Ozone OSHA PEL checker.

The ozone row in Table Z-1

This is the Ozone row of Table Z-1, Limits for Air Contaminants, in 29 CFR 1910.1000, as published in the eCFR. The values are printed exactly as the table prints them.

The ppm column is the working figure for air sampling: a time-weighted average of 0.1 ppm. The mg/m3 column is the same limit by mass, 0.2 mg/m3. The page does not show what a safe level is. It shows the number OSHA enforces.

Reading the footnotes

Each column heading carries a footnote marker. The eCFR prints them as follows.

• 1: The PELs are 8-hour TWAs unless otherwise noted; a (C) designation denotes a ceiling limit. They are to be determined from breathing-zone air samples.
• (a): Parts of vapor or gas per million parts of contaminated air by volume at 25 °C and 760 torr.
• (b): Milligrams of substance per cubic meter of air. When entry is in this column only, the value is exact; when listed with a ppm entry, it is approximate.
• (c): The CAS number is for information only. Enforcement is based on the substance name. For an entry covering more than one metal compound, measured as the metal, the CAS number for the metal is given—not CAS numbers for the individual compounds.

For this row, the ppm figure is a volume ratio at 25 °C and 760 torr. The 0.2 mg/m3 figure is its approximate mass equivalent, because the row lists a ppm value as well. Enforcement goes by the substance name in the first column, not the CAS number.

Why this entry is an 8-hour average

Neither number in the ozone row starts with (C), so footnote 1 treats the limit as an 8-hour TWA. A short peak above 0.1 ppm can therefore be allowed if the whole shift averages below it. Paragraph (a)(2) of the section reads: “An employee's exposure to any substance in Table Z-1, the exposure limit of which is not preceded by a “C”, shall not exceed the 8-hour Time Weighted Average given for that substance in any 8-hour work shift of a 40-hour work week.”

Entries that start with (C) are ceilings under paragraph (a)(1), and for those exposure shall at no time exceed the printed limit.

Skin designation

The Skin designation column for ozone is blank in the eCFR table.

Worked example

These readings are invented, to show the paragraph (d)(1) arithmetic. One employee's shift has two hours at 0.15 ppm, two hours at 0.075 ppm and four hours at 0.05 ppm of ozone.

E = (2 × 0.15 + 2 × 0.075 + 4 × 0.05) ÷ 8 = 0.08125 ppm. That is below the printed 0.1 ppm, even though the first two hours were above it.

The CFR works its own Substance A example the same way, for a 100 ppm limit, and arrives at 81.25 ppm.

Computation formulae in paragraph (d)

Paragraph (d)(1)(i) gives the cumulative exposure formula for an 8-hour shift: E = (Ca Ta + Cb Tb + . . .Cn Tn) ÷ 8, where E is the equivalent exposure for the working shift, C is the concentration during any period of time T where the concentration remains constant, and T is the duration in hours of the exposure at the concentration C. The value of E shall not exceed the 8-hour time weighted average specified in subpart Z of 29 CFR part 1910 for the substance involved.

Paragraph (d)(2)(i) gives the formula for mixtures: In case of a mixture of air contaminants an employer shall compute the equivalent exposure as follows: Em = (C1 ÷ L1 + C2 ÷ L2) + . . .(Cn ÷ Ln), where C is the concentration of a particular contaminant and L is the exposure limit for that substance specified in subpart Z of 29 CFR part 1910. The value of Em shall not exceed unity (1). The paragraph introducing these formulae applies them to substances for which 8-hour time weighted averages are listed.

What paragraph (e) says about controls

This page does not recommend any exposure-control measure. For reference, paragraph (e) of the section is printed as follows: “To achieve compliance with paragraphs (a) through (d) of this section, administrative or engineering controls must first be determined and implemented whenever feasible. When such controls are not feasible to achieve full compliance, protective equipment or any other protective measures shall be used to keep the exposure of employees to air contaminants within the limits prescribed in this section. Any equipment and/or technical measures used for this purpose must be approved for each particular use by a competent industrial hygienist or other technically qualified person. Whenever respirators are used, their use shall comply with 1910.134.”

Limits of this page

This page covers Table Z-1 and the paragraphs of 1910.1000 quoted above. It does not say that an exposure below a printed limit is safe, it does not cover Table Z-2 or Table Z-3 substances, other OSHA substance-specific standards, state-plan rules or recommended limits published by other bodies, and it does not tell you how to sample, how to control exposure or which respirator to use. The checker compares one number you type with the printed figure and applies the “shall not exceed” wording as written, so a reading equal to the limit is not above it. Anything involving a real workplace belongs with a qualified industrial hygienist, your safety data sheet and the OSHA office for your area. The eCFR lists the newest content version of this section as May 30, 2017.

Sources

Sources opened and read November 2, 2026.

• eCFR: 29 CFR 1910.1000, Air contaminants, Table Z-1 and paragraphs (a), (d) and (e) (text requested as of October 29, 2026; read November 2, 2026)
• eCFR versioner API: version history of 29 CFR 1910.1000 (read November 2, 2026)