Hydrazine OSHA PEL checker.

The hydrazine row in Table Z-1

The row below is copied from Table Z-1, Limits for Air Contaminants, in 29 CFR 1910.1000 as published in the eCFR, with the values exactly as printed. The number that matters is 1 ppm: parts of hydrazine vapour per million parts of air, averaged over an 8-hour shift. The 1.3 mg/m3 figure is the same limit expressed as mass per cubic metre of air.

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, that gives three points. The ppm figure is measured by volume at 25 °C and 760 torr. The 1.3 mg/m3 figure is only an approximate conversion, so use 1 ppm when you compare a reading. And enforcement goes by the substance name, so the CAS number 302-01-2 is a lookup aid, not part of the limit.

Why this entry is an 8-hour average

Neither number in the hydrazine row is preceded by (C), so footnote 1 makes it an 8-hour time weighted average (TWA). That means a short excursion above 1 ppm is not a breach by itself, as long as the shift average stays within the limit. 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 preceded by (C) are different. They are ceiling values under paragraph (a)(1), which says exposure shall at no time exceed the printed limit. Hydrazine is not one of them.

Skin designation

The Skin designation column for hydrazine is marked X in the eCFR table. The text of 1910.1000 does not define the designation beyond that column, so this page does not interpret it. Read the full section and OSHA's guidance at the source link before relying on it.

Worked example

Illustration of the paragraph (d)(1) arithmetic only, with invented readings. Suppose one employee's shift has two hours at 1.5 ppm, two hours at 0.75 ppm and four hours at 0.5 ppm of hydrazine. Then E = (2 × 1.5 + 2 × 0.75 + 4 × 0.5) ÷ 8 = 0.813 ppm. That is 81% of the printed 1 ppm 8-hour limit, so this invented shift is below it even though the first two hours were above 1 ppm. The number to take from the example is the average, not the highest reading. The same method is the one the CFR uses in its own Substance A example for a 100 ppm limit, 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.

The mixture formula handles several substances at once. Each contaminant is divided by its own limit, so a result of 1 means the combined exposure has used up the whole allowance. 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 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. The hydrazine row (302-01-2, 1 ppm, 1.3 mg/m3, X in the skin column) was re-read in the eCFR on November 12, 2026 and matched. The eCFR lists May 30, 2017 as the latest substantive change to this section. Other bodies, such as NIOSH and state programs, publish their own limits, which this page does not cover.

• 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)