Carbon monoxide OSHA PEL checker.

The carbon monoxide row in Table Z-1

The table below is the Carbon monoxide row of Table Z-1, Limits for Air Contaminants, in 29 CFR 1910.1000, copied as the eCFR prints it.

The 50 ppm figure means fifty parts of carbon monoxide per million parts of air by volume, averaged over an 8-hour shift. The 55 mg/m3 figure is the same limit by mass, and it is only approximate because the table also gives a ppm value. The 25 ppm default in the checker above is just a placeholder reading, half the limit.

Reading the footnotes

The column headings carry footnote markers. 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: ppm is measured by volume at 25 °C and 760 torr, mg/m3 is the approximate mass equivalent, and 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 carbon monoxide row is preceded by (C), so footnote 1 treats it as an 8-hour TWA. 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 are preceded by (C) in the table are ceiling values under paragraph (a)(1), which says exposure shall at no time exceed the printed limit.

Skin designation

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

Worked example

This example only shows the paragraph (d)(1) arithmetic, and the readings are invented. Suppose one employee's shift has two hours at 75 ppm, two hours at 37.5 ppm and four hours at 25 ppm of carbon monoxide.

Multiply each concentration by its hours and divide by 8: E = (2 × 75 + 2 × 37.5 + 4 × 25) ÷ 8 = 40.625 ppm. That is the shift's equivalent exposure, and it is below the printed 50 ppm limit.

The result says the shift average passes the table's number. It does not mean the 75 ppm hours were harmless, and it says nothing about a shift with a different mix of readings. The CFR works the same method for a 100 ppm substance in its own Substance A example, which comes to 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 reads Table Z-1 and the paragraphs of 1910.1000 quoted above. It does not say that an exposure below the printed limit is safe. It also does not cover Table Z-2 or Z-3 substances, other OSHA substance-specific standards, state-plan rules, or recommended limits from other bodies, and it does not explain sampling, exposure controls or respirator choice.

The checker compares the 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. For a real workplace, talk to a qualified industrial hygienist, read your safety data sheet and contact 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)