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The Exposure Limit on Your SDS Was Set in 1968: How OSHA's Z Tables Work Under 1910.1000
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The Exposure Limit on Your SDS Was Set in 1968: How OSHA's Z Tables Work Under 1910.1000

Most OSHA permissible exposure limits date to 1971. What the Z tables in 1910.1000 require, the additive formula for mixtures, and where sampling duty starts.

by iSi Environmental

Pull the safety data sheet for any solvent in your plant and read Section 8. The OSHA permissible exposure limit printed there is, in almost every case, the number OSHA adopted in 1971 from the 1968 ACGIH threshold limit values, and it has not moved since.

OSHA tried to move it once. The Air Contaminants final rule of January 19, 1989 (54 FR 2332) lowered 212 exposure limits and added 164 new ones. The Eleventh Circuit vacated it on July 7, 1992 in AFL-CIO v. OSHA, 965 F.2d 962. OSHA suspended enforcement on March 23, 1993, then removed Table Z-1-A and restored the pre-1989 numbers on June 30, 1993 (58 FR 35338). Nothing comprehensive has been attempted since.

That reading is OSHA’s own. Its annotated exposure limit tables state that “many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of worker health.”

Which turns “we are under the PEL” from a conclusion into a question. Twelve questions answer it, starting with what 29 CFR 1910.1000 actually requires.

What is an OSHA permissible exposure limit?

A permissible exposure limit is the legally enforceable airborne concentration for a substance, set either in the Z tables of 29 CFR 1910.1000 or in a substance-specific Subpart Z standard. A limit preceded by “C” is a ceiling that may not be exceeded at any time. A limit without “C” is an 8-hour time-weighted average that may not be exceeded in any 8-hour shift of a 40-hour week.

The two forms behave differently in the field. Where instantaneous monitoring of a ceiling is not feasible, 1910.1000(a)(1) has it assessed as a 15-minute time-weighted average, not to be exceeded at any point in the day. For a non-ceiling value, 1910.1000(a)(2) makes the whole shift the averaging basis, and neither form is a health-based threshold OSHA reviews on a schedule.

What are OSHA’s Z tables and which substances are in which one?

Three tables sit inside 1910.1000. Table Z-1 is the main air contaminant list and carries 610 table rows in the current eCFR text, which is not the same thing as 610 substances. Table Z-2 carries 21 rows and uses a three-part structure. Table Z-3 covers mineral dusts, with 20 rows.

Reconcile the row count against OSHA’s own count rather than treating the two as one figure. The agency states it has occupational exposure limits for about 470 substances, roughly 30 of them under a comprehensive standard (79 FR 61384). Rows run higher because Z-1 lists some substances on several rows under different notations and carries catch-all entries such as particulates not otherwise regulated. Roughly 650 rows covering about 470 substances is the honest statement of it.

Z-2’s three numbers, set by 1910.1000(b), are an 8-hour average, an acceptable ceiling, and an acceptable maximum peak above that ceiling for a stated short duration. A plan built around the 8-hour average tests one of the three.

How do I calculate exposure when workers are exposed to several substances at once?

Use the additive formula at 1910.1000(d)(2). Divide each substance’s measured concentration by its own 8-hour limit, then sum the fractions. The sum may not exceed unity. Two solvents each measured at 60 percent of their individual limits put the employee at 1.2 and in violation, though neither substance alone exceeds anything.

This is the most under-applied provision in the standard, for a procedural reason rather than a technical one. The laboratory reports analyte by analyte, each result clears against its own limit, the report reads compliant, and nobody sums the fractions. The data proving the violation was already in the file. Paragraph (d)(1) carries the arithmetic for partial-period sampling. Mixed-solvent paint booths, degreasing lines and blended-thinner coatings are where the sum changes the answer.

Which substances does 1910.1000 govern, and which have escaped to their own standard?

Three answers, and they decide what the plant owes.

The substance has its own comprehensive standard. Asbestos (1910.1001), lead (1910.1025), hexavalent chromium (1910.1026), benzene (1910.1028), formaldehyde (1910.1048) and respirable crystalline silica (1910.1053) are on that list, with roughly two dozen others across Subpart Z. Each carries its own limit, an action level, a monitoring schedule, medical surveillance and training, so 1910.1000 is not the operative rule. Worked examples: silica, hexavalent chromium and the statistics behind a lead sampling result.

The substance is in a Z table with no comprehensive standard. Here 1910.1000 is the entire rule: a number, the computation formulas, the controls hierarchy, and nothing else. Creosote sits here, regulated as coal tar pitch volatiles rather than under a creosote standard, as does phthalic anhydride.

The substance is in no Z table at all. There is no permissible exposure limit, which is not the same as no obligation. Inhalable microplastics in recycling operations is the cleanest current example, and the last question covers what applies instead.

The self-test needs no phone call. Read Section 8 of each safety data sheet, then check whether the substance has its own section in the 1910.1001 through 1910.1053 range. If it does, that section governs and it carries deadlines. An ACGIH or NIOSH value with no OSHA limit puts you in the third case. An OSHA limit meaningfully higher than that value puts you in the gap this post is about. How many samples it takes to say anything defensible is a separate decision (Bayesian versus frequentist exposure assessment).

How old are OSHA’s permissible exposure limits?

Most date to 1971 and were adopted from the 1968 ACGIH threshold limit values. OSHA’s 2014 rulemaking record states that its limits “remain frozen at the levels at which they were initially adopted” and are “largely based on acute health effects.” OSHA has limits for about 470 substances while roughly 8,300 are in significant commerce (79 FR 61384).

A limit set to prevent irritation or narcosis by the end of a shift was not necessarily set to prevent a chronic outcome over a twenty-year career. The coverage gap is arithmetic: EPA’s Chemical Data Reporting list exceeds 7,674 chemicals against OSHA’s 470, so most of what moves through a coating or adhesive operation has no federal airborne limit.

Why hasn’t OSHA updated its exposure limits?

It tried and lost in court. The Air Contaminants rule of January 19, 1989 (54 FR 2332) lowered 212 limits and added 164 new ones. The Eleventh Circuit vacated it on July 7, 1992 in AFL-CIO v. OSHA, 965 F.2d 962. OSHA restored the pre-1989 limits at 58 FR 35338 and has not attempted a comprehensive update since.

The 1989 numbers are not law and are never a current limit. NIOSH prints them in Pocket Guide Appendix G under the heading “Exposure Limits NOT in Effect,” a benchmark OSHA’s enforcement guidance still references rather than an enforceable number.

Narrower attempts failed after it: a 1995 effort on seven chemicals produced no rulemaking, and neither did a 1997 industry and labor process. The 2014 Request for Information (RIN 1218-AC74), closed April 8, 2015 after an extension at 80 FR 15702, drew 39 comments and produced no rule.

Does complying with the PEL mean my workers are protected?

Not necessarily, and OSHA says so in print. Its annotated tables page states that “many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of worker health” and that “these adopted limits are not sufficiently protective of worker health.”

Its enforcement guidance goes further. The August 5, 1993 standard interpretation issued after the vacatur tells compliance officers that exposures above the vacated 1989 limits but within the enforceable Table Z-1 limits “may support a 5(a)(1) citation” where the officer documents serious health effects at comparable levels and specific employer knowledge of the hazard. A plant that knows its exposure sits between the health-based guideline and the OSHA limit and does nothing is assembling that second element on OSHA’s behalf.

What are the NIOSH REL, ACGIH TLV and Cal/OSHA PEL, and do they apply to my plant?

None of them is enforceable outside its own jurisdiction. OSHA publishes all three alongside its own limits on its annotated tables page precisely because they “may better protect workers.” NIOSH recommended exposure limits are federal recommendations, ACGIH threshold limit values are copyrighted health-based guidelines from a private association, and Cal/OSHA limits bind only employers under California jurisdiction.

ACGIH publishes threshold limit values under copyright, so we do not reproduce them here. Read them in the column OSHA maintains on its annotated exposure limit tables, beside the enforceable federal number. For a plant outside California the useful move is to adopt the lower figure as an internal action target. A documented target with a control plan behind it is defensible; documented awareness with nothing behind it is the opposite.

Do Kansas, Missouri, Oklahoma or Texas have different exposure limits than federal OSHA?

No. None of Kansas, Oklahoma, Texas, Missouri, Nebraska, Colorado, Arkansas or Louisiana operates an OSHA-approved State Plan covering private-sector employers, so the federal Z tables apply directly and unmodified. Twenty-two states and territories do run private-sector State Plans, and California maintains the most extensive separate list of exposure limits among them.

A multi-site employer with a California facility therefore runs two exposure-limit tables at once, which is why OSHA carries the Cal/OSHA column; for a Kansas or Missouri plant it is a reference point, not an obligation.

Does 1910.1000 require me to do air monitoring?

No. The section contains no sampling or exposure-assessment paragraph. It sets the limits, the computation formulas and the controls hierarchy. The duty to characterize an exposure comes from the substance-specific Subpart Z standards where one applies, from hazard communication, from the respiratory protection standard’s hazard evaluation requirement, and from the General Duty Clause.

1910.1200 requires that employees be informed about the chemicals they work with, and 1910.134 requires the employer to identify and evaluate respiratory hazards, including a reasonable estimate of exposures. 1910.1000 sets the number you may not exceed and says nothing about finding out whether you are exceeding it, so “we have never sampled” is not compliance. It is the absence of any basis for the respirator decisions already made.

Can I use respirators instead of engineering controls to meet a PEL?

No. 1910.1000(e) requires administrative or engineering controls to be determined and implemented whenever feasible, with protective equipment used only where those controls cannot achieve full compliance. Any equipment or technical measure must be approved for the particular use by a competent industrial hygienist or other technically qualified person, and respirator use must comply with 1910.134.

“Determined and implemented” puts the feasibility determination inside the obligation. The employer owes a reasoned answer on whether local exhaust, enclosure, substitution or a work-practice change could achieve compliance, and that answer is a document that reopens on any process or material change. Where respirators are the answer, the full 1910.134 program applies, and one built without an exposure characterization fails the hazard evaluation requirement first.

Is OSHA changing any exposure limits right now?

Not the Z tables. No comprehensive rulemaking on permissible exposure limits is pending, and the 2014 Request for Information closed in 2015 with no rule. What is moving is narrower: OSHA has grouped 16 Subpart Z substance standards into a proposed amendment of their respiratory protection provisions; informal public hearings on that group ran in the series that began August 19, 2026 (91 FR 33131), and no final rule has issued.

That item sits on OSHA’s deregulatory rulemaking page rather than a health-standards agenda, and 1910.1000 is absent from the list. If you run respirators under one of those 16 standards, read the docket; if you are waiting for the Z tables to be modernized, there is nothing on the calendar.

What is actually moving, and what is not

Three attempts at modernization have failed across 35 years, so an imminent update would run against that record. The General Duty Clause is itself a deregulatory target at the moment. OSHA proposed an “Interpretation of the General Duty Clause: Limitation for Inherently Risky Professional Activities” on July 1, 2025 (RIN 1218-AD71, 90 FR 28370). It is aimed at inherently risky professional activities and does not on its face reach the chemical overexposure theory in the 1993 interpretation. The direction matters anyway: the agency is narrowing the clause, not widening it.

Enforcement capacity is contracting alongside it. Inspections ran 23,531 from April through September 2025 against 29,229 a year earlier, willful citations fell 42 percent, and inspector headcount stood at 736 in January 2026 against 846 in February 2024 (OSHA internal statistics and the DOL Inspector General). Penalties did not rise: the serious maximum is $16,550 and the willful or repeat maximum is $165,514, the 2025 amounts carried into 2026 unadjusted (OSHA memorandum, May 21, 2026; see the 2026 penalty freeze), and the 70 percent size-based reduction now reaches 25 employees instead of 10 (Field Operations Manual Chapter 6).

Now the signal that runs the other way, because it governs the decision. 1910.1000 is not on the deregulatory list, the Z tables are untouched, and the 1993 interpretation has never been withdrawn. The enforceable floor is stable. What has contracted is the probability of inspection, not the standard, and the civil liability and workers’ compensation exposure that follows an actual overexposure does not depend on how many compliance officers OSHA employs.

Can OSHA cite me if a chemical has no permissible exposure limit?

Yes, under section 5(a)(1) of the OSH Act, the General Duty Clause. OSHA’s August 5, 1993 interpretation directs compliance officers to consider a 5(a)(1) citation for unregulated substances where they can show a recognized hazard and serious health effects, drawing on sources such as NIOSH recommended exposure limits and ACGIH threshold limit values, with Regional Administrator and Regional Solicitor consultation required.

State the conditions precisely, because the overstated version is everywhere. The interpretation says such an exposure may support a citation. It requires documented serious health effects at comparable exposure levels and specific employer knowledge of the hazard. And it instructs that “citations shall be issued only after consultation with the Regional Administrator and the Regional Solicitor,” which takes the call out of the compliance officer’s hands.

That brake is why these citations are uncommon relative to how often the gap exists, and why the gap is a poor thing to rely on: the element hardest for OSHA to build is the one employers build for them.

The work that closes this is not reading the tables. It is the inventory, resolving each substance to the standard that governs it, sampling enough to say something defensible, summing the fractions across the mixtures, and documenting the feasibility determination before the respirator decision, all dated before an inspection rather than after. iSi’s industrial hygiene group has run roughly 600 of these engagements for more than 320 client organizations since 2001, out of Wichita and Kansas City and across 40 states. If you want the exposure picture for a process rather than a stack of single-analyte lab reports, start with industrial hygiene services or the local pages for Wichita and Kansas City.

Frequently Asked Questions

What is an OSHA permissible exposure limit?

The legally enforceable airborne concentration for a substance, set in the Z tables of 29 CFR 1910.1000 or in a substance-specific Subpart Z standard. A limit marked C is a ceiling that may not be exceeded at any time; an unmarked limit is an 8-hour time-weighted average.

Are OSHA’s exposure limits up to date?

No. Most date to 1971 and were adopted from the 1968 ACGIH threshold limit values. OSHA’s own annotated tables state that many PELs are outdated and inadequate for ensuring protection of worker health, and a 1989 comprehensive update was vacated in court.

Does staying under the PEL mean workers are protected?

Not necessarily. OSHA enforcement guidance allows a General Duty Clause citation where exposures sit above health-based guidelines but under the enforceable limit, and the mixture formula at 1910.1000(d)(2) can put a facility in violation even when every individual substance is under its own limit.

Sources

All verified 2026-10-30.

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