What Is an OSHA PEL, and How Do I Find the One for My Chemical?

A permissible exposure limit (PEL) is the legal ceiling on how much of a substance a worker may breathe. For most substances it lives in Table Z-1 of 29 CFR 1910.1000 as an 8-hour time weighted average. But the fastest way to find the limit for a product you actually own is not the tables at all — it is Section 8 of that product’s safety data sheet, which is required to carry the PEL for every hazardous ingredient listed in Section 3.

The detail that decides it — what “8-hour TWA” and a ceiling “C” limit actually mean, when Table Z is the wrong place to look, and why no PEL does not mean safe — is set out below.

1. The three tables, and the letter that changes everything

29 CFR 1910.1000 opens by stating that exposure to any substance listed in Tables Z-1, Z-2 or Z-3 “shall be limited in accordance with the requirements of the following paragraphs”. The tables are not interchangeable:

• Table Z-1 holds most substances. A limit here is an 8-hour time weighted average unless it is preceded by a “C”.
• Table Z-2 holds a smaller set with a more complex structure — an 8-hour average, an acceptable ceiling, and an acceptable maximum peak above that ceiling for a stated maximum duration.
• Table Z-3 holds mineral dusts.

The “C” prefix is the one people miss. Paragraph (a)(1) says exposure to a Table Z-1 substance whose limit is preceded by a “C” “shall at no time exceed the exposure limit given for that substance”, and adds that where instantaneous monitoring is not feasible, the ceiling is assessed as a 15-minute time weighted average which “shall not be exceeded at any time during the working day”.

2. What “8-hour TWA” actually means

For a Table Z-1 substance without the “C”, paragraph (a)(2) says exposure “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”. Two consequences follow that matter in practice:

• The limit is about the average across the shift, so an hour at four times the limit and seven hours at nothing can still comply — unless there is also a ceiling.
• The reference is a 40-hour week. Shifts longer than eight hours, or weeks longer than forty, are not what the number was built around, and the arithmetic no longer flatters you.

3. Where the safety data sheet fits — and why it is the fast route

Appendix D to 29 CFR 1910.1200 requires Section 8 of a safety data sheet to give, for every ingredient or constituent listed in Section 3, the OSHA permissible exposure limit, the ACGIH threshold limit value (TLV), and any other exposure limit used or recommended by the preparer, where available — along with appropriate engineering controls and individual protection measures.

That makes the sheet an index into the tables, keyed by the product you actually bought rather than by chemical name. You do not need to know that your degreaser contains a Table Z-1 substance; Section 3 names the ingredient and Section 8 gives you its number. See the 16 sections of a safety data sheet for what else each section is obliged to carry.

Two cautions. The sheet reports limits “where available”, so a blank is not proof there is no limit — and under 1910.1200(g)(3) an empty subheading is supposed to say it is empty. And a sheet can be behind the current tables, which is a question of whether your copy is the current one.

4. When Table Z is the wrong place to look

A number of substances have their own expanded OSHA standard, and where one exists it governs — with its own limit, its own monitoring triggers and often its own written program. Respirable crystalline silica at 29 CFR 1910.1053 is the example most small employers meet, and 1910.1000 itself refers to it. If you are in a trade that generates silica dust, the HazCom sheet and the Table Z entry are not the standard you are being measured against: see HazCom for stone fabricators, which sets out that distinction.

The practical test: before you rely on a Table Z number, check whether that substance has a section of its own in subpart Z. If it does, read that one.

5. Two substances at once are not two separate problems

Paragraph (d) of 1910.1000 gives two computation formulae. The first, (d)(1), handles a shift of varying exposure to one substance: E = (CaTa + CbTb + … CnTn) ÷ 8, where C is the concentration during a period of constant exposure and T is the duration in hours, and E must not exceed the 8-hour time weighted average limit.

The second, (d)(2), is the one for a mixture of air contaminants: Em = C1/L1 + C2/L2 + … Cn/Ln, where C is the concentration of each contaminant and L its limit in subpart Z, and E_m shall not exceed 1. In other words, exposures add up. A workplace where three solvents each sit under their own limits can still be over the line taken together — and Section 3 of each sheet is where you find out what you are actually mixing.

6. No PEL does not mean safe

Many substances in ordinary use have no OSHA PEL at all. That is a gap in the tables, not a finding about the chemical, and it is the reason Appendix D requires Section 8 to carry the ACGIH TLV and any other recommended limit alongside the OSHA number. Where the two differ you have two figures and a decision to make; the lower of them is the more conservative basis for choosing a control.

It is also worth remembering what a PEL measures: airborne concentration, breathed. It says nothing about skin contact, eye damage or what happens if the substance is swallowed — which is what Sections 2, 4 and 8 of the sheet are for, and why an exposure limit is never the whole hazard assessment.

7. Using it, in five minutes

1. Open the product’s safety data sheet and read Section 3 for the hazardous ingredients and their concentrations.
2. Read Section 8 for the OSHA PEL and ACGIH TLV of each of those ingredients.
3. Note whether any limit is a ceiling, because that one cannot be averaged.
4. Check whether the substance has its own standard in subpart Z; if so, that is the rule.
5. If several products are used in the same area at the same time, remember paragraph (d)(2): the exposures are added, not considered separately.

Frequently asked questions

What is an OSHA PEL?

A permissible exposure limit is the legal maximum airborne concentration of a substance a worker may be exposed to. 29 CFR 1910.1000 states that exposure to any substance listed in Tables Z-1, Z-2 or Z-3 shall be limited in accordance with the requirements of that section. Most limits are 8-hour time weighted averages; some are ceilings that may not be exceeded at any time.

Where do I find the PEL for a specific product?

Section 8 of its safety data sheet. Appendix D to 29 CFR 1910.1200 requires Section 8 to give, for every ingredient listed in Section 3, the OSHA permissible exposure limit, the ACGIH threshold limit value and any other exposure limit used or recommended by the preparer, where available. That makes the sheet an index into the OSHA tables keyed by the product you actually bought.

What does a C before a PEL mean?

It marks a ceiling value. Under 1910.1000(a)(1), exposure to a Table Z-1 substance whose limit is preceded by a C shall at no time exceed that limit, and where instantaneous monitoring is not feasible the ceiling is assessed as a 15-minute time weighted average that shall not be exceeded at any time during the working day. A ceiling cannot be averaged out across a shift.

Does an 8-hour PEL apply to a 12-hour shift?

The limit is written against an 8-hour work shift in a 40-hour work week, which is the basis 1910.1000(a)(2) states. Longer shifts and longer weeks are outside the assumption the number was built on, so the same average represents a larger total dose.

What if a chemical has no OSHA PEL?

Many substances in ordinary use have none. That is a gap in the tables rather than a finding about the chemical, which is why Appendix D requires Section 8 to carry the ACGIH TLV and any other recommended limit alongside the OSHA figure. Note also that a substance with its own expanded standard in subpart Z, such as respirable crystalline silica at 1910.1053, is governed by that standard rather than by the Table Z entry.

Related guides

• The 16 sections of a safety data sheet
• Do safety data sheets expire?
• HazCom for stone fabricators (and why silica is a separate standard)
• The written PPE hazard assessment
• How to build a chemical inventory
• Chemical storage compatibility