Air Contaminant Exposure Limits

TABLE Z-1 lists the permissible exposure limits (PELs) for many airborne contaminants and employers must use these limits to ensure employees’ airborne exposures do not exceed the listed values. Employers use the Limits for Air Contaminants in 1910.1000 TABLE Z-1 as the baseline PELs for general industry unless a substance is covered by a more specific OSHA standard (for example, asbestos at 1910.1001 or benzene at 1910.1028).

You must make sure airborne concentrations do not exceed either the ppm or the mg/m3 value listed — they are equivalent ways of expressing the same PEL and exceeding either is a violation. The Table Z-1 limits in 1910.1000TABLEZ-1 shows both units so employers and IHs can use whichever unit their sampling method reports; when needed convert between them using the contaminant’s molecular weight and standard conditions to check compliance.

A “Skin” designation in 1910.1000 TABLE Z-1 means that dermal (skin or eye) absorption, direct contact, or mucous membrane exposure can contribute significantly to the employee’s overall exposure. Employers must control both inhalation and skin exposures using engineering and administrative controls and provide protective equipment and hygiene practices as needed (for example, gloves, splash protection, and washing facilities) in accordance with general PPE requirements at 1910 (see employer obligations under applicable PPE provisions such as 29 CFR 1910.132).

When Table Z-1 directs you to another standard (for example, benzene: “see 1910.1028”), the specific standard for that substance takes precedence for compliance and additional requirements. Follow the substance-specific standard and its procedures rather than the generic Table Z-1 entry, as explained in 1910.1000 TABLE Z-1.

A parenthetical “(C)” in 1910.1000 TABLE Z-1 denotes a ceiling limit — the employer must ensure the contaminant concentration never exceeds that value at any time. Employers must use controls, work practices, and monitoring to prevent instantaneous excursions above the ceiling value.

A STEL (short-term exposure limit) is the maximum average exposure allowed over a short sampling period (often 15 minutes) and differs from the 8‑hour time-weighted average (TWA) PEL listed in Table Z-1; employers must comply with both where a STEL is specified. See the specific STEL notation in 1910.1000 TABLE Z-1 and control exposures so neither the TWA nor the short-term limit is exceeded.

“Total dust” and “Respirable fraction” in 1910.1000 TABLE Z-1 are separate PELs: the total dust PEL covers all inhalable particulates from a source while the respirable fraction PEL applies only to the small particles that reach the deep lung. Employers must measure and control the appropriate fraction listed (total or respirable) for the material and task to ensure compliance.

For asbestos work that is remediation or similar to construction activities (even in residences), OSHA has said those activities are covered by the construction asbestos standard 29 CFR 1926.1101 rather than the general industry standard 1910.1001. See OSHA’s asbestos remediation interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14 for details and application to property remediation work.

When Table Z-1 points you to a specific standard (for example, “see 1910.1014”), you must follow that standard’s text and requirements for exposure limits, monitoring, and worker protection. The Table entry is a pointer; the substantive requirements live in the referenced standard.

Yes — a substance’s classification can trigger application of other OSHA standards; for example, storing large quantities of equipment containing a Category 1 flammable gas can make a process subject to OSHA’s Process Safety Management standard 29 CFR 1910.119 when the aggregated amount on site in one location meets or exceeds the threshold quantity. See OSHA’s interpretation on aggregating flammable refrigerants in stored appliances at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06 for how PSM may apply.

If a substance has a substance-specific standard (for example chromium(VI): see 1910.1029 or lead: see its specific standard), the substance-specific standard’s requirements and PELs control operations and monitoring for that substance rather than the generic Table Z-1 entry. Use the Table only for substances that do not have a separate specific standard, as indicated by the cross-reference in 1910.1000 TABLE Z-1.

Employers must monitor employee exposures when there is reason to believe exposures may exceed a PEL and perform additional monitoring to evaluate controls and changes, using a sampling schedule appropriate to the hazard and workplace — the monitoring obligation is described in 1910.1000. Employers should base frequency on initial measurements, process changes, and control effectiveness; if exposures approach or exceed the table limits, conduct more frequent monitoring and implement controls.

You can demonstrate compliance by comparing your measurement (ppm or mg/m3) directly to the corresponding Table Z-1 value; if you need to convert units use the contaminant’s molecular weight and standard conversion formulas so your result matches the Table unit. The Table format in 1910.1000 TABLE Z-1 allows either unit but the concentrations compared must be consistent and accurate for compliance documentation.

When a Table Z-1 entry is a recognized carcinogen (often indicated by cross-reference or specific standard citations), employers should minimize exposures to the lowest feasible level using engineering controls, work practices, and personal protective equipment and follow any additional requirements in the applicable substance-specific standard. See the carcinogen entries and their cross-references in 1910.1000 TABLE Z-1 and the substance-specific standards cited there (for example see 1910.1011, 1910.1014 as applicable).

State-plan states must enforce standards that are at least as effective as federal OSHA but may adopt more stringent requirements; employers in those states must follow the State plan’s rules when they are more protective. OSHA’s letters of interpretation explain that employers should check their State plan’s requirements in addition to federal 1910.1000 TABLE Z-1 (see the discussion of State plans in OSHA’s rim wheel servicing interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-08-01).

You must control both inhalation and dermal risks: use engineering controls (ventilation, enclosure), safe work practices, and provide appropriate PPE (gloves, splash protection) and hygiene facilities to prevent skin contact. The need for dermal protection is signaled by the Table’s skin designation; implement PPE consistent with general PPE obligations in 1910 and the specific guidance in 1910.1000 TABLE Z-1.

Employers are required to make applicable exposure and hazard information available to employees, but there is no OSHA requirement to post the entire Table Z-1 on-site; employers must, however, provide employees access to the standards and specific exposure information, monitoring results, and safety data sheets as required by applicable OSHA provisions. See the 1910 authorities and the Table in 1910.1000 TABLE Z-1 for the regulatory context — maintain records and make them available consistent with OSHA recordkeeping and standard-specific rules.

You must ensure that the airborne concentration of each hazardous component does not exceed its individual PEL in 1910.1000 TABLE Z-1 (or any substance‑specific standard that applies). Measure the exposure to each component (or use validated combination assessment methods) and control the highest exposures first using engineering and administrative measures; document monitoring and controls to show each component is below its applicable limit.

Under 1910.1000TABLEZ-1 the table lists airborne exposure limits using both parts per million (ppm) and milligrams per cubic meter (mg/m3) where applicable: the first value is the limit expressed in ppm and the paired number is the equivalent in mg/m3 as shown on the table.

• Use whichever unit matches your sampling results, but compare the measured value to the corresponding column in 1910.1000TABLEZ-1.
• If your sampling method returns mg/m3, compare to the mg/m3 column; if it returns ppm, compare to the ppm column.

Under 1910.1000TABLEZ-1 a parenthetical “(C)” before a value indicates a ceiling limit — a concentration that must not be exceeded at any time.

• A ceiling (C) value is different from a TWA: it is an instantaneous maximum you must not allow employees to exceed.
• Use short‑term sampling or direct‑reading instruments to ensure concentrations never go above the (C) level.

Under 1910.1000TABLEZ-1 an “X” indicates the chemical is subject to a substance‑specific OSHA standard or other regulatory requirement in addition to the Table Z‑1 limits.

• If a chemical in Table Z‑1 has an X, you must comply with the Table Z‑1 exposure limits and follow the referenced substance‑specific standard.
• Example: ethylene oxide is listed in Table Z‑1 but is referenced to 1910.1047; follow the detailed requirements in that standard for medical surveillance, engineering controls, and training.

Under 1910.1000 you must follow the cross‑referenced substance‑specific standard instead of relying only on the Table Z‑1 entry.

• When Table Z‑1 says “see 1910.xxxx,” the substance has its own standard (e.g., ethylene oxide — follow 1910.1047) with specific requirements such as exposure monitoring, medical surveillance, or engineering controls.
• Use Table Z‑1 for quick reference, but implement the detailed provisions in the cross‑referenced standard when present.

Under 1910.1000TABLEZ-1 the PEL (8‑hour TWA) for ethyl benzene is 100 ppm (435 mg/m3) as shown in the table.

• Sample and compare your measured concentrations to the listed TWA of 100 ppm (435 mg/m3).
• If exposures approach or exceed that TWA, implement engineering controls, work practices, or respiratory protection as required under 1910 and 1910.1000TABLEZ-1.

Under 1910.1000TABLEZ-1 the table distinguishes limits for total dust and respirable fraction; typical values in the table are 15 mg/m3 for total dust and 5 mg/m3 for the respirable fraction unless otherwise specified.

• When a material entry lists both "Total dust" and "Respirable fraction," measure accordingly and compare to the matching limit in 1910.1000TABLEZ-1.
• Use appropriate sampling methods (e.g., respirable cyclone samplers) to distinguish respirable fraction from total dust.

Under 1910.1000TABLEZ-1 the PELs for Particulates Not Otherwise Regulated (PNOR) are 15 mg/m3 for total dust and 5 mg/m3 for the respirable fraction.

• Treat PNOR exposures using those limits unless a more specific standard for the material applies.
• Control measures should follow the hierarchy of controls; if engineering and administrative controls do not keep exposures below the PELs, provide appropriate respiratory protection under 1910.134 (respiratory protection).

Under 1910.1000TABLEZ-1 you must follow the substance‑specific standard [1910.1053] for respirable crystalline silica rather than relying only on the generic Table Z‑1 numbers.

• The silica standard 1910.1053 contains the applicable PEL/action levels, required exposure monitoring, medical surveillance, and control measures specific to crystalline silica.
• Use Table Z‑1 only for materials not covered by a more specific standard.

Under 1910.1000TABLEZ-1 you must comply with the lead‑specific standard [1910.1025] for inorganic lead exposures rather than only using Table Z‑1 numbers.

• 1910.1025 includes detailed requirements for medical surveillance, air monitoring, engineering controls, housekeeping, and worker training that go beyond generic PEL comparisons.
• Implement the lead standard’s provisions whenever the work involves inorganic lead.

Under 1910.1000TABLEZ-1 you must follow the formaldehyde standard [1910.1048] for formaldehyde exposures, which contains specific exposure limits, monitoring, medical surveillance, and other protections.

• The formaldehyde standard 1910.1048 sets action levels, permissible exposure limits, and programmatic duties that apply in addition to any Table Z‑1 reference.
• Apply the detailed requirements of [1910.1048] whenever formaldehyde is present in the workplace.

Under 1910.1000TABLEZ-1 you must treat talc that contains asbestos by applying the asbestos standard [1910.1001] limits and requirements rather than the generic talc values in the table.

• The asbestos interpretation in OSHA’s letters emphasizes that asbestos is covered by its own rules; see the asbestos remediation guidance: https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14 for more context on when to use the construction asbestos standard vs. general industry.
• Follow the asbestos requirements in [1910.1001] for monitoring, controls, and medical surveillance when asbestos is present in talc or other materials.

Under 1910.1000TABLEZ-1 you must follow the specific standard referenced — in this case follow the requirements in [1910.1012] for ethyleneimine rather than relying on generic Table Z‑1 limits.

• Substance‑specific standards like 1910.1012 include tailored provisions (e.g., monitoring, engineering controls, medical surveillance) that apply to those chemicals.
• Use the Table Z‑1 cross‑reference as a pointer to the detailed standard you must implement.

Under 1910.1000TABLEZ-1 you must ensure exposures do not exceed the short‑term exposure limit (STEL) or ceiling value shown in the table; if you measure excursions near those limits, take corrective action immediately.

• Use appropriate short‑term sampling or direct‑reading monitors to capture peak values and compare them to the STEL or ceiling in 1910.1000TABLEZ-1.
• If excursions exceed limits, implement engineering controls, change work practices, limit worker time in the area, or provide respiratory protection under 1910.

Under OSHA’s PSM guidance, storing multiple pre‑charged units with a Category 1 flammable gas on site in one location can be a PSM‑covered process if the aggregate weight of the refrigerant meets or exceeds the 10,000‑pound threshold.

• OSHA’s interpretation addressing this exact scenario concludes that storage and on‑site movement of pre‑charged air conditioners/heat pumps that aggregate to the threshold are subject to [29 CFR 1910.119]; see the PSM interpretation: https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06.
• If your site meets the threshold, you must comply with [1910.119] PSM requirements (process safety information, process hazard analysis, operating procedures, emergency planning, etc.).

Under 1910.1000TABLEZ-1 you must comply with the substance‑specific standard’s detailed requirements (engineering controls, monitoring, medical surveillance) in addition to meeting the exposure limit shown in Table Z‑1.

• Substance‑specific standards commonly require extra actions (e.g., medical surveillance under [1910.1047] for ethylene oxide or [1910.1025] for lead), so follow the specific standard’s programmatic duties as well as the Table Z‑1 limit.
• Use Table Z‑1 as an exposure reference but implement the expanded protections required by the X‑marked standard.

Under 1910.1000TABLEZ-1 a dash ("-") in the table means OSHA has not established a numeric PEL in Table Z‑1 for that substance; you must determine applicable controls and check whether a substance‑specific OSHA standard or other authority applies.

• If there is no numeric PEL in Table Z‑1, check for cross‑references in the table (e.g., "see 1910.xxxx") and follow any substance‑specific standard.
• If no OSHA numeric limit or specific standard exists, apply the general duty to protect workers and use recognized industrial hygiene practices to assess and control exposures; consult 1910 and other consensus guidance as appropriate.

The respirable fraction PEL for silicon is 5 mg/m3 as an 8‑hour time-weighted average. See the exposure limits in 1910.1000TABLEZ-1 which list respirable fractions and total dust values for silicates such as silicon.

The PEL for silver (metal and soluble compounds, expressed as Ag) is 0.01 mg/m3 as an 8‑hour TWA. See the table entry for silver in 1910.1000TABLEZ-1 for the numeric limit.

A “(C)” designation denotes a ceiling limit that must not be exceeded at any time. The table explains that a “(C) designation denotes a ceiling limit” in the footnotes of 1910.1000TABLEZ-1, so employers must ensure short-term concentrations never exceed that ceiling value.

The PEL for sulfuric acid is 1 mg/m3 as an 8‑hour time-weighted average. See the sulfuric acid entry in 1910.1000TABLEZ-1 for this limit.

PNOR exposures are covered by the inert or nuisance dust limit found in Table Z-3. The table notes state that “All inert or nuisance dusts…not listed specifically by substance name are covered by the Particulates Not Otherwise Regulated (PNOR) limit which is the same as the inert or nuisance dust limit of Table Z-3,” so employers should consult 1910.1000TABLEZ-1 and 1910.1000TABLEZ-3 when applying PNOR limits.

If an entry appears only in the mg/m3 column, the value is exact. The footnotes to 1910.1000TABLEZ-1 explain that “When entry is in this column only, the value is exact; when listed with a ppm entry, the value is approximate.” Employers must therefore treat sole mg/m3 entries as exact numeric limits.

Enforcement is based on the substance name, not the CAS number. The table footnotes state that “The CAS number is for information only. Enforcement is based on the substance name,” so employers should identify exposures by substance name in 1910.1000TABLEZ-1 when determining compliance.

For cotton waste processing operations, the 8‑hour TWA for respirable dust is determined using a vertical elutriator cotton dust sampler or an equivalent instrument. The footnotes to 1910.1000TABLEZ-1 state that the 8‑hour TWA applies to respirable dust as measured by a vertical elutriator or equivalent for the specified cotton processing operations.

Yes — the PELs in the table are 8‑hour time-weighted averages unless otherwise noted. The table states explicitly that “The PELs are 8‑hour TWAs unless otherwise noted,” so employers should treat the numeric limits in 1910.1000TABLEZ-1 as 8‑hour TWAs unless a different designation (for example, a ceiling “(C)”) is provided.

The PEL for zinc oxide fume is 5 mg/m3 as an 8‑hour TWA. See the zinc oxide fume listing in 1910.1000TABLEZ-1 for this value.

Employers should consult Table Z-2 or Table Z-3 when the Table Z-1 footnotes direct them to do so, such as for operations or sectors where another specific standard’s exposure limit is stayed or not in effect. The notes in 1910.1000TABLEZ-1 reference 1910.1000TABLEZ-2 and 1910.1000TABLEZ-3 for those specific situations, so follow those cross-references when the footnotes indicate.

Yes — storing pre‑charged appliances that together contain a Category 1 flammable gas in quantities at or above the threshold can make the storage operation a PSM-covered process. OSHA’s interpretation addressing aggregation of Category 1 flammable gases explains that storage and on-site movement of such pre‑charged units meet the definition of a “process” and, if the aggregate weight on site in one location equals or exceeds the 10,000‑pound threshold, the activity is subject to [29 CFR 1910.119], as discussed in OSHA’s letter on PSM flammable gas aggregation (June 6, 2024).