Exposure limits for airborne substances

A (C) before a limit means the exposure is a ceiling value that must not be exceeded at any time. Employers must ensure an employee’s breathing‑zone air sample never shows concentrations above the ceiling value in Table 1 for that substance (for example, 1926.55(a)(1)).

• If continuous instantaneous monitoring is possible, use it to verify the ceiling is not exceeded. If instantaneous monitoring is not feasible, treat the ceiling as a 15‑minute time‑weighted average as described in 1926.55(a)(2).
• Implement engineering or administrative controls first to prevent any exceedance; if those don’t achieve compliance, use protective equipment approved by a competent industrial hygienist as required by 1926.55(b).

(See 1926.55(a)(1) and 1926.55(a)(2).)

You must measure and control employee exposure so the 8‑hour time‑weighted average (TWA) for any Table 1 or 2 substance without a (C) does not exceed the listed limit over a work shift. 1926.55(a)(2).

• The 8‑hour TWA averages all exposures over the full work shift (weighted for durations at differing concentrations). Use appropriate breathing‑zone air sampling methods to determine the TWA.
• Start with engineering and administrative controls to reduce exposures, per 1926.55(b); only use respirators when those measures cannot achieve full compliance and follow 1926.103 when respirators are used.

(See 1926.55(a)(2) and 1926.55(b).)

An employer must first implement feasible engineering and administrative controls to limit employee exposures before relying on personal protective equipment. 1926.55(b).

• Engineering controls include ventilation, local exhaust, substitution, or process enclosure. Administrative controls include scheduling, work rotation, and limiting access to high‑exposure areas.
• If controls alone cannot achieve full compliance, employers may use protective equipment or other measures, but any equipment and technical measures must be approved for the particular use by a competent industrial hygienist or other technically qualified person as required by 1926.55(b).
• Whenever respirators are used, comply with 1926.103 for proper selection, fit, training, medical evaluation, and maintenance.

(See 1926.55(b) and 1926.103.)

No. Paragraphs (a) and (b) of 1926.55 do not apply to airborne asbestos, tremolite, anthophyllite, or actinolite dust. See 1926.55(c).

• For construction work involving asbestos‑containing building materials (ACBM), the construction asbestos standard, 1926.1101, applies; OSHA has confirmed in its letter that asbestos remediation work in property remediation is covered under 1926.1101 rather than the general industry rule when the work involves ACBM (see OSHA’s asbestos remediation interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14).

An “X” designation in Table 1’s Skin designation column indicates that the substance is a dermal hazard—skin absorption is an important route of exposure. (See the footnote in Table 1 to 1926.55).

• When a substance has an X, employers should control skin contact (gloves, protective clothing, hygiene measures) as part of exposure control, in addition to controlling inhalation exposure per 1926.55.

(See 1926.55 Table 1.)

When Table 1 directs you to another OSHA standard for a substance, you must follow the specific requirements in that referenced standard. For example, methylene chloride in Table 1 is linked to 1910.1052, so you must follow the procedures, monitoring, and controls specified in 1910.1052 in addition to the general requirements of 1926.55.

• Always check the cross‑reference in Table 1; the specialized standard may include lower limits, medical surveillance, or other specific duties.

(See 1926.55 Table 1 and 1910.1052.)

If respirators are required, the employer must follow [1926.103] requirements for respirator use (selection, medical evaluation, fit testing, training, and maintenance). 1926.55(b) requires engineering/administrative controls first; respirators are allowed only when those cannot achieve compliance.

• Ensure a competent person approves the protective equipment for the specific use as required by 1926.55(b).
• Implement a written respiratory protection program, conduct medical evaluations, perform fit testing, and train users as required by 1926.103.

(See 1926.55(b) and 1926.103.)

Whenever any employee is exposed to formaldehyde, the construction employer must follow the separate formaldehyde standard at 1910.1048. The Table 1 entry for formaldehyde directs you to 1926.1148 and notes that 1910.1048 applies whenever any employee is exposed (see 1926.55).

• Follow the formaldehyde‑specific requirements (monitoring, medical surveillance, training, exposure limits) in 1910.1048 and the construction implementation provisions cited in 1926.1148.

(See 1926.55 Table 1 and 1910.1048.)

For operations and sectors where the respirable crystalline silica standard 1926.1153 applies, follow that silica‑specific standard rather than the generic Table 1 entries. The Table 1 footnotes point you to 1926.1153 for crystalline silica exposures.

• 1926.1153 contains specific exposure limits, monitoring, work practices, engineering controls, medical surveillance, and training requirements for construction operations.
• If you are in an operation or sector where the silica standard is stayed or not in effect, follow the Table 2 or the formula and footnotes in 1926.55 as applicable.

(See 1926.55 footnotes and 1926.1153.)

The letter “E” denotes a simple asphyxiant where the limiting factor is available oxygen; employers must ensure oxygen levels remain at or above safe limits and control explosion hazards per part 1926. (See the explanatory notes in 1926.55).

• Because oxygen deficiency is the hazard, monitor oxygen in confined or enclosed spaces and ensure the oxygen concentration is at least 19.5% (or the applicable safe level), and control ignition sources where flammable atmospheres could form.
• For questions about oxygen‑deficient atmospheres and HVAC design or when military HVAC systems are involved, OSHA’s interpretation on oxygen‑deficient atmospheres references the Respiratory Protection Standard 1910.134 and clarifies coverage issues (see https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16).

(See 1926.55 notes and 1910.134; see also OSHA interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.)

If instantaneous monitoring isn’t feasible, the employer must assess the ceiling as a 15‑minute time‑weighted average that must not be exceeded at any time during the work day, per 1926.55(a)(2).

• Use appropriate sampling methods to measure concentrations over 15‑minute periods and ensure no 15‑minute average exceeds the ceiling value.
• Maintain engineering controls and, if needed, approved protective equipment as required by 1926.55(b).

(See 1926.55(a)(2).)

When a Table 1 entry covers multiple metal compounds measured as the metal, the CAS number listed is for the metal itself—not the individual compounds; enforcement is based on the substance name. (See the explanatory notes in 1926.55.)

• This means you should measure and evaluate exposures as the metal (for example, chromium, nickel, etc.) per the metal‑based limit and any specific metal standards cited (e.g., 1926.1126 for chromium compounds).

(See 1926.55 notes and the specific metal standards cited in Table 1.)

If the exposure limit in 1926.1126 is stayed or not in effect, the Table 1 footnotes state the exposure limit for chromium(VI) is a ceiling of 0.1 mg/m3 or 0.1 mg/m3 (as CrO3) as an 8‑hour TWA as noted in the footnotes (see notes n and o in 1926.55).

• Where the specific chromium standard 1926.1126 applies and is effective, follow its requirements; if it is stayed, apply the fallback limits cited in 1926.55.

(See 1926.55 footnotes and 1926.1126.)

When Table 1 or its footnotes cross‑refer to a construction standard (for example, asbestos references 1926.1101), the employer must comply with that construction standard’s specific requirements rather than the generic Table limits. See 1926.55.

• For asbestos work, follow the full scope of 1926.1101, which includes work practices, monitoring, regulated areas, PPE, medical surveillance, and training.
• OSHA has clarified that remediation involving asbestos‑containing building materials in property remediation is covered by the construction asbestos standard, 1926.1101 (see OSHA’s asbestos remediation interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14).

(See 1926.55(c) and 1926.1101.)

The Table 1 entry for "Particulates not otherwise regulated" (PNOR) uses the same limits as Particulates Not Otherwise Regulated: 15 mg/m3 total dust as an 8‑hour TWA and the respirable fraction limit when listed. See the PNOR entry in Table 1 of 1926.55.

• Use this limit for organic and inorganic particulates that are not otherwise regulated in Table 1.
• Always apply engineering controls first per 1926.55(b) and perform breathing‑zone sampling to verify compliance.

(See 1926.55 Table 1.)

Any equipment and technical measures used because engineering or administrative controls cannot achieve full compliance must first be approved for each particular use by a competent industrial hygienist or other technically qualified person, per 1926.55(b).

• Document the basis for approval and the qualified individual’s credentials. This shows due diligence in selecting effective protective measures when controls alone are inadequate.

(See 1926.55(b).)

When Table 1 lists both ppm and mg/m3 for a substance, employers must meet the limit expressed in the table (both are listed for convenience; mg/m3 values are approximate when shown alongside ppm). See the Table 1 header and footnotes in 1926.55.

• Use appropriate sampling and analytical methods to measure the concentration in the unit required by enforcement (typically breathing‑zone air samples).
• If there is uncertainty about conversion or measurement methods, consult a competent industrial hygienist for the correct sampling strategy and method.

(See 1926.55 Table 1.)

You must control both inhalation and dermal exposure routes when a substance has inhalation limits and a Skin (X) designation in Table 1; implement inhalation controls per 1926.55 and control skin contact through protective clothing, gloves, and hygiene practices approved by a competent industrial hygienist as required in 1926.55(b).

• Use engineering controls (ventilation, enclosures) first to reduce airborne concentrations.
• Implement PPE and skin protection when engineering/admin controls cannot fully eliminate dermal contact.

(See 1926.55 Table 1 and 1926.55(b).)

If instantaneous (real‑time) monitoring is available and feasible, use it to ensure exposures never exceed a ceiling value; if it is not feasible, assess the ceiling as a 15‑minute time‑weighted average as prescribed by 1926.55(a)(2).

• Consider the contaminant’s toxicity, the process variability, and the availability of validated real‑time instruments when selecting the method.
• Document the rationale for the chosen monitoring approach and ensure controls prevent exceedances; when in doubt, consult a competent industrial hygienist.

(See 1926.55(a)(1) and 1926.55(a)(2).)

Yes. Storing pre‑charged appliances that contain a Category 1 flammable gas on site in one location in amounts at or above the PSM threshold quantity can make the storage process subject to OSHA’s PSM Standard; OSHA confirmed this in its PSM interpretation addressing aggregated flammable refrigerants (see https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06).

• PSM applies when the quantity of a covered flammable gas in one location equals or exceeds 10,000 pounds and the activity (storage, on‑site movement, handling) meets the definition of a process under [29 CFR 1910.119]. See OSHA’s PSM interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06 for details.

(See OSHA interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06 and consult [29 CFR 1910.119] via OSHA’s standards page.)

If your sector is excluded from 1926.1128, the Table 1 notes state that the limit is 10 ppm TWA. See the explanatory note (g) in 1926.55.

• If your sector is covered by 1926.1128, follow that standard’s requirements, including any lower limits or additional provisions.

(See 1926.55 notes and 1926.1128.)

It means that where talc contains asbestos, you must not use the generic Table 1 particulate limits but must comply with the asbestos construction standard 1926.1101 and its asbestos exposure limits and work practices. See the footnote guidance in 1926.55.

• Follow the asbestos‑specific requirements in 1926.1101 for regulated areas, monitoring, engineering controls, PPE, and medical surveillance.
• OSHA’s asbestos remediation interpretation also clarifies that remediation involving ACBM is covered under 1926.1101 (see https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14).

(See 1926.55 footnotes and 1926.1101.)

The formula (% SiO2 + 5) is used to calculate a threshold limit for respirable crystalline silica in operations or sectors where the respirable crystalline silica standard 1926.1153 is stayed or otherwise not in effect; see the Table 2 and footnotes in 1926.55.

• The percentage of crystalline silica is determined from airborne samples unless other validated methods apply (see note k in 1926.55).
• When 1926.1153 is in effect for your operation, follow its specific exposure limits and requirements.

(See Table 2 and footnotes in 1926.55 and 1926.1153.)

You should document the evaluation showing that feasible engineering and administrative controls could not achieve compliance, the protective equipment selected, and the competent industrial hygienist’s approval for that specific use, as required by 1926.55(b).

• The documentation should include the control alternatives considered, reasons they were infeasible, the technical justification for the chosen equipment, and the name/credentials of the approving qualified person.
• Keep records available for inspection and for internal verification that PPE and other measures are appropriate and maintained.

(See 1926.55(b).)

Start with 1926.55 Table 1 and its footnotes; if Table 1 cross‑references a substance‑specific construction standard (for example, 1926.1101 for asbestos, 1926.1126 for chromium, or 1926.1153 for silica), follow that specific standard’s requirements.

• If a substance is linked to a different OSHA standard (e.g., methylene chloride to 1910.1052), comply with that standard in addition to the general duties in 1926.55.

(See 1926.55 Table 1 and footnotes and the cited standards such as 1926.1101, 1926.1126, and 1926.1153.)

The footnote tells you that for those listed materials (for example, talc containing asbestos or tremolite asbestiform) you must use the asbestos exposure limits and requirements in the construction asbestos standard 1926.1101 instead of the generic Table 1 limits in [1926.55].

• Compliance then requires asbestos‑specific practices: regulated areas, specific monitoring methods, work practices, engineering controls, PPE, medical surveillance, and training described in 1926.1101.

(See 1926.55 footnotes and 1926.1101.)