occupational Safety and Health Administration. 2025 Annual Adjustments to OSHA Civil Penalties These figures are adjusted annually for inflation.
And where no PEL exists for a substance, employers still aren’t off the hook. Section 5(a)(1) of the OSH Act, the General Duty Clause, requires every employer to keep a workplace free from recognized hazards likely to cause death or serious physical harm.18Occupational Safety and Health Administration. Occupational Safety and Health Act of 1970 OSHA can cite employers under this clause for respiratory hazards that lack a PEL, provided the agency can show the hazard was recognized, employees were exposed, serious harm was likely, and a feasible correction existed.19Occupational Safety and Health Administration. Enforcement Policy for Respiratory Hazards Not Covered by OSHA PELs A General Duty Clause citation cannot rest solely on the fact that exposure exceeded a recommended NIOSH REL or ACGIH TLV; OSHA must prove all four elements independently. The absence of a PEL is not permission to ignore a known respiratory hazard.